MVHR with active cooling

[worldwidewebs]

Following on form the PHPP calls it looks like we'd benefit from some active cooling. I know Jeremy has the Genvex Premium 1 and is very happy with it, but are there any others out there worth considering? The only other that I've seen so far is the Paul/Zehnder one but that's coming out at about £7.5k plus vat - the Genvex Premium 2 that we'd need is about £5k from Denmark and £5.5k from the UK (both plus vat). I'd obviously like to get that down as much as possible if I can

[Jeremy Harris]

Worth considering an ordinary MVHR and adding an air-to-air heat pump heat and cool units.  Depending on the layout this could be a lot cheaper and provide more effective cooling.

It's what we'd have done if we'd realised at the design stage that there was a possible problem.  I'd have not bought the Genvex Premum 1L but would have gone for a much cheaper standard MVHR and fitted a single air-to-air unit with the outlet high up in the central atrium of our house.  These single units are only around £600 to £800 and are far more powerful than the Genvex.

Alternatively, if you're fitting an ASHP, then get a reversible one (most monoblocks are, I believe) and then just fit a big duct cooler in the outlet from the MVHR to cool the air down.  Again, massively cheaper than fitting something like the Genvex, and just as capable, if not more so.

[worldwidewebs]

That's interesting and very helpful, thanks Jeremy. I'm assuming that something like this is what I'd need to look at is it? http://www.fujitsu-general.com/uk/products/split/s-duct/aryg14lltb.html (we're not having an ASHP)

 

[PeterW]

Fujitsu split units come up on eBay a lot - they are about £200 for the duct unit plus the condenser 

[Frogeye]

18 hours ago, JSHarris said:

Alternatively, if you're fitting an ASHP, then get a reversible one (most monoblocks are, I believe) and then just fit a big duct cooler in the outlet from the MVHR to cool the air down.  Again, massively cheaper than fitting something like the Genvex, and just as capable, if not more so.

JSH, could you put this is layman's terms for me if possible. 

Does this mean you would put an additional refrigerant loop from the ASHP to an additional duct cooler placed in line with MVHR air supply? 

[Stones]

I looked into fitting a duct heater / cooler into my MVHR, to be run as an independent circuit from my ASHP.  Certainly doable, but the biggest restriction on capability is the low flow rates of MVHR which means a rather large duct heater / cooler would be required.  In the end, I've decided to make provision to retrofit, but see how the house actually performs in reality.  An A2A heat pump purely for cooling (or instant boost heating) is an option for us, but only I think because we have a large open plan living space with vaulted ceiling.

[Mikey_1980]

Does it need to be PHPP certified?  we have the ESP MVHR which has a built in ASHP for heating/Cooling (2.2kw) its big but well made, they have supplied and fitted for around £7k and have done a really excellent job on the ducting and finishing, they have insulated every pipe run they have put in as well which I wasn't expecting

[Jeremy Harris]

20 hours ago, worldwidewebs said:

That's interesting and very helpful, thanks Jeremy. I'm assuming that something like this is what I'd need to look at is it? http://www.fujitsu-general.com/uk/products/split/s-duct/aryg14lltb.html (we're not having an ASHP)

 

Yes, pretty much any small split should do the job.  There are loads available that are aimed at those with hot conservatories, and they are often cheap and around the right capacity to cool the whole of a well-insulated and sealed house.  You can also get multi-splits, one external unit and several internal units, that may still end up being more cost effective that using an MVHR with a relatively low cooling capability.  Our Genvex Premium 1L does not provide a massive cooling capability in practice, as, like all MVHR heating/cooling systems it is very limited by the duct airflow rates, so can only really trim the room temperatures a bit, not remove a few kW of heat from solar gain at all.

You could make a normal MVHR at least as effective as one with a heat pump in if a cooling/heating exchanger was added to the room air feed main duct.

3 hours ago, Frogeye said:

JSH, could you put this is layman's terms for me if possible. 

Does this mean you would put an additional refrigerant loop from the ASHP to an additional duct cooler placed in line with MVHR air supply? 

  These are water-fed, using chilled or heated water from the ASHP, so are easy to plumb in and control.  There's no need to mess around with refrigerant, you just run a flow and return water pipe to the duct heat exchanger.  If you fit a duct heat exchanger with a built in condensate tray (like this one: http://www.veab.com/documents/cwk/broschyr/CWK_VEAB_Heat_Tech_GB.pdf  )

One of those duct coolers fitted into the main duct from a normal MVHR would provide the same sort of performance as the MVHR units with the built-in heat pumps, but at a lot lower price if you already have an ASHP.

FWIW, we find that by far the most effective way of getting rid of excess heat from solar gain is to just cool the floor slightly.  I've been cooling our floor to around 19 deg C and that has a massive impact on keeping the house cool, far, far greater than using the Genvex in cooling mode.  The reason it's so effective is that it absorbs a fair bit of the solar gain at source, from the sun trying to heat up areas of the floor, by swiftly moving that heat out before the floor has a chance to warm up and start warming up the house.  It doesn't make the floor cold to walk, either, my other half tends to walk around on the travertine flooring in bare feet and reckons that at 19 deg C it doesn't feel at all uncomfortable.

 

[worldwidewebs]

20 hours ago, JSHarris said:

Yes, pretty much any small split should do the job.  There are loads available that are aimed at those with hot conservatories, and they are often cheap and around the right capacity to cool the whole of a well-insulated and sealed house.  You can also get multi-splits, one external unit and several internal units, that may still end up being more cost effective that using an MVHR with a relatively low cooling capability.  Our Genvex Premium 1L does not provide a massive cooling capability in practice, as, like all MVHR heating/cooling systems it is very limited by the duct airflow rates, so can only really trim the room temperatures a bit, not remove a few kW of heat from solar gain at all.

Thanks for your responses, Jeremy.

Given that these units are really aimed at a single room, do you have a view as to how well a single unit would work if placed in a central location within a well-insulated and air-tight house (about 305m2 in total over 2 floors)? I see there are must-splits available but would this really be overkill? Would the MVHR do a good job of moving the cooled air around the house or is this where a multi-split comes in? The PHPP calculations suggested an anticipated cooling load of about 1.6kW (based on internal blinds giving 25% solar reduction). Given that we may not have blinds on all the 'problem' windows then the cooling load would obviously go up. 

20 hours ago, JSHarris said:

You could make a normal MVHR at least as effective as one with a heat pump in if a cooling/heating exchanger was added to the room air feed main duct.

These are water-fed, using chilled or heated water from the ASHP, so are easy to plumb in and control.  There's no need to mess around with refrigerant, you just run a flow and return water pipe to the duct heat exchanger.  If you fit a duct heat exchanger with a built in condensate tray (like this one: http://www.veab.com/documents/cwk/broschyr/CWK_VEAB_Heat_Tech_GB.pdf  )

One of those duct coolers fitted into the main duct from a normal MVHR would provide the same sort of performance as the MVHR units with the built-in heat pumps, but at a lot lower price if you already have an ASHP.

Just to confirm, you're saying that this option is not as good as using an air-to-air heat pump?

20 hours ago, JSHarris said:

FWIW, we find that by far the most effective way of getting rid of excess heat from solar gain is to just cool the floor slightly.  I've been cooling our floor to around 19 deg C and that has a massive impact on keeping the house cool, far, far greater than using the Genvex in cooling mode.  The reason it's so effective is that it absorbs a fair bit of the solar gain at source, from the sun trying to heat up areas of the floor, by swiftly moving that heat out before the floor has a chance to warm up and start warming up the house.  It doesn't make the floor cold to walk, either, my other half tends to walk around on the travertine flooring in bare feet and reckons that at 19 deg C it doesn't feel at all uncomfortable.

That is useful to know. How did you go about cooling the floor - is this just a case of dialling down the temp on the UFH system or did you need to do something clever?

[Stones]

Have a look here:

https://www.systemair.com/en-GB/UK/Products/Product-selector/Fans1/

quite a useful calculator that lets you vary input values (water temp, flow rate etc) to determine the size of duct heater / cooler you would need if going down the MVHR route.

I used it to establish how much a duct heater / cooler could deliver at normal MVHR air flow rates and on boost. 

[Jeremy Harris]

9 hours ago, worldwidewebs said:

Thanks for your responses, Jeremy.

Given that these units are really aimed at a single room, do you have a view as to how well a single unit would work if placed in a central location within a well-insulated and air-tight house (about 305m2 in total over 2 floors)? I see there are must-splits available but would this really be overkill? Would the MVHR do a good job of moving the cooled air around the house or is this where a multi-split comes in? The PHPP calculations suggested an anticipated cooling load of about 1.6kW (based on internal blinds giving 25% solar reduction). Given that we may not have blinds on all the 'problem' windows then the cooling load would obviously go up. 

Just to confirm, you're saying that this option is not as good as using an air-to-air heat pump?

That is useful to know. How did you go about cooling the floor - is this just a case of dialling down the temp on the UFH system or did you need to do something clever?

Whether a single split would be OK depends on the house layout.  In our case we have a very high atrium/hall, right up to the ridge height internally, and right in the centre of the house.  It's also probably one of the warmest parts of the house.  I'm sure a single small split indoor unit placed very high in that space would be pretty effective, as cool air would flow into both bedrooms (if the doors were left open) and down to the whole of the downstairs.  Other layouts might not be as conducive to this approach.

The duct heater/cooler will be as least as effective as an MVHR with a built in air to air heat pump, I'm sure.  Even the smallest ASHP is around twice the capacity of the Genvex and similar systems.  The limit isn't the heat pump, it's really the air flow capacity of the MVHR, which isn't enough, in practice, to have a massive effect.

The floor is actively cooled, as described in the blog post.  The ASHP is just switched to cooling mode and pumps water around the floor at about 12 to 14 deg C, which seems to be about ideal.  The floor surface doesn't drop below about 19 deg C, so never feels uncomfortable, the effect is primarily one of drawing away solar gain from the floor before it can heat it up.

 

[worldwidewebs]

On 30 May 2016 at 19:03, JSHarris said:

The floor is actively cooled, as described in the blog post.  The ASHP is just switched to cooling mode and pumps water around the floor at about 12 to 14 deg C, which seems to be about ideal.  The floor surface doesn't drop below about 19 deg C, so never feels uncomfortable, the effect is primarily one of drawing away solar gain from the floor before it can heat it up.

I'm still mulling the options over but having again spoken with the chap who did our PHPP I'm looking a bit deeper into this option. If I were to get an air to water ASHP to perform the cooling of the slab, would the same unit potentially also be able to do the air con bit too? I'm assuming it would but it just seems a minefield!

We'll still have the gas boiler for DHW so would also use it for the UFH too - so gas boiler for heating and DHW but ASHP for cooling. Is this a reasonably sensible approach or a bit bonkers?

[Jeremy Harris]

Yes, it would do the air cooling.  Recently I was looking at fan coil units, as these are designed to take chilled water (from an air-to-water ASHP) and work pretty much like conventional split air con units.  Many are commercial-looking, but there are some around that look like any other wall or ceiling mount unit.

[worldwidewebs]

Having researched the air-to-air units purely for air con it seemed all pretty straight forward, but with the air-to-water it seems a lot more complex and I'm struggling to separate the wheat from the chaff! Given that all I want is cooling for the UFH and air con, could you possibly point me at the type of product I should be looking at? Most of the stuff I see also needs a cylinder, although maybe it's my lack of understanding getting in the way

[Bitpipe]

Webs, I know you have a challenging window design but for more traditional arrangements the best approach is to prevent the solar gain in the first place through shading.

We specced recessed external blinds to our east windows and also put exterior blinds to the east and south velux and it's keeping the house cool at present. The effect of warm air is also really noticeable when a trade leaves a door open. 

[Jeremy Harris]

It might also be worth looking at what is going on in this thread (towards the bottom):

where I'm currently looking at the effectiveness of external films applied to glazing to significantly reduce the solar gain (as in by 60 to 70% or more).

External blinds would very definitely have been a better option, but weren't possible for the gable and would have caused further planning problems on other windows, whereas the film doesn't.

[worldwidewebs]

Actually, the cooling load with 25% shading provided by internal blinds (we'll have more than that) isn't actually that high (1.2kW) but I know there will be times that I just want to chill the place right down. I'm like that, you see   Obviously, now is the time to understand what is and what isn't available/possible

I know that I can put a roof light in which will help through stack ventilation and the Genvex Premium 2 gives about 1.6kW of cooling, so in theory it's all taken care of. But, for example, putting in an air-con unit will give that bit extra (and then I could replace the Genvex with a cheaper option) and Jeremy has posted some very interesting observations about cooling the slab. If I can work out what I need to provide a little bit of air con and also cool the slab then I think I'm all set. Didn't I make that all sound very easy?  

The window films are also something I've looked at but I'd need to see them in place before going for them - much like Jeremy is doing now in fact, so I watch with interest.

During conversation with the PHPP chap he said the best place for the air con outlet, assuming there was only one, would not actually be in the warmest part of the house near the front gable as this would likely give rise to large local differences in temperature which would lead to convection currents (drafts). The better option, he felt, was to put it in the kitchen area. The extracted cool air could also be used to help cool the incoming air. 

Going back to the ASHP for a moment, if all I wanted was to chill the water for the UFH and to provide some air con, what 'bits' would I need? Assume an air-to-water heat pump (monobloc?), manifold and pump for the UFH coil (same ones as for heating or additional ones?) - not sure on how it does the air con though as all the ones I've seen so far are air-to-air heat pumps. I'm at that stage where I have a lot of unknown unknowns!!!

[PeterW]

I'd be looking more at the use of a chiller in the the MVHR feed rather than the fan coils. 

Commercial fan coil units are ok but they produce cold air in one place only - the water units tend not to have the ability to modulate as much so you will create a cold spot rather than cool the overall air. 

I don't agree with the PHPP chap either - cooling a kitchen is not something I would do to ensure that I got cold elsewhere by virtue of the MVHR heat exchange ! You would create the potential for condensation in the unit as the cold outgoing air hits the warmer incoming air. Also, most units have a summer bypass for warm days so that would be rendered useless in that scenario

A simple duct cooler between the unit and the manifold if you have a radial setup would suffice - that would cool all living areas and create a flow of cooler air throughout 

 

[worldwidewebs]

Thanks Peter - useful advice. When you say 'duct cooler', I've consulted Mr Google and no products jump out at me  - I just seem to get inline fans. Do you have a link to something that would work to provide as a starting point for research in that area please?

[PeterW]

This sort of thing 

http://www.veab.com/documents/cwk/broschyr/CWK_VEAB_Heat_Tech_GB.pdf

its basically a radiator in a tin box .... I had considered making one myself but at last check these aren't overly expensive 

 

[Stones]

When I looked at this, there were two problems.  The first was the limited air flow in an MVHR system, and the second was the size of duct cooler you would have to fit to get any meaningful cooling.  At best I found I was only going to be able to deliver around 0.5kWh worth of cooling (or heating) through the MVHR (based on the flow temps I would be working with from the ASHP).

Look at the page I linked to earlier.

https://www.systemair.com/en-GB/UK/Products/Product-selector/Fans1/

They supply duct heaters and coolers and their calculator allows you to play around with input criteria - target air temp, air flow rate, flow temps etc to determine the size of unit you would need and how much kWh it will deliver.  Have a search for VEAB as well.

[worldwidewebs]

Perfect, many thanks  

[PeterW]

Agree with what Stones says - you can't get a lot of cooling from these things which in one sense is good as it means the output you need from an ASHP is low. 

The upside is that you can potentially use it to heat too and bring the temperature of incoming air up by a couple of degrees but I wouldn't  call it active heating as to do that you need big coils and very hot water !

[Jeremy Harris]

First off. MVHR air cooling is pretty ineffective in practice.  It may well be rated at a reasonably high cooling capacity, but the air flow rate has to be high in order to deliver that, and the MVHR just cannot usually deliver enough cool air to make a significant difference.

The suggestion of cooling the kitchen and letting the MVHR cooler extract handle the distribution is just daft, on a couple of levels.  In summer the MVHR will be on bypass, so all that will happen is that the cooler air will be blown straight outside. There's also the point already made that even if the cooler air was magically made to flow around the MVHR system somehow, then it would have very little effect because of the low flow rate and low temperature differential.  The suggestion itself shows a staggering level of ignorance by the PHPP chap that would have me concerned enough to doubt every other thing he's done or said.  It really is a very fundamental flaw in his understanding of core principles of heat transfer and the way MVHR operates.

As above, duct coolers are the same in performance terms as an active MVHR, like the Genvex Premium range.  On the other hand, there are wall or ceiling mounted fan coil units that have a massive greater cooling capacity, because they recirculate room air at a very much higher flow rate than the MVHR.

Floor cooling certainly works well for us, where we have a significant area of stone flooring that would otherwise get heated by solar gain and transfer that heat to the air in the house, but it may well not be a universal panacea, as it will depend on whether the solar gain is heating a significant floor area, or whether it's mainly heating walls, kitchen surfaces etc.  If it's the latter, then floor cooling may well not be that effective.

[Stones]

Jeremy,

Do you have a link to the fan coil units you have been looking at?