The calculation of lighting use is based on the installed fixed lighting, and on the contribution of daylight. This appendix details the calculations automatically carried out in DEAP based on user entries and is based on SAP 10.
DEAP first calculates the annual base lighting requirement, ΛB (klmh/yr):
ΛB = 11.2 x 59.73 x (TFA x N)0.4714
Where:
The total lighting requirement is subdivided into two parts for further consideration: fixed lighting and portable lighting. The fixed lighting requirement, Λreq (klmh/yr) is assumed to be 2/3rds of the total:
Λreq = 2/3 x ΛB x Cdaylight
Where Cdaylight = C2 as derived below. The procedure differs depending on availability of the lighting design details. However, portable lighting is treated the same way in both cases.
The specific lamps to be considered are only those associated with fixed fittings within the dwelling. Portable fittings are not assessed as part of the dwelling and so are assigned an average efficacy of 21.3 lm/W11 in all cases. Portable lighting is assumed to account for one-third of the total lighting, so the energy required for portable lighting, EL,portable (kWh/yr), is:
EL,portable = 1/3 x ΛB x Cdaylight / 21.3
This applies to assessments with and without an available lighting design.
A reference fixed lighting capacity, CLref (lm), is defined based upon supplying adequate illumination to all rooms.
CLref = 330 x TFA
Where the lighting design is known, assessors can use the information detailed in the EPREL database, or certified data, to calculate a non-default value for entry in DEAP. The assessor enters the number and type of lamps in the dwelling, including rated power (W) and luminous efficacy (lm/W) for each. Efficacy may be inferred based on lamp type if unavailable.
The capacity of the fixed lighting provided, CL,fixed (lm), is calculated as:
CL,fixed = ∑ (luminous efficacyLamp × WattsLamp)
The average efficacy of fixed lighting provided, εfixed (lm/W), is calculated as:
εfixed = CL,fixed / ∑ power of fixed lighting outlets
The fixed lighting provision, Λprov (klmh/yr), is calculated as:
Λprov = Λreq x CL,fixed / CL,ref
If the capacity of lighting provided is less than required for adequate lighting top-up lighting is assumed to be used such that sufficient lighting is provided. The amount of lighting supplied by top-up lighting, Λtopup (klmh/yr), is:
Λprov < Λreq/3, then Λtopup = Λreq/3 - ΛprovΛprov ≥ Λreq/3, then Λtopup = 0The energy required for fixed lighting, EL,fixed (kWh/yr), excluding the top-up, is then calculated by dividing by the average efficacy of the fixed lighting provided.
Λreq ≥ Λprov, then EL,fixed = Λreq / εfixedΛreq < Λprov, then EL,fixed = Λprov / εfixedThe energy required for top-up lighting, EL,topup (kWh/yr), is assumed to be provided by lamps of average efficacy (from portable lamps).
EL,topup = Λtopup / 21.3
The total energy required for lighting, EL (kWh/yr), is the sum of the fixed, top up and portable components:
EL = EL,fixed + EL,topup + EL,portable
Where the lighting design details are not available. A generic factor to calculate installed lighting capacity is applied:
CL,fixed = 185 x TFA
Average efficacy is assumed to be fixed at 85lm/W in all cases.
Analysis of typical house types gives the following approximate correction factor, C2, for lighting energy use depending on the ratio of glass area to floor area, glass transmittance and light access factor.
GL ≤ 0.095, then C2 = 52.2 G2 – 9.94 GL + 1.433GL > 0.095, then C2 = 0.96GL = Ʃ 0.9 x AW x gL x FF x ZL
TFA
where:
The summation allows for different window and rooflight types (the light access factor is different for windows and rooflights).
To calculate the heat gains due to lighting, it is assumed that 85% of the annual lighting electricity consumption occurs during the heating season (Oct-May). Of this, it is assumed that 90% contributes to internal gains, the remainder being accounted for by other sources, such as lighting of unheated spaces. The average rate of heat gain from lighting is:
GL = EL x 0.85 x 0.9 x (1000 / (24 x HsDays)) [W]
Where HsDays is the duration of the heating season in days (243 days).
Light bulbs and light fittings outside of the dwelling should not be counted but should be counted if they are in unheated spaces of the dwelling (such as porches or garages). Portable (not fixed) lights, lights on cooker hoods and bathroom shaving mirrors should not be included in the count of fixed lighting in the dwelling.
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1Based on averages for dwellings from survey carried out by BRE