Comfort cooling MVHR

[AliG]

I found some mention of this in other posts but not my specific question.

 

Now that the hot weather is back I have noticed that on occasion the master bedroom in our current house is a little uncomfortable at around 25C although opening the windows soon fixes this.

 

In the new place the master bedroom has a lot more glass, basically a west facing glazed gable and insulation levels are higher.

 

This got me thinking should I consider "comfort cooling" which I often see advertised on flats in London.

 

I believe that @JSHarris has this on his MVHR, I think via running his heating in reverse?

 

In my case I would have to change the MVHR unit to one that allows cooling. It is partly an attractive option because we will have 3 MVHR units (Dantherm) but one supplies the most used rooms in the house with the most glass  so I would only have the extra cost of changing that one unit.

 

I spoke briefly to the heating engineer and he felt it wasn't worth it as there would be an considerable increase in costs because we would have to also up spec the pipework to allow for the possibility of water condensing in it. It would effectively have the same costs as putting in an AC system.

 

He felt that summer bypass is enough, certainly in Scotland it would be rare for the actual outside air temperature to be well above 20C, especially in the evenings. Also we can always open the windows.

 

If this isn't enough he recommended looking at solar reduction film for the windows or a through the wall AC unit.

 

Does anyone have any thoughts or experience of using comfort cooling and how well summer bypass works in practice?

[Jeremy Harris]

We have an MVHR unit that includes an air-to-air heat pump, so can heat and cool.  We never use it for heating, but as I'm sitting here typing this, with an outside air temperature of 25.6 deg C, the MVHR outlets are feeding nice cool air at around 12 deg C into the house.  It isn't powerful enough to cool the house down if it has been allowed to get too hot, but is quite effective at maintaining a comfortable temperature.  The most effective way of cooling the house is the under floor cooling system, run from the ASHP that can also heat the floor in winter.  That's not running right now, as it's set to come on if the house gets above 22.5 deg C, but when it does, we find that cooling the floor is more powerful at reducing the house temperature than the MVHR.

 

Summer bypass is not very effective during the day here, but does provide cooling at night, when the outside temperature drops below room temperature.  However, we are in a sheltered location, with the house set in a cutting in a south-facing slope, and that does mean we have higher than average outside air temperatures.

 

BTW, there is no problem with condensation in the ducts, as they will always be well above dew point.  There is a lot of condensation in the MVHR unit when the cooling is on, with a constant trickle of condensate running out of the drain pipe.

Edited June 1, 2017 by JSHarris

[AliG]

Thanks Jeremy.

 

The location is not sheltered and as opening a window at night usually provides decent cooling I suspect that summer bypass would work well at night. I am less bothered about daytime temperatures.

 

I was going to ask if running the cooling massively increases the running costs of the MVHR then I remembered that your PV panels will be genratins enough electricity to rn a small town when the weather is good 

 

I was surprised about what he said re the pipework and condensation, sounded overly careful.

 

I know some people have UFH based cooling but as my UFH does not run off a heat pump I don't have that option. It is perhaps a good reason to choose that option.

[Barney12]

Weve added the GSHP fed heat/cooling battery to our MHRV. Its yet to be commissioned so I can't comment on its operation but on paper it should achieve the same effect as Jeremy has detailed. Airflow are clear to point out that it's suplimentary cooling not air conditioning. Obviously burying 100m of pipe 1.2m deep is probably not an option for you now! But if your cold water supply is cool enough you might be able to achieve something similar with a simple heat exchanger?

 

I too was told by a HVAC engineer (the guy we use at work) that if we cooled the air intake we would need to upgrade all our duct runs to insulated duct to prevent condensation dripping into the rooms. After conversation with BPC (and Airflow) they confirmed that only the air intake to the MHRV unit needed to be insulated and also needed to be at least 1m from the intake to the unit. 

[Jeremy Harris]

2 hours ago, AliG said:

I was going to ask if running the cooling massively increases the running costs of the MVHR then I remembered that your PV panels will be genratins enough electricity to rn a small town when the weather is good 

 

Very true, we were still exporting over 5kW with the cooling on this afternoon....................

[dogman]

On 2017-6-1 at 18:09, Barney12 said:

Weve added the GSHP fed heat/cooling battery to our MHRV. Its yet to be commissioned so I can't comment on its operation but on paper it should achieve the same effect as Jeremy has detailed. Airflow are clear to point out that it's suplimentary cooling not air conditioning. Obviously burying 100m of pipe 1.2m deep is probably not an option for you now! But if your cold water supply is cool enough you might be able to achieve something similar with a simple heat exchanger?

 

I too was told by a HVAC engineer (the guy we use at work) that if we cooled the air intake we would need to upgrade all our duct runs to insulated duct to prevent condensation dripping into the rooms. After conversation with BPC (and Airflow) they confirmed that only the air intake to the MHRV unit needed to be insulated and also needed to be at least 1m from the intake to the unit. 

@Barney12 Is this the unit that BPC sell. What size did you get in relation to your house size?

 

[Barney12]

56 minutes ago, dogman said:

@Barney12 Is this the unit that BPC sell. What size did you get in relation to your house size?

 

 

Yes. This one: https://www.bpcventilation.com/airflow-bv400-618 

I've actually discovered that its simply a re-badged Helios kit. There is a PDF to the kit here: Ground-to-brine heat exchanger SEWT (Kit) - Byggahus 

 

I dont actually have it though!  I ordered and paid for it mid/late April and long story short, they had supply issues, they sent their 'display' kit, it had various bits missing and it went back and I'm still waiting for its replacement. 

 

All I currently have is a length of pipe buried in the ground. To be completely honest if I hadn't have gone to the huge expense of burying the pipe I would have by now demanded my money back. 

 

I'm also still waiting for my Airflow MHRV unit, I have everything else just not the most expensive bit!! 

 

I sense Airflow (and in turn BPS) may have some significant supply chain issues.

[willbish]

Ive recently been trying to chose a MVHR unit and have approached a few companies who design & supply.

 

As I will be cooling my slab with ASHP its just a little extra work to add a duct cooler to the Intake. I've been advised there may be condensation issues as cooling the intake air will increase the relative humidity.

 

@JSHarris when you say

On 01/06/2017 at 15:37, JSHarris said:

BTW, there is no problem with condensation in the ducts, as they will always be well above dew point.  There is a lot of condensation in the MVHR unit when the cooling is on, with a constant trickle of condensate running out of the drain pipe.

Is this regarding your air to air MVHR or your additional duct cooler?

 

Has anyone else installed a duct cooler and what is necessary/advised to take measures to prevent condensation?

 

Many thanks

 

 

 

[Jeremy Harris]

Both the duct cooler and the MVHR produce a fair bit of condensation and both have drain trays and condensate drains.  The MVHR generates a lot of condensation when in cooling mode, enough for there to be a constant trickle of water down the drain, as the cooled surface inside the unit seems to operate at a pretty low temperature; it's not unusual to see it operating at around 3 or 4 deg C at times.

 

Condensation inside the ducting after any cooler isn't really possible, as the ducts will always be warmer than the cooling surface, and the air will have given up a lot of its water vapour as it passes through the cooler.  The air on the house supply side of the cooler will be pretty dry, so it's very unlikely that any of the ducts will ever get below the local dew point for the air they are carrying.  There is a risk that the outside of the ducts that are carrying cool, dry, air may attract condensation, but in practice I've found that the twin wall semi-rigid ducting seems to be well enough insulated for this not to be a problem.  All our fresh air supply ducts are also well away from any areas in the house that might have higher levels of water vapour, like the kitchen and bathrooms, which probably helps.  All our fresh air supply ducts also run in the first floor void, which is filled with rockwool acoustic insulation, which may or may not help.

[joe90]

Ours is not a cooling MVHR and it’s in a warm roof but the incoming flexible ducting has produced lots of condensation so I have had to insulate it.

[Jeremy Harris]

Good point, the incoming ducts from outside definitely need insulation, as both can get pretty cold.  In our case, if we ever use the heating function in the MVHR the exhaust air can easily be well below zero; I've seen it down to about -5 deg C at times.

[willbish]

Thanks gents,

 

From the installations Ive seen it looks best practice to insulate incoming ducts regardless of whether they are inside the thermal envelope or not.

 

33 minutes ago, JSHarris said:

Condensation inside the ducting after any cooler isn't really possible, as the ducts will always be warmer than the cooling surface, and the air will have given up a lot of its water vapour as it passes through the cooler.

That's reassuring ?

 

35 minutes ago, JSHarris said:

There is a risk that the outside of the ducts that are carrying cool, dry, air may attract condensation, but in practice I've found that the twin wall semi-rigid ducting seems to be well enough insulated for this not to be a problem.  All our fresh air supply ducts are also well away from any areas in the house that might have higher levels of water vapour, like the kitchen and bathrooms, which probably helps.  All our fresh air supply ducts also run in the first floor void, which is filled with rockwool acoustic insulation, which may or may not help.

I will most likely be using the 75mm semi rigid ducts too.

Out of interest how do you know you don't have a slight condensation issue? Were all your systems up & running, before the ceilings were covered up?

 

[Jeremy Harris]

6 minutes ago, willbish said:

 

 

 

Out of interest how do you know you don't have a slight condensation issue? Were all your systems up & running, before the ceilings were covered up?

 

 

Some of the ducts are visible in the services room, so if there was any problem it would show there, as they will be cooler there (as that's where the manifold/plenums are located) than they would be anywhere else in the house.

[willbish]

And I would guess you service room is always going to be slightly warmer than the rest of the house, which would also help to highlight any issue.

[TFnovice]

New here, liking the forum very much and particularly interested in this thread!  We are building a timber framed house (not passive) and I am trying to get a handle on the heating and, hopefully, cooling.  The range of options and new tech is bewildering.

 

For the heating we are on mains gas so I ruled out GSHP early on (for better or worse) and assumed a gas boiler with in screed UFH on both floors.  Pretty straight forward, but ideally I would like some (non AC) cooling too as we will get a lot of solar gain.  Some of this will be mitigated with shutters, blinds or window film, but not all.

 

Having initially been told you can't cool MVHR I have now come across two options, one which uses a GSHP bore hole and the other which sounds very similar to the system JSHarris has described above.  Both aim to offer whole house heating and cooling.  Neither are cheap and nor are they supplied by large well known companies and so I am a little wary.

 

The comment above about cooling the floor slab is also new to me and sounds very interesting.  Can anyone provide a link to a not too technical explanation and possibly the kit involved to achieve this?

 

 

[Jeremy Harris]

Ground Source Heat Pumps tend to be expensive, and will rarely recover the higher installation cost over their lifetime in terms of running cost savings, IMHO.  We did look at installing one initially, but soon changed our minds when we looked at the prices.  An ASHP will cost more to install than a gas boiler, I suspect, but does give the option of being able to both heat and cool the UFH, which we've found an advantage. 

 

if you have a sufficiently well insulated and air tight house, then you can cool it OK with an active MVHR, like the Genvex unit we have, which can both heat and cool the house using its internal air-to-air heat pump.  This only provides a limited amount of cooling though, not enough to overcome a lot of solar gain.

 

If you have mains gas, then I think the most cost effective option might be to stick with a gas boiler for the heating and hot water and just install a stand alone air-to-air heat pump.  These are pretty cheap and can provide a higher cooling capability than cooling built in to an MVHR.

[Sue B]

When we built our first house in 2008 we bought an add on for the MVHR system for comfort cooling.  Our electric bills shot through the roof the first year we used it and we noticed no cooling effect at all.  I wouldn’t buy again.

 

Visiting MVHR stands this time round, when we relay our experience, the experienced suppliers nod sagely and agree with our findings.  The same with the central vacuum systems.  We wouldn’t bother again but I love the idea.

[Jeremy Harris]

3 minutes ago, Sue B said:

When we built our first house in 2008 we bought an add on for the MVHR system for comfort cooling.  Our electric bills shot through the roof the first year we used it and we noticed no cooling effect at all.  I wouldn’t buy again.

 

Visiting MVHR stands this time round, when we relay our experience, the experienced suppliers nod sagely and agree with our findings.  The same with the central vacuum systems.  We wouldn’t bother again but I love the idea.

 

 

All I can say is that we are very happy with our Genvex Premium 1L MVHR, with it's built-in comfort cooling and heating.  It does exactly what it says in the spec, and happily pumps cool air (at around 8 to 10 deg C) out of all the fresh air feed terminals when it's in cooling mode.

 

As for electricity consumption, then at full power in cooling mode it draws between 400 and 500 watts.  As cooling is only required when the sun is shining the running costs for us, with loads of PV on the roof are zero.  However, if we didn't have PV then the Genvex would cost around £0.08 per hour to run, so not exactly expensive.

 

I can only imagine that you were sold something defective, that failed to do what it was supposed to.  That doesn't mean that all products of this type are as equally flawed, though.

[Sue B]

Could be Jeremy although I think you can probably understand our reluctance to try again.  It was 10 years ago and things have moved on as well.

[TFnovice]

14 hours ago, JSHarris said:

If you have mains gas, then I think the most cost effective option might be to stick with a gas boiler for the heating and hot water and just install a stand alone air-to-air heat pump.  These are pretty cheap and can provide a higher cooling capability than cooling built in to an MVHR.

 

Thanks for the reply.  When you say air-to-air heat pumps are you talking about this sort of thing?  https://www.daikin.co.uk/en_gb/product-group/air-to-air-heat-pumps.html

 

I was hoping that there would be some sort of combined system that would do it all.  I would like to avoid boxes on the wall for cooling as they aren't very attractive.  I have found this combined heating/cooling MVHR system which the manufacturer claims is significantly better than, for example, the Zehnder ComfoCool. Does anyone have any experience of this system? http://www.totalhome.co.uk/images/HPVSummaryPage18.pdf

 

If I wanted to go down the route of cooling the UFH in the slab, can that only be done with ASHP?

[Jeremy Harris]

Yes, that's the sort of system.

 

We have a Genvex Premium 1L MVHR with a built-in air-to-air heat pump (this model - and this is the cheapest/best supplier I know of: http://www.sundthus.dk/genvex-ge-premium-1l-hoejre/ ).  Total cost, including delivery to the UK, came to £4,305, after we'd reclaimed the 25% Danish VAT.  The same unit from Total Home Environment was quoted at well over £8.000 delivered, with a higher delivery charge than we paid to get the unit from Denmark...

 

MVHR cannot shift much heat though, so unless you have a house that's built to close to passive standards I doubt that an MVHR cooling system would work well for you.

[TFnovice]

1 hour ago, JSHarris said:

Yes, that's the sort of system.

Thanks - I'll have a look at those in a bit more detail.

 

1 hour ago, JSHarris said:

We have a Genvex Premium 1L MVHR

I saw you had mentioned this elsewhere and your set up sounds very well thought through and effective. Total Home claims their own design system is significantly better at cooling than the Genvex or the Zehnder.  Is there any way to measure that without actually seeing it in operation (I'm no engineer as you may have guessed)? 

 

1 hour ago, JSHarris said:

MVHR cannot shift much heat though, so unless you have a house that's built to close to passive standards I doubt that an MVHR cooling system would work well for you.

My thinking was more that when the ext temp is higher than the int temp of the house, even with a summer bypass you would be drawing in warmer air which seems crazy.  The cooling is really just to keep the air flow but stop that from happening.

 

2 hours ago, TFnovice said:

If I wanted to go down the route of cooling the UFH in the slab, can that only be done with ASHP?

This sounds an interesting option - can anyone answer this question please?  And maybe point me in the direction if how it works?

 

[Jeremy Harris]

21 minutes ago, TFnovice said:

I saw you had mentioned this elsewhere and your set up sounds very well thought through and effective. Total Home claims their own design system is significantly better at cooling than the Genvex or the Zehnder.  Is there any way to measure that without actually seeing it in operation (I'm no engineer as you may have guessed)? 

 

My experience with TH was not good.  Their supposed design service was, like the price of the equipment they sell, massively over-priced and I was far from convinced from the detailed quotes they provided that the system would even work properly, let alone be effective and efficient.  I'd have a look around at a range of possible suppliers I think, and see what others can offer.

 

21 minutes ago, TFnovice said:

My thinking was more that when the ext temp is higher than the int temp of the house, even with a summer bypass you would be drawing in warmer air which seems crazy.  The cooling is really just to keep the air flow but stop that from happening.

 

The bottom line is that any MVHR system just cannot do that much in terms of shifting heat, as the flow rates are so low.  Solar gain can easily be ten or twenty times greater than the rate at which an MVHR can remove heat, with the net result that using MVHR to heat or cool a house really only works for a house that's close to passive house standard, where the heating and cooling requirement are a lot smaller.  If you're looking to build to this sort of insulation and, more importantly, airtightness level, then using active MVHR (one with an internal heat pump) can work well, but it wouldn't be very effective for a house built to just meet current building regs.

 

21 minutes ago, TFnovice said:

This sounds an interesting option - can anyone answer this question please?  And maybe point me in the direction if how it works?

 

We can heat and cool our slab using a cheap ASHP.  The cooling works far better than I expected and is noticeably more powerful in its effect than the MVHR in cooling mode.  Dead easy to do, as the vast majority of ASHPs have a reversing valve and are quite capable of running in cooling mode, it's just a matter of wiring up a cooling thermostat to set the ASHP into cooling mode and turn on the UFH.

[TFnovice]

37 minutes ago, JSHarris said:

I'd have a look around at a range of possible suppliers I think, and see what others can offer.

Thanks - I'll do that.

35 minutes ago, JSHarris said:

We can heat and cool our slab using a cheap ASHP.  The cooling works far better than I expected and is noticeably more powerful in its effect than the MVHR in cooling mode.  Dead easy to do, as the vast majority of ASHPs have a reversing valve and are quite capable of running in cooling mode, it's just a matter of wiring up a cooling thermostat to set the ASHP into cooling mode and turn on the UFH.

And can I use a gas boiler for heat and an ASHP for cooling on the same UFH system do you know?

[Dreadnaught]

@TFnovice, just a side note on overheating for well insulated houses. The best mitigant for this is not active ASHP cooling, openable windows, or even shutters but by good house design.

 

Depending on the constraints on your site it may be possible to orient your house, and especially the glazing, and and add shading overhangs and other features that reduce summer overheating dramatically. For example, in the case of Ben Adam Smith of the House Planning Help podcast, his forecast rate of summer overheating by these design measures for his own house was zero percent. In reality, of course, its impossible to fully avoid overheating. However, if your house is also modelled using PHPP then you can see the effect of design changes. Personally, when I chose my architect, was careful to choose one that was familiar with both PHPP and these concepts.

 

Many people who aspire to a (near-ish) passive house don't realise that, with a highly insulated house, space heating becomes easy and it is overheating that becomes the more major concern. Unfortunately, often they discover this only after they take-up occupation.

 

Hope that's helpful.