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Adventures in Ventilatory Home Cooling

Discussion in 'Environmental Discussion' started by SageBrush, Jun 15, 2011.

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  1. SageBrush

    SageBrush Senior Member

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    I am very fortunate to live in a wonderful climate. Four seasons, high altitude, low humidity. Summers are mostly low 90s F peak each day, but nights are in the 60s F and sometimes high 50s.

    Today's mean temperature is 77F. Not bad for the house overall as a target, but I figure I can use ventilation at night to cut down on in-house temperature swings, *and* lower the mean temperature. My efforts thus far have resulted in a mean temp of 74F with a range from 71 - 79 through 24 hours. I'd like to knock off another couple degrees if possible ... ...

    Approach for now:
    20 watt fan operated from about 9pm - 7am in our upper stairs bedroom.
    80 watts of fans powered up between 4 - 5 am (when I get up): one outside the house pushing cool air in, one fan on the other side of the house pushing warmer house out out. Fans turned off at 07:30 am

    Windows and doors closed during the day on the wind side, left open on opposing side to keep in-house humidity down and to provide a small air exchange. All windows are shaded during the day, and unshaded at night. I open the screen opposite the fan pushing cool air into the home in the morning to aid airflow for those hours, but otherwise use screens to keep unwanted guests out of the house.

    Energy use is about 0.5 kwh/day. I spend perhaps 5 minutes a day total checking wind patterns and making the rounds to open/close stuff.

    Any ideas for mods/improvements ?
  2. xs650

    xs650 Senior Member

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    We get a reasonable temperature swing here too, usually a 30 degree temperature swing in the summer.

    As long as it doesn't get over the low 90s our inside temperature usually stays under 79F, which is our AC on temperature, so no AC. Our house is well insulated and the windows are mostly shaded during summer days, with 90% solar block screens on the few that aren't. We just open several windows at night, no fans although I'm considering adding one.

    Something we do differently is shut all the windows during the day, making sure to use vent fans while showering or cooking and avoiding other humidity generating activities like running the dishwasher until the windows are open for the night.

    If I accidentally leave a window or two open during the day, the house heats up noticeably faster. You might consider closing all your windows in the daytime. We don't have a house humidity problem. Our climate is fairly low humidity in the summer but not as low as desert or a lot of high altitude areas.
  3. hyo silver

    hyo silver Awaaaaay

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    Back in the day on the prairies, the trick was to leave everything wide open at night and shut everything up during the day. That way, the house stayed full of cool air and never got unbearably hot, despite the often brutal conditions outside. Obviously, that's not going to work in most cities, but the same idea applies. The chimney effect works very well if you've got windows on multiple floors - open the top and bottom ones, and let the air flow. Keeping direct sun off things by using drapes will help keep the house cooler. Electronics also put out a surprising amount of heat.
  4. SageBrush

    SageBrush Senior Member

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    Thanks for the suggestions.

    Last summer I tried closing up the windows during the day and did not like the interior air quality. The other (for me) very nice benefit of leaving the windows open on the non-windy side of the house is hearing outside sounds. I don't realize how much I appreciate outdoors brought inside until I am in a closed building for a while and start feeling a desire to leave the enclosed, superficial environment. It is probably a side-effect of growing up outside in open spaces.

    Hyo, it took me a couple of years to finally come up with window blinds my family finds aesthetic, and function well for passive solar: I put two blinds up on every window. The outside-facing blind is made of light reflecting horizontal slats, and the interior-facing blind is woven bamboo or other wood. The interior look reminds me of Japanese paper with ribbing.
  5. tomlouie

    tomlouie Member

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    Have you considered window tint film sheets? They cut down on UV and IR transmission, so keeps house cooler in summer and warmer in winter.
  6. SageBrush

    SageBrush Senior Member

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    ^^ Tom
    My windows are used for heat gain in the winter.
  7. xs650

    xs650 Senior Member

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    I figured you had your reasons.

    There are heat exchangers for ventilation that would reduce heat gain, but they co$t to buy and take power to operate. I expect you already know about them. They also wouldn't solve your desire for outdoor sounds either. I don't mind our windows being shut during the day, but don't like the 2 to 10 nights year where it doesn't cool off enough to open the windows at night.
  8. chogan2

    chogan2 Senior Member

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    Consider using a larger fan at night. In the pre-AC South, whole-house attic fans were common. Every one I've seen has been a brute. I pulled the one from my house (allergy issues) -- roughly 3' across, looks like 1 hp motor. That would be order of 35x your 20 watt fan. Either they massively over-spec'ed them back in the day, or you are possibly under-spec'ed for optimal cooling. Considering what you'd be trying to do -- cool 75 degree household furnishings with (average?) 65 degree air -- I'd bet higher air flow would result in more net cooling. Not sure how you would test that other than trying a larger fan. Possibly, if the temperature of the air flow into the fan at dawn is much different from the outside temp then you may be missing some opportunity for cooling.

    Edit: Other analogy would be an AC blower motor. At least a hp there, typically. You've replaced the evaporator coil with the outdoors, and you're cooling the house down in 8 hours not 30 minutes, but still you can't remove a lot of heat energy with 10 degrees difference in temp, air as the working fluid, and a 20 watt fan.

    Yet a third perspective would be to figure out your air changes due to the 20 watt fan. I'm seeing numbers like 10 CFM/watt for small fans. So 200 CFM with no back pressure. If I did the math right, for 8' ceiling, that's one air change per hour for a 1500 sq ft house. When I look up recommended air change rates for AC systems, its 10 to 18 per hour for nighttime cooling. So again a big difference.

    Last edit: Yeah, this guide to whole-house fan cooling has even higher rates of air turnover, but I think they are trying to cool with the breeze, not merely trying to remove heat from the house:

    http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12357

    Edit: On the solar gain issue, I just got done making a skylight cover for my church, with exactly that in mind -- on in the summer, off in the winter. Google "solar screen" to see the equivalent for windows. Popular in Florida and similar climates. But they substantially darken the room -- essentially block visible and IR in the same proportion.
  9. skruse

    skruse Senior Member

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    Anything that has high thermal mass (specific heat) helps slow down the gain or loss of energy. This includes ceramic tile floors, interior brick and water, air locks on doors. It is always more cost effective to hold onto what you already have vs. "go get more." Storm liners on drapes are a big plus.
  10. sipnfuel

    sipnfuel New Member

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    If you can run the sprinklers at night or in the early morning that can not only save on your watering costs due to lower evaporation, but it also does tend to cool the air which sometimes helps ambient temps inside the house as well.
  11. SageBrush

    SageBrush Senior Member

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    I have about 500 square feet of tile, and have been wondering if it is worth the trouble to wet them in the early morning to cool them down with evaporation. It is easy enough to calculate the dissipated heat, but I do not know what fraction that is of my total daily heat gain. Any guesses for a 2800 s.f. house ?
  12. wick1ert

    wick1ert Senior Member

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    My step-dad in Indiana had a whole house exhaust fan installed, IIRC. He said that running it during the day results in very minimal A/C usage.

    I found in the past, running window fan units pulling the air in at night made the house get down to around 70 or below, depending upon outdoor temperatures (we have much higher humidity and not as much swing at night as you).

    The other suggestion of tint on windows, is making a good difference for me. I notice the back of the house doesn't heat up at badly as it used to. Of course, those windows get blasted by the sun in the evening, as it passes outside a neighbors tree. My Oak tree in the backyard isn't quite big enough yet to shade my house at this point. I think I have the 35% on the back windows of the house. Didn't notice much difference in winter, either.
  13. cyclopathic

    cyclopathic Senior Member

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    I hate you :sick:
  14. SageBrush

    SageBrush Senior Member

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    Did I mention the clean air, awesome mountains, and pretty women ? :D
  15. hyo silver

    hyo silver Awaaaaay

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    Living 'outside' for any length of time, you've probably learned that your real weather protection is your clothing. A house is just a place to keep all your stuff. They have their advantages, but it means being isolated from the natural world, and having to stay in one place all the time. What kind of life is that? :p
  16. hyo silver

    hyo silver Awaaaaay

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    Do you live in Vancouver too? I had no idea. :p
  17. SageBrush

    SageBrush Senior Member

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    :rockon:
  18. wick1ert

    wick1ert Senior Member

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    But we gots dirty air (#1 cancer state in the USA), a few rolling hills, and the people of walmart all over.....can we trade? lol
  19. SageBrush

    SageBrush Senior Member

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    Thanks for the ideas :)

    I have central ducting for AC heating and cooling. I can think again about using it for more ventilation if needed during really hot spells. If I am not mistaken the fan uses 1 kw, so I have been avoiding its use. I should have mentioned that homes in my locale do not have attics.
  20. xs650

    xs650 Senior Member

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    Wetting your inside tiles would run your humidity up to 100% and make the inside of your house like living in an armpit. If you are on a slab floor, then the tiles should already be cooler than the air in the house.

    The other poster's comments about too small fan size to be effective were right on. Assuming your house has an average of 9 foot ceilings, you have 2800x9=25,200ft^3 of air in your house. That air weighs about 1800 lbs. Your walls, ceiling, floors and furniture weigh many, many times that. One of the reasons for so many air changes per hour is to get enough circulation to cool down those solid masses which hold far more thermal energy than the air in your house.

    You might have noticed that when you close your windows in the morning that the temperature rises a few degrees in less than an hour then the rises at a slower rate. The quicker rise at the start is due to heating from the house structure and solid contents.

    With your low energy approach to living (a good thing) you prolly don't want a 1/2 horsepower motor running all night to cool down your house structure and contents, but something more than you have might fit your overall desires.

    FWIW, I don't bother with fans, just open windows at night but I'm not trying to be as energy efficient as you are.

    Rather than using your AC blower, there is a lower power way to move air. You could consider which way the air normally flows through your house and add a couple of window fans that help the air flow in that direction. It will take a lot less power to move the air directly in a window or two and through your house than it would to cram it through AC ducts and filters. The window fans should be in panels that close off the window so that the rest of the window is closed off and no air goes back out the same window you just sucked it into.
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