MVHR with active cooling

[Thorfun]

2 minutes ago, Dan F said:

Yes.  This is the same for UFH heating and DHW as each has different flow temperatures typically. Do you see this as an issue?

 

ok, so in the winter the UFH will be off when DHW is being heated? in that case I guess doing the same in the summer isn't an issue. and I guess then that, as we're planning on Solar PV, I can heat the DHW using Solar PV via an immersion so the need to stop the cooling with be mitigated.

5 minutes ago, Dan F said:

"if the above is true then surely that makes the stand alone solution viable?"

?

so, that was thinking that if we couldn't have cooling while heating DHW then if we wanted both at the same time having the cooling built in to the MVHR meant that would be possible. but if I can heat the DHW from Solar PV then it's not necessary.

[ProDave]

The way mine works is I have two motorised valves, one for heating and one for DHW.  Only one is open at a time depending on what it is doing.

 

To add cooling, either via a duct cooler or fan coil units, I would add another motorised valve.

 

Mine ASHP has a separate "cooling" thermostat input.  When that is activated the ASHP starts up in cooling mode.  It would be simple to arrange a cooling thermostat to open the cooling motorised valve, and the feedback contacts on that motorised valve to activate the ASHP cooling input.

 

I haven't done this yet, I was still trying to find some cheap fan coil units, but the other idea is to pipe the cooling to a duct cooler and cool via the MVHR, you would want to switch it to a boost speed for that to be effective.

[Nickfromwales]

9 hours ago, ProDave said:

I haven't done this yet, I was still trying to find some cheap fan coil units, but the other idea is to pipe the cooling to a duct cooler and cool via the MVHR, you would want to switch it to a boost speed for that to be effective.

Current endeavours have been to utilise the duct cooler, slab cooling, and when adverse conditions exist, a re-circulating duct system separate from the MVHR ( and in addition to it ) to target specific spaces with high flow cooled air movement. That leaves the rest of the MVHR serviced spaces on the lower fan speed and seems a more sympathetic solution.  

[Thorfun]

can an ASHP send cold water to 2 x duct coolers if required? one on each MVHR unit? or, if having a 2 x unit MVHR system (see below thread for my dilemma on that choice) would you have to 'choose' which MVHR unit got the duct cooler?

 

[Dan F]

1 hour ago, Thorfun said:

can an ASHP send cold water to 2 x duct coolers if required? one on each MVHR unit? or, if having a 2 x unit MVHR system (see below thread for my dilemma on that choice) would you have to 'choose' which MVHR unit got the duct cooler?

 

Any of those options should be possible shouldn't it?  Isn't it just a sizing+plumbing exercise?

[Thorfun]

1 hour ago, Dan F said:

 

Any of those options should be possible shouldn't it?  Isn't it just a sizing+plumbing exercise?

well, I guess so, but I would presume that the ASHP only has one auxiliary send/return for this sort of thing so the plumbing would need feed both. I just wouldn't know if that was ok or if there was a pipe length maximum or some form of degradation by splitting the feed? I wouldn't of thought so but it's definitely not my area of expertise! 

[Dan F]

17 minutes ago, Thorfun said:

well, I guess so, but I would presume that the ASHP only has one auxiliary send/return for this sort of thing so the plumbing would need feed both. I just wouldn't know if that was ok or if there was a pipe length maximum or some form of degradation by splitting the feed? I wouldn't of thought so but it's definitely not my area of expertise! 

 

Not mine either.. @Nickfromwales might be able to comment...

[PeterW]

1 hour ago, Thorfun said:

well, I guess so, but I would presume that the ASHP only has one auxiliary send/return for this sort of thing so the plumbing would need feed both. I just wouldn't know if that was ok or if there was a pipe length maximum or some form of degradation by splitting the feed? I wouldn't of thought so but it's definitely not my area of expertise! 

Just the same principle that you apply to balancing radiators. Flow control valves on each duct battery and  flow valves would help too. Could even use a 2 port UFH manifold but you would need to make sure you insulate the pipework well to stop condensation. 

[Thorfun]

17 minutes ago, PeterW said:

Just the same principle that you apply to balancing radiators. Flow control valves on each duct battery and  flow valves would help too. Could even use a 2 port UFH manifold but you would need to make sure you insulate the pipework well to stop condensation. 

I have also heard that the MVHR ducts need to be insulated if using cooling as well. so I was thinking about insulating them (or getting insulated ducts) just in case we choose cooling in the future.

 

and shouldn't all pipework be insulated anyway? I remember going to visit an MBC house that was being built when we were looking at TF companies and the plumber there was insulating all his pipe work. so I assumed that was just the norm these days?

[PeterW]

46 minutes ago, Thorfun said:

and shouldn't all pipework be insulated anyway?

Depends ..! Yes it should but it’s sometimes not. And it needs more than the 9mm poly crap some plumbers use. Joints should be taped too. 

[Thorfun]

39 minutes ago, PeterW said:

Depends ..! Yes it should but it’s sometimes not. And it needs more than the 9mm poly crap some plumbers use. Joints should be taped too. 

interesting....I'll revisit this subject when I get around to plumbing first fix.

[Michaela]

thanks Bitpipe and Dan F.  I will likely look at this now in the spring next year.

[joth]

On 13/08/2020 at 18:43, Dan F said:

We will be using a ComfoPost unit (https://www.zehnder.co.uk/comfopost-range) to cool MVHR supply air to upstairs room

 

I only just realized, these were only announced the smaller CW6 ComfoPost last month. (It's mentioned in this month's Self Build mag).

Do you already have a price for it at all? 

Apparently last year I exclaimed about how expensive the much larger CW12 was, but even that link is dead now.

 

Just debating this approach (and insulating supply ducts) vs stand alone fan coil...

 

[Dan F]

41 minutes ago, joth said:

 

I only just realized, these were only announced the smaller CW6 ComfoPost last month. (It's mentioned in this month's Self Build mag).

Do you already have a price for it at all? 

Apparently last year I exclaimed about how expensive the much larger CW12 was, but even that link is dead now.

 

Just debating this approach (and insulating supply ducts) vs stand alone fan coil...

 

 

Don't have price no.   In my view it comes down to heating/cooling load.  If heating/cooling load is low (due to level of insulation and blinds) then doing this via MVHR vs. a seperate system seems a no brainer to me.   Whereas if heating/cooling load is higher then of course seperate fancoil system makes more sense to meet capacity.

 

 

[tanneja]

If I wanted to make use of a duct cooler or fan coil, it seems I would need an ASHP.  We were already considering one for it's cooling capabilities and backup heating should the boiler struggle at any time.  I had assumed this unit would be a 4way minisplit servicing 4 main areas of the house.

 

Is the current most practical thinking that rather than a minisplit connected to room internal units (wouldn't manage to cool each room, just essential areas), the less invasive and more economic way to cool all rooms in the house with one ASHP is to have a dual feed from the ASHP, one to a duct cooler / fan coil, and the other to the UFH?

 

I have read all the advice on cooling impact given the low air flow, and yet given people in this thread think it is viable, I am torn as to the best provision to make for a comfortable home.

 

I offer my thanks in advance for any wisdom.

Edited October 6, 2020 by tanneja

[Dan F]

2 hours ago, tanneja said:

We were already considering one for it's cooling capabilities and backup heating should the boiler struggle at any time. 

Do you need boiler and ASHP?  Considered just ASHP?

 

2 hours ago, tanneja said:

I had assumed this unit would be a 4way minisplit servicing 4 main areas of the house.

That's one option, you could also consider doing it via MVHR, just this approach will only work well if you have very low heating/cooling load.   If you aslso using UFH and have high levels of insulation, then central cooing/heating via ASHP+MVHR is more  practical.

 

2 hours ago, tanneja said:

Is the current most practical thinking that rather than a minisplit connected to room internal units (wouldn't manage to cool each room, just essential areas), the less invasive and more economic way to cool all rooms in the house with one ASHP is to have a dual feed from the ASHP, one to a duct cooler / fan coil, and the other to the UFH?

It's not really a case of what is the most current or practical thinking, but more about what is best fit for your build given your heating/cooling load, if you have ASHP/MVHR or not,  and if you can insulate MVHR ducts or not.

 

We are using ASHP and  heating/ cooling will be indpendnealty controllable ground-floor UFH combined with first-floor MVHR duct heating/cooling.

 

 

[Bitpipe]

16 hours ago, tanneja said:

If I wanted to make use of a duct cooler or fan coil, it seems I would need an ASHP.  We were already considering one for it's cooling capabilities and backup heating should the boiler struggle at any time.  I

 

How could a new boiler 'struggle' in an efficiently built house with a low demand for heat? If the mains gas runs out?

 

Either go for one or the other, not both.

 

If you're not on mains gas than ASHP is the way to go and it will deliver perfect temperatures for low temp UFH but you need to have a means of heating your DHW to 60^o plus to avoid legionnaires. Can be used for UFH cooling (best with passive slab) and can also be used to drive duct cooling for MVHR.

 

Mains gas is still cheaper to run I believe and you have more installation options (trades) as it's the default option. Current boilers are highly efficient, will generate DHW at required temperatures but will need mixed down for low temp UFH.

 

Just be aware that MVHR is designed for ventilation and not space heating / cooling - the flow rates are very low., even on boost.

 

While it will contribute, heating or cooling your space via MVHR will only really act as a trim function and will only be really effective in a very highly insulated airtight house (passive or equivalent). 

[tanneja]

Thanks @Dan F @Bitpipe.  We have already got a relatively new combi boiler so are committed to that.  We were provisioning for AC powered by an ASHP.  It just occurred to me that it could be there for heating in case of failure of the combi boiler for any reason, waiting for an engineer to come (not that the combi cant give us sufficient heating and water when operating normally).  Any ASHP would be installed primarily for it's cooling effect (not very relevant with the weather as it is now, but for stretches of this year it was unpleasantly hot to be inside). 

 

Trying to get my provisioning right, I'm unsure what our cooling requirement will be when the house is finished, but I expect it to be greater than zero, despite having SKN 176II glass on the main solar gain prone elevations, and white render (the grey roof tiles won't help probably).

 

Wanted to leave a way for an ASHP to be installed and enter into the house, before nicely externally insulating (EPS) and rendering, and also have a pathway for pipework internally for either room mounted AC units, or alternatively link it to the MVHR and UFH.  Each strategy would require different provisioning for routes for the coolant pipes.  I take what you have each said, and will see if I can think about positionally provisioning both approaches.

[joth]

@tanneja

Do you need A/C everywhere or just in a few key rooms? (e.g. living room + master bed). If the latter, then you'll probably find it far far cheaper and more reliable to put a dedicated air-to-air A/C unit into those room(s) than use an ASHP. This can aslo provide emergency backup or boost heating too, is no less  efficient than an ASHP,  and shares no common components so avoids critical component failure mode. (compared to trying to plumb a boiler and an ASHP into a single UFH system, sods law says it's the circulation pump or control system that packs up first)

 

Just a thought.

 

[Bitpipe]

On 08/10/2020 at 09:17, tanneja said:

Trying to get my provisioning right, I'm unsure what our cooling requirement will be when the house is finished, but I expect it to be greater than zero, despite having SKN 176II glass on the main solar gain prone elevations, and white render (the grey roof tiles won't help probably).

 

Wanted to leave a way for an ASHP to be installed and enter into the house, before nicely externally insulating (EPS) and rendering, and also have a pathway for pipework internally for either room mounted AC units, or alternatively link it to the MVHR and UFH.  Each strategy would require different provisioning for routes for the coolant pipes.  I take what you have each said, and will see if I can think about positionally provisioning both approaches.

 

Making provision for future services is a smart move, spare ducting is cheap and easy to install during the build (to run pipes and power) and can be robustly plugged at both ends i.e. a tightly scrunched ball of chicken wire (to keep out rodents) on a pull wire, some LE foam and some airtightness tape. If you never need it then forget about it. If you do, you'll be very grateful as it would be very tricky to retrofit.

 

Are you installing solar PV? If you use in roof trays then you won't see it much and you'll save money on tiles underneath. Even if you don't export and claim what's left of FiT, the PV will help power any ASHP or split air conditioning.

 

My guess is that the latter would have the most immediate relief, slab cooling is going to help but be a slower to react system.

 

[Levo]

I am in the process of planning an MVHR for my house and was considering the heating cooling capabilities of it and did some quick research, here are my findings.

The Specific Heat Capacity of Air (around room temp) is 0.00034 kWh/(m3*C).

What this means is if you were extracting 50m3 an hour for the Full Hour from your bathroom at 28C and sending it back to the house which is kept at ~20C (8C difference), that whole energy would amount to 50*8*0.00034 = 0.13 KWh ?.

If you were trying to cool a 140 sqm (~350M3) house and  using a duct cooler at nominal (ACH=0.4) levels , say blowing air at 10C (Delta C =25-10 = 15), the cooling capacity would be

140m3*15C*0.00034 = 0.7KWh. Basically not much, just about enough to neutralize 2 people giving out 350Wh each.?

On the other hand if you had a 140 sqm (~350M3) breezy house with 3-5-10 ACH, on a winters day with 20C differential (0C outside 20C inside) you would be loosing

Which is quite considerable.

I hope I got my calculations right...

Hope this helps.

[Gone West]

15 hours ago, Levo said:

Basically not much, just about enough to neutralize 2 people giving out 350Wh each.

I don't know what your 'people' are up to but AFAIK adults sitting produce less than 100W and average adults walking produce around 120W.

[Dan F]

@Levo If you want to use MVHR for cooling you will want to use a much lower temperature.  Where did you get the 8C from?

 

From ComfoPost data sheet:

- Water temp IN.          7C
- Water temp OUT       12C
- Air temp       IN           27C
- Air temp       OUT      12C

- Flow rate.                   144m3/hr

- Power:                        1.9kW

 

Heating you can get 1.75kW from the same system, but to get this power you'd need a 55C water flow temperature.. so not going to be very nearly as efficient as using UFH at 35C flow.  Running at 0.6 ACH will improve power, but not by that much.

 

We will be using this system, but only as complientary heating/cooling of the first floor.. primarily approach to heating/cooling is UFH.   That said, given out total cooling load (PHPP calculated) is only 1.3kW, MVHR-only cooling would in theory work.

 

[Levo]

11 hours ago, PeterStarck said:

I don't know what your 'people' are up to but AFAIK adults sitting produce less than 100W and average adults walking produce around 120W.

? you are right, I did a very rough calc for that example, and the wrong one I guess.

[Levo]

1 hour ago, Dan F said:

@Levo If you want to use MVHR for cooling you will want to use a much lower temperature.  Where did you get the 8C from?

>That was a heating example; i.e. whether the heat recouped from a Bathroom and/or kitchen would help any. I tend to blast the bathroom with an electric fan to warm up before shower. Never actually checked what temp, so assumed it would be 8C higher than the normal room temp in the house.

 

1 hour ago, Dan F said:

 

From ComfoPost data sheet:

- Water temp IN.          7C
- Water temp OUT       12C
- Air temp       IN           27C
- Air temp       OUT      12C

- Flow rate.                   144m3/hr

- Power:                        1.9kW

> I am not familiar with Comfopost, just looked up the Specific Heat Capacity of Air and based my calculation on that but your example seem to use the same 15C delta as I used. I also checked one of the 2.5KW Fujitsu Split air cons and they quote 700m3/h fan rates. Even if they didn't need the full 700m3/h and only needed 4-500m3/h to achieve 2.5KW cooling, you will likely achieve only a fraction of the 1.9KW @140m3/h, I think.

 

1 hour ago, Dan F said:

Heating you can get 1.75kW from the same system, but to get this power you'd need a 55C water flow temperature.. so not going to be very nearly as efficient as using UFH at 35C flow.  Running at 0.6 ACH will improve power, but not by that much.

>I have a 1970s house and not one of them passive houses?. So, I personally satisfied myself that the MVHR at 100-150M3/h rates will not make any dent either on heating or cooling my house.

 

Just a word of caution on air source heat pumps, I know they are improving every year but no matter what the manufacturers say, their pumping capacity degrades the closer you get to 0C and go below. I have some friends with Air sourced UFH  in the south of England who live in a reasonably new (~5 year old) property and complain the house doesn't warm up on cold nights.