How to cool my home naturally without air conditioningTips and Advice
Recently I met up with a group of friends in a park for a BBQ. We were using the built-in council BBQ and everything was taking a long time to cook because of a stiff breeze that was blowing across the park which was taking the heat away from the hot plate. If we’d have had a lid to put on the BBQ keeping the breeze off it, it would have got hotter faster and cooked everything far more quickly.
Homes are a bit like that too. We go out during the day and leave the house securely locked up. Over the course of a hot summer’s day, the air inside our home gets hotter and hotter, unable to circulate and mix with the breeze outside the home. As a result, we come home to a very hot and stuffy house and turn on the costly air con. An Architect can help save you save money in the long term by creating a sustainable design that includes ways to cool your home naturally without air conditioning.
Solution 1: Air conditioning (not natural or green and costly)
A lot of people confronted with this situation will reach for the air conditioner remote and switch it on to cool their home. Now, this tactic works but it takes a lot of time and at today’s power prices cost’s a fair bit of money. And that’s because the air inside your home has had all day to get hot. Now you’re trying to cool it instantly by pumping cold air in through your air conditioning unit. That cold air is running straight into the hot air that has nowhere to go; as a result, it takes quite a while for the air conditioning to cool the hot air already trapped inside your home.
Now, this really is the hard way to cool a home. Let me give you an example that better explains the point I am trying to make …
If you have ever parked your car outside in the sun for a few hours on a hot summer’s day you will know that when you open the door the heat inside your car is dangerously hot. So do you jump in and switch the air conditioning on flat out? Well I know I do, but I also wind the windows down and start driving to allow the hot air to escape while the cold air blows in through the air con.
If you’ve never done this before I urge you to try it. Within minutes your deadly hot car interior will be pleasantly cool and on the way to being cold. In just a few minutes the hot air is gone and you can put your windows up and relax in the comfort of your climate controlled environment.
So what’s this got to do with homes? Well, you might think that you’ve guessed where I’m going with this but you might not be 100% correct.
If you guessed that I am suggesting that you open up your windows and doors and let the hot air escape then you’re partially correct. But it’s not as simple as just opening a window and hoping the hot air will blow away.
Solution 2: Home exhaust fans
You see the car example works best because the moving car sucks air in from the outside pushing the hot air out. But you’re house can’t move, so what happens on those days when there is little breeze and therefore little air movement?
Well for most people it’s a matter of waiting for the overworked air conditioner to slowly cool your home down, but there is another option.
There are a number of companies that produce natural home cooling systems that are based on large fans and vents. These fans are designed to suck rather than blow.
Typically these fans are mounted in the roof cavity. Directly underneath them are metal louvres that open up to allow air to be sucked up from the interior of your home. Essentially they work by sucking in air through your windows (you need to open your windows first) and then blowing it out through exhaust vents built into your eaves or placed on your roof. In effect, these massive fans create the same effect as a moving car and can quickly replace the hot stale air (as well as any odours) from inside your home.
These systems claim to be able to naturally cool a home without the need for air conditioning on even the hottest, most still days where there is no breeze in sight. I personally think that might be a tad extreme and that on the very worst of days you might still need to switch on the air conditioner, but I’m sure these systems do a great job on most days and particularly at night.
And for those people who hate waking up with a sore throat from having the air conditioning on all night, these systems offer a viable alternative, although you would probably want security screens fitted given that you do need to leave some windows open to allow the system to draw the outside air in.
Most of these systems have a very low running cost, certainly under that of most reverse cycle or ducted air conditioners, but what if there was a way to draw the heat out of your home without needing to run anything electrical at all?
Well there are a number of ways to do this, so let’s look at more environmentally friendly ways that you can cool your home that cost nothing at all to run.
Solution 3: Venturi Effect
Well, clever architectural designs can offer a number of electronic free solutions and one of these is based on the Venturi Effect.
The Venturi Effect is the combination of the Bernoulli Effect and the Continuity Equation. But in case you’re not familiar with either of those things, let me instead explain it using a diagram.
Here we can see an opening at the top of the house, which typically would be some louvres that can be opened and shut as required. The breeze passes through these louvres and then out the other side. The moving air draws in the air below it, in this case out of a particular room in a house. This effect is limited if the rest of the house is closed off, however opening windows, doors or low set louvres will allow fresh cool air to be drawn in from outside as the rising hot air is drawn out and away.
But whilst this system works well on days when there is a breeze blowing, what happens on those days when there is little to no breeze?
Solution 4: Thermal Buoyancy
Hot air – that is air that has been heated – is less dense than cold air. As a result of this, the less dense hot air will always rise above the colder more dense air. This is why hot air rises and is the principle that allows hot air balloons to float above the ground and it is known as thermal buoyancy.
More relevant is the fact that thermal buoyancy is the principle that chimneys are built around. Hot air and rises up the chimney taking the smoke with it. Now if you light a fire in a fireplace and put a lot of green timber on before the coals build up a lot of heat you will probably quickly smoke the house out as the air in the fireplace is not yet hot enough to rise up the chimney quickly. However, when the fire is generating a lot of heat, that hot air rises up the chimney causing a difference in air pressure which causes the air immediately around the fireplace to be drawn in. This is known as a draft and helps keep the fire going by drawing in combustible air. This subtle drawing in of air stops the smoke from escaping into the room as it’s sucked up the chimney and expelled into the cooler denser air outside.
So what do open fires and chimneys have to do with cooling your home? Well actually plenty.
You see the principle of hot air rising and drawing in the cooler dense air can aid in creating a draft through your home that can allow the hot air to escape whilst drawing cooler air inside as shown in this diagram below:
The effectiveness of this system can be enhanced by creating what is known as a solar chimney. Solar chimneys are constructed of materials that allow for a higher level of heat transmission. In other words, they heat the air inside them more quickly. The hotter the air inside the solar chimney the faster it rises, the faster it rises the greater the difference in air pressure the faster cooler air is drawn in through the lower louvres or open windows.
Glass is an effective material for heat transmission, therefore a wall of glass panels on the outside of the physical wall of the home could aid in the rapid heating of the air in the space between the two. Placing exhaust vents in the wall of the home would then result in the air inside the home to be drawn out quickly as the hot air rises in the solar chimney. Open a window on the opposite side of the home and air would circulate through creating comfortable conditions even if no breeze were blowing outside.
So as you can see this system, whilst often enhanced by any sort of a breeze, is not completely dependent on a breeze to be effective. At the very least this type of design can assist in driving the hot air out of your home in much the same way that driving with the windows down in your car sucks the hot air out allowing the air conditioning to be more effective more rapidly.
So if you’re looking for a natural, healthier way to cool your home that works even when the breezes have stopped blowing, talk to a sustainable Architect about the options available for your home. Telephone (07) 3899 9450
DION SEMINARA, DION SEMINARA ARCHITECTURE
Hi, I am Dion Seminara, practicing architect and licensed general builder for 20 years as well as an environmental sustainable design (ESD) expert. I graduated from Queensland University of Technology (QUT) with honours, QLD in 1989. Registered as an architect in 1991 and registered as a builder in 1992, I am also a fellow member of the Australian Institute of Architects (AIA). Having received 12 ArCHdes Residential Architecture Awards, LJ Hooker Flood Free Home Design Award and the 2016 AIA Regional Commendation for Public Architecture, my expertise with both residential renovation (to all types of houses, especially Queenslanders, 50s/60s/80s), new contemporary homes and luxury residences has earned me a reputation as one of Brisbane's architectural specialists in lifestyle design architecture, interior design and landscape design.