divorcingjack

UFH Cooling without ASHP

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Morning all, 

 

Due to the unseasonably warm weather, and the imminent on-site arrival of our plumber, my thoughts have turned to the cooling of the house. We have a lot of glazing, and have already designed in external shading. I read with interest the JSHarris blog post about using the ASHP in cooling mode with the UFH to cool the floor slab - genius idea. Unfortunately, we don't have an ASHP. We have a system boiler and thermal store. 

 

My plumber scratched his head a bit and talked about additional valves and whatnot, but was a bit puzzled by the whole idea of using the UFH for the opposite to it's intended purpose. 

 

Questions - will switching the UFH to use the cold water supply actually make any difference to the temperature of the floor, or is this a stupid idea? I'm thinking that the area in front of our large windows will get super-hot, so circulating the heat away from this area to the cooler areas of the house would surely help? 

 

What on earth does my plumber need to do to make this work? 

 

Please feel free to tell me I am being an idiot. I have just had a baby, so I'm not firing on all cylinders at the minute. 

 

Thanks all ;)

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If you have a large amount of solar thermal gain I am not sure that cooling the slab will make a lot of difference and it may feel uncomfortable in the evening and morning.  Can you not apply solar film to the windows and control the issue at source?

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If wondered about using an outdoor ground coil as the heat dump. You could simply pump the UFH water out and around the ground coil and it would loose heat to the ground outside.

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11 minutes ago, Triassic said:

If wondered about using an outdoor ground coil as the heat dump. You could simply pump the UFH water out and around the ground coil and it would loose heat to the ground outside.

 

Should work at least as well as an ASHP, as the ground temperature below about 1m down is fairly constant and typically around 8 deg C.  I've found that pumping water around our UFH at 12 deg C is very effective, so a suitably sized ground loop should be fine.

 

Whether it's cheaper than an ASHP I don't know, as the cost of trenching a GSHP collector (which is essentially what would be needed for the ground cooling loop) can be quite high.

 

The cheapest way to cool a house (apart from designing it with appropriate levels of shade and using a high decrement delay structure) is probably an air-to-air heat pump.  These are pretty cheap, under £1k, and will very effectively cool a house if the internal unit is mounted somewhere high, where cool air can freely circulate.  If the house has PV, then the chances are that the running cost for the air cooling will be zero, as it will only really be needed when the sun is out.

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1 hour ago, divorcingjack said:

will switching the UFH to use the cold water supply actually make any difference to the temperature of the floor,

The water in UFH should be in a closed loop and treated. I achieve a similar effect, in a small way, as I have a 90l buffer for the UFH heating. Mains incoming water flows through a coil in this buffer. This raises the mains a few degrees and the buffer cools to about 14C, I can circulate this cooler water through UFH. This is only useful while we are using water in the house - if taps are off for an extended period there is no cooling.

 

In the end you need to do the calcs to understand the effect. Above method "removes" perhaps 1 or 2kWh per 24hrs. On a hot day and with solar gain you will be gaining a lot more energy, so while there will be some cooling it may not be sufficient.

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Sunamp are, I believe, going to release a unit with an integral mini heat pump which stores 'cold' rather than hot heat energy. 

I'm currently awaiting some further detail so I can recommend / integrate them, but if you've got PV and no ability to trench for geothermal loops or have an ASHP ( which I think is exactly @divorcingjack's situation ) then this seems a good product to look at. 

Basically when the suns shining your cooling, but the same can be said about a split air con unit. The only benefit of wet cooling via the UFH is no breeze and no stale air. Also I'm not sure about how MVHR and air con would live together. 

@JSHarris, could the air con unit feed to a heat exchanger in the MVHR ductwork as a pre / post cooler ?

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7 minutes ago, Nickfromwales said:

 

@JSHarris, could the air con unit feed to a heat exchanger in the MVHR ductwork as a pre / post cooler ?

 

Not really, as the MVHR air flow rate is a great deal lower than a typical air-to-air heat pump.  Our Genvex MVHR does have a tiny air-to-air heat pump built in, but it will only provide around 1.5 kW of cooling, which isn't a lot if you've got any large, unshaded, glazed areas facing the sun.  The limit on the Genvex is really imposed by the low air flow rate, as even a cheap split air-to-air unit like this: https://www.appliancesdirect.co.uk/p/tcl-12wminv/tcl-tcl12wminv  will provide around 3.5 kW of cooling for less than £400.

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8 minutes ago, JSHarris said:

The limit on the Genvex is really imposed by the low air flow rate, as even a cheap split air-to-air unit like this: https://www.appliancesdirect.co.uk/p/tcl-12wminv/tcl-tcl12wminv  will provide around 3.5 kW of cooling for less than £400.

 

Wow, and it's an air-to-air heat pump, if I'm reading this right. Obviously only good for a single room, but at £370 it's about the same price as those ridiculously expensive Dyson pedestal fans.

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2 minutes ago, richi said:

 

Wow, and it's an air-to-air heat pump, if I'm reading this right. Obviously only good for a single room, but at £370 it's about the same price as those ridiculously expensive Dyson pedestal fans.

 

If you have a house with a large central space, and that's reasonably well insulated, with only modest amounts of uncontrolled solar gain, I'm sure 3.5 kW of cooling would be pretty effective for the whole house.  I thought about fitting one very high up in the very top of our entrance hall, which is right in the centre of the house and around 6m high, as I'm sure that would have provided more than enough cooling on even the hottest days, and I doubt it would use more than around 1 kW of our generated PV power.

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14 minutes ago, richi said:

 

Wow, and it's an air-to-air heat pump, if I'm reading this right. Obviously only good for a single room, but at £370 it's about the same price as those ridiculously expensive Dyson pedestal fans.

Agree, that's a bargain. A shitty in-room one second hand was coming in at around £150 for anything half decent. Then you've got to vent the hot waste air to outside. :S  

 

11 minutes ago, JSHarris said:

and I doubt it would use more than around 1 kW of our generated PV power.

Between 1 and 1.2kW electrical consumption whether heating or cooling. 

Thats a no brainer. Would there be an issue running this in a small attic room ? Super dry air etc ? I assume the fan speed is controllable to match the requirements of the room.  

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14 minutes ago, Nickfromwales said:

Agree, that's a bargain. A shitty in-room one second hand was coming in at around £150 for anything half decent. Then you've got to vent the hot waste air to outside. :S  

 

Between 1 and 1.2kW electrical consumption whether heating or cooling. 

Thats a no brainer. Would there be an issue running this in a small attic room ? Super dry air etc ? I assume the fan speed is controllable to match the requirements of the room.  

 

No problems at all in running it in any room, the indoor unit just has three pipes, two for the refrigerant and one drain pipe for the condensate.  Needs an F gas ticket holder for the install, but there are pre-gassed versions around that get around that.  Anyway, pumping the unit out with a vacuum pump and gassing it up is a quick and easy job that can be done after all the installation work has been done, as these things are gassed up from the outdoor unit.  Any refrigeration engineer can gas one up in under an hour, or you can break the rules and do it yourself. 

 

I gassed up a conservatory air con a few years ago, using a borrowed vacuum pump, bottle of refrigerant and UV dye leak test light.  The process is pretty simple, just connect the vacuum pump and suck the system right down, then wait for half an hour or so to allow any moisture inside to come out as vapour, and to check for leaks using the vacuum gauge.  Then just connect the refrigerant bottle up, put it on some scales to weigh it and fill the system with the right amount, ideally with some leak check dye as well.  Then you just seal off the filling valve, run the unit up and check the pipe joints for leaks with the UV light. 

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OK, thanks for all the replies chaps. Looks like an £370 air to air AC unit like the one jeremy recommended ( was that a recommendation, or just an example?) could be a good choice. If we think about it now, we could probably conceal it pretty well, as it's pretty ugly to have on show. 

 

The ground coil would have been an excellent idea, had we done it during our extensive excavations. Bugger it - it's all filled in with compacted hardcore now and would be an absolute arse to dig out again :( 

 

Sooooo... what would have to go through the wall with this unit? Typically, the zinc portion of the house has been clad now and I'm none too keen on trying to put a hole through it. The brickwork section is not complete yet though, so there are options. 

 

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I guess the three pipes that @JSHarris mentions -- 15mm? -- and power for the outside unit

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6 minutes ago, divorcingjack said:

 Looks like an £370 air to air AC unit like the one jeremy recommended ( was that a recommendation, or just an example?) could be a good choice. If we think about it now, we could probably conceal it pretty well, as it's pretty ugly to have on show.

 

Not a recommendation really, although I have bought appliances from that supplier and found their service to be pretty good.  It was just the first hit I had when doing a quick web search - there may be better value units around.

 

6 minutes ago, divorcingjack said:

 Sooooo... what would have to go through the wall with this unit? Typically, the zinc portion of the house has been clad now and I'm none too keen on trying to put a hole through it. The brickwork section is not complete yet though, so there are options.

 

Just three holes, or one larger hole.  There are two refrigerant pipes, that are around  8mm to 10mm, but are insulated, plus a condensate drain pipe, that is often only around 12mm to 15mm, and usually pumped via a small peristaltic pump inside the indoor unit.  The condensate drain can connect to a waste pipe in the house if that is easier.

 

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Is the condensate neutral? No issue with just a drip pipe to outside ?

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2 minutes ago, Nickfromwales said:

Is the condensate neutral? No issue with just a drip pipe to outside ?

 

 

Yes, it's distilled water, so ideal for use for topping up batteries or use in a steam iron.  You can just collect it in a container if you wish, but these things can generate several litres of condensate a day, so any container needs to have an overflow.

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10 minutes ago, Nickfromwales said:

Sunamp are, I believe, going to release a unit with an integral mini heat pump which stores 'cold' rather than hot heat energy. 

I'm currently awaiting some further detail so I can recommend / integrate them, but if you've got PV and no ability to trench for geothermal loops or have an ASHP ( which I think is exactly @divorcingjack's situation ) then this seems a good product to look at. 

Basically when the suns shining your cooling, but the same can be said about a split air con unit. The only benefit of wet cooling via the UFH is no breeze and no stale air. Also I'm not sure about how MVHR and air con would live together. 

@JSHarris, could the air con unit feed to a heat exchanger in the MVHR ductwork as a pre / post cooler ?

 

 

That's interesting - we considered running a closed loop of UFH pipe outside the insulation layer of the basement to dump heat in summer from the GF UFH circuit but abandoned the idea early on as it was getting too complicated. 

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This discussion has been really helpful, thank you all. Looks like an split AC unit is going to be the simplest solution for us. 

 

Any advice on good brands/things to look out for? I know Panasonic are considered reliable and I'm assuming an inverter based unit is best? 

 

Thanks, 

dj 

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How about an old freezer.  Put a water coil in it, plumb it into your UF pipework, and when it is hot, turn thee freezer on and divert the heating water via the coil in the freezer (put the freezer outside in thee shade).

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That is actually a genius idea. I actually have an old freezer that I picked up for free when buying our fridge that's going in the house. 

 

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It’s the same way that python coolers in bars work ... coil of copper pipe (the python) runs through either a water or ice bath. 

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All you need is a bit of unwanted UFH pipe, a pump maybe and a valve or two.

You could stick the pipe in a bucket full of anti-free (or salty water) as that may control the temperature a bi better.

 

Let us all know if you give it a go.

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Just a quick reality check here. 

 

A big domestic freezer may draw as much as 200 W, so assuming it has a COP of around 3.5, it will have a cooling capacity of around 700 W. 

 

Our ASHP has a cooling capacity of about 6,000 W, and that has a reasonable effect on a very well insulated house.

 

Is it worth all that hassle to get at most around 700 W of cooling?

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14 hours ago, JSHarris said:

Just a quick reality check here. 

 

A big domestic freezer may draw as much as 200 W, so assuming it has a COP of around 3.5, it will have a cooling capacity of around 700 W. 

 

Our ASHP has a cooling capacity of about 6,000 W, and that has a reasonable effect on a very well insulated house.

 

Is it worth all that hassle to get at most around 700 W of cooling?

Agreed. 

The SA cooler units are, iirc, 6 / 9 / 12kW or thereabouts before the loss of the HP, so I think a freezer based design may be ok for a room, but whole of house will just inundate it and run it to an early grave. If you live near a recycling centre it may be ok as you'll have a good source of replacement freezers :D

 

18 hours ago, divorcingjack said:

That is actually a genius idea. I actually have an old freezer that I picked up for free when buying our fridge that's going in the house. 

Not the way I'd envisage a modern solution to look :S I wonder how much heat the unit would give off whilst 'cooling' ? :/ 

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On 19 May 2018 at 09:49, Nickfromwales said:

 

Not the way I'd envisage a modern solution to look :S I wonder how much heat the unit would give off whilst 'cooling' ? :/ 

 

LOL! The back of the house is tight up against a row of knackered old 50's prefab asbestos roofed garages, so it'll fit right in! But.. point taken. 

 

Although, we visited the house during a really hot spell on saturday and it was surprisingly cool inside, so this might not be as much of a problem as we feared. But, we're going to build in a hidden housing for an AC unit just in case. Many thanks for all the replies and advice. 

 

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