Max Halliwell looks at what can be deduced from heat pump manufacturers’ performance figures when the temperature drops below zero.

Many of my colleagues have recently made the switch to hybrid, plug-in vehicles but they have discovered that the amount of mileage they will get from each charge of the battery often bears little resemblance to the official figures published on the manufacturers’ websites.

Things like how cold it is outdoors, the amount of acceleration and how hard they brake all affect how many ‘eco’ miles they can get out of every journey, often resulting in much less electric miles than they expected.

And the same is true of a heat pump, especially when the temperature drops below zero.

This is why we’ve taken the bold step of putting our own 14kW Ecodan up against other manufacturers as the performance talked about in a ‘sales’ pitch can bear little reality to operation when it’s really cold outside.

Once you start to look at performance ranging from 12 ºC, down to -7 ºC, you can really start to see where the differences lie.

Max Halliwell5 Max Halliwell Product Manager for Mitsubishi Electric's range of renewable heating systems

Sub-zero performance

We’re quite fortunate in the UK that we don’t face significant sub-zero temperatures for much of the year but the latest cold snap has seen temperatures drop to -7ºC or more as we faced a particularly harsh period.

Most conventional inverter-driven heat pumps suffer from a decrease in heating capacity at low ambient temperatures, yet a quick scan of the headline performance figures do not always reflect this.

Much like the fuel performance and emissions figures from the car manufacturers, it is always worth looking beyond the headline ‘sales’ figures and digging a bit deeper into the overall performance – at all times of the year and across a range of operating temperatures.

Despite offering larger capacity models many manufacturers systems fail to maintain their heating capacities, suffering significant drop off at low ambient temperatures.

If you are using air source heat pumps to keep a larger home warm, this can present you with a real drop in heating performance and a likely increase in energy use and running costs.

True capacity

Homeowners need a system that will deliver regardless of the outdoor temperature

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True capacity

The capacity problem

Ecodan maintains heating performance down to -7 degrees Centigrade

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Zuban capacity

True capacity

The reliable choice, whatever the weather

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True capacity Zuban

14kW = 14kW

I’ve worked for Mitsubishi Electric now for more than a decade and I know our engineering colleagues spend months and months testing and retesting the performance of our equipment, before they will release any data that we can use to market what we believe are the best systems available.

Sometimes this can be a little frustrating because we are up against other manufacturers who make bigger and bolder claims about performance and release figures that look higher than ours.

At the same time though, I have a lot of respect for the conservatism of our factories because we know that the figures they release are tried and tested – and in most cases, our equipment will actually perform better than listed.

Our 14kW Ecodan air source heat pump is a case in point and comes up against other machines that appear to offer greater capacities of 15kW; 16kW and even 17.5kW.

Once you start to look at performance ranging from 12 ºC, down to -7 ºC, you can really start to see where the differences lie.

This is important because, just like the performance of your car, it makes a difference not only to how comfortable your ‘journey’ is, but also to how much it will cost you in ‘fuel’.

A different approach

I’ve already mentioned our ‘conservative’ approach to only publishing figures that have been checked and rechecked by our technicians and the same has been generally true of the way we market ourselves against other brands.

We prefer to let our advanced products do the talking for us, in the knowledge that our factories have absolute confidence in the figures we publish.

Sometimes though, you come up against so much ‘noise’ about figures and performance that we have taken the decision to publish data – taken from our own and other manufacturers published data, so that customers have all possible information necessary to help them when looking for the best renewable heating system to suit their own particular building.

Max Halliwell is Product Manager for Mitsubishi Electric's range of renewable heating systems

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