How Efficient Is an Air Source Heat Pump Water Heater?
How efficient is an air source heat pump water heater? An air source heat pump water heater is far more efficient than a standard direct electric water heater, as it moves heat from the surrounding air rather than generating all its heat through electrical resistance. A heat pump water heater can attain a Coefficient of Performance, or COP, of about 2.5 to 4.0, depending on the model and operating conditions. This means that for every 1 kWh of electricity that the water heater uses, it may provide about 2.5 to 4 kWh of heat.
What is COP?
One of the key measurements that is used to describe the heat pump efficiency is the Coefficient of Performance.
For example:
* A COP of 2.5 means 1 kWh of electricity produces approximately 2.5 kWh of heat.
* A COP of 3.0 means 1 kWh of electricity produces approximately 3 kWh of heat.
* A COP of 4.0 means 1 kWh of electricity produces approximately 4 kWh of heat.
By comparison, a traditional electric immersion heater has an effective Coefficient of Performance near to 1, because about 1 kWh of electricity is turned to about 1 kWh of heat.
This is why an air source household hot water heater can generate much less electricity to provide the same amount of hot water.
For further product details, capacities and application information, visit our dedicated heat pump water heater pages:
Wall hung heat pump hot water heaters
Residential heat pump hot water heaters
Commercial heat pump hot water heaters
What Factors Affect Heat Pump Water Heater Efficiency?
The efficiency of an air source heat pump domestic hot water heater is not constant. It changes according to the operating conditions.
The primary factors are:
- Air temperature at origin
- Stored hot water temperature
- Type of refrigerant
- Efficiency of compressor
- Cylinder heat losses
- Hot water needs
- Use of immersion heater
The higher the temperature of the supply air, the easier it is for the heat pump to extract thermal energy.
Likewise, the higher the required water temperature, the harder the compressor must work. This increased temperature lift can reduce the COP.
Why does storage temperature matter?
Heat pumps typically perform best at moderate water temperatures.
Heating residential hot water to very high temperatures demands additional compressor effort and can compromise overall efficiency.
Heating domestic hot water to very high temperatures demands additional compressor effort and can compromise overall efficiency.
However, domestic hot water systems also need to consider hygiene and Legionella control, so many heat pump water heaters include a high-temperature cycle.
Depending on the product, the high temperature may be achieved by the heat pump itself, an electric immersion heater, or a combination of both.
Frequent use of the immersion heater will reduce the overall seasonal efficiency of the system.
How Efficient Are R290 Heat Pump Water Heaters?
Many modern air source heat pump water heaters use R290 refrigerant, also known as propane.
R290 has a very low Global Warming Potential and is well suited to higher-temperature applications, including domestic hot water production.
A well-designed R290 heat pump water heater can maintain strong efficiency while producing useful hot water temperatures, although actual performance still depends on air temperature, storage temperature and system design.
Are Air Source Heat Pump Water Heaters Energy Efficient?
Yes. A correctly sized air source heat pump water heater can be one of the most energy-efficient ways to produce stored domestic hot water using electricity.
The greatest savings are normally achieved when replacing a cylinder that relies entirely on direct electric immersion heating.
To maximise efficiency, the unit should be correctly sized for the property’s domestic hot water demand, installed in a suitable location and operated at an appropriate storage temperature.
In practical terms, an air source heat pump water heater with a COP of around 3 could use roughly one-third of the electricity required by direct electric resistance heating to deliver the same amount of useful heat, before considering other system losses and operating conditions.