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41 minutes ago, newhome said:

 

This may be irrelevant but a couple of houses ago I had a house with an almost flat roof. I think yours is too? Mine was 2 storey and the upstairs was unbearable in very hot weather. Downstairs was fine (same size glass installed up and down pretty much). It was an old house so won’t have been built to the insulation standard of yours clearly but I’m just throwing it out there in case some of your issue might be caused by your roof. 

 

Does the German flat roof practice of having pools of water on the membrane help with this?

 

That was demonstrated in an early Grand Designs in doing up a semi in London, and it leaked :-). I trust that they usually work better than that.

 

 

 

Edited by Ferdinand

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Thanks for your post @lizzie , it sounds like you are having similar issues to us. We have experienced some quite high internal temperatures at night, but haven't yet put any blinds or fabrics on the windows so are at the beginning of getting things right. I've still got to sort out the MVHR but doubt this will make a lot of difference.

 

We have large windows on the SSE elevation. The sun is heating the internal fabric of the house and good levels of airtightness the heat has nowhere to go unless of course we open windows. We are fortunate to have six 3G Velux windows, which are ideal for purging the hot air, but we have to open windows on the ground floor to do this. When we go out, security then becomes a problem, as our large IdealCombi Futura+ windows do not have a security latch when ajar. I've taken this up with them.

 

Hence my looking at solar film - thanks Jeremy for your details. We don't have privacy issues but need to strike the right balance between reducing solar radiation and allowing good visibility. I've taken up your point about laminated glass with IdealCombi too.

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23 minutes ago, newhome said:

 

This may be irrelevant but a couple of houses ago I had a house with an almost flat roof. I think yours is too? Mine was 2 storey and the upstairs was unbearable in very hot weather. Downstairs was fine (same size glass installed up and down pretty much). It was an old house so won’t have been built to the insulation standard of yours clearly but I’m just throwing it out there in case some of your issue might be caused by your roof. 

Thanks but I don't think so.  Our roof is not truly flat but is technically a flat roof for pitch I think however we actually have 2 roofs one on top of the other. We have the insulated flat deck roof  provided by the TF company which is I believe a warm roof and on top of that we have another roof formed by shaped trusses to create our angles this I think is termed a cold roof as it has no insulation.  In effect it is just decorative creating the angles.  Whole lot topped off with single ply membrane.

 

There is no doubt the problem is cause by the unshaded glazing If I can get some shade on the glass the temp will drop rapidly.

 

I said we needed more shading as  the house was being built, it seemed obvious to me we were creating a potential problem with solar gain.  No one took any notice of me.  

 

There are a lot of things on this build where I was too trusting, we took the view we are not builders and so pay a professional to do what we could not so how/why would we be trying to check what we were being told........big mistake.............  when it became apparent a short way into the build that we had problems in all sorts of areas it was too late to undo some of it hence I am still trying to sort out issues - unrelated to solar gain - lots of the problems can be traced back to the slab not being right and the frame being erected lop sided and not square on the slab. It has cost umpteen extra thousands and of course delays. Where I would be without some really wonderful tradesmen who have gone over and above in trying to rectify and/or compensate for the problems caused by slab/frame not being right at the start I don't know but thats a whole other story!.

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Just now, RandAbuild said:

The other thing I am considering is a sail awning...

Good idea if you can do it.  We are exposed on the top of a ridge it wouldn't last 5 minutes LOL

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13 minutes ago, lizzie said:

Thanks but I don't think so.  Our roof is not truly flat but is technically a flat roof for pitch I think however we actually have 2 roofs one on top of the other. We have the insulated flat deck roof  provided by the TF company which is I believe a warm roof and on top of that we have another roof formed by shaped trusses to create our angles this I think is termed a cold roof as it has no insulation.  In effect it is just decorative creating the angles.  Whole lot topped off with single ply membrane.

 

There is no doubt the problem is cause by the unshaded glazing If I can get some shade on the glass the temp will drop rapidly.

 

I said we needed more shading as  the house was being built, it seemed obvious to me we were creating a potential problem with solar gain.  No one took any notice of me.  

 

There are a lot of things on this build where I was too trusting, we took the view we are not builders and so pay a professional to do what we could not so how/why would we be trying to check what we were being told........big mistake.............  when it became apparent a short way into the build that we had problems in all sorts of areas it was too late to undo some of it hence I am still trying to sort out issues - unrelated to solar gain - lots of the problems can be traced back to the slab not being right and the frame being erected lop sided and not square on the slab. It has cost umpteen extra thousands and of course delays. Where I would be without some really wonderful tradesmen who have gone over and above in trying to rectify and/or compensate for the problems caused by slab/frame not being right at the start I don't know but thats a whole other story!.

 

 

What did the architect have to say about the need for shading?

 

My experience was that most of the architects I spoke to weren't that clued up about it - one even suggested that having a lot of South facing glazing would make for a wonderful sunny aspect.

 

One thing that is relatively cheap and works well is solar sails, set up to provide shaded areas and an architectural feature.  Not great if you're in a very windy area, but otherwise they seem to work well.  I like the idea of using tensioned fabric structures like this, and you can get some extremely tough materials that mean you could have them as a permanent feature (subject to checking things like the snow loading).

 

Edited to say that I cross posted with @RandAbuild, saying much the same!

Edited by JSHarris
added cross post info
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1 minute ago, JSHarris said:

 

 

What did the architect have to say about the need for shading?

 

My experience was that most of the architects I spoke to weren't that clued up about it - one even suggested that having a lot of South facing glazing would make for a wonderfull sunny aspect.

 

One thing that is relatively cheap and works well is solar sails, set up to provide shaded areas and an architectural feature.  Not great if you're in a very windy area, but otherwise they seem to work well.  I like the idea of using tensioned fabric structures like this, and you can get some extremely tough materials that mean you could have them as a permanent feature (subject to checking things like the snow loading).

 

Edited to say that I cross posted with @RandAbuild, saying much the same!

Yes architects seem to ignore practicalities like sun and summer!

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32 minutes ago, lizzie said:

Good idea if you can do it.  We are exposed on the top of a ridge it wouldn't last 5 minutes LOL

 

 

I wouldn't dismiss a properly engineered tensioned fabric sail without checking.  We had them at a place I worked, made from something like the stuff curtainsider lorries use, in white, with, I think, a fibreglass core sandwiched between the white plastic external material.  These sails were tensioned with stainless steel wire and yacht rigging turnbuckles and there was a heck of a lot of tension in the fabric, so much so that it barely moved in the wind.  There was a similar system used to shade the upper seats of the London 2012 stadium; somewhere I have some photos I took when I was there during its construction, that might show how they were fitted and tensioned, I'll have a look later.

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1 hour ago, Ferdinand said:

Does the German flat roof practice of having pools of water on the membrane help with this?

 

:S:S don’t think my 50 year old house would have coped with that! I spent more time worry that water might pool on the roof rather than thinking of ways to encourage it to do so. 

 

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@JSHarris thank you I would be interested to see.

 

We are right on top of a ridge wind comes clear across the valley 40 miles or more from the Malvern Hills nothing to slow it down.  We have extra strapping on our roof to make sure the wind does not lift it.  It was all engineered for wind and loading and our lovely carpenter put more strapping on as he didnt think the engineers had specified enough....he had been working up there in all weathers so knew how fierce it could be. Local houses have had ridge tiles taken off by the wind.  One of the things I liked was the exposed location with clean air constantly blowing in.

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Just a few things around MVHR I picked up from this thread so far I want to understand better. I know the flow is too low to provide any meaningful cooling. 

  • In summer if it's 28 outside and 21 inside, doesn't the cooler exhaust air cool down in in coming warm fresh air? Sort the opposite of what it normally does?
  • You're still going to get some uptick of heat unless you shut it down completely though?
  • Summer bypass just draws in air at 28 degrees doesn't it?! What's the use of that except at night? 
  • An aircon unit in the main living area will cool down that space but MVHR will start throwing that cooling outside (albeit at a slow pace) and not distribute it around the house, would that be accurate?
  • Is there such a thing as a recirculate option with MVHR units like you have in a car for when you drive through smoke? The advantage is you get air circulation even when someone's BBQ'ing outside but also if you have one room actively cooled, you get the benefit throughout the whole house (eventually!). 

 

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12 minutes ago, mike2016 said:

Just a few things around MVHR I picked up from this thread so far I want to understand better. I know the flow is too low to provide any meaningful cooling. 

  • In summer if it's 28 outside and 21 inside, doesn't the cooler exhaust air cool down in in coming warm fresh air? Sort the opposite of what it normally does?

 

 

Yes, initially, but the house will start to warm up and so there will come a point where this effect isn't worth having.  In general, our MVHR is on 100% bypass by mid-morning at the moment, which is the point where it senses no benefit from having the heat exchanger in circuit.

 

12 minutes ago, mike2016 said:
  • You're still going to get some uptick of heat unless you shut it down completely though?

 

 

Yes.

 

12 minutes ago, mike2016 said:
  • Summer bypass just draws in air at 28 degrees doesn't it?! What's the use of that except at night? 

 

Spot on - better to shut the MVHR off once it goes to 100% bypass during the day, unless you have an active MVHR which cools the fresh air.

 

12 minutes ago, mike2016 said:
  • An aircon unit in the main living area will cool down that space but MVHR will start throwing that cooling outside (albeit at a slow pace) and not distribute it around the house, would that be accurate?

 

Yes, the MVHR may well do as you say.  There's some merit in never letting the house get warm inside, so that you can use the limited airflow from cooled air provided to (or from) a duct cooler in the MVHR to maintain a comfortable temperature (I'm ironing out the details of doing just this for our system right now).

 

12 minutes ago, mike2016 said:
  • Is there such a thing as a recirculate option with MVHR units like you have in a car for when you drive through smoke? The advantage is you get air circulation even when someone's BBQ'ing outside but also if you have one room actively cooled, you get the benefit throughout the whole house (eventually!). 

 

Not as such, but turning the MVHR off has much the same effect in practice, and is what we do if someone lights a bonfire.  You can live in the house quite comfortably with the MVHR off and the doors and windows closed for a few hours - I watch the CO2 and it rarely gets above about 800 ppm and that's considered an OK figure.

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1 hour ago, mike2016 said:
  • In summer if it's 28 outside and 21 inside, doesn't the cooler exhaust air cool down in in coming warm fresh air? Sort the opposite of what it normally does?

 

Yes, MVHR acts to maintain any temperature difference between inside and outside. It doesn't matter whether it's hotter inside or out.

 

1 hour ago, mike2016 said:
  • You're still going to get some uptick of heat unless you shut it down completely though?

 

Heat will increase, in the same way that a house will be cooled slightly by MVHR in winter. The difference is that in winter, the sources of heat in the house (central heating, people, cooling, showers, etc) tend to counteract this effect. In summer, there's no source of incidental cooling, and it's unusal in the UK to have active cooling.

 

1 hour ago, mike2016 said:
  • Summer bypass just draws in air at 28 degrees doesn't it?! What's the use of that except at night? 

 

Assuming an automatic system, summer bypass only operates when the outside air temperature is lower than the inside air temperature, as tends to happen at night as it cools down outside. Summer bypass won't turn on if it's 28 outside and 21 inside. If it does, a setting is wrong or something is broken!

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6 minutes ago, jack said:

In summer, there's no source of incidental cooling, and it's unusal in the UK to have active cooling.

 

Except for evaporative cooling, for example by drying clothes indoors. Such incidental evaporative cooling is modelled in PHPP.

 

More generally, humidity is worth considering when considering comfort and energy. One thing I am evaluating is having an enthalpy heat exchanger in my MVHR.

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12 minutes ago, jack said:

Summer bypass won't turn on if it's 28 outside and 21 inside. If it does, a setting is wrong or something is broken!

 

In reading the specification of some MVHR units, some seem to trigger the summer bypass solely on the basis of an external temperature. Some seem to be based on a algorithm linked to internal and external temps. I wonder if any take notice of humidity or other characteristics. 

 

(And, as mentioned before, some don't have a summer bypass at all. And instead say they have a "simulated" one, which as far as I can tell means simply turning off the extract fan).

Edited by Dreadnaught

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20 minutes ago, Dreadnaught said:

 

One thing I am evaluating is having an enthalpy heat exchanger in my MVHR.

 

They are a lot more expensive aren't they? Active Cooling also drives up the cost of the models available although JSHarris got a great deal abroad on his......

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13 minutes ago, mike2016 said:

They are a lot more expensive aren't they?

 

To swap the heat exchanger is quite a few hundred quid I think but if you buy the enthalpy exchanger when you buy the MVHR, the marginal cost is a lot less, about £2 - £300 I think. Some models, like the Paul Climos 200, come with the enthalpy exchanger as standard. Swapping by the way is usually a trivially easy procedure.

 

I am exploring how enthalpy-exchanger-based MVHRs are treated by PHPP. For sensible heat, an enthalpy heat exchanger is less efficient than a normal one. Say 84% compared with 94% for a normal one. But once latent heat is included, overall energy efficiency of the enthalpy heat exchanger exceeds that of a normal one. I am not sure whether that is fairly represented in PHPP. Commonly, humidity (the moisture content of the air) complicates simple energy calculations and is often overlooked.

 

Edited by Dreadnaught

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I've turned off our MVHR during this hot spell, as I think (not scientifically) it was contributing to the overheating

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41 minutes ago, Dreadnaught said:

Except for evaporative cooling, for example by drying clothes indoors. Such incidental evaporative cooling is modelled in PHPP.

 

Fair enough, although how much indoor drying do people do (genuine question) and what's the net effect on house temperature? Other than allowing towels to dry after showers, we don't dry any clothes inside in summer, and I doubt we're that unusual.

 

40 minutes ago, Dreadnaught said:

In reading the specification of some MVHR units, some seem to trigger the summer bypass solely on the basis of an external temperature. Some seem to be based on a algorithm linked to internal and external temps. I wonder if any take notice of humidity or other characteristics. 

 

Mine (Brink) definitely uses indoor and outdoor temps - from the manual:

 

678035553_Summerbypass.thumb.GIF.6df0a535dd2c2f0abb6817c5b2032ff9.GIF

 

Are there really summer bypass (not simulated) systems that operate solely based on outdoor temperature? Do they assume that on very hot days your house is already hotter than it is outside? If so, that's a bizarre assumption.

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16 minutes ago, Dreadnaught said:

I am exploring how enthalpy-exchanger-based MVHRs are treated by PHPP. For sensible heat, an enthalpy heat exchanger is less efficient than a normal one. Say 84% compared with 94% for a normal one. But once latent heat is included, overall energy efficiency of the enthalpy heat exchanger exceeds that of a normal one. I am not sure whether that is fairly represented in PHPP. Commonly, humidity (the moisture content of the air) complicates simple energy calculations and is often overlooked.

 

On cold days in winter, a standard heat exchanger does recover quite a lot of latent heat from moist air. You'd have to average out performance over a year to be sure.

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1 hour ago, jack said:

Assuming an automatic system, summer bypass only operates when the outside air temperature is lower than the inside air temperature, as tends to happen at night as it cools down outside. Summer bypass won't turn on if it's 28 outside and 21 inside. If it does, a setting is wrong or something is broken!

 

Or unless the unit has active cooling, when it goes to 100% bypass and turns on the air-to-air heat pump...

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4 minutes ago, jack said:

 

On cold days in winter, a standard heat exchanger does recover quite a lot of latent heat from moist air. You'd have to average out performance over a year to be sure.

 

 

Very true - a look at the volume of condensate coming down the drain pipe shows just how much water is being condensed out, which in turn is a good indication of the amount of heat being recovered from phase change.

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27 minutes ago, jack said:

Are there really summer bypass (not simulated) systems that operate solely based on outdoor temperature? Do they assume that on very hot days your house is already hotter than it is outside? If so, that's a bizarre assumption.

 

My observation was from this quote "Usually activates based on automatic external temperature point e.g. 21°" from this document from Zehnder, https://www.zehnder.co.uk/download/102348/en_uk-63373.pdf.

 

They might have been simplifying.

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3 minutes ago, Dreadnaught said:

My observation was from this quote "Usually activates based on automatic external temperature point e.g. 21°" from this document from Zehnder, https://www.zehnder.co.uk/download/102348/en_uk-63373.pdf.

 

They might have been simplifying.

 

Interesting document, thanks. I guess they could be simplifying, but it does seem to be comparing an outside temp (only) approach with an inside+outside temps function.

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30 minutes ago, jack said:

how much indoor drying do people do (genuine question)

 

I will need to do all my drying inside the house. I'm adding one of those ceiling drying rails in my laundry room. I have limited outdoor space. I considered a MVHR linked drying cupboard and would still like one.

 

My PHPP assumes 3.5 kWh of useful energy per drying event and 57 such events per year. About 200 kWh in total of cooling per year. Not much.

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