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Heating and cooling: Overheating

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  1.  
    • CommentAuthorCerisy
    • CommentTimeFeb 9th 2019
     
    I've posted before regarding our issues with overheating last summer for the hot weeks we experienced here in Normandy. Our new house is insulated to PH standards and we struggled to lose heat. This is forecast to be an increasing issue and as we are not "spring-chickens" we need to address the problem.

    Our MVHR unit is a Titon with summer bypass. Unfortunately the Titon summer bypass is automatic and cuts in when the air coming into the unit is hotter than the air being expelled. As the supply pipe comes through the loft, which of course gets very hot during the day, it kicked in during the afternoon. I quickly disabled the summer bypass so it didn't pull in hotter air and as it sounded like we were living next to Heathrow! So what to do for this year ...

    Firstly we can simply switch off the MVHR when it gets silly hot and use our tilt turn windows at night to reduce the temp in the house and freshen the air (why didn't I think of that last year? Probably as I fitted the system and it seemed counter intuitive to switch it off!). Secondly we could replace the Titon with a alternative model that has manual summer bypass that we could use at night - still switching off the unit during the day.

    The end game I guess is to install air-conditioning - one downstairs and one in our bedroom. They would need to be linked to installing PV to cover the electricity usage of course, but as the cost of that drops maybe not too expensive, even in France!

    Any thoughts guy? Regards, Jonathan
    •  
      CommentAuthordjh
    • CommentTimeFeb 9th 2019
     
    Posted By: CerisyUnfortunately the Titon summer bypass is automatic and cuts in when the air coming into the unit is hotter than the air being expelled.

    That doesn't sound right, or sensible. Certainly under those conditions the summer bypass on our Brink would be closed. It only opens if the house is over the set temperature and the external temperature is less than the internal temperature. Are you sure that's what it does, and that's what it's supposed to do?

    FWIW, our summer bypass opens at night in the summer and closes during hot days. I expect that's what all automatic bypasses are supposed to do.

    If there's a duct through your loft, it should be very well insulated. Is it?

    If it was very noisy, it sounds like you also have the Summer Boost feature. Why not just turn that off if you don't want it? You could also reduce the boost speed to something more acceptable.
    • CommentAuthortony
    • CommentTimeFeb 9th 2019
     
    Mad drawing air in through the loft in summer no wonder you have the overheating problem.
    • CommentAuthorCerisy
    • CommentTimeFeb 9th 2019
     
    Agreed Tony - but it will be difficult to change the supply duct from the loft and soffit. Trying to take it out through the heavily insulated walls ain't going to be easy.

    The explanation of the function of the unit came from the manufacture! Yes, the supply duct could be better insulated, but the bypass function will still be wrong. Not sure about the summer boost - if it has it yes that would explain the noise - I'll check the manual! Normal boost speed is fine - bathrooms cleared quickly.
    • CommentAuthorjfb
    • CommentTimeFeb 9th 2019
     
    Are there other ways to reduce summer heat? External shading from solar gain maybe?
    •  
      CommentAuthordjh
    • CommentTimeFeb 9th 2019
     
    Posted By: CerisyThe explanation of the function of the unit came from the manufacture!

    I'd go back to them and get them to explain it again then. Specifically how that arrangement keeps you cool in summer. In writing of course.
    • CommentAuthortony
    • CommentTimeFeb 9th 2019
     
    It is no good shading windows if you are blowing solar heated air into the building
    • CommentAuthorCerisy
    • CommentTimeFeb 10th 2019
     
    All the south windows are shaded by either large overhanging eaves or a long front porch. The east and west windows are more problematic as, of course, the sun is at a lower angle, but we have fitted external roller shutters to keep that heat out.

    Good point djh - should have done that before trying to sort it myself! Doh!

    Tony, I'm back to switching it off when too hot - maybe that's an answer to these really well insulated houses??
    • CommentAuthortony
    • CommentTimeFeb 10th 2019
     
    I have one too, my air intake is straight from outside and it is rare that outside air is problematically hot
    I run summer bypass pretty much six months of the year slowing the speed right down and raising it at night during any rare heatwaves.
    •  
      CommentAuthordjh
    • CommentTimeFeb 10th 2019
     
    Posted By: CerisyI'm back to switching it off when too hot - maybe that's an answer to these really well insulated houses??

    I mostly leave ours running during summer. When its very hot I slow it down during the day (the bypass will have closed but the less-than-100% efficiency means the ventilation is still slightly heating the house - much less than opening the windows though) and speed it up at night (when the bypass will have opened again and be cooling the house). But with our system it's very clear the automatic bypass acts to stabilise the temperature in the house most of the year.
    • CommentAuthorCerisy
    • CommentTimeFeb 11th 2019
     
    Thanks guys - I'll do some more work on it. It is usually a couple of degrees warmer down here so I need to do something as we face a warmer world. Regards, Jonathan
    • CommentAuthorfinny
    • CommentTimeFeb 20th 2019
     
    What is your winter heating system?
    • CommentAuthorgyrogear
    • CommentTimeFeb 20th 2019
     
    No crawlspace, I imagine ?

    Otherwise, how much mass ? and how distributed ?
    It is important to keep the house core, COOL !

    A few tubs of cold water, suitably camouflaged in surreptitious corners and cubbies etc. might do wonders in absorbing a bit of heat. Drop the blinds at night, slide the downstairs windows open not to mention roof velux (with mosquito nets) and let the house just do its thing - if you have 25°C at midnight, you might get 17°C at 4 a.m. Around 10-ish, start chuckling water on the terrace !

    gg
    • CommentAuthorCerisy
    • CommentTimeFeb 21st 2019
     
    Our principle heating is a small wood burning stove, with underfloor heating in the two bathrooms giving a little extra heat. The hot water tank is heated by solar panels and is 400l, so that also adds to the overall heat in the house, especially in the summer!!

    The house is low thermal mass - timber frame - so not much of a core to keep cool. We are in the countryside so flies are a constant annoyance, although the suggestion of having the windows downstairs open is a good one - thanks. Now to sort out some mosquito nets. Thanks.
    • CommentAuthorgyrogear
    • CommentTimeFeb 21st 2019 edited
     
    Posted By: CerisyThe hot water tank is heated by solar panels and is 400l, so that also adds to the overall heat in the house,


    You could severely insulate it !

    I wrapped mine heavily in some of that famously detested "multicouche réflective" / multilayer and it worked wonders !
    I am now building a rigid enclosure out of XPS.

    gg
    • CommentAuthorfinny
    • CommentTimeFeb 23rd 2019
     
    If the UFH is wet then run cold mains through it.. or ideally some local surface watercourse..
    If not then some passive ventilation.. Find the biggest cold thing outside near your house...like the ground or that handy watercourse.. duct air through it and into the lowest point of the house, open similar sized vents in the upstairs at the same time.. Hey presto.
  17.  
    Can you access the loft and add more insulation to the supply pipes? could be as simple as just burying the pipes in loft roll insulation?
    • CommentAuthortony
    • CommentTimeFeb 24th 2019
     
    It will need more than that as the system takes air from the loft and delivers it into the house.
    •  
      CommentAuthordjh
    • CommentTimeFeb 24th 2019
     
    Posted By: tonyIt will need more than that as the system takes air from the loft and delivers it into the house.

    Where did he say that?
    • CommentAuthorgoodevans
    • CommentTimeFeb 25th 2019
     
    If you have passive house insulation standards and do not open the windows you will loose the heat battle in summer.

    The windows will let in say 400 watts of energy per m2 when not shaded, electrical appliances will add to that, DHW tank also - but of the order of say 100 watts.

    If the MVHR is set up logically i.e. summer bypass only at night time then during the day it will generate a little heat - say 50 watts or so.

    However MVHR on boost purge with summer bypass at night at 80 l/s will only loose 100 watts for each degree C temp difference outside to inside - say 800w for 10 degrees 7 hours or so.

    You will need to actively cool or open the windows at night I think. The MVHR alone will not be able to shift sufficient heat to offset the daytime gains.
    • CommentAuthorCerisy
    • CommentTimeFeb 25th 2019
     
    No tony, the air comes from outside via the vents in the soffit. The issue with the loft is the supply ducts come through the superheated loft and, yes, I could and will add more insulation.

    However, as goodevans explains, the battle against summer overheating is difficult to manage. The large overhanging eaves shade the upstairs south elevation windows at mid-day in the summer and the long front porch do the same with the ground floor windows. The shutters add shading to the east and west elevations and reduce reflected heat, etc.

    The odd summer boost feature on our MVHR probably means that we will try switching it off when it gets too hot and open more windows at night - well, it's worth a try!!!

    Thanks for the advice guys.
    •  
      CommentAuthordjh
    • CommentTimeFeb 25th 2019 edited
     
    I asked Titon about their summer bypass, since I couldn't find full details online. This is what they said; it sounds like older units weren't terribly clever but they have improved over time:

    The older versions have fixed temperature settings when the unit will go into bypass, this has been sensed in one of two ways, again variable due to the age of the unit.

    The oldest units look at the air temperature coming of the heat cell and would open the bypass if the temperature is between 20 & 24°C (ABS & ABD models)

    The most common unit which is just being upgraded, looks at the temperature of the air coming from outside and also the air coming from the wet rooms. If the incoming air from outside is greater than 15°C and incoming from the wet rooms is greater than 22°C bypass will activate, also the wet room air temperature must be higher than the outside temperature by 1°C (MB & HMB models)

    The unit we are currently offering has the ability to change the two air temperatures to suit the occupant and also has the option for switching the bypass manually (HMB Aura T ready).

    Note if you have an older HMB unit then this could be upgraded to have the function stated above.

    You didn't say which model you have but maybe it can be upgraded. I'd argue that their oldest models are not fit for purpose.
    • CommentAuthorCerisy
    • CommentTimeFeb 26th 2019
     
    Wow - thanks djh. I'll follow it up and let you know.
    • CommentAuthorgyrogear
    • CommentTimeFeb 26th 2019
     
    Posted By: finnyIf the UFH is wet then run cold mains through it..


    But what if it is wet but electric ?
    :shamed:

    gg
  25.  
    Erm... wouldn't advise putting any water through the UFH system that doesn't have inhibitor in it and hasn't been well filtered...

    You'd need to put a humongous amount of drinking water through the floor to make any difference to the temperature of the house... If you do have water to spare, then spread it around and let it evaporate.
    • CommentAuthorCerisy
    • CommentTimeMar 12th 2019
     
    Thanks for the suggestion djh, I checked with Titon and - surprise, surprise, our unit is too old to be upgraded. Admittedly we did buy it in 2012 and it was probably at the end of it's production run then (it was an excellent price!!!).

    So if I want to sort out the summer bypass option I will have to replace the unit - now that'll be fun, striping off the ducts and rearranging the tiny services space!

    Any recommendations for a decent MVHR unit???
    •  
      CommentAuthordjh
    • CommentTimeMar 12th 2019
     
    I'm very happy with our Brink unit but there are other brands that seem quite good (Paul & Zehnder were two I looked at). But some of the latest Titon units seem to be OK; maybe they will offer you a good price for a replacement?
    • CommentAuthorowlman
    • CommentTimeMar 20th 2019
     
    Have you ruled out the Air/Air heat-pump i.e. aircon?
    • CommentAuthorCerisy
    • CommentTimeMar 28th 2019
     
    Air con is on the list. We need to sort out the MVHR first and see how that affects the summer temperatures.

    I think I would try and fit PV along side the air con, so we will need to get some cash together!

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