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Abstract The temperature and humidity independent control (THIC) system, which controls indoor temperature and moisture separately, may be an attractive alternative to existing conventional HVAC systems forits prominent improvement on the overall system performance and utilization of low grade energy resources. In order to verify the effectiveness of THIC system, a pilot project has been implemented in an office building in Shenzhen, China. In the system, liquid desiccant fresh air handling units driven by heat pumps are utilized to remove the entire latent load of outdoor air supplied for the whole building, and chilled water at the temperature of 17.5 ◦C from chiller is pumped and distributed into dry fan coil units and radiant panels to control indoor temperature. This paper presents the results of field test of the system, which shows that the system can provide a comfortable indoor environment even in very hot and humid weather. The COP of the entire THIC system can reach 4.0. According to the energy usage data recorded from the year 2009, the energy consumption of the THIC system in the tested office building was 32.2kWh/(m2 yr), which demonstrates magnificent energy-saving potential compared with the conventional air-conditioning system (around 49kWh/(m2 yr)).8850
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1. Introduction
In the conventional HVAC system that removes moisture by condensation, air is cooled and dehumidified simultaneously. In most cases, sensible load of building covers the majority part of the whole cooling load while the latent load (moisture load) takes only a small part. However, as the required cooling source temperature of dehumidification is much lower than that of cooling, the chilled water temperature has to be reduced to meet the demand for condensation dehumidification. Moreover, the ratio of sensible load to latent load varies largely due to the changes of outdoor climate, number variance of indoor occupants, indoor equipments and lighting utilization mode and so on. Therefore, the indoor temperature and humidity, the two key parameters, can hardly be satisfied with condensation by the cooling coil only. In practice, the common reaction to the increased humidity is to reduce the set-point temperature and then re-condition the air after passing the cooling coil to the proper temperature, which results in a plenty of energy wastefulness.
To avoid the aforementioned problems, temperature and humidity independent control (THIC) air-conditioning system stands out as an appropriate pattern that temperature and humid-ity can be regulated independently with temperature control subsystem and humidity control subsystem respectively. Besides, the coil temperature for cooling in the temperature control subsystem can be considerably increased, e.g. from current 7 ◦C to 17◦C, so that improvement on the performance of chillers or even free cooling from ambient could be obtained. Many investigations have been carried out on the hybrid desiccant dehumidification and air-conditioning system, which integrates liquid/solid desiccant units with a conventional cooling system to avoid excess cooling. Liquid desiccant units developed quickly in recent years, for its advantages of dehumidifying at a temperature higher than the air’s dew-point to avoid reheat procedure in the system, and regenerating desiccant at a low temperature which can be driven by low-grade heat sources.Many studies focusing on improving its performance with process optimization have been conducted in depth, such as Yadav, DryKor Ltd., and Liu et al.. Chen et al.designed an independent dehumidification air-conditioning system with a hot water-driven liquid desiccant and a chiller that provides 18–21 ◦C chilled water for an office building in Beijing, which saved about 30% cooling cost compared with conventional system. The performance of a hybrid system tested by Ma et al. was 44.5% higher than conventional vapor compression system at a latent load of 30% and this improving could be achieved by 73.8% at a 42% latent load. Besides, the specific research on the feasibility and performance of the hybrid system in hot and humid regions is promoted.