Passive cooling: Our summer solution
Passive cooling: Our summer solution
In many areas in the world cooling your home in summer is the biggest single contributor to high electric bills – even bigger than getting your home temperature up in winter. So, if this is a concern to you, read on and see how we solved our problem of cooling our home in summer with ”passive cooling.”
Average summer temperatures in our area
In the area where we stay, Mossel Bay, on the southern coast of South Africa, summer temperatures seldom go higher than 28 deg. C (= 82.4 F). We feel comfortable with a temperature between 21 and 23 deg. C (69.8 F – 73.4 F) inside our house in summer. We do not have any electric air conditioners, fixed or mobile. These appliances have improved over the years, but we’ve decided to see how far we could get with “passive cooling” and we’ve achieved our goals in that way.
Passive cooling as solution to our summer heat problem
1. Roof cavity: A layer of 10 cm (4 inches) low emission material in the roof cavity on the ceiling proofed good enough to prevent the high temperature inside the roof cavity (go up to 50 deg. C/122 deg. F from time to time!) to filter through to ceiling into the living area.
2. Western side of the house: The western side of our house was fully exposed to the sun in the afternoon. The wall absorbed so much heat from the hot afternoon sun that it eventually radiated through the wall into the bedrooms on that side, even though the walls are properly insulated. We addressed this problem in two ways: A. By planting three trees next to the house, so that when fully grown (see image above) they would eventually prevent the sun from hitting that wall. After a few years this was achieved, as can be seen in the picture. B. By putting three 1500 liters water storage tanks (for gathering rain water) in the space between the trees and the wall. These blocked the sun completely from at least a part of the wall. Although we had to be contend with some discomfort for a couple of years at first, the current situation is close to perfect.
3. Blocking the sun from entering the windows: In summer the afternoon sun enters our living room (facing south-west) and creates a considerable amount of heat exactly where and when we do not want it. We did not install double glazing or low-e glass, none of which was considered necessary at the time. We then installed “roller sunscreens” or “reflective roll-up blinds”, which we pull down in summer the moment the sun starts creeping into our living room. They reflect virtually all the heat of the sun, but let through 85% of the light. Perfect! (We also use these “reflective roll-up blinds” to block the morning sun from entering a big window on the eastern side of our living room.) Although the is not a roll-up blind/”roller sunscreen”, it does exactly the same thing, blocking the heat in summer from entering the house and help preventing the heat from escaping through the windows in winter. Gila LES361 Heat Control Residential Window Film
4. Drawing cool air into the house: The ground floor of our house is always nice and cool in summer. We open some windows on the shady side of these rooms and then open some windows on the top storey where we live. This causes a draught by means of which the cold air is sucked from the lower storey to the relatively warmer storey above. This is a common and very effective way of cooling your house as illustrated in a number of images.
5. Water feature: We also built a cascading water feature along the eastern side of the house. Although this was initially done just for landscaping purposes, we soon realized that it also cooled down that part of our garden, which helped to create a cool area along the eastern side of the house. The video below is of that water feature.
6. Painting the roof: The color of the roof of your house is of crucial importance. A dark-colored roof absorbs more heat than a light-colored one. A white roof will be 30 deg. F cooler than a dark roof in peak summer and 50-60 deg. F cooler when painted with a specialized paint which reflects the rays of the sun and has high infrared emissivity (according to the Sacramento Municipal Utility District (SMUD). This will translate into considerable savings on cooling costs throughout the summer. The “cool roof” concept is so important, that some cities (like NYC, California, Sacramento and Pittsburg) in the USA have joined the movement and even offer tax incentive to people willing to paint their roofs. We did not paint our roof, we did paint the roof of a friend of ours and the impact was massive.
Water feature next to our house
Electric cooling options
If passive cooling concepts are not going to work for you and cooling down your home in summer is imperative, you have four options left:
a. Electric fans: These are very cheap and does not cool the air at all. It only circulates air. However, when the air hits your skin, it does help to evaporate your sweat and that has a cooling effect. The electric fan uses a fraction of electricity as compared to AC units, but, obviously, are not as effective. The Honeywell TurboForce Fan, HT-900 is currently (August 2014) the Number 1 bestseller in household fans.
b. Evaporative coolers: These units function on the principle that evaporating water cools air down. Air is sucked through a membrane (wick) saturated with water, which causes some of the water to evaporate. This action causes the air to cool down and the stream of air which flows from the front of the unit into the room is considerably cooler than the ambient air temperature. A variety of models are available, like the SPT SF-608R Portable Evaporative Air Cooler.
c. Portable AC units: The portable AC unit is very handy, since you can move it where you need it – from room to room. The Honeywell MN12CES 12,000 BTU Portable Air Conditioner with Remote Control is a popular unit with good reviews and ratings.
d. Fixed AC units: With the fixed AC unit you are going for cooling of at least a whole room and not just the people in the room. The most popular model in this class (August 2014) is the Frigidaire FRA052XT7 5,000-BTU Mini Window Air Conditioner, with close to 1000 reviews.