Something in the air

Tim Bennett, Hybrid Heating Systems Ltd, asks if air source heat pumps have now come of age

In a recent survey that we commissioned, we discovered that 40 percent of enquires for ground source heat pumps were actually better suited for air source heat pumps, such are the advances in this technology.

The SPF ratings for these two technologies has changed dramatically since the introduction of the inverter driven compressor mono block ASHPs; essentially, this allows the compressor speed to drop as the ambient temperature increases, resulting in higher efficiencies for moderate heating demands.

A ground source heat pump will typically have a COP of around 4.1 with the ambient temperature having little effect. At 7 ̊C, a fixed speed compressor ASHP could deliver just under 4.0 while an inverter product could be over 4.2. Just think about how many days we have in theUKwhere the temperature is above this, about 300!

These inverter products are ideal for the regular sized dwelling and can be used in a bivalent installation with existing boilers and heating systems for retrofits, to ensure adequate heating on the most severe days. 70 percent of our enquiries suit ASHPs used in this configuration, resulting in a viable return on investment, as there is generally only a need to partially upgrade and not replace the existing heating system.

Mono block ASHPs are considered as ‘plug and play’ installations. It typically takes 2-3 days to mount the ASHP outside and connect up to the distribution system compared to a GSHP, where there are costly ground works and the need to accommodate an internal unit.

Taking that into account, the “better” GSHP efficiency may only actually equate to £300 pa saving on running costs which means that it could take 20 years to recover the additional investment!