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Passive climate control in Spanish office buildings for long periods of time
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Building and Environment 43 (2008) 2005–2012 www.elsevier.com/locate/buildenv
Passive climate control in Spanish office buildings for long periods of time J.A. Orosa, A. Baalin˜a Departamento de Energı´a y P, Escuela Te´cnica Superior de N. y M., Universidade da Corun˜a, Paseo de Ronda 51, P.C.: 1501 A Corun˜a, Spain Received 24 July 2007; received in revised form 29 November 2007; accepted 1 December 2007
Abstract Recent studies have shown that the effect of the internal wall coating on an indoor thermal environment can be seen for short periods of time [Hameury S. Moisture buffering capacity of heavy timber structures directly exposed to an indoor climate: a numerical study. Building and Environment 2005;40(10):1400–12]. However, for long periods of time this effect is hidden by the air renovation and vapour release. These passive methods are gaining popularity because they are energy conscious and environmentally friendly. However, there is little published data on mass transfer between building envelopes and indoor air [Simonson CJ, Salonvaara MH. Mass transfer between indoor air and a porous building envelope: part I—field measurements. In: Proceedings of healthy buildings, vol. 3, 2000; Simonson CJ, Tuomo O. Moisture performance of buildings envelopes with no plastic vapour retarders in cold climates. In: Proceedings of healthy buildings, vol. 3, 2000]. The main objective of this study is to show the internal wall coating effect on indoor air conditions by means of the indoor air parameters. These measurements were taken in 25 office buildings during different seasons. Our results will allow us to understand the internal coating effect for long and short periods of time and, therefore, the thermal comfort and indoor air quality conditions. r 2007 Elsevier Ltd. All rights reserved. Keywords: Indoor air; Office; Passive methods; Humidity; Energy saving
1. Introduction This article studies the use of passive methods to control the relative humidity inside office buildings located in A Corun˜a (Spain). In general, a smooth, washable surface is considered more desirable and plastic emulsion paint is the most universal interior finish used in the western world. Porous outer walls are particularly distrusted by modern architects and engineers. Their argument is that air from inside the house, where the water vapour concentration is nearly always greater than that of outdoors, will move into the wall and in a cold climate the water vapour may occasionally condense with risk of damage to the wall. Architects therefore specify the use of an impermeable coating in the form of paint or plastic foil close to the interior surface to prevent the inside moisture from
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diffusing through the wall faster than it can evaporate to outdoor. Condensation damage is, however, known in modern buildings to have vapour barriers and more or less nonabsorbent materials in the walls. The reason for this is that any hole in the barrier will allow air to flow into parts of the wall which have no ability to delay condensation by adsorbing water vapour. After condensation has occurred, the nearly impermeable wall hinders the evaporation of water out of the wall [1]. Some authors think that parameters which reflect adsorption/desorption by all surfaces, surface condensation and drying, are considered negligible when data, in 24 h intervals is studied for a long period of time, simplifying the moisture balance [2]. Hameury [3] has shown that the buffering effect of a massive wood wall is appreciable especially at low ventilation rates. We have studied concrete walls covered with coating or paper whose buffering capacities are worse than wood but are more suitable for heat storage applications [3,4].
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On the other hand, researchers are carrying out studies to test if permeable coatings moderate indoor humidity after long periods of time (long term effects). For example, Simonson [5,6] concluded that moisture storage has a marked effect on the indoor humidity for about 2 weeks after a change in weather. When the weather changes from moderate to humid, the time that the moisture storage affects the performance is greater [5]. As hygroscopic materials affect indoor room temperature and relative humidity [5–7], the use of RH as one of the control parameters in a new HVAC control methodology provides energy saving [8]. Moreover, the moisture content in the materials does not change significantly the thermal transmittance in the insulation materials [9]. Bearing in mind all these influences our results have demonstrated the effect of walls on indoor air conditions. In this paper we will study and quantify the longterm effect in existing Spanish bank office buildings for the duration of a year to conclude if the moisture balance can be simplified. We have analysed data for 5 h during the unoccupied period when the ventilation rates were low.
2. Materials One of the components of the measuring apparatus was a multi-gas monitor. The ventilation rate was performed using concentration decay method, measuring SF6 as tracer gas with a Bru¨el&Kjaer multi-sampler made up of the following main components: (a) a photo-acoustic infrared detection microprocessor-controlled gas analyser; (b) an air multi-sampler with six sampling ports and (c) application software to remote control the gas analyser and a personal computer. The apparatus was equipped with a transducer to measure the temperature of the air at the point of sampling and an SF6 filter U0988 with accuracy 70.01 ppm and single point calibrated with certified calibration gas of concentration 10 ppm. Temperature and humidity were measured using an Innova 1221 data logger equipped with a temperature transducer MM0034, based on thermistor technology, and a humidity transducer MM0037, made up of a light emitting diode (LED), a light sensitive transistor, a mirror, a cooling element and a thermistor. The accuracies were 70.2 and 70.3 1C (dew point temperature), respectively. Tinytag Plus 2 dual channel dataloggers with thermistor and capacitive sensors were also installed to record temperature and relative humidity values with accuracies 70.2 1C and 73% HR, respectively.
3. Methods The method we have adopted is an analysis of the indoor air humidity balance and the variables that are present in the following model.
3.1. Models In order to determine if coating effect is a consideration for long periods of time, the indoor air humidity balance must be performed. There are several models that explain the humidity balance for an indoor environment. The model of Eq. (1) was used to predict and control indoor temperature and humidity as a result of the external conditions [10]. The first term of Eq. (1) represents the storage of moisture in the air volume of the room. The second term refers to people by respiration and perspiration. A typical moisture release of 0.17 l/h/avg man is estimated, for medium activity and surrounding air temperature of 20 1C of [11]. In this paper we studied bank offices with a mean level occupation of six persons per office, three workers and three clients. Therefore, a moisture release of about 5.1 l, into the surrounding air was estimated during the morning period. The third term is the moisture contributed by materials and furnishings. This moisture is released when the ambient humidity level starts to drop. Three to eight liters/day may be released in the early fall [6]. The last term of Eq. (1) is the outdoor ambient air. This moisture source depends on the air leakage rate and/or controlled ventilation. For an existing building, the air leakage rate can be measured by a tracer gas analysis of the building [11]. ASHRAE Standar 62-89 requires a minimum fresh air of 7.08–11.83 dm3/s per person. As we can conclude from this model, the amount of adsorbed water vapour depends on the wall structure, the porosity of the material and the moisture content of the surrounding air. If the material is exposed to constant air humidity for long enough, equilibrium between air and material humidity will be reached [12]. 3.2. Walls As we have explained, the third term of the model shows the effect of walls on indoor air. To get a good comparison, all the offices present the same wall structure, indoor activity and two zones that we call workers’ and clients’ zone, respectively. Workers’ zone is the region where employees serve the clients located in the clients’ zone and separated by a safety glass, see Figs. 1 and 2. These zones clearly will have different ventilation rates. The studied offices have an internal coating, see Table 1, that can be sorted as permeable (P), impermeable (I), semipermeable (SP) or semi-impermeable (SI) taking into account the buffering effect shown in this paper. The offices without extreme buffering effect are identified with letter E. The following are the components of the wall’s structure; concrete and bricks. This type of wall has been analysed by Meininghaus et al. [13] and Kirchner et al. [14] and they concluded that a concrete and brick wall has a high potential for taking up organic compounds from the indoor air. This buffer effect of the building envelope on
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Clients’ zone
Employees’ zone
Fig. 1. Office building zones.
1 2
8 3
4
5
6
7
Fig. 2. Layers of a standard wall. 1. External coating (Marble); 2. Concrete (1 cm.); 3. Brick (8 cm.); 4. Air barrier (3 cm.); 5. Polystyrene (3 cm.); 6. Brick (8 cm.); 7. Concrete (1 cm.); 8. Internal coating (plaster, 1 cm.) Table 1 Wall coatings of the studied offices Office
Coating
P1 P2 P3
Paper
P4
Plaster
E1 E2 E3 E4 E5 E6
Paint
SI1
Wood
SI2 P5 SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8
Plastic
I1 I2 I3 I4
Glass
the indoor air quality may be beneficial, since peak concentrations are reduced, and compounds may be stored in the walls of a house.
2007
To determine concrete moisture storage capacity Simonson’s method can be employed when the indoor air relative humidity changes. In his work, he demonstrates that samples of porous concrete with salt adsorb or desorb the moisture when the environment humidity changes [15]. In our study, concrete with less salt content is used, therefore moisture buffering will influence indoor air conditions but to a lesser extent. The concrete moisture capacity is calculated [15], for example, using the sorption curve between 40% and 60% RH as follows, see Eq. (2). The moisture diffusivity is calculated analogous to thermal diffusivity as in Eq. (3). For a thickness of 1 cm and a surface of 1 m2, the concrete moisture capacity is 0.382 (g/%RH). This value is quite interesting compared with the 0.673 (g/%RH) of wood [5], because it demonstrates the potential of concrete for moisture buffering. It should also be noted that the definition of moisture diffusivity from Eq. (3) neglects the moisture storage in the air within the porous material [16,17]. This effect is negligible for most hygroscopic materials. 3.3. Vapour driving potential The second term of the model includes another moisture source on indoor air as a result of the driving potential. The reasons by which we analysed the indoor air based on the partial vapour pressure were explained by Trechsel [11]. It was also concluded that the driving potential for vapour transport is the gradient of vapour pressure at the surface as shown in Eq. (4). It was also concluded that as moisture is transported through a finite volume in a medium, the amount of moisture retained by the volume is altered during any transient stage of the transport process. The basic reason for this is a change in local temperature or vapour pressure. There is, however, some doubt that the vapour pressure is the driving force for diffusion through walls when there is not air pressure difference. In the building literature it is often assumed, without a shadow of a doubt, that vapour pressure is the defining variable when discussing water movement in walls, but there is evidence that it is the relative humidity difference that drives diffusion through absorbent materials [1]. For these reasons, the vapour partial pressure has been used for determining an index that allows a comparison of the effect of the coverings, by means of the equations defined by the ASHRAE. The uncertainty of the calculated vapour pressure was 70.07 kPa. This index will be used to consider the excesses of the indoor versus outdoor partial vapour pressure, following Hens’ work [2]. 3.4. Calculation of ventilation rate The last term of the model in Eq. (1) depends on indoor and outdoor water vapour content and air ventilation rate. In these offices heating is used to control the indoor
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temperature during the cold season but in summer temperatures freely oscillate. Indoor relative humidity and indoor vapour pressure are not controlled at all. The ventilation rate is desirable to maintain a slight overpressure within the room to stop dust and pollutants from entering. This rate can be measured by the tracer gas decay technique based on both the emission of SF6, suitably mixed with the indoor air and the following mass balance (Eq. (5)). The air exchange or infiltration rate I is given by Eq. (6). As there is not a source of tracer gas, F(t) ¼ 0 and, assuming I is constant, a solution to Eq. (5) is Eq. (7) or (8). The offices show the same distribution of the studied zones separated by a safety glass. Only one office does not have separation between employees’ and clients’ zones. Therefore, the sampling of SF6 has been made in two representative offices during occupied period, one of them without communication between zones and the other one with communication. A monitor multi-gas 1302 was used for the tracer gas monitoring. Ventilation rates were measured simultaneously to take into account the air exchange between zones. Calculated values show an uncertainty less than 70.002 h1.
mines the memory of a material, such that events that happened more than 4 * t before time t have no affect on the sorption at time t [12]. The studied offices are not of recent construction, therefore the sampling has been performed when the materials already are properly stabilized. The humidity generation period in the offices corresponds with 5 h of activity from 9:00 to 14:00, hence we have studied the non-occupied period for a year (long term). Sampling has been made with a frequency of 5–10 min during the unoccupied period of each season. We have studied the unoccupied period because the ventilation rates are lower allowing a better study of the materials behaviour. Sensors were placed, following Hens’ method [2] and ISO 7730 [19], in a particular location according to the indoor conditions. They were moved away from heat disturbances originating from heat sources such as computers. In each office, two sensors were placed to monitor simultaneously the indoor air both in the clients’ zone and in the employees’ zone.
3.5. Climatic data
Once the vapour pressure differential between indoor/ outdoor conditions was calculated, a statistical study of the averages of those values was taken. The comparison of averages was carried out by means of analysing the variance of a factor (one-way Anova) using the statistical software SPSS 11.0, for a level of significance of 0.05. This analysis was initially taken by using the daily average values of the summer and winter seasons in order to compare the evolutions of all offices during the unoccupied period and to determine if they are considered equal or in the opposite case, if they define groups. These groups will show the same evolution for a level of significance of 0.05.
The values of the outdoor conditions were obtained by means of weather stations next to the city, to avoid the buildings affecting the measured values of the outer conditions. The Environmental Information system of Galicia (SIAM) [18] facilitates those accessing information on the environment and climatology. Another organization that provides the meteorological data is the Forest and Environmental Research Center of Louriza´n (Ministry of Environment of the Xunta de Galicia). This centre is made up of 42 stations of climatologic observation, distributed throughout the Galician region. In 1988, it began the installation of a modern network of automatic stations of meteorological observation. In 2000, 23 new stations arrived which transmit information in real time. 3.6. Indoor air Twenty-five office buildings located in A Corun˜a were monitored in different zones and seasons. Temperature and indoor relative humidity conditions were sampled by means of Tinytag dataloggers (Meaco Europe), which allowed continuous monitoring for long periods of time. 3.7. Sampling period The material moisture content is related to the history of the humidity of the indoor air via an exponentially weighted time averaging term, controlled by a materialdependent time parameter tc. This time parameter deter-
3.8. Statistical study
4. Results 4.1. Climatic conditions The outer climate has been provided by MeteoGalicia [20] with a 10 min frequency. Figs. 3–5 show averaged data monthly. One can observe that A Corun˜a has a moderate climate where temperatures are neither too low in winter nor too high in summer. Also, a high relative humidity can be observed as a result of its proximity to the sea. Fig. 5 shows the absolute humidity from which can be deduced a humid summer and winter, but extreme values are never reached. 4.2. Ventilation rates The measured ventilation rates ranged from 1.05 h1 in the clients’ zone to 0.93 h1 in the employees’ zone.
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Temperature (°C)
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20
4.4. Season analysis
15
The obtained results have shown that coverings considered as semi-permeable, have the same behaviour, whereas those permeable and impermeable are different between themselves for a level of significance of 0.05. Now, we will be able to know if it is necessary to take into account the effect of coverings on indoor conditions. Firstly, as mechanical ventilation is not working and the offices are nearly air tight, we consider the ventilation rate during the unoccupied period less than 0.5 ach following the results in multi-storey buildings of La Corun˜a [21]. During the occupied period indoor partial vapour pressure cannot be compared to the outdoor as a result of the high ventilation rate that causes the same indoor and outdoor conditions, therefore the difference is usually null. Another factor to be considered is that during the occupied period the heating system is working, along with the loss of heat from people. Although the indoor partial vapour pressure is normally higher than the outdoor one, the hygroscopic inertia of the environment can sometimes revert the former situation, as Hens’ comments [2]. In summer there is a greater tendency to reduce the excess of partial vapour pressure, while in winter indoor partial vapour pressure is clearly higher than the outdoor one. In Table 2, daily average values of indoor–outdoor partial vapour pressure differences are shown for the unoccupied period in the 25 offices during summer and winter. The monitored unoccupied period is from 14:00 to 19:00 because these measurements show the real effect of the coverings on the indoor air without being influenced by the excessive ventilation rates of the occupied period. Once the Anova study was made for a level of significance of 0.05, three groups A, B and C were detected and were considered with homogeneous behaviour. These groups appear separated by two discontinuous lines. In addition, we can see that the offices which exceed the lower significance limit during summer season will exceed the opposed limit during winter. For example, offices P1, P2, P3, P4 and P5 show the highest excess of indoor partial vapour pressure during winter and the lowest during the summer. These offices have the most permeable internal coverings like paper which let humidity transfer to the building structure. We found the opposite behaviour in offices I1, I2 and I3, where the indoor partial vapour pressure is the highest during summer and the lowest during winter. In these offices there were more impermeable coverings like paintings. Instantaneous values of indoor/outdoor temperatures and vapour pressures during typical winter and summer days in some of the bank offices are shown in Figs. 6–9. These figures show the extreme behaviour of the building environment and they are in accordance with Table 2. For example, in Fig. 6 the permeable coating P4 has an indoor
10 5 0 1
2
3
4
5
6
7
8
9
10
11
12
9
10
11
12
10
11
12
Month
Relative Humidity (%)
Fig. 3. Outdoor temperature.
94 92 90 88 86 84 82 80 78 1
2
3
4
5
6 7 Month
8
Fig. 4. Outdoor relative humidity.
Absolute Humidity (kg/kg)
2009
0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
1
2
3
4
5
6 7 Month
8
9
Fig. 5. Outdoor absolute humidity.
Calculated values have shown a mean of 1 h1 with a standard deviation of 0.05 h1. These values indicate the increase of ventilation rates in the clients’ zone mainly as a result of the infiltrations produced by the entrance and exit of people through the front door. Nevertheless, these values are relatively close to the required minimum ventilation rate in both zones.
4.3. Data analysis The statistical study of the Anova has been based on a null hypothesis that all the averages of the indoor conditions in offices with different coverings during the unoccupied periods are equal. The alternative hypothesis is that the averages are different. A level of significance of 0.05 has been chosen for this case.
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2010
Permeable 4-Winter Partial vapour pressure (Pa)
Table 2 Internal–external partial vapour pressure difference 1600 1400 1200 1000 800 600 400 0:00
Permeable Outdoor
6:00
12:00 Time (Hours)
0:00
18:00
Fig. 7. Time variations of indoor and outdoor partial vapour pressure in office P4 (permeable coating) during a winter day.
Partial vapour pressure (Pa)
Impermeable 3-Summer
I, Impermeable; P, Permeable; SI, semi-impermeable; SP, semi-permeable; E, no effect.
2000 1900 1800 1700 1600 1500 1400 0:00
Impermeable Outdoor
6:00
12:00 Time (Hours)
18:00
0:00
Fig. 8. Time variations of indoor and outdoor partial vapour pressure in office I3 (impermeable coating) during a summer day.
Impermeable 3-Winter Partial vapour pressure (Pa)
Partial vapour pressure (Pa)
Permeable 4-Summer 2200 2000 1800 1600 1400 1200 1000 0:00
Permeable Outdoor
6:00
12:00 Time (Hours)
18:00
0:00
Fig. 6. Time variations of indoor and outdoor partial vapour pressure in office P4 (permeable coating) during a summer day.
partial vapour pressure lower than the outdoor one in the unoccupied period during summer and the opposite behaviour can be observed in Fig. 7 during winter. The impermeable coating I3 in Fig. 8 shows less outdoor partial
1400 1350 1300 1250 1200 1150 1100 12:00
Impermeable Outdoor
18:00
0:00 Time (Hours)
6:00
12:00
Fig. 9. Time variations of indoor and outdoor partial vapour pressure in office I3 (impermeable coating) during a winter day.
vapour pressure than indoor in summer, reverting this tendency in winter (Fig. 9). These results are in accordance with [6,22] where, for all ventilation rates, the permeable test case shows lower
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maximum humidity in summer and higher minimum humidity in winter than the impermeable test case. As an intermediate case, we considered those coverings that present certain tendency towards both sides of the mean. For example, the wood covering (SI1), which presents superficial treatment to avoid its deterioration but, even so, a tendency has been detected to revert its position with respect to the average value indicated by the gross black line. Another intermediate case of opposite tendencies is the office SP7, which shows a certain tendency towards an impermeable covering. There are offices that hold their position with seasons, as is the case of some paintings (E2). The offices with plastic coatings showed a variable buffering effect so they can be considered as semi-permeable (SP8), semi-impermeable (SI2) and permeable (P5). This behaviour can be related to the degree of wear on the surface of the coatings. As a result of this study it is possible to indicate that indoor coverings have an influence on the indoor environment for a long-term average study. It is important to take this influence into account to avoid error. We must consider that our study was carried out in offices with an air barrier and, in some cases, with vapour retarder because of paintings. This type of wall is like those studied by Hens [2] and different from Simonson constructions [23] but the obtained results show the same tendencies. 4.5. Air quality and energy saving We have concluded that an absorbent structure will moderate the indoor relative humidity during the relatively brief opening hours. Some authors are in accordance with these results and show new permeable structure advantages like energy saving, noise reduction and smaller space occupied by the distribution ducts [1,4,8]. For example, at low ventilation rates below 0.5 h1 diffusion through materials may reduce the concentration of VOCs in a room. The right choice of wall materials can have an impact on the indoor air quality, for example, walls with a high degree of permeability [13]. Another example is that a rather small air conditioning system can then re-establish the correct climate during a long period when the building is vacant, and therefore there is no need for outdoor ventilation [1]. If sorption effects take place, the time required to ventilate a gaseous compound out of a room can change considerably. 5. Conclusions We have demonstrated that permeable coverings improve indoor conditions in spite of the use of an air barrier and less permeable coverings such as wood. This effect confirms that during a long-term study the internal permeable coverings maintain their regulation property as a result of the existence of more than 4 h of excessive
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indoor humidity previous to the studied period. These results confirm the studies of Simonson. During the occupied period, when the temperature is higher, the emission of VOCs from materials is favoured. In addition, it is possible to wait for a regulating effect of the permeable coverings on VOCs so they are adsorbed during the occupied period and released when the air is cleaner allowing better indoor air quality. These two theories would allow, with a more intelligent design, energy saving in indoor air renovation, especially during the first moments of occupancy in the enclosure. This effect and its implications on the indoor thermal comfort can be analysed in later studies. Appendix
V
dcin ¼ G þ M þ nV ðcout cin Þ, dt
(1)
where t is the time (s), V the volume of the room (m3), n the air ventilation rate (s1), c the water vapour content (kg/m3), G the moisture generation rate (kg/s) and M the sum of moisture quantities contributed by buildings components (kg/s). rV 1000 , (2) C m ¼ ðu60%Rh u40%RH Þ 20 where Cm is the moisture capacity (g/%RH), u is the moisture content (kg/kg), r is the density of the material (k/m3) and V is the volume of the material (m3). am ¼
kd , ðC m =ð1000V ÞÞ100=Pvsat
(3)
where Pvsat is the saturation pressure for water vapour at 22 1C (Pa), kd the water vapour permeability (kg/(s m Pa)), Cm the moisture capacity (g/%RH) and am the moisture diffusivity (m2/s). J v ¼ m grad p;
(4)
where m is the water vapour permeability of the medium (kg/(s m Pa)), Jv the water vapour flux density (kg/m2 s) and grad p the driving potential (Pa/m). dCðtÞ ¼ F ðtÞ qðtÞCðtÞ, dt
(5)
where C(t) is the tracer gas concentration (dimensionless), dC(t)/dt the time derivative of concentration, q(t) volumetric airflow rate out of the building (m3/h), F(t) volumetric tracer gas injection rate (m3/h), t the time and V the building volume (m3). IðtÞ ¼
qðtÞ , V
(6)
where I is in air changes per hour (h1). C ¼ C 0 expðItÞ, 1 C0 I ¼ ln . t C
(7) (8)
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References [1] Padfield T. The role of absorbent building materials in moderating changes of relative humidity. PhD thesis, Department of Structural Engineering and Materials, The Technical University of Denmark, October 1998. [2] Hens H. Indoor climate in student rooms: measured values. IEAEXCO energy conservation in buildings and community systems annex 41 ‘‘moist-eng’’ Glasgow meeting. [3] Hameury S. Moisture buffering capacity of heavy timber structures directly exposed to an indoor climate: a numerical study. Building and Environment 2005;40(10):1400–12. [4] Hameury S, Lundstrom T. Contribution of indoor exposed massive wood to a good indoor climate: in situ measurement campaign. Energy and Buildings 2004;36:281–92. [5] Simonson CJ, Salonvaara M, Ojalen T. Improving indoor climate and comfort with wooden structures. Espoo 2001.Technical Research Centre of Finland, VTT Publications 431.200p.+ app 91 p. [6] Salonvaara MH, Simonson CJ. Mass transfer between indoor air and a porous building envelope: Part II. Validation and numerical studies. In: Proceedings of healthy buildings, vol. 3, 2000. [7] Aydin I, Colakoglu G, Colak S, Demirkir C. Effects of moisture content on formaldehyde emission and mechanical properties of plywood. Building and Environment 2006;41(10):1311–6. [8] Osanyintola OF, Simonson CJ. Moisture buffering capacity of hygroscopic building materials: experimental facilities and energy impact. Energy and Buildings 2006;38:1270–82. [9] Nicolajsen A. Thermal transmittance of a cellulose loose-fill insulation material. Building and Environment 2005;40(7): 907–14. [10] Lu¨ X-S, Viljanen M. Predicting and controlling indoor thermal and moisture content—the effect of material storage capacity. In: Proceedings of healthy buildings, vol. 3, 2000. [11] Trechsel HR, editor. Moisture control in buildings. ASTM manual series, February 1994. [12] Plathner P, Littler J, Stephen R. Dynamic water vapour sorption: measurement and modelling. In: Proceedings of indoor air quality ’99, 1999.
[13] Meininghaus R, Knudsen HN, Gunnarsen L. Impact of sorption and diffusion on indoor air pollution. In: Proceedings of indoor air quality ’99, 1999. [14] Kirchner S, Badey JR, Knudsen HN, Meininghaus R, Quenard D, Saarela K, et al. Sorption capacities and diffusion coefficients of indoor surface materials exposed to VOCS: proposal of new test procedures. In: Proceedings of indoor air quality ’99, 1999. [15] Yongling W, Ruilun Z, Zizhong D. Primary research on moisture absorption and desorption function of aerocrete as building element material for dehumidification. In: Proceedings of healthy buildings, vol. 3, 2000. [16] Olutimayin SO, Simonson CJ. Measuring and modeling vapor boundary layer growth during transient diffusion heat and moisture transfer in cellulose insulation. International Journal of Heat and Mass Transfer 2005;48:3319–30. [17] Talukdar P, Osanyintola OF, Olutimayin SO, Simonson CJ. An experimental data set for benchmarking 1-D, transient heat and moisture transfer models of hygroscopic building materials, part II: experimental, numerical and analytical data. International Journal of Heat and Mass Transfer 2007, in press /http://dx.doi.org/ doi:10.1016/j.ijheatmasstransfer.2007.03.025S. [18] Environmental Information system of Galicia 2007 (SIAM). Siam. /http://www.Siam-cma.org/S. [19] International Standard ISO 7730-2005. Ergonomics of the thermal environment. Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. [20] MeteoGalicia. Anuario climatolo´xico de Galicia 2002. Consellerı´ a de Medio Ambiente. Xunta de Galicia. ISBN: 84-453-3520-0. [21] Rodrı´ guez E, Baalin˜a A, Va´zquez A, Castellanos L, Santaballa JA, Infante CR. Indoor air quality evaluation using carbon dioxide levels in bedrooms in a A Corun˜a, Spain. In: Proceedings of indoor air ’99, vol. 5, Edinburgh (Scotland), 1999. p. 335–40. [22] Simonson CJ, Salonvaara MH. Mass transfer between indoor air and a porous building envelope: part I. Field measurements. In: Proceedings of healthy buildings, vol. 3, 2000. [23] Simonson CJ, Tuomo O. Moisture performance of buildings envelopes with no plastic vapour retarders in cold climates. In: Proceedings of healthy buildings, vol. 3, 2000.
Building and Environment 43 (2008) 2005–2012 www.elsevier.com/locate/buildenv
Passive climate control in Spanish office buildings for long periods of time J.A. Orosa, A. Baalin˜a Departamento de Energı´a y P, Escuela Te´cnica Superior de N. y M., Universidade da Corun˜a, Paseo de Ronda 51, P.C.: 1501 A Corun˜a, Spain Received 24 July 2007; received in revised form 29 November 2007; accepted 1 December 2007
Abstract Recent studies have shown that the effect of the internal wall coating on an indoor thermal environment can be seen for short periods of time [Hameury S. Moisture buffering capacity of heavy timber structures directly exposed to an indoor climate: a numerical study. Building and Environment 2005;40(10):1400–12]. However, for long periods of time this effect is hidden by the air renovation and vapour release. These passive methods are gaining popularity because they are energy conscious and environmentally friendly. However, there is little published data on mass transfer between building envelopes and indoor air [Simonson CJ, Salonvaara MH. Mass transfer between indoor air and a porous building envelope: part I—field measurements. In: Proceedings of healthy buildings, vol. 3, 2000; Simonson CJ, Tuomo O. Moisture performance of buildings envelopes with no plastic vapour retarders in cold climates. In: Proceedings of healthy buildings, vol. 3, 2000]. The main objective of this study is to show the internal wall coating effect on indoor air conditions by means of the indoor air parameters. These measurements were taken in 25 office buildings during different seasons. Our results will allow us to understand the internal coating effect for long and short periods of time and, therefore, the thermal comfort and indoor air quality conditions. r 2007 Elsevier Ltd. All rights reserved. Keywords: Indoor air; Office; Passive methods; Humidity; Energy saving
1. Introduction This article studies the use of passive methods to control the relative humidity inside office buildings located in A Corun˜a (Spain). In general, a smooth, washable surface is considered more desirable and plastic emulsion paint is the most universal interior finish used in the western world. Porous outer walls are particularly distrusted by modern architects and engineers. Their argument is that air from inside the house, where the water vapour concentration is nearly always greater than that of outdoors, will move into the wall and in a cold climate the water vapour may occasionally condense with risk of damage to the wall. Architects therefore specify the use of an impermeable coating in the form of paint or plastic foil close to the interior surface to prevent the inside moisture from
Corresponding author. Tel.: +34 981 167000; fax: +34 981 167 107.
E-mail address: [email protected] (J.A. Orosa). 0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2007.12.001
diffusing through the wall faster than it can evaporate to outdoor. Condensation damage is, however, known in modern buildings to have vapour barriers and more or less nonabsorbent materials in the walls. The reason for this is that any hole in the barrier will allow air to flow into parts of the wall which have no ability to delay condensation by adsorbing water vapour. After condensation has occurred, the nearly impermeable wall hinders the evaporation of water out of the wall [1]. Some authors think that parameters which reflect adsorption/desorption by all surfaces, surface condensation and drying, are considered negligible when data, in 24 h intervals is studied for a long period of time, simplifying the moisture balance [2]. Hameury [3] has shown that the buffering effect of a massive wood wall is appreciable especially at low ventilation rates. We have studied concrete walls covered with coating or paper whose buffering capacities are worse than wood but are more suitable for heat storage applications [3,4].
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On the other hand, researchers are carrying out studies to test if permeable coatings moderate indoor humidity after long periods of time (long term effects). For example, Simonson [5,6] concluded that moisture storage has a marked effect on the indoor humidity for about 2 weeks after a change in weather. When the weather changes from moderate to humid, the time that the moisture storage affects the performance is greater [5]. As hygroscopic materials affect indoor room temperature and relative humidity [5–7], the use of RH as one of the control parameters in a new HVAC control methodology provides energy saving [8]. Moreover, the moisture content in the materials does not change significantly the thermal transmittance in the insulation materials [9]. Bearing in mind all these influences our results have demonstrated the effect of walls on indoor air conditions. In this paper we will study and quantify the longterm effect in existing Spanish bank office buildings for the duration of a year to conclude if the moisture balance can be simplified. We have analysed data for 5 h during the unoccupied period when the ventilation rates were low.
2. Materials One of the components of the measuring apparatus was a multi-gas monitor. The ventilation rate was performed using concentration decay method, measuring SF6 as tracer gas with a Bru¨el&Kjaer multi-sampler made up of the following main components: (a) a photo-acoustic infrared detection microprocessor-controlled gas analyser; (b) an air multi-sampler with six sampling ports and (c) application software to remote control the gas analyser and a personal computer. The apparatus was equipped with a transducer to measure the temperature of the air at the point of sampling and an SF6 filter U0988 with accuracy 70.01 ppm and single point calibrated with certified calibration gas of concentration 10 ppm. Temperature and humidity were measured using an Innova 1221 data logger equipped with a temperature transducer MM0034, based on thermistor technology, and a humidity transducer MM0037, made up of a light emitting diode (LED), a light sensitive transistor, a mirror, a cooling element and a thermistor. The accuracies were 70.2 and 70.3 1C (dew point temperature), respectively. Tinytag Plus 2 dual channel dataloggers with thermistor and capacitive sensors were also installed to record temperature and relative humidity values with accuracies 70.2 1C and 73% HR, respectively.
3. Methods The method we have adopted is an analysis of the indoor air humidity balance and the variables that are present in the following model.
3.1. Models In order to determine if coating effect is a consideration for long periods of time, the indoor air humidity balance must be performed. There are several models that explain the humidity balance for an indoor environment. The model of Eq. (1) was used to predict and control indoor temperature and humidity as a result of the external conditions [10]. The first term of Eq. (1) represents the storage of moisture in the air volume of the room. The second term refers to people by respiration and perspiration. A typical moisture release of 0.17 l/h/avg man is estimated, for medium activity and surrounding air temperature of 20 1C of [11]. In this paper we studied bank offices with a mean level occupation of six persons per office, three workers and three clients. Therefore, a moisture release of about 5.1 l, into the surrounding air was estimated during the morning period. The third term is the moisture contributed by materials and furnishings. This moisture is released when the ambient humidity level starts to drop. Three to eight liters/day may be released in the early fall [6]. The last term of Eq. (1) is the outdoor ambient air. This moisture source depends on the air leakage rate and/or controlled ventilation. For an existing building, the air leakage rate can be measured by a tracer gas analysis of the building [11]. ASHRAE Standar 62-89 requires a minimum fresh air of 7.08–11.83 dm3/s per person. As we can conclude from this model, the amount of adsorbed water vapour depends on the wall structure, the porosity of the material and the moisture content of the surrounding air. If the material is exposed to constant air humidity for long enough, equilibrium between air and material humidity will be reached [12]. 3.2. Walls As we have explained, the third term of the model shows the effect of walls on indoor air. To get a good comparison, all the offices present the same wall structure, indoor activity and two zones that we call workers’ and clients’ zone, respectively. Workers’ zone is the region where employees serve the clients located in the clients’ zone and separated by a safety glass, see Figs. 1 and 2. These zones clearly will have different ventilation rates. The studied offices have an internal coating, see Table 1, that can be sorted as permeable (P), impermeable (I), semipermeable (SP) or semi-impermeable (SI) taking into account the buffering effect shown in this paper. The offices without extreme buffering effect are identified with letter E. The following are the components of the wall’s structure; concrete and bricks. This type of wall has been analysed by Meininghaus et al. [13] and Kirchner et al. [14] and they concluded that a concrete and brick wall has a high potential for taking up organic compounds from the indoor air. This buffer effect of the building envelope on
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Clients’ zone
Employees’ zone
Fig. 1. Office building zones.
1 2
8 3
4
5
6
7
Fig. 2. Layers of a standard wall. 1. External coating (Marble); 2. Concrete (1 cm.); 3. Brick (8 cm.); 4. Air barrier (3 cm.); 5. Polystyrene (3 cm.); 6. Brick (8 cm.); 7. Concrete (1 cm.); 8. Internal coating (plaster, 1 cm.) Table 1 Wall coatings of the studied offices Office
Coating
P1 P2 P3
Paper
P4
Plaster
E1 E2 E3 E4 E5 E6
Paint
SI1
Wood
SI2 P5 SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8
Plastic
I1 I2 I3 I4
Glass
the indoor air quality may be beneficial, since peak concentrations are reduced, and compounds may be stored in the walls of a house.
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To determine concrete moisture storage capacity Simonson’s method can be employed when the indoor air relative humidity changes. In his work, he demonstrates that samples of porous concrete with salt adsorb or desorb the moisture when the environment humidity changes [15]. In our study, concrete with less salt content is used, therefore moisture buffering will influence indoor air conditions but to a lesser extent. The concrete moisture capacity is calculated [15], for example, using the sorption curve between 40% and 60% RH as follows, see Eq. (2). The moisture diffusivity is calculated analogous to thermal diffusivity as in Eq. (3). For a thickness of 1 cm and a surface of 1 m2, the concrete moisture capacity is 0.382 (g/%RH). This value is quite interesting compared with the 0.673 (g/%RH) of wood [5], because it demonstrates the potential of concrete for moisture buffering. It should also be noted that the definition of moisture diffusivity from Eq. (3) neglects the moisture storage in the air within the porous material [16,17]. This effect is negligible for most hygroscopic materials. 3.3. Vapour driving potential The second term of the model includes another moisture source on indoor air as a result of the driving potential. The reasons by which we analysed the indoor air based on the partial vapour pressure were explained by Trechsel [11]. It was also concluded that the driving potential for vapour transport is the gradient of vapour pressure at the surface as shown in Eq. (4). It was also concluded that as moisture is transported through a finite volume in a medium, the amount of moisture retained by the volume is altered during any transient stage of the transport process. The basic reason for this is a change in local temperature or vapour pressure. There is, however, some doubt that the vapour pressure is the driving force for diffusion through walls when there is not air pressure difference. In the building literature it is often assumed, without a shadow of a doubt, that vapour pressure is the defining variable when discussing water movement in walls, but there is evidence that it is the relative humidity difference that drives diffusion through absorbent materials [1]. For these reasons, the vapour partial pressure has been used for determining an index that allows a comparison of the effect of the coverings, by means of the equations defined by the ASHRAE. The uncertainty of the calculated vapour pressure was 70.07 kPa. This index will be used to consider the excesses of the indoor versus outdoor partial vapour pressure, following Hens’ work [2]. 3.4. Calculation of ventilation rate The last term of the model in Eq. (1) depends on indoor and outdoor water vapour content and air ventilation rate. In these offices heating is used to control the indoor
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temperature during the cold season but in summer temperatures freely oscillate. Indoor relative humidity and indoor vapour pressure are not controlled at all. The ventilation rate is desirable to maintain a slight overpressure within the room to stop dust and pollutants from entering. This rate can be measured by the tracer gas decay technique based on both the emission of SF6, suitably mixed with the indoor air and the following mass balance (Eq. (5)). The air exchange or infiltration rate I is given by Eq. (6). As there is not a source of tracer gas, F(t) ¼ 0 and, assuming I is constant, a solution to Eq. (5) is Eq. (7) or (8). The offices show the same distribution of the studied zones separated by a safety glass. Only one office does not have separation between employees’ and clients’ zones. Therefore, the sampling of SF6 has been made in two representative offices during occupied period, one of them without communication between zones and the other one with communication. A monitor multi-gas 1302 was used for the tracer gas monitoring. Ventilation rates were measured simultaneously to take into account the air exchange between zones. Calculated values show an uncertainty less than 70.002 h1.
mines the memory of a material, such that events that happened more than 4 * t before time t have no affect on the sorption at time t [12]. The studied offices are not of recent construction, therefore the sampling has been performed when the materials already are properly stabilized. The humidity generation period in the offices corresponds with 5 h of activity from 9:00 to 14:00, hence we have studied the non-occupied period for a year (long term). Sampling has been made with a frequency of 5–10 min during the unoccupied period of each season. We have studied the unoccupied period because the ventilation rates are lower allowing a better study of the materials behaviour. Sensors were placed, following Hens’ method [2] and ISO 7730 [19], in a particular location according to the indoor conditions. They were moved away from heat disturbances originating from heat sources such as computers. In each office, two sensors were placed to monitor simultaneously the indoor air both in the clients’ zone and in the employees’ zone.
3.5. Climatic data
Once the vapour pressure differential between indoor/ outdoor conditions was calculated, a statistical study of the averages of those values was taken. The comparison of averages was carried out by means of analysing the variance of a factor (one-way Anova) using the statistical software SPSS 11.0, for a level of significance of 0.05. This analysis was initially taken by using the daily average values of the summer and winter seasons in order to compare the evolutions of all offices during the unoccupied period and to determine if they are considered equal or in the opposite case, if they define groups. These groups will show the same evolution for a level of significance of 0.05.
The values of the outdoor conditions were obtained by means of weather stations next to the city, to avoid the buildings affecting the measured values of the outer conditions. The Environmental Information system of Galicia (SIAM) [18] facilitates those accessing information on the environment and climatology. Another organization that provides the meteorological data is the Forest and Environmental Research Center of Louriza´n (Ministry of Environment of the Xunta de Galicia). This centre is made up of 42 stations of climatologic observation, distributed throughout the Galician region. In 1988, it began the installation of a modern network of automatic stations of meteorological observation. In 2000, 23 new stations arrived which transmit information in real time. 3.6. Indoor air Twenty-five office buildings located in A Corun˜a were monitored in different zones and seasons. Temperature and indoor relative humidity conditions were sampled by means of Tinytag dataloggers (Meaco Europe), which allowed continuous monitoring for long periods of time. 3.7. Sampling period The material moisture content is related to the history of the humidity of the indoor air via an exponentially weighted time averaging term, controlled by a materialdependent time parameter tc. This time parameter deter-
3.8. Statistical study
4. Results 4.1. Climatic conditions The outer climate has been provided by MeteoGalicia [20] with a 10 min frequency. Figs. 3–5 show averaged data monthly. One can observe that A Corun˜a has a moderate climate where temperatures are neither too low in winter nor too high in summer. Also, a high relative humidity can be observed as a result of its proximity to the sea. Fig. 5 shows the absolute humidity from which can be deduced a humid summer and winter, but extreme values are never reached. 4.2. Ventilation rates The measured ventilation rates ranged from 1.05 h1 in the clients’ zone to 0.93 h1 in the employees’ zone.
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4.4. Season analysis
15
The obtained results have shown that coverings considered as semi-permeable, have the same behaviour, whereas those permeable and impermeable are different between themselves for a level of significance of 0.05. Now, we will be able to know if it is necessary to take into account the effect of coverings on indoor conditions. Firstly, as mechanical ventilation is not working and the offices are nearly air tight, we consider the ventilation rate during the unoccupied period less than 0.5 ach following the results in multi-storey buildings of La Corun˜a [21]. During the occupied period indoor partial vapour pressure cannot be compared to the outdoor as a result of the high ventilation rate that causes the same indoor and outdoor conditions, therefore the difference is usually null. Another factor to be considered is that during the occupied period the heating system is working, along with the loss of heat from people. Although the indoor partial vapour pressure is normally higher than the outdoor one, the hygroscopic inertia of the environment can sometimes revert the former situation, as Hens’ comments [2]. In summer there is a greater tendency to reduce the excess of partial vapour pressure, while in winter indoor partial vapour pressure is clearly higher than the outdoor one. In Table 2, daily average values of indoor–outdoor partial vapour pressure differences are shown for the unoccupied period in the 25 offices during summer and winter. The monitored unoccupied period is from 14:00 to 19:00 because these measurements show the real effect of the coverings on the indoor air without being influenced by the excessive ventilation rates of the occupied period. Once the Anova study was made for a level of significance of 0.05, three groups A, B and C were detected and were considered with homogeneous behaviour. These groups appear separated by two discontinuous lines. In addition, we can see that the offices which exceed the lower significance limit during summer season will exceed the opposed limit during winter. For example, offices P1, P2, P3, P4 and P5 show the highest excess of indoor partial vapour pressure during winter and the lowest during the summer. These offices have the most permeable internal coverings like paper which let humidity transfer to the building structure. We found the opposite behaviour in offices I1, I2 and I3, where the indoor partial vapour pressure is the highest during summer and the lowest during winter. In these offices there were more impermeable coverings like paintings. Instantaneous values of indoor/outdoor temperatures and vapour pressures during typical winter and summer days in some of the bank offices are shown in Figs. 6–9. These figures show the extreme behaviour of the building environment and they are in accordance with Table 2. For example, in Fig. 6 the permeable coating P4 has an indoor
10 5 0 1
2
3
4
5
6
7
8
9
10
11
12
9
10
11
12
10
11
12
Month
Relative Humidity (%)
Fig. 3. Outdoor temperature.
94 92 90 88 86 84 82 80 78 1
2
3
4
5
6 7 Month
8
Fig. 4. Outdoor relative humidity.
Absolute Humidity (kg/kg)
2009
0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
1
2
3
4
5
6 7 Month
8
9
Fig. 5. Outdoor absolute humidity.
Calculated values have shown a mean of 1 h1 with a standard deviation of 0.05 h1. These values indicate the increase of ventilation rates in the clients’ zone mainly as a result of the infiltrations produced by the entrance and exit of people through the front door. Nevertheless, these values are relatively close to the required minimum ventilation rate in both zones.
4.3. Data analysis The statistical study of the Anova has been based on a null hypothesis that all the averages of the indoor conditions in offices with different coverings during the unoccupied periods are equal. The alternative hypothesis is that the averages are different. A level of significance of 0.05 has been chosen for this case.
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2010
Permeable 4-Winter Partial vapour pressure (Pa)
Table 2 Internal–external partial vapour pressure difference 1600 1400 1200 1000 800 600 400 0:00
Permeable Outdoor
6:00
12:00 Time (Hours)
0:00
18:00
Fig. 7. Time variations of indoor and outdoor partial vapour pressure in office P4 (permeable coating) during a winter day.
Partial vapour pressure (Pa)
Impermeable 3-Summer
I, Impermeable; P, Permeable; SI, semi-impermeable; SP, semi-permeable; E, no effect.
2000 1900 1800 1700 1600 1500 1400 0:00
Impermeable Outdoor
6:00
12:00 Time (Hours)
18:00
0:00
Fig. 8. Time variations of indoor and outdoor partial vapour pressure in office I3 (impermeable coating) during a summer day.
Impermeable 3-Winter Partial vapour pressure (Pa)
Partial vapour pressure (Pa)
Permeable 4-Summer 2200 2000 1800 1600 1400 1200 1000 0:00
Permeable Outdoor
6:00
12:00 Time (Hours)
18:00
0:00
Fig. 6. Time variations of indoor and outdoor partial vapour pressure in office P4 (permeable coating) during a summer day.
partial vapour pressure lower than the outdoor one in the unoccupied period during summer and the opposite behaviour can be observed in Fig. 7 during winter. The impermeable coating I3 in Fig. 8 shows less outdoor partial
1400 1350 1300 1250 1200 1150 1100 12:00
Impermeable Outdoor
18:00
0:00 Time (Hours)
6:00
12:00
Fig. 9. Time variations of indoor and outdoor partial vapour pressure in office I3 (impermeable coating) during a winter day.
vapour pressure than indoor in summer, reverting this tendency in winter (Fig. 9). These results are in accordance with [6,22] where, for all ventilation rates, the permeable test case shows lower
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maximum humidity in summer and higher minimum humidity in winter than the impermeable test case. As an intermediate case, we considered those coverings that present certain tendency towards both sides of the mean. For example, the wood covering (SI1), which presents superficial treatment to avoid its deterioration but, even so, a tendency has been detected to revert its position with respect to the average value indicated by the gross black line. Another intermediate case of opposite tendencies is the office SP7, which shows a certain tendency towards an impermeable covering. There are offices that hold their position with seasons, as is the case of some paintings (E2). The offices with plastic coatings showed a variable buffering effect so they can be considered as semi-permeable (SP8), semi-impermeable (SI2) and permeable (P5). This behaviour can be related to the degree of wear on the surface of the coatings. As a result of this study it is possible to indicate that indoor coverings have an influence on the indoor environment for a long-term average study. It is important to take this influence into account to avoid error. We must consider that our study was carried out in offices with an air barrier and, in some cases, with vapour retarder because of paintings. This type of wall is like those studied by Hens [2] and different from Simonson constructions [23] but the obtained results show the same tendencies. 4.5. Air quality and energy saving We have concluded that an absorbent structure will moderate the indoor relative humidity during the relatively brief opening hours. Some authors are in accordance with these results and show new permeable structure advantages like energy saving, noise reduction and smaller space occupied by the distribution ducts [1,4,8]. For example, at low ventilation rates below 0.5 h1 diffusion through materials may reduce the concentration of VOCs in a room. The right choice of wall materials can have an impact on the indoor air quality, for example, walls with a high degree of permeability [13]. Another example is that a rather small air conditioning system can then re-establish the correct climate during a long period when the building is vacant, and therefore there is no need for outdoor ventilation [1]. If sorption effects take place, the time required to ventilate a gaseous compound out of a room can change considerably. 5. Conclusions We have demonstrated that permeable coverings improve indoor conditions in spite of the use of an air barrier and less permeable coverings such as wood. This effect confirms that during a long-term study the internal permeable coverings maintain their regulation property as a result of the existence of more than 4 h of excessive
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indoor humidity previous to the studied period. These results confirm the studies of Simonson. During the occupied period, when the temperature is higher, the emission of VOCs from materials is favoured. In addition, it is possible to wait for a regulating effect of the permeable coverings on VOCs so they are adsorbed during the occupied period and released when the air is cleaner allowing better indoor air quality. These two theories would allow, with a more intelligent design, energy saving in indoor air renovation, especially during the first moments of occupancy in the enclosure. This effect and its implications on the indoor thermal comfort can be analysed in later studies. Appendix
V
dcin ¼ G þ M þ nV ðcout cin Þ, dt
(1)
where t is the time (s), V the volume of the room (m3), n the air ventilation rate (s1), c the water vapour content (kg/m3), G the moisture generation rate (kg/s) and M the sum of moisture quantities contributed by buildings components (kg/s). rV 1000 , (2) C m ¼ ðu60%Rh u40%RH Þ 20 where Cm is the moisture capacity (g/%RH), u is the moisture content (kg/kg), r is the density of the material (k/m3) and V is the volume of the material (m3). am ¼
kd , ðC m =ð1000V ÞÞ100=Pvsat
(3)
where Pvsat is the saturation pressure for water vapour at 22 1C (Pa), kd the water vapour permeability (kg/(s m Pa)), Cm the moisture capacity (g/%RH) and am the moisture diffusivity (m2/s). J v ¼ m grad p;
(4)
where m is the water vapour permeability of the medium (kg/(s m Pa)), Jv the water vapour flux density (kg/m2 s) and grad p the driving potential (Pa/m). dCðtÞ ¼ F ðtÞ qðtÞCðtÞ, dt
(5)
where C(t) is the tracer gas concentration (dimensionless), dC(t)/dt the time derivative of concentration, q(t) volumetric airflow rate out of the building (m3/h), F(t) volumetric tracer gas injection rate (m3/h), t the time and V the building volume (m3). IðtÞ ¼
qðtÞ , V
(6)
where I is in air changes per hour (h1). C ¼ C 0 expðItÞ, 1 C0 I ¼ ln . t C
(7) (8)
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[13] Meininghaus R, Knudsen HN, Gunnarsen L. Impact of sorption and diffusion on indoor air pollution. In: Proceedings of indoor air quality ’99, 1999. [14] Kirchner S, Badey JR, Knudsen HN, Meininghaus R, Quenard D, Saarela K, et al. Sorption capacities and diffusion coefficients of indoor surface materials exposed to VOCS: proposal of new test procedures. In: Proceedings of indoor air quality ’99, 1999. [15] Yongling W, Ruilun Z, Zizhong D. Primary research on moisture absorption and desorption function of aerocrete as building element material for dehumidification. In: Proceedings of healthy buildings, vol. 3, 2000. [16] Olutimayin SO, Simonson CJ. Measuring and modeling vapor boundary layer growth during transient diffusion heat and moisture transfer in cellulose insulation. International Journal of Heat and Mass Transfer 2005;48:3319–30. [17] Talukdar P, Osanyintola OF, Olutimayin SO, Simonson CJ. An experimental data set for benchmarking 1-D, transient heat and moisture transfer models of hygroscopic building materials, part II: experimental, numerical and analytical data. International Journal of Heat and Mass Transfer 2007, in press /http://dx.doi.org/ doi:10.1016/j.ijheatmasstransfer.2007.03.025S. [18] Environmental Information system of Galicia 2007 (SIAM). Siam. /http://www.Siam-cma.org/S. [19] International Standard ISO 7730-2005. Ergonomics of the thermal environment. Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. [20] MeteoGalicia. Anuario climatolo´xico de Galicia 2002. Consellerı´ a de Medio Ambiente. Xunta de Galicia. ISBN: 84-453-3520-0. [21] Rodrı´ guez E, Baalin˜a A, Va´zquez A, Castellanos L, Santaballa JA, Infante CR. Indoor air quality evaluation using carbon dioxide levels in bedrooms in a A Corun˜a, Spain. In: Proceedings of indoor air ’99, vol. 5, Edinburgh (Scotland), 1999. p. 335–40. [22] Simonson CJ, Salonvaara MH. Mass transfer between indoor air and a porous building envelope: part I. Field measurements. In: Proceedings of healthy buildings, vol. 3, 2000. [23] Simonson CJ, Tuomo O. Moisture performance of buildings envelopes with no plastic vapour retarders in cold climates. In: Proceedings of healthy buildings, vol. 3, 2000.