ASHP in a new build - any advice, dos or donts to a complete newbie

[ProDave]

For the wanting "cool bedrooms" this is where no heating at all upstairs works.  Some heat will leak upstairs but it is easy to keep a bedroom at 18 degrees with the downstairs at 20.  Manage the heat flow upstairs by keeping bedroom doors closed when you don't want any more heat going up.

[mjc55]

9 minutes ago, ProDave said:

For the wanting "cool bedrooms" this is where no heating at all upstairs works.  Some heat will leak upstairs but it is easy to keep a bedroom at 18 degrees with the downstairs at 20.  Manage the heat flow upstairs by keeping bedroom doors closed when you don't want any more heat going up.

We are building single storey!

[IanR]

6 hours ago, AartWessels said:

Which will happen in an airtight house with mvhr anyway. 

 

Not in my airtight (<0.1 ACH) house with MVHR. I choose to have the bedrooms slightly cooler than living areas, and office slightly warmer.

 

2 hours ago, mjc55 said:

So, would the one-zone solution work given that?

 

Possibly. If you have a single zone, you can still adjust the flow rate of each loop so that you control what proportion of the total space heating energy is sent to each loop. You can set those proportions so the rooms are roughly the same temperature, or with some generally warmer and some cooler. But, you are then fixing that proportionality. So, whether it's a shoulder month, deepest winter, over-cast or sunny, each room will get the same proportion of the total space heating energy.

 

It doesn't allow the space heating to react to dynamic events that change the proportion of the space heating energy a particular room needs. ie. solar gain, occupancy, cooking the Sunday lunch. Although UFH no matter how it is controlled will struggle to react to short-term dynamic changes.

 

This would not work for my house that makes best use of solar gain (during the heating season), which effects a third to a half of the rooms in the house.

 

The reported benefit of a single zone seems to be the elimination of a buffer, or more specifically a 4 port buffer. That's not necessarily so, you could still zone without a buffer as long as you have sufficient volume of water always open to the ASHP, ie. a loop or loops always open with sufficient flow rate, or a 2 port buffer/volumiser to meet the manufacturers minimum requirement. To me that feels like playing a game with short cycling so that you are just above the minimum requirements from the manufacturer. OK, but not ideal.

 

With my install most rooms are their own zone with modulating actuators all controlled by Loxone and I have a 200l 4 port buffer. In the heating season the ASHP generally runs for not less than an hour and from my rough calcs. achieves a slightly better COP than "advertised". My only involvement with the system is to decide the start and end of heating season, other than that it looks after itself.

 

On days with a few hours of winter sun, the UFH in rooms on the South-East and South-West sides will be off, but those on the North-East and North West will be on, but after a couple of over-cast winter days, all rooms will need their UFH on. If I tried to run it as a single zone then on those sunny winter days I'd either be overheating on the South side or cold on the North.  I could of course block out the winter solar gain, but that would increase my heating costs and spoil the views.

There is of course an additional capital cost for the buffer and extra pump and additional day-to-day costs for running the extra pump and minor standing losses of the buffer, so you'd need to justify their inclusion.

 

The longer ASHP run times provided by buffer can improve the COP, but others say there is an efficiency hit to the COP due to badly designed buffers that experience "mixing". I can't comment on the latter as I've never seen any evidence of it myself. Personally, I wouldn't put a buffer together with an ASHP that was not a recommended combination from the manufacturer, which would restrict the options.

 

The other benefits the buffer provide me is to circulate the UFH without the ASHP on, to redistribute solar gain, and to also run a wet duct heater/chiller on the MVHR without the UFH on. The energy transfer of the wet duct heater is far below what the ASHP can modulate down to so it couldn't be run directly off the ASHP. Just to add though, the wet duct heater/chiller can only "trim" temperatures, it's seldom used on its own.

Edited September 13 by IanR

[JohnMo]

5 hours ago, mjc55 said:

We are building single storey!

Same theory applies keep the heat low in bedrooms, don't put radiator on or leave them on low, keep doors closed. Works ok in our house. If you want even temps leave the door open. If you want it really cool (needs to be cool outside) close your bedroom door and open a window.

[mjc55]

2 minutes ago, JohnMo said:

Same theory applies keep the heat low in bedrooms, don't put radiator on or leave them on low, keep doors closed. Works ok in our house. If you want even temps leave the door open. If you want it really cool (needs to be cool outside) close your bedroom door and open a window.

 

That is why we want to zone the UFH to be honest.

 

[JohnMo]

4 hours ago, IanR said:

 

It doesn't allow the space heating to react to dynamic events that change the proportion of the space heating energy a particular room needs. ie. solar gain, occupancy, cooking the Sunday lunch. Although UFH no matter how it is controlled will struggle to react to short-term dynamic changes.

If you do proper Weather Compensation the circulation pump is always on (no thermostat) and with UFH the floor surface temperature is pretty close to room temp. So if floor temp on any given day is 22 and the room 21, heat is given to the room, however if the room gets solar gain and goes up to 23, there is a negative dT and the floor actively takes heat away. This heat is seen in the return temp back to the ashp and the heat pump modulates its output down.

 

4 hours ago, IanR said:

The other benefits the buffer provide me is to circulate the UFH without the ASHP on, to redistribute solar gain, and to also run a wet duct heater/chiller on the MVHR without the UFH on. The energy transfer of the wet duct heater is far below what the ASHP can modulate down to so it couldn't be run directly off the ASHP. Just to add though, the wet duct heater/chiller can only "trim" temperatures, it's seldom used on its own.

WC does that as a matter of course also - circ pump is always on, if you want. The upper grey line on the below chart is circulation pump flow rate.

 

Attached a 10 to 13 deg day, 24 hr snap shot, the highlighted area is DHW heating.  Zero control except target flow temp, and compressor start and stop hysteresis. Circulation pump is on, it just changes speed as required. Space heat CoP is 6.2 running at around 10 degs. Whats not to like. As it gets colder the cycles become longer, even on a day where heating wasn't absolutely required, no cycle times were less than 20 minutes on.

 

 

 

 

 

 

 

[JohnMo]

49 minutes ago, mjc55 said:

That is why we want to zone the UFH to be honest.

Sorry you lost me?

[IanR]

9 minutes ago, JohnMo said:

This heat is seen in the return temp back to the ashp and the heat pump modulates its output down.

 

Which works fine for the room with solar gain, but your ASHP has just modulated down and the the rooms without solar gain are now not getting enough energy, so will start to chill off. At this point you need to change the proportion of the space heating energy that the non solar gain rooms get compared to the solar gain effected rooms, in order to maintain each at their target temps.

 

9 minutes ago, JohnMo said:

 Whats not to like.

 

It works for you so that's great, you appear to have put many hours into to getting yours to run correctly, changing settings on the ASHP controller that most domestic users wouldn't know where to start with, but for other houses there are better solutions. It is mid-September, so current COP isn't going to tell us much. I typically switch my system over to heating season around mid-November.

 

Thankfully there doesn't need to be a "one size fits all" solution, there are plenty of options.

[JohnMo]

43 minutes ago, IanR said:

mid-September

Tell that to Scotland, was 2.5 last night. Highest average temp over the last 4 days was 9 degs.

 

A 6 Deg OAT is getting 4.9 CoP and a 2.5 OAT getting 4.7 CoP.

43 minutes ago, IanR said:

Thankfully there doesn't need to be a "one size fits all" solution, there are plenty of options.

You pay - you choose. Forums like this give people options, to allow an informed choice. No right answer just informed posts.

 

Buffers that are big, I see zero issue with, very little mixing occurs, you can fill the buffer to your heating temp via WC, very little cycling very little over temperature required from the heat pump - but not many people have room for a DHW let alone another 200L or bigger buffer. I just use my floor as a buffer.

 

Small buffers on the other hand, that most installer fit, are the devils work. Plenty of mixing elevated return flow temperature knocking down the CoP considerably.

 

43 minutes ago, IanR said:

you appear to have put many hours into to getting yours to run correctly

Not really, I have spent lots of time learning about low energy, low flow temp heating systems. And used these lessons through trial and error on my own system. Mostly because I have enjoyed it. Most people are paying a very high price for a heat pump install, they should be getting this level learning as part of the price - not many seem too.

 

Did an experiment the other day, ran the heat pump at a fixed flow temp, set a thermostat at target house temp. House temp super stable, just like well set up WC. Like for like outside temp CoP dropped from 6 to 5.

 

 

Edited September 13 by JohnMo

[mjc55]

1 hour ago, JohnMo said:

Sorry you lost me?

 

Earlier you said

 

Quote

Same theory applies keep the heat low in bedrooms, don't put radiator on or leave them on low, keep doors closed. Works ok in our house. If you want even temps leave the door open. If you want it really cool (needs to be cool outside) close your bedroom door and open a window.

 

I read that as meaning that zoned UFH allows this to happen, sorry!

 

So open doors mean that there is no real differential if multi zone closed doors allow the set temperature of that zone to be in charge?  

[JohnMo]

45 minutes ago, IanR said:

ASHP has just modulated down and the the rooms without solar gain are now not getting enough energy, so will start to chill off

Not really, the heat pump is never off, the compressor only will go off. So if you need a floor surface temp of 22 to keep room temperature stable, once the return temp gets 22 the compressor restarts tops up the floor. With the flow on all the time, the floor temp never drops below a useful temperature.  All set via the WC curve.

[JohnMo]

19 minutes ago, mjc55 said:

 

Earlier you said

 

 

I read that as meaning that zoned UFH allows this to happen, sorry!

 

So open doors mean that there is no real differential if multi zone closed doors allow the set temperature of that zone to be in charge?  

Multi zone or single zone if all your doors are open, your rooms will generally be at the same temp. Close the doors there is some individual room temp control. But the output of UFH or radiators can fine tuned by changing the dT across either floor loops or across a radiator to fine tune individual rooms i.e balancing. You really need a zone to do that.

 

To give you background I had a zone in every room a big 160L buffer, I slowly simplified and almost halved gas consumption. Applied the simple is best approach to the heat pump, last year it was cheaper than gas by a good margin.

[IanR]

2 hours ago, JohnMo said:

Not really, the heat pump is never off, the compressor only will go off. So if you need a floor surface temp of 22 to keep room temperature stable, once the return temp gets 22 the compressor restarts tops up the floor. With the flow on all the time, the floor temp never drops below a useful temperature.  All set via the WC curve.

 

? Not sure how your ASHP is reacting to your floor surface temp, I believe it's reacting to the averaged return temp, but that's not the point.

 

Creating a simple example with a two room house, Room A averages a 600W heat loss and Room B a 400W heat loss. The ASHP pushes 1kW into the house and the flow rate in the loops have been fixed to push 60% of the energy into A and 40% into B, maintaining the temperatures for each at their target. The 60:40 proportion is fixed as they are not zoned. Room A starts to receive 500W of solar gain and starts to over-heat, the warming floor of A starts to take less energy from the UFH and the ASHP, in time, modulates down to 500W. The 60:40 proportions are still fixed, so Room A gets 300W from the ASHP and 500W from solar gain, so with 800W total delivered to the room A it continues to over heat, but Room B is now only getting 200W from the ASHP, so starts to chill. The average temp across the house is fine but neither room is at its target temperature.

[JohnMo]

 

8 hours ago, IanR said:

Room A starts to receive 500W of solar gain and starts to over-heat, the warming floor of A starts to take less energy from the UFH and the ASHP, in time, modulates down to 500W. The 60:40 proportions are still fixed

 

The above isn't quite correct, when the rooms are in steady state conditions, they will be getting 60:40 split of energy and always getting a 60:40 split of water flow. But as room temp gets closer to floor temp or radiator temp the dT between the two reduces, so the heat output also decreases from the emitter.

 

So, Room A is in an over heat condition (or just a little warmer than target), Room A emitter dT reduces, therefore heat output reduces. In an overheat condition the emitter output goes to zero. Example floor surface temp 22, room 22 UFH output is 0W.

8 hours ago, IanR said:

The 60:40 proportions are still fixed, so Room A gets 300W from the ASHP and 500W from solar gain, so with 800W total delivered to the room

 

So as a result of Room A being warmer, the system equilibrium is no longer a 60:40 energy split - it has become 0:100 (or anything in between), so although water flow is still being distributed in a 60:40 split, no energy is being emitted into Room A, so all heat can go to Room B. The heating system does not contribute to making overheating worse.

[JohnMo]

8 hours ago, IanR said:

Not sure how your ASHP is reacting to your floor surface temp, I believe it's reacting to the averaged return temp, but that's not the point.

Yes correct. Average return temp also very close to the floor temp when the ASHP compressor is off. As soon as heat input is turned off, the whole floor tries to get to an equal temperature, so return temp is a very good gauge. And as floor to room dT is proportionally to output Watts, all you are doing with weather compensation is changing the dT to get the Watts you need to keep room temp constant.

 

The closer the floor temp is to room temperature, the better it self modulates its output to match circumstances such as solar gain, doors being opened etc.

[IanR]

1 hour ago, JohnMo said:

Example floor surface temp 22, room 22 UFH output is 0W.

 

The output can't be 0W unless the floor temp of the over-heating room is equal to the the WC defined flow temp, while there is a ΔT between flow and floor energy will continue to be exchanged. From your data it appears that @ 11°C OAT your WC is setting the Flow Temp to around 28°C so it will continue to push energy into the 22°C floor, until the ASHP can't modulate down to stop the flow temp over-shooting the WC set target, when it will switch the compressor off. The over-heating room will cause the compressor to switch off  before the non-solar gain room's energy requirements are met.

[JohnMo]

7 minutes ago, IanR said:

that @ 11°C OAT your WC is setting the Flow Temp to around 28°C

Correct, flow temp will 28. Flow temp doesn't equal floor surface temp, there is a temperature gradient away from the pipes.

 

But at 11 degrees the compressor runs for about 20 to 30 mins and is off for about 3+ hrs. While the compressor is running heat radiates from the floor pipes in to concrete, so floor surface temp gets a small increase in temperature, it's not 28 degs.

 

If my heat pump would turn down to less than a kW at 11 degs, it would be set to the lowest flow temp I could - it would not run to 28 degs. I have tried to run shorter cycles at a lower temperature, but energy transfer wasn't great. 

 

So the fact is as I sit here, the heat pump compressor ran 3 hrs ago, water is being circulated at 22 degs, summer house is being heated by 22 Deg water. It is unlikely the heat pump will do anything other than DHW for the rest of the day. If I get solar gain in the lounge the floor output will go negative and that heat will be redistributed.

 

27 minutes ago, IanR said:

The over-heating room will cause the compressor to switch off  before the non-solar gain room's energy requirements are met.

No not so, if you are getting a lot of solar gain, the compressor goes off, but the floor is a huge buffer, it always at or above minimum temperature required to keep room temperature stable. Last year I was using the floor as a storage heat, heating for 7 hrs (longer when below -3) , extracting heat for 17 hrs. House had a 0.5 Deg fluctuations generally.

[IanR]

4 hours ago, JohnMo said:

Correct, flow temp will 28. Flow temp doesn't equal floor surface temp, there is a temperature gradient away from the pipes.

 

Of course. The 28°C -> 22°C gradient in the slab is relatively stable pre-solar gain due to the room losses maintaining a 21°C internal temp and the slab boundary settling at a 1°C ΔT. (It's not really stable, there's a small hysteresis that occurs when the HP compressor switches on and off.)

 

When the solar gain adds an additional 500W into the room, the air temp increases, and reduces the energy coming out of the slab, but until the compressor switches off the rising flow temp continues to push energy into the slab until the flow temp hits 28°C. When the compressor switches off the temp gradient in the slab does not remain fixed, the slab temp equalises through its thickness (2nd law of thermal dynamics), trying to get to a single homogenous temp, say (28°C+22°C)/2 = 25°C. If the internal air temp is lower than this then some slab energy will move to the internal air, if it is higher then some energy from the air will move to the slab. Either way the slab surface temp increases as room over-heats.

The HP will be periodically checking the averaged return temp waiting for it to drop the bottom of it hysteresis. The slab warming in the over-heating room increases the averaged flow/return temp of the ASHP and therefore reduces the time the HP will run for and will fall short of the energy needs of room B, so Room B will chill off.

 

4 hours ago, JohnMo said:

No not so, if you are getting a lot of solar gain, the compressor goes off, but the floor is a huge buffer, it always at or above minimum temperature required to keep room temperature stable. 

 

Yep, compressor switches off, and the room without solar gain continues to take energy from from the slab, so the slab starts to cool. The over-heating room stops the ASHP coming on for as long as the cooling room needs it to in order to maintain its temperature, so it gets colder.

 

There are no controls in the system to maintain the 22° slab surface temp, this is just a product of the temp gradients and boundary conditions. When the steady state is disturbed by a dynamic change the surface temp in any given area of the slab will change. It is not possible for the UFH to push 28°C water through a slab that averages a lower temperature without energy passing from the UFH to the slab until the air temp in the room is equal to or greater than the flow temp and the slab temp has averaged out at the flow temp. The warmer the over-heating room gets the shorter the compressor will run and teh colder the non solar gain effect room will become.

 

For any given house its a matter of scale of incidental heating (solar, occupancy, cooking) and whether the temp changes away from target are acceptable to the occupant. For my house it would not be possible to run on a single zone and still allow the solar gain in. For days on end I will have no heating on in 50% of the house effected by solar gain, but on in the rooms on the Northern side. Those solar gain effected rooms require 0W from the ASHP and it is not possible to pass flow temp water through the floor in those rooms without a transfer of energy from the UFH into the slab, so those rooms would over-heat.

Edited September 14 by IanR

[JohnMo]

As I said my heat pump compressor runs for 20 mins and is then off a few hours at 11 degs. So I doubt the sun coming out and the heat pump being on would, A. likely occur within the same time period, and B in that 20 minute period I am only adding 1.3kWh to the slab. My wife just had the hairdryer on and put close to that into the air.

 

As I said we are only here to give opinions, ours are different and that's good. Your system works for you, mine works for me.

[IanR]

26 minutes ago, JohnMo said:

As I said my heat pump compressor runs for 20 mins and is then off a few hours at 11 degs.

 

The conversation wasn't about your specific installation, I have no doubt a single zone works for you, although not in the way you visualise it. I responded to your point on how a single zone responds to a dynamic change:

 

20 hours ago, JohnMo said:

If you do proper Weather Compensation the circulation pump is always on (no thermostat) and with UFH the floor surface temperature is pretty close to room temp. 

 

Which isn't correct for all houses, mine as an example.

[JohnMo]

4 hours ago, IanR said:

have no doubt a single zone works for you, although not in the way you visualise it.

Not sure I understand that point. I know exactly how my system responds to change and I can get plenty with south west facing windows, that made me learn quickly.

 

Have a look on open energy monitor there are plenty of systems set exactly as mine is, they work, mine works, your works for you. I am happy with that, obviously you're not. Fundamental difference in view, so I will leave the conversation now, to stop going round in circles.

Edited September 14 by JohnMo

[AartWessels]

On 13/09/2024 at 08:46, G and J said:

I have read on here many times that in cooler months upstairs bedrooms run a couple of degrees cooler than downstairs with what appears to be almost standard running setup of MVHR, ASHP, single zone UFH downstairs, no heating upstairs, decent level insulation.

 

MVHR doesn’t, it appears, force all rooms to the same temperature as it simply doesn’t move enough air round to achieve that.  That’s why it’s not the useful for cooling.  It might distribute heat a bit, but not enough to equalise.  
 

Given that lower upstairs temperature I think the super simplicity of that setup is very attractive.

I agree that if you don't heat upstairs, the mvhr and the thermal mass heated will not compensate for the heat loss. 

And indeed, a lower ufh power upstairs will keep the rooms slightly cooler than the living area. Differentiating the temperature in different rooms on the same thermal mass seems a bit unlikely, unless there is a heat loss issue. 

[TerryE]

IMO, if you have a reasonably low energy build with UFH then you need to think very carefully about the pros and cons of multiple zones, upper floor heating, etc.. There's a lot to be said for KISS (Keep It Simple Stupid) IMO, as this saves in installation costs, complexity and through life maintenance.  E.g. upper floor heating is a PITA.  You can run UFH at ~30°C so you can run your ASHP at a low temp and have a significant boost in CoP in doing so.  Low temp rads take up lots of wall space and are expensive to install.  We have no heating on our 1st and 2nd floors, but use a cheap oil-fill electric rad for a few hours on cheap rate electricity during the really cold months just to top-up upstairs.

[saveasteading]

17 minutes ago, TerryE said:

upper floor heating is a PITA

I've seen some aluminium skirting that the pipes click into. This seems tidy and easy enough to do and is my current plan for upper rooms.

Anybody tried it?

[JohnMo]

53 minutes ago, saveasteading said:

I've seen some aluminium skirting that the pipes click into. This seems tidy and easy enough to do and is my current plan for upper rooms.

Anybody tried it?

Not tried it, not sure if you intend to use it with a heat pump? Output could be rubbish at low flow temps.

 

Our summer house has a fan coil, at the moment it is just getting circulation water from the house, and the odd blip of heat at night from the heat pump and seems to keep the summer house temp quite even between 19 and 20. Circulation temp is around 21 degs, so just using the floor as a big buffer.