A house or a building can be thought of as being an envelope, which shelters an indoor space from the weather outside. The objective of the envelope is to maintain a comfortable inside environment. One approach is to build the building and then force the inside temperature to be comfortable by using fans, heaters, air conditioners, window louvers or computerised control schemes. A better way is to design the building with more consideration for its environment so that the need for active space heating or cooling by mechanical or electrical means is substantially reduced, if not totally eliminated.
The principles applied in climate-sensitive design are based on the idea of using natural conditions to the best advantage. The principles of orientation, heat storage and cooling can be combined with specific building materials to achieve climate sensitive design. Energy efficient housing design principles encompasses all the available techniques of creating a ‘healthy’ interaction between indoor and outdoor climate conditions in buildings. This would include the use of solar passive design strategies to build houses more energy efficient and simultaneously increase thermal comfort in the houses, but also water conservation, use of renewable energies, greening activities and the use of energy efficient stoves. Solar passive design principles include design and orientation of the house, and the building material used (that is mass, glazing, insulation, use of daylight, ventilation and other systems which might be required).
The sun rises daily in the east and sets in the west. In summer in South Africa, it will pass almost directly over-head at noon, whilst in winter its path will be low in the northern sky. This is true for any location south of the equator, and the further south you go, the lower the sun will be in the northern sky – north of the equator the sun follows a path that is low in the southern sky. Therefore, to let the sun inside the house in winter, most windows should be on the northern side. Windows on the east and west tend to lose more heat than they gain in winter and they can cause overheating in summer since they receive hot morning and afternoon sun. A roof overhang over northern windows shades the windows in summer while allowing sunshine in during winter, due to the lower position of the sun in the sky – the sun shines in under the overhang to heat the inside of the house.
Some practical advice…
- The longer side of the house should be orientated east-west so that it faces north to ensure that the house receives the maximum amount of sunlight throughout the day. Internal rooms should be planned in such a way that the most frequently used rooms, such as the lounge are situated on the north side of the house;
- The largest windows of the house should be fitted on the northern side;
- The roof overhang on the northern side of the house should be calculated to be at an altitude angle equal to 90 degrees minus latitude, as measured at the windowsill. When it is not possible to make this calculation precisely, a good guideline to follow is that the overhang on the northern side of the house should at least be 400mm to 600mm in length;
- A roof overhang should ideally be combined with a strip of grass or vegetation to prevent the surface from warming up.
If the sun is allowed to stream in through a window, the room will warm up. If there is a concrete floor or thick walls, they too will warm up and stay warm for a long time and release heat slowly into the room after the sun has gone down. The walls and floor act as thermal mass to store the heat gained. Stone, concrete, brick, adobe and rock chips are all good thermal storage materials, which can be incorporated in walls, floors and a fireplace.
Some practical advice…
- The floor slab should be constructed of a material that has a high thermal mass, e.g. brick or concrete to store heat during the day and release it at night. For this reason it is important that the floor slab is left uncovered by carpets;
- If you have curtains or blinds in front of the windows, it is important that they are open during the winter day to let the sunshine in and heat the floor. The curtains should be closed once the sun goes down to keep the heat inside the room;
- Insulate the building perimeter and use doors and windows that shut tightly
Cooling a Building
Besides providing heat during winter, successful climate sensitive buildings are cool in summer. Sufficient overhang protects the north facing windows from the high summer sun while at night, the house must be well ventilated to cool the place down. Insulation and thermal storage that retain heat in winter will keep the building cool during hot days. In very hot climates ventilation is important. For example, a front porch is used to cool the air before it circulates through the house via the windows, which open on the porch. Plants and trees are also cooling, preventing heat be ing reflected off bare ground while a deciduous creeper growing over a porch will shade it in summer and let the sun through in winter when the leaves fall.
The skin of a building is made up of various materials, which may reflect, absorb, store, transmit or resist heat. In winter, retarding heat loss is as important as admitting sunlight, so the roof needs insulation, normally in the form of a ceiling with additional bulk insulation on top. A wide variety of commercial insulation materials are available on the market, or in low-income houses, a layer of crumpled newspaper is better than no insulation at all, but fire risks should be considered. Thick curtains help to insulate windows while in very cold climates people use double-glazing (two sheets of glass with a gap between them) to reduce heat loss through windows. Similarly, a double wall (a double brick wall with an air gap in between) can be used to prevent losses and gains through walls. The shape of a building is also important from an energy point of view. A tall, slender building has a high surface area to volume ratio. Ideally a building should be compact, with a low surface area to volume ratio, since the building’s surface is the element through which the heat transfer occurs.
Some practical advice…
- Ceiling insulation will reduce the need for heating the home and could reduce energy costs by 50%
- Walls can be insulated with a non-conducting material such as polystyrene sheets. Plastering is also regarded as the most effective method of insulating wall as it improves the moisture resistance of a wall;
- Mud bricks are an excellent source of insulation, as is most forms of traditional building material such as thatch roofs and clay walls and floors;
- In South Africa, window and door frames are most often made of steel except in the coastal areas where rust is a problem and wood is the material of choice. Wood however, provides a better insulation than steel.
Climate sensitive design principles can be incorporated to various degrees in office buildings, social housing, private homes as well as apartment buildings and townhouses. Incorporating energy efficient design principles, especially in the delivery of low cost housing, would have numerous benefits to the poor families living in these houses. Low-cost houses may be cheap to build, but their running costs are astronomical. Because of the use of energy-inefficient materials, it is sometimes warmer outside the house than inside. The costs of keeping these houses heated come out of the earning of the people who can least afford to pay them – heating can cost poor people up to 60% of their income. Furthermore, poor families use dirty, dangerous fuels such as coal and paraffin to heat their homes. These fuels cause indoor and outdoor air pollution, respiratory diseases as well as being dangerous in terms of causing fires and burns.
Can it work for me?
Definitely! If you are considering building a new house or if you want to increase the comfort levels of your home – make it warmer in winter and cooler in summer. More importantly, if you want to save money and reduce the cost of heating or cooling your house, you should seriously consider incorporating some interventions in your home. Although it is much cheaper to incorporate these principles and implement the measures before the house is constructed, it is possible to retrofit existing structures. EEHD building principles are valid for electrified and non-electrified buildings. Some interventions are low to no cost (house orientation, positioning and size of windows, use of plants and colour and good ventilation); some are medium cost (roof overhang, energy efficient appliances) and some are high cost (wall, roof and ceiling insulation; additional glazing and draft proofing around windows and doors).
Benefits of EEHD
There are tangible benefits through the use of EEHD principles such as:
- Increased comfort (not too hot or too cold) and improve quality of life;
- An improvement in the health of people living in the house;
- Reduction of energy demand because less energy is required to heat or cool the house;
- Savings on energy costs (electricity & heating bills), releasing funds for other basic essentials such as food, clothing and education;
- Financial benefits through energy and subsequent monetary savings; and
- Environmental benefits through reduced air pollution; which is a result of less ‘dirty’ fuels being used; and
- Improved air quality reduces the cases of respiratory and associated illness.
- Benefit to Eskom and the municipality through reduced/eliminated peak electricity demand
Bear in mind that although the upfront cost of insulting your roof for example, may seem high, think about the savings you will achieve over the life-span of your house. The avoided cost of heating your home or reducing your heating expense will pay of the investment in a short period.
Natural building materials and eco-friendly roof insulation should be used wherever possible. The principles of climate sensitive design described above are not only applicable to South Africa but also the rest of the world (remember if you live in the northern hemisphere, swap the north for south in the tips above). Solar power for homes is gaining in popularity as a clean, green energy source that can never be depleted! Having a north-facing roof in South Africa is the ideal for maximum efficiency for solar water heaters. Solar water heating can and should be incorporated into new buildings (or retrofitted to older buildings) as these can reduce electricity bills by up to 50%. Solar geysers are relatively costly but, at current Eskom tariffs, they typically amortize their cost within 36 months. Water conservation systems should also be incorporated into buildings. Rainwater harvesting is a logical step as South Africans and the global community face real water scarcity. Pollution of our waterways can be reduced by lessening greywater in our sewage systems (grey water is the main component by volume). Grey water should be used for garden irrigation and/or toilet flushing (why use drinking water to flush toilets?). See how a gray water irrigation system works on White River Country Estate. Water Rhapsody and Yes Solar (solar energy solutions) have combined to offer environmentally sound water systems and SABS-approved solar water heaters made by Solsquare (Germany). We are also authorized JoJo Tank dealers in Mpumalanga and Limpopo. We offer all your water and solar energy green plumbing under one roof. Contact us for a free quote on a solar geyser, water system or JoJo water tanks (and water tank stands).