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Connective thinking on building envelope – Human body exergy analysis
International Journal of Heat and Mass Transfer 90 (2015) 1015–1025
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International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt
Connective thinking on building envelope – Human body exergy analysis Mateja Dovjak a,⇑, Masanori Shukuya b,1, Aleš Krainer a,2 a b
Chair for Buildings and Constructional Complexes, Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova cesta 2, 1000 Ljubljana, Slovenia Department of Restoration Ecology and Built Environment, Tokyo City University, 3-3-1 Ushikubo-Nishi, Tsuzuki-ku, Yokohama 224-8551, Japan
a r t i c l e
i n f o
Article history: Received 24 April 2015 Received in revised form 6 July 2015 Accepted 6 July 2015
Keywords: Building envelope system Thermal exergy transfer Exergy consumption Human body exergy balance Climate type Connective thinking
a b s t r a c t The purpose of this paper is to analyse the efficiency of building interventions both from building and user point of view. With exergy analysis based on the connective thinking approach, thermal exergy flows through the building envelope are analysed jointly with human body exergy balance. Two cases of building envelope systems, thermally well-insulated case and thermally non-insulated case, are located at four typical climates (temperate, cold, hot/dry, hot/humid). ‘‘Warm’’ and ‘‘cool’’ exergies transferred by radiation, convection and conduction at the interior surface of an envelope are calculated with methodology developed by Shukuya (2013) [7,35]. Human body exergy balance (hBExB) is calculated with software developed by Asada (2010) [6]. Results show that thermal insulation significantly reduces the exergy consumption rate (ExCr) within building envelope systems in all climates. Additionally, it allows the interior surfaces of building envelope to emit ‘‘warm’’ radiant exergy into the room space in temperate and cold climates, while on the other hand to emit ‘‘cool’’ radiant exergy instead of ‘‘warm’’ radiant exergy in hot/dry and hot/humid climates. Thermal insulation has important benefits on hBExB in all climates; it decreases human body exergy consumption rate (hbExCr) due to lower input exergy and higher output exergy. Exergy analysis based on the connective thinking approach helps us to understand all interactions between building systems and human body and consequently approach to the quantitative evaluation of comfort and healthy living and working conditions. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction In order to attain strategic goals on energy efficiency in building sector there appears a strong necessity for a novel approach. Current activities on energy efficiency are often sophisticated and oriented into one-directional way of solving problems, based on mechanical measures. However, the study on exergy consumption patterns for space heating in Slovenian buildings [1] showed that interventions performed on building envelope systems resulted in 6.25 times higher total building exergy saving potential than interventions in the efficiency of mechanical systems. Additionally, the combination of building system improvements and occupant’s behavioural changes resulted in a reduction of 75–95% of exergy consumption of heating and cooling [2]. Simple actions have influence not only on significant energy savings but also on improved thermal comfort conditions [3] and occupant’s behavioural changes [2]. Shukuya [3] revealed that improved ⇑ Corresponding author. Tel.: +386 1 4768609; fax: +386 1 4250688. E-mail addresses: [email protected] (M. (M. Shukuya), [email protected] (A. Krainer). 1 Tel.: +81 45 910 2552; fax: +81 45 910 2553. 2 Tel.: +386 1 4768609; fax: +386 1 4250688.
Dovjak),
http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.07.021 0017-9310/Ó 2015 Elsevier Ltd. All rights reserved.
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thermal comfort in winter resulted from higher mean radiant temperature and less exergy-consumption rate of the human body [3]. Bioclimatic building design arises from the location, building and human performance. All sustainable interventions should be defined in the direction of attaining health, comfort and stimulative living and working conditions as well as in the environmental protection. In general, connective thinking or the ability to connect knowledge across topics and subjects [4], is greatly missing among scientist, engineers and architects. The basic tool that results from the connective thinking approach is exergy analysis. Exergy analysis is a powerful thermodynamic technique for assessing and improving the efficiency of processes, devices and systems, as well as for enhancing environmental and economic performance [5]. Exergy analysis enables us to consider all interactions between the processes inside the human body and those in the indoor or outdoor environment [6,7]. The purpose of this paper is to analyse the efficiency of building interventions from building and user point of view. The study is focused on two cases of building envelope systems, thermally well-insulated case and thermally non-insulated case, positioned under four climate conditions (temperate, cold, hot/dry and hot/humid). With exergy approach, thermal exergy flows through the building envelopes are jointly analysed with human body
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Nomenclature Icl M Q Q/T RH S T U
v
effective clothing insulation, clo metabolic rate, met heat transfer, kJ entropy transfer by heat transfer, kJ/K relative humidity, % entropy, kJ/K temperature, °C or K thermal transmittance of building envelope, W/(m2 K) exergy, kJ water-vapour pressure in the room space, Pa water-vapour pressure of the outdoor air, Pa saturated water-vapour pressure at body-core temperature, Pa saturated water-vapour pressure at outdoor air temperature, Pa velocity, m/s
Subscripts ai ao cl cr mr sk o isw
indoor air outdoor air clothing body-core mean radiant skin environmental interior surface of an envelope
X pvr pvo pvs(Tcr) pvs(To)/pvr
exergy balance (hbExB). Understanding these interactions is the key factor for defining measures for the attainment of comfort and healthy living and working conditions with increased performance efficiency.
2. Exergy concept The origin of the word exergy goes back to 1940s, when in the United States in the M.I.T. School of Engineering, the terms ‘‘availability’’ and ‘‘available energy’’ were introduced [8,9]. Today, an equivalent term exergy has found global acceptance. The term exergy was introduced in Europe in the 1950s [10]. The property exergy is the work potential of a system in a specific environment and represents the maximum amount of useful work that can be obtained as the system is brought to equilibrium with the environment [5,8]. Unlike energy, the value of exergy depends on the state of environment. The portion of energy that cannot be converted to work is called unavailable energy. Unavailable energy is simply the difference between the total energy of a system at a specified state and the difference between total energy of a system at a specified state and the exergy of that energy [3,6–8]. Exergy as a powerful tool for the optimisation of a system may be introduced in every natural or built environments. For example, building envelope is a closed system, since no mass crosses the system boundary during the process. Entropy generation and destruction of exergy, i.e. exergy consumption, during a heat transfer process through a finite temperature difference is presented in Fig. 1. Heat transfer due to finite temperature difference is irreversible, and thereby some amount of entropy is generated as a result. The entropy generation is always accompanied by exergy consumption. Heat transfer Q, which is here in Fig. 1 defined to be positive from interior space to outdoor environment, through the surface at temperature Tisw is always accompanied by entropy
esw gen cons
exterior surface of an envelope generated consumed
Abbreviations breath air sum of exergies contained by the inhaled humid air cool, in ‘‘cool’’ exergy flow rate incoming onto the building envelope cool/warm convective exergy cool/warm convective exergy absorbed by/discharged from the whole skin and clothing surfaces cool/warm radiant exergy cool/warm radiant exergy absorbed by/discharged from the whole skin and clothing surfaces exhalation, sweat exhalation and evaporation of sweat ExCr exergy consumption rate within building systems hbExCr human body exergy consumption rate hbExB human body exergy balance inner part metabolic thermal exergy PMV predicted mean vote index stored stored exergy in the core and in the shell warm, in ‘‘warm’’ exergy flow rate incoming incoming onto the building envelope warm, out ‘‘warm’’ exergy flow rate outgoing from the building envelope
transfer in the amount of Q/Tisw and exergy transfer in the amount of (1 To/Tisw)Q [3,6–8]. As denoted for both winter and summer cases in Fig. 1, both of exergy flowing outside in winter and that flowing inside in summer are positive (in winter, due to To < Tesw and Q > 0, (1 To/Tesw)Q > 0; in summer, due to To > Tesw and Q < 0, (1 To/Tesw) Q > 0). ‘‘Warm’’ and ‘‘cool’’ exergy concepts were derived from the two laws of thermodynamics with environmental temperature [6,7]. ‘‘Warm’’ or ‘‘cool’’ exergy presents the amount of exergy contained in a substance relative to its environment. The substance has ‘‘warm’’ exergy as a quantity of state if its temperature is higher than the environment and ‘‘warm’’ exergy is the ability of thermal energy contained by the substance to disperse into the environment. The substance has ‘‘cool’’ exergy as a quantity of state if its temperature is lower than the environment, and ‘‘cool’’ exergy is the ability of the substance in which there is lack of thermal energy compared to the environment, to let the thermal energy in the environment flow into it [6,7]. Exergy concept has been introduced in various disciplines with the goal to optimise of chemical, biological and mechanical systems as well as for environmental protection. The use of exergy concept in the built environment was first introduced in the field of solar-energy utilisation by Isao Oshida [11] and further in building heating systems by Masanori Shukuya [12] and thermal comfort by Abdelaziz Hammache [13]. The relationship between human body exergy consumption rate (hbExCr) and a combination of indoor air temperature and mean radiant temperature was studied by Isawa et al. [14], Shukuya et al. [6,15,16], Prek [17], Shukuya [3,18], Prek and Butala [19]. Simone et al. [20] examined the relation between hbExCr and the human thermal sensation. The whole human body exergy balance (hBExB) under typical summer conditions in hot and humid regions was analysed by Iwamatsu and Asada [21] and Shukuya et al. [6]. Tokunaga and Shukuya [22] investigated the hBExB calculation under ‘‘unsteady-state’’ conditions.
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Fig. 1. Entropy generation and exergy consumption during ‘‘steady-state’’ heat transfer process through a building envelope with a finite temperature difference (left-winter case, where Tisw > Tesw; right-summer case, where Tisw < Tesw). Tisw is interior surface temperature of an envelope, Tesw is exterior surface temperature of an envelope, To is environmental temperature, Q is heat transfer, Sgen is entropy generated, Xcons is exergy consumed, Q/Tisw is the entropy transfer due to heat transfer, at the interior surface of an envelope, Q/Tesw is the entropy transfer, at the exterior surface of an envelope.
Predicted mean vote approach, adaptive comfort model and calculation of hbExCr were compared by Schweiker and Shukuya [23]. Additionally, Schweiker and Shukuya [24] performed a study on the effect of preference of using air-conditioning on the exergy consumption pattern within built environment. Prek and Butala [25] investigated the exergy-based correlation between thermal comfort and thermal environment. In the study by Mady et al. [26], the exergy destroyed and exergy efficiency of human body were analysed as a function of age and environmental conditions. The exergetic aspect of daylighting together with luminous and thermal comfort aspects was discussed in the study by Maki and Shukuya [27]. Dovjak [28] and Dovjak et al. [29] studied the effect of individual differences on hbExB. Since 2013, lots of new studies have been dealing with exergy analyses of the human body. Wu et al. [30] proposed a novel human body exergy consumption formula to determine indoor thermal conditions for optimal human performance in an office. Performance indicators for individuals under physical activity based on the concepts of exergy destroyed and exergy efficiency were applied by Mady et al. [31]. Caliskan [32] performed energy and exergy analyses of the human body for summer season of Izmir city in Turkey. An innovative low exergy heating and cooling system (LowEx system) was designed [33] and tested [34] in a model room for burn patient. The designed LowEx system enabled the creation of healing and comfort conditions for individual user with minimal possible energy use [33,34]. Shukuya et al. [35] developed a methodology for the calculation of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of a wall. ‘‘Unsteady’’ exergy analysis of glucose metabolism of a model neuron was performed by Genc et al. [36]. The results [36] showed that both exergy loss and work potential rates increased with increasing blood glucose concentration. The new method was applied to the case of office worker in typical and extreme weather conditions in Finland by Ala-Juusela and Shukuya [37]. The results agreed well with previous analyses, and pointed out that minimum hBExCr coincides with the comfortable one in summer conditions. The recent study by Mady et al. [38] proposed two terms of the exergy analysis to evaluate the thermal comfort condition: destroyed exergy and exergy transfer to the environment.
constructional complexes that delimit indoor and outdoor environment): thermally non-insulated case and thermally well-insulated case. Thermally non-insulated case is a reinforced concrete wall, whose thickness is 120 mm. Thermally well-insulated case is a reinforced concrete wall with 200 mm of exterior positioned cellulose fibre board (Table 1). Both cases were assumed to be located at four typical climates (temperate, cold, hot/dry and hot/humid) (Tables 1 and 2). The climate characteristics for the selected locations (Ljubljana in temperate climate, Yakutusk in cold climate, Riyadh in hot/dry climate and Yokohama in hot/humid climate) were defined according to climate database [39]. Indoor microclimatic conditions were assumed according to the climate type (Table 3). The interior and exterior surface temperatures are obtained by solving the energy balance equations with the assumption of ‘‘steady-state’’ conditions (Table 4).With exergy approach, thermal exergy flows through the building envelopes are jointly analysed with human body exergy balance (hBExB).‘‘Warm’’ and ‘‘cool’’ exergies transferred by ‘‘steady-state’’ radiation, convection and conduction at the interior surface of a wall were calculated with methodology developed by Shukuya et al. [35]. The effect of building interventions on thermal comfort was analysed with human body exergy balance model [6]. Characteristics of virtual person are presented in Table 5. 3.1. Human body exergy balance model The thermodynamic system of the human body consists of a core and a shell and is positioned in two cases of virtual room (thermally non-insulated and thermally well-insulated) located at four typical climates. Thermal exergy balance of the human body [6] was derived by combining the water, the energy and the entropy balance equations. Basic equations can be equipped both to ‘‘steady-state’’ and to ‘‘unsteady-state’’ conditions. All of them are the resultant equations of the mathematical operations described by Shukuya et al. [6], together with the environmental temperature for exergy calculation. The general form of the exergy balance equation for the human body as a system is represented in Eq. (1) [6,7]. Components of exergy input and output are presented in Table 6 [6].
Exergy input Exergy consumption 3. Methods The effect of building interventions was analysed from building and user point of view with exergy approach. The analysis was focused on two cases of building envelope systems (i.e.
¼ Exergy stored þ Exergy output
ð1Þ
To maintain homeostatic conditions, it is important that optimal hbExC rate and stored exergy values are attained with an efficient combination of exergy input and exergy output. Thermal
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Table 1 Characteristics of building envelope systems. Building case Climate
Case t-a Temperate
Case t-b Temperate
Case c-a Cold
Case c-b Cold
Case hd-a Hot/dry
Case hd-b Hot/dry
Case hh-a Hot/humid
Case hd-b Hot/humid
U value [W/(m2 K)]
3.93
0.19
3.93
0.19
3.93
0.19
3.93
0.19
Table 2 Climate characteristics. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Location Latitude/longitude
Ljubljana, Slovenia 46.22° North 14.48° East 1 385 May 14
Yakutusk, Russia 62.08° North, 129.75° East 9 103 March 21
Riyadh, South Arabia 24.7° North 46.8° East 3 612 August 36
Yokohama Japan 35.4° North 139.6° East 9 10 August 27
72
61
10
70
1
2
3
3
Time zone from Greenwich Elevation [m] Selected month Tao [°C] (average monthly) RHao [%] (average monthly) vao [m/s] (average monthly)
Tao = outdoor air temperature; RHao = relative humidity of outdoor air;
vao = wind speed.
comfort conditions were analysed by human body exergy balance (hBExB), calculated human body exergy consumption rates (hbExCr), together with conventional energy-concept based index, predicted mean votes (PMV), with spread sheet software developed by Hideo Asada [6]. For the calculation of thermal exergy transfer through building envelope systems, the indoor microclimatic conditions were different from the outdoor microclimatic conditions. The indoor microclimatic conditions were assumed according to the climate type. The interior and exterior surface temperatures were obtained by solving the energy balance equations with the assumption of ‘‘steady-state’’. For the calculation of thermal exergy transfer through the building envelope systems and for the calculation of human body exergy balance the same environmental temperature was used, i.e. outdoor air temperature (To). It was assumed that outdoor radiant temperature was equal to outdoor air temperature.
4. Results and discussion 4.1. Thermal exergy transfer through building envelope systems Building interventions should be defined considering the exergy processes in the building together with the exergy processes in the human body. Thermal insulation presents an important intervention in all climates. The effect of thermal insulation on the level of building envelope was analysed with methodology developed by Shukuya [35]. Fig. 2 shows numerical examples of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of an envelope
Table 3 Assumed indoor microclimatic conditions. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Tai [°C] RHai [%] vai [m/s]
20 50 0.1
20 50 0.1
26 50 0.1
26 50 0.1
Tai = indoor air temperature; RHai = relative humidity of indoor air; velocity.
vai = room
air
located at temperate climate (Cases t-a, t-b), cold climate (Cases c-a, c-b), hot/dry climate (Cases hd-a, hd-b) and hot/humid (Cases hh-a, hh-b). Cases t-a, c-a, hd-a and hh-a present thermally non-insulated envelopes and Cases t-b, c-b, hd-b and hh-b present thermally well-insulated envelopes. ‘‘Warm’’ or ‘‘cool’’ exergy presents the amount of exergy contained in a substance relative to its environment. The substance has ‘‘warm’’ exergy as a quantity of state if its temperature is higher than the environment and ‘‘warm’’ exergy is the ability of thermal energy contained by the substance to disperse into the environment. The substance has ‘‘cool’’ exergy as a quantity of state if its temperature is lower than the environment, and ‘‘cool’’ exergy is the ability of the substance in which there is lack of thermal energy compared to the environment, to let the thermal energy in the environment flow into it [6,7]. First, let us focus on the thermally non-insulated envelope (Case t-a) and thermally well-insulated envelope (Case t-b) located at temperate climate (Fig. 2). In Case t-a, the interior surface temperature of a reinforced concrete wall, is l6.9 °C (Tisw). If the room air temperature (Tai) is kept at 20 °C, then ‘‘warm’’ exergy flows into the wall across its interior surface at 46.3 (mW)/m2 by convection. In a concrete wall without thermal insulation, ‘‘warm’’ exergy flow going from the interior surface of the envelope by conduction is at the rate of 238.6 (mW)/m2. In Case t-b, the interior surface temperature increases up to 19.9 °C (Tisw) due to the enhancement of thermal insulation, i.e. cellulose fibre board of 200 mm. This results in the ‘‘warm’’ exergy flow rate transferred by convection from the interior boundary air layer to the interior surface of the envelope at 4.3 (mW)/m2 and ‘‘warm’’ exergy flow rate by conduction at 22.8 (mW)/m2. The increase of 3.0 K in the surface temperature, Tisw, results in a significant increase in ‘‘warm’’ radiant exergy emission rate, from 79.1 to 312.8 (mW)/m2. The comparison of two Cases t-a and t-b confirms that thermal insulation plays a crucial role in the reduction of the rate of exergy transfer from the envelope surface into the envelope inside by conduction (215.8 (mW)/m2 difference) due to higher value of (Tisw Tesw) and (1 (To/Tisw)) in Case t-b. In both cases there is ‘‘warm’’ exergy transfer into the envelope due to To 6 Tesw < Tisw. A larger difference of (Tai Tisw) in Case t-a results in higher rate of ‘‘warm’’ exergy transfer into the interior surface of the envelope by convection (42.0 (mW)/m2 difference). On the other hand, a
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M. Dovjak et al. / International Journal of Heat and Mass Transfer 90 (2015) 1015–1025 Table 4 Calculated interior and exterior surface temperatures. Building case Climate type
Case t-a Temperate
Case t-b Temperate
Case c-a Cold
Case c-b Cold
Case hd-a Hot/dry
Case hd-b Hot/dry
Case hh-a Hot/humid
Case hd-b Hot/humid
Tesw [°C] Tisw [°C] Tmr [°C]
14.9 16.9 18.5
14.1 19.9 20.0
14.6 0.9 9.5
20.7 19.0 19.5
34.4 31.1 28.6
35.9 26.3 26.1
26.8 26.5 26.3
26.9 26.0 26.0
Tai = indoor air temperature; RHai = relative humidity of indoor air; perature of an envelope; Tmr = mean radiant temperature.
vai = room air velocity; Tesw = exterior surface temperature of an envelope; Tisw = interior surface tem-
Table 5 Virtual person’s characteristics. M [met]
Icl [clo]
1
0.3 1.0
M = metabolic rate; Icl = effective clothing insulation. Icl variates according to climate conditions.
larger difference of (Tisw To) in Case t-b results in higher rate of ‘‘warm’’ radiant exergy emitted from the interior surface of the envelope compared to Case t-a (233.7 (mW)/m2 difference). In both cases there appear ‘‘warm’’ radiant exergy rates due to Tisw > To. Beside the emission of ‘‘warm’’ radiant exergy, ‘‘warm’’ radiant exergy is also absorbed by the envelope surface, due to Tmr > To. Higher rate of radiant exergy absorbed by the envelope surface arises in Case t-b than in Case t-a (138.0 (mW)/m2 difference) due to larger difference of (Trm To) in Case t-b. Thermal insulation significantly decreases exergy consumption at the surfaces caused by the absorption of radiation (21.1 (mW)/m2 difference) due to a smaller difference of (Tmr Tisw) in Case t-b. Similar findings can also be seen in cold climate for both cases. In Cases c-a and c-b, Tisw turns out to be 0.9 and 19.0 °C (Fig. 2). In these two cases, the room air is assumed to be 20 °C. Thermal insulation provided by a 200 mm tick cellulose fibre board plays a significant role in the reduction of exergy consumption rate from 852.8 (mW)/m2 in Case c-a to 2.1 (mW)/m2 in Case c-b, thereby increasing the rate of ‘‘warm’’ radiant exergy emission (11501.8 (mW)/m2 difference). It also decreases the rate of ‘‘warm’’ exergy transfer by convection between Case c-a and Case c-b (2104.0 (mW)/m2 difference) and conduction (10802.3 (mW)/m2 difference). In Cases hd-a and hh-a, Tisw turns out to be 31.1 and 26.5 °C. In these two cases, the room air is assumed to be 26 °C. ‘‘Cool’’ exergy of 205.3 and 2.1 (mW)/m2 comes from room air into the envelope surface by convection due to Tai 6 Tisw < To. If some amount of solar radiation is incident on the exterior surface of the envelope
Table 6 Components of exergy input and output [6]. Exergy input
Exergy output
Warm exergy generated by metabolism Warm/cool and wet/dry exergies of the inhaled humid air
Warm and wet exergy contained in the exhaled humid air Warm/cool and wet/dry exergy contained in resultant humid air containing the evaporated sweat Warm/cool radiant exergy discharged from the whole skin and clothing surfaces Warm/cool exergy transferred by convection from the whole skin and clothing surfaces into the surrounding air
Warm and wet exergies of the liquid water generated in the core by metabolism Warm/cool and wet/dry exergies of the sum of liquid water generated in the shell by metabolism and dry air to let the liquid water disperse Warm/cool radiant exergy absorbed by the whole skin and clothing surfaces
without thermal insulation, radiant exergy emission from the interior surface may well be ‘‘warm’’. Air conditioning unit in a room without sufficient amount of thermal insulation has to extinguish the ‘‘warm’’ exergy flow into the room space by a large consumption of ‘‘cool’’ exergy. In Cases hd-b and hh-b, Tisw is lowered down from 31.1 to 26.3 °C and from 26.5 to 26.0 °C by thermal insulation, respectively. This brings about the emergence of larger ‘‘cool’’ radiant exergy emission (984.7 (mW)/m2 in Case hd-b and 10.0 (mW)/m2 in Case hh-b). On the other hand, in Cases hh-b and hd-b, external thermal insulation equipped for a concrete wall decreases the rate of ‘‘cool’’ exergy flow by conduction (569.8 (mW)/m2 difference between Cases hd-a and hd-b and 5.8 (mW)/m2 in Cases hh-a and hh-b). In hot/dry and hot/humid climate exergy consumption rates are decreased (65.3 (mW)/m2, 0.6 (mW)/m2 differences). This is due to the assumption that mean radiant temperature is changed from 28.6 to 26.1 °C in hot/dry climate and from 26.3 to 26.0 °C in hot/humid climate. Thermal insulation enables the interior surface of the envelope to emit ‘‘cool’’ radiant exergy while extinguishing the ‘‘warm’’ exergy to come in the room space by radiation and convection primarily due to the absorption of solar radiation at the exterior surface. Let us focus on the detailed comparison among the cases. Table 7 presents the results of numerical calculations of exergy flow rates by convection, conduction and radiation, and exergy consumption for eight building cases. The rate of ‘‘cool/warm’’ radiant exergy emitted from interior surface of the envelope is the highest in the case of thermally well-insulated envelope positioned in cold climate (Case c-b: 15568.9 (mW)/m2) due to the largest difference of (Tisw To). ‘‘Cool/warm’’ radiant exergy rate is the lowest in the case of thermally non-insulated envelope positioned in hot/humid climate (Case hh-a: 2.5 (mW)/m2) due to the smallest difference of (Tisw To). Condition Tisw > To results in ‘‘warm’’ radiant exergy rates emitted from interior surface envelopes positioned in cold and temperate climates (Cases t-a, t-b, c-a, c-b). The condition of Tisw < To results in ‘‘cool’’ radiant exergy rate in hot/dry and hot/humid climate (Cases hd-a, hh-a, hd-b, hh-b). The rate of ‘‘cool/warm’’ radiant exergy absorbed by the envelope surface is the highest in thermally well-insulated envelope positioned in cold climate (Case c-b: 15951.5 (mW)/m2) due to the largest difference of (Tmr To). The rate of ‘‘cool/warm’’ radiant exergy absorbed by the envelope surface is the lowest in the case of thermally well-insulated envelope positioned in hot/humid climate (Case hh-b: 5.8 (mW)/m2) due to the smallest difference of (Tmr To). The condition of Tmr > To results in ‘‘warm’’ radiant exergy rate in temperate and cold climate (Cases t-a, t-b, c-a, c-b). The condition of Tmr < To results in ‘‘cool’’ radiant exergy absorbed by the envelope surface positioned in hot/dry and hot/humid climates (Cases hd-a, hd-b, hh-a, hh-b). Exergy consumption at the surface due to the absorption of radiation is the largest in thermally non-insulated envelope positioned in cold climate (Case c-a: 852.8 (mW)/m2) due to the largest value of (Tmr/Tisw). Exergy consumption is the smallest in the case of thermally well-insulated envelope positioned in hot/humid climate (Case t-b: 0.002 (mW)/m2) due to due to low value of (Tmr/Tisw).
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Fig. 2. Numerical examples of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of a thermally noninsulated envelope and thermally well-insulated envelope located at temperate climate (Cases t-a, t-b), cold climate (Cases c-a, c-b), hot/dry (Cases hd-a, hd-b) and hot/humid (Cases hh-a, hh-b). The numbers in the rectangles indicate the rate of exergy consumption at the surfaces due to the absorption of radiation.
The rate of exergy transfer by conduction is the highest in thermally non-insulated envelope in cold climate (Case c-a: 11870.3 (mW)/m2) due to a large (Tisw Tesw) difference. The rate of exergy transfer from room air to envelope by conduction is the lowest in the case of thermally well-insulated envelope in hot/humid climate (Case hh-b: 0.6 (mW)/m2) due to a small (Tisw Tesw) difference. Condition To 6 Tesw < Tisw results in ‘‘warm’’ exergy rate in Case t-a, Case t-b, Case c-a and Case c-b. The
condition of Tisw 6 Tesw < To results in ‘‘cool’’ exergy rate in (Cases hd-a, hd-b, hh-a, hh-b). The rate of exergy transfer from room air into the envelope surface by convection is the highest in thermally non-insulated envelope positioned in cold climate (Case c-a: 2303.9 (mW)/m2) due to the largest (Tai Tisw) difference. The rate of exergy transfer from room air into the envelope surface by convection is lowest in the case of thermally well-insulated envelope positioned in hot/humid
in = 62.0 in = 21.3 in = 631.8 in = 205.3 in = 1068.0 in = 199.9 in = 11870.3 in = 2303.9
out = 245.8 in = 571.9
Cool, Cool, 0.15 Cool, Cool, Cool, Cool, 65.4 Cool, Cool, out = 15568.9 in = 15951.1 out = 4067.1 in = 9236.5
in = 22.8 in = 4.3
Warm, Warm, 852.8 Warm, Warm, out = 312.8 in = 320.8
in = 238.6 in = 46.3
Warm, Warm, 0.1 Warm, Warm, out = 79.1 in = 182.8
Warm, Warm, 21.2 Warm, Warm, flow rate by emission of radiation [(mW)/m2] flow rate by absorption of radiation [(mW)/m2] consumption [(mW)/m2] flow rate by conduction [(mW)/m2] flow rate by convection [(mW)/m2] Exergy Exergy Exergy Exergy Exergy
14.0 14.9 16.9 20.0 18.5 To [°C] Tesw [°C] Tisw [°C] Tai [°C] Tmr [°C]
Warm, in = ‘‘warm’’ exergy flow rate incoming onto the building envelope; warm, out = ‘‘warm’’ exergy flow rate outgoing from the building envelope; cool, in = ‘‘cool’’ exergy flow rate incoming onto the building envelope; cool, out = ‘‘cool’’ exergy flow rate outgoing from the building envelope.
in = 6.4 in = 2.1
Cool, out = 10.0 Cool, in = 10.3 0.002 Cool, in = 0.6 Cool, in = 0.2 out = 2.5 in = 5.8
Cool, Cool, 0.6 Cool, Cool,
Case hd-b
Warm, Warm, 2.1 Warm, Warm,
out = 984.7 in = 1010.0
27.0 26.8 26.5 26.0 26.3 36.0 35.9 26.3 26.0 26.1 36.0 34.4 31.1 26 28.6 21.0 20.7 19.0 20.0 19.5 21.0 14.6 0.9 20.0 9.5 14.0 14.1 19.9 20.0 20.0
Hot/humid
Case hh-a Case hd-b Case hd-a Case c-b
Hot/dry Cold
Case c-a Case t-a Building case
Case t-b Temperate Climate type
Table 7 Calculated exergy flow rates by convection, conduction and radiation, and exergy consumption for eight building cases.
27.0 26.9 26.0 26.0 26.0
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climate (Case hh-b: 0.2 (mW)/m2) due to the smallest (Tai Tisw) difference. The condition of To 6 Tisw < Tai results in ‘‘warm’’ exergy rate in (Cases c-a, c-b, t-a, t-b). The condition of Tai 6 Tisw < To results in ‘‘cool’’ exergy rate in (Cases hd-a, hd-b, hh-a, hh-b). In temperate, cold, hot/dry and hot/humid climates, thermal insulation decreases the rate of exergy consumption at the interior surface of the envelope (from 850.7 (mW)/m2 or 99.8% decrease in cold climate to 21.1 (mW)/m2 or 99.5% decrease in temperate climate) and thereby increases the rate of emitting ‘‘warm’’ or ‘‘cool’’ radiant exergy (from 738.9 (mW)/m2 or 75.0% increase in hot/dry climate to 11501.8 (mW)/m2 or 73.9% increase in cold climate). It also contributes to decreasing the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by convection (from 2104.0 (mW)/m2 or 91.3% decrease in cold climate to 184.0 (mW)/m2 or 89.6% decrease in hot/dry climate), and the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by conduction (from 10802.3 (mW)/m2 or 91.0% decrease in cold climate to 215.8 (mW)/m2 or 90.4% decrease in temperate climate). Note that thermal insulation enables the interior surface of the envelope to emit ‘‘warm’’ or ‘‘cool’’ radiant exergy, which is preferable, while extinguishing the ‘‘cool’’ or ‘‘warm’’ exergy to come in the room space by radiation and convection. This proves the importance of giving the priority of bioclimatic interventions. Thermal insulation has important advantages also for building occupants, with positive effects on human body exergy balance. Due to controlled surface temperatures as well as controlled exergy fluxes though building envelope, thermal insulation reflects in optimal human body exergy balance as will be discussed in the next section. 4.2. Human body exergy balance Fig. 3 presents human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and hh-a for hot/humid climate) and in a room with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and Case hh-b for hot/humid climate). If virtual person (M = 1 met, Icl = 1 clo) is exposed to the conditions in a room located at temperate climate (Tai = 20 °C, RHia = 50%, vai = 0.1 m/s; To = 14 °C, RHao = 72%), human body exergy balances between thermally non-insulated room (Case t-a) and thermally well-insulated room (Case t-b) are different (see Table 8). In the condition of Case t-a, radiant exergy rate absorbed by the whole skin and clothing surfaces is 0.15 and 0.26 W/m2 in Case t-b. In both cases there appears ‘‘warm’’ radiant exergy rate, because Tmr > To. The sum of exergy rate contained by the inhaled humid air is 0.01 W/m2 (breath air in Fig. 2) for both cases. That presents ‘‘dry’’ exergy, because outdoor and indoor air temperatures are the same, but the outdoor relative humidity is higher than the indoor relative humidity. ‘‘Warm/cool’’ exergy rate transferred by convection on the whole skin and clothing surfaces is zero for both cases. The major input exergy is the metabolic thermal exergy rate (represented by inner part, Fig. 3). This means that the thermal exergy rates of 4.67 W/m2 for virtual person in Case t-a and 4.58 W/m2 for virtual person in Case t-b are generated by ‘‘che mical’’ exergy consumption for a variety of cellular activities, ‘‘warm’’ and ‘‘wet’’ exergies of liquid water generated in the core and in the shell and ‘‘warm’’ exergy stored in the core and in the shell. They are mainly influenced by the metabolic rate and the Carnot factor (1 To/Tcr) as well as water-vapour pressure in the room space and water-vapour pressure of the outdoor air (pvr/pvo), saturated water-vapour pressure at the outdoor air temperature and water-vapour pressure in the room space (pvs(To)/pvr). Virtual person has higher metabolic thermal exergy rate in Case t-a due to larger value of (pvs(To)/pvr) than virtual person in Case t-b. The respective portions of the exergy rates of 4.67 and
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Table 8 Human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and hh-a for hot/humid climate) and a room with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and hh-b for hot/humid climate). Calculated values of exergy inputs, outputs, hbExCr and stored exergy are presented as rates [W/m2]. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Building case
Case t-a
Case t-b
Case c-a
Case c-b
Case hd-a
Case hd-b
Case hh-a
Case hd-b
PMV Tcl [°C] Tsk [°C] Tcr [°C]
0.1 25.1 32.7 36.8
0 25.7 33.1 36.8
0.7 21.6 30.9 36.8
0.1 25.5 32.9 36.8
0.3 32.3 34.1 36.8
0 31.7 33.8 36.8
0 31.8 33.8 36.8
0 31.6 33.7 36.8
Cool/warm radiant exergy in
Warm = 0.15
Warm = 0.26
Warm = 5.71
Warm = 10.46
Cool = 0.44
Cool = 0.78
Cool = 0.01
Cool/warm convective exergy in Breath air in From inner part HbExCr Stored exergy Exhalation, sweat out Cool/warm radiation out Cool/warm convection out
Cool/ warm = 0 0.01 4.67 2.99 0 0.31 Warm = 0.9 Warm = 0.62
Cool/ warm = 0 0.01 4.58 2.8 0 0.31 Warm = 1.01 Warm = 0.74
Cool/ warm = 0 0.39 13.21 4.96 0 1.97 Warm = 11.64 Warm = 0.74
Cool/ warm = 0 0.39 11.28 3.18 0 2.06 Warm = 14.08 Warm = 2.81
Cool = 0.25
Cool = 0.27
0.06 2.25 2.08 0 0.81 Cool = 0.11 Cool/ warm = 0
0.06 1.56 1.87 0 0.66 Cool = 0.15 Cool/ warm = 0
Cool/ warm = 0 Cool/ warm = 0 0.01 2.39 1.79 0.002 0.14 Warm = 0.18 Warm = 0.3
4.58 W/m2 have to be consumed and their surplus values have to be released into ambient environmental space to keep the body structure functioning. They present outgoing exergies. The rates of ‘‘warm’’ exergy stored in the core and in the shell are 0 W/m2 for both cases. It means that there is no stored exergy in this example of calculation. In general, thermal exergy stored in the body core and the skin layer emerges when there is a change in Tcr and Tsk. Usually in comfort conditions, the amount of exergy stored is negligibly small, compared to the exergy consumption, exergy output and input. The exergy rates of exhalation and evaporation of sweat are 0.31 W/m2 for both cases. They are influenced by the differences of (Tcr To), (Tcl To), and values of (Tcr/To), (Tcl/To), (pvr/pvo), and saturated water-vapour pressure at body core temperature (pvs(Tcr)/pvr). ‘‘Warm’’ radiant and ‘‘warm’’ convective exergy rates discharged from the whole skin and clothing surfaces are higher for virtual person exposed to conditions in Case t-b than in Case t-a, mainly due to higher value of Tcl. The rates of exergy consumption for thermoregulation, which is the difference between the rate of input exergy, the rate of stored exergy and the rate of output exergy, are 2.99 W/m2 for virtual person exposed to conditions in Case t-a and 2.80 W/m2 in Case t-b. Virtual person has lower hbExCr in Case t-b than t-a, mainly due to the lower input exergy rates by metabolic thermal exergy and higher output exergy rates by ‘‘warm’’ radiant exergy and ‘‘warm’’ transfer by convection. Human body exergy balances for virtual person (M = 1 met, Icl = 1 clo) exposed to conditions in a room located at cold climate (Tai = 20 °C, RHai = 50%, vai = 0.1 m/s; To = -21 °C, RHao = 61%) differ from those in temperate climate (Tai = 20 °C, RHia = 50%, vai = 0.1 m/s; To = 14 °C, RHao = 72%) for thermally non-insulated and thermally well-insulated room. The metabolic thermal exergy rates (13.21 W/m2 for Case c-a, 11.28 W/m2 for Case c-b) are approximately 2.6 times larger than those in temperate climate (4.67 W/m2 for Case t-a, 4.58 W/m2 for Case t-b), mainly due to larger values of (Tcr/To) and (Tsk/To), and larger differences of (Tcr To) and (Tsk To). The rates of warm exergy stored in the core and in the shell are 0 W/m2 for both climates. Larger difference of (To Tmr) results in higher value of ‘‘warm’’ radiant exergy rate absorbed by the whole skin and clothing surfaces (5.71 W/m2 for Case c-a, 10.46 W/m2 for Case c-b compared to both Cases in temperate climate (0.15 W/m2 for Case t-a, 0.26 W/m2 for Case t-b). The exergy rates of exhalation and evaporation of sweat are 1.97 W/m2 for Case c-a and 2.06 W/m2 for Case c-b and are higher than in
Cool/ warm = 0 0.01 2.35 1.78 0.007 0.13 Warm = 0.17 Warm = 0.28
temperate climate, due to larger differences of (Tcl To), (Tcr To) and larger values of (Tcl/To), (Tcr/To), (pvr/pvo) and (pvs(Tcr)/pvr). ‘‘Warm/cool’’ radiant and convective exergy rates discharged from the whole skin and clothing surfaces for both cases are higher in cold climate (11.64 and 0.74 W/m2 for Case c-a; 14.08 and 2.81 W/m2 for Case c-b) than in temperate climate, mainly due to the larger differences of (Tcl To) and (Tcl Tai). The rates of exergy consumption for thermoregulation are 4.96 W/m2 for Case c-a and 3.18 W/m2 for Case c-b. Both virtual persons have larger hbExCr than in temperate climate, mainly due to much higher input exergy rates. If we compare the advantages of thermal insulation in cold climate and in temperate climate, similar conclusions can be drawn. Thermal insulation in cold climate contributes to decreasing the hbExCr (for 1.78 W/m2 that is 35.9% reduction) due to lower input exergy rates of metabolic thermal exergy as well as higher output exergy rates by exhalation and evaporation of sweat, ‘‘warm’’ radiation and ‘‘warm’’ convection. Virtual person (M = 1 met, Icl = 0.3 clo) exposed to conditions in a room located at hot/dry climate (Tai = 26 °C, RHai = 50%, vai = 0.1 m/s; To = 36 °C, RHao = 10%) has lower hbExCr (2.08 W/m2 for Case hd-a, 1.87 W/m2 for Case hd-b) than in cold climate (4.96 W/m2 for Case c-a, 3.18 W/m2 for Case c-b) and temperate climate (2.99 W/m2 for Case t-a, 2.80 W/m2 for Case t-b), mainly due to the smaller input exergy by metabolic thermal exergy rate (2.25 W/m2 for Case hd-a, 1.56 W/m2 for Case hd-b). In hot/dry conditions there appears ‘‘cool’’ radiant exergy rate absorbed by the whole skin and clothing surfaces (0.44 W/m2 for Case hd-a; 0.78 W/m2 for Case hd-b) due to To > Tmr. Conditions (Tai < Tcl < To) result in ‘‘cool’’ convective exergy rate transferred from the air onto the whole skin and clothing surfaces (0.25 W/m2 for Case hd-a; 0.27 W/m2 for Case hd-b). Exhalation and evaporation of sweat are 0.81 W/m2 for Case hd-a and 0.66 W/m2 for Case hd-b. These values are lower than in cold climate due to smaller differences of (Tcr To), (Tcl To), and smaller values of (Tcr/To), (Tcl/To), (pvr/pvo), and higher than in temperate climate due to larger value of (pvs(Tcr)/pvr). In hot/dry climate there appear ‘‘cool’’ radiant exergy rates discharged from the whole skin and clothing surfaces (0.11 W/m2 for Case hd-a, 0.15 W/m2 for Case hd-b) due to To > Tcl. The values are lower than in cold and temperate climates due to smaller value of (Tcl/To). There is no exergy transfer from the skin or cloth into the air. Vice versa, if virtual person (M = 1 met, Icl = 0.3 clo) is exposed to conditions in a room located at hot/humid climate (Tai = 26 °C,
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Fig. 3. Human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and Case hh-a for hot/humid climate) and with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and Case hh-b for hot/humid climate). Calculated values of exergy inputs, outputs, hbExCr and stored exergy are presented in [W/m2]. Breath air = sum of exergies contained by the inhaled humid air; cool/warm convective exergy = cool/warm convective exergy absorbed by/discharged from the whole skin and clothing surfaces; cool/warm radiant exergy = cool/warm radiant exergy absorbed by/discharged from the whole skin and clothing surfaces; exhalation, sweat = exhalation and evaporation of sweat; inner part = metabolic thermal exergy; PMV = predicted mean vote index, stored = stored exergy in the core and in the shell; Tcl = clothing temperature (°C); Tcr = body core temperature (°C); Tsk = skin temperature (°C).
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RHai = 50%, vai = 0.1 m/s; To = 27 °C, RHao = 70%) he/she has the lowest hbExCr (1.79 W/m2 for Case hh-a and 1.78 W/m2 for Case hh-b). The lowest hbExCr results mainly due to the lower input exergies by metabolic thermal exergy rates (2.39 W/m2 for Case hh-a, 2.35 W/m2 for Case hh-b) due to smaller differences between (Tsk To), and smaller values of (Tcr/To), (Tsk/To) than in other climates. Both persons in a room located at hot/humid climate have the lowest exergy rates of exhalation and evaporation of sweat (0.14 W/m2 for Case hh-a, 0.13 W/m2 for Case hh-b), mainly due to the smaller value of (pvr/pvo). ‘‘Warm’’ radiant and convective exergy rates discharged from the whole skin and clothing surfaces are small (0.18 W/m2, 0.30 W/m2 for Case hh-a; 0.17 W/m2, 0.28 W/m2 for Case hh-b), because of small value of (Tcl/To). Results of previous studies [3,14,17] proved that at thermally neutral conditions, lower hbExCr appeared. Simone et al. [20] and Wu et al. [30] concluded that minimum hBExCr occurs under thermal conditions in which human thermal sensation was close to ‘‘slightly cool’’. The results by Ala-Juusela and Shukuya [37] agree well with the previous analyses, and pointed out that minimum hbExCr coincides with comfortable conditions in summer. Generally speaking, our results show the same, especially if we compare hbExCr for both cases located at the same climates. Lower hbExCr and more comfortable conditions (PMV closer to 0) result from thermally well-insulated cases in all climates (Cases t-b, c-b, hd-b, hh-b). However, if we compare hbExCr and PMV values among various climates, we can find out that the value of hbExCr itself strongly depends on climatic characteristics. For example, lower hbExCr appears in Case hd-a (2.08 W/m2), where PMV is 0.3 and higher hbExCr in Cases t-b (2.80 W/m2) in where PMV is 0. Similar conclusions were made by studies by Mady [38] and Dovjak [28], Dovjak et al. [34]. Mady [38] indicated that the destroyed exergy is minimal for thermal comfort conditions and relative humidities between 40% and 60%. Additionally, Mady [38] pointed out that the destroyed exergy is also minimal for low relative humidities and high temperatures. Human body exergy analyses on individual test subjects [28,34] revealed that hbExCr and each part of hbExB are affected by mutual influence of environmental parameters and personal factors. Generally speaking, for an average test subject exposed to conditions within the range of thermal comfort, lower hbExCr is obtained. Nevertheless, individual differences among us with deviations of microclimate parameters from thermal comfort range may affect each component of hbExB and decrease or increase hbExCr. Therefore, optimal values of exergy inputs, exergy outputs with hbExCr should be our mission. Health and comfort conditions result in optimal combination of hBExB and hbExCr. At this point, thermal insulation has significant benefits from building and user perspective, as it is presented in our paper. In temperate, cold, hot/dry and hot/humid climates, thermal insulation reduces the rate of exergy consumption at the interior surface of the envelope and thereby increases the rate of emitting ‘‘warm’’ or ‘‘cool’’ radiant exergy. It also contributes to the reduction of the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by convection, and the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by conduction. This proves the importance of the priority to introduce bioclimatic interventions, i.e. thermal insulation with other low-exergy technologies [7]. Note that active technologies, such as widely used air-conditioning units, without sufficient amount of thermal insulation, extinguish the ‘‘warm’’ exergy flow into the room space by a large consumption of ‘‘cool’’ exergy. This results in discomfort or even unhealthy conditions with higher exergy consumption for space cooling [7]. Thermal insulation has important advantages also for building occupants with positive effects on each component of hBExB.
Due to increased surface temperatures in cold and temperate climates, decreased surface temperatures in hot/dry and hot/humid climates and controlled exergy fluxes though building envelope, it reflects in optimal human body exergy balance. In all climates thermal insulation decreases hbExCr due to lower rate of input exergy and higher rate of output exergy. To attain health and comfort conditions, the combination of thermal insulation with other building interventions shall be introduced. Bioclimatic interventions should include measures against overheating as well as uncontrolled cooling of the building envelope [40,41]. Shukuya [7] suggests bioclimatic interventions for indoor thermal environment control such as natural ventilation together with external solar shading. The outcome of naturally ventilated room space together with external solar shading is pleasant coolness. This conditions result in the lowest hbExCr with some ‘‘cool’’ radiant exergy to be available from the interior envelope surface in the room space [7] .
5. Conclusion Exergy analysis based on the connective thinking approach helps us understand interactions between building systems and human body. That is the key factor for the attainment of comfort and healthy living and working conditions. Based on the results of the study, the following conclusions can be made: Results show that thermal insulation reduces the exergy consumption rate within building envelope systems by approximately 99.7% in all climates. It allows the interior surfaces of building envelope systems to emit ‘‘warm’’ radiant exergy into the room space in temperate and cold climates, while on the other hand it allows to emit ‘‘cool’’ radiant exergy instead of ‘‘warm’’ radiant exergy in hot/dry and hot/humid climate. Important advantage of thermal insulation on human body is its reflection into optimal human body exergy balance. In all climates thermal insulation decreases human body exergy consumption rate (6.4% decrease in temperate climate, 35.9% decrease in cold climate, 10.1% decrease in hot/dry climate, 0.6% in hot/humid climate) due to much lower input exergy rates by radiant exergy and metabolic thermal exergy as well as higher output exergy rates by exhalation and evaporation of sweat, radiation and convection. For health and comfort conditions a combination of thermal insulation with other building interventions shall be introduced. Additional exergetic studies are required to examine the efficiency of other bioclimatic interventions based on the connective thinking approach. Conflict of interest None declared. Acknowledgments Research program Building Construction and Building Physics, UL FGG, funded by the Ministry of Higher Education, Science and Technology, Republic of Slovenia; COST action C24 Analysis and design of innovative systems with LowEx for application in build environment, CosteXergy; Mediterranean Building Rethinking for Energy Efficiency Improvement (MARIE), 2007-2014 Programme MED, 1S-MED10-002.
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Contents lists available at ScienceDirect
International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt
Connective thinking on building envelope – Human body exergy analysis Mateja Dovjak a,⇑, Masanori Shukuya b,1, Aleš Krainer a,2 a b
Chair for Buildings and Constructional Complexes, Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova cesta 2, 1000 Ljubljana, Slovenia Department of Restoration Ecology and Built Environment, Tokyo City University, 3-3-1 Ushikubo-Nishi, Tsuzuki-ku, Yokohama 224-8551, Japan
a r t i c l e
i n f o
Article history: Received 24 April 2015 Received in revised form 6 July 2015 Accepted 6 July 2015
Keywords: Building envelope system Thermal exergy transfer Exergy consumption Human body exergy balance Climate type Connective thinking
a b s t r a c t The purpose of this paper is to analyse the efficiency of building interventions both from building and user point of view. With exergy analysis based on the connective thinking approach, thermal exergy flows through the building envelope are analysed jointly with human body exergy balance. Two cases of building envelope systems, thermally well-insulated case and thermally non-insulated case, are located at four typical climates (temperate, cold, hot/dry, hot/humid). ‘‘Warm’’ and ‘‘cool’’ exergies transferred by radiation, convection and conduction at the interior surface of an envelope are calculated with methodology developed by Shukuya (2013) [7,35]. Human body exergy balance (hBExB) is calculated with software developed by Asada (2010) [6]. Results show that thermal insulation significantly reduces the exergy consumption rate (ExCr) within building envelope systems in all climates. Additionally, it allows the interior surfaces of building envelope to emit ‘‘warm’’ radiant exergy into the room space in temperate and cold climates, while on the other hand to emit ‘‘cool’’ radiant exergy instead of ‘‘warm’’ radiant exergy in hot/dry and hot/humid climates. Thermal insulation has important benefits on hBExB in all climates; it decreases human body exergy consumption rate (hbExCr) due to lower input exergy and higher output exergy. Exergy analysis based on the connective thinking approach helps us to understand all interactions between building systems and human body and consequently approach to the quantitative evaluation of comfort and healthy living and working conditions. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction In order to attain strategic goals on energy efficiency in building sector there appears a strong necessity for a novel approach. Current activities on energy efficiency are often sophisticated and oriented into one-directional way of solving problems, based on mechanical measures. However, the study on exergy consumption patterns for space heating in Slovenian buildings [1] showed that interventions performed on building envelope systems resulted in 6.25 times higher total building exergy saving potential than interventions in the efficiency of mechanical systems. Additionally, the combination of building system improvements and occupant’s behavioural changes resulted in a reduction of 75–95% of exergy consumption of heating and cooling [2]. Simple actions have influence not only on significant energy savings but also on improved thermal comfort conditions [3] and occupant’s behavioural changes [2]. Shukuya [3] revealed that improved ⇑ Corresponding author. Tel.: +386 1 4768609; fax: +386 1 4250688. E-mail addresses: [email protected] (M. (M. Shukuya), [email protected] (A. Krainer). 1 Tel.: +81 45 910 2552; fax: +81 45 910 2553. 2 Tel.: +386 1 4768609; fax: +386 1 4250688.
Dovjak),
http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.07.021 0017-9310/Ó 2015 Elsevier Ltd. All rights reserved.
[email protected]
thermal comfort in winter resulted from higher mean radiant temperature and less exergy-consumption rate of the human body [3]. Bioclimatic building design arises from the location, building and human performance. All sustainable interventions should be defined in the direction of attaining health, comfort and stimulative living and working conditions as well as in the environmental protection. In general, connective thinking or the ability to connect knowledge across topics and subjects [4], is greatly missing among scientist, engineers and architects. The basic tool that results from the connective thinking approach is exergy analysis. Exergy analysis is a powerful thermodynamic technique for assessing and improving the efficiency of processes, devices and systems, as well as for enhancing environmental and economic performance [5]. Exergy analysis enables us to consider all interactions between the processes inside the human body and those in the indoor or outdoor environment [6,7]. The purpose of this paper is to analyse the efficiency of building interventions from building and user point of view. The study is focused on two cases of building envelope systems, thermally well-insulated case and thermally non-insulated case, positioned under four climate conditions (temperate, cold, hot/dry and hot/humid). With exergy approach, thermal exergy flows through the building envelopes are jointly analysed with human body
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Nomenclature Icl M Q Q/T RH S T U
v
effective clothing insulation, clo metabolic rate, met heat transfer, kJ entropy transfer by heat transfer, kJ/K relative humidity, % entropy, kJ/K temperature, °C or K thermal transmittance of building envelope, W/(m2 K) exergy, kJ water-vapour pressure in the room space, Pa water-vapour pressure of the outdoor air, Pa saturated water-vapour pressure at body-core temperature, Pa saturated water-vapour pressure at outdoor air temperature, Pa velocity, m/s
Subscripts ai ao cl cr mr sk o isw
indoor air outdoor air clothing body-core mean radiant skin environmental interior surface of an envelope
X pvr pvo pvs(Tcr) pvs(To)/pvr
exergy balance (hbExB). Understanding these interactions is the key factor for defining measures for the attainment of comfort and healthy living and working conditions with increased performance efficiency.
2. Exergy concept The origin of the word exergy goes back to 1940s, when in the United States in the M.I.T. School of Engineering, the terms ‘‘availability’’ and ‘‘available energy’’ were introduced [8,9]. Today, an equivalent term exergy has found global acceptance. The term exergy was introduced in Europe in the 1950s [10]. The property exergy is the work potential of a system in a specific environment and represents the maximum amount of useful work that can be obtained as the system is brought to equilibrium with the environment [5,8]. Unlike energy, the value of exergy depends on the state of environment. The portion of energy that cannot be converted to work is called unavailable energy. Unavailable energy is simply the difference between the total energy of a system at a specified state and the difference between total energy of a system at a specified state and the exergy of that energy [3,6–8]. Exergy as a powerful tool for the optimisation of a system may be introduced in every natural or built environments. For example, building envelope is a closed system, since no mass crosses the system boundary during the process. Entropy generation and destruction of exergy, i.e. exergy consumption, during a heat transfer process through a finite temperature difference is presented in Fig. 1. Heat transfer due to finite temperature difference is irreversible, and thereby some amount of entropy is generated as a result. The entropy generation is always accompanied by exergy consumption. Heat transfer Q, which is here in Fig. 1 defined to be positive from interior space to outdoor environment, through the surface at temperature Tisw is always accompanied by entropy
esw gen cons
exterior surface of an envelope generated consumed
Abbreviations breath air sum of exergies contained by the inhaled humid air cool, in ‘‘cool’’ exergy flow rate incoming onto the building envelope cool/warm convective exergy cool/warm convective exergy absorbed by/discharged from the whole skin and clothing surfaces cool/warm radiant exergy cool/warm radiant exergy absorbed by/discharged from the whole skin and clothing surfaces exhalation, sweat exhalation and evaporation of sweat ExCr exergy consumption rate within building systems hbExCr human body exergy consumption rate hbExB human body exergy balance inner part metabolic thermal exergy PMV predicted mean vote index stored stored exergy in the core and in the shell warm, in ‘‘warm’’ exergy flow rate incoming incoming onto the building envelope warm, out ‘‘warm’’ exergy flow rate outgoing from the building envelope
transfer in the amount of Q/Tisw and exergy transfer in the amount of (1 To/Tisw)Q [3,6–8]. As denoted for both winter and summer cases in Fig. 1, both of exergy flowing outside in winter and that flowing inside in summer are positive (in winter, due to To < Tesw and Q > 0, (1 To/Tesw)Q > 0; in summer, due to To > Tesw and Q < 0, (1 To/Tesw) Q > 0). ‘‘Warm’’ and ‘‘cool’’ exergy concepts were derived from the two laws of thermodynamics with environmental temperature [6,7]. ‘‘Warm’’ or ‘‘cool’’ exergy presents the amount of exergy contained in a substance relative to its environment. The substance has ‘‘warm’’ exergy as a quantity of state if its temperature is higher than the environment and ‘‘warm’’ exergy is the ability of thermal energy contained by the substance to disperse into the environment. The substance has ‘‘cool’’ exergy as a quantity of state if its temperature is lower than the environment, and ‘‘cool’’ exergy is the ability of the substance in which there is lack of thermal energy compared to the environment, to let the thermal energy in the environment flow into it [6,7]. Exergy concept has been introduced in various disciplines with the goal to optimise of chemical, biological and mechanical systems as well as for environmental protection. The use of exergy concept in the built environment was first introduced in the field of solar-energy utilisation by Isao Oshida [11] and further in building heating systems by Masanori Shukuya [12] and thermal comfort by Abdelaziz Hammache [13]. The relationship between human body exergy consumption rate (hbExCr) and a combination of indoor air temperature and mean radiant temperature was studied by Isawa et al. [14], Shukuya et al. [6,15,16], Prek [17], Shukuya [3,18], Prek and Butala [19]. Simone et al. [20] examined the relation between hbExCr and the human thermal sensation. The whole human body exergy balance (hBExB) under typical summer conditions in hot and humid regions was analysed by Iwamatsu and Asada [21] and Shukuya et al. [6]. Tokunaga and Shukuya [22] investigated the hBExB calculation under ‘‘unsteady-state’’ conditions.
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Fig. 1. Entropy generation and exergy consumption during ‘‘steady-state’’ heat transfer process through a building envelope with a finite temperature difference (left-winter case, where Tisw > Tesw; right-summer case, where Tisw < Tesw). Tisw is interior surface temperature of an envelope, Tesw is exterior surface temperature of an envelope, To is environmental temperature, Q is heat transfer, Sgen is entropy generated, Xcons is exergy consumed, Q/Tisw is the entropy transfer due to heat transfer, at the interior surface of an envelope, Q/Tesw is the entropy transfer, at the exterior surface of an envelope.
Predicted mean vote approach, adaptive comfort model and calculation of hbExCr were compared by Schweiker and Shukuya [23]. Additionally, Schweiker and Shukuya [24] performed a study on the effect of preference of using air-conditioning on the exergy consumption pattern within built environment. Prek and Butala [25] investigated the exergy-based correlation between thermal comfort and thermal environment. In the study by Mady et al. [26], the exergy destroyed and exergy efficiency of human body were analysed as a function of age and environmental conditions. The exergetic aspect of daylighting together with luminous and thermal comfort aspects was discussed in the study by Maki and Shukuya [27]. Dovjak [28] and Dovjak et al. [29] studied the effect of individual differences on hbExB. Since 2013, lots of new studies have been dealing with exergy analyses of the human body. Wu et al. [30] proposed a novel human body exergy consumption formula to determine indoor thermal conditions for optimal human performance in an office. Performance indicators for individuals under physical activity based on the concepts of exergy destroyed and exergy efficiency were applied by Mady et al. [31]. Caliskan [32] performed energy and exergy analyses of the human body for summer season of Izmir city in Turkey. An innovative low exergy heating and cooling system (LowEx system) was designed [33] and tested [34] in a model room for burn patient. The designed LowEx system enabled the creation of healing and comfort conditions for individual user with minimal possible energy use [33,34]. Shukuya et al. [35] developed a methodology for the calculation of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of a wall. ‘‘Unsteady’’ exergy analysis of glucose metabolism of a model neuron was performed by Genc et al. [36]. The results [36] showed that both exergy loss and work potential rates increased with increasing blood glucose concentration. The new method was applied to the case of office worker in typical and extreme weather conditions in Finland by Ala-Juusela and Shukuya [37]. The results agreed well with previous analyses, and pointed out that minimum hBExCr coincides with the comfortable one in summer conditions. The recent study by Mady et al. [38] proposed two terms of the exergy analysis to evaluate the thermal comfort condition: destroyed exergy and exergy transfer to the environment.
constructional complexes that delimit indoor and outdoor environment): thermally non-insulated case and thermally well-insulated case. Thermally non-insulated case is a reinforced concrete wall, whose thickness is 120 mm. Thermally well-insulated case is a reinforced concrete wall with 200 mm of exterior positioned cellulose fibre board (Table 1). Both cases were assumed to be located at four typical climates (temperate, cold, hot/dry and hot/humid) (Tables 1 and 2). The climate characteristics for the selected locations (Ljubljana in temperate climate, Yakutusk in cold climate, Riyadh in hot/dry climate and Yokohama in hot/humid climate) were defined according to climate database [39]. Indoor microclimatic conditions were assumed according to the climate type (Table 3). The interior and exterior surface temperatures are obtained by solving the energy balance equations with the assumption of ‘‘steady-state’’ conditions (Table 4).With exergy approach, thermal exergy flows through the building envelopes are jointly analysed with human body exergy balance (hBExB).‘‘Warm’’ and ‘‘cool’’ exergies transferred by ‘‘steady-state’’ radiation, convection and conduction at the interior surface of a wall were calculated with methodology developed by Shukuya et al. [35]. The effect of building interventions on thermal comfort was analysed with human body exergy balance model [6]. Characteristics of virtual person are presented in Table 5. 3.1. Human body exergy balance model The thermodynamic system of the human body consists of a core and a shell and is positioned in two cases of virtual room (thermally non-insulated and thermally well-insulated) located at four typical climates. Thermal exergy balance of the human body [6] was derived by combining the water, the energy and the entropy balance equations. Basic equations can be equipped both to ‘‘steady-state’’ and to ‘‘unsteady-state’’ conditions. All of them are the resultant equations of the mathematical operations described by Shukuya et al. [6], together with the environmental temperature for exergy calculation. The general form of the exergy balance equation for the human body as a system is represented in Eq. (1) [6,7]. Components of exergy input and output are presented in Table 6 [6].
Exergy input Exergy consumption 3. Methods The effect of building interventions was analysed from building and user point of view with exergy approach. The analysis was focused on two cases of building envelope systems (i.e.
¼ Exergy stored þ Exergy output
ð1Þ
To maintain homeostatic conditions, it is important that optimal hbExC rate and stored exergy values are attained with an efficient combination of exergy input and exergy output. Thermal
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Table 1 Characteristics of building envelope systems. Building case Climate
Case t-a Temperate
Case t-b Temperate
Case c-a Cold
Case c-b Cold
Case hd-a Hot/dry
Case hd-b Hot/dry
Case hh-a Hot/humid
Case hd-b Hot/humid
U value [W/(m2 K)]
3.93
0.19
3.93
0.19
3.93
0.19
3.93
0.19
Table 2 Climate characteristics. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Location Latitude/longitude
Ljubljana, Slovenia 46.22° North 14.48° East 1 385 May 14
Yakutusk, Russia 62.08° North, 129.75° East 9 103 March 21
Riyadh, South Arabia 24.7° North 46.8° East 3 612 August 36
Yokohama Japan 35.4° North 139.6° East 9 10 August 27
72
61
10
70
1
2
3
3
Time zone from Greenwich Elevation [m] Selected month Tao [°C] (average monthly) RHao [%] (average monthly) vao [m/s] (average monthly)
Tao = outdoor air temperature; RHao = relative humidity of outdoor air;
vao = wind speed.
comfort conditions were analysed by human body exergy balance (hBExB), calculated human body exergy consumption rates (hbExCr), together with conventional energy-concept based index, predicted mean votes (PMV), with spread sheet software developed by Hideo Asada [6]. For the calculation of thermal exergy transfer through building envelope systems, the indoor microclimatic conditions were different from the outdoor microclimatic conditions. The indoor microclimatic conditions were assumed according to the climate type. The interior and exterior surface temperatures were obtained by solving the energy balance equations with the assumption of ‘‘steady-state’’. For the calculation of thermal exergy transfer through the building envelope systems and for the calculation of human body exergy balance the same environmental temperature was used, i.e. outdoor air temperature (To). It was assumed that outdoor radiant temperature was equal to outdoor air temperature.
4. Results and discussion 4.1. Thermal exergy transfer through building envelope systems Building interventions should be defined considering the exergy processes in the building together with the exergy processes in the human body. Thermal insulation presents an important intervention in all climates. The effect of thermal insulation on the level of building envelope was analysed with methodology developed by Shukuya [35]. Fig. 2 shows numerical examples of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of an envelope
Table 3 Assumed indoor microclimatic conditions. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Tai [°C] RHai [%] vai [m/s]
20 50 0.1
20 50 0.1
26 50 0.1
26 50 0.1
Tai = indoor air temperature; RHai = relative humidity of indoor air; velocity.
vai = room
air
located at temperate climate (Cases t-a, t-b), cold climate (Cases c-a, c-b), hot/dry climate (Cases hd-a, hd-b) and hot/humid (Cases hh-a, hh-b). Cases t-a, c-a, hd-a and hh-a present thermally non-insulated envelopes and Cases t-b, c-b, hd-b and hh-b present thermally well-insulated envelopes. ‘‘Warm’’ or ‘‘cool’’ exergy presents the amount of exergy contained in a substance relative to its environment. The substance has ‘‘warm’’ exergy as a quantity of state if its temperature is higher than the environment and ‘‘warm’’ exergy is the ability of thermal energy contained by the substance to disperse into the environment. The substance has ‘‘cool’’ exergy as a quantity of state if its temperature is lower than the environment, and ‘‘cool’’ exergy is the ability of the substance in which there is lack of thermal energy compared to the environment, to let the thermal energy in the environment flow into it [6,7]. First, let us focus on the thermally non-insulated envelope (Case t-a) and thermally well-insulated envelope (Case t-b) located at temperate climate (Fig. 2). In Case t-a, the interior surface temperature of a reinforced concrete wall, is l6.9 °C (Tisw). If the room air temperature (Tai) is kept at 20 °C, then ‘‘warm’’ exergy flows into the wall across its interior surface at 46.3 (mW)/m2 by convection. In a concrete wall without thermal insulation, ‘‘warm’’ exergy flow going from the interior surface of the envelope by conduction is at the rate of 238.6 (mW)/m2. In Case t-b, the interior surface temperature increases up to 19.9 °C (Tisw) due to the enhancement of thermal insulation, i.e. cellulose fibre board of 200 mm. This results in the ‘‘warm’’ exergy flow rate transferred by convection from the interior boundary air layer to the interior surface of the envelope at 4.3 (mW)/m2 and ‘‘warm’’ exergy flow rate by conduction at 22.8 (mW)/m2. The increase of 3.0 K in the surface temperature, Tisw, results in a significant increase in ‘‘warm’’ radiant exergy emission rate, from 79.1 to 312.8 (mW)/m2. The comparison of two Cases t-a and t-b confirms that thermal insulation plays a crucial role in the reduction of the rate of exergy transfer from the envelope surface into the envelope inside by conduction (215.8 (mW)/m2 difference) due to higher value of (Tisw Tesw) and (1 (To/Tisw)) in Case t-b. In both cases there is ‘‘warm’’ exergy transfer into the envelope due to To 6 Tesw < Tisw. A larger difference of (Tai Tisw) in Case t-a results in higher rate of ‘‘warm’’ exergy transfer into the interior surface of the envelope by convection (42.0 (mW)/m2 difference). On the other hand, a
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M. Dovjak et al. / International Journal of Heat and Mass Transfer 90 (2015) 1015–1025 Table 4 Calculated interior and exterior surface temperatures. Building case Climate type
Case t-a Temperate
Case t-b Temperate
Case c-a Cold
Case c-b Cold
Case hd-a Hot/dry
Case hd-b Hot/dry
Case hh-a Hot/humid
Case hd-b Hot/humid
Tesw [°C] Tisw [°C] Tmr [°C]
14.9 16.9 18.5
14.1 19.9 20.0
14.6 0.9 9.5
20.7 19.0 19.5
34.4 31.1 28.6
35.9 26.3 26.1
26.8 26.5 26.3
26.9 26.0 26.0
Tai = indoor air temperature; RHai = relative humidity of indoor air; perature of an envelope; Tmr = mean radiant temperature.
vai = room air velocity; Tesw = exterior surface temperature of an envelope; Tisw = interior surface tem-
Table 5 Virtual person’s characteristics. M [met]
Icl [clo]
1
0.3 1.0
M = metabolic rate; Icl = effective clothing insulation. Icl variates according to climate conditions.
larger difference of (Tisw To) in Case t-b results in higher rate of ‘‘warm’’ radiant exergy emitted from the interior surface of the envelope compared to Case t-a (233.7 (mW)/m2 difference). In both cases there appear ‘‘warm’’ radiant exergy rates due to Tisw > To. Beside the emission of ‘‘warm’’ radiant exergy, ‘‘warm’’ radiant exergy is also absorbed by the envelope surface, due to Tmr > To. Higher rate of radiant exergy absorbed by the envelope surface arises in Case t-b than in Case t-a (138.0 (mW)/m2 difference) due to larger difference of (Trm To) in Case t-b. Thermal insulation significantly decreases exergy consumption at the surfaces caused by the absorption of radiation (21.1 (mW)/m2 difference) due to a smaller difference of (Tmr Tisw) in Case t-b. Similar findings can also be seen in cold climate for both cases. In Cases c-a and c-b, Tisw turns out to be 0.9 and 19.0 °C (Fig. 2). In these two cases, the room air is assumed to be 20 °C. Thermal insulation provided by a 200 mm tick cellulose fibre board plays a significant role in the reduction of exergy consumption rate from 852.8 (mW)/m2 in Case c-a to 2.1 (mW)/m2 in Case c-b, thereby increasing the rate of ‘‘warm’’ radiant exergy emission (11501.8 (mW)/m2 difference). It also decreases the rate of ‘‘warm’’ exergy transfer by convection between Case c-a and Case c-b (2104.0 (mW)/m2 difference) and conduction (10802.3 (mW)/m2 difference). In Cases hd-a and hh-a, Tisw turns out to be 31.1 and 26.5 °C. In these two cases, the room air is assumed to be 26 °C. ‘‘Cool’’ exergy of 205.3 and 2.1 (mW)/m2 comes from room air into the envelope surface by convection due to Tai 6 Tisw < To. If some amount of solar radiation is incident on the exterior surface of the envelope
Table 6 Components of exergy input and output [6]. Exergy input
Exergy output
Warm exergy generated by metabolism Warm/cool and wet/dry exergies of the inhaled humid air
Warm and wet exergy contained in the exhaled humid air Warm/cool and wet/dry exergy contained in resultant humid air containing the evaporated sweat Warm/cool radiant exergy discharged from the whole skin and clothing surfaces Warm/cool exergy transferred by convection from the whole skin and clothing surfaces into the surrounding air
Warm and wet exergies of the liquid water generated in the core by metabolism Warm/cool and wet/dry exergies of the sum of liquid water generated in the shell by metabolism and dry air to let the liquid water disperse Warm/cool radiant exergy absorbed by the whole skin and clothing surfaces
without thermal insulation, radiant exergy emission from the interior surface may well be ‘‘warm’’. Air conditioning unit in a room without sufficient amount of thermal insulation has to extinguish the ‘‘warm’’ exergy flow into the room space by a large consumption of ‘‘cool’’ exergy. In Cases hd-b and hh-b, Tisw is lowered down from 31.1 to 26.3 °C and from 26.5 to 26.0 °C by thermal insulation, respectively. This brings about the emergence of larger ‘‘cool’’ radiant exergy emission (984.7 (mW)/m2 in Case hd-b and 10.0 (mW)/m2 in Case hh-b). On the other hand, in Cases hh-b and hd-b, external thermal insulation equipped for a concrete wall decreases the rate of ‘‘cool’’ exergy flow by conduction (569.8 (mW)/m2 difference between Cases hd-a and hd-b and 5.8 (mW)/m2 in Cases hh-a and hh-b). In hot/dry and hot/humid climate exergy consumption rates are decreased (65.3 (mW)/m2, 0.6 (mW)/m2 differences). This is due to the assumption that mean radiant temperature is changed from 28.6 to 26.1 °C in hot/dry climate and from 26.3 to 26.0 °C in hot/humid climate. Thermal insulation enables the interior surface of the envelope to emit ‘‘cool’’ radiant exergy while extinguishing the ‘‘warm’’ exergy to come in the room space by radiation and convection primarily due to the absorption of solar radiation at the exterior surface. Let us focus on the detailed comparison among the cases. Table 7 presents the results of numerical calculations of exergy flow rates by convection, conduction and radiation, and exergy consumption for eight building cases. The rate of ‘‘cool/warm’’ radiant exergy emitted from interior surface of the envelope is the highest in the case of thermally well-insulated envelope positioned in cold climate (Case c-b: 15568.9 (mW)/m2) due to the largest difference of (Tisw To). ‘‘Cool/warm’’ radiant exergy rate is the lowest in the case of thermally non-insulated envelope positioned in hot/humid climate (Case hh-a: 2.5 (mW)/m2) due to the smallest difference of (Tisw To). Condition Tisw > To results in ‘‘warm’’ radiant exergy rates emitted from interior surface envelopes positioned in cold and temperate climates (Cases t-a, t-b, c-a, c-b). The condition of Tisw < To results in ‘‘cool’’ radiant exergy rate in hot/dry and hot/humid climate (Cases hd-a, hh-a, hd-b, hh-b). The rate of ‘‘cool/warm’’ radiant exergy absorbed by the envelope surface is the highest in thermally well-insulated envelope positioned in cold climate (Case c-b: 15951.5 (mW)/m2) due to the largest difference of (Tmr To). The rate of ‘‘cool/warm’’ radiant exergy absorbed by the envelope surface is the lowest in the case of thermally well-insulated envelope positioned in hot/humid climate (Case hh-b: 5.8 (mW)/m2) due to the smallest difference of (Tmr To). The condition of Tmr > To results in ‘‘warm’’ radiant exergy rate in temperate and cold climate (Cases t-a, t-b, c-a, c-b). The condition of Tmr < To results in ‘‘cool’’ radiant exergy absorbed by the envelope surface positioned in hot/dry and hot/humid climates (Cases hd-a, hd-b, hh-a, hh-b). Exergy consumption at the surface due to the absorption of radiation is the largest in thermally non-insulated envelope positioned in cold climate (Case c-a: 852.8 (mW)/m2) due to the largest value of (Tmr/Tisw). Exergy consumption is the smallest in the case of thermally well-insulated envelope positioned in hot/humid climate (Case t-b: 0.002 (mW)/m2) due to due to low value of (Tmr/Tisw).
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Fig. 2. Numerical examples of ‘‘warm’’ and ‘‘cool’’ exergies transferred by radiation, convection, and ‘‘steady-state’’ conduction at the interior surface of a thermally noninsulated envelope and thermally well-insulated envelope located at temperate climate (Cases t-a, t-b), cold climate (Cases c-a, c-b), hot/dry (Cases hd-a, hd-b) and hot/humid (Cases hh-a, hh-b). The numbers in the rectangles indicate the rate of exergy consumption at the surfaces due to the absorption of radiation.
The rate of exergy transfer by conduction is the highest in thermally non-insulated envelope in cold climate (Case c-a: 11870.3 (mW)/m2) due to a large (Tisw Tesw) difference. The rate of exergy transfer from room air to envelope by conduction is the lowest in the case of thermally well-insulated envelope in hot/humid climate (Case hh-b: 0.6 (mW)/m2) due to a small (Tisw Tesw) difference. Condition To 6 Tesw < Tisw results in ‘‘warm’’ exergy rate in Case t-a, Case t-b, Case c-a and Case c-b. The
condition of Tisw 6 Tesw < To results in ‘‘cool’’ exergy rate in (Cases hd-a, hd-b, hh-a, hh-b). The rate of exergy transfer from room air into the envelope surface by convection is the highest in thermally non-insulated envelope positioned in cold climate (Case c-a: 2303.9 (mW)/m2) due to the largest (Tai Tisw) difference. The rate of exergy transfer from room air into the envelope surface by convection is lowest in the case of thermally well-insulated envelope positioned in hot/humid
in = 62.0 in = 21.3 in = 631.8 in = 205.3 in = 1068.0 in = 199.9 in = 11870.3 in = 2303.9
out = 245.8 in = 571.9
Cool, Cool, 0.15 Cool, Cool, Cool, Cool, 65.4 Cool, Cool, out = 15568.9 in = 15951.1 out = 4067.1 in = 9236.5
in = 22.8 in = 4.3
Warm, Warm, 852.8 Warm, Warm, out = 312.8 in = 320.8
in = 238.6 in = 46.3
Warm, Warm, 0.1 Warm, Warm, out = 79.1 in = 182.8
Warm, Warm, 21.2 Warm, Warm, flow rate by emission of radiation [(mW)/m2] flow rate by absorption of radiation [(mW)/m2] consumption [(mW)/m2] flow rate by conduction [(mW)/m2] flow rate by convection [(mW)/m2] Exergy Exergy Exergy Exergy Exergy
14.0 14.9 16.9 20.0 18.5 To [°C] Tesw [°C] Tisw [°C] Tai [°C] Tmr [°C]
Warm, in = ‘‘warm’’ exergy flow rate incoming onto the building envelope; warm, out = ‘‘warm’’ exergy flow rate outgoing from the building envelope; cool, in = ‘‘cool’’ exergy flow rate incoming onto the building envelope; cool, out = ‘‘cool’’ exergy flow rate outgoing from the building envelope.
in = 6.4 in = 2.1
Cool, out = 10.0 Cool, in = 10.3 0.002 Cool, in = 0.6 Cool, in = 0.2 out = 2.5 in = 5.8
Cool, Cool, 0.6 Cool, Cool,
Case hd-b
Warm, Warm, 2.1 Warm, Warm,
out = 984.7 in = 1010.0
27.0 26.8 26.5 26.0 26.3 36.0 35.9 26.3 26.0 26.1 36.0 34.4 31.1 26 28.6 21.0 20.7 19.0 20.0 19.5 21.0 14.6 0.9 20.0 9.5 14.0 14.1 19.9 20.0 20.0
Hot/humid
Case hh-a Case hd-b Case hd-a Case c-b
Hot/dry Cold
Case c-a Case t-a Building case
Case t-b Temperate Climate type
Table 7 Calculated exergy flow rates by convection, conduction and radiation, and exergy consumption for eight building cases.
27.0 26.9 26.0 26.0 26.0
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climate (Case hh-b: 0.2 (mW)/m2) due to the smallest (Tai Tisw) difference. The condition of To 6 Tisw < Tai results in ‘‘warm’’ exergy rate in (Cases c-a, c-b, t-a, t-b). The condition of Tai 6 Tisw < To results in ‘‘cool’’ exergy rate in (Cases hd-a, hd-b, hh-a, hh-b). In temperate, cold, hot/dry and hot/humid climates, thermal insulation decreases the rate of exergy consumption at the interior surface of the envelope (from 850.7 (mW)/m2 or 99.8% decrease in cold climate to 21.1 (mW)/m2 or 99.5% decrease in temperate climate) and thereby increases the rate of emitting ‘‘warm’’ or ‘‘cool’’ radiant exergy (from 738.9 (mW)/m2 or 75.0% increase in hot/dry climate to 11501.8 (mW)/m2 or 73.9% increase in cold climate). It also contributes to decreasing the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by convection (from 2104.0 (mW)/m2 or 91.3% decrease in cold climate to 184.0 (mW)/m2 or 89.6% decrease in hot/dry climate), and the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by conduction (from 10802.3 (mW)/m2 or 91.0% decrease in cold climate to 215.8 (mW)/m2 or 90.4% decrease in temperate climate). Note that thermal insulation enables the interior surface of the envelope to emit ‘‘warm’’ or ‘‘cool’’ radiant exergy, which is preferable, while extinguishing the ‘‘cool’’ or ‘‘warm’’ exergy to come in the room space by radiation and convection. This proves the importance of giving the priority of bioclimatic interventions. Thermal insulation has important advantages also for building occupants, with positive effects on human body exergy balance. Due to controlled surface temperatures as well as controlled exergy fluxes though building envelope, thermal insulation reflects in optimal human body exergy balance as will be discussed in the next section. 4.2. Human body exergy balance Fig. 3 presents human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and hh-a for hot/humid climate) and in a room with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and Case hh-b for hot/humid climate). If virtual person (M = 1 met, Icl = 1 clo) is exposed to the conditions in a room located at temperate climate (Tai = 20 °C, RHia = 50%, vai = 0.1 m/s; To = 14 °C, RHao = 72%), human body exergy balances between thermally non-insulated room (Case t-a) and thermally well-insulated room (Case t-b) are different (see Table 8). In the condition of Case t-a, radiant exergy rate absorbed by the whole skin and clothing surfaces is 0.15 and 0.26 W/m2 in Case t-b. In both cases there appears ‘‘warm’’ radiant exergy rate, because Tmr > To. The sum of exergy rate contained by the inhaled humid air is 0.01 W/m2 (breath air in Fig. 2) for both cases. That presents ‘‘dry’’ exergy, because outdoor and indoor air temperatures are the same, but the outdoor relative humidity is higher than the indoor relative humidity. ‘‘Warm/cool’’ exergy rate transferred by convection on the whole skin and clothing surfaces is zero for both cases. The major input exergy is the metabolic thermal exergy rate (represented by inner part, Fig. 3). This means that the thermal exergy rates of 4.67 W/m2 for virtual person in Case t-a and 4.58 W/m2 for virtual person in Case t-b are generated by ‘‘che mical’’ exergy consumption for a variety of cellular activities, ‘‘warm’’ and ‘‘wet’’ exergies of liquid water generated in the core and in the shell and ‘‘warm’’ exergy stored in the core and in the shell. They are mainly influenced by the metabolic rate and the Carnot factor (1 To/Tcr) as well as water-vapour pressure in the room space and water-vapour pressure of the outdoor air (pvr/pvo), saturated water-vapour pressure at the outdoor air temperature and water-vapour pressure in the room space (pvs(To)/pvr). Virtual person has higher metabolic thermal exergy rate in Case t-a due to larger value of (pvs(To)/pvr) than virtual person in Case t-b. The respective portions of the exergy rates of 4.67 and
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Table 8 Human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and hh-a for hot/humid climate) and a room with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and hh-b for hot/humid climate). Calculated values of exergy inputs, outputs, hbExCr and stored exergy are presented as rates [W/m2]. Climate type
Temperate
Cold
Hot/dry
Hot/humid
Building case
Case t-a
Case t-b
Case c-a
Case c-b
Case hd-a
Case hd-b
Case hh-a
Case hd-b
PMV Tcl [°C] Tsk [°C] Tcr [°C]
0.1 25.1 32.7 36.8
0 25.7 33.1 36.8
0.7 21.6 30.9 36.8
0.1 25.5 32.9 36.8
0.3 32.3 34.1 36.8
0 31.7 33.8 36.8
0 31.8 33.8 36.8
0 31.6 33.7 36.8
Cool/warm radiant exergy in
Warm = 0.15
Warm = 0.26
Warm = 5.71
Warm = 10.46
Cool = 0.44
Cool = 0.78
Cool = 0.01
Cool/warm convective exergy in Breath air in From inner part HbExCr Stored exergy Exhalation, sweat out Cool/warm radiation out Cool/warm convection out
Cool/ warm = 0 0.01 4.67 2.99 0 0.31 Warm = 0.9 Warm = 0.62
Cool/ warm = 0 0.01 4.58 2.8 0 0.31 Warm = 1.01 Warm = 0.74
Cool/ warm = 0 0.39 13.21 4.96 0 1.97 Warm = 11.64 Warm = 0.74
Cool/ warm = 0 0.39 11.28 3.18 0 2.06 Warm = 14.08 Warm = 2.81
Cool = 0.25
Cool = 0.27
0.06 2.25 2.08 0 0.81 Cool = 0.11 Cool/ warm = 0
0.06 1.56 1.87 0 0.66 Cool = 0.15 Cool/ warm = 0
Cool/ warm = 0 Cool/ warm = 0 0.01 2.39 1.79 0.002 0.14 Warm = 0.18 Warm = 0.3
4.58 W/m2 have to be consumed and their surplus values have to be released into ambient environmental space to keep the body structure functioning. They present outgoing exergies. The rates of ‘‘warm’’ exergy stored in the core and in the shell are 0 W/m2 for both cases. It means that there is no stored exergy in this example of calculation. In general, thermal exergy stored in the body core and the skin layer emerges when there is a change in Tcr and Tsk. Usually in comfort conditions, the amount of exergy stored is negligibly small, compared to the exergy consumption, exergy output and input. The exergy rates of exhalation and evaporation of sweat are 0.31 W/m2 for both cases. They are influenced by the differences of (Tcr To), (Tcl To), and values of (Tcr/To), (Tcl/To), (pvr/pvo), and saturated water-vapour pressure at body core temperature (pvs(Tcr)/pvr). ‘‘Warm’’ radiant and ‘‘warm’’ convective exergy rates discharged from the whole skin and clothing surfaces are higher for virtual person exposed to conditions in Case t-b than in Case t-a, mainly due to higher value of Tcl. The rates of exergy consumption for thermoregulation, which is the difference between the rate of input exergy, the rate of stored exergy and the rate of output exergy, are 2.99 W/m2 for virtual person exposed to conditions in Case t-a and 2.80 W/m2 in Case t-b. Virtual person has lower hbExCr in Case t-b than t-a, mainly due to the lower input exergy rates by metabolic thermal exergy and higher output exergy rates by ‘‘warm’’ radiant exergy and ‘‘warm’’ transfer by convection. Human body exergy balances for virtual person (M = 1 met, Icl = 1 clo) exposed to conditions in a room located at cold climate (Tai = 20 °C, RHai = 50%, vai = 0.1 m/s; To = -21 °C, RHao = 61%) differ from those in temperate climate (Tai = 20 °C, RHia = 50%, vai = 0.1 m/s; To = 14 °C, RHao = 72%) for thermally non-insulated and thermally well-insulated room. The metabolic thermal exergy rates (13.21 W/m2 for Case c-a, 11.28 W/m2 for Case c-b) are approximately 2.6 times larger than those in temperate climate (4.67 W/m2 for Case t-a, 4.58 W/m2 for Case t-b), mainly due to larger values of (Tcr/To) and (Tsk/To), and larger differences of (Tcr To) and (Tsk To). The rates of warm exergy stored in the core and in the shell are 0 W/m2 for both climates. Larger difference of (To Tmr) results in higher value of ‘‘warm’’ radiant exergy rate absorbed by the whole skin and clothing surfaces (5.71 W/m2 for Case c-a, 10.46 W/m2 for Case c-b compared to both Cases in temperate climate (0.15 W/m2 for Case t-a, 0.26 W/m2 for Case t-b). The exergy rates of exhalation and evaporation of sweat are 1.97 W/m2 for Case c-a and 2.06 W/m2 for Case c-b and are higher than in
Cool/ warm = 0 0.01 2.35 1.78 0.007 0.13 Warm = 0.17 Warm = 0.28
temperate climate, due to larger differences of (Tcl To), (Tcr To) and larger values of (Tcl/To), (Tcr/To), (pvr/pvo) and (pvs(Tcr)/pvr). ‘‘Warm/cool’’ radiant and convective exergy rates discharged from the whole skin and clothing surfaces for both cases are higher in cold climate (11.64 and 0.74 W/m2 for Case c-a; 14.08 and 2.81 W/m2 for Case c-b) than in temperate climate, mainly due to the larger differences of (Tcl To) and (Tcl Tai). The rates of exergy consumption for thermoregulation are 4.96 W/m2 for Case c-a and 3.18 W/m2 for Case c-b. Both virtual persons have larger hbExCr than in temperate climate, mainly due to much higher input exergy rates. If we compare the advantages of thermal insulation in cold climate and in temperate climate, similar conclusions can be drawn. Thermal insulation in cold climate contributes to decreasing the hbExCr (for 1.78 W/m2 that is 35.9% reduction) due to lower input exergy rates of metabolic thermal exergy as well as higher output exergy rates by exhalation and evaporation of sweat, ‘‘warm’’ radiation and ‘‘warm’’ convection. Virtual person (M = 1 met, Icl = 0.3 clo) exposed to conditions in a room located at hot/dry climate (Tai = 26 °C, RHai = 50%, vai = 0.1 m/s; To = 36 °C, RHao = 10%) has lower hbExCr (2.08 W/m2 for Case hd-a, 1.87 W/m2 for Case hd-b) than in cold climate (4.96 W/m2 for Case c-a, 3.18 W/m2 for Case c-b) and temperate climate (2.99 W/m2 for Case t-a, 2.80 W/m2 for Case t-b), mainly due to the smaller input exergy by metabolic thermal exergy rate (2.25 W/m2 for Case hd-a, 1.56 W/m2 for Case hd-b). In hot/dry conditions there appears ‘‘cool’’ radiant exergy rate absorbed by the whole skin and clothing surfaces (0.44 W/m2 for Case hd-a; 0.78 W/m2 for Case hd-b) due to To > Tmr. Conditions (Tai < Tcl < To) result in ‘‘cool’’ convective exergy rate transferred from the air onto the whole skin and clothing surfaces (0.25 W/m2 for Case hd-a; 0.27 W/m2 for Case hd-b). Exhalation and evaporation of sweat are 0.81 W/m2 for Case hd-a and 0.66 W/m2 for Case hd-b. These values are lower than in cold climate due to smaller differences of (Tcr To), (Tcl To), and smaller values of (Tcr/To), (Tcl/To), (pvr/pvo), and higher than in temperate climate due to larger value of (pvs(Tcr)/pvr). In hot/dry climate there appear ‘‘cool’’ radiant exergy rates discharged from the whole skin and clothing surfaces (0.11 W/m2 for Case hd-a, 0.15 W/m2 for Case hd-b) due to To > Tcl. The values are lower than in cold and temperate climates due to smaller value of (Tcl/To). There is no exergy transfer from the skin or cloth into the air. Vice versa, if virtual person (M = 1 met, Icl = 0.3 clo) is exposed to conditions in a room located at hot/humid climate (Tai = 26 °C,
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Fig. 3. Human body exergy balances for a virtual person in a room without thermal insulation (Case t-a for temperate climate, Case c-a for cold climate, Case hd-a for hot/dry climate and Case hh-a for hot/humid climate) and with thermal insulation (Case t-b for temperate climate, Case c-b for cold climate, Case hd-b for hot/dry climate and Case hh-b for hot/humid climate). Calculated values of exergy inputs, outputs, hbExCr and stored exergy are presented in [W/m2]. Breath air = sum of exergies contained by the inhaled humid air; cool/warm convective exergy = cool/warm convective exergy absorbed by/discharged from the whole skin and clothing surfaces; cool/warm radiant exergy = cool/warm radiant exergy absorbed by/discharged from the whole skin and clothing surfaces; exhalation, sweat = exhalation and evaporation of sweat; inner part = metabolic thermal exergy; PMV = predicted mean vote index, stored = stored exergy in the core and in the shell; Tcl = clothing temperature (°C); Tcr = body core temperature (°C); Tsk = skin temperature (°C).
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RHai = 50%, vai = 0.1 m/s; To = 27 °C, RHao = 70%) he/she has the lowest hbExCr (1.79 W/m2 for Case hh-a and 1.78 W/m2 for Case hh-b). The lowest hbExCr results mainly due to the lower input exergies by metabolic thermal exergy rates (2.39 W/m2 for Case hh-a, 2.35 W/m2 for Case hh-b) due to smaller differences between (Tsk To), and smaller values of (Tcr/To), (Tsk/To) than in other climates. Both persons in a room located at hot/humid climate have the lowest exergy rates of exhalation and evaporation of sweat (0.14 W/m2 for Case hh-a, 0.13 W/m2 for Case hh-b), mainly due to the smaller value of (pvr/pvo). ‘‘Warm’’ radiant and convective exergy rates discharged from the whole skin and clothing surfaces are small (0.18 W/m2, 0.30 W/m2 for Case hh-a; 0.17 W/m2, 0.28 W/m2 for Case hh-b), because of small value of (Tcl/To). Results of previous studies [3,14,17] proved that at thermally neutral conditions, lower hbExCr appeared. Simone et al. [20] and Wu et al. [30] concluded that minimum hBExCr occurs under thermal conditions in which human thermal sensation was close to ‘‘slightly cool’’. The results by Ala-Juusela and Shukuya [37] agree well with the previous analyses, and pointed out that minimum hbExCr coincides with comfortable conditions in summer. Generally speaking, our results show the same, especially if we compare hbExCr for both cases located at the same climates. Lower hbExCr and more comfortable conditions (PMV closer to 0) result from thermally well-insulated cases in all climates (Cases t-b, c-b, hd-b, hh-b). However, if we compare hbExCr and PMV values among various climates, we can find out that the value of hbExCr itself strongly depends on climatic characteristics. For example, lower hbExCr appears in Case hd-a (2.08 W/m2), where PMV is 0.3 and higher hbExCr in Cases t-b (2.80 W/m2) in where PMV is 0. Similar conclusions were made by studies by Mady [38] and Dovjak [28], Dovjak et al. [34]. Mady [38] indicated that the destroyed exergy is minimal for thermal comfort conditions and relative humidities between 40% and 60%. Additionally, Mady [38] pointed out that the destroyed exergy is also minimal for low relative humidities and high temperatures. Human body exergy analyses on individual test subjects [28,34] revealed that hbExCr and each part of hbExB are affected by mutual influence of environmental parameters and personal factors. Generally speaking, for an average test subject exposed to conditions within the range of thermal comfort, lower hbExCr is obtained. Nevertheless, individual differences among us with deviations of microclimate parameters from thermal comfort range may affect each component of hbExB and decrease or increase hbExCr. Therefore, optimal values of exergy inputs, exergy outputs with hbExCr should be our mission. Health and comfort conditions result in optimal combination of hBExB and hbExCr. At this point, thermal insulation has significant benefits from building and user perspective, as it is presented in our paper. In temperate, cold, hot/dry and hot/humid climates, thermal insulation reduces the rate of exergy consumption at the interior surface of the envelope and thereby increases the rate of emitting ‘‘warm’’ or ‘‘cool’’ radiant exergy. It also contributes to the reduction of the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by convection, and the rate of ‘‘warm’’ or ‘‘cool’’ exergy transfer by conduction. This proves the importance of the priority to introduce bioclimatic interventions, i.e. thermal insulation with other low-exergy technologies [7]. Note that active technologies, such as widely used air-conditioning units, without sufficient amount of thermal insulation, extinguish the ‘‘warm’’ exergy flow into the room space by a large consumption of ‘‘cool’’ exergy. This results in discomfort or even unhealthy conditions with higher exergy consumption for space cooling [7]. Thermal insulation has important advantages also for building occupants with positive effects on each component of hBExB.
Due to increased surface temperatures in cold and temperate climates, decreased surface temperatures in hot/dry and hot/humid climates and controlled exergy fluxes though building envelope, it reflects in optimal human body exergy balance. In all climates thermal insulation decreases hbExCr due to lower rate of input exergy and higher rate of output exergy. To attain health and comfort conditions, the combination of thermal insulation with other building interventions shall be introduced. Bioclimatic interventions should include measures against overheating as well as uncontrolled cooling of the building envelope [40,41]. Shukuya [7] suggests bioclimatic interventions for indoor thermal environment control such as natural ventilation together with external solar shading. The outcome of naturally ventilated room space together with external solar shading is pleasant coolness. This conditions result in the lowest hbExCr with some ‘‘cool’’ radiant exergy to be available from the interior envelope surface in the room space [7] .
5. Conclusion Exergy analysis based on the connective thinking approach helps us understand interactions between building systems and human body. That is the key factor for the attainment of comfort and healthy living and working conditions. Based on the results of the study, the following conclusions can be made: Results show that thermal insulation reduces the exergy consumption rate within building envelope systems by approximately 99.7% in all climates. It allows the interior surfaces of building envelope systems to emit ‘‘warm’’ radiant exergy into the room space in temperate and cold climates, while on the other hand it allows to emit ‘‘cool’’ radiant exergy instead of ‘‘warm’’ radiant exergy in hot/dry and hot/humid climate. Important advantage of thermal insulation on human body is its reflection into optimal human body exergy balance. In all climates thermal insulation decreases human body exergy consumption rate (6.4% decrease in temperate climate, 35.9% decrease in cold climate, 10.1% decrease in hot/dry climate, 0.6% in hot/humid climate) due to much lower input exergy rates by radiant exergy and metabolic thermal exergy as well as higher output exergy rates by exhalation and evaporation of sweat, radiation and convection. For health and comfort conditions a combination of thermal insulation with other building interventions shall be introduced. Additional exergetic studies are required to examine the efficiency of other bioclimatic interventions based on the connective thinking approach. Conflict of interest None declared. Acknowledgments Research program Building Construction and Building Physics, UL FGG, funded by the Ministry of Higher Education, Science and Technology, Republic of Slovenia; COST action C24 Analysis and design of innovative systems with LowEx for application in build environment, CosteXergy; Mediterranean Building Rethinking for Energy Efficiency Improvement (MARIE), 2007-2014 Programme MED, 1S-MED10-002.
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