Hybrid HVAC systems with chemical dehumidification for supermarket applications

ABSTRACT HVAC systems in supermarkets must assure both thermal comfort for occupants and suitable climatic conditions for refrigerated cases, which operate better with low ambient relative humidity (40-45%). Since open display cases substantially reduce sensible load and moderately reduce latent load, ambient sensible/total heat load ratio is less than usual. Thus, if dehumidification is carried out with a traditional cooling coil, over-sizing of the coil and re-heating of the treated air are necessary, with energy and economic waste. To offset these disadvantages, hybrid HVAC systems with chemical dehumidification may be employed. In this paper a case study is presented in which a traditional HVAC system is compared to hybrid systems with chemical dehumidification. Dynamic simulation codes (DOE and DesiCalcTM) and Test Reference Year data (TRY), opportunely elaborated, have been used. Annual operating costs have been estimated and large savings have been obtained with hybrid systems. Considerable reduction of electric energy demand as well as better control of thermal-hygrometric conditions were noted. A simple payback of about 1 year has been obtained. Finally, a virtual retrofitting operation on 30% of the existing HVAC systems in Italian supermarkets has shown significant operating cost savings.