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> Keeping your home Cool in Summer or Warm in Winter for free!

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article imageLast updated 6:38 pm, Thursday 25th October 2012

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Yes, you too can reduce nearly to zero (well as good as being free) the cost of living in a comfortable home and do it in a way that is good for the environment & makes your home a green home as well. If you are interested please read on; we have tried to provide as much helpful advice as possible so do read this to the end as there are tips and hints all the way through.

The physics of comfort...

Being 'comfortable' is something you feel, i.e. only the immediate state of the environment right next to you (what your sitting on, wearing and the air around you) determine if you are 'comfortable'. The conditions in the next room or outside have no direct effect on your perception of comfort, it's the conditions immediately experienced by you that do.

So what specific factors determine 'comfort'? They are:
  • Air movement or flow against your skin.
  • Air temperature at your skin.
  • The temperature of what you are touching.
This fact that we only feel the warmth (or cold) of the immediate environment around us is something we can 'play' with and utilize, see later.

The 1st trick - exploit the daily Solar cycle

During an average day a property will warm up due to solar heating; i.e. sunlight comes in through the windows and heats up whatever it touches and the air it goes through. Now in the middle of winter this is quite a desirable thing to have happen, as you are getting heating for free. But in Summer this can turn your house into a furnace!

So how do you get the best of both worlds? A simple trick, exploit the fact that in Winter the Sun is lower in the sky and in Summer it is almost straight overhead. So a window with an overhang on it of the right size would shade out the Summer Sun, whilst allowing in the Winter Sun..

NOTE: In the Southern hemisphere this works only for North facing windows and in the Northern hemisphere only South facing windows. More on what to do with windows on the other sides of buildings later.

Also you need to be careful of during Summer about letting too much solar energy into your house - as light heats whatever it passes through or touches. So use window dressings like horizontal blinds and drapes to reduce the glare. We recommend that you do not use vertical blinds, as you cannot set them to a constant light level over the day and you will be forever fiddling with them. You can also get glass with a special IR blocking coating, but this will stop any winter sun heat gains; i.e. only use in places where you are getting too much solar gain regardless.

The 2nd Trick - Thermal mass within the building

Thermal mass is simply a 'mass' (i.e. a wall or a floor) that acts as a 'heat store' or 'heat sink'; i.e. it readily takes in heat over a period of time, then releases it over a period of time. Bricks and tiles are the most common form. Such thermal mass allows you to 'time shift' temperature conditions by storing heat (or cool) from one time period and applying it to a later one. This in effect averages out large temperature spikes as the heat transfer occurs over a long period of time.

So why is this useful? Well, if you had an internal 'bare' brick wall in your house, by opening windows at night it would cool down. Then if during the day you closed your windows you would create a closed environment with a cool brick wall in the middle; thereby helping to maintain the cool relative to the external temperature.

Similarly in Winter, if you opened your windows on warmer days and heated your wall (or had it positioned to catch the winter sun), then at night you closed your windows; you would trap the heat from the wall to keep you warm.

The real trick here is how you place your thermal mass. Tiles close to North facing windows (in Australia) would keep you cooler in Summer and warmer in Winter (think about the solar cycle).

Thermal mass walls you really want both inside in the path of the winter sun (i.e. North Side) and some on the South side as well - this way part of your thermal mass is 'passive' and acts to reduce the natural temperature changes in the house.

Note: If you have a concrete slab in your house, your need for an additional thermal mass could be less, it really depends on if the concrete slab is able to easily 'interact' with the environment of your living space. i.e. if its is mostly tiled, good; if it's hidden under wooden flooring or carpet, bad.

Note2: It is possible to employ other materials like brick veneer, concrete blocks, stone, mud bricks, rammed earth and even containers of water in walls (i.e. a fish tank!) to act as thermal mass.

See this page for details on how to work out the correct ratio of glass to thermal mass to have in your property (remembering it was written for the Northern hemisphere, so reverse the North/South references as required). Also see here for the Southern hemisphere equivalent.

For an instance of how effective utilizing thermal mass in house design can be have a look at this article; basically water with a solar greenhouse was used to wipe out heating bills for a house for getting on for 20 years! Also have a look at this article for a building in UK using thermal mass, timbrel vaulting and passive design techniques to also wipe out heating and cooling bills.

The 3rd trick - Cross Ventilation

Cross ventilation is simply being able to set your property up so that the prevailing winds on your site can be easily used to move air through your property. This is done by placing windows so that the wind can blow through them on opposite walls in a room or building, rather than on adjacent walls (i.e. you want to minimize the resistance to the movement of air through the space).This combined with the ability to close off sections of the property which you don't use (and hence do not need ventilation) can be very effective in quickly cooling the rooms you do use.

An enhancement to this is on the side that the winds 'blow' from add shade - this way air that was in shade (and hence cooler) gets blown into your house - so making you cooler. Trees are ideal for this.

Also cross ventilation can make it easier to help heat a home in Winter; i.e. if the Winter day is considerably warmer than the night, having good cross ventilation will allow you to open the windows and easily heat up your house during the day.

The 4th trick - ceiling fans

Fans are often forgotten about, but can be very effective. The fact they keep moving air 'plays' with your perception of temperature by aiding heat loss off your skin - in effect it 'blows' the heat off you! Also ceiling fans in winter can be set to run the other way, so helping in keeping warm air near to you. The good thing with ceiling fans is that they take up no floor space and are considerably safer than a floor mounted fan (thinking of little fingers here).

A ceiling fan, properly set up, can make the room feel as much as 7 degrees cooler than it actually is, for a few dollars a month running costs..

The 5th trick - wall insulation

Wall insulation helps stop the internal temperature interacting with the external environmental temperature. This makes it cheaper to keep cool in Summer and warm in winter as a greater temperature difference can be maintained for the same effort (i.e. cost). Usual ways of having a higher insulation rated wall include:
  • Old fashioned cavity wall; i.e. two brick walls with an internal air gap in them.
  • Brick veneer; i.e. an outer brick wall with an inner wood based wall. The insulation is usually 'sandwiched' behind the inner wall.
  • Thermalite block construction - basically building with big bricks with an inner layer of insulation.
  • Aerated Concrete Blocks - basically blocks made out of 'foamed' concrete, so has a higher level of insulation than normal concrete blocks but rather more fragile & not as strong, so special construction techniques need to be employed.
  • Cavity wall insulation - basically a cavity wall with an insulating foam injected into the air gap. This improves the insulation properties but care needs to be taken to not 'bridge' the damp proofing properties of the gap.
  • Straw-bale wall construction - this is basically building the walls using straw-bales with rendering. The straw-bales provide a high degree of insulation but very little construction strength.

The 6th trick - roof insulation

More often than not, a roof space in summer turns into a furnace - without suitable roof insulation on top of the ceiling space below the heat will transmit down into the living space or it will prevent heat escaping up and out. So very quickly the living space will heat up in response. Classic sign of this that the property around midday on a hot day will suddenly go into 'furnace mode' as the heat from above and outside conspire to overheat the living space; then no matter what you do you can't get the temperature back down.

So to avoid overheating in summer and being too cold in winter make sure you fit good quality roof bats (insulation). Look for ideally insulation rated to R4.0, this will exceed the minimal required by the Australian standards, but it will ensure you are getting the best benefit from having the insulation in place. Combine this with some form of roof space ventilation and you should be set, see here for examples.

Insulation Grants in Australia

Please do make sure you do the following when cashing in the insulation grants:
  • Do check the installers credentials and ask for at least 3 references. Why? Well given the current market conditions and sudden demand for the installation of roof insulation; a lot of potential 'cowboys' are thinking it is easy money to put in a few batts and be done with it..
  • Do make sure that light fittings, like down lights, are not 'buried' under the insulation - these things have a tendency to get very hot and if surrounded by insulation are likely to catch fire! You can get metal surrounds for the down-lights to always provide a safe distance.
  • Also do look at putting in a roof vent at the same time - this will avoid the roof space over heating and provide useful ventilation to avoid damp.

The 7th trick - stopping window heat transmission

Windows, as well as letting light in, also act as quite good heat or cold 'conductors' with the outside world. Both the glass and the frame of most windows readily conduct heat. Therefore you need to block or reduce this heat transfer into your living space if it proves to be a problem (which may not be the case if you have done all of the above). To be effective you need good quality thick curtains and a pelmet to stop the air cycling across the window by putting it in its own still blanket of air. The curtain needs to span the whole window and be tight in to the wall and go all the way down to the floor to stop the air cycling. Still air so 'trapped' will stop the heat or cold making its way into the property. Also the still air in itself will provide a degree of insulation.

Another good way to stop the heat getting in during Summer is to have white roller blinds (or near to white as you can put up with). This way the heat of the sunlight is reflected back out the window during summer. Roller blinds also prevent some of the cold coming in during Winter, but as not as good as a proper curtain.

The combination of full curtain and roller blind are particularly good for bedrooms, in that when the blind is down and the curtain closed, the room is completely blacked out and largely sound proofed from the outside world. Great for a good nights sleep! Also the roller blind is great for providing privacy whilst allowing some light in.

Another option, if you are building or renovating, is to use what are termed 'thermal break' window frames. These are windows frames where a low heat conducting material is placed in the middle of the frame all the way round, this stops the metal frame acting as a heat conductor between the inside and outside. Although only consider this is you do not want to use the curtain and pelmet method, or you live in somewhere very cold, as it is unlikely you will recover the cost outlay in savings made.

Another option, if you want to avoid changing window fittings is to use a UV blocking window film. These come in a variety of shades, from nearly clear to very silvered. It pays to shop around for these and not 'skimp' as you want a film which will last. An added benefit is that the film will also help ensure privacy as from the outside the inside will appear darkened.

The 8th trick - external cooling

Not so much a trick as setting things up outside so that cooler air can 'ride' into your house after dusk. Basically if you have a water feature or a lawn to a high side of your house the evaporation off this will result in a down current of cooler air at night. So during summer, when you open the windows at night to ventilate, you get a cooling 'boost'.

BTW This is not a 'new' technique - for instance Moroccan house gardens are designed with the house around a central garden area, the garden provides shade and cooled air that carries into the house around the outside. This is also why you have Mediterranean courtyards within a house with a water feature, this not only provides water the evaporation cools the courtyard to provide a place to escape the heat.

Of course, you will want to set things up to stop the opposite happening, i.e. heat riding into your property during the Summer. By this I mean avoid having rocks or asphalt on the lower North side of your property, they will just heat up and 'waft' heat towards your property - adding to your problems. Instead have low shrubs or trees to provide some degree of shade.

The 9th trick - use trees to shade your roof

If you put trees to the East and West of your property, then come the morning or evening they cast partial shade across your roof on summer. This will help reduce the temperature you experience in the property.

If you have water tanks or other large structures you can put them to the East and West of your properties external walls as well - they will reduce the heat load on those walls by casting shade onto them.

If you have Air Conditioning...

Even if you have an air conditioner, it would be wise to do what is mentioned above, as it will reduce your need for A/C and hence reduce your bills and increase the life the A/C unit to boot!

Also look at making sure the A/C unit outside on a split system air conditioner is itself in some form of shade, otherwise you will paying for the A/C unit to cool itself. Also make sure the filters are clean. If you do both of these tips, you could save yourself up to 20% on the running costs.

Also do make sure you are heating/cooling the minimal area - no need to air condition everywhere when you only stay on one or two rooms the most! So close the doors to unused rooms and shut off any vents or ducts to them if possible.

Remember the better your house is at maintaining a comfortable temperature on its own, compared to the external temperature; the less need you will have to run the Air Conditioning.

Other things to consider..

Gaps - Check around doors and windows for significant gaps, below about 2mm don't bother (drag will help deal with it). Use a good quality sealer designed to deal with the job. This will help equally with keeping cool as keeping warm.

Roof ventilation - During Summer the roof space can literally bake and if there is no where for that heat to go it will build a stack of hot air in the roof which will eventually force itself into your living space from the ceiling down (through ceiling fans, down lights, etc). Therefore install just enough ventilation to stop the stacking effect.

Close doors - Don't leave all your doors open, close the doors to rooms you do not use. In this way you have reduced the area to maintain cool or warm.

Natural ventilation - Try to learn from the old ways of keeping buildings cool, like WindCatchers.

CFLs - Use Compact Fluorescent Light bulbs (CFLs) inside. CFLs use 75% less energy and produce 75% less heat than incandescent light bulbs which will save you money as well on cooling.

Showers - Turn on the exhaust fan in your bathroom when taking a hot shower, as this removes much of the humid air produced by the shower. This works because humidity makes it feel warmer.

Don't buy into open plan house designs - Having a house with few internal doors means it is very difficult to 'close off' the areas of the house you do not want to heat or cool. This can easily directly translate into higher energy bills, unless your house has extensive complete insulation to compensate. If you feel the need to 'see' space, go for double doors or movable screens; or put up more mirrors, but don't knock through that wall...

Clothing - May seem obvious to state, but if in Winter you can get the family into the habit of wearing a jumper and similar loose but warm clothes; you will save a fortune in heating costs, as you will be using your own body heat to help keep you warm, so allowing you to reduce the heating thermostat.

Turn down (or up) the thermostat - Basically for each degree you turn down (or up when cooling) the thermostat towards the outside temperature you reduce your heating costs and green house emissions by roughly 10%.

Use an electric blanket at night - Again, simple but effective. No need to heat the whole bedroom when you are just in the bed.. Also consider the old hot water bottle. Sometimes the old ways are the best.

External surface area compared to internal volume - A building design which has a large surface area in relation to its internal volume (i.e. lots of external walls and not much internal space) will have a harder time maintaining the preferred internal temperature compared to building with a larger internal volume compared to the external wall surface area..  The reason for this is quite simple, the more external walls the more area the external environment temperature has an 'impact' upon. The best normal house shape to minimize this effect is a simple 2 story 'square' house. If you are prepared to live in an igloo shaped house you will take this effect to a minimum as a sphere is the minimum surface area to cover the maximum volume in ratio.

Conclusion

Finding ways of keeping you house cool in Summer and warm in Winter for less cost is actually quite beneficial to the environment, as you are reducing your environmental impact through consuming less resources. In fact this is a variation of Ecologically Sustainable Development (ESD); whereby you are taking active steps to reduce your environmental impact now to the benefit of future generations.

Recommended Reading

  • The Solar House: Passive Heating and Cooling by Daniel D. Chiras

    Passive solar heating and passive cooling—approaches known as natural conditioning—provide comfort throughout the year by reducing, or eliminating, the need for fossil fuel. Yet while heat from sunlight and ventilation from breezes is free for the taking, few modern architects or builders really understand the principles involved.

    Now Dan Chiras, author of the popular book "The Natural House," brings those principles up to date for a new generation of solar enthusiasts.

    In "The Solar House," Chiras sets the record straight on the vast potential for passive heating and cooling. Acknowledging the good intentions of misguided solar designers in the past, he highlights certain egregious erros and shows how to avoid them. More importantly, Chiras explains in methodical detail how today’s home builders can succeed with solar designs.

  • Passive Solar House: The Complete Guide to Heating and Cooling Your Home by James Kachadorian
We suggest you also have a look at the Passive Solar section in our Online Store for more books full of useful information.

Related Articles and Links

Related Tags: heating, cooling, heating costs, passive solar, solar cycle, thermal mass, cross ventilation, ceiling fans, roof insulation, air conditioning, straw-bale, climate change

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