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Abstract: The combined use of dedicated outdoor air ventilation (DV) and dry cooling (DC) air-conditioning system to decouple sensible and latent cooling for desirable space air conditions, better indoor air quality, and energy efficiency is proposed for hot and humid climates like Hong Kong. In this study, the performance and energy saving potential of DCDV system in comparison to conventional systems (constant air volume (CAV) system with and without reheat) for air conditioning of a typical office building in Hong Kong are evaluated. Through hour-by-hour simulations, using actual equipment performance data and realistic building and system characteristics, the cooling load profile, resultant indoor air conditions, condensation at the DC coil, and energy consumptions are calculated and analyzed. The results indicate that with the use of DCDV system, the desirable indoor conditions could be achieved and the annual energy use could be reduced by 54% over CAV system with reheat. The condensate-free characteristic at the DC coil to reduce risk of catching disease could also be realized. [Copyright &y& Elsevier]

Abstract: Recent research studies advocates decoupling dehumidification from cooling to improve indoor air quality and reduce energy consumption. The feasible use of heat pipe at the air handler dedicated for outdoor air treatment (HPDV system) in accomplishing this objective is investigated in this study. To evaluate the performance and the energy saving potential of the proposed HPDV system, the design parameters of 75 Grade A office buildings in Hong Kong were collected. Ten representative buildings were subsequently identified for further study to achieve a confidence level of 95%. The annual cooling load profiles of the 10 representative buildings were simulated by the use of HTB2. Based on the realistic cooling load profiles and the heat pipes of effectiveness 0.35–0.6, the proposed HPDV system in achieving the intended objectives were evaluated. It was found that the savings for the 10 representative buildings were comparable. The reduction in cooling and reheating energy was between 23 and 44kWh/m2, which corresponds to 1.2% and 7.9% saving in annual energy use for air-conditioning. The results indicate that HP of different effectiveness can be applied to save energy for over 70% of the air-conditioned hours; of which only 0.03–6.3% of the time the decoupling objective cannot be achieved (abbreviated as NHRS). Based on the results of the study, a simplified model relating NHRS with heat pipe effectiveness has been established. The model can help designers more quickly determine how NHRS can be weighted against other factors such as the additional plant room space and the financial implications. The results confirm the feasible use of the HPDV system in achieving the intended objectives for subtropical climate like Hong Kong where air-conditioning demand is highly variable, and is required year-round. [ABSTRACT FROM AUTHOR]

Abstract: Residential air-conditioning becomes a common feature in our daily life. They are typically installed at high level known as ceiling-based system (CAC). With the increasing use of floor-based air-conditioning system in commercial buildings for energy saving, it is proposed in this study to locate a top discharge/front return air-conditioner at floor level to resemble a floor-based air-conditioning system (FAC) to curb energy use in residential buildings. Given the concerns about draught discomfort and thermal stratification associated with floor-based air-conditioning systems, the objective of this study is to evaluate the air distribution performance and to quantify the possible energy benefits. Bedroom was chosen as a sensitive case for detailed air distribution performance evaluation. Experimental study, CFD simulations and energy simulations were conducted in achieving the specific objectives. CAC and FAC were installed in a bedroom-like environmental chamber for experimental study at different indoor and outdoor conditions. The air velocities and temperatures at various positions and levels inside the chamber were measured to determine the air distribution performance indices (ADPI) and airflow draft risk (DR). The cooling output, power consumption and coefficient of performance (COP) of the two units were measured and calculated for comparison. The experimental results show that ADPI of CAC and FAC are 92.3% and 84.6%, respectively. COP of FAC is 8.11% higher than CAC, and the corresponding DR are comparable. The experimental results were used to validate the CFD simulations as well as providing actual performance data for predicting the energy use of applying CAC and FAC in a case-study building. CFD simulations and draught assessment confirmed that there is no potential draught discomfort and thermal stratification associated with the use of FAC. Energy simulations predicted that the associated energy saving is 6.9%. Wider use of FAC in residential buildings is therefore recommended. [Copyright &y& Elsevier]