HVAC dehumidification systems for thermal comfort: a critical review

This paper, on the basis of the main literature indications, deals with moisture control in buildings during the summer season; so, the dehumidification of the air is analysed. Dehumidification is considered as a key feature of HVAC systems for thermal comfort. Initially, the principles of mechanical and chemical dehumidification are shown. The first one utilises mechanical means-compression refrigeration systems-to cool the air and so to dehumidify it; the latter removes the water vapour from the air by transferring it towards a desiccant material (adsorption or absorption). In the mechanical dehumidification field, a proper control of ambient temperature and humidity can be obtained by means of an air handling unit (AHU) which treats outside air alone, while recirculating air is treated by a simple cooling coil. Various possible AHU configurations are examined. Afterwards, HVAC systems for a theatre and for a supermarket are analysed. The use of hybrid systems with desiccant wheel for these applications has provided the following main results: remarkable savings in operating costs and higher plant costs (a simple payback time of 2-3 years for supermarket); a notable reduction of the power electric demand; a better control of ambient humidity.