Re: [EnergyPlus_Support] Re: lux and watts

Thanks Ery,Â

but we need to go one step further. Â I want to use the daylighting:controls. Â To do this I need to to fill in the Illuminance SetPoint at First Reference Point field. Â This field uses lux as a unit. Â Quoting from the IinputOutputReference:"The desired lighting level (in lux) at the First Reference Point. This is the lighting level that would be produced at this reference point at night if the overhead electric lighting were operating at full input power."

If I understand it correctly, starting from the desired lighting level, I have to design my lighting system in lumen and define the power demand in watts.

It makes sense.

thanks again.

Vincent

On Sun, Jun 22, 2014 at 7:19 PM, Ery Djunaedy ery.mailinglist@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Â

Vincent

The efficacy of the lights is in your input, EnergyPlus will take
whatever you define as the efficacy.

If you define 10W/m2 for a zone, and your daylight sensor is set at
500 lux, then YOU are telling EnergyPlus that your light is at 50
lumen per watt.

You can change the LPD to 1 W/m2, with the same 500 lux setpoint, then
YOU are telling EnergyPlus that your light is at 500 lumen per watt.

EnergyPlus always assumes that in the absence of daylighting, your
electric lights will be able to meet the daylight sensor setpoint.

It's not a mystery under the hood, but it is simply your input.

Makes sense?

Ery

On Thu, 19 Jun 2014, vincent lacour vlacour@xxxxxxxxx [EnergyPlus_Support] wrote:

> Thanks Rahul, but this does not address the issue. Everything in
> Daylighting:controls is inLUX whereas everything in Lights is in Watts.
> What is missing is the efficiency of the lights, i.e. how much LUMEN you
> can get with 1W. With a led you get 50 lumen; with an incandescent light
> bulb you get only 10 lumen. There must be a lumen/watt ratio under the
> energyplus hood, but where????
>
>
> On Thu, Jun 19, 2014 at 6:09 PM, rahula7@xxxxxxxxx [EnergyPlus_Support] <
> EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
>
> >
> >
> > If you look at the Daylighting:Controls object, there are a number of
> > fields:
> > - Lighting control type
> > - Minimum input power fraction for continuous dimming control
> > - Minimum input power fraction for continuous dimming control
> > - Number of control steps
> >
> > These fields combine to determine how much lighting power will be supplied
> > after subtracting the daylight contribution. It's all there in the I/O
> > Reference.
> >
> > Rahul
> >
> >
> >

--
Dr. Ery Djunaedy
Research Scientist - Building Simulation Specialist
Integrated Design Lab University of Idaho
306 S 6th ST, Boise, ID 83702
Phone: 208-429-0220