ASHP for UFH

[Jimcub]

I have underfloor heating in my conservatory that we live in year round, run off our gas combi boiler.

I would like to instal a ASHP to run just my UFH only, that leaves the gas boiler to heat water and radiators.

at the moment we only use in winter the radiators in the hall and bathroom ( this has electric UFH as well ).

although we have 3 bedrooms and 2 bathrooms we don’t use the up stairs due to health issues, the house is well insulated.

conservatory is 20x20’ and built in 2017 with heat reflective roof panels, I may replace the roof with a solid one in the future, I installed the UFH and last winter we run it with the thermostat set at 23oC .

this works well for us and is comfy so we wish to keep it this way, the cost to run is between £25 to £27 a day in gas. So am I right in thinking a ASHP will be the economical way foreword

kind words only Jim  

[Conor]

ASHP won't be any cheaper with the current electric prices. It's greener, not cheaper. I'd spend the £10k+ on other building fabric upgrades.

[Bozza]

Jim, unless I’ve misunderstood you’re paying £750 per month in gas only, to heat a ground floor of a house only?  If that’s correct, even with high energy prices you will probably have a very poorly insulated house whereby an ASHP won’t solve your problems.

 

I would suggest you take advice from Energy Savings Trust or equivalent agencies.  
 

Conor is right, you are better spending money on things that will improve insulation.
 

 

[JohnMo]

What flow temp are you currently using? that will get you close determination of expected running cost. But you are chucking huge amounts of heat at the conservatory.

 

Sounds like a small area to heat, why on earth would a gas boiler heating that area cost so much?

 

£25 a day at 11p per kWh is 230kWh or about 10kW average heat input.

 

36m2 area so about 230W/m2

 Which if correct is insanely high. It a wonder you can walk on the floor.

 

So something in the original post is not right.  So we need more information.

 

What are the pipe centres in the floor.

What is the flow temp

Do you know the floor buildup

What glazing do you have, single, double..?

 

 

[Jimcub]

Yes I know it’s high but our conservatory has wide far reaching views and an abundance of animals and birds, so that is the main reason we sit in there so not looking at 4 walls.

the cost is high because it’s a conservatory which are not insulated as a building would be, I don’t mind paying for the privilege of a good view knowing my child will inherit a nice house.

as for the floor the builder who built the conservatory and floor only got as far as the 6” concrete sub floor, I laid 150mm styrene base then a dpm, the UFH was designed by a specialist firm who then supplied the goods. I specified what the room was so it would heat efficiently and we came up with 3 zones just for that floor area 33sqm, 150mm of screed warmed up over a month  and then tiled.

yep floor is warm and thermostat is out of the sun, there is only the 2 of us 1 dog and 100 stick insects to keep warm, neither of us are in good health so just want to live a decent life while watching the pennies. 

[Jimcub]

The £25 ish is only when it gets down below freezing otherwise approx £8 to £10 a day

[SteamyTea]

2 hours ago, Jimcub said:

20x20’ and built in 2017

Anyone know what the floor insulation levels were 6 years ago, if it needed any at all.

20' is 6.1m, we went metric in the early 1970s.

[Conor]

Jim, just sounds like my parents. I get it. Their favourite room in the house, pretty much uninsualted, but they live there during the day and heat it according. They close it off in the evening and then use the living room. Only only thing I can suggest for saving energy costs here is to get the insualted roof on, and look at the option of upgrading the glazing. 

[Bozza]

Ok so your conservatory is warm in summer and freezing cold in winter, just like my parents one.  Their solution, to only use it in the summer, doesn’t work for you.  As an alternative to upgrading the conservatory insulation do you have another room in the house that can give you a decent view, even if it involved putting in a larger (efficient) glazing that you could use in the winter.  Or windows in what is currently a wall.  A cheaper option than putting in ASHP which definitely won’t help and might even be useless in trying to heat up a poorly insulated conservatory.

 

 

 

 

 

 

[SteamyTea]

Air to Air Heat Pump is an option, gives cooling in the summer as well.

At a CoP of 4, it is similar to the gas cost.

If electricity goes below 30p/kWh and gas is about 8p/kWh that is.

But as I mentioned earlier, if you have UFH and little insulation, you are heating the ground. An A2AHP gets around part of that problem.

The units are quite cheap as well.

[Sparrowhawk]

11 hours ago, SteamyTea said:

Air to Air Heat Pump is an option, gives cooling in the summer as well.

I've been staying in the garden of a house in Scotland this week. They have a 6x6m conservatory on the back built in 2018 and heated with an air to air heat pump (Mitsubishi MUZ-EF50VE rated cooling 5kW, heating 5.8kW; head specs unknown). I got chatting as it was the first heat pump I've seen and I was impressed how quiet it was in cooling mode.

 

They were not happy. Where they are winter gets to -10C and the regular blowing of cold air into the conservatory as the heat pump does its de-ice cycle had really turned them off it. That and it's expensive to run and doesn't keep the conservatory warm in winter (but the cooling works in summer).

 

I did a back-of-the-envelope heat loss calculation (using the theoretical U-values shown on their planning application). At 20C inside and -10C outside and with 0ACH the conservatory needed 2.5kW to keep at temperature. If it has 3ACH those add another 2.4kW to the requirements.

 

Expensive but seemingly plenty of capacity on the coldest of days. I wonder if the head can cope with outputting enough heat?

 

They've gone back to using a couple of oil filled radiators in winter which they say work great. The HP is relegated to an expensive addition to cool it for a few weeks of the year.

 

13 hours ago, SteamyTea said:

Anyone know what the floor insulation levels were 6 years ago, if it needed any at all.

20' is 6.1m, we went metric in the early 1970s.

 

This conservatory floor had a quoted U-value of 0.18 and the specified build-up was... the planning portal is inaccessible, I'll update later.

 

@SteamyTea the floor buildup was:

 

Concrete Floor Specification
Floor finish on 3mm underlay on
22mm chipboard on
50 x50mm timber battens,
125mm A142 mesh reinforced concrete floor on
100mm XTRATHERM POLYISO XT ZERO ODP
insulation on
1000 gauge D.P.M.,sealed to new and existing
D.P.C.s
on 25mm blinding on
150mm minimum well compacted hardcore
Floor U-Value = 0.18W/m2K

Edited June 22, 2023 by Sparrowhawk

[DamonHD]

Should someone even be trying to heat a large conservatory in the depths of a severe winter beyond frost protection?

 

Rgds

 

Damon

[JohnMo]

Just now, DamonHD said:

Should someone even be trying to heat a large conservatory in the depths of a severe winter beyond frost protection?

 

Rgds

 

Damon

It does make you wonder. All the talk about heating poverty, global warming...

 

4 hours ago, Jimcub said:

The £25 ish is only when it gets down below freezing otherwise approx £8 to £10 a day

So on a slightly different tack, could your high consumption of gas be due to short cycling?

 

You mentioned you had 3 zones in the conservatory, did you actually mean 3 loops operating from a single thermostat?

 

When you are heating the conservatory are you heating the rest of the house at the same time?

 

What boiler do you have?

 

Do you know how your boiler runs, does it run for a long period while doing heating or is it a fairly short on time and off for about 10 mins, then on - repeat?

 

[Sparrowhawk]

10 hours ago, DamonHD said:

Should someone even be trying to heat a large conservatory in the depths of a severe winter beyond frost protection?

What surprised me was how little heat it needed when compared to normal housing stock. If my 1920s house ever got -10C outside, my thermal calculations say a 3x2m room with 2 outside walls will need 1.3kW at 0ACH to keep warm, so per square metre of floor area this conservatory is more efficient than my house.

[Jimcub]

The floor has 100mm polystyrene slab then DPM with UFH pipes stapled to this, then I think 3” of screed and tiles on top. 

there are 3 loops in one zone 

we have an uninterrupted view down a valley and we are elevated up so it’s a good view, windows go from back of house to down the side as it’s a L shaped wrap around.

why did we buy it well we thought of a brick extension, but this came up on flea bay 3 years old and complete with Sanderson thermal blinds cost me £350 a no brainier really. Was installed by a builder who had experience of this type of build. 

boiler was put in year before build and it’s a Bali platinum 24k. We also had the flu moved to out of the roof as it exited onto the decking ( just why ? )