Which ASHP are set up to cool

[Triassic]

I’m looking at which ASHP to buy and wanted one with cooling capability. What am I looking for? Make, model etc.

[ProDave]

My LG Therma V has a cooling function that I won't actually be using.   I am not sure I would recommend it though, so see what others suggest.

[Jeremy Harris]

They can all cool as well as heat, as they have to in order to defrost.  The question boils down to how easy it is to over-ride any MCS/RHI restrictions that may have been made to the unit for the UK market (you can't claim RHI if the unit has an easy way to cool without changing non-user settings).

 

In the case of my Carrier unit, the cooling just wasn't documented, and as supplied the unit only had the heating and hot water controls identified, and all the wiring diagrams for the options excluded any cooling option.  It was only by looking at the connections for the control wiring that I spotted an unused terminal that happened to be the one that switches the unit into cooling mode.

 

I believe the other units are broadly similar. @jack found that the cooling function could be enabled by going into the settings on his unit, I believe.  I have ours set up with two thermostats, one controls heating the other controls cooling, which is pretty simply in terms of wiring.

[Gav_P]

This is interesting... is this for Air to Air heat pumps or does it work for Air to Water? Does this mean I could potentially cool my UFH in summer? 

 

 

[Jeremy Harris]

8 minutes ago, Gav_P said:

This is interesting... is this for Air to Air heat pumps or does it work for Air to Water? Does this mean I could potentially cool my UFH in summer? 

 

 

 

 

Mine's an air to water heat pump and I use the cooling mode to cool the UFH in summer.  It's surprisingly effective, and works a lot better than I thought it would.  I fitted a second room thermostat to switch the ASHP to cooling more, so we have two, side by side, one controlling the heating and the other controlling the cooling.

[jack]

On 15/07/2018 at 12:56, JSHarris said:

I believe the other units are broadly similar. @jack found that the cooling function could be enabled by going into the settings on his unit, I believe.  

 

That's right, I had to go into service mode to access this setting.

 

The installation manual didn't describe what you had to do to get into service mode, but I found out how online. From memory, the unit also came with a slip of paper in the box telling you how to access cooling mode, but I couldn't find that when I went to do it!

[Gav_P]

11 minutes ago, JSHarris said:

 

 

Mine's an air to water heat pump and I use the cooling mode to cool the UFH in summer.  It's surprisingly effective, and works a lot better than I thought it would.  I fitted a second room thermostat to switch the ASHP to cooling more, so we have two, side by side, one controlling the heating and the other controlling the cooling.

 

Wow, that’s intersting news. I was a bit concerned going down the ASHP route, but it keeps offering up more benefits over traditional oil boilers.

 

did you need the carrier command unit to change any setting to make it work? (I don’t have one of these currently)

[joe90]

My carrier unit rebadged Kingspan has cooling, set by the command unit and a link removed in the wiring. Not planning to use it at the moment but an option for the future if required.

[ProDave]

MY LG Therma V air to water heat pump has a cooling function, but I am not planning to use it.

[ragg987]

Hitachi user. You enable cooling by a link change which is in the delivered documents. I use an original Hitachi controller for heating and cooling, it has the ability to program automatic switchover.

 

Note that cop while cooling is not as high as when heating.

 

[Dreadnaught]

15 minutes ago, ragg987 said:

Note that cop while cooling is not as high as when heating.

 

Why is that, I wonder? It is because the system is always optimised for heating? If so, I wonder how.

[Ed Davies]

Practice may be slightly different but probably not much different: in theory the cooling COP should be one less than the heating COP because the energy in the electricity going into the pump contributes to the heating but not to the cooling.

 

I = thermal energy going into the heat pump (from outside when heating, from the house when cooling). What matters when cooling.

 

O = thermal energy coming out of the heat pump (to the house when heating, to the outside when cooling). What matters when heating.

 

E = electrical energy going into the heat pump.

 

Assuming no other losses then O = I + E.

 

Cooling COP = I/E.

 

Heating COP = O/E = (I + E)/E = I/E + E/E = I/E + 1 = cooling COP + 1.

[Dreadnaught]

@Ed Davies that's a good point. It reminds me of @TerryE's comment in his excellent posts about using the slab as a heat store posted in Boffins Corner. He mentioned that the low-wattage UFH circulation pump was over time fundamentally just another kWh of heat going into the slab.

Edited October 2, 2018 by Dreadnaught

[Ed Davies]

Yep. Similarly, if the heatpump is in the house then the losses from it contribute to the heating but detract from the cooling. If the HP is outside (as ASHPs usually are) they contribute to the cooling (sort of) but are no help at all for heating.

[ragg987]

1 hour ago, Ed Davies said:

in theory the cooling COP should be one less than the heating COP

Seems right, I get around 4 when heating and 3 when cooling.

[Jeremy Harris]

6 hours ago, Gav_P said:

 

Wow, that’s intersting news. I was a bit concerned going down the ASHP route, but it keeps offering up more benefits over traditional oil boilers.

 

did you need the carrier command unit to change any setting to make it work? (I don’t have one of these currently)

 

You don't need the command unit to get cooling to work, provided the cooling temperature has already been programmed into the unit.  The command unit sends data to the ASHP to change the settings, which are then stored in non-volatile memory inside the ASHP itself.

 

Changing the Carrier-based units from heating to cooling is just a matter of the way you wire up the 12 V dry contact controls, as shown on this diagram I drew up:

 

[Gav_P]

@JSHarris Ah, so the link wire between 3&7 could effectively be replaced with a switch (closed = heat, open = cooling)? Is it that simple? 

[Gav_P]

I’ve also notice in your diagram the link between 13&15... does this crank up the output temp when calling for DHW?

 

[Jeremy Harris]

11 minutes ago, Gav_P said:

@JSHarris Ah, so the link wire between 3&7 could effectively be replaced with a switch (closed = heat, open = cooling)? Is it that simple? 

 

Yes, it's that simple!

 

10 minutes ago, Gav_P said:

I’ve also notice in your diagram the link between 13&15... does this crank up the output temp when calling for DHW?

 

 

Yes, it does.

 

In both cases the temperature that the ASHP will run at depends on what's been programmed into it, either during manufacture or from the command unit, so without knowing the internally stored settings it's hard to be sure how cold the flow will be in cooling mode or how hot the flow will be in DHW mode.  My guess is that the internal control board may be set to the default values in the command unit manual.

[Gav_P]

Brill. Thanks.

 

 

[joe90]

If it helps here are the default values from my carrier unit.

[jfb]

resurrecting an old thread  - can someone enlighten the unenlightened?

in summer when you are asking for slab cooling how does it provide hot water? is it as simple as switching over from heating to cooling at different times (presumably with dhw taking precedent)?

[Jeremy Harris]

9 minutes ago, jfb said:

resurrecting an old thread  - can someone enlighten the unenlightened?

in summer when you are asking for slab cooling how does it provide hot water? is it as simple as switching over from heating to cooling at different times (presumably with dhw taking precedent)?

 

 

I set ours up with a motorised valve in the buffer tank loop (the buffer provides hot water preheat in our system).  This valve is normally open in heating mode, but closes when the ASHP is in cooling mode.  There's a tank thermostat that can over-ride the cooling mode and switch the ASHP to heating mode, opening the valve to the buffer in the process, if need be, so hot water always has priority.

[jack]

17 minutes ago, jfb said:

is it as simple as switching over from heating to cooling at different times (presumably with dhw taking precedent)?

 

Exactly that.

[ProDave]

The thing that makes it easy to understand is almost all heat pumps only ever heat hot water OR space heating, never both at the same time.  Mainly so it can operate at a lower temperature when space heating.  this fact alone makes it easy to run in cooling mode on the "heating" circuit when required.

 

Ours has a switched output for a motorised valve so you can use a different medium for cooling if you want to, e.g. a fan coil unit