Study On Dehumidification Characteristics And Application Fundamentals Of Room Air Conditioners

Room air conditioner(RAC) has been widely used in residential buildings in China and consumed a lot of energy, high energy efficiency and optimization design for RAC are very important to building energy savings. The research works on RAC are mainly concentrated on the EER(energy efficiency ratio) and human behavior influence on energy consumption currently but seldom focus on the dehumidification characteristics which are also very important for the performance of RAC. When the RAC with high EER value is mainly used for dehumidification purpose, it may not work efficiently, the dehumidification performance of RAC influences energy use greatly in practical applications. The systemic theoretical and experimental study on RAC dehumidification characteristics were carried out in this thesis. The research work was as follows:EER was splitted into two parts—SHEER(sensible heat energy efficiency ratio) and LHEER(latent heat energy efficiency ratio), the definitions of SHEER and LHEER were given and LHEER was used to evaluate the dehumidification and energy saving characteristics of RAC. LHEER made it possible to quantify RAC dehumidification characteristic in an index form. Experiments with 16 different indoor air conditions were done to compare two RACs which had same rated cooling capacity, the results showed when a RAC had higher EER in the rated condition, it was not indicated that it had higher EERs in any other conditions. LHEER was also a very important index to evaluate RAC energy saving performance.The influence of climate to air conditioning system cooling loads was analyzed under Guangzhou and Beijing weather conditions, the calculation was done in the typical air conditioning design day, the whole summer instantaneous cooling load, including sensible cooling load and latent cooling load, was simulated by De ST-h. The results showed: application SHR(sensible heat ratio) in cold region was about 0.6~0.8, while application SHR in south China hot and humid region was about 0.5~0.7, application SHR below 0.7 was accounted more than 95% of the time in the cooling season. The relative humidity in conditioned space in hot and humid region was higher than the designed value due to the mismatch of application SHR and equipment SHR(0.7~0.8) of current RAC.The field experiment in a bedroom in residential building located in Maoming City, Guangdong Province was done. The experimental data showed that the indoor air humidity in hot and humid region was not ideal, the relative humidity was above 60% generally, sometimes over 70%. Decreasing RAC set temperature could improve indoor humidity environment and make occupants feel more comfortable, but it would increase electricity consumption, when indoor air temperature was set from 26℃ to 25℃, RAC electricity consumption increased by 50%.The calculation formula of condensate water flow rate of RAC and correlation formula of EER and LHEER were presented through theoretical derivation. The influence of evaporative temperature, condensation temperature, inlet air condition on RAC dehumidification characteristics was analyzed and it was concluded that raising evaporative temperature to improve EER would result in lower LHEER. Analysis and calculation showed that, if indoor air design condition in hot and humid region changed from 27℃DB/19℃WB to 26℃DB/20℃WB, the design condition would be closer to the actual condition and smaller equipment SHR and higher EER could be implemented in RAC design.The EVAP-COND Software was used to simulate the performance of RAC fin-tube heat exchanger in wet conditions, the simulation results were obtained and the influence of tube diameter, air flow rate, refrigerant circuitry and inlet air parameter on heat exchanger was analyzed. It was found that reducing tube diameter and designing fine refrigerant circuitry were benefitial to heat transfer and dehumidification capacity, there exists an air flow rate corresponding to maximum condensate water flow rate.Experimental study was carried out in enthalpy method testing lab, performance of RAC was tested in conditions of different combinations of indoor air temperature and relative humidity, influence of indoor air temperature and relative humidity on RAC cooling capacity, EER and LHEER were analyzed and conclusions were obtained.An innovative RAC with the functions of cooling and dehumidifying in hot weather while only dehumidifying in wet weather was developed. The principal and structure were given, and the air psychrometric process was analyzed and indoor heat exchanger was designed. The calculation showed that the innovative RAC maintained indoor air temperature at 22℃ and relative humidity at 60% in wet weather, comparing to a system consisting of a common RAC and an electric heater, the energy saving rate was 65%.This research work and the conclusions in this thesis could provide theoretical supports and reference data for the modification of room air conditioner and room air conditioner energy efficiency national standards, and also could be used in the field of air conditioner product design, research and development.