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DESIGN FOR CLIMATE CHANGE: How Passive Cooling Keeps Your House Cool During Heatwaves

Updated: Apr 17, 2023

Your Own Home is Becoming Unbearable

A big problem that an increasing number of Canadians are facing is the issue of overheating. Traditionally, Canadians have not had to worry about cooling; it's been a heating-dominant climate. There's no question that winter storms are becoming more extreme, but heatwaves are worsening too.

It's 11 at night and you’re tossing in bed, you can’t sleep. It was muggy indoors all day and dark too since all the blinds were closed to keep out the hot sun, but you can still feel the heat off the South walls. It’s been a terribly hot few days; you’re not able to focus on your work. The Slurpee machine at the 7-11 broke down, and there’s no relief in the shade. It's still uncomfortably warm everywhere in your home despite all the noisy fans going, just pushing the warm air around. You grab a tall glass of water, but the ice trays are still liquid, and the iced cream is melted. The fridge stinks of spoiled food; it wasn’t designed to keep up with these temperatures. You consider an air-conditioned hotel room for a couple of nights just so you can get some rest and get some work done, but online you see everything’s booked. You check for maybe another portable AC unit or two - everywhere is out of stock. This isn't the first heatwave and it’s not likely to be the last. It's hot outside, and it's getting hotter.

Sweating male runner cooling himself with a water bottle

The Problem

Home air conditioning has increasingly been used since the late 1940s to keep a house cool in hot weather. People are increasingly looking to passive cooling and other air con alternatives to keep the house cool in summer naturally as hotter, longer, more frequent heatwaves and rising energy rates turn the cost of home air conditioning from a common comfort into an increasingly expensive survival feature.

With the increased length and frequency of heat waves and the increase in summer daytime high temperatures, most people recognize - whatever their beliefs on climate change - that temperatures have been growing less comfortable and that home cooling is becoming a need. The astute Canadian understands that conditions will continue to deteriorate over the coming years and decades. The temperatures will continue to rise. We will need cooling in the home for longer portions of the year. In some parts of the world, it's becoming impossible to live.

The health danger is very real, and it’s not that far away. There’s something called wet bulb temperature. In short, if the combination of the ambient air temperature and the ambient relative humidity is above ~35.5-36C, the human body will begin to cook.

"...if you've got a fan blowing hot air around you, you're going to cook." - Craig Crandall, professor at University of Texas Southwest

For instance, if the relative humidity was 50% and the air temperature is 45C, the wet bulb temperature is just over 35. The proteins in the body begin to fall apart – “denature” – they cook. In the table below, you can see how the combination of temperature and humidity affect livability. Anything in light orange is very uncomfortable. The thresholds in orange are combinations at which you need to change your environment or leave if you cannot. The results in very dark orange are wet bulb temperatures at which flesh starts cooking, and you begin to die.

Table showing wet bulb thermometer temperatures resulting from a combination of ambient air temperature and relative humidity; lethal temperature range is highlighted
In the red, you are dead

Hot History

Obviously if the cooling strategy in place is insufficient or if there is no cooling system or strategy in place that's really when people will turn into meat. Even before that point though, people - especially the elderly - are dying from heat related illnesses. Europe suffered a highly lethal heat wave in 2003 during which there was an excess mortality of 80,000 people. Since then, 2000 people are dying every year in Europe just from overheating, and it's not stopping [2006], [2010], [2012] [2018] [2019]. The Middle East - where the cultures are accustomed to high heat - is now facing a rise in overheating deaths.

I remember my first brush with shifting weather was the summer of 1987. I was camping by a lake an hour or so from Edmonton. The temperature got up to 39C – never saw that before. Edmonton had also never seen a tornado, but that summer, an F4 tornado just ripped through the city. Thankfully only a couple dozen casualties, but a huge amount of physical damage. Since then, I've lived in apartment buildings in South-facing suites with no exterior shading devices. One didn’t even have mechanical ventilation. The other had ventilation and a couple of portable air conditioning units, but they could only bring the indoor temperature down to 31C from the 34C outdoors. Like the story at the start of the article, the refrigerator couldn’t keep up, and some of the food had to be tossed.

Hold On, Before You Call Up the Aircon Guys...

A lot of people are starting to ask themselves, maybe I should look at getting central air conditioning? An A/C system is pretty much a given in most parts of Australia, some urban centres in Southeast Asia, cities in the Middle East, Southern US, and other parts of the world or big cities that have traditionally been hot. There have to be a few companies who can retrofit your place with a decent air-con system, right?

Well, the typical setup - new or retrofit - is pretty stupid.

Imagine you’ve got a small boat with a big hole in the bottom and an upside-down roof. Water rushes in through the hole, and any rain fills up the roof. Now imagine that you stuff the hole with paper towel, buy a small pump to deal with the water still coming in, see it’s not working, then buy a big pump system that needs its own generator and the generator needs its own little boat. Everybody else does the same running around with little generator boats behind them, so the price of gas for the generators goes up. That imaginary scenario is a pretty close parallel to how buildings and AC systems are designed in developed parts of the world.

I told you - it's stupid.

The diagrams below show the basic operation if you have a furnace. If you have electric baseboard heating, it's not much different; the small portable air conditioner or the air conditioning system's heat pump is the only cooling device.

Colour diagram of a furnace-heated home in summer with a portable air conditioner
Poor little A/C unit handicapped by heat from hot water

Colour diagram of furnace-heated house with heat pump for cooling
An air conditioning system must overcome hot water heat

A typical building does a very poor job of controlling solar heat gain, and even moderate-performance windows are letting in a thousand percent more energy than solid wall. Immediately many will cry for their precious view, but there’s no view when everyone's blinds are closed. The kicker? Interior window coverings of any sort are largely ineffective; once solar radiation has passed through the glass, it is basically trapped inside the building.

Some people who see the problem feel frustrated for a few reasons.

1. Expensive Band-Aid

The traditional solution - the conventional solution right now - is only a band-aid fix; it’s expensive, and it’s inefficient. The simple fix to overheating is installing a central air conditioning system that can be added on to basically any existing house for $10,000-$15,000. It's a band-aid solution in part, because it's going to cost more over time because you’ll need it more of the year, more hours of the day, as electricity prices are going up. That's not going to be viable in the future.

2. Ineffective Band-Aid

My clients value using resources wisely. Today’s system is still a leaky system, inherently inefficient - probably three times more efficient than equipment from decades ago – but it's not designed to be super airtight, just airtight enough. There is equipment today that is three times more efficient than that. The air-conditioning units are redundant equipment; at the same time as you have equipment to make hot water in your home, you have separate equipment that's trying to take heat out of your home. Something else you need to know is that cooling equipment is designed for bringing down the temperature of the incoming air a certain amount. There will come a point at which it’s so hot outside that the AC won’t be cooling down the interior air enough to be comfortable. Your air conditioning bill is going to skyrocket in the coming years, and the system will become less effective yet more crucial to survival.

3. Broken Home

If you don't have some means of cooling the house, you're not going to be able to enjoy your home. Home is the one safe place that you really should be able to come back to relax and to enjoy. Your central air conditioning solution is going to underperform or fail more as you become elderly and as keeping cool becomes critical to avoiding the substantially increased risk of death from heat related illness.

Here's the Solution

Now, if you do solve this problem, 50 years down the road, you can be sitting quite comfortably in your well-lit living room, reading a book and your annual cooling bill is the same cost as a nice dinner out with a few friends.

So understanding why we absolutely need cooling and why we need a new solution, we look at the key techniques to nearly eliminate the need for active cooling. Collectively, these techniques create a passive cooling design. Passive cooling design is closely related to passive solar design in that it leverages geometry and other unpowered physical features to control the indoor temperature. The strategy is comprised of architecture, the form, the layout of the building and of the site, the systems, the details, the construction of the building.

"...the power of passive cooling... it really can be amazingly, amazingly effective." - building scientist Alexandra Rempel, assistant professor University of Oregon

Passive Cooling elements:

  1. Placement and orientation of the building Living rooms, dining areas, and kitchens should be on the sunset side of the house Bedrooms should be on the sunrise or polar side of the house

  2. Selective placement, sizing, and operability of windows Fewer, smaller windows on the polar side of the building Larger windows on the equator-facing wall

  3. Deep overhangs and deliberate recesses Cantilevered roofs or overhanging floors above reduce summer heat gain from sunshine

  4. Fixed and operable shading devices Fixed devices include brise-soleils and awnings Operable devices include rolling, swinging, or sliding exterior shutters and are automatic or operated manually The devices must be on the exterior of the building to be effective

  5. Judicious placement of trees Deciduous trees in front of East and West windows control low-angle sunlight in the summer while allowing valuable natural heating in the winter as the sun shines through the bare trees

  6. Airtightness Hot exterior air must not be allowed to enter and displace cooled air inside

  7. Natural ventilation Forms and features can create convective currents or cross-ventilation Either capture breezes or leverage air pressure differentials

  8. Heat pumps Use the heating equipment in a reverse operation to move heat to the exterior

  9. Interior layout Place rooms to suit appropriate window locations Locate plumbing fixtures to minimize piping runs of hot water

  10. Appropriate use of thermal mass Thermal mass on the building façade acts as a buffer to mitigate solar heat gain Indoor thermal mass should not be exposed to summer sun

Simple colour diagram of HRV and hot water heat pump for cooling a house in summer
HRV and heat pump in combination can re-use waste heat to minimize the cooling load

One big mistake people make though, before they even look into the how of the thing is ask "what's the cost of passive cooling? What will it cost?" That's not a valid question because it's not a thing that you add on as you would central air conditioning system. It might not cost anything. It can actually come out to be cost neutral if done really well under the right circumstances. If you were to compare, for example an aerodynamically shaped car with a very boxy car, one is far more efficient yet doesn’t cost any more. It doesn't cost any more to make the car aerodynamically shaped, but the impact is cost savings. It works the same way with passive cooling strategies: it doesn’t cost more to rearrange the design of the house. After you've configured and built to control the temperature naturally, it costs you nothing to keep going. What active cooling requirement is left is only a tiny fraction of what you would otherwise need.

You Want to Do Something About It

Adding traditional air conditioning today may result in more devastating, new power plant facilities or possible rolling blackouts as is done in California or Texas, for example, to address their consumption a big part of which is AC. 6% of home electricity use in the United States is just for air conditioning. BC hydro is struggling with meeting electrical demand already. Only five years down the road or so, the projected demand from population growth in the province goes beyond the projected supply. They don't have any additional power plants planned – nobody’s going to create new dams now - so tossing in a maelstrom of air conditioning systems adds to the load, and the only option left is rolling blackouts.

The big reason why this design strategy of passive cooling and incorporated active cooling is the better way to go is because it is going to be still viable 40, 50 years down the road.

It’s important that you as a homeowner do address this now the smart way, because you may not be able to deal with the power bill down the road for the air conditioning system or even just half a dozen different portable air conditioning units around the house. You might not be able to afford installing an air conditioning system or even operating one and have to ask your kids to help you out with paying for it. That’s a hit to your dignity.

Alternatively you could lose your independence. You might not be able to live in your house because you can’t keep it cool enough to be habitable. You may have to move to a retirement home assuming they have adequate cooling. if you don't address it at all, okay, well the worst that could happen is you could very well die or face the possible threat of dying from heat related illness.

On the other hand, what you will gain if you incorporate these passive cooling strategies is freedom from financial slavery. Sustainable comfort. You’ll retain your independence. Installing a typical air conditioning system at this point is shouldering a burden that’s only going to grow.

I Can Show You How to Solve This Problem

So you probably know by now that you need a bit of guidance. You know there's a solution. You're just looking for the right guidance and I am qualified to provide it. I'm a certified passive house designer. I've been studying cooling strategies, Passive House buildings for the past three years and for the past two specifically multifamily buildings in the lower mainland since the detached house is a less viable form. Whereas a Passive House single-family home typically struggles to create and retain adequate heat, apartment buildings designed to Passive House are already facing overheating today. Their designers are forced to be creative with different cooling strategies since the Passive House limitations don’t allow for installing a conventional AC system.

My design system configures the building to nearly eliminate the need for active cooling and develops an active cooling system that does not add much to the project to achieve. If you want to learn more about applying these 10 passive cooling strategies, you can download the free DCA Beginner's Guide to Climate-Proofing Your House in which I showcase my Live Strong Age Well system.

If you've done plenty of reading and are ready to look at the next steps toward your Long Life home, fill our your spark synopsis and contact me using the form below!


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