Abstract
The use of desiccant-coated heat exchangers (DCHE) in air conditioning systems possesses great advantages in the independent control of both temperature and humidity, as well as low energy consumption and high coefficient of performance (COP). The paper presents a novel high temperature cooling system that uses metal-organic frameworks (MOFs) as sorbents for humidity control. MOFs are a new class of porous crystalline materials consisted of metal clusters and organic linkers, which have an excellent performance of water sorption due to the large specific surface areas and high porosity. In this research, we directly coat MOFs on the heat exchange surface of evaporator and condenser. The evaporator can simultaneously remove both the sensible and latent loads of the incoming air without reducing the temperature below its dew point. The regeneration of wet MOFs is completely driven by the residual heat from the condenser. We also make comparison between the MOF-coated cooling system and conventional desiccants coated ones (i.e. silica gel, zeolite) by way of tests and calculation. The results indicate that the dehumidification capacity of the MOF-coated heat exchanger outperforms other conventional desiccant coated ones under low regeneration temperature (∼50°C). The MOF-coated system has a high COP, up to 7.9, and can save 36.1% of the energy required, compared to the traditional vapour compression system with reheating. The amphiphilic MOFs used in the study have high water uptake and low regeneration temperature, and they thus have the potential for being scaled up for large-scale applications in energy efficient air conditioning systems.
Highlights
Electricity demand for heating, ventilation and air conditioning system (HVAC) has gradually been a significant contributor to building energy consumption in the past decades
The results indicate that the dehumidification capacity of the metal-organic frameworks (MOFs)-coated heat exchanger outperforms other conventional desiccant coated ones under low regeneration temperature (~50°C)
Given the set outdoor air condition, two baselines with uncoated heat exchanger were used in comparison with MOF-coated heat exchanger as shown in Figure 4a: Air process 1, traditional high temperature cooling without dehumidification; Air process 2, traditional vapor compression cooling with refrigeration-based dehumidification
Summary
Electricity demand for heating, ventilation and air conditioning system (HVAC) has gradually been a significant contributor to building energy consumption in the past decades. This because more buildings are supplied with HVAC system to reach desired indoor thermal comfort [1]. By cooling the air below dew point, the humidity load is removed by condensation. Such a large temperature difference generally leads to a low COP and even an additional reheating process, and a lower sensible heat ratio like in some hot and humid climates may further worsen the condition [2,3]. Dealing only with the sensible load, the system can raise the evaporation temperature to a higher range, so the COP and energy efficiency of the system can be dramatically improved [6,7]
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