Central Air Conditioning Systems with Partial Indirect Evaporative Cooling and Utilization of Cold and Heat of Ventilation Emissions

A promising trend in air conditioning systems is the use of indirect evaporative cooling, but in the classic version it is effective in dry and hot climates. For the need to maintain comfortable air parameters in public buildings, it is not possible to fully implement such a process in the conditions of Ukraine (the relative humidity of the outside air ranges from 63 to 75 %). The aim of the work is to increase the energy efficiency of air conditioning systems with standard equipment through partial evaporative cooling and use for cooling water in cooling towers of the air removed from the rooms during the warm season, and in the cold season - use of the exhaust air for preheating the supply air in heat exchanger. A corresponding system diagram was developed and computational studies of a direct-flow circuit and a circuit with recirculation were carried out for one of the educational buildings of the Igor Sikorsky Kyiv Polytechnic Institute. According to the results of calculating the direct-flow circuit in the warm period, the energy efficiency of indirect evaporative cooling was 23.5 %. The annual amount of recovered heat of ventilation emissions for this scheme in the cold period was 3731 GJ / year, and the economic effect - 1473185 UAH / year. For a circuit with recirculation during a warm period, the greatest effect of indirect evaporative cooling is achieved with a recirculation rate of 10 %, and for the overall decrease in the cooling capacity of the air conditioner during this period the greatest impact is not indirect evaporative cooling, but recirculation. In the cold season, the greatest utilization effect is also achieved with a 10 % recirculation rate.

Thermal Comfort and Energy Analysis of a Hybrid Cooling System by Coupling Natural Ventilation with Radiant and Indirect Evaporative Cooling

A hybrid cooling system which combines natural ventilation with a radiant cooling system for a hot and humid climate was studied. Indirect evaporative cooling was used to produce chilled water at temperatures slightly higher than the dew point. With this hybrid system, the condensation issue on the panel surface of a chilled ceiling was overcome. A computational fluid dynamics (CFD) model was employed to determine the cooling load and the parameters required for thermal comfort analysis for this hybrid system in an office-sized, well-insulated test room. Upon closer investigation, it was found that the thermal comfort by the hybrid system was acceptable only in limited outdoor conditions. Therefore, the hybrid system with a secondary fresh air supply system was suggested. Furthermore, the energy consumptions of conventional all-air, radiant cooling, and hybrid systems including the secondary air supply system were compared under similar thermal comfort conditions. The predicted results indicated that the hybrid system saves up to 77% and 61% of primary energy when compared with all-air and radiant cooling systems, respectively, while maintaining similar thermal comfort.

Application of indirect evaporative cooling strategies for a warm-humid climate

Energy consumption in buildings for air conditioning has augmented worldwide by the escalation in global warming. The application of passive cooling is a promising approach to mitigate this situation. The aim of this research was to assess and characterize the performance of indirect evaporative cooling strategies combined with other passive cooling techniques, applied in experimental modules, aimed at providing hygrothermal comfort. Results showed that the investigated strategies presented lower temperatures than the external conditions and the control module. The alternative that combined indirect evaporative cooling with thermal mass, solar protection, and night radiative cooling was the most promising, with a temperature reduction of 4.2 K, relative to the mean exterior temperature, and a decrease of 8.3 K of its maximum temperature relative to the maximum exterior temperature. An additional strategy was implemented in this alternative using a phase change material, that further reduced its temperature by 6.3 K, relative to the mean exterior temperature and a reduction of 11.5 K of its maximum temperature compared to the maximum exterior temperature. It is expected that these findings are applicable in actual buildings in warm-humid regions to reduce energy consumption for air conditioning, whilst improving hygrothermal comfort and health of occupants.