All-in-one unit delivers precisely tempered fresh air requirements
Meeting the ventilation requirements of a building of any sophistication can require a lot of plant and be a significant user of energy — both of which are addressed by an integrated system developed by Flakt Woods. In a single unit, ReCooler HP combines fans to move the air, a thermal wheel to transfer both sensible and latent heat, and a reverse-cycle heat pump to further heat or cool the incoming fresh air as required.
That’s it. There is no need for an external chiller, condenser or boiler. Not requiring such external plant also eliminates the need for any pipework. All that is needed is ductwork — we are moving air, after all — and an electrical supply.
Chris Jones, sales engineer for ReCooler HP, also likes to emphasise the use of energy-efficient motors with variable-speed control and the inverter-driven compressor in the heat pump.
All good stuff, but it is how ReCooler HP minimises the energy used to temper incoming ventilation air that really marks it out.
A PowerPoint presentation on ReCooler HP includes a couple of diagrams that explain the concept in winter and summer operation. They are both for outdoor conditions that are more extreme than those generally experienced in the UK.
Let’s begin with the winter operation with ambient air at -5°C and extract air at 24°C (see diagram).
The first stage is for the Semco thermal wheel to extract heat from the outgoing air to heat the incoming air. That process warms the incoming air to 15.4°C while cooling the outgoing air to -0.4°C.
Incoming air at 15.4°C is too cool to deliver to the space, so the integral heat pump extracts heat from the outgoing air at 0.4°C to boost the temperature of the incoming air to 19.1°C while reducing the temperature of the outgoing air to -2.6°C.
It is worth remarking on the energy-efficiency benefit of the heat source for the heat pump being exhaust air at -0.4°C rather than ambient air at -5°C.
The incoming air then picks up a little more heat from the fan to raise its temperature to 20°C before it is ducted to the space.
The schematic for summer operation has incoming air at 30°C and air leaving the space at 24°C.
The effect of the thermal wheel is to cool the incoming air 25°C while heating the exhaust air to 29°C.
The next stage is for the heat pump to further cool the incoming air to 18.2°C by rejecting heat into the outgoing air stream, which raises its temperature to 36.5°C.
As the incoming air is delivered by the supply fan to the space its temperature receives a slight boost to 19°C.
The thermal wheel plays a key role in overall energy efficiency by achieving 50% of the cooling and 80% of the heating requirement. The remaining heating and cooling is done by the heat pump. The thermal wheel also transfers humidity, reducing the need for mechanical cooling in the summer. Indeed Chris Jones says that the seasonal energy efficiency for cooling is greater than 10.
Not only does ReCooler HP address capital costs, space requirements and energy efficiency but that energy efficiency is maximised by the selection and operation of the key components.
The heat pump, for example, has scroll compressors with permanent-magnet motors and a DC inverter drive that can modulate down to 10%.
Yan Evans, vice president for the UK sales unit, explains that the concept fully embraces the company’s e3 concept (environment, economical, expertise). He stresses that energy efficiency is a key requirement for today’s products and that there is also a growing demand for prefabricated solutions. Just as important as energy efficiency is space efficiency — especially for projects in London.
There are eight models of ReCooler HP for air flows from 0.8 to 6.5 m3/s. Nominal cooling capacities from the thermal wheel and heat pump are from 35 to 175 kW. Heating capacities are from 21 to 57 kW.