Checklists - THORN Lighting

Checklists7.2 EconomicsWhen refurbishing an existing installation it is important tobe able to quantify the benefits of the new lighting systemcompared with the existing system. These benefits are quantifiedin terms of the payback period. This is a comparison of theexpenditure in terms of investment costs to buy and install anew system, compared with the savings in annual operatingcosts through having the new system. Thus if a payback timeis 5 years this means that after 5 years the savings from usingthe new system have cancelled out the costs of buying the newsystem.Worksheet 7.2 aids in the calculation of this value. Formulaeused is this worksheet are:Luminaire costs = Number of luminaires x cost of one luminaireLamp costs = number of luminaires x number of lamps per luminaire x cost of one lampInstallation costs = number of luminaires x installation cost per luminaireRoom cleaning costs = cost of room cleaning x service life of system (years)room cleaning interval (years)Luminaire cleaning costs = cost of luminaire cleaning x service life of system (years)luminaire cleaning interval (years)Lamp replacement costs = cost of lamp replacement x service life of system (years)lamp replacement interval (years)Energy costs = (number of luminaires x system power of luminaire x service life of system xannual burning hours x energy cost per kWh x %energy savings due tocontrols)/1000Operating costs = room cleaning costs + luminaire cleaning costs + lamp replacement costs + energy costsAnnual operating costs = operating costs / service life of systemPay back period =investment cost proposed installation – investment cost existing installationannual operating costs existing installation - annual operating costs proposed installation(Note that the model given in Worksheet 7.2 is a static modelin that it ignores the costs of depreciation of equipment andinterest payments).Checklists | 183

Building ProjectLuminaire type (1)Luminaire dataNumber of lamps per luminaire (2)System power of luminaire (W) (3)Operating dataService life of system (years) (4)Annual burning hours (5)Lamp replacement interval (years) (6)Luminaire cleaning interval (years) (7)Room cleaning interval (years) (8)Number of luminairesLamp lumens maintenance factor (9)Lamp survival factor (10)Luminaire maintenance factor (11)Room surface maintenance factor (12)Maintenance factor [ (9)x(10)x(11)x(12) ] (13)Number of luminaires (14)Itemised investment costsCost of one luminaire (15)Cost of one lamp (16)Installation costs per luminaire (17)Itemised operating costsCost of lamp replacement (18)Cost of luminaire cleaning (19)Cost of room cleaning (20)Energy costs per KWh (21)%Energy savings due to control system (22)Investment costsLuminaire costs [ (14)x(15) ] (23)Lamp costs [ (14)x(2)x(16) ] (24)Installation costs [ (14)x(17) ] (25)Investment costs [ (23)+(24)+(25) ] (26)Operating costsRoom cleaning costs [ (20)x(4) / (8) ] (27)Luminaire cleaning costs [ (19)x(4) / (7) ] (28)Lamp replacement costs [ (18)x(4) / (6) ] (29)Energy costs [ (14)x(3)x(4)x(5)x(21)x(22) / 1000 ] (30)Operating costs [ (27)+(28)+(29)+(30) ] (31)Annual operating costs [ (31) / (4) ] (32)184 | ChecklistsExistinginstallationPay back period* = (26)Proposed – (26)Existing (years)(32)Existing – (32)ProposedPay back period* = – = years–*excludes depreciation and interest0000ProposedinstallationWorksheet 7.2