Passive/Low Energy House.
The ideal energy system is one from a renewable,low carbon source which meets its end demand as efficiently as possible.This is at the heart of Sustainable Building Services.Building service providers should aim to influence the work done and decisions made by their clients and other professionals in the interests of Sustainability.
The ideal housing project should approach the issue of sustainability from a holistic viewpoint.Decisions made from the outset will account for sustainability in house design and fabrication;materials selection and procurement;construction technologies and methods and waste production and disposal.
The governing issues are Energy and CO2 emissions;water use;pollution;waste and lifecycle impacts of materials and equipment.
A Passive House is a sustainable,energy efficient,low emisions building with a comfortable and healthy living environment without the use of an active space heating system.The concept is based on maximising heat gains and minimising heat losses.DHW is provided from a renewable energy source.Ideally the house would be carbon neutral.The ultimate Passive House would be an off grid stand alone installation with renewable operational energy and stored back up.
The Passivhaus Standard is a construction guide for buildings to achieve this .The design and construction of a house to this standard will result in a thermally efficient envelope which will maximise free heat gains while minimising space heating requirements.Compliance with the standard requires that space heating and primary energy use target figures,as set out in the standard,are not exceeded.
Structural air tightness and minimal thermal bridging are essential.
Structural air tightness means that air leakage in or out of the building is eliminated or minimised as far as possible.
Thermal bridging refers to materials in a building envelope through which heat is transferred at a significantly higher rate than the surrounding materials.
The avoidance of air leakage and thermal bridging means that a more thoughtful approach to building detail and greater care in construction are required than might have traditionally been the norm.
A whole house mechanical heat recovery system is standard in a passive house both to ensure the freshness and purity of indoor air and to capitalise to the maximum on passive heat gains.
In a Passive House,solar heat gains and internal heat gains from all sources contribute to a huge proportion of total heating requirements by comparison with a conventional house.
If a short term or supplemental heat boost is required a small heating system-powered from a renewable source- should suffice.
Ideally a passive house is one where the home owner has control over the location and orientation of the house.This is rarely the case and as often as not there will limited control over the orientation of the house and even less over the location.It will rarely be the case that any one component of a project be given total priority---design solely on energy issues OR design solely to maximise a site’s scenic potential and surroundings.Pragmatic compromise would ordinarily be the norm.However where location and orientation are in the control of the home owner and where the ultimate aim is to build a Passive House,energy considerations must dominate.It is important to bear in mind that control over location of the house on the site and the orientation of the house,which would have traditionally been site optimisation issues,can be pivotal first steps towards achieving Passive House standard.It is all about passive heat gains.Earth based materials can be used to store heat from passive heat gains.
The areas where the home owner can invariably strive for full control are Building Fabric,Glazing,Air Tightness,Heat Recovery/Ventilation and energy use.
It is therefore crucial that these areas be given be given serious thought at design stage and the greatest care and attention during construction.
From the standpoint of general wellbeing,it is important that the home environment places as few strains on the body as possible.The creation and regulation of this environment is central part of a building design.The way in which a house is built,the materials that it is made from,the way light enters it and the quality of the air within it are basic requirements for consideration by the designer at the early stages.
The Air Tightness demands of a Passive House are extremely stringent and require discernment by the householder in all matters affecting the internal environment of the house.
Matters to be impact analysed are such as Radon infiltration,General cleanliness and lifestyle.Certainly active Radon protection needs to be in place in a Passive House.
Structural elements and components cannot be overlooked as regards their environmental contribution.This is particularly the case in timber construction but should not be overlooked in other building systems.Contributions from structural elements are likely to be long term and maybe permanent or prohibitevely difficult to eliminate.
The aspects of structural elements for consideration are preservative treatments for timber components,materials in insulations and plaster finishes.
Clearly paints and finishes are another area where a householder can take full control of their environmental impacts through the use of natural paints and finishes.
An area which is often overlooked is that of soft furnishings-curtains,carpets,cushions etc, and care needs to be taken in the selection of such with the increased build up of environmenal emissions in an air tight building.
There will be people who may well go as far as giving consideration to clothing.This is extreme but not to be ruled out.
Thought should be given to environmental emissions from fixtures and appliances especially Home Theatre and Sound Systems etc.The ionic balance of air is disturbed by electric fields from such equipment.Prolonged exposure to air with an excess of positive ions can create create emotional imbalance and can even account for physical disorders.Some level of control on the numbers and distribution of this equipment should be considered.Ionisers can be considered in cases where concessions on equipment are not realistic.
The latter three above would fall somewhat into the area of Life Style and life style has a large part to play in the final effectiveness of a low energy building.The Sustainable approach is something which must be bought into by the occupants if the thought and effort that go into their building is to repay itself.
HEATING and VENTILATION
Heat moves from regions of high temperature to regions of lower temperature by Convection,Conduction or Radiation.All these types of heat movement are present in a building.Convection relies on movement of air to take place.Conduction takes place through a solid or liquid.Radiation does not require any medium to move and is a direct result of a bodies temperature.All bodies radiate heat.
Condensation results from heat movement by evaporation.Evaporation is a from of convective heat movement.
Because the balancing of heat requirements relates to air movements,apart from maintaining the balance of heat in a building,air plays an important role in removing waste matter and pollutants from a building. For these reasons,Heating and Ventilation is regarded as a single issue in building design.Ventilation expels stale air and pollutants as well as supplying fresh air and distributing heat within the building.
The best model on which to base the design of a Heating and Ventilation(H&V) system for a building is the human body.The roof is the head,the walls are the clothing and the floor is the feet.Convection losses occur when air passes over the body and is reduced by clothing.It can be easily seen that the fabric of the building is critical.Radiation losses in the body are largely from the head and from the roof in a house.Conduction losses are largely through the feet and through the floor of a building.If the clothes of a building are made from naturally cold and highly conductive materials,the building will lose too much heat for comfort.
The majority of human heat loss within a building is by radiation either to the cold elements of the building or to cool air.
Convection accounts for the next largest heat loss and is caused by air movement across the body.
Broadly speaking if the air is too cold or is moving too fast the occupants will feel cold.The H&V system must warm up cold air and control the rate at which it moves through the building.
Moisture production is also controlled by means of temperature and air movement.The body of a building produces moisture which must be expelled from the building.If a building does not have enough fresh air,as with a human body,it will sweat.
Heating and Ventilation are crucial to the internal environment of a building.Because they are central to the Low Energy and Energy Efficient house,they must be at the core of the building design and decisions about them must be made in the earliest stages.