Heat pump and gas combi boiler in perfect harmony
Daikin Europe has combined the benefits of combi boilers and heat pumps for space heating with the launch of the Altherma Hybrid heat pump. It is aimed squarely at the combi boiler market of around a million units a year in the UK for replacement and new installations. The concept is that an Altherma heat-pump system and gas-fired (natural or LPG) combi boiler work seamlessly together to deliver space heating. DHW is provided by the combi boiler working by itself.
The installed base of combi boilers in the UK is about 8 million.
An Altherma outdoor unit is connected by refrigerant pipework to a Hydrobox unit onto the front of which is mounted an Intergas combi boiler with a hot-water output of 33 kW and heating output of 27 kW. The overall combination resembles a combi boiler and can be retrofitted into the same space. The ‘indoor unit’ is 902 mm high, 450 mm wide and 405 mm deep.
Depending on the heating requirement, the COP of the heat pump as affected by outside temperature, and the costs of gas and electricity as programmed into the controller, the system automatically decides if space heating should be provided solely by the heat pump bypassing the boiler, heat pump and combi boiler working together in series, or solely by the boiler.
A combination of air-source heat pump and condensing gas-fired boiler working in this way is up to 35% more efficient than a gas-fired condensing boiler alone.
An important feature for replacement projects is that the flow temperature can range from 25 to 80°C and is weather compensated. It is therefore suited to existing systems.
Daikin suggests that over a year, up to 70% of the energy required for space heating may be provided by the heat pump, either on its own or in hybrid mode with the combi boiler.
An installation will qualify for an RHI of 7.3 p/kWh for renewable heat generated by the heat pump, provided a suitable heat meter and electric-meter arrangement is installed.
In a recent field trial, one of these hybrid systems replaced a boiler in a home with an 18 MWh heating and hot-water load for a year. In the first year of operation, CO2 emissions were reduced by about 1.5 t.
Daikin’s analysis of capital, installation, running costs and RHI payments indicate a payback of about 10 years compared with a combi boiler.
To install hybrid systems, installers must be Gas Safe registered and qualified in handling F gases. They also need to be certified by the Microgeneration Certification Scheme. That’s quite a package, but Daikin offers installer support as part of developing this market.