Performance of Daikin Altherma hybrid heat pump/boiler is assessed

Daikin, Altherma, heat pumps, boiler, space heating, renewable energy

The first Daikin Altherma hybrid heat pump to be installed in the UK, in a family home in Wigan, has achieved impressive performance figures and significant benefits in running costs. The system combines a gas condensing combi boiler and an air-to-water heat pump to create an efficient domestic heating and hot-water system that is ideal for replacing gas-fired boilers. The system has a capacity of 27 kW for central heating and 33 kW for hot water. The outdoor heat-pump unit has an output of 5 kW. The system replaced a gas combi boiler.

Monitoring through the nine months to 31 March 2015 showed that the heat pump could provide 50% of space heating — 5731 kWh of the 11 490 kWh required. Primary energy efficiency was 105%, and seasonal performance factor was 3.6.

The renewable energy produced by the heat pump equated to a Renewable Heat Incentive payment of £307. The total running cost of the Altherma hybrid for space heating was £466 against an estimated £549 for a gas-boiler-only installation — a theoretical saving of 15%.

The 140 m2 brick-built mid-terrace house was built in the 1900s and has been updated with double-glazed windows, a loft conversion and insulation to modern standards.

The Altherma hybrid uses a heat pump and boiler working in series, rather than in parallel as for most bi-valent systems. In hybrid mode, heating water is pre-heated by the heat pump, reducing the energy used by the boiler. In ‘economical’ mode (which minimises heating costs based on electricity and gas prices, heat-pump efficiency, heat load and required water-leaving temperature) up to 35% higher heating efficiencies can be achieved over a gas condensing boiler alone.

A room-by-room heat-loss calculation was carried out prior to installation to ensure that an adequately sized heating system was installed and if the existing radiators could be retained. The design flow temperature is up to 60°C when the outside temperature is -2.2°C, so the radiators and pipework did not need to be replaced. When the external temperature reaches 15°C, the design flow temperature is 35°C. These calculations were carried out in accordance with MIS 3005, the Microgeneration Certification Scheme (MCS) standard covering the design, supply, installation and commissioning of a heat pump. Using the MCS guidelines, the heat loss for the property was estimated to be 9kW at -2.2 °C.

Energy bills are reduced by up to £85 a year compared with a gas boiler, based on the current gas price for the home of 4 p/kWh and electricity of 12 p/kWh.

For more information on this story, click here: October 2016, 133
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