Two circuits for cooling?

[SBMS]

Is it necessary to get a heat pump that can run two independent circuits when doing cooling? One for UFH and one for fancoils - to run at different temperatures?  If so, are there any downsides to this setup when it comes to heating?

[JohnMo]

11 minutes ago, SBMS said:

Is it necessary to get a heat pump that can run two independent circuits when doing cooling?

No, just run whole lot on a single circuit to achieve a mean flow temp of about 16 degs and no lower than about 12 which is at or slightly below dew point.

 

13 minutes ago, SBMS said:

If so, are there any downsides to this setup when it comes to heating?

You are making things complicated and expensive to install for little or no gains.

 

[SBMS]

15 minutes ago, JohnMo said:

No, just run whole lot on a single circuit to achieve a mean flow temp of about 16 degs and no lower than about 12 which is at or slightly below dew point.

 

You are making things complicated and expensive to install for little or no gains.

 

If lagging pipes why not run fan coils at a lower temperature, and ignore dew point?

[Nickfromwales]

16 minutes ago, SBMS said:

If lagging pipes why not run fan coils at a lower temperature, and ignore dew point?

I guess I'd play about with lowering the flow temp incrementally, to gauge the effect, as it's prob not good to go too far and have the system cycling because the cooling effect outperforms it's task?

 

Isn't the HP working a lot harder for longer to do major temp drops too?

[SBMS]

9 minutes ago, Nickfromwales said:

I guess I'd play about with lowering the flow temp incrementally, to gauge the effect, as it's prob not good to go too far and have the system cycling because the cooling effect outperforms it's task?

 

Isn't the HP working a lot harder for longer to do major temp drops too?

I’m at the stage of specifying the system and I’d need to decide whether to run two circuits or not, at this stage? The fan coil units I am looking at output 1.6kw cooling for example with an input temp of 10 degrees. If I run these at 15 or 16 I assume that output will drop something like 20%? Hence wondering if I should run two circuits 

[Nickfromwales]

1 minute ago, SBMS said:

I’m at the stage of specifying the system and I’d need to decide whether to run two circuits or not, at this stage? The fan coil units I am looking at output 1.6kw cooling for example with an input temp of 10 degrees. If I run these at 15 or 16 I assume that output will drop something like 20%? Hence wondering if I should run two circuits 

It'll drop to 20%, not by 20%, that's a major drop for a fan coil.

 

Circuits? Please give more info, eg pipe size etc, and if you're referring to doing 2 runs to 2 FCU's vs 1 & 1? 

[SBMS]

7 minutes ago, Nickfromwales said:

It'll drop to 20%, not by 20%, that's a major drop for a fan coil.

 

Circuits? Please give more info, eg pipe size etc, and if you're referring to doing 2 runs to 2 FCU's vs 1 & 1? 

Still getting my head around all this so be kind..! As I understand it, I’m pushing cool water round the system. My thinking is to have UFH downstairs and then around 7 fan coil radiators in bedrooms and landing spaces. I will lag all pipes to the FCUs (possibly prelagged piping). Don’t know size had assumed 15mm (standard?).
 

I can have a single circuit when cooling but the temperature of the water in that circuit is going to be dictated by the UFH and danger of dew/condensation so consensus seems to be to run that at 15 degrees. If I had one single circuit my FCUs would also receive 15 which inhibits their cooling capacity a fair amount. I think that some heat pumps (we are probably going for an aroTherm) support cooling two circuits. The first circuit would do the UFH at 15 and the second would do the FCUs at 10 degrees. I assuming the ASHP would be producing 10 degree water and it would be blended to warm it for the UFH circuit.

 

All of the above is my assumption and about the limit of my understanding without yet speaking to the installer.

[Nickfromwales]

15 minutes ago, SBMS said:

Still getting my head around all this so be kind..! As I understand it, I’m pushing cool water round the system. My thinking is to have UFH downstairs and then around 7 fan coil radiators in bedrooms and landing spaces. I will lag all pipes to the FCUs (possibly prelagged piping). Don’t know size had assumed 15mm (standard?).
 

I can have a single circuit when cooling but the temperature of the water in that circuit is going to be dictated by the UFH and danger of dew/condensation so consensus seems to be to run that at 15 degrees. If I had one single circuit my FCUs would also receive 15 which inhibits their cooling capacity a fair amount. I think that some heat pumps (we are probably going for an aroTherm) support cooling two circuits. The first circuit would do the UFH at 15 and the second would do the FCUs at 10 degrees. I assuming the ASHP would be producing 10 degree water and it would be blended to warm it for the UFH circuit.

 

All of the above is my assumption and about the limit of my understanding without yet speaking to the installer.

You're quite close, so I don't need to be kind, also I have been dabbling/learning about cooling since 2019, and am still learning as the market, its products (and R&D), and suitability becomes better known.

 

FCU's are a dead safe bet afaic, and yes the issue would be with diminishing 'energy' arriving at each unit (if installing multiples) so I'd do the insulated runs and have them all as radial runs back to a manifold; this gives more flexibility for downstream fine-tuning etc imho.

 

I now see what you mean by 2 circuits, 2 types of emitters supplied either direct from HP low temp output in cooling mode or via an Esbe mixing valve for slightly warmer water to get to the UFH. This is exactly what I have done for 2 previous clients projects, so am 'feeling ya!'. IIRC we sent 11-12^oC to the AHU and 15-16^oC to the UFH in these instances, one a PH+ ICF build and the other an MBC PH TF, both with rafts founds.

[SBMS]

5 minutes ago, Nickfromwales said:

You're quite close, so I don't need to be kind, also I have been dabbling/learning about cooling since 2019, and am still learning as the market, its products (and R&D), and suitability becomes better known.

 

FCU's are a dead safe bet afaic, and yes the issue would be with diminishing 'energy' arriving at each unit (if installing multiples) so I'd do the insulated runs and have them all as radial runs back to a manifold; this gives more flexibility for downstream fine-tuning etc imho.

 

I now see what you mean by 2 circuits, 2 types of emitters supplied either direct from HP low temp output in cooling mode or via an Esbe mixing valve for slightly warmer water to get to the UFH. This is exactly what I have done for 2 previous clients projects, so am 'feeling ya!'. IIRC we sent 11-12^oC to the AHU and 15-16^oC to the UFH in these instances, one a PH+ ICF build and the other an MBC PH TF, both with rafts founds.

Thanks - does The heat pump need to be aware of multiple circuits or is this done via manifolds and blending etc?

[Nickfromwales]

I should say I am not a fan of FCU (wall mounted 'radiators') in a modern domestic setting, far too utilitarian afaic.

 

My favoured option, looking into this quite intensively atm for a new clients proposal, is to have the FCU remote and ducted to the open areas such as landings, hallways, and associated thoroughfares, so the system does the job with as little 'intrusion' into the interior architecture as is possible.

 

My ethos is that the M&E proposal should provide a non-intrusive solution where the dwelling can maintain a pre-selected ambient temp vs switch on to deal with the issue; if this ethos is adopted then the requirement for injecting large amounts of heat energy at adverse times of the day should be mitigated against, ergo the system is on 'long and low' and is working away in the background with as little audibility or inconvenience as is practicable.

 

Heat will move to cold, so by purging the living spaces, landings and thoroughfares, the living spaces and 1st floor bedrooms should naturally stay at much more acceptable ambient temps, and be 'cool' after the sun goes down and well in advance of putting ones head down of an evening. This also suggests that the brunt of this transfer of nuisance heat (energy) can be offset by the thing causing the issue (solar PV > sun).

[Nickfromwales]

14 minutes ago, SBMS said:

Thanks - does The heat pump need to be aware of multiple circuits or is this done via manifolds and blending etc?

This is where all my crackpot ideas fell face down in the early days tbh.

 

I ended up with Stiebel Eltron ASHP and controls / mixing arrangements etc, as their kit just does this all so utterly seamlessly. Very expensive kit, but when you sit down with self-build newbies and give them all the information, they soon realise what a comprehensive solution these delivered, and how little input as occupants they then had to provide.

 

Just one box on the wall, and you tell it "I want to be x temp", and it does so, irrespective of sun/rain/snow.

 

Combine this with the SE kit having an output that manipulates the MVHR too, to provoke a pre-determined boost when cooling, and the circle is complete.

 

The heat pump division of CVC (Oxon) have worked with me on these projects, turning my visions into reality (with a few intensive debates along the way); I am a stubborn mule of a man and want the best each time. They still answer the phone to me, so all good lol.

[Nickfromwales]

27 minutes ago, SBMS said:

Thanks - does The heat pump need to be aware of multiple circuits or is this done via manifolds and blending etc?

Sorry, a few beers in.

 

To answer your exact question. In cooling the HP is told to output the lowest temp setting that a particular emitter will require, so for FCU's or AHU's the temp is set as low as 10/11^oC, and the HP has zero idea of where this is ending up.

 

From the HP this 'chilled' water goes to the buffer tank.

 

The UFH sucks this water out, mixing it with the grouped return, via an Esbe digital mixer and upstream dedicated PWM pump; mixing required to cap the max cooled flow temp at ~15-16^oC (user-engineer definable per situation of course).

 

For the circuit for AHU (in my previous 2 scenarios) the flow from the buffer just gets pumped direct, no need for additional mixing to occur, and job done.

 

There isn't a manifold to speak of, just 2x pump sets (or more), with 1x being blended for UFH, so I guess you'd say that originated from a low loss header created by the plumbing arrangement post buffer. Obligatory manifolds for the UFH loops, but no pump/blender on them with the SE design.  

 

Prob best to add that at 10/11oC the pre-insulted pipe with 6.5mm wall thickness (mentioned elsewhere(?)) would be quite inadequate, but tbh I doubt a well thought through and comprehensive design would require such low temps.

 

This kind of system design absolutely must be about prevention not cure!

[JohnMo]

So going back to basics

 

What is your heat loss - the number to start heat pump sizing from?

 

What is your average heat gain on the worst day?

 

7x 1.5kW and UFH is a huge heat pump!

[SBMS]

1 hour ago, JohnMo said:

So going back to basics

 

What is your heat loss - the number to start heat pump sizing from?

 

What is your average heat gain on the worst day?

 

7x 1.5kW and UFH is a huge heat pump!

We touched on this before on another thread where I got ripped apart as my cooling load was enormous as I had done it on a worst case basis which I think you’d said wasn’t realistic.  

Heat loss is around 7kW (it’s a big house). Installer is sizing for an 12kW arotherm I think - and that’s probably sensible with DHW and a bit of headroom. Will

probably need it this large for cooling.

 

I’m going to do some more work on this cooling demand and try and get an average cooling load demand - I have a heat loss calculation which is fine but must admit am struggling to model the average heat gain on the worst day. Any hints on how to easily model this? 

Edited August 3 by SBMS

[SBMS]

1 hour ago, JohnMo said:

 

7x 1.5kW and UFH is a huge heat pump!

Worth saying that these are just the output capacity of the fan coils not the cooling/heating demand for the room. 
 

[JohnMo]

12kW is a huge heat pump for a new build. Isn't it a 3 phase heat pump?

 

For a heat loss of 7kW, big house circa 400m² I assume?

 

You need a minimum system volume of 150L to ensure back up heater isn't used during defrost.

Piping needs to to be sized to cope with 2000L an hour flow rate.

 

Even the 7kW puts out over 7kW at -3, that is big enough. The 12kW machine doesn't turn down that much I believe, so when it's a more normal day in winter of 7 degs, your heat pump is just going to be massive.

 

Get a new installer - would be my advice. A mitsubishi 8kW (not 8.5kW) would be better or a Panasonic.

 

Plus the aerotherm your installer will charge extra to get cooling to work! It's not a standard feature so needs an expensive widget added.

[nod]

I spoke to three different companies about cooling All three cut me short and said absolutely not Two citing warranty issues and the installers that we settled 25 years experience Stated the benefits arnt worth the hassle 

He showed me around his home at he had a couple of separate air con units 

Why are installers so against cooling 

It would be nice to flick a switch 

 

[SBMS]

30 minutes ago, JohnMo said:

12kW is a huge heat pump for a new build. Isn't it a 3 phase heat pump?

 

For a heat loss of 7kW, big house circa 400m² I assume?

 

You need a minimum system volume of 150L to ensure back up heater isn't used during defrost.

Piping needs to to be sized to cope with 2000L an hour flow rate.

 

Even the 7kW puts out over 7kW at -3, that is big enough. The 12kW machine doesn't turn down that much I believe, so when it's a more normal day in winter of 7 degs, your heat pump is just going to be massive.

 

Get a new installer - would be my advice. A mitsubishi 8kW (not 8.5kW) would be better or a Panasonic.

 

Plus the aerotherm your installer will charge extra to get cooling to work! It's not a standard feature so needs an expensive widget added.

Yes it’s large around 480sqm internal space (rooms in roof). To be fair they’ve calculated a higher heat load using their standard MCS calculator of around 10kw. Heatpunk calculated 9.8kw.  I will work it with them, would rather not switch and they’re a good outfit and we used them on last build. 

any advice on calculating an average cooling demand?

[SBMS]

23 minutes ago, nod said:

I spoke to three different companies about cooling All three cut me short and said absolutely not Two citing warranty issues and the installers that we settled 25 years experience Stated the benefits arnt worth the hassle 

He showed me around his home at he had a couple of separate air con units 

Why are installers so against cooling 

It would be nice to flick a switch 

 

What did you do in the end? Separate ac units?

[Nick Laslett]

@SBMS, looking at your responses in the heat loss thread you had -10° as the coldest design temp and 4 Air Changes an hour in the spreadsheet. 

 

 

On 17/01/2022 at 15:08, SBMS said:

Thanks, that makes sense.  The coldest day value (+20, -10) is coming out at around 7776 (7.7kW), average is around 4.1kW.

 

 

Quote

 

I've plumbed in the following values:

 

 

Air changes per hour =	4
MVHR efficiency =	85%
Wall U value =	0.19
Floor U value =	0.1
Roof U value =	0.16
Average window U value =	0.8
Average door U value =	1.2
Average roof light U value =	1.3

 

Along with the following dimensions of our property

 

 

Internal wall area =	272.00	m2
Internal roof area =	125.00	m2
Internal floor area =	128.00	m2
House total internal volume =	700	m³

 

My understanding is that the 4 air changes per hour is the minimum air purge requirement in building regs for domestic dwelling. This is not the steady state figure you should be using for the spreadsheet. 
 

Also, are you sure -10 in the actual average coldest temp where the house is located?

 

My house is a similar size to yours, with similar U-values, but my heat loss is around 4kWh.

 

[SBMS]

2 minutes ago, Nick Laslett said:

@SBMS, looking at your responses in the heat loss thread you had -10° as the coldest design temp and 4 Air Changes an hour in the spreadsheet. 

 

 

 

 

 

My understanding is that the 4 air changes per hour is the minimum air purge requirement in building regs for domestic dwelling. This is not the steady state figure you should be using for the spreadsheet. 
 

Also, are you sure -10 in the actual average coldest temp where the house is located?

 

My house is a similar size to yours, with similar U-values, but my heat loss is around 4kWh.

 

Thanks Nick - that post was from 2022 and our current build - we're going again, so different house.

[JohnMo]

MVHR and 4 ach doesn't sound correct. You certainly do not use the air test figure in the calculation as that is artificially pressurised. If your house leaks like seize you wouldn't have MVHR. You would use the flow rate of MVHR. So about 0.5 or less.

 

17 minutes ago, Nick Laslett said:

minimum air purge requirement

That is nothing to do with heat loss, that is opening windows and maybe doors for getting rid of hot air.

 

28 minutes ago, SBMS said:

any advice on calculating an average cooling demand?

It's the inverse of heating really. If it's 30 outside you need to remove 8 degs of heat if you want it 22 degs inside. Solar gain add to that, but from memory you have a couple of hours early sun from the East? An average of 30 over a 24 hrs period isn't that likely to occur often. 

 

Morning solar gain, keep curtains shut and if cooler outside temps just fling a couple of windows open for an hour. Job done, then let cooling tick away the rest of the day.

Edited August 3 by JohnMo

[-rick-]

A few thoughts:

 

1. As a clean sheet design try and design out the need for this sort of complexity as much as possible. If that means oversizing the fancoils to produce the needed output at higher flow temps so be it. You'll have a more efficient system running with a single temp WC with no mixing. Having said that, having a design that could support dual flow temps if there is an error of design is a nice insurance policy.

 

2. Right sizing the overall system is important. Too big and it will perform poorly. Equally, putting effort into making sure the insulation and shading are done right can avoid the need for a big, complex and expensive system.

 

3. If you run the fancoils with low flow temps you are more likely to notice the cold air draft effect of A/C so it's another reason to avoid if possible.

 

4. As @JohnMo said the input temp to the floor can be a little below dew point without much concern as the concrete will average out the temperature (especially if you make sure a flow pipe is always next to a return pipe throughout the loop). So you can probaby run a little

lower than dew point without 2 zones as long as you insulate the pipes.

 

5. @joth wanted the ability to cool the fancoil zone while heating the ufh. This is not what we are talking about here. If you want that it's more involved. Though I would try to design out the need for that situation as much as possible. It would be too easy to fall into a situation where two zones are fighting each other and burning money.

[-rick-]

10 hours ago, Nickfromwales said:

Prob best to add that at 10/11oC the pre-insulted pipe with 6.5mm wall thickness (mentioned elsewhere(?)) would be quite inadequate, but tbh I doubt a well thought through and comprehensive design would require such low temps.

 

What temps would that pipe be adequate for? What would be required for for 10/11oC? Anything pre-insulated on the market?

[Nickfromwales]

19 minutes ago, -rick- said:

 

What temps would that pipe be adequate for? What would be required for for 10/11oC? Anything pre-insulated on the market?

Not that I know of, I just used 19mm or 25mm depending on whether it was running through voids or in the plant room (all copper in the plant rooms); metal seems to be worse than plastic for condensation.