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My UFH quandary and mystery.....


micheal300
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Afternoon all, 

 

Hopefully you can help me with an UFH problem that has been bugging me for some time now (2 years to be precise). 

 

My wife and I bought a beautiful house in summer of 2019, but we didn't really move in until Summer 2020. It's about 3000 sqft, 4 bed, well insulated, good energy rating, sash windows with 4-8-4 double glazing and is heated by a Ground Source Heat Pump (Ochsner 5kW with buffer tank) and underfloor heating (downstairs) and radiators (upstairs). 

 

However, we've never felt that satisfied with the performance of the UFH - the heating via rads upstairs works quite fine and makes for comfortable rooms. 

 

The root problem is that we don't feel that the UFH is capable of heating the downstairs room above 17/18/19 degrees - especially in winter. We have no idea why - originally we thought it was how we operated the system but have ruled that out, then we looked at the heatpump - got that serviced and it's perfect, we also got the manifold upgraded - all good there also. We feel the heating is working as it feels warmer under rugs, sofas, etc but just doesn't seem to get the room warm. 

 

Some observations and anecdotes:

  • The flow temperature is 35-37 degrees and the floor heats to about 23/24 degrees
  • We understand the underfloor heating pipes are in the concrete slab and tied to the re-bar (not sure whether this has any bearing)

 

We'd really appreciate any guidance on identifying the root of the issue. As you'll all appreciate it's so frustrating to be investing so many kWHrs with so little return. 

 

Many thanks

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19 minutes ago, SteamyTea said:

This may be a bit hard to establish, but if there is minimum insulation under the slab, and the pipes are quite deep down, heat will be leaking to the ground.

How much, as a percentage of the floor, is covered by rugs and sofas?

 

I would say max 20-30% maybe at a rough guess

 

The insulation under-slab is one that I have no way of confirming unfortunately

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1 minute ago, micheal300 said:

 

The insulation under-slab is one that I have no way of confirming unfortunately

Assume it was to building regs for when the house was built.

1 minute ago, micheal300 said:

would say max 20-30% maybe at a rough guess

That will impede the power the UFH can deliver.

Try taking the rugs away for a day or two, see if it improves.

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1 hour ago, micheal300 said:

we don't feel that the UFH is capable of heating the downstairs room above 17/18/19 degrees - especially in winter.

It may be that the design of the UFH does not permit any greater heat in the downstairs rooms, in winter.

Supplementary heating might be the answer, or turning up the water temperature as @Declan52 said

Edited by WWilts
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14 minutes ago, micheal300 said:

 

It's a mixed bag through the house - timber, carpet, tile and stone flag

Timber and carpet (especially with underlay) are both good insulators.

Does the area with tile and stone perform better?

 

And is the downstairs circuit definitely at the 35°C to 37°C, or is that the main flow temperature?

 

You don't really want to go too high on the UFH temperature as it hurts the CoP, and rather defeats the object of UFH.

Edited by SteamyTea
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10 minutes ago, SteamyTea said:

Timber and carpet (especially with underlay) are both good insulators.

Does the area with tile and stone perform better?

 

And is the downstairs circuit definitely at the 35°C to 37°C, or is that the main flow temperature?

 

You don't really want to go too high on the UFH temperature as it hurts the CoP, and rather defeats the object of UFH.

Can't discern any great difference between timber/carpet and tile/stone. There is one bedroom with carpet that seems to do reasonably well - i figured it was because it has only one window whereas the other rooms have more glazing. Could area of glazing have a big impact?

 

All the circuits seem to run about the 35/37 mark. 

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6 minutes ago, micheal300 said:

Can't discern any great difference between timber/carpet and tile/stone. There is one bedroom with carpet that seems to do reasonably well

I assume this bedroom is upstairs, with radiators?

7 minutes ago, micheal300 said:

Could area of glazing have a big impact

Yes, it is all down to thermal losses after all.

You can do a basic heat loss calculation and see if your hunch is right.

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You can only use carpet and underlay that are made to specifically work with ufh. Like your quilt in bed they have a tog rating with you needing the lowest tog to allow more heat though.

Do you feel the stone floor warm on your bare feet when the heating is on??

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7 minutes ago, gravelrash said:

if the floor is achieving 24c it sounds like you are loosing heat through building fabric... quite quickly. 

That's what I'm wondering - is 24c optimal?

 

The walls are quite deep and well insulated so I can only assume heat might be getting lost through the windows? It's my theory currently. 

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In a very well insulated house you only need a very small temperature difference between the slab and target room temperature.  The worse the insulation / airtightness, the greater the required temperature difference.  If the issue is with poor below slab insulation, you may do better adding some panel heaters.

 

What age is the house?

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Do you have a measure of how much electricity the heat pump is using to heat the house in a year?

 

There are 2 measured of flow temperature that we need to know.  One is the flow temperature of the water coming from the heat pump.  This will be the higher figure and will need to be reasonably high to run the upstairs radiators.  you should be able to read this from one of the parameters on the controller for the heat pump.

 

The second is the flow temperature into the under floor heating.  Usually on the UFH manifold there is a blending valve that sets the UFH water temperature, and a little thermometer on the manifold to show what the temperature actually is running at.  This is easy to increase a little by adjusting the blending valve on the manifold.

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2 hours ago, micheal300 said:

Could area of glazing have a big impact?

Yes. Walls have U values (thermal leak values) of 0.25 or even much lower.

Glass has U values generally several times higher than 0.25. 
Airtightness helps a lot.
Our SAP expert advised that solar panels would improve the energy efficiency much more than insulation improvements (especially in a house with passably good insulation).
 

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5 hours ago, Mr Punter said:

In a very well insulated house you only need a very small temperature difference between the slab and target room temperature.  The worse the insulation / airtightness, the greater the required temperature difference.  If the issue is with poor below slab insulation, you may do better adding some panel heaters.

 

What age is the house?

It’s relatively new at 15 years

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5 hours ago, ProDave said:

Do you have a measure of how much electricity the heat pump is using to heat the house in a year?

 

There are 2 measured of flow temperature that we need to know.  One is the flow temperature of the water coming from the heat pump.  This will be the higher figure and will need to be reasonably high to run the upstairs radiators.  you should be able to read this from one of the parameters on the controller for the heat pump.

 

The second is the flow temperature into the under floor heating.  Usually on the UFH manifold there is a blending valve that sets the UFH water temperature, and a little thermometer on the manifold to show what the temperature actually is running at.  This is easy to increase a little by adjusting the blending valve on the manifold.


I figure from Jan through to April it was burning about 40 kWhr per day. It wasn’t required through the summer months. 

 

The flow leaving the heat pump is 37 degrees I believe. There is no mixing valve at the manifold and the temperature is in and around the 37 degree mark also. 

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5 hours ago, SteamyTea said:

While I think about it, don't worry about all the different ideas about what may be wrong.

This is just the forum members trying to get to the real problem.


Totally, I’m very grateful for all the feedback so far. Really helpful ?

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24 minutes ago, micheal300 said:


Totally, I’m very grateful for all the feedback so far. Really helpful ?

 

Found myself in the very same position, I have done many things and am just about there. Happy to message you a phone number for a chat if that helps.

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17 hours ago, micheal300 said:

 

I would say max 20-30% maybe at a rough guess

 

The insulation under-slab is one that I have no way of confirming unfortunately

 

Try asking your building control section.

 

For a recent new house they will hold that information, though they may want to keep it to themselves like a squirrel with a hazelnut.

 

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13 hours ago, WWilts said:

Yes. Walls have U values (thermal leak values) of 0.25 or even much lower.

Glass has U values generally several times higher than 0.25. 
Airtightness helps a lot.
Our SAP expert advised that solar panels would improve the energy efficiency much more than insulation improvements (especially in a house with passably good insulation).
 

 

Are you sure he didn't mean improve either a) the EPC number or b) the environmental impact, as solar panels don't really reflect on energy efficiency, as they generate extra free, clean clergy which is pumped in?  Solar panels are a well-known EPC level dodge.

 

A bit pedantic, I admit.

 

(Interestingly, my EPC advisor today said that he thinks non-MCS installed solar panels do count towards the EPC improvement.)

 

@micheal300

 

Is that Heat Pump a bit small? (Just my gut feel).

 

Imo 15 years ago was before most of the significant improvements came into Building Regs (I would date it at around 2010 when energy efficiency became required to a half-decent standard):

 

Quote

(From 2019) In theory, homes built to the 2006 Building Regs had 20% lower CO2 emissions than homes build to the previous 2002 standards. Again, in theory, the current iteration of the energy part of the Regs required a 44% improvement on 2006 standards. And you have to show your model calculations to Building Control in order to put up a new home.

https://cambridgeenergy.org.uk/is-this-the-biggest-change-to-building-regulations-in-the-last-20-years/

 

That suggests that you may need to look for tactical improvements - eg insulate more properly as you open up things to work on etc.

 

One other alternative is to see how good your airtightness is, which accounts for a good deal of heat loss.  Why not get a test done, and see how good it actually is?

 

 

 

 

 

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