Passive air conditioning of a Maryland house: ideas and brainstorming

We live in central maryland in a raised ranch house on 1/2 acre overlooking a valley. Zone 7b. Summers here are humid and can get hot. Im looking for an effective way to set up a passive air cooling system to keep the house cooler and keep the humidity down. I think a lot can be accomplished with our house by creating conditions that provide air draw through the house. I am also going to work on creating some shade over windows and the south side of the house.

As for air movement, one thought I had was taking a roof vent turbine and installing it attached to a pipe or duct that leads into the house instead of venting the roof. Has anybody tried that? I think it could act as a whole house fan except the fan is wind driven on top of the house to pull air up.  If we did that, how would we close it up successfully in the winter?

The other idea im toying with involves the basement. We dont have any ductwork in the house- our heating is propane and electric radiant heat. Im thinking of cutting floor vents in the first story and running ductwork down to open near the cement basement floor. The walls are insulated down there, and the floor is going to be sealed to reduce humidity and moisture transfer. I think these two ideas together will create a stack effect that will draw cool air up from the basement and vent hot air out of the roof.

Any thoughts or ways to expand the concept would be appreciated!

Bryan C Aldeghi wrote:
The other idea im toying with involves the basement. We dont have any ductwork in the house- our heating is propane and electric radiant heat. Im thinking of cutting floor vents in the first story and running ductwork down to open near the cement basement floor.

I did this in our living room.  I ran duct from the basement ceiling to near the basement floor in one spot, and didn't duct the other vent.  I did it to move the heat from the basement where the pellet stove is to the living room that is directly above the stove.The cooler air from the living room falls to the basement floor and the heat from the basement ceiling moves into the living room.

I haven't tried it for cooling.

Hey Bryan :) Welcome to Permies! A VERY good question!
Something to watch with the basement providing the coolness, where is the makeup air for that coming from? I know someone who went with "open the window in the basement" and discovered his slab was condensing the humidity out of the air. He had wet slab from the top, not the underside.

My solution to that problem, (I'm building, I can add more stuff easy right now) is to have my basement air intake come in from way down in my pasture, downhill, in pipes running under the ground. So it will cool the air, let the condensation drop out and drip out the pipe at the bottom, and cooler and dryer air go into my basement. I assume that would be difficult to do right off, but the concept is worth considering.

Whole house fan of a turbine would work well, IF you are watching where it gets the air. if it's just sucking in hot, it's not real useful. It's hard to throttle those to the speed you want them to run. They can be plugged, to a point, with something like a styrofoam cover, but will never end up as insulated as your roof hopefully is, will be a cold point all winter.

Good question! I look forward to the discussion!!! :D

In my childhood home, we had clerestory windows for cooling which got opened in the spring and closed mid-fall. It really made a huge difference.

Hmm... I wonder if skylights might help act as clestory windows without quite the same expense.

Pearl -

What a neat idea to incorporate the pasture into your cooling plan! Its like a diy geothermal.

Trace-
How has that worked out as far as moving humidity around? Do you have any new spots that are extra humid? What do you do about the gents in the summer?

Bryan C Aldeghi wrote:Hmm... I wonder if skylights might help act as clestory windows without quite the same expense.

If they open, yes. But ANY high placed window can do the same thing, and in a wall is ALWAYS cheaper and easier to keep from leaking. What's the highest point of wall you have? Can you put an openable window there? Doesn't have to be exactly at the ceiling. Doesn't have to be huge, works better if it's not, actually, you don't want a lot of air turnover when it's hot out, as all your input air is hot. But enough to drain the heat off slowly. that helps a lot! I don't know how big your house is, but in general, a window that has 12 x 12 opening area is enough for most houses. A mate on the other end of the house is useful too. That's not a serious retrofit to install. A skylight is, and an opening one is always harder to keep from leaking and being drafty in winter.

The idea would be to figure out exactly how much to keep one or two high windows open to keep the heat drained off, and no more than that. It'll end up being a lot less than you expect. In my last house I put in 8 huge windows, ended up with 2 of them open about 1.5 inches. All the rest could have been fixed glass if I had known, would have been a lot better in a lot of ways. I had 720 square inches of opening space, I ended up using about 108 square inches. (That math doesn't look right. The windows weren't open much. 1.5 inches x 3 foot tall window x 2 windows... not sure of 108 at all. 720 I think is correct though. ) Despite my crappy math skills today, the answer is "not much of it at all."

:D

Bryan C Aldeghi wrote:Trace-
How has that worked out as far as moving humidity around? Do you have any new spots that are extra humid? What do you do about the gents in the summer?

Our winters are very dry, so I haven't noticed any changes.  In the summer, the windows are open a lot, so I'm not sure if the vents do anything then.  I haven't really paid attention to be honest.  I just did it to get the heat upstairs in the winter.   Sorry that isn't very helpful.

When I lived in my grandmother's house I put a fan in a third floor window, shut up the rest of the house and turned it on (blowing out) at night.

I could open any window and there was an instant cool breeze coming in.  But of course this does nothing for the humidity.

Bill Mollison suggests an earth tube, a meter down, on a downhill slope  away from the house to drain moisture (a bit like Pearl's, but his is a little simpler using a mostly open to the earth tunnel with a slab covering it and backfilled with Earth. I'm planning on cutting in half Blue plastic water barrels for the tunnel cover, Tunnel needs to be minimum 60 feet long, maxes out it's effect at 300 feet, the one I'm planning will be a little over 100'

He recommends a solar stack which will draw air continuously through the tunnel with no moving parts, but a fan on an high vent or window  would work at a fraction of the cost of an air conditioner.

My humidity in VA gets into the 80- 90+ % range frequently, spilled water just lays there forever laughing at me, and every cleanup has to be followed with a towel dry, so in my case humidity is an absolutely critical control.

Another possible cooling/humidity control might be to run cold water through a pipe with radiator fins and pass the outside air over that , collecting the water for plants (distilled water) a radiant floor might be an ideal source for cold water, (or a swimming pool)and that has crossed my mind as a possibility,   the mechanical complexity of pumps and pipes is a drawback, but might work with limited space.  Perhaps a sub floor and insulation raised over the slab with pipes running between to supply the radiator.

I also have noticed uninsulated cold water supply pipes might also serve as a partial dehumidifier if that moisture were properly dealt with(not just dripping on the floor)

We live in a raised rancher - so half buried basement, and then a ranch house on top. Our ceilings are 8 ft, and the roof line starts just a tad above that. Installing a window in the wall is pretty limited by that ceiling.

All these ideas seem to use the same theory, pull air from a cool part of the house to the warmer, and vent the warmer air out. So its all about drawing air upwards and through. The effect of moving heat will create a breeze. We have a window in the basement facing north which might help with where new air is coming from.

I was reading more and it was emphasized that one od the easiest things to do is ventilate and cool the house at night so that they house vents all the heat from the day before. If you can cool the thermal mass, you can have more time before the house heats up the next day. The cement in our basement is good thermal mass. Perhaps we can add more - a water barrel is fabulous thermal mass that changes temperature slowly. Might have to put something like that in.

I would be reluctant to take on the effort of installing earth tubes at this point. Its a neat idea to file for the future!

In another thread, they are discussing off grid/ passive dehumidification. That seems quite relevant to this discussion -
https://permies.com/t/62494/Passive-dehumidification-control-mold-grid

A couple of things discussed in that thread stand out to me. First is that warm humid air is lighter than dry air. Which entails the higher you can vent it and the more airflow, the less humidity sticks around.

Another thought they shared was using large quantites of charcoal to control humidity fluxs.


Cheers!

We may live in a similar climate Koppen Cfa - Humid Subtropical? (Honestly though, it seems each summer here is getting closer to full tropical conditions.)

Regardless, it does depend on the prevailing house and yard design – cross ventilation opportunities and house alignment are key design elements.

For example, our older style houses are typically weatherboard (timber) elevated on piers, have wide verandah’s, high ceilings, and roof lines with exterior vents on each end of a gable or Dutch gable. Lattice work and blinds also help prevent the sun hitting the house walls.

Modern additions include electric fans throughout the house and sometimes even on the verandah’s to move air around the house perimeter on still, hot and humid summer days. Roof vent turbines, nicknamed whirly-birds here (a Brand name that has stuck), keep the roof space air circulating. These should be matched with ceiling vents that can be closed in winter, but most people don’t do that probably for aesthetic reasons.

Gardens and lawns around the house, with few hard surfaces like concrete, gravel and paving, also reduces heat load.

The combination of roof vents, open gables, ceiling vents and fans maximise air circulation, the shaded verandah’s and grassed surrounds cool the air before entering the house. Often breeze-ways are made to further increase cool air flow.

We usually don’t have basements, the under house void helps cool the house anyway. As Bob noted, the earth tube principle works well, like a chimney with a good draught. Jalousie (louvre) windows work a treat too, and are a very common feature in our late period colonial homes – they’ve also seen a resurgence because they work so well with the climate.

(As you’re probably aware, evaporative air coolers are useless in humid climates.)

Retrofitting a house with a few of these additions should make a significant improvement to comfort.

Our house has neither an air conditioner or a forced air heater. We use a similar idea except it's for heating and it's not passive. Our house is an open loft with 21 foot ceiling, so I installed a small $13 bath vent fan near the top to draw in the hot air that rises rises off of the wood stove and flue.



Then the hot air travels down inside the wall where it exits onto the rear of the stove and into the room.

Bryan C Aldeghi wrote:We live in a raised rancher - so half buried basement, and then a ranch house on top. Our ceilings are 8 ft, and the roof line starts just a tad above that. Installing a window in the wall is pretty limited by that ceiling.

All these ideas seem to use the same theory, pull air from a cool part of the house to the warmer, and vent the warmer air out. So its all about drawing air upwards and through. The effect of moving heat will create a breeze. We have a window in the basement facing north which might help with where new air is coming from.

I was reading more and it was emphasized that one of the easiest things to do is ventilate and cool the house at night so that they house vents all the heat from the day before. If you can cool the thermal mass, you can have more time before the house heats up the next day. The cement in our basement is good thermal mass. Perhaps we can add more - a water barrel is fabulous thermal mass that changes temperature slowly. Might have to put something like that in.

I would be reluctant to take on the effort of installing earth tubes at this point. Its a neat idea to file for the future!

Hey Bryan :) Sounds like you are learning a lot, great!! Thermal mass is fun stuff!
8 foot ceiling is plenty high for adding small windows or vents. it's not a matter of how high, it's a matter of "at the top," if your top is 8 foot, that's where you put an opening. It's to remove the top layer of stratified heat, wherever that layer is. Yours is sitting at the 8 foot mark :)

Doing your air flow night is great, if your air temperature changes enough to make a difference. If you stay hot and muggy all night, thermal mass will not cool down much, if it drops at night, it will work REALLY well. In New Mexico I closed up the house at dawn, and opened it at dusk, as the daytime ran over 100 but the night dropped to 75 or 80, and I'd cool the house as hard as I could, with big fans blowing across my cement floors and thermal mass walls. In NM, in an old mostly uninsulatable house, I stayed cool enough for my taste. I'm in Missouri now, and the muggy summer nights don't drop temperature much, maybe 10 degrees. It's a different set of parameters. Check your day/night temp swing. If the night air doesn't cool much, look at pulling from the cool earth somehow. The earth is a huge thermal mass of stable temperatures. Doesn't have to be earth tubes, that's just what I can do, there are other ways. What is your temp swing?

A question: What kind of budget are you working with here? If you can afford to tear your roof off and install skylights, and build a big veranda porch, that's one end of the budget. If you can afford to buy one barrel to use for thermal mass, and maybe figure out how to put a hole in the wall, that's another. I notice the ideas are all over the board budget-wise here. A visual of what would be affordable would help us see it better.  

A thought on a ranch house: do you have gable end vents in the attic? If so, putting a ceiling vent that you hook to the gable end vent is a simple way to getthe high heat off your ceiling.  

These are all such great suggestions and thoughts!

Our budget is a modest one, but I am pretty handy overall and able to do al lot.

Our house does have gable vents. Thats perfect! Im going to use those to avoid putting holes in the roof. I think that by using them, I can create a version of a whole house vent. The system will have a number of vents throughout the house to pull air upwards and vented through the end gable. I think all the vents could come off a central duct without too much issue. And then have a vent turbine at the gable vent. Combine that with vents to bring air up from the cooler slab in the basement, and I think we have the a solid possibility.

Just a word of caution. Before you bring basement air up into the house, check to see if you are in an area of possible radon. Radon seeps from the soil and into the air. Basements in radon areas can accumulate hazardous levels of radon, which can elevate your risk of cancer. If you have a potential for radon in your area, test the air in your basement before you work on bringing air up into the house. There are things that can be done to mitigate radon.

One good method of passive cooling is to open lower windows on one side of the house and higher windows on the other side, particularly if you can take advantage of prevailing winds. You can take advantage of the chimney effect. This works even on a 1-story ranch house like our current house, but works great on a 2-story house like our old house.

Shade is huge. Plant trees. Build porches.

We have a big front porch that is shaded by a large maple. All that shade makes for air that is usually about 10*F lower than temps out in the sun. We open the lower half of windows on that side of the house and the upper windows on the other side. This encourages air movement through the house.

When we can afford it, we want to build a porch on the back of the house as well, to keep the sun off and cool the air.

Bryan: Cool!!
Remember though, you'll be startled by how little air removal you end up wanting. Make sure you can close off the flow as needed. Too much air going through will heat your house up worse, as the air coming through the basement won't have time to cool, and will just be coming in hot.  

Glad you came up with a good doable option!!

I used a 'wind tower ' to draw air through my house. I control the flow with lourves

John,

That sounds awesome. Do have some more information/ pictures? How did you go about retrofitting your house with a wind tower?

Thanks!
Bryan

Bryan, I dont have photos, sorry.
I have built many homes etc and I dont think I have a single image!!
I study and research, use a note book and steadily get the task done.
At 70, after 45 years of building and drawing plans,  I dont think I will start.
BUT, if you send me some images I may be able to talk you through what I do.
Essentially I make sure all rooms will have an ability for air to come in a window, a doorway and through the ceiling.
I build at the top of a stair area or tall ceiling a column facing the prevailing winds.
The exterior windows are louvres that can be openned and closed to suit the climate. I tend not to adjust them each day, just seasonally.
Grand designs that English show designed a beauty for a development.
Chase me up if you cant find that.
Anyway the wind tower exit is at the tallest part of the house.
I always build small homes, so the tower does not need to be very big.
I aim at 10 % of floor area as the opening size.
I have since read that in the middle east, they work on 20 % of floor area. But the climate is different so my experiements may prove Ok for my area.

"Bryan, I dont have photos, sorry.
I have built many homes etc and I dont think I have a single image!!
I study and research, use a note book and steadily get the task done.
At 70, after 45 years of building and drawing plans,  I dont think I will start.
BUT, if you send me some images I may be able to talk you through what I do.
Essentially I make sure all rooms will have an ability for air to come in a window, a doorway and through the ceiling.
I build at the top of a stair area or tall ceiling a column facing the prevailing winds.
The exterior windows are louvres that can be openned and closed to suit the climate. I tend not to adjust them each day, just seasonally.
Grand designs that English show designed a beauty for a development.
Chase me up if you cant find that.
Anyway the wind tower exit is at the tallest part of the house.
I always build small homes, so the tower does not need to be very big.
I aim at 10 % of floor area as the opening size.
I have since read that in the middle east, they work on 20 % of floor area. But the climate is different so my experiements may prove Ok for my area."

Am I understanding you correctly in envisioning the wind tower as being like a chimney for exhausting heat? Would it help for it to be black to aid in creating a thermosyphon? Thanks!

No
Try and find images of wind towers in Iran etc.
They may be 5 or 6 feet square, at the tallest part of the house and facing the prevailing winds.
They can have shades, louvres etc to control wind flow, they may be open permanently.
You could say, a big chimney with an opening facing the prevailing winds
iranian wind towers etc

I must say I had a couple HVAC individuals come in to give me cites on a ductless framework because I needed AC and a good deal on gas. Of the considerable number of individuals that came through, Cargil from this company: https://smilehvac.ca/ was the most expert and proficient.
The installation works were managed by Cargil with assistance from Valera. Both were incredible and truly went well beyond to oblige my solicitations on setting a few units in troublesome spots. They were proficient, friendly, and kept me educated all through the procedure. Just my two cents on my own AC experience.

One old school way of getting aired cooled is to get that moving air to evaporate water. With clay tiled floors that were freshly mopped and a breeze, evaporative cooling would cool the air.

I think a lot of the ideas mentioned put together might be interesting. Large air intake, transoms, etc. I've been thinking about a vent out that might look like a chimney vent that was black. The sun would heat up the air and rise out, hopefully pulling in the hottest air from the house and circulate the air fairly constantly. Essentially all of this is just using root cellar designs that go through a house, but not needing it to be that efficient. The airflow may even give you some evaporative cooling that would de humidify like a fridgerator. I'm only curious where condensate might form.

Great thread. I went down the rabbit hole on wind towers and found this link that sums up a lot of different concepts mentioned here. Not sure if it helps the original post, but I found it fascinating and thought I would share.
https://www.sciencedirect.com/science/article/pii/S1364032114008351

- Insulation to prevent heat from entering
- Solar Gain minimized by warp around porch, fruiting vine arbor/trellis, trees, outside windows, etc
- Thermal Mass the more thermal mass you have, the slower the house will heatup during the day.
- Air Flow will increase the evaporative cooling that our skin employ, so employ drafts and fans.
- Desiccant Dehumidifier absorbs the humid moisture and then you can recharge it with heat (electric/solar/firewood/gas)
- Makeup Air this air can be cooled and dehumidified by going over a cold surface, (earth tube/ERV/Basement Slab/Fan-Coil Unit)
- Radiant Cooling just like Radiant Heating run coils of pex tubing along/in the floor/wall/ceiling and cycle cold water thru it, watching RH
- Fan-Coil Units with the coil being cold, you will get condensate and your humidity will drop. Cool coil with cold water or cold refrigerant. (dehumidifier/AC/heat pump)