looking at ncm guide it seems that we are allowed to use w/m2 method when lux levels are higher or equal than NCM activity, so there will there never be a penalty for overprovision on lux level because you could choose w/m2 and the subsequent detail design has to adhere to that?
OR are you not to use this and always use 'inference'
in the w/m2 method ,is the ncm control method picking up occupancy and daylight dimming? it has the note in room query that 'applies when ncm simple control is ticked' but in the w/m2 method this isn't ticked? looking at vista it seems to be picking up this control nevertheless??
which method would you choose for early doors stages so that it doesn't get worse when contractor takes over?
lighting in w/m2 vs lux levels and controls
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VirtualEngineer
- VE Beginner
- Posts: 22
- Joined: Mon Jan 05, 2015 11:10 am
Re: lighting in w/m2 vs lux levels and controls
Hi
I try to use power density each time, I think inference is only for existing buildings where you don't have lighting calc's or know Wattage or lux etc.
At design stage or RIBS Stage 2 for energy statement reports etc you could just go with a default power density 3.0 W.m-2/100lux, I usually go with 2.5 W.m-2/100lux at design stage if I am unsure, this typically works out higher than most LED lights that elec' contractors fit nowadays.
When you go on to the Internal Gains (NCM) tab you'll notice some spaces have a default of 3.75 W.m-2/100lux and some have a default of 5.2 W.m-2/100lux so you could take a relative percentage for your design stage i.e. put 3.75 W.m-2/100lux spaces down to 2.5 W.m-2/100lux and 5.2 spaces down to 3.47 W.m-2/100lux (i.e. * 0.66) that should be fine.
I think his would be reasonable, but lighting is always tricky at design stage, it is best to get lighting calc's form a previous job and use the power density values straight off the lighting calc's, but maybe add 20% to be on the right side of wrong.
Or just be super careful and go with the defaults until you know the lighting, again you'll be the right side of wrong, but may commit to more LZC than needed. Though that's usually only a problem for the developer / QS, but they could always 'cost engineer' it out at Stage 3 / Stage 4.
Hope this helps
Cheers
VEng
I try to use power density each time, I think inference is only for existing buildings where you don't have lighting calc's or know Wattage or lux etc.
At design stage or RIBS Stage 2 for energy statement reports etc you could just go with a default power density 3.0 W.m-2/100lux, I usually go with 2.5 W.m-2/100lux at design stage if I am unsure, this typically works out higher than most LED lights that elec' contractors fit nowadays.
When you go on to the Internal Gains (NCM) tab you'll notice some spaces have a default of 3.75 W.m-2/100lux and some have a default of 5.2 W.m-2/100lux so you could take a relative percentage for your design stage i.e. put 3.75 W.m-2/100lux spaces down to 2.5 W.m-2/100lux and 5.2 spaces down to 3.47 W.m-2/100lux (i.e. * 0.66) that should be fine.
I think his would be reasonable, but lighting is always tricky at design stage, it is best to get lighting calc's form a previous job and use the power density values straight off the lighting calc's, but maybe add 20% to be on the right side of wrong.
Or just be super careful and go with the defaults until you know the lighting, again you'll be the right side of wrong, but may commit to more LZC than needed. Though that's usually only a problem for the developer / QS, but they could always 'cost engineer' it out at Stage 3 / Stage 4.
Hope this helps
Cheers
VEng