ASHP and UFH

[Sue B]

We have swung from UFH everywhere, to UFH downstairs only, to towel rads and electric mats in the bathrooms upstairs back to another consideration.......

 

Knowing that the ASHP can be reversed in the summer and do some slight cooling of the slab.  Is it worth laying the pipes upstairs simply for the cooling possibility in the summer?

we haven’t done the calcs yet but are pretty sure we will not need heating upstairs.

Edited March 31, 2019 by Sue B

[le-cerveau]

  On 31/03/2019 at 21:23, Sue B said:

Knowing that the ASHP can be reversed in the summer and do some slight cooling of the slab.  Is it worth laying the pipes upstairs simply for the cooling possibility in the summer?

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I would for convenience as long as the cost isn't prohibitive.  But what floor type are you having upstairs as this will dictate how it is laid.

[Sue B]

Hollow core concrete with carpet.

[Nickfromwales]

  On 01/04/2019 at 05:44, Sue B said:

Hollow core concrete with carpet.

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So the pipes will be ‘cast in’ or retrofit over the slab ?

[le-cerveau]

  On 01/04/2019 at 05:44, Sue B said:

Hollow core concrete with carpet.

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Are you screeding over the over the Hollow Core?

[Sue B]

Screed with the pipes in the screed

[Mr Punter]

You will probably want to screed in any case as the hollowcore is not perfectly flat, especially if prestressed and it will take out the camber.  Regarding the pipework, manifolds and controls, get a price for this and assess for yourself if it is worth the money. If you have solar gain from windows it will probably never cool enough to compensate.

[le-cerveau]

  On 01/04/2019 at 08:29, Sue B said:

Screed with the pipes in the screed

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For the sake of putting it in and the minimal cost compared to trying to retrofit something, I would include UFH in both floors, even if you don''t use it initially.  You can at a later date set up the slab cooling for both floors.

 

I have piped in both floors >400m², the house is passive standard (un-certified) and you cant tell if the heating is on or not as it is so gentle (UFH flow temp of 26^oC) however last summer when it was extremely hot (house just finished) the slab cooling did come on for a few days, usually in late afternoon and of you touched the floor near the manifolds you could just about tell it was cooling, but it had the desired effect in keeping the house livable.

[joe90]

We have no UFH upstairs but heated towel rads and electric UFH in the bathrooms only. Only when our MVHR was not balanced properly did upstairs feel a bit chilly. We have UFH downstairs which only comes on in quite cold weather.

[epsilonGreedy]

  On 01/04/2019 at 09:56, joe90 said:

We have no UFH upstairs but heated towel rads and electric UFH in the bathrooms only. Only when our MVHR was not balanced properly did upstairs feel a bit chilly. We have UFH downstairs which only comes on in quite cold weather.

 

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That is impressive for a brick & block home, are there any other sources of heat? I recall your cavity was more than 100mm.

[Nickfromwales]

  On 01/04/2019 at 12:25, epsilonGreedy said:

 

That is impressive for a brick & block home, are there any other sources of heat? I recall your cavity was more than 100mm.

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He didn’t mention the 4 pairs of socks and 7 jumpers he wears.   

[joe90]

  On 01/04/2019 at 12:25, epsilonGreedy said:

 

That is impressive for a brick & block home, are there any other sources of heat? I recall your cavity was more than 100mm.

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Yes we have 200mm cavity full fill with rockwall slabs. We also have a wood stove In the lounge but have only lit it for short periods on a cold evening fir the effect rather than the heat (28’, she was happy). We get a fair amount of solar gain from a sunspace across the back of the house. I was told we will overheat in the summer but at the moment with this unseasonal sun it’s great, I will let you know what mid summer brings ?(we have the option of reverse engineering the ASHP to cool the slab.)

[joe90]

  On 01/04/2019 at 12:27, Nickfromwales said:

He didn’t mention the 4 pairs of socks and 7 jumpers he wears. 

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No jumpers here and only one pair of socks ?

[Nickfromwales]

  On 01/04/2019 at 05:44, Sue B said:

Hollow core concrete with carpet.

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I don't think I'd do cooling unless it was a solid floor eg wood or concrete / screed. I fear carpet may tend to start excessively absorbing moisture and harbouring it. Just my experience from seeing various floor coverings in many homes, and in particular carpet on an original unheated / un-insulated slab seemed to be damp / mouldy when lifted after a life on the cold floor. 

 

Do you have MVHR? Have you considered a duct heater / cooler in the inlet from atmosphere to raise / lower the temp of the incoming air, prior to it entering the MVHR unit? I'm doing that on a couple of up-coming projects and should yield great results.

On one I've already done, we put heat into the duct heater and it was immediately apparent at the nearest fresh air inlet ( in the bedroom off the MVHR plant room ) so results are definitely there if the sizing / design is done correctly.  

[Sue B]

We are still at planning stage so plenty of time for us to work out what will work best for us.

 

Concrete and screed but no hard floor surfaces as it’s really bad for the dogs joints.  We are having an MVHR as well.

 

In our previous house we had UFH and an MVHR with a comfort cooling box added on.  We used it for the first summer after we’d finished and moved in and our bills went through the roof but the house didn’t feel any cooler.  Things have moved on since then though.  At that point, I had heard of running the UFH through cold but condensation (as you have alluded to) was the problem.

 

We don’t expect the UFH upstairs to ever need to be used for heating but as I have now heard from a few sources about cooling the slab a little using an ASHP, it was an idea as the pipe is cheap to lay before the screed goes down.

 

Presumably, if we get the air-tightness right and the downstairs temp right, the concrete floor/screed upstairs should escape the carpet mould you have found before?

 

[joe90]

  On 01/04/2019 at 19:09, Nickfromwales said:

Do you have MVHR? Have you considered a duct heater / cooler in the inlet from atmosphere to raise / lower the temp of the incoming air, prior to it entering the MVHR unit? I'm doing that on a couple of up-coming projects and should yield great results.

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I thought about this a long time ago and shelved the idea, but!!!. Would you not put the duct heater after the MVHR as the outgoing air might cool the air after going through the MVHR. What is the heat source for the heater?

[Ed Davies]

  On 01/04/2019 at 19:09, Nickfromwales said:

Do you have MVHR? Have you considered a duct heater / cooler in the inlet from atmosphere to raise / lower the temp of the incoming air, prior to it entering the MVHR unit? I'm doing that on a couple of up-coming projects and should yield great results.

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I'd agree with @joe90, that seems a weird thing to do. If the MVHR is 90% efficient, for example, then you'd be throwing away 90% of the heating or cooling achieved via the exhaust duct (MVHR to outside). Much better to put a heater or cooler on the house side of the MVHR presumably in the supply duct (from the MVHR to the house) though there might be reasons to put it in the extract duct (house→MVHR) with only a small loss in efficiency.

[Pete]

  On 01/04/2019 at 19:09, Nickfromwales said:

I don't think I'd do cooling unless it was a solid floor eg wood or concrete / screed. I fear carpet may tend to start excessively absorbing moisture and harbouring it. Just my experience from seeing various floor coverings in many homes, and in particular carpet on an original unheated / un-insulated slab seemed to be damp / mouldy when lifted after a life on the cold floor. 

 

Do you have MVHR? Have you considered a duct heater / cooler in the inlet from atmosphere to raise / lower the temp of the incoming air, prior to it entering the MVHR unit? I'm doing that on a couple of up-coming projects and should yield great results.

On one I've already done, we put heat into the duct heater and it was immediately apparent at the nearest fresh air inlet ( in the bedroom off the MVHR plant room ) so results are definitely there if the sizing / design is done correctly.  

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How do the duct heaters impact on the electricity bill?

[HerbJ]

Presumably, this duct heater/cooler  would only be in  operation as a cooler when the summer bypass is open on the MVHR  Unit?  So, there would be no issue with throwing away the cooling....

Edited April 2, 2019 by HerbJ

[le-cerveau]

  On 02/04/2019 at 09:37, Ed Davies said:

 

I'd agree with @joe90, that seems a weird thing to do. If the MVHR is 90% efficient, for example, then you'd be throwing away 90% of the heating or cooling achieved via the exhaust duct (MVHR to outside). Much better to put a heater or cooler on the house side of the MVHR presumably in the supply duct (from the MVHR to the house) though there might be reasons to put it in the extract duct (house→MVHR) with only a small loss in efficiency.

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There are various types of duct heater.

A pre-heater (outside air-MVHR) is there to raise the temperature of extremely cold outside air before entering the MVHR (frost prevention) and reducing the temperature drop (a heat exchanger can only do so much).

A post-heater (MVHR-house) is there to raise the exchanged air to a desired temp (heat the house).

A cooler can have the same effect, reduce extremely hot (over desired) air temp before entering the heat exchanger or attempting to cool the house.

 

In a pre-heat/cooler you are attempting to reduce the workload of the heating/cooling system in cold/hot weather buy reducing the impact of the MVHR process beyond what it can reasonably do.  In a post-heat/cool you are using the MVHR as your heating/cooling system.  You can do both!

[joe90]

With my set up I could either use direct electricity for the post heater or use DHW in a wet heater which would give me the benefit of the ASHP, COP. The hot water would have to come from the DHW tank as that is near the MVHR unit and we are too late to put pipes from the UFH buffer to the MVHR.

 

The benefit of not using direct electricity is the smell of burning dust from the element after a long period of non use. The DHW temp would be low so the temp raised in the inefficient air transfer would be minimal, but saying that we are only talking of requiring a few degrees. I would almost like to split the delivery manifold in two so I could heat the bedroom air only (and this would only be for a few weeks a year anyway ?

[Ed Davies]

  On 02/04/2019 at 11:43, HerbJ said:

Presumably, this duct heater would only bein  operation when the summer bypass is open on the MVHR  Unit?  So, there would be no issue with throwing away the cooling....

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Duct cooler?

 

But @Nickfromwales mentioned a duct heater/cooler, I'm assuming as a combined unit. You wouldn't be using the heater with bypass so placing it for heating seems reasonable. Apart from the frost protection possibility I don't see any point in putting a heater or cooler in the inlet (outside→MVHR) duct.

 

 

[Ed Davies]

  On 02/04/2019 at 12:48, joe90 said:

The benefit of not using direct electricity is the smell of burning dust from the element after a long period of non use. The DHW temp would be low so the temp raised in the inefficient air transfer would be minimal, but saying that we are only talking of requiring a few degrees.

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Why would the plates of an electric heater need to be any warmer than those for a water heater? OK, you can get away with smaller, higher temperature, plates for an electric heater but they're not necessary and, as you say, could result in burnt dust so just use plates as large as needed for low temperature water and run them at the same temperatures.

[PeterW]

  On 02/04/2019 at 14:03, Ed Davies said:

 

Why would the plates of an electric heater need to be any warmer than those for a water heater? OK, you can get away with smaller, higher temperature, plates for an electric heater but they're not necessary and, as you say, could result in burnt dust so just use plates as large as needed for low temperature water and run them at the same temperatures. 

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I'd go with some sort of willis type arrangement or even a jacuzzi heater inline with a duct heater - cheaper than an electric heater and also simpler to integrate with an existing heating system I expect

[Jeremy Harris]

On the point about adding a cooler on the MVHR intake, this seems not to make sense unless the MVHR has a bypass function.  For practical reasons, associated with trying to retrofit a duct cooler to an existing installation, I'm planning to add one to the outside intake of our system.  This will just be connected to the ASHP flow and return and includes a motorised ball valve that only allows flow through the cooler when the ASHP is in cooling mode, and already cooling the floor.