Possible to cool with UFH and my setup?

[pudding]

Hi,

 

After all the recent hot weather, our house can hit 29degrees inside by the end of the day. Usual story of too much glazing. I've bought a sail shade to put up and cover 2 large windows/slider. But i'm wondering if I can use our UFH to cool the floor too?

 

My set up is a Vaillant GSHP, connected to a 300L buffer tank for the UFH. There are 8 zones split between 2 manifolds, 1 up and 1 down. These are controlled with Heatmiser Neo stats. I've turned the heating function off on the GSHP, so it's only heating the 300L DHW tank right now. So, could I use my set up to run cool water around the floors somehow? I'm just wondering how to turn on the pumps to move the water? 

 

Edit. Also, the floor downstairs is concrete slab, 150mm PIR, UFH loops then screed with tiles or wood on top. Upstairs I doubt it would be of any use but it's hanging UFH speader plates between joists with eng. wood straight on top.

Edited July 10, 2017 by pudding

[Jeremy Harris]

I've found that cooling the UFH works very well.  I just added a cooling thermostat to activate the UFH and turn on the ASHP in cooling mode, with the ASHP set to deliver a 12 deg C flow temperature when in cooling mode.  I find the floor surface nave goes lower than about 18 deg C, so there's no condensation risk.

 

I also had to add a motorised valve to turn off the flow to the buffer tank when in cooling mode, so that tank stays warm.

Edited July 10, 2017 by JSHarris

[pudding]

Thanks for the quick reply. Here's a pic of my setup. 

 

Is the only way (without adding other stats/pumps) to get the water moving around the UFH loops to somehow set all of the room stats to call for 'heating' in order to open all of the room valves and turn the pump on? So I could set all of the room stats to call for a room temp of 30degrees, and with the GSHP and heating off, it will simply pump around the cool water and never meet the demand of 30degs?

[PeterW]

You may have to bypass the TMV - it will be set to a specific temperature and will be trying to provide that to the floor. 

 

May be worth looking at a zone valve "shunt" that when cooling is called it opens the valve and lets the pump go open circuit. 

 

Even with that you may find unless there is a cooler part of the house you will just be moving the heat elsewhere in the house. 

[IanR]

Could there not be greater benefit from a more significant re-plumb?

 

Ideally, you would get the fluid in your ground loops directly circulating (via a blending valve) around your UFH loops to allow "passive" cooling.

 

You'd need to be able to isolate the GSHP and the Buffer from the UFH and to link the supply and return from the ground loops to the UFH pump, as well as opening all the actuators on the UFH manifold(s).

 

The added benefit is that the energy dumped from your house would help re-charge the ground around your ground loops.

[ragg987]

I am not clear what you are trying to achieve.

 

Are you trying to just circulate the water in the UFH round? This is not going to add cooling, but it will redistribute and even out a bit e.g. if you have a sunny window that floor would normally be warmer and this method of water circulation will shift it a bit. I doubt it will have a massive effect, depends on other factors like UFH area and if you have cool aspects (e.g. North facing).

 

or

 

Are you wanting to actively cool the slab in whch case your GSHP needs to have a cooling mode - effectively reversing the compressor to dump heat into the ground and taking it out of the house.

 

3 minutes ago, IanR said:

Ideally, you would get the fluid in your ground loops directly circulating (via a blending valve) around your UFH loops to allow "passive" cooling.

I would expect there to be a heat exchanger between the GSHP loop and the UFH loop, so don't see how this is possible?

[Jeremy Harris]

What I did was to make a UFH control box that has 12V four relays in it, plus some diode logic to switch the relays in set combinations.  One relay controls the ASHP cooling/heating selection, one relay controls the ASHP on/off terminal, one relay controls the UFH valve and pump (this opens the valve in the UFH return line and turns on the pump) and one relay control the valve in the flow to the buffer tank (this is turned off when the system is in cooling more).

 

There are two room stats, one configured as a heating stat, the other configured as a cooling stat.  The heating stat is set to 20.5 deg C, the cooling stat is set to 22.5 deg C. 

 

If the heating stat calls for heat then the heating/cooling relay is set to heating mode, the UFH relay is set to open the UFH valve and turn the pump on, the buffer tank valve relay is set to open the buffer tank valve and the ASHP on/off relay is set to turn the ASHP on.  The ASHP delivers water at 40 deg C, and the TMV on the UFH manifold mixes this down to about 24 deg C.  The buffer tank heats to 40 deg C, or as close as it can get to the flow temperature..

 

If the cooling stat calls for cooling then the heating/cooling relay is set to cooling mode, the UFH relay is set to open the UFH valve and turn the pump on, the buffer tank valve relay is set to close the buffer tank valve and the ASHP on/off relay is set to turn the ASHP on.  The ASHP delivers water at 12 deg C, and the TMV on the UFH manifold  just opens fully, as it can't achieve the set temperature (not a problem).  The buffer tank is isolated for as long as cooling mode is selected.

 

There is an override for hot water, as we use the buffer tank to pre-heat DHW.  When the buffer tank thermostat calls for heat (it's set to 35 deg C) then cooling mode is turned off, heating mode is selected, but the UFH valve and pump are turned off if the heating stat is not calling for heat.  This allows the ASHP to just heat the buffer tank, not the floor.  As soon as the buffer tank thermostat is satisfied, then is cooling more is selected the buffer tank valve closes and the system reverts to cooling the UFH again.

Edited July 10, 2017 by JSHarris

[IanR]

10 minutes ago, ragg987 said:

I would expect there to be a heat exchanger between the GSHP loop and the UFH loop, so don't see how this is possible?

 

With the ground loops potentially at 10 degrees +/- 2, this can be connected directly to the UFH fluid (as a unitary body of "water") to offer passive cooling (no compressor running). you would of course need to have antifreeze in the UFH loops to not dilute down the ground loops. when they are connected together.

 

Edit:

A previous discussion of GSHP Passive Cooling over at eBuild:

http://www.ebuild.co.uk/topic/17728-passive-cooling-using-gshp-ground-loop/page__hl__%2Bgshp+%2Bcooling

Edited July 10, 2017 by IanR
to add link to eBuild discussion

[ragg987]

2 minutes ago, IanR said:

With the ground loops potentially at 10 degrees +/- 2, this can be connected directly to the UFH fluid (as a unitary body of "water") to offer passive cooling (no compressor running). you would of course need to have antifreeze in the UFH loops to not dilute down the ground loops. when they are connected together.

Ah did not realise you could configure a GSHP like this.

 

Agree the cooler and stable ground is a perfect dump for excessive heat - I guess this has the added benefit that you are charging the ground with heat which should improve the COP a bit in the winter.

[Jeremy Harris]

15 minutes ago, ragg987 said:

Are you trying to just circulate the water in the UFH round? This is not going to add cooling, but it will redistribute and even out a bit e.g. if you have a sunny window that floor would normally be warmer and this method of water circulation will shift it a bit. I doubt it will have a massive effect, depends on other factors like UFH area and if you have cool aspects (e.g. North facing).

 

 

We had our system set up to do exactly this before we had the external heat reflective film applied.  It was very effective at keeping the areas of floor that were being heated by the sun at a much lower temperature, just by distributing the heat around the slab.

 

The main effect was to reduce room heating from what would have been hot areas of the floor; just reducing those small areas from around 30+ deg C down to around 20 deg C by recirculation significantly reduced the overall house air temperature.  A large part of this was down to the much reduced temperature differential.  As long as the whole slab stayed below room temperature there was no heating from it at all, and then at night the slab could cool down a bit, ready for the next day.  Overall it worked well, but I never really got a chance to test it during prolonged hot spells, as the cooling system would kick in and actively cool the slab.

 

In the description above, the only thing that has now changed is that I've wired the UFH pump to the UFH valve, so the pump does not run all the time that the programmer has the system turned on.  The UFH pump used to be wired directly to the power feed to the system, switched by the programmer.

[le-cerveau]

@pudding I see the biggest problem that you are using UFH with zones, where @JSHarris has a unified system with only one large zone.  Your zone stats will close off the respective loops above the call for heat temperature so you will be unable to circulate the cool water.  You will require a wiring re-configure to override the zones to allow a flow of water.  So you will need a second stat in any zone you want cooling and when it is activate (call for cooling) it opens the zone valve in the same manned as a call for heat stat.

Then you need to isolate the DHW system. 

Your GSHP may require re-configuring to allow you to access the ground loop (brine), however a quick look at the Valliant web site does not indicate that they have a cooling function (some manufactures provide additional cooling units).  It may be easier to directly tap into the brine circuit before/after the GSHP and just insert a heat exchanger to take the cooling from, personally I would keep the 2 circuits hydraulically separated, otherwise it could get messy.

 

I suspect this will require some considerable either plumbing and electrical re-wiring to work as you desire.

[pudding]

Thanks for the replies all. Yes i think it seems like it not going to work without some quite significant re-wiring/plumbing, and at best all i'll be able to do is re-distribute the heat from the directly solar-heated sections elsewhere without that work. Oh well, next is to see if i can link my recently bought portable air-con into the MVHR without issues.