Air Source Heat Pumps FAQs

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    Air source heat pumps – technical FAQs

    We know that for many people, the benefits of an air source heat pump are of more interest than how they work! But if – like us! – you appreciate the technical details, here are some answers to some frequently asked questions.

    How does an air source heat pump work?

    Heat pumps work essentially the same way that your fridge, or the air conditioning in your car. Your fridge gets cold by extracting the heat from within it and expelling it out of the back (if you feel the back of your fridge when it is running, it will be warm to touch).

    Heat pumps work on the same principle – by extracting the heat energy from the air outside and transferring this heat to your house via your heating system (radiators, UFH, fan convectors etc.).

    Do heat pumps work at low temperatures?

    Most heat pumps will operate down to around -20c. This may seem odd, however, there is still sufficient energy in the air at these temperatures to be extracted; according to science, there is still energy all around us down to absolutely zero (−273.15 °C).

    Of course, the available energy in the air drops as the external temperature drops, so the amount of energy a heat pump can provide will also drop. As such, all our calculations are made at an appropriate design temperature (e.g., -1.8c in the south of England), as ultimately, it is at these temperatures that we need to ensure your heat pump has sufficient output to keep you warm.

    What’s the difference between an air source and ground source heat pump?

    Air source heat pumps are most commonly found in 2 forms: air source and ground source. Both operate on the same basis, but as the name suggests, gather their energy from a different source. Other types such as water source are also available but are far less common.

    Our general guidelines when it comes to air source heat pumps vs ground source heat pumps is the capacity requirement of the property. For example, if your property requires less than 16.5kW to heat then an air source heat pump is generally the most suitable and cost-effective option.

    If your property requires more than 16.5kW to heat, then it is worth investigating ground source heat pumps. Of course, there are exceptions to this rule, and all properties are assessed individually to come up with the best suited technology.

    Can an air source heat pump reduce my heating bills?

    Depending on your current heating fuel, installing an air source heat pump could reduce your heating energy bills. Typically, the largest savings are seen when replacing oil, LPG, electric, or old/inefficient natural gas boilers, however, depending on what you’re currently paying for electricity and gas, heat pumps can sometimes now be cheaper to run that a modern condensing boiler.

    As a rule of thumb, a heat pump uses approximately a quarter of the energy of a modern gas boiler (based on a boiler efficiency of 90% and heat pump SCOP of 3.6), therefore:

    • If your gas tariff is >25% the costs of your electricity tariff, then a heat pump will be cheaper to run than a modern condensing boiler.
    • If your gas tariff is <25% the costs of your electricity tariff, then a heat pump will be more expensive to run than a modern condensing boiler.

    Example 1:

    • Electricity rate = 28p/kWh
    • Gas rate = 8p/kWh
    • Workings = 28/8=3.5
    • Result = Air source heat pump will be cheaper to run

    Example 2:

    • Electricity rate = 30p/kWh
    • Gas rate = p/kWh
    • Workings = 30/7=4.3
    • Result = Air source heat pump will be more expensive to run

    How can an air source heat pumps reduce carbon emissions?

    Air Source Heat Pumps do not burn fossil fuels and are powered by electricity alone. As a result, switching to an air source heat pump can drastically reduce your home’s carbon emissions.

    But of course, just how much you reduce your emissions by depends on the source of your electricity supply. The National Grid is moving to lower carbon methods, but your supply could come from a coal fired power station, meaning your CO2 output would be higher. Your carbon output will also be affected by whether you supplement your heat pump with another renewable energy source, such as PV generation.

    While it’s true that the production of a heat pump makes its own carbon footprint, compared to a non-renewable heat source unit, it will pay for itself over and over during its lifetime.

    A useful source of information on varying CO2 output according to electricity supply can be found here.

    What is the optimum air source heat pump water temperature?

    The efficiency of air source heat pumps increases as the flow temperature decreases. In other words, for maximum efficiency we want to produce water as cool (or less hot!) as possible.

    We refer to this temperature as the ‘design flow temperature’. Historically, gas and oil boilers have been designed to run at high temperatures (around 70c), whereas we typically design heat pump systems to run at 50c of less (<50c for radiator systems and <40c for underfloor heating).

    High temperature air source heat pumps are available these days, however, their efficiency is not as great as a low temperature heat pump. For example, the Daikin H HT model can achieve up to 70c flow temperatures, and the Hitachi Yutaki S80 6HP can achieve a flow temperature up to 80c.

    Despite their lesser efficiencies, high temperature air source heat pumps do have a use and can be used in scenarios where it is not feasible to install larger radiators, or the required output in each room is too great to be achieved at low temperatures (often in older, poorly insulated properties).

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    If you want to know more about air source heat pumps, we’d love to chat. You can get in touch with us by calling 0800 321 3142. Alternatively, please click the button to arrange a callback from one of our team at a time that suits you.

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