Posted by: @Anonymous

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But that isn't the best way to run a heat pump. Weather compensation run 24/7 and if you need a very small nighttime setback of a couple of degrees only

Yeah I tried running 24/7 last year and it was very expensive, seemed to use a lot more gas, probably because we have no weather compared, causing short cycling at 50C flow rates.

Posted by: @jamespa

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If you do this take pictures and get receipts, you may need to get to convince installers it's been done unless the insulation remains visible.

Yeah, this isn't roof or wall insulation, bit hard to explain. Imagine the joists that separate the ground floor ceiling from the upper storey floor, the ends of those joists are just open to the outside air.  In fact they have a covering of tiles, but essentially that was the total insulation, just a tile.  This made the downstairs ceilings and upstairs floors very cold, but the upstairs floors are carpeted, so that made it less obvious. And let's be honest, how often do you touch the ceilings to see if they are cold, you don't, right?

So we have basically been losing warm air from downstairs almost directly to the sky.  I have lifted all the tiles, put rockwool insulation between the joists at the exposed ends.  It will be quite easy to open that up again to show anyone, though the guy that did our EPC nearly a decade ago when we got solar PV never bothered to look.

If you want to take advantage of the £7500 grant, you are subject to MCS calculation methods, so simulation or otherwise is pretty much a waste of time. If you intend DIY installation then that's a different story.

There are ways to test heat loss, how practical they are when you actually live in the house is questionable.

I don't really buy into the heat pump has to be perfectly sized, it has to be suitable. Getting a grossely oversized one is silly, also getting one too small equally silly.

So our house at -3 looses 3kW, at -9 nearer 3.5kW. so you would suppose a 4kW would be fine. But I have a 6kW which works just fine. It's not stressed it just ticks away as needed. Plenty of space capacity wise for DHW even at -9. Since it was installed we have added a summer house which we heat all year also. It has just been added to the house circulation circuit. ASHP still oversized, but happy.

Posted by: @Anonymous

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I don't really buy into the heat pump has to be perfectly sized, it has to be suitable. Getting a grossely oversized one is silly, also getting one too small equally silly.

I don't either, but nor do I buy into the idea that anybody should be forced to do unnecessary pipework upgrades, have an unnecessarily intrusive outdoor unit, or have to get planning permission where otherwise they might not have to.  It could even make the difference between getting planning permission or not and thus scupper the whole project.

Oversizing isn't just, or even primarily, about performance, it's about all the other things that go with it.  You are, I think, coming at this principally from the perspective of 3kW house with a 6kW heat pump.  That really doesn't make much difference in terms of these retrofit on effects.  In  a more typical  8kW retrofit, where the MCS brigade want to fit a 16kW, or even a 12kW heat pump, the difference can be massive!

Decisions should be based on the best facts available, not something principally designed to protect installers.

Posted by: @jamespa

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BS something or other is designed for new build where you know what the construction is, not retrofit where you don't, but hey-ho.

This is exactly why I'm trying to do a real world test simulation.  Our 1960s house has construction of different types in different places and it's impossible to properly estimate heat loss and air changes perfectly.  I'm trying to plug unintended draughts but without a full air pressure test it's unfeasible to really know.

Posted by: @jamespa

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Posted by: @Anonymous

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I don't really buy into the heat pump has to be perfectly sized, it has to be suitable. Getting a grossely oversized one is silly, also getting one too small equally silly.

I don't either, but nor do I buy into the idea that anybody should be forced to do unnecessary pipework upgrades, have an unnecessarily intrusive outdoor unit, or have to get planning permission where otherwise they might not have to.

Oversizing isn't just, or even primarily, about performance, it's about all the other things that go with it.  You are, I think, coming at this principally from the perspective of 3kW house with a 6kW heat pump.  That really doesn't make much difference in terms of these retrofit on effects.  In  a more typical  8kW retrofit, where the MCS brigade want to fit a 16kW, or even a 12kW heat pump, the difference can be massive!

Decisions should be based on the best facts available, not something principally designed to protect installers.

 

Exactly, they said 8kW for us, I need to try and see if that's legit.  I think it probably is, but it's getting that emitted into the places we need it is part of the issue.

We know the rads have 15mm copper flow & return.  We also know the boiler is connected with 22mm copper flow & return.  We know that 22mm pipe runs into the concrete floor.  We don't know how far the 22mm runs, and how long the 15mm pipes are, or how the branches are put together.  My thermal camera shows me where the pipes run, but pressure loss etc. is a mystery.

Posted by: @scalextrix

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Posted by: @jamespa

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Posted by: @Anonymous

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I don't really buy into the heat pump has to be perfectly sized, it has to be suitable. Getting a grossely oversized one is silly, also getting one too small equally silly.

I don't either, but nor do I buy into the idea that anybody should be forced to do unnecessary pipework upgrades, have an unnecessarily intrusive outdoor unit, or have to get planning permission where otherwise they might not have to.

Oversizing isn't just, or even primarily, about performance, it's about all the other things that go with it.  You are, I think, coming at this principally from the perspective of 3kW house with a 6kW heat pump.  That really doesn't make much difference in terms of these retrofit on effects.  In  a more typical  8kW retrofit, where the MCS brigade want to fit a 16kW, or even a 12kW heat pump, the difference can be massive!

Decisions should be based on the best facts available, not something principally designed to protect installers.

 

Exactly, they said 8kW for us, I need to try and see if that's legit.  I think it probably is, but it's getting that emitted into the places we need it is part of the issue.

We know the rads have 15mm copper flow & return.  We also know the boiler is connected with 22mm copper flow & return.  We know that 22mm pipe runs into the concrete floor.  We don't know how far the 22mm runs, and how long the 15mm pipes are, or how the branches are put together.  My thermal camera shows me where the pipes run, but pressure loss etc. is a mystery.

 

22mm is marginal for 8kW, or ok depending on whether you work on 1m/s max flow rate or 1.5 m/s.

Are there 2*22mm (eg upstairs and downstairs) or only 1*22mm.  

Take your annual gas consumption in kWh, divide by 2000h, That gives a very rough sanity check.

Posted by: @johnmo

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I don't really buy into the heat pump has to be perfectly sized, it has to be suitable. Getting a grossely oversized one is silly, also getting one too small equally silly.

 

Text below corrected (retrofit on should read knock on)

I don't either, but nor do I buy into the idea that anybody should be forced to do unnecessary pipework upgrades, have an unnecessarily intrusive outdoor unit, or have to get planning permission where otherwise they might not have to.  It could even make the difference between getting planning permission or not and thus scupper the whole project.

Oversizing isn't just, or even primarily, about performance, it's about all the other things that go with it.  You are, I think, coming at this principally from the perspective of 3kW house with a 6kW heat pump.  That really doesn't make much difference in terms of these knock on effects.  In  a more typical  8kW retrofit, where the MCS brigade want to fit a 16kW, or even a 12kW heat pump, the difference can be massive!

Decisions should be based on the best facts available, not something principally designed to protect installers.

Ps can you actually buy a 3kW heat pump that isn't a higher capacity one down rated?

Posted by: @jamespa

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22mm is marginal for 8kW,

Mostly depends on your circulation pump head losses etc. from pipe length and number of bends etc. There are ways around things. Buffers are looked as really bad things, but a well designed system they can be ok and a real advantage. I would rather a 2 port buffer and add a secondary pump, than have the house pulled apart. 

Simple chart, your dT will be 5 most likely 

Posted by: @scalextrix

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I'm thinking the secret to heat pumps is to try and have all the rad sizes matched to the rooms heat loss and then not use TRVs as much.  Oh and emitter balancing is key as well, our living room is last on the circuit and I think the heat isn't always getting there without the boiler cycling.  Just need some colder weather to rebalance it all.

All sound stuff apart from the TRVs - aim not to use them at all, except when you have no alternative (which should be rare, preferably never eg use the lock shield valve to get a room slightly cooler if that is what you want).

I'm with @jamespa on the problems with heat loss calcs (room and total), the spreadsheets make myriads of assumptions, and often don't include a dropdown entry for you particular circumstances etc etc. They are in effect what I call whatiffery (what if the walls are two metres thick and made of granite?) and chasing air changes is about as much fun as chasing gnats' f@rts. An empirical heat loss is almost always better (assuming it is not done by a lunatic) but it is always a total heat loss, and leaves room losses needing some guesstimation.

I think your gas consumption can give you a total heat loss, even with a fixed low temp, and modulation by cycling rather than weather compensation, provided you keep the IAT constant, ie no setbacks. In such circumstances, gas consumption should correlate fairly well with OAT. You could try adjusting energy use for boiler efficiency, to get the energy delivered to the house, and plot that against OAT. If the two are correlated, then the energy delivered when the OAT is at design temp (around -1 or -2 degrees C for me, yours may vary depending on location) is your design heat loss.

I did something similar, but using energy in, as part of the infamous setback discussion, and found the two were well correlated:

If I assume my heat pump is 300% efficient, then using the chart above, I can estimate my total heat loss at a design OAT of -1 degrees C to be 12kW which just happens to coincide with my carefully calculated (and guesstimated) ones. Other heat loss calculations from installers varied considerably, probably depending on how much whatiffery they did. The dispersion on the chart at lower OAT is most likely a reflection of more variable conditions (+/- wind chill/rain chill?, defrost activity etc). 

Care is needed in matching a heat pump to the heat loss. Often, manufacturers and sellers cheerfully quote a headline figure, but don't tell you that is what it can do on a fine day in spring. My nominal 14kW Midea unit can indeed do 14kW in warm weather, but come the colder weather, the output drops, and by the time it is around zero outside, it can only manage 11 point something kW, rather unfortunate given that is when I need the full 12kW. Most manufacturers do (sort of) publish their heat pump outputs at various OATs and flow (LWT) temps, but they tend to hide it away. My copy of Midea's data is in a password protected pdf with every page marked 'Midea CAC Confidential'. Hiding it away like this is a nonsense, it should widely available, on every brochure and every spec sheet. Not that not all heat pumps are as bad at low OATs as Midea (and Midea clone) heat pumps - the key thing is to check the data for the heat pump you are considering. Furthermore, the lower output at lower OATs isn't necessarily a deal breaker, what matters is that you know about it, and can factor it in.

Posted by: @Anonymous

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I

I would rather a 2 port buffer and add a secondary pump, than have the house pulled apart

Seconded. But do you reckon that the average MCS guy is going to give you the choice?

My underlying issue is that we are told what we 'must' have by most of the industry, based on inaccurate or incomplete data.  We are generally not allowed to make choices based on the best data available.   MCS is required for the grant (essential for many) and permitted rights (unless you want to take a massive risk or go through some hoops which may, or may not, be fringed with fire).   From an installer point of view MCS is essential otherwise they get no business.  So they have an effective stranglehold unless you are prepared to DIY, not take the grant and can get express planning permission.

Taking all this together it's wholly unacceptable.

Posted by: @jamespa

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Are there 2*22mm (eg upstairs and downstairs) or only 1*22mm. 

The current boiler has a single 22mm pipe, but as you suggest that splits into a 22mm feed for upstairs and a 22mm feed for downstairs.  That split occurs inside the airing cupboard so a new installation could have a larger diameter to an ASHP to feed them both if necessary.

If DT5 @22mm can carry 6kW as the chart suggested, that should be enough for each leg. Also the largest room has 2kW heat loss, but has two emitters which could be roughly equally sized, so they would easily be below the 2.75kW cap for 15mm.

After checking some utility bills, annual gas consumption is roughly 16000kWh, will be interesting to see if my insulation works reduce that at all.

This is where my experiment comes unstuck, because the current boiler has a DT11 and so that means the single 22mm feed is enough now, but not enough at DT5. As such I can't really tell if it would work.

Though if I balance my rads now, and create a DT5 across them all, that would be a way to test it?  But I would be limited to 6 kW down the single 22mm boiler feed...