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Technical questions - carbon footprinting, maintenance contracts and rapeseed oil as a fuelJanuary 2009

'Heat Islands - understanding and mitigating heat in urban areas' is available on library loan to BSRIA Members

BSRIA shares the answers to the more frequent technical enquiries from BSRIA's consulting and contracting membership. This month, members want to know about carbon footprinting, the characteristics of rapeseed oil, and modern contract forms.

Carbon footrpinting explained

What is carbon footprinting?

The term carbon footprint is a fairly new term and can be applied to individuals, communities, businesses - or static entities like buildings. There are various definitions. One provided by the Parliamentary Office of Science and Technology in 2006 reads:

"A 'carbon footprint' is the total amount of CO2 and other greenhouse gases, emitted over the full life cycle of a process or product. It is expressed as grams of CO2 equivalent per kilowatt hour of generation (gCO2eq/kWh), which accounts for the different global warming effects of other greenhouse gases."

For buildings, the definition depends who you are and what you can control; or, to a go a step further, that for which you are accountable. For example, a tenant would only be responsible for the energy and waste generated via its business activities. A builder would be responsible for all CO2 emitted by construction.

From a building perspective, carbon footprinting can be separated out into embodied carbon and operational carbon. The embodied carbon footprint requires knowledge of the carbon intensity of the materials used (and wasted) during construction, the energy used on site to construct the building, and the carbon dioxide emitted by all construction traffic to and from site.

In operational terms, the carbon footprint is expressed by the annual production of carbon dioxide in kilograms per square metre of gross internal floor area. This is derived from accurate measurement of the building's electricity and fossil fuel consumption and water use (within the site boundary), with any contribution from renewables deducted.

The operational carbon footprint can be refined with knowledge of the emissions from journeys to and from work based on mode(s) of transport and distance travelled. Waste generated by the business carried out in the building can also be counted.

Theoretically, carbon footprinting should be a life-cycle activity, starting from the inception of a project (including emissions generated by all parties during design development), and of course demolition. Whereupon it can all get rather academic.

Model forms of contract

I am looking for model forms for a plant maintenance contract.

The advantage of using model forms of contract is that all the legal approvals have been previously agreed and are in place, and obviates the need to go through a lengthy and expensive procedure.

The Property Advisers to the Civil Estate (PACE) has issued GC/Works/8 - Specialist term contract for maintenance of equipment. General conditions, model forms and commentary to cover the maintenance of specific plant.

The eight model forms are:

  • Abstract of particulars
  • Invitation to tender
  • Tender form and price schedule
  • Adjudicator's appointment 
  • Project manager's instruction 
  • Payment certificate 
  • Notice of intention to withhold payment 
  • Employers notice of determination

Guidance on maintenance contracts is available in BSRIA Guide BG 3/2008, Maintenance for Building Services. ISBN 978 0 86022 674 1.

Using rapeseed oil as a fuel

What are the characteristics of rapeseed oil as a fuel?

There has been some interest in using biofuels as an option to replace or supplement fossil fuels. Biodiesel made from rapeseed is called rapeseed methyl ester (RME) and must conform to the biodiesel fuel quality standard BS EN 14214.

The main chemical composition of rapeseed oil is made up of 77 percent carbon, 11.4 percent hydrogen, 11 percent oxygen, plus 20 percent sulphur and trace elements of nitrogen and phosphorous. These values are lower values than those for fossil fuels, which means the calorific value is also slightly lower.

Interestingly the trace elements of nitrogen do not result in higher NOx levels than normal diesels. Rapeseed oil is a non-flammable liquid with a viscosity similar to light fuel oil. It requires pre-heating to between 60°C and 90°C depending on the atomisation used.

The key characteristics of rapeseed oil are:

  • Net calorific value: 35 MJ/kg
  • Kinematic viscosity (cST): 38 at 40oC
  • Acidity: pH 4.5 - 5.5
  • Ash weight: <0.01%
  • Density: 0.9kg/litre
  • Pour point: -6oC
  • Flash point: 220oC

Also see 'Alternative fuels scrutinised' Health Estate Journal, January 2008, and 'Biodiesel heating oil: Sustainable heating for the future', IPHE Tech Paper 7, 2006.

Floor area definitions

What is meant by NIA?

NIA (net internal area) can be used as a basis of measurement for the calculation of service charges for the apportionment of occupiers' liability.

NIA is the usable area within a building measured to the internal face of the perimeter walls at each floor level. It will include areas occupied by grilles, lift lobbies, atriums, kitchens and areas occupied by trunking. It will exclude areas such as plant rooms, fuel stores, meter cupboards, permanent plant, and toilets.

A full definition of NIA and similar measurements can be found in RICS Guidance Note Code of Measuring Practice.


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