Hello, everyone! I have a question regarding thermal chimneys, which work passively using convection. (They are used for cooling) My question is: what side of the house should they be on? I know passive solar relies on the south side of the house, so I'm thinking for a thermal chimney to work well, it should be on the south side. Are their other options?

If you want it solar heated in the summer, it doesn't need as much southern exposure as something solar heated in the winter. Plus if it's called a chimney, it probably sticks up. So it would get sun even if it was in the middle or on the north side. On the north side it won't shade the roof, so you still have good places to put solar panels.

But I actually think solar chimneys are rarely a good idea. It's basically the same function as a whole-house fan, but uses solar heat and the inside-outside temperature difference to drive the air flow. If it does that during the day, when it's hotter outside than in, it will provide heating, not cooling. So you need to be sure you can seal it off really well. The goal is to have it bring in cool air at night. In humid climates, that's when relative humidity is highest. It can lead to moisture and mold problems if you rely on it and don't use conventional A/C. If you do use A/C during the day, venting at night can throw away all the dehumidification work you did during the day, and you have to start all over in the morning, so it can increase energy use.

If you pay careful attention to dew points you can find days when venting can save you energy in many climates. But it's not worth building a solar chimney for that--better to use an efficient electric fan an put up a PV covered tower where you would have put the solar chimney, and get all the electricity you need for the fan when you are going to run it, and lots more electricity you can use for somethign else on the other days. So it's really only worth considering a solar chimney in climates where humidity is a non-issue.

Other options? Well, there's PV plus conventional A/C, or there's solar desiccant dehumidification, which youc an then combine with conventional cooling or with indirect evaporative cooling.

Solar chimneys and earth tubes are more trouble than they're worth. They provide zero latent cooling, are expensive to implement & maintain, compared to some PV panels and a mini-split.

They look pretty kewl in hippie historical retrospectives though! :-)

Sorry it took me so long to reply. May I ask why earth tubes are not an effective cooling method? I thought they would at least prove to be adequate, as well as low-maintenance. If you were to build an earth-bermed house, you would need to excavate anyway, so wouldn't putting earth tubes in at the time of construction not be a big deal?

Thermal chimney has been in use for couple of centuries and it generally consist black-painted pattern to absorb maximum heat. It is preferred to bring down the energy cost and to give superior comfort. There are two things which are taken into consideration while installing a thermal chimney: • South facing glass • Thermal mass to absorb, and disperse heat Why it should face to south direction: The position of the thermal chimney should be to south so that it can admit solar energy inside the house. I hope it is helpful…

Posted By AspiringArchitect777 on 16 Nov 2015 12:34 AM
Sorry it took me so long to reply. May I ask why earth tubes are not an effective cooling method? I thought they would at least prove to be adequate, as well as low-maintenance. If you were to build an earth-bermed house, you would need to excavate anyway, so wouldn't putting earth tubes in at the time of construction not be a big deal?

You know that musty basement smell?  Well an air tube buried in the earth will eventually smell like that as dust moisture and such combine to foul the tube.  How do you clean a lot of buried pipe easilly and regularly?  IMO if you want to use earth cooling, a better approach would be to bury water lines, circ water thru the ground pipes to a fan coil and cool interior or fresh above ground ventilation air that way.  Not as passive, but with a PV panel to power the circ pump for the water, and a solar chimney to create the impetus to draw fresh air thru a fan coil...

I agree. In a hot, dry climate (or with dehumidification) one could also pump water through a radiant ceiling/wall/floor.

If you have a two-story building that you are keeping at a temperature below the outdoor temperature with Ronmar's fan coil (also available as a commercial product from Zehnder), you'll have stack effect in the opposite direction to what the solar chimney wants to do. For example, if it was 90 F outside and 75 F inside, and you put the entrance to the solar chimney at the top of the house, you'd need two stories of solar chimney above the house at 90 + 15 = 105 F just to cancel the effect of the cold air in the house wanting to sink. To actually flow air upward, you'd need that monstrous chimney to get up something like 115 or more.

You can build something like that, but you could get a little solar panel and run a fan to send the air through the fan coil for a lot less money.

Yep, changes in density work both ways