Passive Cooling

Q: I've been researching natural building for some time, in preparation for a new domestic building project in South Africa - do you have any useful links for me re natural cooling? I'd like to incorporate an evaporative cooling system (solar driven) in my new adobe home.

A: (Daniel Chiras) There really isn't very much written on passive cooling for residential structures. (There's much more on commercial building.) I've been trying to fill that void in my writings but have been having trouble convincing prominent magazine publishers of its importance. You may want to check out my book, The Solar House: Passive Heating and Cooling. I wrote an entire chapter on passive cooling in that book.

For evaporative cooling, you might want to check out passive cooling towers installed on the Zion National Park's Visitors Center. There's an article on the visitor's center in the May/June issue of Solar Today. Alex Wilson at Environmental Building News wrote the article and might be able and willing to provide additional information. You can contact him at ebnATBuildingGreen.com.

Q: In the southern coastal city of Corpus Christi, Texas, we have 12 mph winds almost year round, and 26 inches of annual rainfall (rains mostly spring and fall), and brutally hot summers, meaning high electric bills for air conditioning. Question: what is the best home design for that area to get lower utility bills? Assuming I already have very thick insulated walls and high ceiling, wide overhangs to shade windows, shaded west walls, active and passive cooling in attics... Is there a BIG? advantage to a home built around a large center opening to trap cool air to release into the home in the morning during the summer...or is some other design a better fit for that area? Interested in building to suit the environment.

A: (Daniel Chiras) You ask one of those questions that is not easily answerable in a sentence or two. If your summers are hot and muggy, you definitely have a challenge ahead of your. Cooling in that climate can be quite difficult.

My advice is to pursue virtually all of the passive cooling measures that I outline in my book, The Solar House. Your goal should be to reduce internal and external heat gain to the maximum extent possible. Chapter 5 covers the subject of residential passive cooling. I've attached a table from a new book I'm working on, The Home Energy Survival Guide. This book is designed for those who want to retrofit their homes. The Solar House is geared toward new construction.

You will see from the table as well as from studying Chapter 5 from The Solar House that there are many things you can do to passively cool a structure in addition to those you have listed in your query to me. These ideas should be pursued to the maximum extent possible. It sounds as if you are on the right track, though.

As for the best design, it's a little hard to say. I would seek a design that allows the best natural cross ventilation. I would look for a design that has the lowest exterior surface area. (I'd be sure to paint the house a light color and install a light colored roof tile.) If the evening temperatures are cool, you could purge heat at night using cross ventilation, but I doubt that is the case in your location. You may need to assist that with window fans or a whole house fan.

Steps to Passive Cooling
Reduce Internal Heat Gain:
Use lights sparingly, Turn lights off when not in use, Remove light bulbs in areas where they’re not needed to avoid over lighting, Turn water heater temperature town to 120oF, Install water heater insulation blanket, Insulate hot water pipes, Eat more cold meals in the summer, Cook outside, Use the microwave in the summer, Bake at night, Run exhaust fan when cooking, Use the cold or warm water settings on washing machine, Wash clothes at night, Hang clothes on outside line, Dry larger loads, Close off utility room, Open window to utility room when the clothes dryer is in use during summer, Turn computers and other electronic devices off when not in use, Watch TV more sparingly, Unplug TV and stereo when not in use, Plug TV and stereo into power strip and turn off when not in use, Turn off furnace pilot light during the cooling season, Let pets spend more time outside in the summer, Spend more time outdoors on porches and patios, Take shorter showers, Open window when showering, Run exhaust fan when showering, Install an efficient showerhead, Hand wash dishes, Switch off drying option on dishwasher

Reduce External Heat Gain:
Plant shade trees, Build artificial shade structures such as arbors and trellises, Install awnings, Install and use window shades, Seal cracks in building envelope, Upgrade insulation, Replace energy-inefficient windows, Repaint with a lighter color, Replace roof shingles with lighter ones or metal roofing or Spanish tiles, Install radiant barriers

Purge Heat:
Use natural ventilation early and late in cooling season and as much as possible during the height of the cooling season, if your climate permits this, Purge heat at night in dry climates, Install and use window fans, Install attic fan, Install whole house fan, Improve efficiency of air conditioning system (seal ducts, replace dirty filters, shade air conditioner, etc.), Replace inefficient air conditioners with more efficient models or evaporative coolers if you are in a dry climate, Install an air-source heat pump, Use fans, Install and use ceiling fans

Q: I would like to build a house in a tropical climate like Chennai, India wherein I can harness the solar energy and use it for heating. But I would also like to lessen the impact of that heat in summer and figure out ways of cooling the place naturally. I had read somewhere (cannot remember where) that there is an architect in Africa who emulates the way ant hills are formed to create an air flow pattern to create a natural cooling mechanism and was trying to find information on that. It is in that context that I came across your site. Do you have any tips pointers on how do achieve my twin goal of cooling the house from the fiery sun while harnessing it for energy purposes?

A: (Kelly) Good passive solar design provides architectural features that naturally shield the summer sun from entering the building, via roof overhangs, deciduous trees or vines, etc. Exactly how to do this depends on the climate and location of the site. In southern India cooling during the hot months is likely a greater concern, so such passive solar should be carefully considered. As for naturally cooling the house, my best advice is to employ earth-sheltering, whereby you can take advantage of the cooler temperatures within the earth to help cool the house. And also to provide plenty of opportunities to ventilate any excess heat.

Q: From my connections in Germany I have learned a lot about passive house construction. One particular system intrigues me and I have not found any studies or papers on it. They are using the constant temperature from mother earth to warm and cool the air that enters the house via an ERV/HRV. They achieve this by burying a 100' air supply pipe between 6'-8'. The temperature shift of the air from entering the pipe to where it comes into contact with the ERV/HRV is about 30 degrees Fahrenheit. Have you heard of such a system? Can you point me in a direction? If this truly works I would like to use this ingenious way of saving energy in the houses I build.

A: (Kelly) Yes, I have heard of this, and it does work. Here are a couple of links related to this that might interest you: seabirdislandand dreamgreenhomes.com

Q: I recently got a job with a 100 + year old museum in Massachusetts. I am looking for effective ways of regulating its atmosphere - this would be quite a transformation process - I would love to hear any ideas that you may have about this problem...

A: (Kelly) One of the best ways to moderate, or regulate, temperatures in indoor environments is to incorporate lots of thermal mass on the inside. This mass should be well insulated from the fluctuations of outside temperatures. This doesn't necessarily address humidity, if this is of concern, so that would have to be handled otherwise. Such thermal mass can be incorporated into the floors, walls, exhibit installations, etc., and can be in the form of heavy masonry materials most likely, such as brick, tile, stone, adobe, concrete...

C: A previous question asked if you can use the radiant floor system to cool as well as heat. My brother has successfully done it in NE even after all the product salesmen said it couldn't be done. His hobby is building houses and experimenting with new things. He designed his woodworking shop with a system that both heats and cools...and he controls the humidity to ensure the finishes on his customecabinets are perfect. Yes, it can be done and its great walking into in the hot summers in NE.

Q: How would the cooling aspects of a passive system work in Alabama? 

A: (Kelly) Any well designed passive solar home generally functions well during warmer times also because of all the thermal mass material that is incorporated into the interior of the home.

Q: I live in Louisiana. We have to cool the houses more that heat them down south. The next home I build, I want to build a cellar and put a radiator in there. Then run pipes either 6 feet under the ground, or run pipes through a tank of water buried under ground or either run the pipes into a deep pond to keep the water cool. Then fix it like a regular A/C unit. Have duct work running through the home down into the cellar and have a blower motor blowing air through the radiator. Would it keep the house be cool?

A: (Kelly) I think that your concept has real merit. The idea of using the cooler temperature underground to help cool homes has been done in a variety of ways. One example is the project described at here, which is actually intended to help heat the incoming air, but it would act in the reverse during the cooling season. A similar arrangement is used with earth-coupled heat pumps. Even just having thermal mass floors that are placed directly over the soil beneath them, without any insulation, will help keep the space cooler.

Q: How do you optimize a home for cooling without traditional A/C methods?

A: (Kelly) There are various ways to cool a house without the use of air conditioning. As with house heating, the first consideration is good insulation in the walls and ceiling, so that heat does not enter the space so readily and the relative cool within is maintained.

One of the best ways to "keep your cool" is to have lots of "thermal mass" stored within the envelope of the home. Thermal mass materials are usually very heavy, masonry materials, like brick, stone, tile, concrete...or even water. These materials can help moderate the fluctuations of air temperature within the house.

Keep the sunlight from penitrating into the house by closing shades on windows during the time they are in the sun.

Then you need to pay attention to the weather outside, and open windows when it is cooler outside than inside...especially if it cools off at night. That way you can capture that "cool" and store it in the thermal mass. As soon as the outdoor temperature swings to being warmer than it is inside, close up the windows. It helps to have an indoor/outdoor thermometer visible in a convenient spot.

Sometimes it can help to run a fan in the attic to help exhaust excess heat up there too. This of course requires some open vents in the attic, preferably one at each end. Put the fan near one of the vents to blow out the hot air.

Q: I live in a 800 sq ft, Hardee plank, asphalt roof, pier & beam beach cottage built in 2009 close to Galveston Bay in Texas. It has all the current R values, insulation, barriers, etc. The floor plan is similar to a double shotgun with 9 ft ceilings. Unfortunately it faces WEST. I have implemented shade sales, vegetation, light paint colors, ceiling fans etc. When I was a child we lived in a post WWII home with an attic fan. My question is: Can I create a thermal stacking effect by opening the attic access door using a box fan to pull the warm air up and out of the ridge vent? Any other cost effective suggestions would be much appreciated since I now live on a fixed income. I can not afford the central A/C.

A: A/C sucks anyway in my opinion. You should do it with passive conditioning. Having grown up in south Texas I am familiar with your climate. You want complete protection from the sun in summer, fall and late spring and ventilation, ventilation, ventilation due to the humidity. Too bad you face west; that's the worst possible orientation for your climate. Whole house fans are the traditional and still one of the most effective approaches to hot humid climates like this.

Q: I live in Tucson, AZ and I am planning on building something akin to a walipini with a passive cooling system. The soil median temperature at depth here is around 75 degrees, I plan on using an earth tube system combined with evaporative cooling in summer. At first I was thinking of using a cool tower ahead of the earth tube system, but then got to thinking that the earth tubes may actually bring the temperature of that evaporated air back up to the temperature of the earth, not to mention running that moist air through the tubes may cause a condensation issue. Then I got to thinking that if I ran the dry air through the earth tubes first it would likely cool it down to about 80 degrees, then at the end of that system feed the air through the evaporator pads and potentially cool it another 15 to 20 degrees, winding up with 60-65 degree air ultimately. On the other end I would have a solar chimney. Does this sound like a reasonable plan and am I thinking along the right lines?

A: Too often people make passive heating and cooling way too complicated. My guess is that if you just look at night time temperatures in Tucson and if they are in the low 70s say at 2am that you're better off with just night vent cooling over a relatively high mass interior without all the complications that come with earth tubes (which have a reputation of growing mold) and cool towers and solar chimneys which require optimized complicated flow rates. Night vent cooling is tried and true but does require a few simple things. Keep the entire building shaded during the day especially early morning and late afternoon. This can be done with carefully designed overhangs, window shades best  on the outside, and planting to reduce diffuse radiation reflected from the ground, patios, driveways etc. For the Tucson climate its best to have the night air flow over some high mass material like 2 inch thick stucco surfaces or adobe interior walls. Its also important that your building be very well insulated. Our rule of thumb is at least R 21 in walls and R 48 in roofs the more the better. Supplement all this with highly efficient ceiling fans. The newer ones are very efficient and are very inexpensive.