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.
Highlights
Heating and cooling systems in buildings consist of three main parts: heating and cooling plant, distribution, and heat emission and removal
For the 30 W/m2 heating load, the exergy required at the floor was 15%, 28% and 38% lower than required by the radiators in the R45, R55 and R70 cases, respectively, and for the 50 W/m2 heating load, the exergy required at the floor was 3%, 18% and 30% lower than required by the radiators in the R45, R55 and R70 cases, respectively. This was despite the fact that floor heating systems required slightly higher water flow rates than in the radiator heating cases due to the lower temperature difference between supply and return water flows requiring a larger flow rate, and slightly higher power inputs to the circulation pumps. These results show that with an increasing space heating load, higher working temperatures are needed in the floor heating system and its benefits compared to R45 decrease as the working temperatures become closer; considerably less exergy was required compared to the R55 and R70 cases
The results show that to benefit from this low exergy demand, an appropriate heat source that can this demand with a low exergy supply is required otherwise, Journal Pre-proof it is not possible to benefit fully from the low exergy demand of a heating system. 4.2.Floor heating connected to different heat sources Figure 5 and Figure 6 show the exergy flow patterns from supply, via consumption, to demand for floor heating connected to an air-to-water heat pump (AWHP), and to a ground-source heat pump (GSHP) under different space heating loads, respectively
Summary
Heating and cooling systems in buildings consist of three main parts: heating and cooling plant (generation), distribution, and heat emission and removal. Schmidt [21] compared different heat sources and emission systems (radiator and floor heating) and concluded that a floor heating system performed close to the ideal condition, i.e., the real exergetic demand of a zone This was mainly due to the low temperature heating possibility of water-based radiant floor heating systems. Journal Pre-proof their performance, i.e., how differences in the rate at which heat must be provided to or removed from the indoor space affect the overall performance To address this gap, the present study compared theoretically, by means of calculations, the exergy performance of different water-based (floor heating, and radiators) and air-based heating systems under different space heating loads. The calculation methodology that was developed could be applied to other building types, in the present case a single-family house was used as a case study
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