What to Look Out for if you Move Into a Newbuild with an ASHP

Something of great concern to me are homeowners who are in favour of heat pump technology but when they actually move into a house with a heat pump it does not live up to their expectations. There are a number of reasons for this unsatisfactory outcome. It is important to remember if you’re not immediately cosy and happy don’t accept the status quo. There should be an experienced company nearby that can help you.

This is Paul’s story:

The heating system has underfloor heating on the ground floor and radiators upstairs.

As well as utilising electricity for heating, hot water, cooking, appliances and lighting Paul also has a plug in hybrid car that he charges usually for 1.5 hours during the night.

Paul has a off peak electricity tariff giving him lower cost electricity overnight.

This case study came about after Paul expressed disappointment with the performance of his system on Linkedin – I asked him why and sent Richard Brown to visit him.

Richard explained that; the way the heating was installed relied on thermostats to signal the heat pump to run. There are 7 thermostats downstairs that were set up to each control separate areas of the ground floor underfloor heating. Some of these were very small areas such as the utility room (2 square metres) and the downstairs loo. Each of these thermostats was able to ‘request’ the heat pump to run, however the heat pump was not able to supply the heat for such a tiny areas therefore the heat pump would often just turn off. I asked why this happens and Richard said it’s like trying to drive a car at 1 mile an hour when the lowest speed is 3 miles an hour – the car just cuts out. The heat pump can get into a ‘vicious cycle’ where the heat pump may be ‘called’ to come on but can’t respond. Richard said this was one of the problems Paul had in his house with the ‘over design’ as Paul referred to it when I spoke to him.

Paul knew he was struggling with his system; it was either too hot or too cold (the Goldilocks effect was eluding him!) The problem that he was experiencing is common if a heat pump system is run on a thermostat – these controls either want to be on or off they don’t ‘maintain’ a set temperature. This problem is exaggerated with underfloor heated because of the slow response time for cooling and heating compared to radiators.

To improve the comfort levels in Paul’s house Richard recommending removing the actuator heads from the underfloor heating manifold (to make the underfloor heating into one big circuit on the ground floor). He recommended that he turned all of the thermostats off except one. The remaining thermostat was selected to be in a central and ‘neutral’ position i.e. not a hot or cold spot of the house. Richard’s recommendation was to leave 1 thermostat set higher than required for example at 23 degrees. The heat pump could then be adjusted using heat curves to provide weather compensation control.

One of the common causes of this problem is that developers get underfloor heating designed by a different company to the heat pump specifier/installer, this leads to a UFH system designed with many thermostats.

Paul has found that the changes made to the system where he is running the system using the one thermostat and having the heating on overnight on the cheap tariff has increased the efficiency of the system by 25% overall, a COP increase of 50%.

Costs have decreased to £3-£4 from £5 – £10 per day in the heating season although there are changes to the system such as an electric car being charged and Paul also now has battery storage.

Paul’s top tips to other homeowners:

• If you have not lived with underfloor heating before give yourself time to get used to it. He explained they initially wanted the floor to feel really warm and sometimes the thermostat would read 26 degrees! The floor should be warm to the touch but not hot. If you have carpet it is likely the carpet won’t be warm as it is a partial insulator of the floor.
• With a new build you have a 2 year ‘house warranty’ to call in the house builder to look at anything you’re not happy with. Use this to get the heat pump installation company back to go through the set up of the system. Paul said ask lots of questions and learn as much as you can from the engineer.
• He also had a problem with the sensors on his hot water cylinder not being sited in the right place which was fixed under the 2 year ‘warranty’.
• Calling in the heating installation contractor did not result in the heating system improvements that Richard quickly identified.  Probably because the building site installers are not specialist heat pump specialists. He recommend getting all the support possible from the house builder but recognising that if you suspect your system is not running as well as it should be call in a local MCS registered heat pump installer to suggest improvements that could be made.
• Paul is really happy with his investment in battery storage, he finds the combination of solar PV, low electricity tariff overnight with the battery very good and recommends a similar combination to other homeowners.
• Paul has a large area of glass in his lounge diner that runs across one side of his house spanning 3 metres in length. He recommends adopting old fashioned methods for retaining heat and cool, he explained they have thick curtains that are drawn in Winter and Summer to cut heat loss and prevent overheating.