CALCULATIONS & WORKED EXAMPLE
Programs
64 Software programs have been developed which predict the energy performance of buildings. The programs have been adopted to assess compliance with the building standards. They can be used by building designers to prepare material to support planning applications. It is not intended that planners should use the programs but familiarity with the relevant terms and processes is encouraged.
65 The software programs 2 relate to the building type.
- For Dwellings: SAP2005 Standard Assessment Procedure, 2005 Edition.
- For Non-Domestic Buildings: SBEM Simplified Building Energy Model.
Emissions Rate Terminology
66 These programs are used to predict:
- The Target Emissions Rate ( TER) of a 'notional' dwelling or building. This is the 2007 building regulations CO 2 emissions standard.
- The Dwelling or Building Emissions Rate ( DER/ BER) of a dwelling or building as it is designed.
67 Emissions rates are measured in kilogram's per square metre of floor area per year, kgCO 2/m 2/annum.
68 The software programs incorporate a range of factors which influence energy use to predict the overall CO 2 emission levels. The building designer selects and inputs details of the design of the building into the relevant program which then calculates the predicted emissions. This provides the designer with the flexibility to vary technologies to achieve the policy target. At this stage location, siting and building design should also be considered. This will reduce the overall energy requirements of the building and therefore the contribution from LZC equipment that is needed to meet the percentage reduction target.
69 The following example calculations provide the detailed technical information omitted from the summary earlier at Figures 3 and 4.
Calculation 1: 2007 Building Regulations CO 2 Emissions Standard
70 Before the precise details of a building can be designed to meet the target the building designer selects and inputs more general information about the proposed 'notional' dwelling or building into the relevant program to determine a Target Emissions Rate ( TER) that should be achieved. This general information includes:
| Dimensions: size and shape. |
| Specified performance values of building elements and systems. |
| Non-domestic only, e.g. factory, office, hotel etc. |
| For the main space heating as different fuels result in different CO 2 emissions. For dwellings this may be mains gas, liquid petroleum gas ( LPG), oil, solid mineral, biomass (see para. 72 below) or electricity. For non-domestic this may be mains gas, if supplied to the site, or oil. |
71 The result of this calculation for the notional dwelling or building, the TER, is the 2007 building regulations carbon dioxide emissions standard. The aim of the target in SPP6 is to reduce this emissions figure by 15% using on-site low and zero carbon equipment.
Box 8.1: Target Emissions Rate Example development comprises: 4 detached dwellings, each with a floor area of 100 sq m 2 semi-detached dwellings, each with a floor area of 80 sq m The total floor area is 560 sq m, therefore the SPP6 policy target is a consideration when determining the applications. Methodology: SAP 2005 calculations are undertaken for both dwelling types providing the following result for the 2007 building regulations carbon dioxide emissions standard, the TER. Notional Dwelling | Detached | Semi-detached |
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TER | 23.13 kgCO 2/m 2/annum | 22.72 kgCO 2/m 2/annum |
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72 Where a notional dwelling is heated mainly by biomass a special calculation is necessary for the Target Emissions Rate. This is because SAP 2005 includes a biomass option, so a comparison with the dwelling as designed will show no benefit. It is proposed that a special Target Emissions Rate is calculated by the building designer based on the main heating being mains gas with a 90% efficient boiler. The 15% reduction in CO 2 emissions is then assessed by special reference to this special Target Emissions Rate.
Calculation 2: Actual Emissions Rate Using Low and Zero Carbon Equipment
73 Once a Target Emissions Rate ( TER) has been established the building designer must consider the potential for incorporating low and zero carbon equipment. The designer then inputs specific details of the equipment, including their relevant values and efficiencies, which they estimate is required to achieve the reduction in CO 2 emissions, into SAP 2005 or SBEM. This will establish the Dwelling or Building Emissions Rate ( DER/ BER) of a dwelling or building as it is designed, including the low and zero carbon equipment.
Box 8.2: Dwelling Emissions Rate with LZC Equipment Continuing with the example... SAP 2005 calculations are undertaken again for both dwelling types providing the following result for the Dwelling Emissions Rate ( DER) of the dwellings as they are designed, including the low and zero carbon equipment. Low & Zero Carbon Equipment: Detached: Ground source heat pumps for space heating
Solar collectors for water heating. Semi-detached: Air source heat pumps for space heating
Solar photovoltaic arrays. Designed | Detached | Semi-detached |
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DER ( LZC) | 19.77 kgCO 2/m 2/annum | 15.16 kgCO 2/m 2/annum |
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Calculation 3: Percentage Reduction
74 To establish whether the building(s) as designed, including low and zero carbon equipment, meets the target percentage reduction in CO 2 emissions, the percentage reduction between the Target Emissions Rate ( TER) and the Dwelling or Building Emissions Rate ( DER/ BER) must be calculated.
75 To calculate the percentage, the DER or BER for the dwelling or building as designed, including the low and zero carbon equipment, should be divided by the TER and multiplied by 100. To determine the percentage reduction, the result is then subtracted from 100. The result should be equal to or greater than the percentage target of the policy. However, this does not establish that the policy has been met.
Box 8.3: Percentage Reduction Continuing with the example... Designed | Detached | Semi-detached |
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TER | 23.13 kgCO 2/m 2/annum | 22.72 kgCO 2/m 2/annum | DER | 19.77 kgCO 2/m 2/annum | 15.16 kgCO 2/m 2/annum | Percentage: | 19.77 | X 100 | 15.16 | X 100 | | 23.13 | 22.72 | Percentage | 85.5% | 66.7% | Percentage: | 100 - 85.5 | 100 - 66.7 | Percentage Reduction | 14.5% | 33.3% |
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Calculation 4: Actual Emissions Rate Without Low and Zero Carbon Equipment
76 A re-calculation of the Dwelling or Building Emissions Rate ( DER/ BER) is required to establish if the building(s) as designed meet the target percentage reduction in CO 2 emissions specifically due to the low and zero carbon equipment.
77 Instead of inputting details of the proposed low and zero carbon equipment, the building designer carries out a re-calculation without them.
- Where the low and zero carbon equipment is to generate electricity, the re-calculation will be for the same building without the equipment; without the low and zero carbon equipment the electricity concerned would be taken from the grid.
- Where the low and zero carbon equipment is to provide heat a basis has to be assumed for an alternative, non-low zero carbon means of providing an equivalent quantity of heat.
78 Figure 5 details the alternatives to be substituted.
Box 8.4: Dwelling Emissions Rate without LZC Equipment Continuing with the example... Designed | Detached | Semi-detached |
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DER (no LZC) | 22.32 kgCO 2/m 2/annum | 22.62 kgCO 2/m 2/annum |
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SAP 2005 calculations are undertaken again for both dwelling types providing the following result for the Dwelling Emissions Rate ( DER) of the dwellings as they are designed but without the low and zero carbon equipment and instead using appropriate alternatives. |
Figure 5. Alternatives to Low and Zero Carbon Equipment
Source | Alternatives |
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Use | Instructions for Without LZCT |
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Biomass | Dwelling main heating. | Gas boiler to minimum building regulation specification (86% efficiency, programmer, thermostat and TRVs or time and temperature zone control if more than 150m2). |
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Dwelling secondary heating. | Electric secondary heating per building regulations (There must always be secondary heating for this calculation). |
Non-domestic. | Gas boiler to minimum building regulation specification efficiency and controls. |
Fuel Cells | | Same as biomass. |
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Photovoltaics | | No photovoltaics. |
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Hydro | Small-scale hydro-electric e.g. from river. | No hydro system. |
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Wind | | No wind turbine. |
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Solar Power | | No solar collector. |
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Geothermal | | No geothermal source, all heat provided by alternative system proposed for the building, or if none follow rules for biomass. |
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CHP | Dwelling/micro- CHP | Boiler using the same fuel as the micro- CHP. |
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Community CHP for dwellings. | Boiler using the same fuel as CHP plant. If the latter is biomass change to mains gas (see biomass above). |
Non-domestic. | Boiler using the same fuel as CHP plant. If the latter is biomass change to mains gas (see biomass above). |
Ground Source Heat immersion. | Dwelling. | Air source heat pump providing space heating only. Domestic hot water by electric Pump |
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Non-domestic. | Gas boiler, as per rules of biomass. |
Water Source Heat Pump immersion. | Dwelling. | Air source heat pump providing space heating only. Domestic hot water by electric |
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Non-domestic. | Gas boiler, as per rules of biomass. |
Air source Heat Pump | Dwelling. | Air source heat pump providing space heating only. Domestic hot water by electric immersion. |
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Non-domestic. | Gas boiler, as per rules of biomass. |
Heat Exchange/ Recovery Systems | Dwelling. | Natural ventilation with intermittent extract fans (3 fans for total floor area up to 80 m_, 4 fans if greater than 80 m_). |
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Non-domestic. | Mechanical ventilation without heat recovery, specific fan power of ventilation system 80% of that for the proposed building. |
Calculation 5: Percentage Reduction due to Low and Zero Carbon Equipment
79 To determine whether the building(s) as designed meets the target percentage reduction in CO 2 emissions specifically due to the LZC equipment, the percentage reduction between the Target Emissions Rate ( TER) and the Dwelling or Building Emissions Rate ( DER/ BER) without the low and zero carbon equipment must be established.
80 To calculate this the difference between the two DER figures should be established. This should then be divided by the TER and multiplied by 100. The result should be equal to or greater than the percentage target to demonstrate that the policy has been met in that the percentage reduction is directly attributable to the LZC equipment.
Box 8.5: Percentage Reduction due to LZC Equipment Continuing with the example... Designed | Detached | Semi-detached | TER | 23.13 kgCO 2/m 2/annum | 22.72 kgCO 2/m 2/annum | DER | 19.77 kgCO 2/m 2/annum | 15.16 kgCO 2/m 2/annum | DER (no LZC) | 22.32 kgCO 2/m 2/annum | 22.62 kgCO 2/m 2/annum | Difference in DER | 2.55 kgCO 2/m 2/annum | 7.46 kgCO 2/m 2/annum | Percentage: | 2 .55 | X 100 | 7.46 | X 100 | 23.13 | 22.72 | Reduction due to LZC equipment | 11% | 32.8% |
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Calculations for Development Consisting of Multiple Dwellings
81 A development of over 500 square metres may contain more than one dwelling or building, as is shown throughout the example.
82 Where each building individually fulfils the percentage target, the development as a whole will fulfil the policy target. Using the example given as a basis, if a development comprised only the semi-detached type of house and 8 in number, this would meet the policy target.
83 Where individual buildings do not fulfil the percentage target, as would be the case for a development comprising only the detached units in the example above, the average emissions of the buildings as designed ( DER/ BER) may be compared to the average target emissions ( TER) for the site. This will involve determining the DER for each dwelling and/or the BER for each building and then an area weighted average over all the dwellings and/or buildings.
Box 8.6: Area Weighted Averages Concluding the example…. Designed | Detached | Semi-det. | Total | Average |
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Dwellings | | | | | Number ( n) | 4 | 2 | | | Floor Area (A) | 100 | 80 | | | Sum Floor Areas ( n x A) | 400 | 160 | 560 | | TER | 23.13 | 22.72 | | | Area weighted TER ( n x A x TER) | 9252 | 3635.2 | 12887.2 | 23.01 | With LZC Equipment | | | | | DER | 19.77 | 15.16 | | | Area weighted DER ( n x A x DER) | 7908 | 2425.6 | 10333.6 | 18.45 | % reduction on TER (As Box 8.3) | 14.5% | 33.3% | 19.8% | | Without LZC Equipment | | | | | DER | 22.32 | 22.62 | | | Area weighted DER ( n x A x DER) | 8928 | 3619.2 | 12547.2 | 22.41 | Difference DERs | 1020 | 1193.6 | 2213.6 | | % reduction on TER (As Box 8.5) | 11% | 32.8% | 17.2% | |
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84 Where the site is assessed as a whole using area weighted figures, as in the example above, and the average reduction in emissions for the site exceeds the percentage target, then the policy criteria has been achieved.