Overheating

[Stones]

With temperatures hitting 25C today this has been the first real test of our house in terms of overheating and how to manage excess heat.

 

When I designed our house, I crunched the numbers, taking into account average and peak daily solar gain.  Due to the large amount of SW facing glass that we have, I knew we were going to have some overheating, based on maintaining an internal air temperature of 21C.  My number crunching indicated that summer overheating resulting from solar gain could be managed by means of the MVHR summer bypass, and opening a window and ventilating with cooler ambient air, and where appropriate, using blinds or drawing curtains.  

 

Up until now, ambient air temperature has always been several degrees lower than internal air temperature making it very easy to control how much of that solar gain we wished to retain.  In practice we haven't had to do much in the way of control, as internal temps have not exceeded 23C in the main living areas, the bedrooms remaining 1C cooler as they are on the north side of our site. 

 

Today's challenge was how would the house perform without any cool ambient air or active cooling  (albeit I do have the capability to cool our slab).  I'll be honest and say I was quite concerned, but I'm glad to report that internal temperatures remained lower than external, peaking at 24C in the living areas, 1C cooler in the bedrooms.  

 

As ambient air temperature fell to 21C late this afternoon, the summer bypass kicked in and began to ventilate cooler ambient air inside (interestingly, when ambient air was higher than internal, the bypass didn't activate) and I opened two windows, one on the ground floor and the velux on the 1st floor mezzanine to create a natural draw through the house to purge some of the warm air out.  This worked brilliantly and rapidly reduced the internal air temperature down to 22C, and shows how effective this method of control is.  

 

How did everyone else fare today?

[ProDave]

 

Our new house, (not yet occupied so no heating, no passive heating from living activities, and no mvhr running yet) reached a peak of 21 inside downstairs today amd 22 degrees upstairs.

 

To the south of our house are trees, and these are almost in full leaf now, blocking out a lot of the daytime direct sunlight, yet in winter when they are bare the sun floods in.  It is really only now the sun is in the West that we get much direct sunlight.

 

It's been 27 degrees here today, and the temperature in the caravan is unbearable. We have t keep all the doors and windows open and the best we can hope for there is to cool it to not much above ambient. All shut up would be stupidly hot.

 

Thunderstorms and back to normal forecast for tomorrow. (British summer = 2 hot days and a thunderstorm)

[Trw144]

Well I seem to be around 24 degrees in most rooms. Patio windows are open, as are the bedroom ones. With the blinds down and air circulating through the temperature drops in the bedrooms in the evenings so it's a warm temperature but by no means unbearable. I do have a lot of glazing

 

Edited May 26, 2017 by Trw144

[Bitpipe]

Similar situation for us - we keep the east facing window shutters down (inc. velux) and the house stays cool, our problem starts when the sun passes over the house and streams through the two 4.5m sliders that face west - this warms the room up quite a bit.

 

I popped out to Ikea today and purchased two of their £10 tensioned curtain wire systems and some linen voile - rigged it up this afternoon and it cuts out most of the solar gain so happy with that. Plan is to erect a pergola / bris soleil outside on the patio (when built) which should give additional shade.

 

Evening purging via the roof velux and tilting east windows is very effective at cooling.

 

Still to figure if the MVHR is helping at all, summer bypass is activated but doesn't feel like its making much of a difference.  

[Trw144]

Mine seems to be running on boost and summer bypass in the daytime at present 

[Frogeye]

I've been a bit too warm over the last few nights with house temp around 24/25 C. However today I have managed to get the UFH into cooling mode and this has had a real impact in a pretty short space of time (hoping my stone floor doesn't suffer as a result). I've also switched the air duct at the top of my vaulted hallway to extract rather than supply and am optimistic that will help drag out some trapped heat.

[Trw144]

What's cooling your ufh?

[jamiehamy]

I'm waiting to get a couple of wireless sensors rigged up inside - the old one died a death with the gyproc. 

 

I've got a traditional thermometer in the middle of the house and it was registering 22degrees tonight, the highest recorded inside so far - however we have not yet got the MHRV system running and there were no open windows or doors. 

 

The slab temperature (no UFH) is around 19.5 degrees in the south section, but drops to 16/17 in the middle and rear sections. We have significant amounts of glazing on the south elevation however it's all solar to reduce the gain and seems to be doing it's job

 

[Jeremy Harris]

We hit an outside air temperature of 28.6 deg C early this afternoon, with the house room temperature peaking at 22.8 deg C.  Today only the MVHR cooling came on, whereas yesterday the UF cooling came on for a couple of hours in the mid afternoon, even though the outside air temperature was a bit lower than today, 27.4 deg C.  The slab was still cool (19.2 deg C) this morning, so that helped absorb a fair bit of today's heat.  By 17:00 the slab was up to 19.8 deg C, so if it's hot again tomorrow then I expect the UF cooling will kick in again.  Last year during a hot spell the UF cooling took the slab down to about 18 deg C, but that was before we had the solar reflective film fitted to the outside of the windows.  The film is amazingly effective, with the inner pane of the glazing staying at close to room temperature, even under full sun.

[SteamyTea]

I think the morning sun hit my temp sensor.

 

[Stones]

@ProDave We had mature trees that shaded the south west facing glazing in our last house -very effective they were too, sadly not something I have any hope of recreating up here. 

 

@Frogeye how long did it take before you noticed the cooling effect - hours? I purposefully left ours off to see what the worst case scenario would be (given the rarity of such a high temperature where I'm located). 

 

Back to normal ambient temp wise for us tomorrow so solar gain becomes useful once more.

[Frogeye]

@Stones I ran the UFC (?) at temperatures down to about 16C (before I realised that I hadn't limited the target setting - now set to 18C). Downstairs I have mostly stone tiled flooring and I would say that I could notice the cooling effect within a couple of hours. In carpeted areas and upstairs it was less obvious but (i think) noticeable this morning - although I turned the 'cooling' off last night and just left the floor in circulation only mode. This morning the apparent UFH flow temperature is 21C and I switched the ASHP cooling back on with it now set to 18C

 

@Trw144 I have a Panasonic Aquarea ASHP and it was remarkable easy to activate the cooling function (normally disabled in the UK because of the RHI scheme). Initially I was a bit scared off by the thought of wiring/ valves etc. but armed with a few installer settings it was all done through the control panel. Check to see what the target temperature is set too though as my buffer tank was trying to get to 10C. I've got a Wunda UFH and have been running with all loops open since installation (why did I buy all those actuators and wireless room stats!!). I just set my target temperature to 30C just to get the pumps running and with the heating switched off at the ASHP this just acts to circulate the water throughout the house and buffer tank sharing the heat burden around the house(which is what I have been doing for the last few weeks)

[Trw144]

@frogeye ahh I see. I m on a gas boiler but have wondered of the benefits of turning the ufh pumps on to circulate heat in the floor around more evenly. 

[Jeremy Harris]

My experience has been that running the UFH/C pump to just recirculate water around works pretty well, in terms of moving heat from warmer areas to cooler areas.  The rooms to the North of our house get virtually no solar gain, so it's useful to shift heat from warmer areas to cooler areas. 

 

This doesn't make a massive difference during prolonged spells of warm weather, the main benefit seems to be in maintaining an even temperature during periods when the outside temperature varies a lot.

 

Actively cooling the floor with the ASHP is very effective, surprisingly so, given that heat rises.  It's more effective at keeping the house cool than the active MVHR unit we have, and is quieter, too.  It never seems to use close to the full capacity of the ASHP, either, that seems to draw around 400 to 600W when it's in cooling mode, and it's only ever in cooling mode on warm days, when the chances are that the PV system is generating a lot more power than this, making the cooling system running costs near zero.

[DH202020]

Switched off MHVR 3 days ago!...

Like some others not so effective in warm outside air temperatures, at one point it was bringing in warmer air than existing room temperature!

 

windows now open 24hr!

closed reflective blinds when in full sun, frames behind blinds warm up considerably...will be considering solar reflective film as Jeremy mentioned on the south/southwest sides.

 

Reflective film: Anyone got recommendations...make?  inside? Outside?

Thanks.

[Ferdinand]

We are not as well specced as many here, but these are our experiences.

 

Our internal temperature has been up around 24C measured this morning, which is a couple too high for my ideal comfort. Creating a through draft via a couple of open windows or doors seems to work to keep it a little cooler.

 

Two questions:

 

1 - Is it feasible to run the ufh as a temperature equaliser in a conventional ufh system? I.e. Gas boiler only and pipes ?

 

2 - How robust are solar films to window cleaning using a pole and clean water? Just interested not planning this as our better solution would be a south facing veranda.

 

Cheers

 

Ferdinand

[dpmiller]

What about using a duct cooler like was mentioned in the Larder thread to take some heat out of the supply? Worthwhile?

[ProDave]

In a well insulated house that reacts slowly to ambient temperature, if you want to cool it, you open the windows ONLY when the air temperature outside is lower.

 

I did this last night, left all the windows open a small amount overnight when the air had cooled down. The house cooled to 18 degrees as a result and now they are all shut again and the house is staying a nice cool retreat from the heat outside.  You don't want to be opening them when it's hotter out than in.

[Jeremy Harris]

37 minutes ago, DH202020 said:

Switched off MHVR 3 days ago!...

Like some others not so effective in warm outside air temperatures, at one point it was bringing in warmer air than existing room temperature!

 

windows now open 24hr!

closed reflective blinds when in full sun, frames behind blinds warm up considerably...will be considering solar reflective film as Jeremy mentioned on the south/southwest sides.

 

Reflective film: Anyone got recommendations...make?  inside? Outside?

Thanks.

 

Generally, we've had outside air temperatures that have been far warmer than the desired room temperature for much of the day over the past week, it's only after the sun goes down that the outside air temperature has been lower than the desired room temperature.  Opening the windows during the day just makes the house warmer, as the MVHR will act to cool incoming warm air early in the day, because the heat exchanger is bidirectional.  What happens is that when the exhaust air from the house is cooler than the incoming fresh air, the incoming fresh air is cooled a bit, so the air delivered to the house will be slightly cooler than the outside air.  This is only a relatively short duration effect, as soon as the house warms up there will be little cooling.

 

At night, when the air outside is cooler, then it makes sense to switch the MVHR to bypass, to night purge the house with cooler air, or perhaps open windows to achieve a similar effect.  As soon as the outside air temperature increases to be greater than the desired room temperature then the bypass needs to be closed, and windows closed as well.  Failure to do this will just result in warmer air being brought into the house, heating it up.

 

Adding active cooling to the MVHR, either by using a unit like ours with a built in air to air heatpump, or by fitting a chilled water duct cooler, has a modest impact.  It isn't enough to cool the house when it's already far too hot, but is is able to maintain a reasonable (around 21 to 22 deg C) temperature if the solar gain is limited, and if we don't open the windows or doors for any length of time.  I did leave the front door open earlier this week, because I was going in and out a lot, and that pushed the house up towards 23 deg C, from the hot air that came in from outside.  It was noticeable that the MVHR, in active cooling mode, wasn't able to reduce the temperature then, it just stopped it from getting any warmer.  At a guess I'd say the outside temperature was around 26 deg C at the time.

 

The heat reflective window film has to go on the outside, so that it reflects long wavelength IR before it can get in and heat up the inner glazing pane.  We have a 3M film fitted, which is extremely effective, the inner pane of the glazing that has it barely gets above room temperature, even in bright sunshine.  Before the film was fitted the inner pane would reach 35 deg C or so on sunny days, so contributing a fair bit to the slight overheating problem we used to have.

 

[Bitpipe]

56 minutes ago, JSHarris said:

 

 

The heat reflective window film has to go on the outside, so that it reflects long wavelength IR before it can get in and heat up the inner glazing pane.  We have a 3M film fitted, which is extremely effective, the inner pane of the glazing that has it barely gets above room temperature, even in bright sunshine.  Before the film was fitted the inner pane would reach 35 deg C or so on sunny days, so contributing a fair bit to the slight overheating problem we used to have.

 

 

How noticeable is the film Jeremy? Was it expensive and how easy to apply?

 

Our two west sliders are the main source of solar gain in the afternoon - have put up some voile which is doing a good job of shading the room but obviously won't stop the glass from heating up.

 

Planning on erecting a pergola  / bris soleil for outside on the patio (once built) to create external shading but interested in film also.  

[Jeremy Harris]

It depends which film you choose as to how noticeable it is.  The film we have on the front gable glazing is deliberately noticeable, as we wanted to add some privacy as well, so opted for a stainless steel like finish, that turns that glazing into a dull mirror from outside.  The bedroom window glazing film is a barely detectable film, that most people wouldn't notice unless it was pointed out to them.

 

@PeterStarck has had the same almost clear film fitted to some of his glazing, I believe, so may be able to give another opinion.  Our experience is that the almost clear film is as effective at blocking excess solar gain as the visibly reflective stuff, but it is a fair bit more expensive.  There is some more detail in these threads:

 

 

 

[NSS]

Should be having our Sageglass commissioned within the next few weeks so will finally find out whether it will control the solar gain as effectively as it 'says on the tin'.

[Gone West]

4 hours ago, JSHarris said:

 

@PeterStarck has had the same almost clear film fitted to some of his glazing, I believe, so may be able to give another opinion.  Our experience is that the almost clear film is as effective at blocking excess solar gain as the visibly reflective stuff, but it is a fair bit more expensive.  There is some more detail in these threads:

 

We had SUN-X Vista 80X external clear film fitted last July to a WNW facing three quarter glazed gable. It's only needed during May, June and July and has been really effective this month. It's not noticeable which was our main requirement but was expensive.

[Stones]

Well, another warm day for us (forecast wrong yet again), but another interesting test of the house. 

 

Last night we reduced internal house temps down to 22C.  The MVHR summer bypass remained on overnight but did nothing other than maintain that 22C.  Through the day, we left all the windows shut and curtains and blinds open.  Ambient air hit 23C, but skies were clear and the sun was shining brightly.  Internal air temperature peaked at 24C again, which we have now reduced back down to 21C by cross ventilation.

 

Two interesting things about today's performance. First that the internal temperature rise was only 2C, which given the amount of sunshine we had, I'm quite surprised at, and secondly, how little impact drawing internal curtains and blinds has on controlling summer gain yesterday, which was comparable solar gain wise.  

 

Drawing curtains / blinds certainly has a psychological effect - the shade / darkening makes you feel cooler, but in our case, not much practical effect.  

 

Cross ventilation works but does rely on two things, lower outdoor temps and a breeze to help with the chimney effect. Clearly, if we wished to control solar gain before it enters the house, we could fit film as others have done, but I'm reluctant to do so given the benefits we get in winter from solar gain, and how infrequently ambient air temperatures reach the dizzying heights of today and yesterday.

 

Activating the ASHP cooling function is next on the agenda, but with several days of overcast weather and 11C - 12C ambient temps forecast, it's going to be a few days before there is any point doing so.

 

One small footnote, my understanding is that PHPP modelling only considers internal air temps of 25C and above as overheating / there being a cooling requirement. 23C is my target maximum. 

 

 

 

 

[ProDave]

The cooler weather is on the way. It was stinking hot this morning, I had to abandon lawn mowing at 9:30 because it was too hot (having started at 8:30 to try and beat the heat)  but by mid day it was clouding over and now it's full, but thin cloud. No sign of the thunderstorms, just the odd spot of rain.  house a comfortable 19 degrees, only 1 degree up from last nights open window cool down.