A theoretical study of the effects of different heating loads on the exergy performance of water-based and air-based space heating systems in buildings

Abstract The present study investigated theoretically the exergy performance of floor heating, radiators, and air heating under three different space heating loads of 10, 30 and 50 W/m2. The effects of different supply and return water temperatures were studied for the radiators, and the effects of different supply air temperatures were studied for the air heating system. All systems were assumed to be connected to a boiler. The floor heating system was further analyzed assuming an air-to-water heat pump, and a ground-source heat pump. Floor heating was the optimal heating system due to its low exergy demand. The separation of thermal environmental conditioning and ventilation was an efficient solution. The results prove thermodynamically that renewables (i.e., ground source heat in the present study) and low temperature heating systems (i.e., floor heating in the present study) are a resource- and exergy-efficient combination proven by their exergy efficiencies up to 10.5%. The critical COP concept was validated (2.57 in this study). The power use of auxiliary components might seem negligible in terms of energy; however, it is critical in terms of exergy as it affects the exergy performance drastically. The relative importance of auxiliary power becomes more critical at low space heating loads.