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HVAC Tips to keep your house cool in summer

  1. Aug 7, 2018 #1

    sophiecentaur

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    There are a lot of strategies that can help to avoid it being total hell indoors in this hot weather.

    We've had many threads about Air Con and Air Coolers but these things are not widely used in the UK and it's too late to contemplate AC because they've all been sold!! There are other ways, though.

    It's hard to realise just how much the fabric of the house heats up, whatever you do with doors and windows. The received wisdom seems to be to shut all doors and windows and to close curtains. It certainly works in downstairs rooms for us. Some idiot members of the Great British Public were interviewed on TV and said that strategy is "rubbish" and that the Met Office had no idea!! That system works well but you can do better by closing internal doors and not using fans in unoccupied rooms. The heating effect of a poorly insulated house seems to be actually more obvious than the heat loss in winter. Ceilings can get noticeably hot during the day and I've found that avoiding the use of a fan helps to reduce heating of the room air (no convection with heat source at the top)
    A crazy thing that I have noticed is that, despite a good flow of cool nighttime air, the room still feels hot due to radiation from the ceiling and walls. The once popular hot air heating systems lost credibility when it was realised that the cold walls made a room feel far cooler than the air temperature would suggest. Same thing but just the other way round. Radiation counts.
    I was wondering if anyone has other pet methods for survival (apart from going to the local library all day).
     
  2. jcsd
  3. Aug 7, 2018 #2
    Fan in a first floor window blowing in the house and a fan in the attic blowing outside? Put ivy on your outside walls to block the radiation?
     
  4. Aug 7, 2018 #3

    Bystander

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    Shade trees? Other heat sinks? And, "it's not the heat, it's the humidity." What've your dew points been running?
     
  5. Aug 7, 2018 #4

    anorlunda

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    Wow, it must be hot indeed in Europe. It has been hot here in North America too.

    You need to consider the time constant of the heat stored in the structure and the contents. I think the traditional folk rule is 72 hours. Therefore, you cant compare your tactics today with the results today. Keep a log and see if those good practices make it somewhat better 3 days later.
     
  6. Aug 7, 2018 #5
    Poorly insulated house is the root of most comfort problems. You could paint the roof and walls white to reflect some of the suns radiant heat.

    I once spent a summer in a US Air Force barracks without working air conditioning. Typical summer outside temperatures were nighttime low of 60 to 70 deg F, and daytime high of 100 to 110 deg F. The building was concrete block painted white on the outside. It stayed comfortable inside after we convinced everybody to shut down the ventilation blower during the day, and run it all night. The humidity, at least, was low. They couldn't fix the AC in summer, but waited until the following winter.
     
  7. Aug 7, 2018 #6

    Tom.G

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    Even if the attic is insulated, forced attic ventilation is effective. Put a good-size (24 in.?) exhaust fan in one wall near the peak. Run it during the day to keep the attic temp down, and if cool at night keep it running with the door open between attic and living space to cool everything (open a few windows). In the US they are even available with a built-in thermostat. Put the fan on the leeward side of the prevailing winds.

    If the exterior walls are not insulated, insulation can be blown in from the outside without major disruption. It's even a do-it-yourself job if you can do light carpentry work, can draft an assistant and don't mind working on a ladder.
     
  8. Aug 8, 2018 #7
    Except for nights. When it's about the cool night air, no fan is enough.

    Maybe I can add something useful to this topic after all. We tend to put our holiday to September. This way we can stay in the air conditioned office when it is hot and we have a good chance for a holiday not ruined by excess heat.
    I really can't understand summer holidays.

    Also, we keep a tent at the garden for sleeping when it is hot. By ten at night it's already cool enough to sleep, while in the house it's still like hell because of the walls.
    The tent should be moved in every few days so it won't hurt the grass.

    Ps.: just noticed that what I wrote is not really about keeping the house cool... Sorry. We gave up on that.
     
    Last edited: Aug 8, 2018
  9. Aug 8, 2018 #8

    sophiecentaur

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    Circulating air through the roof void sounds a good idea but I don't think it's good to take air from the main house volume. That would involve pulling hot air into the house. Our present strategy of keeping doors etc. closed results in our internal temperature (downstairs) being at least 5C below outside. But the outside air temperature is a lot lower than the roof tiles get with sun on them. It would, indeed, be easy to instal and two fans would allow a choice of flow direction to match the wind direction and keep the fabric as cool as possible.
    My house is a'dormer' design so the loft space is an awkward shape and very restricted to work in so experiments with extra insulation are not a very attractive idea. I need a helpful trained monkey to do all that stuff.
    The UK government is very half hearted about help with energy saving. They have 'initiatives', every so often but they are mainly window dressing and I have not qualified for one reason or another, when I have investigated. The Feed In tariff for PV installations was good if your house (and you) fitted the requirements but all the benefits were paid for by the rest of the Energy consumers. More window dressing to make a past government look green.
     
  10. Aug 8, 2018 #9

    sophiecentaur

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    The humidity outside here has been quite respectable - below 30% when the temperature is over 30C. We spent a couple of weeks around New York and the humidity made living without AC pretty bad at times.
    Actually, it's another topic but I was wondering just how good the available humidity meters are. The basic principle seems a bit 'hopeful' to me for accuracy.
     
  11. Aug 8, 2018 #10

    OmCheeto

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    Although I do have an A/C unit, it's a bit small at 600 watts, so I do have to be mindful of heat sources.
    I discovered last week that one room in particular got much warmer than the rest of the house, did some IR thermal scanning and found it was mostly due to a single window. It's 2 m2, and by my rough calculations accounts for 25% of my total heat flow. So I hung a large aluminized tarp to shield it. It seems to help a lot.

    Today it's supposed to be 99°F/37°C, so I may turn on my attic fan. It's a 12 volt experiment left over from last year, and isn't permanently wired.
    Currently, it's about 9 am(savings time, so 8 am in real time) in the morning, and the temperature outside is the same as in. About 72°F/22°C.
    Attic temperature is 70°F/21°C, so it appears I have a bit of time left.*
    Crawl space temperature is a surprising 67°F/20°C. I'd have thought it would be much cooler than that.

    *Done!
     
  12. Aug 8, 2018 #11
    As soon as hotter outside than in, Windows shut, curtains closed, 'occupied' rooms' fans running during day.
    Soon as outside temperature cooler than interior, open curtains on shaded side, open windows, fire up the BIG air-mover to stir the air from the heat trap in stair well.
    Despite desk and wall fans in bedroom, still slept 'sweaty starfish' mode on bath towel on top of bed.
    Cool enough to sleep comfortably around dawn.
    Rinse and repeat...
     
  13. Aug 8, 2018 #12
    Don't watch youtube on $400 lenovo laptops.
     
  14. Aug 8, 2018 #13

    Tom.G

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    Although I didn't state it, I was trying to indicate that during daytime the attic was to be ventilated while isolated from the rest of the house. During cooler nights, you can use the same fan to draw cool air thru the house by opening the door to the attic.

    Sorry for the ambiguity.
    Tom
     
  15. Aug 8, 2018 #14
    I once owned a house in Houghton, Michigan. The roof was poorly insulated, so it was hot in the summer, and had major ice dams in the winter. It had a cathedral ceiling (no attic), so adding insulation was not possible, even if I had a skinny trained monkey helping. So we added insulation to the outside of the roof. Invited a bunch of friends and victims to a roofing party. Stripped off the existing shingles, put down a 2" layer of foam, laid 2X4's on top of the foam, nailed the 2X4's to the rafters using 6" long pole barn nails, put 1/2" plywood on the 2X4's, tar paper, and shingles. The 1.5" air gap between the plywood and the foam, combined with soffit and ridge vent, did an excellent job of ventilating. The house was very noticeably cooler in hot weather, and the ice dams were completely eliminated. And we got the job done in one weekend, except for minor touch up and painting.

    Side note: American 2X4's are a standard lumber size. Many years ago, they were 2" X 4", then 1.63" X 3.63", and now 1.5" X 3.5" in cross section.
     
  16. Aug 9, 2018 #15

    sophiecentaur

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    Interesting story. External added insulation is rare in the UK but I have seen examples. The reason, I think, is that the weather (up til now) has actually not been extreme enough and the modification is not cheap. There would be another difficulty in my case as we are semi detached and it would spoil the look of a well matched pair of cottages. Planning authorities in some areas would forbid it, too, despite the advantages.
    In the end, I think I will need to bite the bullet and get the roof sorted with internal insulation by paying someone else to do it. (Ouch)
     
  17. Aug 9, 2018 #16

    OmCheeto

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    Well, that was interesting.
    The fan made things worse!

    I think it's because the exterior surface of the roof's temperature was 68°C/154°F, and that's where half of the intake air was coming from.
    The other half of the intake air was ambient exterior temperature: 29°C/85°F
    Just guesstimates on the proportions of course. It's much too hot to do anything more than eyeball things in this kind of weather.

    Anyways, this is good to know.

    Hopefully, we have some more nasty hot weather again tomorrow, so I can continue this experiment.

    Obligatory graph:

    2018.08.09.attic.fan.testing.png
     
  18. Aug 9, 2018 #17

    Tom.G

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    The attic fan could be pulling some outside air in thru the living area. But that peak around 40000 seconds is only 0.36°C and the following downward trend, staying below outdoor ambient for 4Hrs, indicates some unaccounted hidden factors. (How does a sealed box decrease in temperature while being in a hotter ambient?)

    Around Noon to 1pm of the first day for instance, perhaps the Sun was hitting some windows. There is a hint of the same on the second day.

    p.s. The thermal time lag (outdoor to indoor) appears to be 2 to 3 Hrs. Is the roof facing East, with perhaps partial shade about 4pm?
     
  19. Aug 9, 2018 #18

    jim hardy

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    I ran a garden hose up to the roof and placed three yard sprinklers along the peak.
    Around noon and a a couple times mid to late afternoon i turn them on for five or ten minutes.
    I see steam coming from the hot shingles and feel a slight difference in radiant heat inside the house.

    I'm not instrumented so it's un-scientific
    but it's quite a visual effect and the talk of the neighborhood.

    I will add an attic fan when up there this winter wiring a new room. Maybe an attic temperature meter, too.

    old jim
     
  20. Aug 10, 2018 #19

    OmCheeto

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    hmmmm.... None of this makes any sense to me. I suspect it's mostly my fault, as I should have repeated that I do have an A/C unit in operation, and the internal temperature should be ignored. Consider it a "baseline".

    Interestingly, the outside temperatures were both within 1°C of each other for days 1 and 2.
    Also interesting, is that even though the attic exhaust fan was run at opposite times of day, the attic temperatures were also within 1°C of each other.
    This indicates that the exhaust fan had near zero effect.
    I suspect this is due to the area of the roof/ceiling of ≈84 m2, along with a solar irradiation factor of 1000 watts/m2, yields 84,000 watts.
    My guess is that my attic system is currently designed for natural convection, and would require more modification than just a fan to fix this.

    New obligatory graph, with less noise, and more information:
    2018.08.10.house.cooling.analysis.png
    There be very tall trees to the south and west of my house.

    I have 3 roof-peak vents, and about a dozen soffit vents. If you do install an attic fan, I would recommend not leaving open any spare roof-peak vents, as they kind of negate that type of improvement, IMHO.
     
  21. Aug 10, 2018 #20

    Tom.G

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    12V fan, likely not a high volume air mover.
    Probably some folks here could calculate what air flow rate is needed to keep the exhaust tempurature to, say, a 5°C rise. Any takers?
     
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