York Heatpumps - any experience?

[Beelbeebub]

EDIT: I've just re-read the spec sheet and the 5,7,9kw units *all have the same charge* 1.25kg!

 

So it looks like they are all physically identical and have the same charge.....so what is the difference (apart from price)?  Surely the performance should be identical in all regimes? 

 

 

I'll ask next time I speak to technical.

[JamesPa]

1 hour ago, Beelbeebub said:

So it looks like they are all physically identical and have the same charge.....so what is the difference (apart from price)? 

Standard practice in some industries for some time.  Sell the same physical product at different prices with software imposed limits. 

 

The issue of course, as you point out, is that the minimum output doest scale with the max.  Relatively few manufacturers seem to be open about modulation capability, a few more will tell you if you ask, and some won't tell you at all.  Pretty disgraceful as it's a key parameter in proper system design (although much of this industry doesn't know about proper system design).

Edited July 28, 2023 by JamesPa

[JohnMo]

So in practice does that mean they really just change the running speed to get different capacity ratings. So although they could be the same unit, the 5kW would near silent, the big one not so?

 

Or is it the small one has next to no modulation, while the big one can modulate down to about 4 to 4.5kW?

[JohnMo]

I suppose going back to my previous post about cool energy, at least the advertising is clear about modulation.

 

@JamesPa have you asked them (Cool Energy) about a heat pump, as with another thread they do MCS installs and seem amiable to a different approach?

[JamesPa]

54 minutes ago, JohnMo said:

@JamesPa have you asked them (Cool Energy) about a heat pump, as with another thread they do MCS installs and seem amiable to a different approach?

I havent.  Their 4.3-9.5kW model is sadly really marginal for my application (8.5-11kW MCS, depending on assumptions, 7.5kW measured, 45C flow temp) and larger models are, well larger ie 2 fan, which doesn't fit the space I have. 

 

But I've just noticed that the 5.52kW-10kW model is now available again so I will.  If my interpretation of the spec is correct modulation ratio is not great though.  I will ask as they seem to be using good components so it should surely be better.

Edited July 28, 2023 by JamesPa

[Beelbeebub]

1 hour ago, JamesPa said:

I havent.  Their 4.3-9.5kW model is sadly really marginal for my application (8.5-11kW MCS, depending on assumptions, 7.5kW measured, 45C flow temp) and larger models are, well larger ie 2 fan, which doesn't fit the space I have. 

 

But I've just noticed that the 5.52kW-10kW model is now available again so I will.  If my interpretation of the spec is correct modulation ratio is not great though.  I will ask as they seem to be using good components so it should surely be better.

Habe we been looking at modulation a bit wrong?

 

AFAIK we.look at the max power at a given outside temp and the.min power and then call that the ratio

 

So for the vaillant another 5kw

 

 

AT -7 the max power is 5.6kw and min is 1.6. a pretty impressive 3:1 of max. At 0C it's even better, 6.9->1.6kw or near 4:1

 

But shouldn't we be taking the minimum at a higher temp? After all that is when you actually will need to modulate down.

 

So the arotherm at 15C is 2.5kw minimum, so a less impressive 2:1(ish).

 

To some extent it depends where you take your min and max temps, the modulation from -2 to 10 is going to be better than -7 to 15.

 

 

We often see this image, showing the falling HP max capacity as outside temp falls and heat demand increases.

 

 

 

But maybe that graph needs the lowest power output at a given temperature shown. Then you can also see at what temperature you heatpump needs to start cycling as hearing demand falls below minimum output.

 

[Beelbeebub]

Basically this diagram, where green is lower limit and purple the "cycling zone"

[JamesPa]

15 minutes ago, Beelbeebub said:

But shouldn't we be taking the minimum at a higher temp? After all that is when you actually will need to modulate down.

Yes.  The interesting figure (at least to me) is max at -2 (or whatever your design min is) vs min at (say) 12.  Above (say) 12 you are going to be on-off heating anyway, or more likely daytime heating only which will help with the numbers.  So with the graph you present above 6.5:2.2 (120rps @ -2 vs 30rps @ 12, about 3:1 which seems quite common for the better models (at least those that bother telling you).

 

Of course if the pump is massively oversized much of the available modulation ratio will be used up at the lower end, which is where buffers come in with all the problems they bring, and right-sizing is preferable.

 

Its a pity that there isn't a requirement to specify modulation ratio in a useful way.

Edited July 28, 2023 by JamesPa

[JohnMo]

Heat pumps are rated and sold to suit the supplier. They always produce loads of heat when it's warm, which diminishes as the OAT drops.  This is why they (MCS and others) say size for 99.6% of the year. So you are not oversizing. Oversizing is never an issue when it's cold, but is an issue when it's normal winter temps sort of around 5 to 10 degs. You need way less heat, but your heat pump is producing way to much power even at min turn down.

[JohnMo]

38 minutes ago, JamesPa said:

which is where buffers come in

Or simpler, cheaper is to keep radiators or UFH loops engaged to match the ASHP suppliers min water volume. So a 5kW ASHP even without modulation, with about 50L engaged will be quite happy and not short cycle at about 0.5kW heat demand.

[Beelbeebub]

3 minutes ago, JohnMo said:

Or simpler, cheaper is to keep radiators or UFH loops engaged to match the ASHP suppliers min water volume. So a 5kW ASHP even without modulation, with about 50L engaged will be quite happy and not short cycle at about 0.5kW heat demand.

How does that work?

 

If you house needs 1kw to stay at 20C and your HP can only modulate down to 2kw, either your house eventually warms up or your HP has to shut off for a while.

 

The only way I can see system volume helping is if it is large enough to act as a.thermal store in it's own right *and* you can keep circulating it even when the compressor is off. 

 

I can see how that might work with an external pump system like a Samsung, you could have a 3way valve that bypasses the heatpump and just circulates the water until it cools sufficiently, but how would that help with monoblocks with built in pumps?  Or do they do just that?

[JohnMo]

Heat pumps stop and start heating just like boilers do, but the circulation pump continues to run. Controlled stop starts of the heating cycle are fine so a run time of circa 10 mins or more is fine. Anything shorter is short cycling and wastes energy.  The working volume of water is the prime reason for ok cycling or short cycling. Various formula are available to calculate the min working volume and cycle times.

 

So if you are heating rate is fixed, the more water you have to heat the longer it takes. So can either install a buffer or keep system volume engaged by have a single or a couple of large zones.

[Beelbeebub]

47 minutes ago, JohnMo said:

Heat pumps stop and start heating just like boilers do, but the circulation pump continues to run. Controlled stop starts of the heating cycle are fine so a run time of circa 10 mins or more is fine. Anything shorter is short cycling and wastes energy.  The working volume of water is the prime reason for ok cycling or short cycling. Various formula are available to calculate the min working volume and cycle times.

 

So if you are heating rate is fixed, the more water you have to heat the longer it takes. So can either install a buffer or keep system volume engaged by have a single or a couple of large zones.

So whilst the compressor is.off, the water pump continues - sort of like overrun on a boiler?  Presumably there is a.bitmof loss of heat as the water is flowing outside the thermal envelope and through the plate heat exchanger and back for the "off" period but it's negligible?

[JohnMo]

A little worse than a normal internal boiler, no worse than an external oil boiler, possible a lot better due to the lower flow temps.

[JohnMo]

Heating cycle of my ASHP

 

[dpmiller]

^ and all this stuff is configurable in the better stuff (or in some cases likely uses fuzzy logic to get ahead of the game a wee bit)

 

eg with CoolEnergy an overshoot temp can be added to the PID control, so that it has more time to ramp down power and is likely to do a hard shutoff. Conceivably this reduces reliance on a buffer.

[Beelbeebub]

6 minutes ago, dpmiller said:

^ and all this stuff is configurable in the better stuff (or in some cases likely uses fuzzy logic to get ahead of the game a wee bit)

 

eg with CoolEnergy an overshoot temp can be added to the PID control, so that it has more time to ramp down power and is likely to do a hard shutoff. Conceivably this reduces reliance on a buffer.

Reducing the need for a buffer would seem to be a good thing for heat pumps.

 

It's an additional thing to buy, find space for and fit.

 

It seems to me the big issue is basically the thermal inertia of the house (including the heating system) and a buffer is just adding thermal inertia to the heating system.

 

A buffer is an easy way to add thermal mass to the system *if it is needed*.

 

If you have UFH that should act as a buffer vessel. 

 

I think there is mileage in using the DHW tank as a buffer vessel in some cases (mainly where there is a higher flow temp like a retrofit)

 

Maybe it's time to being back cast iron radiators! 😁

 

[JamesPa]

15 minutes ago, dpmiller said:

^ and all this stuff is configurable in the better stuff (or in some cases likely uses fuzzy logic to get ahead of the game a wee bit)

Just like flow temp is on condensing boilers.  And what did installers do with those....just saying!

[JohnMo]

15 minutes ago, dpmiller said:

configurable in the better stuff

I think it would have to amendable in all cases. Certainly on mine I can change every control point and the curve.

[JohnMo]

But as @JamesPapoints most installer install and walk away.

 

7 minutes ago, Beelbeebub said:

If you have UFH that should act as a buffer

Only if you have a large volume of water engaged. The floor absorbs heat slowly a small circuit will not stop short cycling.

 

9 minutes ago, Beelbeebub said:

there is mileage in using the DHW tank as a buffer

If you design for poor CoP, otherwise it's a bad idea.

 

10 minutes ago, Beelbeebub said:

being back cast iron radiators

First heat cycle will be good as a ready source to a sorb heat, but once heated, it just a radiator what goes in comes out

[JamesPa]

17 minutes ago, JohnMo said:

I think it would have to amendable in all cases. Certainly on mine I can change every control point and the curve.

Agree.  I was just observing that we can't trust the industry to do a good job.

 

For what it's worth my house measured consumption was 7.5kw at the coldest point last winter, and most of the time sat at a steady 4-5kW.  It dipped below this only at the end of the season by which time I was on part time heating anyway.  So for my specific circumstance, as long as a hp gets to 4kW without cycling, a little above half the peak, that's ok.  Other houses will be different of course depending on thermal mass, but mine is nothing special in heating or insulation terms so quite a few may be similar.  2:1 is easily achieved, but not if the unit fitted is well oversized!

 

Also it's not binary, if the hp modulates down to 4 and the demand is 3 then the hp needs to be on 3/4 of the time.  So long as there is enough system volume this shouldn't cause excessively short cycles.  The excess power in this case is only 1kW so it will cycle only after enough energy is delivered at 1kW to heat the water above the overrun limit.

Edited July 29, 2023 by JamesPa

[DanDee]

17 minutes ago, Beelbeebub said:

Maybe it's time to being back cast iron radiators! 😁

This mupp done it because the lady of the house wanted the look, people are telling him they are 9 time more expensive per kW output than double panel rads, he is arguing that they are only twice more expensive. To sum up his video, he orders the wrong size, he thinks it has a bigger output that the reality, he is telling people the wrong info, he doesn't even mention the benefit of the extra volume of water.

 

[DanDee]

22 minutes ago, Beelbeebub said:

It seems to me the big issue is basically the thermal inertia of the house (including the heating system) and a buffer is just adding thermal inertia to the heating system.

 

A buffer is an easy way to add thermal mass to the system *if it is needed*.

 

If you have UFH that should act as a buffer vessel. 

The ideal building for inertia would be brick and concrete, no wood in between levels but concrete, with external insulation.

 

UFH in concrete all around doesn't need a buffer.

 

In addition to a DHW tank a second tank with a very large coil, splitting the volume in half would be ideal for a big family with the second tank acting half as a buffer and the other half pre warming the DHW.

[DanDee]

18 minutes ago, JohnMo said:

First heat cycle will be good as a ready source to a sorb heat, but once heated, it just a radiator what goes in comes out

 

It would actually be the perfect in room buffer, for the spring/autumn seasons.

[DanDee]

Did anyone looked into the fact that once the heat requirement is under the minimum output of the HP, it shouldn't be allowed to try and weather compensate, but just be controlled as a boiler, on a fixed low flow temp? This part of the automation seems to work great only when the output/requirement can match, for the rest of the time it just starts and stops every 5(random number) minutes.