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 Post subject: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 12:59 pm 
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Joined: Mon Feb 27, 2012 9:53 am
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Location: 16
Anyone have this system,and what are your views on it. In the new house this will be our heating system, water heated by normal immersion heater in a cylinder, obviously to get to a high temp, according to what I have found out, is that the max floor temp will be about 29 degrees, so that's fine, however when its cold outside the unit becomes less efficient, where we live can get cold and I need to keep a nice temp of 22 degrees, as said its a new house so well insulated, so if you have this type of system are you happy with it? there is as you would expect a lot of mixed discussion about it on the net, the builder etc tell me that it will work as described. Thanks


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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 2:05 pm 
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Joined: Sun Aug 26, 2012 5:38 pm
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Location: Je ne suis pas Charlie
Will watch this with interest. I recently put down an insulated floor and screeded the UFH pipe ready for similar.
My plan is to use a heat pump for the pool and via a heat exchanger heat the floors when necessary. I would like to use the heat pump as a pre heat for the water tank as well.

There are some heat pumps rated for high temperature. There are variable speed inverter drive heat pumps that can produce a COP of 16 in the right conditions, The chap at Panasonic I spoke to highly recommended the inverter drive as it works at a pace required and not just flat out so any defrost cycle is less debilitating to the overall electric bill.

I am going to see some of the new units on 16th of November.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 2:37 pm 
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I cannot contribute regarding the use of the heat exchanger, but 29 degrees sounds a bit cool to me.
Remember this is the floor temperature and not the room temperature.

Our oil fired wet system leaves the floor feeling warm to the touch especially during the depths of winter and early in the morning in Spring and Autumn. This delivers a room temperature of 23C.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 3:43 pm 
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lastoneout, you said wet system, do you mean wet radiators?

as UFH is, in this case also wet. The thing about a warm floor 29c is your feet are warm and transmit this to your head so you feel OK. Obviously the room warms to but the whole floor is a radiator not just small pockets of heat so the temp doesn't need to be as high.

By contrast the BIL had tiled floors with conventional radiators but without the insulation your feet and calfs felt cold so the rest of you felt cold. You literally had to put feet on the sofas to feel comfortable.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 4:42 pm 
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No, not radiators (well not on the ground floor), underfloor heating.

As you rightly say the whole floor is a radiator and, just like a wall mounted radiator, it runs hotter than the ambient temperature in the room. The temperature differential is smaller than a wall mounted rad, because as you rightly say it is a much larger area, but nevertheless it does need to run hotter than ambient and based on our experience with a different heat source, 29C max would seem a bit on the low side.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 4:44 pm 
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OK, that's good to know, more ammo when I meet the heat pump company next week.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Tue Nov 07, 2017 6:42 pm 
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I suspect it all depends on the conditions of use.

Under static conditions - constant external temperature, no wind chill etc - a 6 degree difference between the floor and room might well work in a well insulated building with all doors and windows closed.

Meanwhile in the real world, it is 8-10 degrees during a bright sunny winter day, the system handles this quite easily (probably running at less than the 29 max quoted above) but then as the sun sets, the external temperatures start to fall very quickly, the system then has to ramp up and put a lot of heat into that massive concrete lump called the floor. If constrained by a low maximum temperature then the rate at which it can pump heat in compared with the rate of loss of heat from the house as a whole is such that it cannot possibly cope. Then add in a chill wind to suck more heat out of the building......

Our system is set with a 55 degree cut out - and this to protect the floor and things stood on it (like me). I don't think it has ever been near that, but I am sure we have been above 40C - but we are in an exposed position with low winter temperatures even by French standards.

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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Wed Nov 08, 2017 8:32 am 
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Thanks, so no one is 100% sure yet, the figure of 29 degrees was off the net, will find out more about the system as we go along, it would be nice to keep this thread alive as I believe that this subject will be discussed more and more, as new houses get built, and people start to retro install more up to date and efficient heating systems. Let us know how it went Teapot, an ambient temp of 23 would suit us fine as long as it worked at minus 10/15. Spec


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 Post subject: Re: Air to water heat pumps and UFH
PostPosted: Wed Nov 08, 2017 9:58 am 
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The Charted Institute of Plumbing and Heating Engineers publish design guides on UFH, at the moment I cannot reference my copies, but I did post "many moons ago" on the forum, how to work out your heat requirements, http://www.thefranceforum.net/viewtopic.php?f=16&t=8181, this will give you a start in finding out your heat load, and is the same for UFH as it is for normal radiator heating

Sorry but you will have to google the address of the C I P H E, but its in England

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