Criterion 1: Achieving an acceptable Building CO2 emission rate
This involves the calculation of a predicted carbon dioxide emission rate from the building and compares this with a building with identical geometry and functions but with nominal specifications similar to minimum standards. A naturally ventilated building will need to emit 23% less, an air conditioned building 28% less than a building built to nominal specifications.
Emissions represent only those from providing the main building services (heating: space and water, cooling, ventilation and lighting).
Thus a building built to the minimum requirements for fabric and services (Criterion 2) will not be compliant and in the event of the predicted emissions being unacceptable we will provide guidance on changes to the specification which will achieve compliance. Probable areas for improvement could be:
Improve U values in fabric and glazing
Alter glazing ratio on specified faces
Use a different fuel for hot water heating (eg electric-gas)
specify more efficient heating equipment and controls
reduce lighting circuit wattage
install automated controls for lighting
We will discuss with you the suitability of the different options so that the most appropriate and cost effective changes can be implemented. One of the most effective ways of reducing the fuel consumption cannot be assessed simply from design specifications as it relates to the quality to which the building is constructed and is assessed through an (obligatory: see Criterion 4) air tightness test. We will discuss with you a target value which will be used in the calculation. It may be possible to achieve compliance simply on achieving a good standard of air tightness.
To derive the CO2 rating we will require the following categories of data:
Building Geometry
Details of building geometry and significant obstructions (scale plans)
Construction type for internal walls and floors/ceilings
Construction type and U values for external walls, roofs, floors, windows and doors
Details around junctions in external elements
Building Services
The following will be required for every system and area it serves
Heating system type (boiler and distribution), efficiencies, zoning and controls
Hot Water system type (boiler and distribution), hot water plumbing layout may be needed
Lighting system circuit wattage (ideally) or type and controls
Location and fan power, (if applicable: recirculation/heat recovery) for all mechanical ventilation systems
Where present, we will require details of
any renewable or low energy (eg CHP) systems
efficiencies for air conditioning, mechanical ventilation plant and ducting
We will assume that any data you provide is accurate, it will be assumed that key data is verified during/post construction by Building Control.
The greater the detail you are able to provide, the lower CO2 figure will result. iSBEM will assume worst performance from a generic type of system. Where the specific product is known then its performance specification will most likely represent an improvement over the generic value.
We realise that all this information may not be available in which case we will make assumptions and advise you of these. Where a significant benefit can be made by a better specification we will advise you.
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