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Hybrid heat pumps: the best of both worlds

Hybrid heat pumps are an attractive option for combi boiler replacement, particularly as they are eligible for domestic Renewable Heat Incentive payments, argues Nancy Jonsson

With the launch of the domestic Renewable Heat Incentive (dRHI) in April, renewable systems are becoming a more viable and attractive home heating method. Several renewable systems are eligible under the dRHI but perhaps the most versatile are hybrid systems, which combine familiar technology – a gas boiler – with a more efficient renewable heating solution, such as an air-to-water heat pump.

The Daikin Altherma hybrid heat pump system, for example, combines a gas condensing combi boiler and an air-to-water heat pump and is suitable for homes with a heat load of 12kW – 20kW. It can be connected directly to existing pipework and operates at water flow temperatures of up to 80°C, eliminating the need to replace radiators. The combi boiler provides instantaneous domestic hot water, with flow rates of 13 l/min (dT 35°C).

The compact indoor unit, which includes the boiler and the heat pump, fits in the same space as a conventional wall-hung boiler. This split refrigerant system includes an outdoor unit that can be installed up to 20m away. All connections are easily accessible, making the unit quick to commission and easy to maintain. In fact, the gas boiler can be commissioned before the outdoor heat pump unit, making it ideal for urgent jobs.

The Daikin Altherma Hybrid system is up to 35 per cent more efficient in heating than the most efficient gas condensing boilers. It has two settings for heating: ‘ecological’ or ‘economical’. In ecological mode, the user can decide to minimise the ecological impact of their heating system by limiting carbon emission rates.

In the economical setting, the smart controller automatically searches for the most economical operating conditions for the lowest running costs based on energy prices (electricity and gas), heat pump efficiency and heat load. There are four operating modes and the heat pump will automatically switch between each to achieve the most cost efficient operation.

At higher outdoor temperatures, when the heat pump has sufficient capacity to cover the heat load, only the heat pump will operate. As the outdoor temperature decreases and the heat load increases, the first hybrid mode is selected, and the boiler is switched on to provide additional capacity.

When the weather gets even colder, the Daikin Altherma hybrid heat pump’s unique flow control function automatically reduces the flow rate, thereby reducing the return and flow temperature to maintain the system’s efficiency. This delays dependency on the gas boiler for as long as possible. Finally, on the coldest days, and as it becomes less cost efficient, the heat pump switches off and the boiler provides the full heating capacity.

Over an entire year, up to 70 per cent of the energy required for space heating is provided by the heat pump, either on its own, or in combination with the condensing boiler in hybrid mode. In this mode, heating water is pre-heated by the more efficient heat pump, reducing the energy consumed by the boiler.

The unique control logic in the Daikin Altherma hybrid heat pump optimises this combined operation, making it cost-effective, whatever the outdoor temperature. This helps customers to reduce their energy bills and ensures comfort all year round.

Because they run alongside traditional heating, hybrid systems have to be metered to be eligible for domestic RHI payments. Homeowners also have to prove their system is being properly maintained to continue to receive tariff payments, so installers should advise customers to ensure that the system is regularly serviced.

Hybrid heat pumps offer a fantastic business opportunity for installers to target a much wider market of households looking to improve their energy efficiency and reduce fuel bills.

Daikin UK offers a comprehensive support package for installers, with hybrid training and specialist advice throughout the design, installation and commissioning process. To install a Daikin Hybrid heat pump system, installers need to be Gas Safe registered and Fgas qualified. If the householder wants to apply for dRHI payments, they will need to choose an installer certified by the Microgeneration Certification Scheme (MCS) and select MCS accredited products, such as the Daikin system.

For homeowners using gas or LPG boilers coming to the end of their working life, a hybrid system, including a new boiler, will deliver the lower running costs associated with renewable heating and provide the opportunity to take advantage of dRHI payments.

For installers willing to invest in training and accreditation, hybrid systems are an excellent way to introduce new customers to renewable energy technologies, especially where the system is packaged with a familiar gas combi boiler.

// The author is the product manager, heating and renewables, at Daikin UK //

3 July 2014

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