Low-temperature ventilation pre-heater in combination with conventional room heaters

• Effects of combing air-heater with existing radiator heating systems were analyzed.
• These combined systems covered a space heat loss at −15 °C using 40 °C supply water.
• Combined systems operated at 20–22.5% lower temperatures than conventional systems.
• The COP in combined systems was 8–18% higher than in conventional heating systems.
• Lowering of supply water temperature by 1 °C will increase the COP by 1–2%.

The main focus of the present study was to find design requirements for an air-heater that would be able to operate at low pressure loss and low-temperature water supply. The idea was to combine this low-temperature air-heater with existing radiator systems so that they can operate at similar low-temperature supply as used in floor heating systems. Results indicated that the proposed air-heater was able to lift the temperature of supply air at 10 l/s from −15 °C to 18.7 °C using 40 °C water supply. In addition, a thermal performance analysis showed that radiator systems equipped with the proposed air-heater could meet a space heat loss of 35.6 W per square meter floor area, using supply water of 40 °C. It was also shown that the heat pump efficiency in the hydronic system with proposed air-heater was 8–18% higher than in system without air-heater. All results in the present study were obtained by analytical (semi-empirical) and numerical (Computational Fluid Dynamics – CFD) calculations.