MVHR with active cooling

[Jeremy Harris]

This Daikin brochure has some info: www.daikin.co.uk/binaries/ECPEN13-410_Fan%20coil%20units%20with%20BLDC%20technology_UK%20version_tcm511-291488.pdf

Most seem to be unhoused units, intended to be built in to spaces, with just a couple of grilles for the inlet and outlet air, but there are some around that look very much like conventional split air con internal units.

A search for "fan coil" units will probably find load of industrial looking things, but there are some that are sized so they could fit in a floor/ceiling void, for example.

[PeterW]

http://www.ebay.co.uk/itm/Air-con-Ceiling-concealed-fan-coil-unit-/191892184051?hash=item2cadaa5bf3:g:QPYAAOSw3mpXI4-f

Similar bit of kit

[Jeremy Harris]

Yes, that's exactly the sort of thing, except I think that one is intended to run on a refrigerant circuit, rather than a water circuit (both are available and are similar internally).  Typically these units are OK for a couple of kW each, some up to around 4 or even 5 kW, so a lot more powerful in a room than an MVHR cooled fresh air feed.  Our Genvex can deliver around 1kW of cooling to the whole house, maybe at best 200W to a single room.

[Stones]

After working out the fairly minimal heating/cooling capability of a MVHR  duct heater/cooler I had come to the conclusion that it wasn't worth installing, but as a precaution I would make provision for retrofitting one at a later date if I found it was required.

From what I've read so far about fan coil units, they look ideal for what I want, and the really good news is that the pipework and wiring provision that I was planning doesn't need to change.

[Michaela]

I am looking for a solution for cooling.  I have a new build passive house with a Paul MVHR system and I would like to get an AirCon system that could somehow funnell cool air into the mvhr unit for circulation around the house.  The house is so well insulated that the passive heat from appliances etc causes temp build up and its very hot. 

Any and all ideas welcome

Mike

[Bitpipe]

19 minutes ago, Michaela said:

I am looking for a solution for cooling.  I have a new build passive house with a Paul MVHR system and I would like to get an AirCon system that could somehow funnell cool air into the mvhr unit for circulation around the house.  The house is so well insulated that the passive heat from appliances etc causes temp build up and its very hot. 

Any and all ideas welcome

Mike

 

By design MVHR moves air at a low rate, even on boost. Air has a very low specific heat capacity so is very inefficient at transferring heat (or coolth). This is fine for MVHR as its intended for ventilation and not heating or cooling. So even if you introduce some cold air, it will not be in sufficient volume to make a huge difference. It can act as a trim, injecting some heat / coolth but won't move the needle substantially.

 

You're better off trying to install a split air con unit, will require making penetrations in your airtight fabric.

 

An alternative, if you have a passive slab with ASHP, is to run it cold just above the dew point.

 

We keep our passive house cool by doing stack ventilation at night and then closing up to keep the cold air in the house. 

 

Whats your solar gain like, that's the major source of overheating for most of the year.

[Dan F]

1 hour ago, Michaela said:

I am looking for a solution for cooling.  I have a new build passive house with a Paul MVHR system and I would like to get an AirCon system that could somehow funnell cool air into the mvhr unit for circulation around the house.  The house is so well insulated that the passive heat from appliances etc causes temp build up and its very hot. 

Any and all ideas welcome

Mike

 

We will be using a ComfoPost unit (https://www.zehnder.co.uk/comfopost-range) to cool MVHR supply air to upstairs room.  @Bitpipe is spot on though the limitatins of using this approach.  In our case, this is on top of i) external shading ii) UFH cooling so it really is just a solution that allows us to compliment ground floor UFH if/when needed on first floor, rather than our primary overheating strategy. Given we're still building, it's yet to be seen if we'll actually use this much though..

 

To use this approach you need to:

- Have ASHP to supply cold water.

- Insulate the ductwork that will be supplying cold air.

- Be confident that it will supply enough cooling power for your needs, this will depened on solar gain, orientation, shading etc.  (or use it alongside something else)

 

The ComfoPost data sheets give you an idea of how much cooling power you can get from one of these units based on water temperature and ariflow rates.  VEAB is another manufactuer of these units.

Edited August 13, 2020 by Dan F

[willbish]

2 hours ago, Dan F said:

Insulate the ductwork that will be supplying cold air.

Do you intend on insulating all your mvhr supply ducts after the duct cooler?

[Dan F]

17 minutes ago, willbish said:

Do you intend on insulating all your mvhr supply ducts after the duct cooler?

 

Yes.  But there will be a single insulated duct from duct cooler to a first-floor manifold in roof-space.  This means that the insulated 89mm duct runs are shorter, and as it's only the supply ducts so it's not a big deal, especially if you do it as part of first-fix.

 

[willbish]

After reading elsewhere on the forum I had thought that insulating post manifold and cooler would not be necessary but now I am not so sure.

 

As the duct cooler can drain condensate, then the ducting after the cooler will be warmer than the cooling surface and prevent further condensation. 

 

What sort of air temps are you expecting inside your ducts?

 

[Thorfun]

this topic's revival is timely as it's something I'm looking in to at the moment. trying to plan out our MVHR system and we want some cooling. not air con but the ability to take the edge off hot days. we're planning external blinds to reduce solar gain and may not ever need the cooling but we'd rather we had it and not need it than need it and not have it (although that is an expensive way of thinking!)

 

I've seen these Komfovent RHP units on BPC which seem to fit the bill, albeit they are pricey. https://www.bpcventilation.com/komfovent-rhp-600-u

 

but then there's these coil coiling units by Quiet-Vent that seem to offer a similar thing but in a separate unit. https://www.bpcventilation.com/quiet-vent-comfort-cooler

 

anyone had any experience on either of these?

 

(please note, I've not done any calculations yet as to the sizing of the MVHR unit but 3 quotes I've had so far seem to think I need 2 x units so using the RHP units could end up really expensive, unless I use one of those for the upstairs bedrooms to take the edge off for sleeping and a normal MVHR for downstairs and the basement. but I will perform the calculations to see if I can use a single large unit at some point soon)

[Dan F]

43 minutes ago, willbish said:

After reading elsewhere on the forum I had thought that insulating post manifold and cooler would not be necessary but now I am not so sure.

 

As the duct cooler can drain condensate, then the ducting after the cooler will be warmer than the cooling surface and prevent further condensation. 

 

What sort of air temps are you expecting inside your ducts?

 

The insulation, I thought, was primarily to ensure the cold air gets to the rooms and isn't lost in the roof space.   Comfopost datasheet uses 7C in datasheet, but this would depend on cooling demand I think...

 

Edited August 13, 2020 by Dan F

[willbish]

3 minutes ago, Dan F said:

 

The insulatio, I thought, was primarily to ensure the cold air gets to the rooms and isn't lost in the roof space.   Comfopost datasheet uses 7C in datasheet, but this would depend on cooling demand I think...

 

Ahh so you're ducting goes outside the thermal envelope, then that makes sense. 

 

I cant imagine that cooled air inside the ducts will be cold enough and moving fast enough to cause condensation on the external surface. But some real world reassurance would be nice!

[Dan F]

14 minutes ago, Thorfun said:

this topic's revival is timely as it's something I'm looking in to at the moment. trying to plan out our MVHR system and we want some cooling. not air con but the ability to take the edge off hot days. we're planning external blinds to reduce solar gain and may not ever need the cooling but we'd rather we had it and not need it than need it and not have it (although that is an expensive way of thinking!)

 

That is exactly the same situation as us.  Our calculated cooling demand is 1.1W/m2 with blinds so that's only 335W so any cooling via MVHR for upstairs will be plenty.

 

20 minutes ago, Thorfun said:

but then there's these coil coiling units by Quiet-Vent that seem to offer a similar thing but in a separate unit. https://www.bpcventilation.com/quiet-vent-comfort-cooler

 

Do you have/plan an ASHP?  If you do then you simply need a duct cooler (VEAB or ComfoPost).  If I didn't already have an ASHP planned i'm not sure i'd consider those overpriced MVHR based approaches at all, and would instead look at aircon/fan coil.

 

22 minutes ago, Thorfun said:

I've not done any calculations yet as to the sizing of the MVHR unit but 3 quotes I've had so far seem to think I need 2 x units so using the RHP units could end up really expensive, unless I use one of those for the upstairs bedrooms to take the edge off for sleeping and a normal MVHR for downstairs and the basement. but I will perform the calculations to see if I can use a single large unit at some point soon)

 

This might be down to the manufacturers that the suppllier you got quote from use.  Not all MVHR manufacturers have large volume units, so they may prefer to seel you a 2 x vent-axia rather than go with a different brand.

 

[Dan F]

2 minutes ago, willbish said:

Ahh so you're ducting goes outside the thermal envelope, then that makes sense. 

 

I cant imagine that cooled air inside the ducts will be cold enough and moving fast enough to cause condensation on the external surface. But some real world reassurance would be nice!

 

No it doesn't, it's a warm loft.  But you still really want to get the cooled area to the room..  There might also be a condensation aspect to it, but like you I would have assumed any condensation happens in the duct cooler itself primarily especially if all ducting is in the thermal envelope.

[willbish]

24 minutes ago, Thorfun said:

this topic's revival is timely as it's something I'm looking in to at the moment. trying to plan out our MVHR system and we want some cooling. not air con but the ability to take the edge off hot days. we're planning external blinds to reduce solar gain and may not ever need the cooling but we'd rather we had it and not need it than need it and not have it (although that is an expensive way of thinking!)

 

I've seen these Komfovent RHP units on BPC which seem to fit the bill, albeit they are pricey. https://www.bpcventilation.com/komfovent-rhp-600-u

 

but then there's these coil coiling units by Quiet-Vent that seem to offer a similar thing but in a separate unit. https://www.bpcventilation.com/quiet-vent-comfort-cooler

 

anyone had any experience on either of these?

 

(please note, I've not done any calculations yet as to the sizing of the MVHR unit but 3 quotes I've had so far seem to think I need 2 x units so using the RHP units could end up really expensive, unless I use one of those for the upstairs bedrooms to take the edge off for sleeping and a normal MVHR for downstairs and the basement. but I will perform the calculations to see if I can use a single large unit at some point soon)

 

Looking at the price of either of those I would only want to fit if you definitely have a calculated need for it. 

I am going to fit a simple duct cooler https://www.bpcventilation.com/cold-water-duct-cooler-range 1/3 of the price, run by ASHP

[MikeSharp01]

5 hours ago, Bitpipe said:

We keep our passive house cool by doing stack ventilation at night and then closing up to keep the cold air in the house. 

Does the design include a specific stack or are you just using strategic roof windows as vents high up? How do you let the air in low down?

 

[Dan F]

7 minutes ago, willbish said:

 

Looking at the price of either of those I would only want to fit if you definitely have a calculated need for it. 

I am going to fit a simple duct cooler https://www.bpcventilation.com/cold-water-duct-cooler-range 1/3 of the price, run by ASHP

 

Exactly and you can use it for supplementary heating too if required.

[Thorfun]

12 minutes ago, Dan F said:

Do you have/plan an ASHP?  If you do then you simply need a duct cooler (VEAB or ComfoPost).  If I didn't already have an ASHP planned i'm not sure i'd consider those overpriced MVHR based approaches at all, and would instead look at aircon/fan coil.

yes, we're having an ASHP, but it will be situated quite a long way from the MVHR unit which will be in the basement plant room, so I was looking at an all-in-one solution as it would be simpler, albeit more expensive. but I'll check out those other options and see if the distance from ASHP to MVHR would be an issue.

13 minutes ago, Dan F said:

This might be down to the manufacturers that the suppllier you got quote from use.  Not all MVHR manufacturers have large volume units, so they may prefer to seel you a 2 x vent-axia rather than go with a different brand.

yep, agreed. which is why I will eventually do my own calculations and then source the correct unit! I like to get quotes to compare options but it doesn't mean I'll be forced to use one of them.

 

12 minutes ago, willbish said:

 

Looking at the price of either of those I would only want to fit if you definitely have a calculated need for it. 

I am going to fit a simple duct cooler https://www.bpcventilation.com/cold-water-duct-cooler-range 1/3 of the price, run by ASHP

 

the same as @Dan F suggested. thanks. I'll definitely add them to the list of things to research if the distance between the ASHP and MVHR isn't an issue.

[Nickfromwales]

24 minutes ago, MikeSharp01 said:

Does the design include a specific stack or are you just using strategic roof windows as vents high up? How do you let the air in low down?

 

Basement  

[Dan F]

25 minutes ago, Thorfun said:

we're having an ASHP, but it will be situated quite a long way from the MVHR unit which will be in the basement plant room, so I was looking at an all-in-one solution as it would be simpler, albeit more expensive.

 

Not simpler really as you'd have 2 x ASHP, but simpler plumbing yes.  It's not just the distance but how much space you have for flow/return pipes.  Moderate distance isn't a major issues if pipes are well enough insulated. 

 

Zehnder aren't the cheapest MVHR unit, but they do sell high capacity units which can easily do a large house.  Airflow also have high-capacity units.

[MikeSharp01]

8 hours ago, Nickfromwales said:

Basement

Yes but how - the basement will be air tight and need to be secure so is it louver's or some such?

[Bitpipe]

17 minutes ago, MikeSharp01 said:

Yes but how - the basement will be air tight and need to be secure so is it louver's or some such?

 

No design, just happy accident.

 

We have high level Integra Velux in the roof over the central stairway / atrium and I just open the GF slider that sits over the basement lighwell / mezzanine and lock it at 6". As it sits behind a Juliet balcony, there's no real security issue.

 

Had I designed it, I would have had the air coming in via the basement somehow per Nick's suggestion - there is only one door down there but it can't be securely opened. That said, basement is lovely and cool this week, daughter has been sleeping down there in her TV room.

[Thorfun]

11 hours ago, willbish said:

 

Looking at the price of either of those I would only want to fit if you definitely have a calculated need for it. 

I am going to fit a simple duct cooler https://www.bpcventilation.com/cold-water-duct-cooler-range 1/3 of the price, run by ASHP

trying to get my head around using the ASHP to feed the duct cooler. I assume that the ASHP would need to be run in cooling mode to get the cool water fed to the duct cooler, right? and I also assume that as we'd be looking to cool the house then the UFH would be in 'cooling' mode as well or just bypassed as we don't want to put heated UFH on when it's hot enough to want to cool the house!

 

but what happens if we use the ASHP for DHW? do ASHPs auto-switch between cooling/heating mode so when a demand for DHW is met it will switch to generate heat and then when that demand is gone it will go back to cooling mode? and then while the DHW demand is being met the duct cooler won't work so there's a period of time when the house isn't being 'cooled'.

 

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

 

(I've not done the design for DHW yet so I'm assuming it'll be via the ASHP)

Edited August 14, 2020 by Thorfun

[Dan F]

1 hour ago, Thorfun said:

I assume that the ASHP would need to be run in cooling mode to get the cool water fed to the duct cooler, right?

Yes.

 

1 hour ago, Thorfun said:

the UFH would be in 'cooling' mode as well or just bypassed as we don't want to put heated UFH on when it's hot enough to want to cool the house!

Yes.  To get the most out of duct cooler you'd want a flow temp from ASHP of around 5C, but would need to ensure UFH temp is not much less than 17C to avoid condensation on floor.  This can be achieved with correct design though.

 

1 hour ago, Thorfun said:

do ASHPs auto-switch between cooling/heating mode so when a demand for DHW is met it will switch to generate heat and then when that demand is gone it will go back to cooling mode? and then while the DHW demand is being met the duct cooler won't work so there's a period of time when the house isn't being 'cooled'.

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

 

1 hour ago, Thorfun said:

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

?