Best Practice > Best Practices
A low or zero carbon design refers to a building that has a negligible or zero nett energy consumption in one year. A building that consumes no or little energy in one year will significantly cut down on greenhouse gas emissions and running costs.
Micro Energy Generation refers to the generation of heat and power by individuals to help reduce or eliminate their dependence on the national grid and therefore contribute to the reduction or elimination of carbon emissions.
Micro Generation embraces a range of technologies such as those indicated below;
The use of domestic scale combined heat and power equipment such as the above can contribute significantly to self sufficient energy generation and costs.
The use of passive solar design principles in the design of a building can reduce heating, cooling and lighting demands.
In order to get the most from passive solar design one needs to be aware of the following passive solar heating techniques;
In order to take most advantage of passive solar gain it is important that the following issues are considered;
Passive solar design and taking advantage of a site microclimate both enhances the energy and environmental performance of a building. Ideally the building should take the maximum advantage of the site’s solar radiation and daylight, as well as good shelter from the wind.
The main orientation of the building should be within 30° of south in an East / West direction. Houses orientated east of south will benefit from the morning sun. Those orientated west of south will catch the late afternoon sun – which can help delay the evening heating period.
A location on a south facing slope optimises solar access whilst minimising overshadowing from adjacent buildings. It also allows for higher density planning.
Direct gain is the most basic form of solar gain. Solar energy enters through south-facing glazing and is absorbed by thermal mass incorporated into the floor and walls. Heat is stored in the thermal mass during the day and later released during the night into the living space. This re-radiation of ‘stored’ heat can maintain a comfortable temperature during cool nights and can extend through several cloudy days without ‘recharging’.
Terms used with thermal mass storage:
This term relates to the ability of a material to absorb heat and then release the heat or conduct it throughout the material. Thermal lag times are influenced by:
Thermal admittance is useful during the design process and describes the ability of a material to exchange heat with the space over a time period of 24hrs. Thermal admittance is influenced by:
Ultimately admittance has an upper limit determined by the rate of heat transfer from the material’s surface to the adjacent air – though this can be increased through ventilation providing convective heat transfer.
The most effective construction materials are those with the highest volumetric heat capacity. In general, dense materials will generally have a higher thermal mass than less dense products. For example, dense concrete blockwork, rammed earth and mud bricks have a high effective thermal mass when compared to lightweight blockwork or wood.
For thermal mass to be effective there must be minimal thermal resistance between the occupied space and the mass of the structure. The temperature fluctuations within the building fabric are greatest at the surfaces. Relatively thin layers of plaster can have a significant effect on the thermal mass by providing thermal resistance.
The seasonal effects of thermal mass:
In winter, thermal mass in the floor or walls absorbs radiant heat from the sun through south, east and west-facing windows. During the night, the heat is gradually released back into the room as the air temperature drops. This maintains a comfortable temperature for some time, reducing the need for supplementary heating during the early evening.
The most difficult period in winter is the early morning. The heat released during the night has dissipated, temperatures have dropped and the sun has yet to begin the heating process. During this time it will probably be necessary to use supplementary heating to warm the thermal mass before the air temperature rises.
Locating thermal mass
Sunspaces / thermal buffering
A sunroom can be integrated into a building design in essentially two ways. Situated on the sunny side of the building they can be integrated as either a ‘lean to’ or an ‘embedded’ concept.
Both approaches have distinct advantages and disadvantages as described below:
The sunspace functions as an intermediate space between the inside and outside of the building. By effectively adding another layer to the building envelope, the sunspace becomes a thermal buffer rather in the manner of air within a cavity wall.
A further effect of the sunspace is to shelter the envelope from wind chill and rain – this factor becomes increasingly important in northerly and exposed locations
Warm air can flow into adjoining spaces via openable vents located in the common wall at the top of the sunspace. Cool air is returned from the living spaces through lower vents to be heated as part of the convective loop.
Mechanical ventilation can extend the penetration of pre-heated ventilation into areas of the house that are not adjacent to the sunspace. Heat is collected from the upper part of the sunspace and blown via ducting to other areas of the house.
Heat is transferred to the living spaces through a masonry common wall. (see thermal walls).
Opinion is currently divided as to the effectiveness of combining storage walls with sunspaces. Debate centres around the winter period when the wall has its greatest potential, yet when equally solar radiation is at its most diffuse.
As distinct from the immediate use of pre-heated air, thermal storage affords the capacity to store heat for future use. The traditional form of heat storage is the ‘rock store’. Heated air from the sunspace is mechanically driven to containers of crushed rock. Heat transfer is then effected by one of two methods:
Though the former enables a degree of remoteness between the store and the space to be heated, the latter method has the advantage of being simple, passive and is generally more popular.
In practice, rock stores perform reasonably well. However, very large amounts of rock are required to store relatively small am heat. For example, about 60 tonnes of rock are required to satisfy the storage requirement for a solar space heating system for an area of 100 square metres.
In its minimal form, the sunspace becomes a draught lobby. Heat is lost when doors and windows are opened to the outside. By providing sufficient space for the outer door to be closed before opening the inner door, the draught lobby functions something like an air lock.
Sunspaces are easily overheated in summer. The problem can be resolved by:
Air tightness around windows and doors should be particularly effective to reduce heat loss to the sunspace when that space cools to temperatures lower than the adjoining living area
If automatic vent operation is not provided, the building user needs to be fully aware of the need to control the vents correctly Where automatic controls are provided, users should be able to set them for desired levels of comfort.
The Energy Performance of Buildings Directive 2002/91/EC (EPBD) was passed into law by the European Parliament in December 2002 and adopted by the 25 member states, including the UK, in January 2003.
The main aim of the Directive is to promote the improvement of energy performance of buildings and it is left to each member state of the European Union to develop a framework for energy performance calculation.
Essentially, this will provide an energy rating for a building similar to a consumer item such as a fridge or freezer. The ratings vary from A (the most efficient) through to G (the least efficient). The rating is shown on an Energy Performance Certificate (EPC) Click here for more information.
The EPC itself is based on calculations set out in the Reduced Data Standard Assessment Procedure (RdSAP) which itself is a condensed form of the Standard Assessment Procedure (SAP) Existing buildings that require an EPC will get one based on RdSAP calculations while new buildings will require an EPC based on the full SAP calculations.
Building Control sets minimum standards for U values for various building types.
Typically, for a dwelling house the best elemental U values are as below for a dwelling with a SAP rating of 60 or less :
Accredited Details have been developed to help the construction Industry achieve the minimum construction standards so that they comply with the requirements of Part L of the Building Regulations.
It is important to understand that the above Typical Best U Values and Accredited Construction Details are minimum standards. In order to achieve minimum / ultimately zero energy useage in a building one has to look to improve these standards.
One way to improve the energy efficiency of a building is to adopt a BREEAM (Building Research Establishment Environmental Assessment Method) assessment methodology to the design of a building.
This is a government adopted agency and provides a way to measure the energy performance of a building using sustainable materials. The BREEAM assessment methodology covers all building types right through to bespoke buildings.
The following link gives an overview of how BREEAM works, what ground it covers and the scoring system associated with BREEAM, how BREEAM works and what can be achieved by employing a BREEAM approach to building design.
Reducing the amount of air leakage form a building can dramatically improve energy efficiency. The energy that we use to heat our homes is primarily created by burning fossil fuels that produces carbon dioxide. If we reduce the air leakage of a building we also reduce the amount of energy required to maintain comfort levels and in turn reduce carbon dioxide emissions.
Air leakage is the air tightness of a building through uncontrolled means such as cracks and gaps in the building envelope. Any ventilation system installed in a building is seen as a source of controlled air flow and is therefore not considered as air leakage. At a very basic level, air leakage may be seen as unwanted draughts.
Air pressure testing is a method of measuring and quantifying the air leakage of a building in accordance with Building Regulation requirements. Air pressure testing of a proportion of all new domestic housing is a legal requirement in accordance with the guidance given in Approved Document Part L1A – Conservation of fuel and power in new dwellings of the Building Regulations. Testing the air tightness of existing dwellings can highlight areas of problems that can be treated cost effectively to improve the energy efficiency of the dwelling as a whole.
Air tightness tests are usually carried out during the construction and commissioning process of a building when the external envelope is fully complete, with windows and external doors in place. Remedial work may need to be carried out on a building that fails an air pressure test.
A building that is sustainable must by nature be constructed using locally sustainable materials: i.e. materials that can be used without any adverse effect on the environment and which are produced locally, reducing the need to travel. There are key criteria that can be used to judge whether a material is sustainable or not:
It is also important in the use of sustainable materials that an effort is made to source sustainable materials locally through suppliers and that once sourced and specified that this is communicated effectively to the contractor. If you need help with design use a ‘Green Architect.’ The Royal Institution of British Architects can advise you on finding a suitable practitioner.
The need to find new types of renewable energy is urgent – not only as oil reserves are running out but there is increasing competition from China and India for the limited world reserves.
There are several different types of energy being produced today. Solar and wind power are now well-known as early-stage alternative renewable energies. But there are the other potential energy sources such as those listed below:
Biomass is a different type of energy altogether and it is still very much in its infancy, but using renewable, continually-growing plant material seems to be a sensible option. Large areas of agricultural land would have to be turned over to these crops, and using biomass fuel could make a significant contribution to reducing global warming because the fuel has a low heat output and would need to be used in greater quantity.
Once a dam is built, generating power from the build-up of water is inexpensive. This is quite a limited source of power as it depends upon the continued elevation of the water.
Other downsides to the use of hydro power is that dams potentially threaten human life if they collapse and they certainly affect fish stocks. They also create environmental damage for surrounding areas if they flood. Unfortunately all reservoirs eventually fill with sediment and the rate of this is unknowable.
This option too seems a tremendous possibility – burning our rubbish and using its byproduct. Again, this is also in its infancy. It is known to have a low sulphur dioxide emission, but the by-product created (known as fly ash) can contain metals such as cadmium and lead.
Hydrogen has first to be obtained by the electrolysis of water, or by breaking down natural gas. It is an energy type which is highly explosive and must be compressed to be contained and carried. It is also very costly to produce, yet we are seeing the first generation of cars powered by this form of energy.
Sub-metering contributes to good energy management and the strategy for energy metering in a building should be included in the building maintenance handbook.
Most buildings have incoming meters for billing purposes. They measure the total input of the specific fuel to the site. Regular meter readings will provide some information about the overall energy consumption, but it reveals little about where the energy problems lie. Installing sub-metering throughout a building to monitor the specific uses of the fuel being metered can help identify which end-use or service (e.g. lighting, fans, pumps etc.) is performing well or badly, allowing more targeted action.