Conduction: Good and Poor Thermal Conductors.

There are many problems involved in the heating, cooling and insulating of a modern energy efficient house. However, certain measures can be taken in order to save energy and prevent excess energy gain. There are a variety of ways of solving these problems relating to heating, cooling and insulation in the home.

Conduction: Good and Poor Thermal Conductors

Heat is easily lost through the exterior walls of a house because of the conductivity of the materials the walls are built with (ie brick). Using higher levels of insulation can reduce this problem. This technique reduces heat transfer from the heated interior to the cold outside during winter, and insulated the house from heat in summer. The following are a variety of methods of framing used to overcome these problems.

Optimum value engineering – this method utilises strategically placed wood in order to create space for insulation

Structured insulated panels - plywood or oriented-strand board is laminated to foam board. The foam may be 4 to 8 inches thick. Because the panels acts as both the framing and the insulation, the quality of construction is often superior and takes less time than optimum value engineering.

Insulating concrete forms - two layers of foam board (one inside the house and one outside the house) act as the form for a steel-reinforced concrete centre. It’s the fastest technique and least likely to have construction mistakes.

Conduction also plays a part in choosing floor coverings. Carpeting and wood floors insulate, but tile, slate, concrete or brick floors help conduct the heat back into the rooms in winter, and helps keep the house cooler in summer.

Radiation of heat through windows:

The typical home loses more than 25 percent of its heat through windows. Even modern windows insulate less ...

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Radiation of heat through windows:

The typical home loses more than 25 percent of its heat through windows. Even modern windows insulate less than a wall. Therefore, an energy-efficient house in a heating-dominated climate should, have few windows on its southern, eastern, and western sides. Total window area should also not exceed 8 to 9 percent of the floor area for those rooms.

Double glazed windows are an extremely effective method in preventing heat loss through windows. This involves two pieces of glass instead of one, with a layer of air between them, which acts as the insulator. Adding a third or fourth layer can increase the benefits even more. The amount of air inside the space is also a factor in how efficient the windows are – the larger the space, the more effective. This is relevant to the width of approximately one inch, because spaces larger than one inch wide encourage convection currents. Other gases, such as argon have been substituted for air, as they are less dense, and have a lower conductivity than air.

Overhangs and the position of the sun

North facing windows should have extended eaves. The eave blocks the high summer sun (and heat). However, in the low winter sun, heat is still able to radiate into the house. The following diagram represents this:

However, this principle does not apply to the east and west windows, as when the sun rises and sets, its rays are almost horizontal, and therefore even the widest eaves would not be sufficient.

Window coverings:

There are a variety of window coverings that help to shield radiation from the sun in summer. The best way of reducing heat flow through such windows is by using external shades. However, internal drapes used in conjunction with external coverings can ensure further protection.

Trees:

Having a multitude of evergreen trees (trees that have leaves all year) can create problems, as heat cannot radiate past the trees in winter, leaving the house without extra heat. This problem can be solved by planting deciduous trees (trees that lose their leaves in winter) is a beneficial factor in an energy efficient house. These trees in summer will block heat and shade the house, but in winter will allow the heat to radiate into the house.

Convection currents:

Convection currents can be beneficial in maintaining air quality and cooling air. Ceiling fans, high windows or cupolas help to create natural convection currents. If a house has more than one storey, than convection currents can also be beneficial. Heating systems are implemented in the lower floors, and convection currents carry the hot air up to other levels, through floor grills. However, if there aren’t any floor grills, the warm air will stay at ceiling level and will not be utilised for heating. As the cool air is pushed down, this means that if other appliances such as fans are not utilised, in winter convection currents are a hindrance.