Vacation home in Utah — How can I cool my home without AC?
Junie-b
| Posted in Energy Efficiency and Durability on
Vacation home in Utah. It’s vacant. Inside temperature is 92 F, outside temperature is 102. How can I cool the home without AC?
It’s a round home in southern Utah with cathedral ceilings. The metal roof is round like parasol. It’s vacant. What can I do to get hot air out of the home?
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If the finish color of the metal roof is light and solar-reflective, short of air conditioning there isn't a whole lot you can do. If there is power to the site, with fan controls that allow you to automatically ventilate the place at night when the outdoor temps are lower than inside you can probably reduce the peak and average indoor temps.
Given that it's vacant, what level of cooling meets your goals here?
June,
To thoroughly ventilate this home when temperatures are cooler (at night) with a whole-house fan, you usually have to leave the windows open at night, so that approach is hard to manage if the house is vacant.
If your house is vacant, I would say that the interior temperature doesn't matter much. If it matters, install an air conditioner.
If it's an off-grid house -- somewhere where you can't install an air conditioner -- you're going to have to learn to live with these Utah temperatures.
June,
A few more thoughts:
1. If the outdoor temperature really is 102°F for an extended period of time, and your indoor temperature is 92°F without air conditioning, you're doing something right. In general, the indoor temperature will eventually adjust to be close to the average outdoor temperature (or will be higher, due to solar heat gain through windows and the operation of your refrigerator if you have one).
2. To reduce solar heat gain, make sure that your windows (especially your east-facing windows and your west-facing windows) are shaded on the exterior. If it's a vacant home, you could install exterior shutters.
3. Adding insulation between your roof and the living space will reduce heat gain from above.
In the hot, very dry climate of Utah, sometimes evaporative coolers, sometimes called "swamp coolers" might have some usefulness. Takes water, and fans to cool, but no compressors for refrigeration. Read about them, but never seen one.
You can do night ventilation without windows being open by either:
a) Use a vent through the wall for intake, with a "backflow damper" to close it when the fan isn't running. Locate that vent low, so that the natural air flow during the day won't open it. You can also use a motorized damper, but a backflow damper is simpler and cheaper.
b) Use a balanced set of two fans, one blowing in and one blowing out, both with dampers.
In addition to regular evaporative coolers, there are "indirect evaporative coolers" that don't introduce humidity into the space being cooler. Coolerado is one brand.
Any thoughts on Velux Sky light solar powered, has remote to program opening at set times, will close auto if it rains, or batteries in remote low, concider to open evening to let hot air escape home it stays open 25 minutes then closes. Any pro's or cons on this?
The features on the auto skylight sound like they do a lot of what you want. But skylights have a lot of disadvantages. See https://www.greenbuildingadvisor.com/articles/dept/building-science/pros-and-cons-skylights
That's probably also an expensive solution compared to the others, especially when you consider that just opening a hole at the top won't do as much as opening a hole at the top for hot air to go out, and opening a hole at the bottom for cool air to come in.
June,
You would need to have a lot of faith in the reliability of the skylight technology to leave it to open and shut a hole in the roof in a vacant house
A skylight is a really BAD idea in this situation, even if it could be open & closed reliably. Solar gains from skylights during the summer are ENORMOUS compared to windows, due to the high angle of the summer sun.
Even north facing windows get substantial solar gains, and having exterior operable shutters for ALL windows (not just east & west windows) to be closed when you leave will reduce the total gain for the house. Skylights would also need to have opaque exterior shutters too.
For passive nighttime ventilation to have much effect it has to be all night, not just 25 minutes. Air does not have much thermal mass compared to the structural materials and contents of the house, and it takes many tens or even hundreds of air exchanges to bring a 92F interior down to 80F ventilating with 70-75F nighttime air. A dampered vent stack taller than the house combined with a dampered intake vent near ground level on the other side of the house from the stack, under differential temperature thermostat control that opens the dampers whenever the indoor temp was more than a few degrees higher than the outdoor temp, and closes whenever the outdoor temp is higher than the indoor temp is probably a reasonable approach.
If it's off-grid you need the standby power to be low, and use minimal active power. A 12" or bigger hot air duct zone damper (on a comparable diameter stack) is probably the right way to go, possibly with a venturi- type cap (often used for barn ventilation) to get a bit of wind-assist flow is probably a reasonable approach. If it's a huge house you may need more than one.
Here's a link to an article with more information on evaporative coolers: Saving Energy With an Evaporative Cooler.