Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler
Abstract
:1. Introduction
2. Structure and Working Process of ERIEC Air-Conditioning Fresh Air Unit
3. ERIEC Design Methodology
3.1. Structure and Operating Parameters Design
3.2. Recommended Design Air Speed
3.3. Recommended Design Air Speed
4. ERIEC Cooling Capability
4.1. ERIEC Heat Transfer Efficiency
4.2. Numerical Solution of ERIEC Cooling Capacity
4.3. Calculation of ERIEC Cooling Capacity for Summer Air Conditioning Design Conditions in Typical Chinese Cities
5. Economic Analysis of ERIEC Design and Selection
5.1. Power Consumption of ERIEC Fans
5.2. Power Consumption of ERIEC Pumps and ERIEC Water Consumption
5.3. Power Consumption Saved by ERIEC
5.4. Economic Calculation of ERIEC Recommended Selection
6. Conclusions
- Based on the ERIEC heat and mass transfer analytical solution model and numerical solution procedure developed by our research team, the cooling capacity of ERIEC fresh air units of thirty typical cities in five climate zones of China: severe cold, cold, mild, hot summer and cold winter, and hot summer and warm winter were calculated to obtain the fresh air outlet state parameters, wet bulb efficiency, enthalpy efficiency and the fresh air load borne under the summer outdoor design conditions. In severe cold regions, cold regions, hot summer and cold winter regions, and hot summer and warm winter regions, as the moisture content of fresh outdoor air will gradually increase in summer, condensation occurs on the primary side and the moisture content of fresh air treated by ERIEC units is reduced more often. This will lead to an increase in the fresh air latent heat load borne by the ERIEC unit.
- The results of numerical calculations applying ERIEC to 30 cities show that the wet bulb efficiency of each city is 0.67–0.98, which increases as the outdoor design wet bulb temperature decreases; the enthalpy efficiency is 0.76–1.29, which increases as the outdoor design wet bulb temperature increases; and the ERIEC is able to bear between 53% and 100% of the fresh air load; as such, the matching surface cooler only needs to bear a small amount of residual cold load.
- In this paper, the design parameters of the ERIEC air conditioning fresh air unit structure, primary and secondary air velocity, heat exchange area, water consumption of spray water, plate type and other design parameters are given by calculation for eight models of a fresh air volume of 1000–10,000 m3/h commonly used in engineering, and their economic analysis is carried out under the recommended parameters.
- In addition to the structure design and size, the performance of the fresh air system using indirect evaporative cooling would be affected by the outdoor dry bulb temperature and the moisture content. In the paper, the analysis and discussion are for the regions of the outdoor dry bulb temperature from 24.3 °C to 36 °C, and the moisture content from 5.4 g/kg to 22.5 g/kg. As such, when the system is applied in the same or similar weather conditions, the discussion results are applicable. However, further research is needed for the selection design in areas where the weather parameters differ greatly from those studied.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
A | heat transfer area (m2) |
H | cooler height (m) |
L | cooler length (m) |
heat capacity ratio of condensation water to secondary air | |
heat capacity ratio of spray water to secondary air | |
Lef | Lewis factor |
Pr | Prandtl number |
Re | Reynolds number |
d1,w | the moisture content of air in equilibrium with condensation water (kg/kg) |
d2,w | moisture content of air in equilibrium with spray water (kg/kg) |
x,y | coordinate direction |
, | dimensionless coordinate direction |
m | mass flow rate of air (kg/s) |
mw | spray water volume (kg/s) |
i | enthalpy of air (kJ/kg) |
h | heat transfer coefficient (kJ/(m2·°C)) |
hm | mass transfer coefficient (kg/(m2·s)) |
r | latent heat of water evaporation (kJ/kg) |
T | thermodynamic temperature (K) |
t | dry bulb temperature (°C) |
d | moisture content of air (kg/kg) |
Cp | Specific heat at constant pressure kJ/(kg·K) |
n | number of heat exchange channels |
NTU | number of heat transfer units |
E | fees (RMB) |
R | circulating water concentration ratio |
P | energy consumption (W) |
Le | Lewis number |
hn | Enthalpy of indoor state point (kJ/kg) |
hw | Enthalpy of outdoor fresh air state point (kJ/kg) |
hw’ | Enthalpy of the state point of fresh air treated by ERIEC unit (kJ/kg) |
wd | discharge water consumption (m3/h) |
τtotal | the total operating time of the ERIEC fresh air unit (h) |
Greek symbols | |
λ | thermal conductivity, W/m·°C |
σ | condensation area ratio |
Γ | Spray water mass per unit length kg/(m·s) |
η | efficiency |
θ | channel spacing (m) |
δ | thickness (m) |
ρ | density (kg/m3) |
ω | water consumption (m3/h) |
τ | operating time |
∆ | difference value |
Subscripts | |
1 | primary/fresh air |
2 | secondary air |
w | water |
in | inlet |
out | outlet |
pl | wall |
total | total amount |
s | saturation vapor pressure |
c | condensate water |
wb | wet bulb |
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Research Literature | Heat Exchanger Type | Research Methods | Recommended Wind Speed (m/s) |
---|---|---|---|
Xing et al. [17] | Plate type indirect evaporative cooler | Theoretical Simulation | Primary wind speed of 2.232 |
Zang et al. [18] | Folded plate indirect evaporative cooler | Experimental Research | Primary wind speed of 2.5 Secondary wind speed 2.5–3 |
Li et al. [19] | Curved plate type indirect evaporative cooler | Measured calculations | Primary wind speed 3.5–5 |
Liu et al. [20] | Folded plate indirect evaporative cooler | Experimental Research | Primary wind speed 1.5–2.5 Secondary wind speed 2–3 |
Huang et al. [21] | Metal foil plate type indirect evaporative cooler | Experimental Research | Primary wind speed 2.2–2.8 |
Parameter Meaning | Expression of Parameters |
---|---|
the ERIEC heat exchanger number of transfer units | |
Lewis coefficients in condensation and evaporation processes | |
the heat capacity ratios of secondary air to spray water and condensed water | |
the secondary air mass flow ratio | |
the ratios of heat transfer coefficients of spray water liquid film, condensed water liquid film and primary air to heat exchange wall | |
the ratios of heat transfer coefficients of primary air, spray water liquid film and condensate water liquid film to secondary air |
Climate Zones | City | W | W’ | Wet-Bulb Efficiency | Enthalpy Efficiency | ERIEC Percentage % | ||
---|---|---|---|---|---|---|---|---|
t1,in (°C) | t1,wb,in (°C) | t1,out °C | d1,out g/kg | |||||
Severe cold regions | Xining | 26.4 | 16.6 | 19.7 | 7.8 | 0.87 | 0.89 | 100.00 |
Urumqi | 33.4 | 18.3 | 20.3 | 7.0 | 0.89 | 0.90 | 100.00 | |
Hohhot | 30.7 | 21.0 | 21.1 | 11.7 | 0.80 | 0.81 | 100.00 | |
Harbin | 30.6 | 23.8 | 22.1 | 15.3 | 0.71 | 0.85 | 55.74 | |
Changchun | 30.4 | 24.0 | 22.2 | 15.4 | 0.70 | 0.90 | 55.50 | |
Shenyang | 31.4 | 25.2 | 22.7 | 16.1 | 0.69 | 1.04 | 55.60 | |
Cold regions | Lhasa | 24.0 | 13.5 | 18.8 | 5.4 | 0.98 | 0.97 | 100.00 |
Lanzhou | 31.3 | 20.1 | 20.8 | 10.2 | 0.83 | 0.85 | 100.00 | |
Yinchuan | 31.3 | 22.2 | 21.5 | 13.1 | 0.78 | 0.80 | 84.30 | |
Taiyuan | 31.6 | 23.8 | 22.1 | 15.3 | 0.74 | 0.78 | 55.74 | |
Xi’an | 35.1 | 25.8 | 22.9 | 16.4 | 0.74 | 0.89 | 55.85 | |
Beijing | 33.6 | 26.3 | 23.1 | 16.7 | 0.70 | 1.07 | 55.90 | |
Shijiazhuang | 35.2 | 26.8 | 23.4 | 17.0 | 0.72 | 1.03 | 55.48 | |
Tianjin | 33.9 | 26.9 | 23.4 | 17.1 | 0.69 | 1.14 | 55.56 | |
Ji’nan | 34.8 | 27.0 | 23.4 | 17.2 | 0.71 | 1.08 | 55.17 | |
Zhengzhou | 35.0 | 27.5 | 23.6 | 17.5 | 0.70 | 1.16 | 55.69 | |
Hot summer and cold winter regions | Chengdu | 31.9 | 26.4 | 23.1 | 16.8 | 0.67 | 1.23 | 55.97 |
Chongqing | 36.3 | 27.3 | 23.6 | 17.3 | 0.72 | 1.05 | 55.86 | |
Guilin | 34.2 | 27.3 | 23.6 | 17.4 | 0.68 | 1.18 | 55.09 | |
Hangzhou | 35.7 | 27.9 | 23.8 | 17.7 | 0.70 | 1.17 | 55.68 | |
Hefei | 35.1 | 28.1 | 23.9 | 17.9 | 0.68 | 1.24 | 55.26 | |
Nanjing | 34.8 | 28.1 | 23.9 | 17.9 | 0.68 | 1.26 | 55.26 | |
Nanchang | 35.6 | 28.3 | 24.0 | 18.0 | 0.69 | 1.24 | 55.64 | |
Wuhan | 35.3 | 28.4 | 24.0 | 18.0 | 0.68 | 1.29 | 56.22 | |
Changsha | 36.5 | 29.0 | 24.3 | 18.5 | 0.69 | 1.28 | 55.42 | |
Hot summer and warm winter regions | Guangzhou | 34.2 | 27.8 | 23.8 | 17.7 | 0.67 | 1.26 | 55.18 |
Fuzhou | 36.0 | 28.1 | 23.9 | 17.9 | 0.70 | 1.21 | 56.87 | |
Haikou | 35.1 | 28.1 | 23.9 | 17.9 | 0.68 | 1.24 | 55.26 | |
Mild regions | Kunming | 26.3 | 19.9 | 20.7 | 15.7 | 0.74 | 0.74 | 100.00 |
Guiyang | 30.1 | 23.0 | 21.8 | 17.3 | 0.73 | 0.76 | 57.24 |
Air volume (m3/h) | 1000 | 2000 | 3000 | 4000 | 5000 | 6000 | 8000 | 10,000 | |
Recommended heat exchange area (m2) | 14.00 | 33.48 | 59.29 | 77.91 | 111.36 | 133.76 | 223.00 | 279.00 | |
Recommended board type (mm) | 500 × 500 | 600 × 600 | 700 × 700 | 700 × 700 | 800 × 800 | 800 × 800 | 1000 × 1000 | 1000 × 1000 | |
Epl (RMB) | 262.92 | 628.75 | 1113.47 | 1463.15 | 2091.34 | 2512.01 | 4187.94 | 5239.62 | |
Ppump (W) | 59 | 118 | 179 | 235 | 294 | 354 | 472 | 590 | |
Epump (RMB) | 1012.44 | 2024.88 | 3071.64 | 4032.60 | 5045.04 | 6074.64 | 8099.52 | 10,124.40 | |
wtotal (L/h) | a | 6.8 | 14.2 | 22.6 | 30.0 | 39.2 | 47.0 | 66.8 | 83.6 |
b | 12.5 | 25.7 | 40.4 | 53.7 | 69.6 | 83.5 | 117.0 | 146.0 | |
Ewater (RMB) | a | 1177.49 | 2458.87 | 3913.42 | 5194.80 | 6787.87 | 8138.52 | 11,567.09 | 14,476.18 |
b | 2164.50 | 4450.21 | 6995.66 | 9298.69 | 12,051.94 | 14,458.86 | 20,259.72 | 25,281.36 | |
PERIEC (KW) | a | 2.24 | 4.63 | 7.25 | 9.63 | 12.50 | 15.00 | 21.04 | 26.30 |
b | 3.19 | 6.59 | 10.33 | 13.74 | 17.78 | 21.33 | 29.93 | 37.41 | |
SERIEC (104 RMB) | a | 3.84 | 7.94 | 12.44 | 16.52 | 21.45 | 25.74 | 36.10 | 45.12 |
b | 5.48 | 11.31 | 17.73 | 23.58 | 30.51 | 36.61 | 51.35 | 64.19 | |
EI (104 RMB) | a | 3.59 | 7.43 | 11.63 | 15.45 | 20.06 | 24.07 | 33.71 | 42.13 |
b | 5.14 | 10.60 | 16.61 | 22.10 | 28.59 | 34.31 | 48.10 | 60.13 |
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Guo, C.; Li, Y.; Li, X.; Bai, R.; Dong, C. Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler. Sustainability 2023, 15, 7371. https://doi.org/10.3390/su15097371
Guo C, Li Y, Li X, Bai R, Dong C. Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler. Sustainability. 2023; 15(9):7371. https://doi.org/10.3390/su15097371
Chicago/Turabian StyleGuo, Chunmei, Yu Li, Xianli Li, Ruxue Bai, and Chuanshuai Dong. 2023. "Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler" Sustainability 15, no. 9: 7371. https://doi.org/10.3390/su15097371
APA StyleGuo, C., Li, Y., Li, X., Bai, R., & Dong, C. (2023). Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler. Sustainability, 15(9), 7371. https://doi.org/10.3390/su15097371