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Heat pumps

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[Sustainable products] Ignore manufacturer hype and choose simple, correctly sized heat pumps, says Sandy Patience

This month’s report by the Energy Saving Trust (EST), Getting Warmer: A Field Trial of Heat Pumps, will encourage the installation of ground source (GSHP) and air source (ASHP) heat pumps in areas of application where they are most effective, particularly in off-gas homes, in new-builds and when a house has been well-insulated.

The slightly more efficient GSHPs work by extracting heat from the ground and upgrading it to a useful temperature. In most instances GSHP works best with the ‘low-grade’ heat associated with space heating, rather than higher temperature DHW.

Prior to the trial, the industry was becoming mired in the kind of controversy familiar to those recently involved in the domestic wind turbines debacle. Yet again, the concern was that the performance promised was not being delivered in practice.

Heat pumps are only effective where the heat gained is a significant multiple of the electrical energy invested in running the pump. The ratio between the two is known as the Coefficient of Performance (COP). The ‘system efficiency’ ratio is slightly more onerous in that electricity for the entire heating system is included as the input. It is important to realise that manufacturers publish idealised COP figures as produced under laboratory conditions to EN14511. Above 3.0 is generally regarded as acceptable.

The EST report reveals that, for a small proportion of GSHP installations, system efficiency figures of above 3.0 were achieved, but ‘mid-range’ came in between 2.3 and 2.5; figures well below industry hype. Further analysis of the weaker performers suggested that installations had suffered from inadequate design and installation along with poor user understanding of controls.

Critically, the report proves that systems sized correctly and designed for simple operation are the more successful. The EST recommends that carefully monitored installations should be carried out by companies who provide the complete service.




Designed for domestic application, the single compressor heat pump range incorporates both the ground and underfloor circulation pumps, high-specification acoustic hoods and double vibration isolation to reduce noise and vibration.

Manufacturer Kensa
Model Compact range
Outputs at 0-35oC 4-12kW
COPs to EN14511 at 0-35oC 3.91-4.07
Compressor type Scroll
Working temperatures on collector hose side -5-15ºC
Dry weight 85-110kg
Height/width/depth 900 x 550 x 570mm
Country of manufacture UK




Opti technology incorporates an intelligent control system that ensures that the performance is adjusted to the prevailing requirements and conditions of the heating system. This makes the heat pump work under the most ideal conditions available.

Manufacturer Danfoss
Model DHP-L Opti range
Outputs at 0-35oC 6-16kW
COPs to EN14511 at 0-35oC 3.99-4.34
Compressor type Scroll
Working temperatures on collector hose side -10-20ºC
Dry weight 145-165kg
Height/width/depth 1,538 x 596 x 690mm
Country of manufacture Sweden


Vent Axia

Vent Axia

Thernamic pumps provide space heating, cooling and domestic hot water. The range includes single-phase units from 4 to 24kW. A high temperature series is also available from 4 to 20kW, which is capable of heating at temperatures of up to 65 °C.

Manufacturer Vent-Axia
Model Thernamic High Capacity range
Outputs at 0-35oC 12-24kW
COPs to EN14511 at 0-35oC 3.97-4.07
Compressor type Scroll
Working temperatures on collector hose side -5-15ºC
Dry weight 165-180kg
Height/width/depth 900 x 900 x 570mm
Country of manufacture UK




The range includes a highly efficient and effective scroll-type compressor, which allows around 65ºC flow temperature from the appliance and high COP ratings. Pumps can be combined with solar collectors for hot-water production.

Manufacturer Worcester, Bosch Group
Model Greenstore System range
Outputs at 0-35oC 6-11kW
COPs to EN14511 at 0-35oC 3.8-4.6
Compressor type Scroll
Working temperatures on collector hose side -5-20ºC
Dry weight 149-164kg
Height/width/depth 1,520 x 600 x 600mm
Country of manufacture Sweden




The range features an integrated heat-pump manager that monitors, regulates and controls the entire heating system. It also allows the heat pump to be integrated with existing heating systems, making it suitable for retrofit applications.

Manufacturer Dimplex
Model SI MEH range
Outputs at 0-35oC 6-11kW
COPs to EN14511 at 0-35oC 4.0-4.5
Compressor type Scroll
Working temperatures on collector hose side -5-25ºC
Dry weight 118-133kg
Height/width/depth 805 x 650 x 462mm
Country of manufacture Germany




The F1145 is equipped with a control unit to maintain a comfortable indoor climate, both cost-effectively and safely. Information about status, operation time and all temperatures in the heat pump are shown on the large and easy-to-read display.

Manufacturer NIBE
Model F1145 range
Outputs at 0-35oC 5-12kW
COPs to EN14511 at 0-35oC 4.12-4. 44
Compressor type Scroll
Working temperatures on collector hose side -15-25ºC
Dry weight 140-178kg
Height/width/depth 1,520 x 600 x 620mm
Country of manufacture Sweden


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