Unmet Hours

Daylighting controls

I have two questions about daylighting controls. 1- When I use "Continuous" for lighting control type and run the model with EnergyPlus as the simulation engine in OS, the "Electricity Consumption" is as the same as not choosing any lighting control type (the value is 584 kWh) and when I use "Stepped" or "Continuous/Off", the value decreases to 42 kWh. But, when I run the model with Radiance and choose any of the three lighting control types, the electricity consumption decreases to 125 kWh from 584 kWh. Why the "Continuous" option doesn't work when running with EnergyPlus?

2- I have one zone with an exterior window. the dimension of the room (assumed as an office space) is 6m*8m and the height is 3m. I am analysing the heating/cooling load and the electricity consumption for different cases. where is the best place to put the daylighting control sensor? In the center of the room or for example 1.60m far from the window (in the middle row) where it is assumed that the user is sitting?

To your first question, I can only say that in Radiance the control type is disregarded and always uses the "continuous" control type. As to why you see no change in EnergyPlus when using control type continuous but do see a reduction in energy use when selecting the other two types, I'll have to do some more investigation or talk to some of the EnergyPlus users over here.

As to your second question, the simple answer is "it depends". Placing the daylight sensor in the center of a 6x8x3 meter space is to tell the lighting control system "wait until the daylight levels are high enough all the way back here, before dimming the lights". A space that deep, with a ceiling that low, will not see very much daylight back there very often, and so an energy analysis of daylighting's efficacy based on daylight illuminance at that point will likely show little to no savings -- not a fair fight. Indeed, what most designers do is zone their lights so that they can dim or switch the lights closer to the perimeter (which receive more daylight, more often) sooner than those in the core. EnergyPlus allows you to emulate this somewhat by placing multiple daylight sensors in the zone and setting each to control a percentage of the total lighting load. Currently the Radiance support in OpenStudio has no such analog, but we hope to change that.