Ventilation unit combines heat pump and thermal wheel
Airsource's Tempair range of heat pumps/ventilation units combine heat-pump and heat-recovery technology to deliver fresh air to high occupancy buildings such as schools, lecture theatres, hotels, offices and hospitals. Units are available to deliver 0.7 to 7.5 m3/s. The first stage of heat recovery is a thermal wheel to transfer heat from the exhaust air stream to the incoming fresh air. As the diagram indicates, with exhaust air at 20°C, the thermal wheel can raise the temperature of incoming fresh air from 0 to 14°C.
The next stage of tempering the incoming air is for a heat pump with a Copeland modulating scroll compressor using R407C to draw yet more energy from the exhaust air via the evaporator and upgrade its temperature so that air can be supplied at 20°C. The condenser effectively acts as a heating coil, adding little, if any extra resistance to airflow.
The overall efficiency is indicated by another scenario. With a supply air volume of 3.1 m3/s, the power required to heat fresh air from -4°C to 19°C is 85.6 kW — which can be achieved with an additional system power input to a Tempair unit of 8 kW, comprising 3 kW of fan power and 5 kW to the heat-pump compressor — a ‘COP’ of over 10. The thermal wheel transfers 62.6 kW from exhaust air to supply air, and the heat pump adds the final 23 kW.
An additional benefit is that in the Summer, the heat pump can provide an element of cooling to the incoming air over and above that achieved by the thermal wheel.
