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Experimental study on two type of indirect evaporative cooling heat recovery ventilator
Available Available online online at at www.sciencedirect.com www.sciencedirect.com
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000 Procedia
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 4105–4110
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Experimental study on two type of indirect evaporative cooling heat recovery ventilator Sheng Huangaa, Wuyan Liaa, Jun Lua,a, **, Yongcai Liaa aa
Faculty Faculty of of the the Urban Urban Construction Construction & & Environment Environment Engineering, Engineering, Chongqing Chongqing University, University, Chongqing, Chongqing, China China
Abstract Abstract Heat Heat recovery recovery ventilator ventilator is is aa feasible feasible way way to to ease ease the the contradiction contradiction between between indoor indoor air air quality quality and and fresh fresh air air handling handling energy energy consumption. The paper presents an experimental analysis of a heat recovery ventilator which uses only sensible consumption. The paper presents an experimental analysis of a heat recovery ventilator which uses only sensible heat heat exchanger exchanger combined with with indirect indirect evaporation evaporation cooling cooling (IEC) (IEC) technology. technology. In In this this study, study, two two different different placement placement methods methods (horizontal (horizontal and and combined vertical) prototypes prototypes of of heat heat recovery recovery ventilator ventilator combine combine with with IEC IEC were were made made and and the the structure structure and and related related parameters parameters of of the the two two vertical) prototypes prototypes were were introduced introduced specifically. specifically. Then, Then, the the porotypes porotypes were were test test on on the the test test rig rig with with different different summer summer operating operating conditions. conditions. Additionally, based on the experimental resulting, the energy consumption saving capability in different China’s Additionally, based on the experimental resulting, the energy consumption saving capability in different China’s regions regions of of the the two two prototypes were were evaluated evaluated by by aa specific specific net net energy energy saving saving parameter, parameter, and and the the result result shows shows that that both both vertical vertical and and horizontal horizontal IECs IECs prototypes can can reduce reduce energy energy consumption consumption during during cooling cooling seasons seasons in in most most regions regions of of China. China. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Peer-review committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Peer-review under under responsibility responsibility of of the the scientific scientific committee Conditioning. Conditioning. Air Conditioning. Keywords: Keywords: Heat Heat recovery; recovery; Indirect Indirect evaporative evaporative cooling; cooling; Experimental Experimental analysis analysis
1.
Introduction
Energy consumption in buildings account for 30 - 40% of the total primary energy use globally [1,2]. A great part of this consumption is used to provide comfort conditions for occupants. This trend result in peak electricity loads increasing sharply in many countries, putting pressure on fossil-fuelled power plants and aggravate the environment * *
Corresponding author. author. Tel.:+86-13808379613; Tel.:+86-13808379613; fax: fax: +86-023-65123777. +86-023-65123777. Corresponding E-mail E-mail address: address: [email protected] [email protected]
1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. 1877-7058 Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Conditioning. Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.09.910
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Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
situation. Currently, the air conditioning system is dominated by mechanical vapor compression systems, which are energy intensive and suffer from poor thermal performance in hot climate regions. There is an effective application of the evaporative cooling which can provide a viable solution for space cooling in hot and dry climate regions. This cooling method utilizes the principle of water evaporative for absorbing the heat existing in the environment, so it consumes much lower electricity than mechanical compression system. Nowadays, there are two types of evaporative cooling systems commonly used including direct evaporative cooling (DEC) system and indirect evaporative cooling (IEC) system. Direct evaporative cooling system utilizing the latent heat of evaporation to lower temperature of air, therefore, the worm air is changed into cool and moist air. Indirect evaporative cooling systems have the advantage of being able to lower the air temperature without increasing humidity of the conditioned space and avoid potential health issues from contaminated water droplets entering occupied spaces (as associated with direct evaporative cooling systems ) [3] The current focus for many researchers includes dealing with new thermodynamic cycles, heat exchanger geometries and materials, humidification systems and evaluation of energy savings compared to conventional devices [4]. Zhao et al. [5] investigated several types of materials, namely metals, fibres, ceramics, zeolite and carbon, which have potential to be used as heat and mass transfer medium in the indirect evaporative cooling systems. The results obtained demonstrate that shape formation ability, durability, compatibility with water-proof coating, contamination risk as well as cost, are more important than thermal conductivity. Metals including cooper and aluminium were considered to be the most adequate materials for IEC unit. Maurya et al. [6] studied three types of cooling pad made of a cellulose, aspen fiber, and coconut coir. The obtained data showed that the saturation efficiency decreases with increase in velocity of air and the cooling capacity increases with air velocity. Experimental works are also focused on performance evaluation of different prototypes. Anisimov et al. [7] experimentally study a novel cross-flow HMX utilizing the M-cycle for dew point indirect evaporative cooling, they found that the novel M-cycle HMX used for indirect evaporative cooling in air conditioning units was high efficiency. Tejero-González et al. [8] studied the performance of two equally-sized cross-flow heat-exchanger prototypes constructed with polycarbonate hollow panels of different cross section. Duan et al. [9] experimentally studied the operational performance and impact factors of a counter-flow regenerative evaporative cooler (REC). The result obtained demonstrate that the enhanced performance of a new REC. Gomez et al. [10] studied a novel indirect evaporative cooling prototype made of polycarbonate in two operating modes. Martinez et al. [11] experimentally studied two different types of evaporative systems: an indirect evaporative cooler and a semi-indirective ceramic evaporative cooler. Kabeel et al. [12] carried out an experimental study into a novel integrated system of indirect evaporative cooler with internal baffles as air pre-cooling unit and evaporative condenser. Boukhanouf et al. [13] conducted the model to study and experimentally investigated a sub-wet bulb temperature indirect evaporative cooling system. Lee et al. [14] experimentally studied the performance of a counter flow regenerative evaporative cooler with finned channels. The results obtained demonstrate that the cooling performance is greatly influenced by the evaporative water flow rate. Bolotin et al. [15] numerically studied two configurations of cross-flow indirect evaporative units: typical air cooler and regenerative air cooler. According to the above-mentioned researchers, by using the indirect evaporative cooling unit, the performance of cooling systems can be improved and electricity consumption can be reduced significantly. In houses of China, due to space constraints, most of heat recovery ventilators are cell installed and the flat plate heat exchangers inside are set horizontal. However, almost all of the studies existing were focus on the exchangers set vertical. Thus, in this study, two different exchanger placement prototypes of indirect evaporative cooling were made and experimental studied. Additionally, the application of these two types of IECs in different regions of China were investigated. nomenclature Q
cooling capacity (kW)
Greek symbols ρ
air density (g·L-1)
δ
specific energy saving parameter (dimensionless)
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
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Abbreviation DEC
direct evaporative cooling
IEC
indirect evaporative cooling
IECs
indirect evaporative cooler/coolers
2.
Experimental setup
To investigate the thermal performance of these two placement IECs, two prototypes with vertical exchanger and horizontal exchanger inside respectively were made. The schematic of vertical prototype is shown in Fig. 1, and the schematic of horizontal prototype is shown in Fig.2. The flat plate heat exchangers of the two prototypes are identical and each has dimensions of 565*765*190 in width, length, and height respectively. The only difference between two exchangers is the way of placement: one is vertical and another is horizontal. As a result, in the horizontal prototype (horizontal IECs), water in return air channel is distributed only on the lower surface and upper surface remains dry while both surface are wet in exchanger of vertical placement. The heat exchanger is made of aluminium plates with counter-cross flow arrangement. Main characteristics are: number of plates is 46, number of channels is 24 (for each air), Plates thickness are 0.1 mm, Plates pitch are 3.95 mm, Gross plate length and width are 400 mm and the plates spacing is obtained through dimples with semispherical shape. Three water nozzles are installed in the upper part of the heat exchanger casing. Water is supplied to nozzles through a commercial pumping unit in both vertical and horizontal IECs. Water inlet
Fan Supply air outlet
Exhaust air inlet Heat exchanger
Exhaust air outlet
Supply air inlet Side view of the horizontal IECs
Fan
Fig. 1. Schematic of vertical IECs (side view)
TH
Fan
Fan
TH
Exhaust air outlet
Supply air outlet Heat exchanger
Supply air inlet
Exhaust air inlet TH
Top view of the prototype
TH Water inlet
Fig. 2. Schematic of horizontal IECs (top view)
In this experiment, two-chamber method was used to test the thermal performance of heat recovery IEC unit. The schematic of the experimental setup is shown in Fig. 3, which consists of two climate chambers (chamberⅠ/ chamber Ⅱ). Each chamber can control inside temperature and humidity independently by surface cooler, electrical heater and
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
4108
humidifier equipped in the temperature and humidity test duct and includes a complete set of temperature and humidity independent control air conditioning system controlled by the computer automatically. As shown in Fig. 3, the constant temperature simulation chamber controls the temperature on range of 5-45℃ and accuracy is ± 0.5 ℃. The water system consists of water pipes, a pump, a pressure regulating valve and a water tank equipped with temperature sensor and electric heaters. Main data calibrated sensors are summarized in Table 1. To ensure that the indoor air quality in a reasonable range of accurate testing, the air supply way is top orifice air supply.
Plenum
1
Plenum
5 Supply air inlet
2
Exhaust air inlet
9
Exhaust air ou tlet
Supply air outlet
3
7 6
Climate chamber 1
4
10
Climate ch amber 2
8
1 Fan 2 Humidifier 3 Heater 4 Surface cooler 5 Temperature & humidity sensors 6 Valve 7 Temperature sensor 8 Water tank 9 Prototype placement 10 Water Pump
Fig. 3. Schematic of test rig for IECs
Temperature and relative humidity of each air stream are measured at both the inlet and outlet sections of the indirect evaporative cooling system casing through HIOKI probes coupled with relative humidity capacitive sensors. The evaporative water temperature was measured by mercury thermometer and the mass flow ratio was calculated by mass changing rate of the water tank. The instruments used in this experiment are listed in Table. 1. Table. 1. Specification of the difference measuring devices Parameters
3.
Devices
Accuracy
Operational range
Air temperature
HIOKI probe
0.5℃
0 -50％
Air temperature
Mercury thermometer
0.1℃
-20 – 110℃
Air relative humidity
HIOKI probe
5％
20％ - 100％
Time
Timer
0.1s
0 – 3600s
Weight
Electronic weigher
0.01kg
0 – 200kg
Experimental results and analysis
According to the literature published so far, most of the researcher hold view that the IECs are suitable for regions with hot and dry climate. However, the performance may be discounted when apply the IECs in moist climate regions. To investigate the adaptation of the two types of IECs, specific energy saving parameter (δ) was defined to evaluate the energy saving performance of these two IECs. This parameter can be calculated by follows: δ = ∑ ������ ρ ��������
��∑��� ���� �� ��
/ ∑ ������ 1 �������
(1)
The term Q represents the exact energy the ventilation machine has recovered and it can be obtained by the regression analysis of the experimental results. The expression ∑��� Φ��� �� takes into consideration the energy
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
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consumption of both the supply air fan and exhaust air fan. �� is a production factor, accounting for the fact that the production of 1 kWh of electrical energy requires much more primary energy. In this case, �� is roughly equal to 3. δ represents the exact energy the IECs saved for per kilogram supply air driven in to the room. It’s necessary to notice that only if the δ is positive, the machine is energy saving. Otherwise, the totally system may not suitable and necessary. To investigate the feasibility and practicality of the vertical and horizontal IECs, Five China’s metropolises represented different typical climates are chosen to calculate the vertical and horizontal IECs’ specific energy saving parameter in there during July and August which are shown in Fig. 4. It can be seen that no matter in which city, the δ is always positive of both vertical and horizontal IECs. It means that two types of IECs can saving energy under typical summer conditions of most area of China. However, there is a big difference of the value of δ because of the different climate characteristics. It can be inferred that greater value of δ connects with hotter and more humid area. Therefore, the IECs operating as a heat recovery unit is not only suitable for the area with hot and dry climate but also (even more) suitable for hot and wet area. But at the same time, it’s worth noting that the δ only evaluate the energy conservation of the equipment while the comfort of the supply air is not taken into consideration. It means that when apply the IECs in hot and wet area, the outlet temperature of the supply air maybe too high to drive into condition area directly and the secondary processing may necessary for the supply air. 6
Horizontal IECs Vertical IECs
Specific net energy saving δ
5
4
3
2
1
0
Beijing
Shanghai
Guangzhou
Chongqing
Xi`an
Fig. 4. Specific net energy saving for vertical and horizontal IECs in five typical cities in China
4.
Conclusions
In this paper, two types of typical heat recovery IECs are introduced and experimental studied. In the experiment, two different placement way prototypes were made and tested on the test rig established specially for this experiment. The application adaptability of both these two IECs in different China’s regions was studied with specific energy saving parameter: δ. The main conclusions of this study are:
Experimental results show that both exchangers can achieve relatively low supply air temperature and provide comfort conditions for occupants. Under different conditions, the thermal performance of horizontal IECs is not as good as the vertical one which indicates that the non-uniform distribution of water film in exhaust air channels of horizontal IECs is counterproductive for the heat and mass transfer process in the exchanger. The influence of ambient air properties in different regions of China was investigated and it was shown that the IECs are not only suitable for the moist area, but also suitable for the moist area. It’s suitable for both vertical and horizontal IECs application in most regions of China. But, in the regions with dry area, the horizontal IECs are not recommended.
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Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
Acknowledgments The research described in this manuscript was supported by National Science Foundation of China (No. 51478058) and Sichuan Science and Technology Support Program (No. 2014GZ0133). References [1] A. Dodoo, L. Gustavsson, R. Sathre, Building energy-efficiency standards in a life cycle primary energy perspective, Energy Build. 43 (7) (2011) 1589–1597. [2] L. Pérez-Lombard, J. Ortiz, F. Juan, J.F. Coronel, I.R. Maestre, A review of HVAC systems requirements in building energy regulations, Energy Build. 43 (2–3)(2011) 255–268. [3] Zhan C, Zhao X, Smith S, et al. Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling. Building & Environment, 2011, 46(3):657-668. [4] Duan Z, Zhan C, Zhang X, et al. Indirect evaporative cooling: Past, present and future potentials. Renewable & Sustainable Energy Reviews, 2012, 16(9):6823–6850. Applied Thermal Engineering, 2017, 115:201-211. [5] Zhao X, Liu S, Riffat S B. Comparative study of heat and mass exchanging materials for indirect evaporative cooling systems. Building & Environment, 2008, 43(11):1902-1911. [6] Maurya R, Shrivastava N, Shrivastava V. Performance Evaluation of Alternative Evaporative Cooling Media. 2014, 5(10):676-684. [7] Anisimov S, Pandelidis D, Jedlikowski A, et al. Performance investigation of a M (Maisotsenko)-cycle cross-flow heat exchanger used for indirect evaporative cooling. Energy, 2014, 76:593-606. [8] Tejero-González A, Andrés-Chicote M, Velasco-Gómez E, et al. Influence of constructive parameters on the performance of two indirect evaporative cooler prototypes. Applied Thermal Engineering, 2013, 51(1–2):1017-1025. [9] Duan Z, Zhan C, Zhao X, et al. Experimental study of a counter-flow regenerative evaporative cooler. Building & Environment, 2016, 104:4758. [10] Gómez E V, González A T, Martínez F J R. Experimental characterisation of an indirect evaporative cooling prototype in two operating modes. Applied Energy, 2012, 97(3):340-346. [11] Martı́Nez F J R, Gómez E V, Martı́N R H, et al. Comparative study of two different evaporative systems: an indirect evaporative cooler and a semi-indirect ceramic evaporative cooler. Energy & Buildings, 2004, 36(7):696–708. [12] A.E. Kabeel, M.M. Bassuoni, Mohamed Abdelgaied. Experimental study of a novel integrated system of indirect evaporative cooler with internal baffles and evaporative condenser. Energy Conversion and Management, 2017:518–525. [13] Boukhanouf R, Alharbi A, Ibrahim H G, et al. Computer modelling and experimental investigation of building integrated sub-wet bulb temperature evaporative cooling system. Applied Thermal Engineering, 2017, 115:201-211. [14] Lee J, Lee D Y. Experimental study of a counter flow regenerative evaporative cooler with finned channels. International Journal of Heat & Mass Transfer, 2013, 65(5):173-179. [15] Bolotin S, Vager B, Vasilijev V. Comparative analysis of the cross-flow indirect evaporative air coolers. International Journal of Heat & Mass Transfer, 2015, 88:224-235.
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000 Procedia
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 4105–4110
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Experimental study on two type of indirect evaporative cooling heat recovery ventilator Sheng Huangaa, Wuyan Liaa, Jun Lua,a, **, Yongcai Liaa aa
Faculty Faculty of of the the Urban Urban Construction Construction & & Environment Environment Engineering, Engineering, Chongqing Chongqing University, University, Chongqing, Chongqing, China China
Abstract Abstract Heat Heat recovery recovery ventilator ventilator is is aa feasible feasible way way to to ease ease the the contradiction contradiction between between indoor indoor air air quality quality and and fresh fresh air air handling handling energy energy consumption. The paper presents an experimental analysis of a heat recovery ventilator which uses only sensible consumption. The paper presents an experimental analysis of a heat recovery ventilator which uses only sensible heat heat exchanger exchanger combined with with indirect indirect evaporation evaporation cooling cooling (IEC) (IEC) technology. technology. In In this this study, study, two two different different placement placement methods methods (horizontal (horizontal and and combined vertical) prototypes prototypes of of heat heat recovery recovery ventilator ventilator combine combine with with IEC IEC were were made made and and the the structure structure and and related related parameters parameters of of the the two two vertical) prototypes prototypes were were introduced introduced specifically. specifically. Then, Then, the the porotypes porotypes were were test test on on the the test test rig rig with with different different summer summer operating operating conditions. conditions. Additionally, based on the experimental resulting, the energy consumption saving capability in different China’s Additionally, based on the experimental resulting, the energy consumption saving capability in different China’s regions regions of of the the two two prototypes were were evaluated evaluated by by aa specific specific net net energy energy saving saving parameter, parameter, and and the the result result shows shows that that both both vertical vertical and and horizontal horizontal IECs IECs prototypes can can reduce reduce energy energy consumption consumption during during cooling cooling seasons seasons in in most most regions regions of of China. China. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Peer-review committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Peer-review under under responsibility responsibility of of the the scientific scientific committee Conditioning. Conditioning. Air Conditioning. Keywords: Keywords: Heat Heat recovery; recovery; Indirect Indirect evaporative evaporative cooling; cooling; Experimental Experimental analysis analysis
1.
Introduction
Energy consumption in buildings account for 30 - 40% of the total primary energy use globally [1,2]. A great part of this consumption is used to provide comfort conditions for occupants. This trend result in peak electricity loads increasing sharply in many countries, putting pressure on fossil-fuelled power plants and aggravate the environment * *
Corresponding author. author. Tel.:+86-13808379613; Tel.:+86-13808379613; fax: fax: +86-023-65123777. +86-023-65123777. Corresponding E-mail E-mail address: address: [email protected] [email protected]
1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. 1877-7058 Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Conditioning. Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.09.910
4106
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
situation. Currently, the air conditioning system is dominated by mechanical vapor compression systems, which are energy intensive and suffer from poor thermal performance in hot climate regions. There is an effective application of the evaporative cooling which can provide a viable solution for space cooling in hot and dry climate regions. This cooling method utilizes the principle of water evaporative for absorbing the heat existing in the environment, so it consumes much lower electricity than mechanical compression system. Nowadays, there are two types of evaporative cooling systems commonly used including direct evaporative cooling (DEC) system and indirect evaporative cooling (IEC) system. Direct evaporative cooling system utilizing the latent heat of evaporation to lower temperature of air, therefore, the worm air is changed into cool and moist air. Indirect evaporative cooling systems have the advantage of being able to lower the air temperature without increasing humidity of the conditioned space and avoid potential health issues from contaminated water droplets entering occupied spaces (as associated with direct evaporative cooling systems ) [3] The current focus for many researchers includes dealing with new thermodynamic cycles, heat exchanger geometries and materials, humidification systems and evaluation of energy savings compared to conventional devices [4]. Zhao et al. [5] investigated several types of materials, namely metals, fibres, ceramics, zeolite and carbon, which have potential to be used as heat and mass transfer medium in the indirect evaporative cooling systems. The results obtained demonstrate that shape formation ability, durability, compatibility with water-proof coating, contamination risk as well as cost, are more important than thermal conductivity. Metals including cooper and aluminium were considered to be the most adequate materials for IEC unit. Maurya et al. [6] studied three types of cooling pad made of a cellulose, aspen fiber, and coconut coir. The obtained data showed that the saturation efficiency decreases with increase in velocity of air and the cooling capacity increases with air velocity. Experimental works are also focused on performance evaluation of different prototypes. Anisimov et al. [7] experimentally study a novel cross-flow HMX utilizing the M-cycle for dew point indirect evaporative cooling, they found that the novel M-cycle HMX used for indirect evaporative cooling in air conditioning units was high efficiency. Tejero-González et al. [8] studied the performance of two equally-sized cross-flow heat-exchanger prototypes constructed with polycarbonate hollow panels of different cross section. Duan et al. [9] experimentally studied the operational performance and impact factors of a counter-flow regenerative evaporative cooler (REC). The result obtained demonstrate that the enhanced performance of a new REC. Gomez et al. [10] studied a novel indirect evaporative cooling prototype made of polycarbonate in two operating modes. Martinez et al. [11] experimentally studied two different types of evaporative systems: an indirect evaporative cooler and a semi-indirective ceramic evaporative cooler. Kabeel et al. [12] carried out an experimental study into a novel integrated system of indirect evaporative cooler with internal baffles as air pre-cooling unit and evaporative condenser. Boukhanouf et al. [13] conducted the model to study and experimentally investigated a sub-wet bulb temperature indirect evaporative cooling system. Lee et al. [14] experimentally studied the performance of a counter flow regenerative evaporative cooler with finned channels. The results obtained demonstrate that the cooling performance is greatly influenced by the evaporative water flow rate. Bolotin et al. [15] numerically studied two configurations of cross-flow indirect evaporative units: typical air cooler and regenerative air cooler. According to the above-mentioned researchers, by using the indirect evaporative cooling unit, the performance of cooling systems can be improved and electricity consumption can be reduced significantly. In houses of China, due to space constraints, most of heat recovery ventilators are cell installed and the flat plate heat exchangers inside are set horizontal. However, almost all of the studies existing were focus on the exchangers set vertical. Thus, in this study, two different exchanger placement prototypes of indirect evaporative cooling were made and experimental studied. Additionally, the application of these two types of IECs in different regions of China were investigated. nomenclature Q
cooling capacity (kW)
Greek symbols ρ
air density (g·L-1)
δ
specific energy saving parameter (dimensionless)
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
4107 3
Abbreviation DEC
direct evaporative cooling
IEC
indirect evaporative cooling
IECs
indirect evaporative cooler/coolers
2.
Experimental setup
To investigate the thermal performance of these two placement IECs, two prototypes with vertical exchanger and horizontal exchanger inside respectively were made. The schematic of vertical prototype is shown in Fig. 1, and the schematic of horizontal prototype is shown in Fig.2. The flat plate heat exchangers of the two prototypes are identical and each has dimensions of 565*765*190 in width, length, and height respectively. The only difference between two exchangers is the way of placement: one is vertical and another is horizontal. As a result, in the horizontal prototype (horizontal IECs), water in return air channel is distributed only on the lower surface and upper surface remains dry while both surface are wet in exchanger of vertical placement. The heat exchanger is made of aluminium plates with counter-cross flow arrangement. Main characteristics are: number of plates is 46, number of channels is 24 (for each air), Plates thickness are 0.1 mm, Plates pitch are 3.95 mm, Gross plate length and width are 400 mm and the plates spacing is obtained through dimples with semispherical shape. Three water nozzles are installed in the upper part of the heat exchanger casing. Water is supplied to nozzles through a commercial pumping unit in both vertical and horizontal IECs. Water inlet
Fan Supply air outlet
Exhaust air inlet Heat exchanger
Exhaust air outlet
Supply air inlet Side view of the horizontal IECs
Fan
Fig. 1. Schematic of vertical IECs (side view)
TH
Fan
Fan
TH
Exhaust air outlet
Supply air outlet Heat exchanger
Supply air inlet
Exhaust air inlet TH
Top view of the prototype
TH Water inlet
Fig. 2. Schematic of horizontal IECs (top view)
In this experiment, two-chamber method was used to test the thermal performance of heat recovery IEC unit. The schematic of the experimental setup is shown in Fig. 3, which consists of two climate chambers (chamberⅠ/ chamber Ⅱ). Each chamber can control inside temperature and humidity independently by surface cooler, electrical heater and
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
4108
humidifier equipped in the temperature and humidity test duct and includes a complete set of temperature and humidity independent control air conditioning system controlled by the computer automatically. As shown in Fig. 3, the constant temperature simulation chamber controls the temperature on range of 5-45℃ and accuracy is ± 0.5 ℃. The water system consists of water pipes, a pump, a pressure regulating valve and a water tank equipped with temperature sensor and electric heaters. Main data calibrated sensors are summarized in Table 1. To ensure that the indoor air quality in a reasonable range of accurate testing, the air supply way is top orifice air supply.
Plenum
1
Plenum
5 Supply air inlet
2
Exhaust air inlet
9
Exhaust air ou tlet
Supply air outlet
3
7 6
Climate chamber 1
4
10
Climate ch amber 2
8
1 Fan 2 Humidifier 3 Heater 4 Surface cooler 5 Temperature & humidity sensors 6 Valve 7 Temperature sensor 8 Water tank 9 Prototype placement 10 Water Pump
Fig. 3. Schematic of test rig for IECs
Temperature and relative humidity of each air stream are measured at both the inlet and outlet sections of the indirect evaporative cooling system casing through HIOKI probes coupled with relative humidity capacitive sensors. The evaporative water temperature was measured by mercury thermometer and the mass flow ratio was calculated by mass changing rate of the water tank. The instruments used in this experiment are listed in Table. 1. Table. 1. Specification of the difference measuring devices Parameters
3.
Devices
Accuracy
Operational range
Air temperature
HIOKI probe
0.5℃
0 -50％
Air temperature
Mercury thermometer
0.1℃
-20 – 110℃
Air relative humidity
HIOKI probe
5％
20％ - 100％
Time
Timer
0.1s
0 – 3600s
Weight
Electronic weigher
0.01kg
0 – 200kg
Experimental results and analysis
According to the literature published so far, most of the researcher hold view that the IECs are suitable for regions with hot and dry climate. However, the performance may be discounted when apply the IECs in moist climate regions. To investigate the adaptation of the two types of IECs, specific energy saving parameter (δ) was defined to evaluate the energy saving performance of these two IECs. This parameter can be calculated by follows: δ = ∑ ������ ρ ��������
��∑��� ���� �� ��
/ ∑ ������ 1 �������
(1)
The term Q represents the exact energy the ventilation machine has recovered and it can be obtained by the regression analysis of the experimental results. The expression ∑��� Φ��� �� takes into consideration the energy
Sheng Huang et al. / Procedia Engineering 205 (2017) 4105–4110 Sheng Huang, et al. / Procedia Engineering 00 (2017) 000–000
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consumption of both the supply air fan and exhaust air fan. �� is a production factor, accounting for the fact that the production of 1 kWh of electrical energy requires much more primary energy. In this case, �� is roughly equal to 3. δ represents the exact energy the IECs saved for per kilogram supply air driven in to the room. It’s necessary to notice that only if the δ is positive, the machine is energy saving. Otherwise, the totally system may not suitable and necessary. To investigate the feasibility and practicality of the vertical and horizontal IECs, Five China’s metropolises represented different typical climates are chosen to calculate the vertical and horizontal IECs’ specific energy saving parameter in there during July and August which are shown in Fig. 4. It can be seen that no matter in which city, the δ is always positive of both vertical and horizontal IECs. It means that two types of IECs can saving energy under typical summer conditions of most area of China. However, there is a big difference of the value of δ because of the different climate characteristics. It can be inferred that greater value of δ connects with hotter and more humid area. Therefore, the IECs operating as a heat recovery unit is not only suitable for the area with hot and dry climate but also (even more) suitable for hot and wet area. But at the same time, it’s worth noting that the δ only evaluate the energy conservation of the equipment while the comfort of the supply air is not taken into consideration. It means that when apply the IECs in hot and wet area, the outlet temperature of the supply air maybe too high to drive into condition area directly and the secondary processing may necessary for the supply air. 6
Horizontal IECs Vertical IECs
Specific net energy saving δ
5
4
3
2
1
0
Beijing
Shanghai
Guangzhou
Chongqing
Xi`an
Fig. 4. Specific net energy saving for vertical and horizontal IECs in five typical cities in China
4.
Conclusions
In this paper, two types of typical heat recovery IECs are introduced and experimental studied. In the experiment, two different placement way prototypes were made and tested on the test rig established specially for this experiment. The application adaptability of both these two IECs in different China’s regions was studied with specific energy saving parameter: δ. The main conclusions of this study are:
Experimental results show that both exchangers can achieve relatively low supply air temperature and provide comfort conditions for occupants. Under different conditions, the thermal performance of horizontal IECs is not as good as the vertical one which indicates that the non-uniform distribution of water film in exhaust air channels of horizontal IECs is counterproductive for the heat and mass transfer process in the exchanger. The influence of ambient air properties in different regions of China was investigated and it was shown that the IECs are not only suitable for the moist area, but also suitable for the moist area. It’s suitable for both vertical and horizontal IECs application in most regions of China. But, in the regions with dry area, the horizontal IECs are not recommended.
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Acknowledgments The research described in this manuscript was supported by National Science Foundation of China (No. 51478058) and Sichuan Science and Technology Support Program (No. 2014GZ0133). References [1] A. Dodoo, L. Gustavsson, R. Sathre, Building energy-efficiency standards in a life cycle primary energy perspective, Energy Build. 43 (7) (2011) 1589–1597. [2] L. Pérez-Lombard, J. Ortiz, F. Juan, J.F. Coronel, I.R. Maestre, A review of HVAC systems requirements in building energy regulations, Energy Build. 43 (2–3)(2011) 255–268. [3] Zhan C, Zhao X, Smith S, et al. Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling. Building & Environment, 2011, 46(3):657-668. [4] Duan Z, Zhan C, Zhang X, et al. Indirect evaporative cooling: Past, present and future potentials. Renewable & Sustainable Energy Reviews, 2012, 16(9):6823–6850. Applied Thermal Engineering, 2017, 115:201-211. [5] Zhao X, Liu S, Riffat S B. Comparative study of heat and mass exchanging materials for indirect evaporative cooling systems. Building & Environment, 2008, 43(11):1902-1911. [6] Maurya R, Shrivastava N, Shrivastava V. Performance Evaluation of Alternative Evaporative Cooling Media. 2014, 5(10):676-684. [7] Anisimov S, Pandelidis D, Jedlikowski A, et al. Performance investigation of a M (Maisotsenko)-cycle cross-flow heat exchanger used for indirect evaporative cooling. Energy, 2014, 76:593-606. [8] Tejero-González A, Andrés-Chicote M, Velasco-Gómez E, et al. Influence of constructive parameters on the performance of two indirect evaporative cooler prototypes. Applied Thermal Engineering, 2013, 51(1–2):1017-1025. [9] Duan Z, Zhan C, Zhao X, et al. Experimental study of a counter-flow regenerative evaporative cooler. Building & Environment, 2016, 104:4758. [10] Gómez E V, González A T, Martínez F J R. Experimental characterisation of an indirect evaporative cooling prototype in two operating modes. Applied Energy, 2012, 97(3):340-346. [11] Martı́Nez F J R, Gómez E V, Martı́N R H, et al. Comparative study of two different evaporative systems: an indirect evaporative cooler and a semi-indirect ceramic evaporative cooler. Energy & Buildings, 2004, 36(7):696–708. [12] A.E. Kabeel, M.M. Bassuoni, Mohamed Abdelgaied. Experimental study of a novel integrated system of indirect evaporative cooler with internal baffles and evaporative condenser. Energy Conversion and Management, 2017:518–525. [13] Boukhanouf R, Alharbi A, Ibrahim H G, et al. Computer modelling and experimental investigation of building integrated sub-wet bulb temperature evaporative cooling system. Applied Thermal Engineering, 2017, 115:201-211. [14] Lee J, Lee D Y. Experimental study of a counter flow regenerative evaporative cooler with finned channels. International Journal of Heat & Mass Transfer, 2013, 65(5):173-179. [15] Bolotin S, Vager B, Vasilijev V. Comparative analysis of the cross-flow indirect evaporative air coolers. International Journal of Heat & Mass Transfer, 2015, 88:224-235.