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Air source heat pumps: What size do you need?

What size air source heat pump do I need?

Considering investing in an air source heat pump for your business?

Selecting the right size for your needs is key to ensuring optimal efficiency, low energy bills and comfort in the workplace for everyone.

So, what size air source heat pump do you need? Here, we’ll look at the different factors involved and why size matters.

How big are air source heat pumps?

Air source heat pump sizes are measured in kilowatts (kW) and are also referred to as a heat pump’s capacity.

Air source heat pumps come in lots of different sizes (or capacities) to suit all sorts of different purposes.

What size you need will depend on lots of different factors that we’ll cover later – such as the size of your building, your heating requirements and the level of insulation.

However, as a rough guide, heat pump sizes can range from 4kW for a small home or office building to multi megawatt for an industrial building.

It’s also worth noting that buildings with high or more complex heating needs may even benefit from more than one heat pump – known as a cascade system.

In this way, heat pumps can cater to high or fluctuating heating demands, by combining their respective capacities.

Ultimately, every building is different. So, there’s no one size fits all, even when you’re comparing similar buildings. Rather, it’s all about calculating your building’s needs to find the right fit for you.

Why does size matter?

A heat pump that’s correctly sized to your building’s needs is essential for so many reasons.

Here are just a few:

  • Runs efficiently
  • Saves energy
  • Lowers energy bills
  • Maximises comfort
  • Reduces carbon footprint

What happens if your heat pump is too small?

A heat pump that’s too small will mean that your unit runs constantly as it fruitlessly tries to reach your heating requirements.

In this way, it may struggle to meet your heating demands, leaving you with a cold building. Plus, it’ll use a lot of energy, leading to a hike in running costs.

What happens if your heat pump is too big?

A heat pump that’s too big will run short cycles, meaning it will cycle on and off often.

This will result in energy wastage and increased wear and tear, which could even lead to early replacement.

It will also cost you more to buy, install and look after than is necessary.

What is the role of buffer tanks in sizing heat pumps?

Buffer tanks play a vital role in sizing heat pumps. They can provide additional capacity to meet peak demand, say for 1 hour in the morning during heat up. This means you can install a smaller heat pump and still meet all your heating needs.

Buffer tanks also ensure that heat is available during de-frost periods. When the heat pump is melting ice from its evaporators, the buffer exports heat and then recharges afterwards.

Buffer tanks also provide a heat battery that means you can avoid using high cost electricity during peak hours by exporting heat from the buffer.

Generally, buffer tanks are simply large volumes of water, although the tank should be properly specified with the correctly sized connections, temperature sensors, heigh- to-diameter ratio and baffle plates. Other technologies are also available like phase change materials.

Whichever technology you choose, we suggest sizing the buffer as big as you possibly can. This means lower cost of heat pump, smaller grid connection, option to save on electricity costs and a super efficient system.

What size air source heat pump do I need?

It’s impossible to say for sure what size heat pump you need, as there are too many factors to take into account.

Instead, a heat pump designer will be able to correctly size your heat pump for you, and design a system in which your heat pump is working together with the rest of your building’s heating system for optimal efficiency and performance.

That said, here are some examples from our recent projects to give you an idea of the broad range of possibilities.

Two university campus buildings

We recently decarbonised two buildings at Northumbria University, which house lecture theatres, offices, cafes and other facilities.

  • 2 x 150kW heat pumps
  • 3 x 200kW heat pumps

Read the Northumbria Uni case study.

Swimming pool

We upgraded a school swimming pool’s heating system as part of a PSDS project, including AHUs, radiators, underfloor heating and a pool heat exchanger.

  • 1 x 350kW heat pump

Read the Normanton School swimming pool case study.

350kW heat pump

Shared office space

As part of a decarbonisation scheme, we installed heat pumps with integrated hot water production units in a shared office building.

  • 2 x Larch 350kW cascade heat pumps

Read the shared office space case study.

350kW cascade heat pumps

How to calculate what size air source heat pump you need

There are lots of different factors that your system designer will take into account when sizing your air source heat pump.

Here are the main ones.

Building type and size

How big are your business premises? What layout does it have?

Things like the number of rooms, floor area, ceiling height and window sizes will all have a part to play in establishing the heating demands of a space.

Often, a larger building with more rooms and bigger windows will need a larger heat pump in order to effectively meet heating requirements. Which brings us onto…

Heating requirements

What room temperature are you after? Do you need your heat pump to provide domestic hot water (DHW) as well as space heating?

If you only need space heating, you’ll usually get away with a smaller heat pump than if you also need DHW.

Meanwhile, industrial heat pumps are often used to provide heat for industrial processes – necessitating a heat pump with a bigger capacity.

Heating demand and patterns

What kind of heating demands and patterns will your heat pump need to meet?

As an example, a university accommodation block will have different temperature requirements from an office that’s only frequented in the daytime.

In particular, if your heat pump is going to be providing DHW, your system designer will need to factor in things like the number of occupants and hot water usage patterns.

Heat loss calculations

How well-insulated is your building?

Your system designer will always start by carrying out heat loss calculations, to establish the building load.

These calculations include assessing things like air leakage and thermal bridging to understand the amount of heat that needs to be supplied to your business premises.

Local climate

What do ambient temperatures tend to be like where your business is based?

The colder it is outdoors, the less efficiently your heat pump will operate. This is because the compressor inside your heat pump will have to work harder to achieve the required flow temperature.

With that in mind, colder regions might need a heat pump with a higher capacity to make sure it can meet your required heating demand.

Heating system

What does your building’s wider infrastructure look like?

Your heat pump has to be finely tuned to work hand in hand with your building’s wider infrastructure – like the emitters (e.g. radiators or underfloor heating).

For instance, the number and type of radiators your building has will influence what size heat pump you need – although it may be best to replace them with larger radiators or underfloor heating.

Restrictions

What restrictions will your system designer need to work around?

For instance, are there noise restrictions that need to be considered? Or, do you need to be able to retrofit a heat pump without making extensive alterations to your building’s existing infrastructure (for instance, because it’s listed or because it’s important to ensure continuous operation)?

Often, if your building can’t easily be adapted, you’ll need a higher capacity heat pump to account for your inadequate insulation or smaller-than-ideal radiators.

COPs

How efficient is the heat pump you’re considering?

Heat pump efficiency can vary between makes and models – even when comparing heat pumps that are the same size.

Generally, this is measured by its Coefficient of Performance (COP), which is essentially the ratio of heating capacity and total power output.

Those with a high COP will be able to produce more heat per kW of electric power, meaning they won’t need to work as hard to reach your heating demands.

Let us worry about heat pump sizing for you

As you can see, there are tons of factors that need to be considered when you’re sizing your heat pump.

So, it’s important to leave it in the hands of professionals who truly know what they’re doing!

Luckily, at Clade, we have over 35 years of experience manufacturing high performing heat pumps and refrigeration equipment – meaning you can rest assured you’re in safe hands!

Get in touch to have our system designers scope out your project and help you settle on the best heat pump capacity for your needs.