ASHP sizing guidance

[wardie9025]

Hi all,

 

We have an extension/refurb ongoing and I'm just looking to finalise the heat pump sizing.  Having taken some advice I'm very likely going for a Panasonic unit.  The dilemma comes to sizing so I thought I would ask to see what peoples experience suggests.  We had some heat loss calcs done that assumed a 5kW heat loss but when I discussed with someone in the know this corresponded to an average heat loss of around 33 w/m2 which seems too low for a 1960s build, even after new extension and relay of concrete floor with 100mm PIR underneath the heating - moderating this up and assuming an average of 50w/m2 gives 8.32kW at -2 external. 

 

Looing at the tables that Panasonic provide, the performance of the HP drops at -2 to 7.38kW so my thinking was do I go for a 9kW T-CAP with no drop off in load at low temps or go up to a 12kW model - concerned about ability to modulate down and maintain good SCOP if I oversize too much!  Efficiency has been the top priority of this part of the whole project.

 

Planning to self install - MCS not worth it.

 

I've included UFH drawings and some assumptions below so welcome any and all feedback!

 

Assumptions:

1. Assumed 50w/m2 heat loss throughout based on advice and looking at the heatgeek table and choosing a reasonably conservative estimate- not used loop cad for the calcs but that does spit out just under 9kW so figure that size would be fine on the basis that it would allow for some over capcity where I've been conservative.
2. Pipes sized at 20mm throughout to minimise pressure drop.  Plan to throttle down on flow rate if needed
3. Pipes goi20230808-41NFR UFH Piping-v1.0.PDFng into 100mm thick screed (couldn't persuade builder last minute to drop the screed and go insulation under slab...long story and I've probably compromised a bit much but hey ho) so high thermal mass.
4. Assumed, 35degC flow temp and a dT 2degC for the design but can increase to dT5 if needed depending on what flow rates the HP needs.
5. Planning for a Panasonic Aquarea J series; self install - BUS not worth it as they just add the 5k on to take it off again.

 

Hit me!!

[JohnMo]

Finger in the air is not good enough for a heat pump.

 

Are you saying you have no insulation under the slab? And your installing UFH?

 

DT 5 will be generally required for a heat pump.

 

Do your own heat loss calc, use the one in boffin corner. This is a whole house one, but certainly good for overall size required.

[ReedRichards]

Two choices when installing a heat pump, I think:

1. You take the £5k grant which obliges you to use an MCS accredited installer who is obliged to make a heat loss calculation to size the heat pump.
2. You forego the grant and don't use an MCS accredited installer but this might stop the heat pump being considered as a permitted development and you would have to apply for Planning Permission.

I might be wrong here but if I am, I'm sure someone will jump in and correct me.

[JamesPa]

15 hours ago, wardie9025 said:

Hi all,

 

We have an extension/refurb ongoing and I'm just looking to finalise the heat pump sizing.  Having taken some advice I'm very likely going for a Panasonic unit.  The dilemma comes to sizing so I thought I would ask to see what peoples experience suggests.  We had some heat loss calcs done that assumed a 5kW heat loss but when I discussed with someone in the know this corresponded to an average heat loss of around 33 w/m2 which seems too low for a 1960s build, even after new extension and relay of concrete floor with 100mm PIR underneath the heating - moderating this up and assuming an average of 50w/m2 gives 8.32kW at -2 external. 

 

Looing at the tables that Panasonic provide, the performance of the HP drops at -2 to 7.38kW so my thinking was do I go for a 9kW T-CAP with no drop off in load at low temps or go up to a 12kW model - concerned about ability to modulate down and maintain good SCOP if I oversize too much!  Efficiency has been the top priority of this part of the whole project.

 

Planning to self install - MCS not worth it.

 

I've included UFH drawings and some assumptions below so welcome any and all feedback!

 

Assumptions:

1. Assumed 50w/m2 heat loss throughout based on advice and looking at the heatgeek table and choosing a reasonably conservative estimate- not used loop cad for the calcs but that does spit out just under 9kW so figure that size would be fine on the basis that it would allow for some over capcity where I've been conservative.
2. Pipes sized at 20mm throughout to minimise pressure drop.  Plan to throttle down on flow rate if needed
3. Pipes goi20230808-41NFR UFH Piping-v1.0.PDFng into 100mm thick screed (couldn't persuade builder last minute to drop the screed and go insulation under slab...long story and I've probably compromised a bit much but hey ho) so high thermal mass.
4. Assumed, 35degC flow temp and a dT 2degC for the design but can increase to dT5 if needed depending on what flow rates the HP needs.
5. Planning for a Panasonic Aquarea J series; self install - BUS not worth it as they just add the 5k on to take it off again.

 

Hit me!!

Or if you can wait a year, measure your actual consumption over winter and factor that, together with the spreadsheet calculation, in.  It sounds like you don't have that luxury, although by the time you get planning consent (if it wasn't included in the conversion pp) then you might not have an option.

 

2 hours ago, ReedRichards said:

Two choices when installing a heat pump, I think:

1. You take the £5k grant which obliges you to use an MCS accredited installer who is obliged to make a heat loss calculation to size the heat pump.
2. You forego the grant and don't use an MCS accredited installer but this might stop the heat pump being considered as a permitted development and you would have to apply for Planning Permission.

I might be wrong here but if I am, I'm sure someone will jump in and correct me.

Correct. 

 

Permitted development requires MCS

 

Grant requires MCS

 

However permitted development doesn't require grant nor vice versa (so you can do MCS without grant under PD, if you can afford it).

[JohnMo]

21 minutes ago, JamesPa said:

Permitted development requires MCS

It actually say MCS or equivalent.

 

https://www.planninggeek.co.uk/gpdo/renewable-energy/class-g/

[JamesPa]

1 hour ago, JohnMo said:

It actually say MCS or equivalent.

 

https://www.planninggeek.co.uk/gpdo/renewable-energy/class-g/

It does indeed, but there is currently no recognised equivalent.  So far as I am aware nobody has yet tested the 'well I did it myself and its as good as MCS' argument. 

 

In reality its unlikely to be a problem unless there is a complaint to the LPA (most likely noise) at which point the EHO will ask the planning department and the planning department will ask for proof of MCS in order to get the EHO off their backs.  If the EHO decides to follow up because there is no MCS then it could get messy.  I suspect if it ended up in court, unless there was a serious breach, the EHO might lose, on the grounds that forcing someone to remove their heating because they hadn't got a specific piece of paper is unreasonable.  

 

My LPA, run by the Green party (!), is really arsy about HP noise (as I have discovered), so if I don't go by the book and there were a complaint, they would be jumping for joy at having caught me out.  Other LPAs may be less awkward.  Note that they can, if they choose, apply more stringent noise specs to express consent applications than apply to PD, there is no direct policy read-over.  Again if it went to appeal I suspect they would lose, but that takes 9 months at present.

 

Its simply madness.  In a situation where there is a suitable location which cant possibly cause a problem with the neighbours, Id be tempted just to install.  But if its 'close' or a quiet neighbourhood (both of which apply to my situation) then maybe not!

Edited August 14, 2023 by JamesPa

[gmarshall]

The planning situation is certainly madness on many levels, but given the stipulation is that it meets the MCS requirements, as long as you download said requirements (MCS020) and apply then yourself (they are pretty straightforward and the only specialist equipment required is a tape measure) then I don't see how you could ever run into a serious issue. 

 

Returning to the other points raised by the OP, itsound like you have a very similar setup to us. We have a 9kw Panasonic in a 60s detached house (120 sq m, decent insulation, ufh downstairs, mvhr, but fundamentally still a 60s house!) that works brilliantly, most of what you are saying sounds perfectly sensible to me. 

 

To go through your post

- Our heat loss cals were just under 6 kW,so similar to you. The spreadsheet on this site is as good as anything. We went for the 9 Kw unit principally to ensure we had some headroom for a future extension. Any bigger would be massively oversized and short cycle (more on that later!)

-20 mm pipes at 100 mm centres certainly won't hurt, but seems like overkill to me- we are on 16mm @ 150 centres which is more than sufficient. 

- The Panasonic units have good weather compensation, ours from memory is set to something like 30-38, so your assumption of an average of 35 is sensible. dT 5 is normal and works for us. Our space heating sCOP for the last 12 months is 4.5. We have UFH downstairs and rads upstairs. 

 

My only concern on your design would be the lack of upstairs heating. Even with our rads upstairs downstairs is noticeably warmer due to the constant heat of the slab. This may be because we mostly run out HP overnight on off peak electric to 'charge' the slab with heat which is very cost effective. It's fine for us, but I don't think it would work without the rads upstairs.

 

Happy to answer any specific questions - we were MCS install as we caught the end of RHI, but I was pretty involved in the design and setup (I know the installer through work) and would definitely self install now, they are fairly simple intuitive systems really. 

 

[JamesPa]

58 minutes ago, gmarshall said:

The planning situation is certainly madness on many levels, but given the stipulation is that it meets the MCS requirements, as long as you download said requirements (MCS020) and apply then yourself (they are pretty straightforward and the only specialist equipment required is a tape measure) then I don't see how you could ever run into a serious issue. 

Strictly it doesn't say this, it says that the installation must meet the 'MCS Planning Standards'.

 

The 'MCS Planning Standards' are defined in MCS-020 and include, in addition to the noise spec, that the installation must be installed by an MCS installer to MCS Standards.

 

MCS have told me that this is deliberate and mandated by MLUHC.  Just saying, not commenting on the implications for future issues.

 

IMHO its totally indefensible, the aspects of the 'MCS Planning Standards' other than the noise spec belong in building regs or consumer protection law not planning law.  Having been told by MCS that this was mandated by DLUHC I have submitted a FOI to DLUHC requesting the relevant documentation and have challenged my MP to explain how the current government defends creating a closed shop through planning law.  I am awaiting responses which will be posted here.

Edited August 14, 2023 by JamesPa

[JohnMo]

I'm with @gmarshall on this.

1 hour ago, gmarshall said:

as long as you download said requirements (MCS020) and apply then yourself (they are pretty straightforward and the only specialist equipment required is a tape measure) then I don't see how you could ever run into a serious issue. 

The MCS standards may say approved bla bla, but the equivalent statement in English and Scottish permitted development rules are vague enough, to allow you to apply common sense. If you don't follow the guidelines on noise and piss of next door, you deserve everything you get.

 

The normal person just does things - they don't read the rules or instructions, that's left to numpties like us, who enjoys reading rules and instruction books.

[gmarshall]

In the unlikely event of it being queried I think presenting your MSC020 calculations would be well received by most reasonable individuals (not commenting on the reasonableness or otherwise of any particular planning departments...)

 

There is also the fact that the average modern heat pump is quieter than the average boiler flue! 

[gmarshall]

55 minutes ago, JamesPa said:

Having been told by MCS that this was mandated by DLUHC I have submitted a FOI to DLUHC requesting the relevant documentation and have challenged my MP to explain how the current government defends creating a closed shop through planning law.  I am awaiting responses which will be posted here.

I await with interest to hear what you get out of this- we really do need political pressure to change all this nonsense! 

[JohnMo]

8 minutes ago, gmarshall said:

There is also the fact that the average modern heat pump is quieter than the average boiler flue! 

And doesn't chuck out plumes of steam etc, most of which isn't good for you.

[JamesPa]

52 minutes ago, gmarshall said:

In the unlikely event of it being queried I think presenting your MSC020 calculations would be well received by most reasonable individuals (not commenting on the reasonableness or otherwise of any particular planning departments...)

Obviously you haven't communicated with my local planning authority!

 

52 minutes ago, gmarshall said:

There is also the fact that the average modern heat pump is quieter than the average boiler flue!

Indeed, and furthermore emits most noise when people are indoors with the windows closed!

 

However obviously you haven't communicated with my local planning authority or indeed their (Green Party) exec member in charge of planning, who defends their stance on the basis that she is a keen gardener and wouldn't want her gardening disturbed by a neighbours heat pump!

 

Need I say more?

 

PS for the avoidance of doubt I agree with you on a practical level.  It's a load of nonsense which somehow our politicians have been suckered into voting for, probably with a bit too much influence from the fossil fuel/boiler industry and/or vested interests in the heat pump installer community. 

Edited August 14, 2023 by JamesPa

[Post and beam]

2 hours ago, JamesPa said:

IMHO its totally indefensible, the aspects of the 'MCS Planning Standards' other than the noise spec belong in building regs or consumer protection law not planning law.  Having been told by MCS that this was mandated by DLUHC I have submitted a FOI to DLUHC requesting the relevant documentation and have challenged my MP to explain how the current government defends creating a closed shop through planning law.  I am awaiting responses which will be posted here.

Is there any value in a parallel approach from a number of us asking the same question of both the DLUHC and our respective MP's . Not a class action, just a deluge of the same question from multiple people?

[wardie9025]

I went to work this morning and forgot about this only to come back to plenty of replies...thank you all!  To try and capture all points and follow on questions in one uber reply:

 

23 hours ago, JohnMo said:

Are you saying you have no insulation under the slab? And your installing UFH?

@JohnMo - there was no insulation under the floor.  There are now no floors with a new slab going down with some insulation on top before a tick screed (see orginal post for why having a screed as well....too late on that one).

 

11 hours ago, ReedRichards said:

You forego the grant and don't use an MCS accredited installer but this might stop the heat pump being considered as a permitted development and you would have to apply for Planning Permission.

@ReedRichards - going for this one.  HP was on the plans submitted to planning permission.

 

8 hours ago, JamesPa said:

Or if you can wait a year, measure your actual consumption over winter and factor that, together with the spreadsheet calculation, in.  It sounds like you don't have that luxury, although by the time you get planning consent (if it wasn't included in the conversion pp) then you might not have an option.

@JamesPa - no sadly don't have this option but as above, was part of our planning submission for the build.

 

4 hours ago, gmarshall said:

Returning to the other points raised by the OP, itsound like you have a very similar setup to us. We have a 9kw Panasonic in a 60s detached house (120 sq m, decent insulation, ufh downstairs, mvhr, but fundamentally still a 60s house!) that works brilliantly, most of what you are saying sounds perfectly sensible to me. 

@gmarshall - good to know and would certainly like to know a bit more detail if you're willing to share, either here or DM?  Where abouts in the country are you?

 

4 hours ago, gmarshall said:

My only concern on your design would be the lack of upstairs heating. Even with our rads upstairs downstairs is noticeably warmer due to the constant heat of the slab. This may be because we mostly run out HP overnight on off peak electric to 'charge' the slab with heat which is very cost effective. It's fine for us, but I don't think it would work without the rads upstairs.

 

Happy to answer any specific questions - we were MCS install as we caught the end of RHI, but I was pretty involved in the design and setup (I know the installer through work) and would definitely self install now, they are fairly simple intuitive systems really

@gmarshall - agreed and lack of upstairs heating is also a concern here.  After speaking with an installer who gets the low temp open zone systems with pure WC control he basically suggested that a) you might get enough heat upstairs from down stairs and U/S tends to be a couple of degrees cooler anyway and b) leave the rads in and then see how you get on, replacing if they aren't good enough.  On point b) there's also a question about whether I want to leave old crappy single panel rads in my nice new HP/UFH system as im fairly confident they wont cut the mustard (not even finned!).  I was also thinking the same, ref "charging" the slab so interested to know more about whether this is just on a timer or how else you have set up?  Which panasonic model do you have?  My other thought for upstairs was self-installed "warm air" heating so run ductwork and a coil into a ceiling diffuser for each room but as this is easier to do post main build from the loft I figured I have some time.  Haven't quite figured out controls for that yet though.....

 

@JohnMo @gmarshall @JamesPa - Ref the noise, I will review and do the calcs for siting to make sure its at an acceptable level.  One question....if approved through planning, is it still subject to the MCS noise limits?  Not wanting to be difficult or annoy the neighbors in anyway and clearly its not a V8 but it would still be good to understand guidance vs constraint in this context??

 

 

 

[JohnMo]

If it's on your plans and approved, without set out conditions, it's approved

[JamesPa]

1 hour ago, wardie9025 said:

One question....if approved through planning, is it still subject to the MCS noise limits?  Not wanting to be difficult or annoy the neighbors in anyway and clearly its not a V8 but it would still be good to understand guidance vs constraint in this context??

 

1 hour ago, JohnMo said:

If it's on your plans and approved, without set out conditions, it's approved

@johnmo is correct, as far as planning is concerned.

 

However if your neighbours complain on environmental health grounds that is an entirely separate body of law.  Your local District/Borough/Unitary is obliged to investigate noise complaints.  In practice they will probably send a warning that a complaint has been received, ask the complainant to keep a log, and only take meaningful action if the 'nuisance' is repeated and after making measurements etc.  You can then be served with an abatement order if the Council deems that a statutory nuisance exists, and fined if you don't comply.  

 

To constitute a statutory nuisance noise must 

• unreasonably and substantially interfere with the use or enjoyment of a home or other premises or
• injure health or be likely to injure health

I don't think its been tested in court yet (doubtless it will be at some point), but its difficult to imagine that a heat pump which meets PD noise rules, has planning consent, and is used for heating would be found to 'unreasonably interfere with the use or enjoyment of a home or other premises' (the emphasis being on the word unreasonably, as its clearly reasonable to heat one's home)

 

However if it doesn't comply with PD noise rules, or some other recognised guidelines, it seems to me that the argument would be somewhat easier to make.

 

So in short the answer to your question is, in my view, 'no' in planning law, but 'probably a good idea' in environmental health law.

 

Hope that helps.

 

Edited August 14, 2023 by JamesPa

[TonyT]

When they visit to inspect have the unit off.

 

that will be a good noise reading.

 

 

[JamesPa]

4 minutes ago, TonyT said:

When they visit to inspect have the unit off.

 

that will be a good noise reading.

 

 

Or perhaps better still on, but not running a DHW cycle.  Then they can see it working but not making very much noise.

[JohnMo]

Just follow the noise rules and calculations of MSC020, to keep yourself on the right side of the noise guidelines. Then your in no worse a situation than a full MCS install. That can get noise complaints just as described above by @JamesPa.

 

Install via MCS is generally just under permitted development rights, if they follow the noise regs and you get a complaint environmental health still get involved. So same same which ever way you look at it.

 

So why pay the MCS premium 

[gmarshall]

14 hours ago, wardie9025 said:

I was also thinking the same, ref "charging" the slab so interested to know more about whether this is just on a timer or how else you have set up?  Which panasonic model do you have? 

Essentially we just run the system on weather comp with the thermostat set to a high temperature (25 degrees I think) during the off peak period, this then ensures the system runs during this period and puts heat into the building and the slab, on all but the coldest days this was enough for us last winter. Took a few tweaks of the weather comp curve but this is easy to do (and fairly satisfying if you like that sort of thing, and if you get the WIFI dongle thing as part of the heat pump set up you can access a lot of data that is useful for this via the installer portal that anyone can register for. I'd advise a wired ethernet cable to it though as otherwise you are trying to get a wifi signal in a faraday cage which can be frustrating!) The room temperature started to rise towards the end of the heating period and then fell slightly over the rest of the day. Room temperature variation no more than 1-2 degrees over 24 hours downstairs, and if we needed more then it would kick back in during the afternoon to top up, but this was no more than 10-20 days all winter I think. We were on old fashioned ECO7 electric last year, hoping the 6 hours on Octopus Intelligent this year will still do the job most of the time (and the cost saving means a few extra afternoon runs is no big deal). 

 

Upstairs, the radiators give more responsiveness, but also much more temperature variance over 24 hours. Without them, I think the temperature variance would be even greater. We put in an entirely new system using standard double panel 1.2m rads in each room. I dont think the single panels we also inherited would have been much use, and i equally had no desire to let the contents of that system anywhere hear the UFH manifold or HP!

 

We are in Nottingham on a Panasonic Aquarea 9kW T-CAP J Series- will DM you.

 

On the planning question, if you have full planning permission with no conditions relating to the HP, then as @JamesPa and @JohnMo say, you should be good to go. Noise complains are noise complaints regardless of installation route, but if what you have done is sensible and in keeping with the ethos of MCS020 the I would be amazed if you ran into any serious issues. My parents have just had to jump through a series of ridiculous hoops for their install as proximity to neighbours meant that the installation was outside the scope of MCS020 that resulted in a full acoustic survey at excessive cost. It is all sorted now but a real example of how silly the planning thing can get- fingers crossed you don’t end up with any daft questions from planning. 

 

 

[JohnMo]

3 hours ago, gmarshall said:

but if what you have done is sensible and in keeping with the ethos of MCS020 the I would be amazed if you ran into any serious issues

At any other time than at the very end of a DHW cycle, I have to look at the fan to see if it's on. Silent from a couple of meters away. Even at the end of the DHW cycle you would not class it a noisy.