Jump to content

Will I need a back up for my ASHP in winter?


Nina F

Recommended Posts

Hi everyone! Based in the East Midlands and starting the journey to our dream house, we are at the planning application stage. We want it to be thermally efficient and use renewable energy where possible.  We are going for a high insulation spec, and air source heat pump with underfloor heating plus solar panels. The architect has encouraged us to have porcelain, stone, concrete or timber flooring (not LVT) to allow the materials of the building to use the thermal mass more effectively. My concern is,  I've just read an article about ASHP which states that they are prone to failure/inefficiency in the depths of winter because they have to work so hard when its really cold, and that you should have a back up heat source such as gas or biofuel boiler. This seems to defeat the aims. Anyone out there any experience of living in a house with ASHP and underfloor heating? 

Link to comment
Share on other sites

Simple answer is they will work fine, as long as they are sized correctly to meet the heating needs on the coldest winter day.

 

No problem with our ASHP here in the Highlands.

 

We do have a wood burning stove as secondary heating, but that is more to do with the abundance of free wood.

  • Like 2
Link to comment
Share on other sites

38 minutes ago, Nina F said:

you should have a back up heat source

Our ASHP has a built-in 6kW back-up heater for if the compressor fails, but I think the idea that you need another fuel source due to  failure/inefficiency is mostly FUD, unless your electiricaly supply is unreliable.

 

If your house is very well insulated and airtight, then a couple of cheap/simple oil-based heaters radiators are very effective as back-up heaters.  We used a couple of these to help heat the house before ASHP was commisisoned.

 

 

Edited by Dan F
  • Like 2
Link to comment
Share on other sites

Hi and Welcome.

 

32 minutes ago, Nina F said:

I've just read an article about ASHP which states that they are prone to failure/inefficiency in the depths of winter because they have to work so hard when its really cold,

 

That's really quite worrying if that's printed in a UK article.

 

Ensure that accurate heat loss calcs are done to help size the ASHP, which is all part of a reputable MCS installation, and you'll have no problems with a Heat Pump.

  • Like 2
Link to comment
Share on other sites

I think the main things that screw up heat pumps are the following.

 

Tying operate like a gas boiler, high temp, lots of on off cycles, you need to setup to run at as lower temperature as practical and let it run for as long as possible.  One day time temp and a small setback at night of only a couple degrees only (even that is pretty much a waste of time in a well insulated house).

 

Lots of zones, so the heat pump can end up running a small circuit which will end up with lots of short cycling.  Have the whole living space as a single zone.  I now also run the shower room, utility and en-suites without thermostats, if anything else calls for heat they get heated by default, this is to increase the circulation volume.

 

Heatgeek.com, has plenty of tips of how to balance the system and set up flow temps.

 

Sizing the heat pump too big, always remember, the design heat load is cover a few hours per year, when it's 8 degrees outside the heating system is only doing about half the work as at -3 deg C.  If in doubt include a buffer to help prevent short cycling.

 

The other thing about well insulated houses they react quite differently to older houses; our heating is by UFH (we have 300mm pipe spacing - 200mm would have made our system quicker acting), pumped at 30 degrees in concrete 100mm screed, the heating comes on for a few hours and is then off until the next day, with a stable temperature.  You really need a simple system, no complex (or expensive) controls.

 

 

  • Like 1
Link to comment
Share on other sites

What JohnMo said :) Just let it tick over all the time. I was so worried that I would cook at night but I don't. Yes it is warm but a very gentle warmth. If you like roasting your feet or burning your face then either get a wood burner or a small electric fire to complement the underfloor.

  • Like 1
Link to comment
Share on other sites

We moved in to our house on Feb and only had a couple 1.5kW heaters running about 12hrs a day to warm the house, plus a couple small dehumidifiers. it's been off totally for two weeks now. If you insulate and detail a house properly, you hardly need any heating at all. So a properly sized heat pump will work fine in all typical East Midlands winter weather. If you install a buffer tank (reccomended), you can install a 3kW immersion coil. If you build to passive House standards that'll warm you nicely.

 

Don't worry about flooring, install whatever you want, will make very little difference to the temperature feel of the house. We've some rooms with carpet, some with laminate, and others bare screed. All the same temp.

Edited by Conor
  • Like 2
Link to comment
Share on other sites

@Nina F

Can you send a link to the article you read please.

 

As others have said, size it correctly and you will not have problems. At worse, a fan heater or two will get you out of short term trouble.

 

When you say a well insulated house, do you know the target U-Values for each component, and remember the floor has to have a lot more than building regs as it is warmer than the house air temperature.

 

When you build, airtightnes is important. 

  • Like 1
Link to comment
Share on other sites

5 minutes ago, Conor said:

Don't worry about flooring, install whatever you want, will make very little difference to the temperature feel of the house. We've some rooms with carpet, some with laminate, and others bare screed. All the same temp.

We are the same, wood, carpet in bedrooms, tiles elsewhere. Choose what suits YOU, not your architect.

  • Like 1
Link to comment
Share on other sites

4 minutes ago, JohnMo said:

We are the same, wood, carpet in bedrooms, tiles elsewhere. Choose what suits YOU, not your architect.

Very true

Its so easy to end up with things that you don’t want 

Simply because you are being told that Everybody is going for this or that 

  • Like 1
Link to comment
Share on other sites

3 hours ago, ProDave said:

Simple answer is they will work fine, as long as they are sized correctly to meet the heating needs on the coldest winter day.

 

No problem with our ASHP here in the Highlands.

 

We do have a wood burning stove as secondary heating, but that is more to do with the abundance of free wood.

thanks so much for your reassurance- we currently live in a draughty old Victorian house and its hard to imagine we will soon be in an efficient warm new build 

  • Like 1
Link to comment
Share on other sites

2 hours ago, SteamyTea said:

@Nina F

Can you send a link to the article you read please.

 

As others have said, size it correctly and you will not have problems. At worse, a fan heater or two will get you out of short term trouble.

 

When you say a well insulated house, do you know the target U-Values for each component, and remember the floor has to have a lot more than building regs as it is warmer than the house air temperature.

 

When you build, airtightnes is important. 

its in the May issue of Build It magazine ( I only have the paper copy) We are still in the early stages but i have been doing some research on U values for windows and doors. 

Link to comment
Share on other sites

In Canada when they design heat pump systems they don’t aim for 100% heating requirement but leave a few of the coldest days each year slightly short on heat as the capital cost outweighs the benefit and some direct electric heating is used to top up on those days 

  • Like 1
Link to comment
Share on other sites

11 minutes ago, tonyshouse said:

In Canada when they design heat pump systems they don’t aim for 100% heating requirement but leave a few of the coldest days each year slightly short on heat as the capital cost outweighs the benefit and some direct electric heating is used to top up on those days 

It is the same here under the MCS system.  99% of the time.  All that means in reality, is those 3 or 4 days a year when it is extremely cold, your house drops down a couple of °C, no the system cutting out and refusing to do anything.

My old house in Aylesbury, which was on gas, did the same one.  Took me ages to realise it was just extremely cold outside.

Link to comment
Share on other sites

4 hours ago, Nina F said:

I've just read an article about ASHP which states that they are prone to failure/inefficiency in the depths of winter because they have to work so hard when its really cold, and that you should have a back up heat source such as gas or biofuel boiler.


Utter tosh which is usual from that magazine ..!! Tell about 1m households in Norway they don’t work when it’s cold … 

  • Like 1
Link to comment
Share on other sites

38 minutes ago, tonyshouse said:

In Canada when they design heat pump systems they don’t aim for 100% heating requirement but leave a few of the coldest days each year slightly short on heat as the capital cost outweighs the benefit and some direct electric heating is used to top up on those days 

My heating requirement is about 2.5kW when it's +20 inside and -10 outside.  I fitted a 5kW ASHP so it can do 200% of my heating.  That's mainly because there are very few ASHP's less than 5kW but any smaller and it would be too slow at heating DHW.

 

In practice it means the heat pump has an easy time and could cope with a lot colder.

  • Like 1
Link to comment
Share on other sites

On 30/03/2022 at 21:16, SteamyTea said:

It is the same here under the MCS system.  99% of the time.  All that means in reality, is those 3 or 4 days a year when it is extremely cold, your house drops down a couple of °C, no the system cutting out and refusing to do anything.

My old house in Aylesbury, which was on gas, did the same one.  Took me ages to realise it was just extremely cold outside.

that's really useful, thanks

Link to comment
Share on other sites

Carpeting is perfectly possible you just need the special underlay that is recommended for underfloor heating. I held off carpeting the hall just in case I thought the lounge and bedrooms were not warm enough. It turns out that they are fine.

Do remember solar gain. We have South and West facing windows and we notice how much difference they make to the room stat when the sun is out.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...