Air Source Heat Pumps

zeupater

gterr wrote: »

.... but we are having difficulties getting a constant supply of warm water to the rads: we just get the odd burst of tepid water from time to time when the rads are demanding heat (TRVs fitted).

If we change the heat curve to V=30 C, H=60 C, we get sufficient warm water to the rads, but Worcester advise we will be losing some efficiency at this setting ....

Hi

Can you put a thermometer on one of the rads and measure what temperature 'tepid' is .... I would have thought that somewhere a little below skin temperature (35C-37C) would be tepid, so somewhere between 20C & 30C (?), so isn't that exactly where you would expect it to be with those settings ??? .... also what temperature are the TRVs upstairs set to ?? ...

HTH
Z

gterr

Hi there,

Thanks, yes I could certainly do that, but the problem isn't that the rad temperature is too low, but that it isn't constant. What's happening is that the radiator gets luke warm for maybe one minute, but then goes cold again, and not because of the TRV setting. It'll stay cold for half an hour than maybe there'll be another brief burst of tepid water in it, then go cold again, even if TRV set to max. At the higher heat curve setting there is a constant supply of warm water (probably at at higher than optimum temperature) to the radiators when they are calling for heat. I'd be very happy with the lower rad temperature if this could be maintained when they were calling for heat.

The control unit on the indoor bit of the heat pump tells me the flow tempereatures in real time - usually between 25 and 35 C.

zeupater

Hi

Is this when the system has been running constantly for a long time or not long after switching on ??

Z

gterr

We run the system 24/7. We back off the U/F heating timer/stats by 2 degrees at night time and in the middle of the day. The radiator circuit is on its own timer: comes on a couple of hours in the morning, and from 4.30 to 10.30 evenings. We only have 4 rads. The bathroom one's TRV is set to max, one study-bedroom's TRV normally set to II to III, the other two rads set to I.

The system gives priority to domestic hot water, so if someone were to have a bath, for instance, we might expect the temp of heating water to fall temporarily, but what we are observing with the radiators isn't linked to this.

zeupater

Hi

If you reduce the undefloor thermostat so that the U/F circuit shuts down do the radiators upstairs heat up then ??

Z

gterr

Don't know. I will try this out. Thanks for the idea.

Do you think this mixing valve set at 50C has any bearing on the problem?

[Deleted User]

gterr wrote: »

Don't know. I will try this out. Thanks for the idea.

Do you think this mixing valve set at 50C has any bearing on the problem?

Very briefly, reading into the supplied information...

It sounds as though the ASHP is heating the ufh/rads directly i.e. not through a thermal store or similar which is heated to a high temp and various heating circuits can be mixed down to the temp required.

So basically you have answered your own question.... TRVs do not directly call for heat and the mixers you are possibly referring to will limit the maximum temp the to the ufh which is fine.

The problem is the heat curve... at mild temps the heat pump is simply not producing hot enough water for conventional rads to work as expected. Two types of heating effectively on the same circuit...

For example, often people put towel rails in bathrooms on the same circuit as the ufh as that is the main heating source, the rail will get mildly warm but never hot enough to heat a room. Its there to look nice and hang towels on...

Perhaps also check flow rates, faulty pumps just to be sure etc

A long term solution may be to replace conventional rads with fan convectors which work at low temps like ufh.

Cardew

The series of posts from #1101 onwards demonstrates a major failing of ASHPs as highlighted in the EST trial report – namely the difficulty of the end user in understanding the operating instructions and/or getting the system to operate efficiently.

The poster(gterr) obviously has good grasp of the principles of heat pumps, but is floundering. If he gets the system ‘adjusted’ to provide adequate heating and hot water he has no way of knowing or measuring the ‘penalty’ in a lowered overall COP.

To make matters worse, settings that work during a mild November could be totally inadequate in a cold January.

I dread to think of how some of my acquaintances would fare if faced with the need to operate an ASHP system, with gas CH they think a combination of room thermostat and TRVs is over-complicated!

It will be interesting to see what comes out of the extended EST trial in the way of recommendations. It seems to me that it is imperative that the Heat Pump manufacturers take responsibility in the commissioning of their equipment and not simply sell units to installers of unknown expertise. The suggestion above for a 'long term solution' (if necessary) is a perfect example!

[Deleted User]

Cardew wrote: »

The series of posts from #1101 onwards demonstrates a major failing of ASHPs as highlighted in the EST trial report – namely the difficulty of the end user in understanding the operating instructions and/or getting the system to operate efficiently.

The poster(gterr) obviously has good grasp of the principles of heat pumps, but is floundering. If he gets the system ‘adjusted’ to provide adequate heating and hot water he has no way of knowing or measuring the ‘penalty’ in a lowered overall COP.

To make matters worse, settings that work during a mild November could be totally inadequate in a cold January.

I dread to think of how some of my acquaintances would fare if faced with the need to operate an ASHP system, with gas CH they think a combination of room thermostat and TRVs is over-complicated!

It will be interesting to see what comes out of the extended EST trial in the way of recommendations. It seems to me that it is imperative that the Heat Pump manufacturers take responsibility in the commissioning of their equipment and not simply sell units to installers of unknown expertise. The suggestion above for a 'long term solution' (if necessary) is a perfect example!

I agree the system here is basically a compromised design. Looks to me like the sort of system that would work fine with say GCH but not a heat pump. From what you are saying I'm guessing manufacturers would have to sign off designs a prior to install?

The way the heat curve works the system is likely to work fine when the temp outside drops but at the moment although not that cold it would be nice to have warm rads which the system is not really set to deliver without making it less efficient.

My longer term recommendation would balance the system and maintain COP. I've never understood using conventional rads with an ASHP set to work efficiently. Happy to write a paragraph on this if required...

EDIT: I should have mentioned timers... It is perfectly ok to have timers for different types of heating on what is basically the same circuit as long as they work at the same temp or have a mixer limiting the max temp for one timed zone e.g. ufh in bathroom.

grahamc2003

gterr wrote: »

Hi there,


For best economy we've been advised to set the heat curve to have a flow temp of 20 C when outside temp is 20 C, ("V")and a flow temp of 55 C when the outside temp is -30 C ("H", theoretical, obviously). This setting works fine for the U/F heating, and the domestic hot water is about 50 C which is also fine, but we are having difficulties getting a constant supply of warm water to the rads: we just get the odd burst of tepid water from time to time when the rads are demanding heat (TRVs fitted).

If we change the heat curve to V=30 C, H=60 C, we get sufficient warm water to the rads, but Worcester advise we will be losing some efficiency at this setting.


Any thoughts would be most welcome!

My thoughts are that, surely, the multitude of settings aren't for the end user are they? Without knowing in detail exactly what these settings actually change within the heatpump, then I can't see how end users can control them. Or the non-ultra-specialist installers for that matter. The ultra-specialist, or manufacturer installers may be able to 'suck and see' a bit better than most, but I bet most of them end up scratching their head most of the time. Heat curves? Sheesh - just been reading another thread where someone is asking if they heat their house and water with their gch, is it more expensive than heating just the water!

I'd say press the 'factory default reset' button if you can find it, if it has one. If it has a 'winter' mode, select that (but why they don't know it's winter anyhow beats me). As to running 'efficiently' - I'd estimate that yourself by watching carefully how much electricity the system uses, and balance that against whether the house is warm enough and the outside temperature. I suspect a small change in one of the setting could have a large change in efficiency.