Sunday, 25 October 2009

Air source heat pump boiler options for the UK market

Air source heat pumps are a easy way of replacing a existing fosile fuel heating system. Off the gas grid locations are particularly expensive to run especially when oil is used and there is always a issue of a big oil tank which needs to be sited on the property which can be unsightly. Air source heat pumps have a outdoor condensing unit (heat collector) which collects the heat from the ambient air. These can be fixed on a wall or level and generally look exactly the same as a air conditioning system outdoor condensing unit.

The Basics :

The outdoor air source condensing unit comprises of a refrigeration compressor, a condensing coil (Ambient air exchanger), fan and water heat exchanger where collected heat from the ambient air is transferred to the water. Most air source heat pumps run on R410a refrigerant gas which has a maximum heat to water transfer temperature of around 60 DegC. Other machines run on R417a which is a replacement for R22 which is now not in use (as from 2010). R417a machines maximum heat to water transfer temperature is 55 DegC, both Gases require a booster electric heater to take the water temperature above 65 DegC to surpass the legionnaires breeding temperature. There is one machine which uses R410a and reaches 65 DegC, this is the Daikin Altherma Heating Only Air Source Heat-Pump Boiler System high temperature unit. This system can be very expensive. Other options are the Sanyo CO2 system which reaches 80 DegC comes as a complete system but uses the heat store principle where a water tank which has multiple coils is used as a central store of heat.

Main manufactures and machines:

Trianco Activair Air Source Heat-pump S500 (5 KW / 18000 Btu) for DHW (basic non-inverter type which requires a heat store water tank to transfer heat to)

Hitachi AquaFree air source heat-pump boiler RWM 3.0FSN1E (10 kW / 33000 Btu) (mainly underfloor application)

Daikin Altherma Heating Only Air Source Heat-Pump Boiler (The best money can buy, works down to -20 DegC)

Hitachi RHUE-3AVHN "all in one" air source heat-pump boiler (8.2 kW / 28000 Btu) DHW/heating ( all in one system with no need to heat store)

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