Cold Room/Pantry linked to GSHP

[Piers]

Hi Everyone! Hope you're all well and not going stir crazy.

 

Over New Year 2020 I visited an old uni friend in Norway. We stayed outside Oslo in a cabin in the woods which his parents built about 10-15 years ago. The building is heated using GSHP and UFH.

 

At one point in our stay I was sent to the basement to retrieve a bottle of white wine from their cold room, which was like a sauna room with the temperature turned way down. It was about 3m by 1.8m, all wood panelled with some shelves and a thick, insulated door with rubber seals. 

 

What particularly piqued my interest was that it was bang next door to their GSHP plant room. And I wanted to know whether the GSHP would be used to both heat the house and cool this "pantry-room". Was the cooling, actually waste from the heating?

 

Now we're (still) designing our new build and have set aside a space in the basement for a plant room and pantry - I'm wondering how I could replicate the set up.

 

Naturally I asked my friend, who didn't have a clue!

 

Is this a set up that anyone has come across before?

 

I've got a few questions and would be grateful for any answers or even a little conjecture!

 

1. Can one use "waste cooling" from a GSHP to cool a room?

2. How does one regulate the temperature?

3. Are there suppliers who sell kits for cool rooms? 

4. Would anyone try DIYing it - insulate a basement box, vent and stick a blimmin' huge door on it?

5. What pitfalls can you envisage?

 

Thanks all and stay safe

Edited April 8, 2020 by Piers

[A_L]

1.Waste cooling? The ground loop fluid leaving the heat pump would be cold enough to act as a source of cold to absorb the heat in the cold room by routing through a heat exchanger (radiator) in the cold room.

 

2. You would have to have two routes for the ground loop fluid to go back to the ground loop area. One via the cold room and one not. Which path is taken would be controlled by a thermostat.

 

3. Doubt it very much

 

4. I wouldn't, for reason see 5

 

5. You would effectively be increasing house heating load by pumping heat from house to ground lump area. This is because by heating the ground loop fluid in the cold room you are reducing the amount extracted from the ground loop area

 

Better to have a dedicated heat pump with its 'hot' output in the house.

[PeterW]

Would only work when the GSHP is calling for heat, which is conversely when you would want heating, and your cold room actually would want cooling when heating is not required

[Piers]

26 minutes ago, PeterW said:

Would only work when the GSHP is calling for heat, which is conversely when you would want heating, and your cold room actually would want cooling when heating is not required

 

True. I'd actually want cooling at all times so would need to work that out

[Piers]

6 hours ago, A_L said:

5. You would effectively be increasing house heating load by pumping heat from house to ground lump area. This is because by heating the ground loop fluid in the cold room you are reducing the amount extracted from the ground loop area

 

I'm not sure I follow, though it's probably my rudimentary understanding of GSHP.

 

I thought that the fluid coming in through the ground loop is "warm" and that going out is "cold". The temperature change being the heat pump acting like a reverse refrigeration unit.

 

If the "cold" fluid exits the building via a radiator in the pantry would that not cool the room and warm the fluid?

 

Does it matter if the "cold" fluid going back out into the ground array has been slightly warmed up after it exits the pump? Surely that what happens in the ground loop anyway?

[A_L]

50 minutes ago, Piers said:

I'd actually want cooling at all times so would need to work that out

 

You probably need hot water every day, the amount of heat requiring removal from the cold room would be quite small and could be part of the supply to the DHW cylinder. A dedicated heat pump would still be better.

 

44 minutes ago, Piers said:

I thought that the fluid coming in through the ground loop is "warm" and that going out is "cold".

 

Only relatively, both are colder than the earth of the ground loop location.

 

1 hour ago, Piers said:

If the "cold" fluid exits the building via a radiator in the pantry would that not cool the room and warm the fluid?

 

Yes

 

1 hour ago, Piers said:

Does it matter if the "cold" fluid going back out into the ground array has been slightly warmed up after it exits the pump? Surely that what happens in the ground loop anyway?

 

I am thinking the extra warmth represents an increased heatloss wrt the house but if the return is also warmer it may balance out ........???

[Piers]

14 hours ago, A_L said:

You probably need hot water every day, the amount of heat requiring removal from the cold room would be quite small and could be part of the supply to the DHW cylinder. 

 

True, that makes sense.

 

14 hours ago, A_L said:

A dedicated heat pump would still be better.

 

Are you suggesting a heat pump just for cooling the pantry room? 

 

Wouldn't that be quite expensive?

 

Can one connect 2 heat pumps to the same ground array or would I need to double up on that?

 

This is where my understanding of GSHP ends!

 

[Jeremy Harris]

We very effectively cool our house by just running the heat pump in reverse, so that cool water is pumped around the UFH pipes in the floor and heat.  Very much like the way a fridge or cold room works.   We have an ASHP, but it would work just as well with a reversible GSHP (if you can find one).  ASHPs can almost always run in reverse, as most do this to defrost.  An ASHP run like this is just the same as a refrigerator.

 

The same principle could be applied anywhere, just seal and insulate a space and then pump heat out of it.  Easy enough to have a selective system that only cools one enclosed space, if needed, in much the same way as UFH might be zoned.

 

There's a condensation risk if it's taken too far, but that's never an issue for us, as we run our system so the floor drops to about 18°C, enough to be very effective at keeping the house cool, but not low enough to be below the dew point for the range of humidity conditions we get here in the UK (at 18°C the RH would have to be over 80% with the room at about 21°C for there to be a condensation risk).

[Piers]

@Jeremy Harris do you get cold feet in the summer?!

 

We could put a standalone aircon/refridgeration unit into the pantry with an extractor vent. Should solve the condensation risk.

 

I was trying to be clever by using the cooled down fluid returning into the ground array to cool the pantry

 

Maybe it's not possible/practical

[Jeremy Harris]

2 minutes ago, Piers said:

@Jeremy Harris do you get cold feet in the summer?!

 

We could put a standalone aircon/refridgeration unit into the pantry with an extractor vent. Should solve the condensation risk.

 

I was trying to be clever by using the cooled down fluid returning into the ground array to cool the pantry

 

Maybe it's not possible/practical

 

 

No, don't really notice it, TBH, other than the house feeling a lot cooler.  18°C doesn't really feel cold, just pleasantly cool.  We have lots of travertine flooring, and my wife tends to walk around in bare feet in summer, when the cooling is on, just because the cool floor feels more pleasant.

 

Leaving aside the very high cost of using a GSHP (killed the idea for us, as it was massively more expensive than an ASHP), why bother with the heat pump at all?  The ground will sit at around 8°C all year around, so just laying a pipe array in the ground, connected to another pipe array in the cool room, with a small circulating pump, would keep the cool room at a pretty constant temperature all year around.  If a thermostat was added to turn the circulating pump on and off then the temperature of the cool room could be adjusted to be whatever you wanted, as long as it was a bit above 8°C.

[Piers]

14 minutes ago, Jeremy Harris said:

Leaving aside the very high cost of using a GSHP (killed the idea for us, as it was massively more expensive than an ASHP), why bother with the heat pump at all?  The ground will sit at around 8°C all year around, so just laying a pipe array in the ground, connected to another pipe array in the cool room, with a small circulating pump, would keep the cool room at a pretty constant temperature all year around.  If a thermostat was added to turn the circulating pump on and off then the temperature of the cool room could be adjusted to be whatever you wanted, as long as it was a bit above 8°C.

 

Now that's an excellent idea - I like it.

 

Any idea how one calculates length of ground array?

[Jeremy Harris]

3 hours ago, Piers said:

 

Now that's an excellent idea - I like it.

 

Any idea how one calculates length of ground array?

 

 

Depends on how much cooling you need.  Very roughly, a GSHP can pull around 1 kW per 10m length of slinky coiled pipe, but that's at a higher temperature differential.  As a guesstimate I'd suggest that maybe 250 W per 10m of slinky coil might be about right for passive cooling.

[SteamyTea]

If you know the thermal properties of the pipe material, the wall thickness and the diameter, you can calculate the heat transfer though it.  Just the same as calculating the U-Value of a wall.

 

[dpmiller]

Isolate the slab in the pantry and have it uninsulated to ground, or loop the mans water feed through it.

[SteamyTea]

40 minutes ago, dpmiller said:

or loop the mans water feed through it.

Ewwww

[Conor]

We're going to do something similar in our basement in the NE corner. Full insulated with 150mm PIR and a sealed door. Only need to keep it around 10-12c. In winter time that will be achieved with ventilation, like a traditional draft larder. In summer, I'm hoping we can use the UFH (maybe even loops in the walls?) on cooling mode once every few days or so to keep the temp in that range.

 

I might put in a provision for piping for a single Aircon unit like @Jeremy Harris did for his bedroom, Just in case slab and wall cooling isn't enough, but I doubt that will be needed as we won't need it cool enough for meat or dairy.

Edited April 10, 2020 by Conor

[Jeremy Harris]

16 minutes ago, Conor said:

I might put in a provision for piping for a single Aircon unit like @Jeremy Harris did for his bedroom, Just in case slab and wall cooling isn't enough, but I doubt that will be needed as we won't need it cool enough for meat or dairy.

 

We've been using the aircon in the bedroom most days for the past couple of weeks, as the house has been a bit warm in this prolonged sunny spell.  Seems a bit odd turning on aircon in March in the UK climate, but Spring is usually the period when we get the most solar gain, a combination of being in a sheltered spot, facing South, with the relatively low angle of the sun causing sunlight to penetrate more deeply into the house.

[Conor]

23 minutes ago, Jeremy Harris said:

 

We've been using the aircon in the bedroom most days for the past couple of weeks, as the house has been a bit warm in this prolonged sunny spell.  Seems a bit odd turning on aircon in March in the UK climate, but Spring is usually the period when we get the most solar gain, a combination of being in a sheltered spot, facing South, with the relatively low angle of the sun causing sunlight to penetrate more deeply into the house.

 

Thanks to insights like this, we're moving away from the traditional over head bris soleil design to something that will provide low sun shading if required. Currently thinking a retractable sail design, anchored from roof above main window to lower level on the outshoot to the SE. 

 

Back to topic: roughly how cool could you get a 100mm screed slab down to in a small (4x4m), highly insulated room with a standard UFH loop and ASHP? Is it just like calculating heating load etc but you just invert the temperatures?

[Jeremy Harris]

8 minutes ago, Conor said:

 

Back to topic: roughly how cool could you get a 100mm screed slab down to in a small (4x4m), highly insulated room with a standard UFH loop and ASHP? Is it just like calculating heating load etc but you just invert the temperatures?

 

I played around with the settings on our ASHP and it would happily deliver water at 4°C in cooling mode.  There's a temperature differential between the flow temperature and the surface temperature, and another differential between the surface and the room temperatures, but I think that, with pipes in the ceiling, or perhaps the walls, it should be possible to cool a space down to maybe 8°C or so fairly easily.  Might even be able to get that low with cooling the floor.  Condensation would be an issue, though, if cooling surfaces to this sort of temperature.

[Conor]

7 minutes ago, Jeremy Harris said:

 

I played around with the settings on our ASHP and it would happily deliver water at 4°C in cooling mode.  There's a temperature differential between the flow temperature and the surface temperature, and another differential between the surface and the room temperatures, but I think that, with pipes in the ceiling, or perhaps the walls, it should be possible to cool a space down to maybe 8°C or so fairly easily.  Might even be able to get that low with cooling the floor.  Condensation would be an issue, though, if cooling surfaces to this sort of temperature.

 

That would be perfect, I'd be happy with 10c in summer. I'd be installing a single room MVHR to mitigate condensation in the summer. The MVHR would also do the cooling duties in winter. Though I'd need think a bit more about that. 

[Jeremy Harris]

47 minutes ago, Conor said:

 

That would be perfect, I'd be happy with 10c in summer. I'd be installing a single room MVHR to mitigate condensation in the summer. The MVHR would also do the cooling duties in winter. Though I'd need think a bit more about that. 

 

The MVHR won't do anything to mitigate condensation, I'm afraid, as that is just a function of temperature and humidity.  Cold surfaces are always going to condense out water from the air if they are below the local dew point, and a surface down at around 8°C will be well below the dew point for a lot of the time, I think (this is the reason fridges and MVHR heat exchangers have a condensate drain).  Not impossible to overcome, though.  Might be possible to include some sort of condensate drain from the cold surface, perhaps, or else look at cooling the air in the space via a small fan coil unit that includes a condensate drain.  The latter might well be the better solution, as it would probably cool the space more quickly after the door has been opened, and it would almost certainly work with a lower temperature differential than would pipes in the floor or wall.

[Conor]

11 hours ago, Jeremy Harris said:

 

The MVHR won't do anything to mitigate condensation, I'm afraid, as that is just a function of temperature and humidity.  Cold surfaces are always going to condense out water from the air if they are below the local dew point, and a surface down at around 8°C will be well below the dew point for a lot of the time, I think (this is the reason fridges and MVHR heat exchangers have a condensate drain).  Not impossible to overcome, though.  Might be possible to include some sort of condensate drain from the cold surface, perhaps, or else look at cooling the air in the space via a small fan coil unit that includes a condensate drain.  The latter might well be the better solution, as it would probably cool the space more quickly after the door has been opened, and it would almost certainly work with a lower temperature differential than would pipes in the floor or wall.

Of course. The air coming in would still be laden with moisture, especially where we are in the coast.

 

You're right, one of those water to air copper coil things in a duct would be an easier and more effective solution. There will be a utility room adjacent so getting a condensate drain sorted will be easy.

[SteamyTea]

If you are keeping fresh fruit and veg in this pantry, then you need to keep the RH high.  Will end up with dried fruit otherwise.

 

Just fit a separate small air conditioning unit.

KISS