Improving an "ok at best" ASHP installation

[pstunt]

Hi,

We have now been living in our "nearly" finished stable conversion for about 6 months. It's a very long and thin building, single story and about 360 sqm with UFH screed floor throughout. Heat is provided by a Grant Aerona 3 17KW ASHP and we do have the option of a LPG ( no mains here ) powered combi if required ( We are quite rural and powercuts for a few days are not uncommon so have small generator for critical stuff ) 
The UFH has 3 manifolds with their own pumps feeding 16 zones ( 26 circuits )  with a wall thermostat for each. The zones and the UFH were designed by a company by Omnie but the ASHP was chosen, supplied and fitted by our builder / plumber and in my view is probably not the greatest installation. There was no real commissioning / balancing or handover and everything I have leant to do is pretty much from you guys here. 

Currently I have effectively all the feeds of 2 of the manifolds permanently open by setting the wall stats to 23c, running the pump 24/7, and adjusting the valves to get the required temperature for that room, the manifold feeding the bedrooms is still controlled by the room stats as we generally have the bedrooms a lot cooler. When I am little more confident I am doing the right thing I guess I can do the same as the other manifolds.

 

The Grant Aerona 3 is not the most user friendly device but I currently have the maximum LWT at 32c and lowest RWT at 27c. I todays milder but weather of 5c it was showing LWT 30c and RWT 28c. I think I am right in saying that is a delta of 2. 

 

I have no idea if this truly the best approach as opposed to setbacks etc. I am also unable say what the actual cop / scop is, as that information is not readily available with this unit. I can say that during that very cold day last week of -5 we used 69 KWh. There were not any formal heat loss calculations carried out. I have only become aware of such things fairly recently. I was simply reassured at the time by my builder that it was the right choice. Like many of you, I have learnt so much in hindsight.

 

I would love to hear views on how I could improve things. I dont even know if I can. One thing I have noticed is that I don't have a flow meter on the return leg to the HP and I dont know if that is a big issue / oversight by the installer. I am guessing this may be key to getting a balanced system and possibly working out the cop ? 

I was wondering if the delta of 2 degrees is too small ? I have read that a good delta is about 5 degrees and I seem to recall the Grant manual suggest 6 degrees but I am getting well out of my depth here as far as knowledge and understanding. 

 

 

 

[SteamyTea]

Before getting bogged down in arithmetic and heat pump settings, do you know how much insulation is under your floor where the UFH is?

[BotusBuild]

Hi. A stable conversion implies that you probably had to add in whatever insulation, air tightness etc. into the building. As you know the quantity and quality of the insulation added, and the level of air tightness you have achieved will be key to how much of the energy you are putting into the building is being retained, and for how long (during that cold snap, energy would have been flowing out of all buildings quicker than normal).

 

If you have not had a heat loss calculation done already, I would have one done to begin with, then at least you will know where you stand with regards the system you have installed. Most importantly this will also tell you whether the Grant ASHP that you have is sufficient to provide the energy input your building requires. Until you know this, fiddling and fettling with the rest of the system should be avoided.

[JohnMo]

Couple questions

buffer yes/no

Weather compensation yes/no

 

When you measured the dT of 2 was the heat pump on an on cycle, just starting or just stopping?  You don't normally have any control dT, as it's managed by the heat pump.

 

28 minutes ago, pstunt said:

don't have a flow meter on the return leg to the HP

Why would you need it?

[sharpener]

23 minutes ago, pstunt said:

I can say that during that very cold day last week of -5 we used 69 KWh.

 

If that is over a 24 hr period it is less than 3kW continuous equivalent.

 

Supposing you were getting a CoP of 3 it represents 9kW heat loss inc DHW. That is around 50% of the HP rating.

 

For 360 sq m it is also 25W/sq m which if you are getting OK room temps at -5 OAT sounds as though you have not got anything much to worrry about. Keep on fine tuning as you are already doing.

 

Someone recently posted a link to the Chofu manual (sorry can't find it) which has a lot more stuff on the Grant Aerona HP which is the same thing re-branded and dumbed down.

 

 

[pstunt]

51 minutes ago, SteamyTea said:

Before getting bogged down in arithmetic and heat pump settings, do you know how much insulation is under your floor where the UFH is?

Yes, mostly 100mm PIR but 150mm in some. I would have done more if I had my time again.

 

48 minutes ago, BotusBuild said:

Hi. A stable conversion implies that you probably had to add in whatever insulation, air tightness etc. into the building. As you know the quantity and quality of the insulation added, and the level of air tightness you have achieved will be key to how much of the energy you are putting into the building is being retained, and for how long (during that cold snap, energy would have been flowing out of all buildings quicker than normal).

 

If you have not had a heat loss calculation done already, I would have one done to begin with, then at least you will know where you stand with regards the system you have installed. Most importantly this will also tell you whether the Grant ASHP that you have is sufficient to provide the energy input your building requires. Until you know this, fiddling and fettling with the rest of the system should be avoided.

 

Perhaps I have got my descriptions wrong. I believe there were no heat / loss calcs. before installation. Recently, I have had the EPC done which took into the account the insulation etc. but I didnt think the information on the final document / or the work sheet gave you the heat calcs.

 

45 minutes ago, JohnMo said:

Couple questions

buffer yes/no

Weather compensation yes/no

 

When you measured the dT of 2 was the heat pump on an on cycle, just starting or just stopping?  You don't normally have any control dT, as it's managed by the heat pump.

 

Why would you need it?

 

No buffer direct to the slab / screed.
Weather compensation on.

Yes, it was operating at it's normal cycle. Not stopping or starting. I will have a look again in a while but it's just coming off it's DHW cycle right now.

Not sure as to why I need the delta but in the manual it says the following when trying to balance the system: " With the system flow temperature approaching its set value, check the temperature difference between the flow and return pipes connected to each heat emitter on the system, starting with the emitter closest to the heat pump. • In the case of a Grant Aerona³ heat pump, this temperature difference should be approximately 6 to 8°C " 
Literally the only hand over advice I got was to "keep the red discs of the circuit valves somewhere in the middle"

Edited January 23 by pstunt

[pstunt]

48 minutes ago, sharpener said:

If that is over a 24 hr period it is less than 3kW continuous equivalent.

 

Supposing you were getting a CoP of 3 it represents 9kW heat loss inc DHW. That is around 50% of the HP rating.

 

For 360 sq m it is also 25W/sq m which if you are getting OK room temps at -5 OAT sounds as though you have not got anything much to worrry about. Keep on fine tuning as you are already doing.

 

Yes, it was over the full 24 hours.

 

We were getting ok temperatures. I reckon I could have raised the max LWT from 32 a degree or so if I was totally reliant on the HP but we also have a log burner in the open living area, which can top up when needed. We live on a farm so no shortage of wood. However, as much as I love the burner it can way too much at times.

Reassuring to hear that it's not too bad. I have no idea how the performance fairs.

[Beelbeebub]

Just a thought.

 

A return water temp of 28C implies either your slab is at 28C - that is pretty warm for a floor slab, what are your floor finishes? My bare concrete slab hits maybe 24C for a 20C air temp though we are very well insulated. If you have wood or carpet then your slab temp. May be higher but 28C is the recommended max floor temp for UFH so I would be surprised. 

 

The other option is that the flow is too fast for the water to give up enough heat.

 

Have you checked the flow rates? I believe the Grant installation kit has a flow adjuster with a sight glass in it so you should have an idea. The Aerona Heatpumps come from the factory with the pump configured for maximum. Grant say this is almost always too high and usually needs to be set back to med or low.

 

If your builders aren't very knowledgeable about the HPs, they may have missed that step. 

 

Combined with the fact the bedroom zones are mostly off, the flow in the other zones will be higher than may have been set anyway. 

[pstunt]

14 hours ago, Beelbeebub said:

A return water temp of 28C implies either your slab is at 28C - that is pretty warm for a floor slab, what are your floor finishes? My bare concrete slab hits maybe 24C for a 20C air temp though we are very well insulated. If you have wood or carpet then your slab temp. May be higher but 28C is the recommended max floor temp for UFH so I would be surprised.

I think you may have given me an idea what the issue may be. I checked the figures this morning and the flow and return were 30/28 c respectively but the temperature of the tiled floor was about 23c with a 19.5 room temp. The  flow and return at the individual pipes of each circuit on the manifiold was 29 / 24. (ish) I was using a laser thermometer on the pipes and floor to these figures so they are only rough guides but the flow and return values from the HP come from the device itself.

I will get some pictures to explain this better when I can but there seems to be some kind of pipework loop with the combi bolier, coupled with some valves which seem to be pressure adjustable ( sorry for the poor description but pics to follow ) and perhaps allowing some of the warmer water to return too soon. Hence the return value being too high. It could of course be the HP reporting a dubious value but I can try and put the laser thermometer at the different points on the pipe work as a guide.