Reducing energy in use

Porches

Unheated ‘buffer’ spaces between the warm inside of the house and the cold outside act as airlocks when people go in and out. This prevents cold air penetrating the house, as tends to happen with a conventional British entrance hall. A draught lobby is traditional in Scotland, and should be thought of as a minimum provision.

The general principle is to use a simple construction to absorb the main force of the wind, and then to let a properly draught-proofed inner door do its job effectively. Porches should be unheated and of simple, cheap construction. They need to be at least 2m2 in area to allow for one door to be closed before the other is opened.

Conservatories

Reducing energy in useUntil recently, a conservatory was considered an unheated space that relied on solar gain to make it usable for around nine months of the year. The construction was relatively simple, with singleglazing to provide good-value space. To reduce heat loss and air leakage, the conservatory could cover as many windows and as much wall as possible.

However, many people now regard a conservatory as a light and pleasant extension of the house, to be occupied and heated all year round; some people have even added air conditioning to deal with overheating in summer. Used in this way, a conservatory becomes not an energy-saving measure but a large extra energy load. In these circumstances, reduce the amount of glazing by having a largely solid and insulated roof with a reduced area of high-performance double-glazing and well-insulated walls and floor.

Another approach is to design conservatories as ‘sunspaces’ and make them too narrow to be useful as rooms in their own right, so removing the temptation to provide heating and use them all year round.

What is crucially important is that a conservatory is not considered as a glazed (and therefore extremely inefficient) extension to the general living space, subject to massive heat loss in winter and at night and to massive solar gain causing overheating when the sun is out in summer. On no account provide heating or air conditioning.

A conservatory on the south side of the house is often the basis of passive solar heating provision. See the section on Renewable Energy (pi68).

Drying space

Provide space for drying clothes by natural means, removing the need for energy-intensive electrical tumble dryers. This might be in the form of a clothes line or rotary clothes line in a garden, or a utility room with a drying rack. Individual heat-recovery ventilators, which have a heat exchanger warming the incoming fresh air, can be useful for this.

Costs and benefits

Sunspaces and porches can save energy and also provide additional living and storage space. They can also create bright sunny space relatively cheaply. Meanwhile, compact building forms will often have a lower initial cost than more complex forms.

Summary: planning the house to save energy

Consider the form of the building, perhaps providing a porch and a space for drying clothes. Treat conservatories with extreme caution.

Construction issues

This section outlines:

  • ways of reducing heat loss through the fabric of the building – insulation, airtightness and thermal bridging
  • the selection of insulation materials and how to determine their appropriate thickness
  • how to avoid condensation
  • the standards in the Building Regulations and other higher standards proposed by the Building Research Establishment (BRE) and the Association of Environmentally Conscious Builders (AECB).

Fabric heat losses

The aim of the design of an energy-efficient building is to minimize heat losses through the building envelope – that is the roof, walls, floors and windows – and heat losses through air leakage, while at the same time maximizing heat gains from the sun. Fitting thermal insulation and draughtstripping to an existing house is one of the most cost-effective ways to save energy and reduce emissions.

Thermal insulation

The first and most important measure is adequate thermal insulation. Air-based insulation uses different materials as the matrix to encapsulate air pockets. These materials can be:

  • of organic origin from natural vegetable matter that is both renewable and recoverable on demolition. These materials generally need little energy to produce. Examples include cork, wood fibreboards, hemp, sheep’s wool and loose cellulose fibre from recycled newspaper
  • of inorganic origin from naturally occurring minerals which are generally not renewable but plentiful. Generally this involves moderately high energy inputs and consequent emissions. Examples include mineral wool, fibreglass, ver- miculite, foamed glass and aerated concrete
  • of fossil-fuel origin, which is not renewable, with generally high energy inputs, emissions and pollution implications from the chemical industry. Examples include expanded and extruded polystyrene, foam polyurethane and foam polyiso- cyanurate. These materials tend to have a higher performance than organic or inorganic insulation materials. Manufacture now cannot involve ozone-depleting gases.

The environmental preference is for insulation materials from natural organic sources. Avoid fossil- fuel-based materials if possible. However, high- efficiency foam boards such as polyurethane can have a place in refurbishment where other insulation materials would be too thick.

Thickness of insulation

There is no one simple prescription for this, as it depends on the type of construction and the fuel to be used for heating, among other factors.

Other issues include:

  • Cost-effectiveness. The cost of extra insulation will reduce fuel costs – up to a point. Beyond that point, the additional insulation does not save enough fuel cost to pay for itself. The critical thickness depends on the cost of the fuel used and the cost of the insulation installed. Surprisingly, however, it is not until you get to thicknesses of around 900mm that the embodied energy in the insulation is more than the energy saved over its life. In general terms, assuming common air-based insulation materials and gas heating, the common view is that anything much above 300mm of insulation is not very cost effective.
  • Practicality of installation. This is often the overriding consideration, especially in refurbishment.

One of the principal difficulties in reducing the emissions of existing houses is incorporating thermal insulation into existing buildings, particularly the walls. External insulation can be installed with residents in occupation, but does require scaffolding. Internal insulation reduces the size of rooms to some extent, and is very disruptive and may mean having to move out whilst it is installed. Cavity walls should be filled and lofts insulated where they exist. External insulation is expensive and changes the external appearance of the building, which may be unacceptable in some circumstances. Other issues include the need for an insulation material that will not deteriorate when wet for cavity wall insulation. This rules out organic materials such as cellulose fibre for this application. Another limitation is that some materials such as cellulose fibre need to be blown into a cavity which has to be formed in some way. Such materials are not rigid in their own right, neither are they load- bearing under a floor slab, for example.

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