Book - School of Science and Technology

Primary energy 661Dependent upon the viewpoint taken, assessment of the effectiveness of a design interms of energy use may be expressed in respect of one of the following:. energy cost. energy demand, at the site. primary energy consumption. CO 2 emissions. carbon emissions.Decisions based on fuel and electricity prices are, of course, subject to the commercial andpolitical climate at the time and the results are in consequence variable. Calculations mayalso be expressed in terms of energy demand at the site, in watt or joule energy units.Energy demand expressed in W/m 2 has been adopted by CIBSE to establish whethera building and its systems satisfy set energy targets. The CIBSE Energy Code sets out amethod for calculating demand and target values, which distinguishes between thermaland electrical demands in order to enable other factors such as national reserves to beconsidered. The criteria used in the BRE Energy Assessment Method (BREEAM) is CO 2emissions.The latest revision to Part L of the Building Regulations, which deals with the conservationof fuel and power in buildings, has adopted a method of demonstratingcompliance based upon calculated carbon emissions per annum (in kg of carbon, kgC)from heating and hot water services, ventilation, air-conditioning and lighting. Typicalcarbon emission factors are given in Table 23.1. The benchmark criteria for officebuildings are derived from the DETR Energy Consumption Guide 19. This gives benchmarksfor `typical' and `good practice', based upon an extensive survey of occupiedbuildings, and recommends that new designs should aim to improve upon the goodpractice figures.Primary energyThis is the quantity contained in fossil fuel, coal, oil and natural gas, etc., from which anoverhead must be deducted to cover consumption in production, transmission and distributionin order to arrive at the net supply received by the actual consumer. Typical netto gross values calculated from CIBSE Energy Codes, 1998 are:Electricity 26%Coal 97%Gas 93%Oil 92%Table 23.1 Carbon emission factorsDelivered energyCarbon emission factor(kgC/kWh)Natural gas 0.053Oil 0.074Coal 0.086Electricity (average at 2001) 0.139Electricity (average over period 2000±2020) 0.115 a predicteda Department of Trade and Industry, Energy Paper, 65.