Ground Source Heat Pumps

DazzlerDazza

beardymarrow said:

It definitely is trial and error, and that's a pain. Cynically, my suspicion is that installers will set it to a level that means the occupants aren't going to call them back out because the house is too cold, and not worry too much about the COP, as that won't impact the installer.

Yeah, I could believe that! Installers probably aren't going to want to be continually hassled by tweaking these settings 

One thing, you said you had to increase the fine because it wasn't warm enough at close to zero? It should have been the slope that was increased to achieve that, and then possibly the fine reducing a bit if that caused the temp to be too hot at warmer external temps?

Hmmm... but by increasing the slope, you will get even more heat (relatively) as outdoor temp decreases i.e. the slope / gradient is the rate of change of required heat with respect to outdoor temp. So it would increase the heat around zero... but it would also increase it at even lower temperatures too, further along the curve - which is not what I needed. When it was really cold, I found that the heat produced was just right.

It seemed logical that what I needed to do was to increase the fine so that the heat around zero was higher, but then lower the slope so that the rest of the curve adjusted accordingly, and not over producing heat.

I'm in the process of knocking up a simple curve simulator so I can play with curve / fine settings and visualise the impact of different combinations. Just struggling to find any spare time...

beardymarrow

DazzlerDazza said:

Hmmm... but by increasing the slope, you will get even more heat (relatively) as outdoor temp decreases i.e. the slope / gradient is the rate of change of required heat with respect to outdoor temp. So it would increase the heat around zero... but it would also increase it at even lower temperatures too, further along the curve - which is not what I needed. When it was really cold, I found that the heat produced was just right.

It seemed logical that what I needed to do was to increase the fine so that the heat around zero was higher, but then lower the slope so that the rest of the curve adjusted accordingly, and not over producing heat.

I'm in the process of knocking up a simple curve simulator so I can play with curve / fine settings and visualise the impact of different combinations. Just struggling to find any spare time...

Got ya. Yes, you're absolutely right, and increasing the fine and lowering the slope was correct. My bad. I missed the bit where you said "Heat at very low temperatures was never a problem." in the original.

DazzlerDazza

With regards the trial and error nature of this...

Coming from a software development world, you'd perform testing under a range of different inputs to validate you are getting the expected outputs.

Unfortunately we can't generate environmental conditions (outdoor temp, wind, sun etc.) on demand so we can't easily calibrate the system for key conditions. I guess we'd need someone with some higher-level powers to arrange that for us

beardymarrow

DazzlerDazza said:

I'm in the process of knocking up a simple curve simulator so I can play with curve / fine settings and visualise the impact of different combinations. Just struggling to find any spare time...

I've built my own Arduino GSHP controller, so reverse engineered the formula

Temp Target = ((20 - OutdoorTemp) * Slope / 6.25) + 20 + FineTune + ((RoomTarget - RoomTemp) * RoomInfluence).

Here's a Rego simulator (not written by me) -https://u.pcloud.link/publink/show?code=XZAxVhVZ3F6aRfUIEsFGfR8u6sSQkHVOE87k in case that's useful too.

lstevensuk

beardymarrow said:

Strummer22 said:

I wonder if it's not quite as simple as adjusting it until it's the 'right' temperature inside. Your thermostat should take care of that. The lower the weather compensation curve is set, the cooler the radiators/UFH and the longer the heating will need to be on to reach the thermostat temp. If your heating is on constantly and your house does not reach the thermostat temp, then the compensation curve is definitely too low and should be increased.

Because heat pumps are most efficient at low flow temperature, the weather compensation curve should be set to the lowest level that will still heat the house (even if that takes hours, assuming you're okay with that) as that will use the least electricity. 

Hello. I think it is that simple (in concept). The thermostat is really in my opinion for tweaking the internal temp, for example if you have a secondary heat source (fire place) or it's a very sunny, but cold day. The pump should be able to usually keep the house temperature stable based on the external temp. The thermostat works by increasing the required rad return when the internal temp drops, it doesn't switch the GSHP on and off as a normal gas boiler one would.

If the curve is set lower than ideal, then :-
The GSHP will cycle as it will easily be able to hit the required rad return temp, remember the IVT pump is on or off, not variable like some newer GSHPs.
The internal temperature in the house will gradually drop over a few hours as not enough heat is being input for stability
The pump will then increase its rad return target in response and work harder to get to that.
The internal temperature in the house will gradually rise as more heat is being input
The GSHP will drop its target rad return
Everything will eventually stabilise, but this will take hours, if not a day, by which time the external temp will have changed and the whole thing starts again.

This will repeat as external temperatures increase and decrease.

In my opinion, the curve should be set to be correct, and then internal thermostat then tweaks it, otherwise you end up with rad returns too low and too high alternately, rather than a more stable average temperature.

I have seen this myself. If I set my curve too low or too high, the internal temp fluctuates and gets compensated for by the internal thermostat. When it's correct, it's usually stable.

Are you using the room influence setting at all? Mine is currently set to 0 due to us waiting to have a radiator installed in that area.

Thanks @Strummer22 that's exactly what I was trying to ask. Is it better to have it at a low (currently I'm on 4.6 and +0.5) or boost that up and see if the UFH can get hotter. That room takes about 6hrs from 15c to 19c if I'm lucky at the moment.

Also thanks @DazzlerDazza that's very interesting that your curve is much higher than mine. What sort of temps is that hitting?
I asked the engineer at Alto same thing - he said just watched the odd video on YouTube! In fact he turned my heat curve down to 4.5 from 4.7 without even knowing my inside temps and what setup I have!

lstevensuk

DazzlerDazza said:

With regards the trial and error nature of this...

Coming from a software development world, you'd perform testing under a range of different inputs to validate you are getting the expected outputs.

Unfortunately we can't generate environmental conditions (outdoor temp, wind, sun etc.) on demand so we can't easily calibrate the system for key conditions. I guess we'd need someone with some higher-level powers to arrange that for us

Same world for me   Maybe we could come up with some tables of data to have a play.

Where does everyone have their outdoor thermostat? Mine is sat inside a barn next to the pump, should it be on the external wall?

beardymarrow

lstevensuk said:

Are you using the room influence setting at all? Mine is currently set to 0 due to us waiting to have a radiator installed in that area.

Yes, I'm using the room influence, set at 5. We have a wood burner in the room next to it, so need to otherwise the heat pujmp would carry on heating the house even when we have the log burner on. You definitely don't want it on, until you've got a rad installed.

I did a few weeks back have a blockage in the rad nearest to the temp sensor when it was really cold outside and that room got gradually colder and colder and the heat pump demand went money poo overnight trying to heat it :-)

beardymarrow

lstevensuk said:

DazzlerDazza said:

With regards the trial and error nature of this...

Coming from a software development world, you'd perform testing under a range of different inputs to validate you are getting the expected outputs.

Unfortunately we can't generate environmental conditions (outdoor temp, wind, sun etc.) on demand so we can't easily calibrate the system for key conditions. I guess we'd need someone with some higher-level powers to arrange that for us

Same world for me   Maybe we could come up with some tables of data to have a play.

Where does everyone have their outdoor thermostat? Mine is sat inside a barn next to the pump, should it be on the external wall?

Mine is on an external north facing wall (so it doesn't get the sun). Barn would be OK if the internal temp of the barn reflects the outside temp. If it's fairly enclosed the temp might lag the outside temp.

beardymarrow

Oh, and get yourselves a Husdata H66. It's an absolute god-send for tweaking stuff (and no, I'm not on commission :-)) graphing the results etc. I used to have an H20 which serial connected to my home PC, but the H66 is standalone (and talks MQTT if you want to integrate into Home Assistant or whatever). House data, Your heat pump in the smart home - Your heat pump in the smart home (husdata.se)

DazzlerDazza

beardymarrow said:

I've built my own Arduino GSHP controller, so reverse engineered the formula

Temp Target = ((20 - OutdoorTemp) * Slope / 6.25) + 20 + FineTune + ((RoomTarget - RoomTemp) * RoomInfluence).

Here's a Rego simulator (not written by me) -https://u.pcloud.link/publink/show?code=XZAxVhVZ3F6aRfUIEsFGfR8u6sSQkHVOE87k in case that's useful too.

Fantastic I'm trying to remember if you've mentioned this before... Did you reverse engineer this from Rego microcode or just from the curve charts in the manual + knowledge of how the internal influence works?

There's some great knowledge on this forum, I just wish I had a bit more time to spend on it.

I assume you all saw the BBC News article the other day about heat pump geeks?

https://www.bbc.co.uk/news/business-64261457

The OpenEnergyMonitor stuff they are doing looks interesting:

https://heatpumpmonitor.org/

In order to calculate COP, however, am I right in thinking that you'd need to install an expensive heat meter (flow rate + temperature)?

@lstevensuk my outdoor sensor is on a North facing wall, out of the sun and wind, and my internal influence is set to 2