Light fixture load - for circuit sizing vs. lighting power density

[HVAC-Novice]

I have light fixtures and assigned the electrical connector to account the load to "spaces". This is for meeting energy code and my understanding is we need to use Watt (real power) and this also would contribute to cooling load (Let's ignore cooling load for now). Energy code refers to W/ft² (and NOT VA/ft²) and light fixture spec sheets refer to Watts (not VA). 

For sizing the circuit we need to use Amps and use VA (apparent power). VA and W are related to power factor Multiplying VA by the powerfactor. So, in an example of a PF of 0.9 and a 90W light fixture, I would have 100VA. So for circuit sizing I use 100VA, but for energy code, I use 90W. 

But in my fixture family I only have Apparent Power and that value is used for space lighting power density. There is the power factor parameter. I tied it to an instant parameter to play with it. But no matter what I set the PF, the space lighting power density stays the same. Revit spaces seem to use apparent power (VA) as Watts and ignore PF.

So far i didn't circuit the lights to a panel and just entered the Wattage as VA and my space lighting power density is correct. but now I need to add actual circuits. If I just use the Watt, my circuits may be too small. but if I enter the (higher) apparent power (accounting for PF) my lighting power density is too high. 

Power factors aren't very small (0.9 to 0.95). So the difference isn't too large. But it bugs me and in some instance it could lead to wrongly sized circuits.

Has anyone noticed the same? Is that an error in Revit? Am I doing it wrong? Is there a workaround? 

I was thinking of using 2 electrical connectors (one for W and lighting in spaces, one for VA and circuiting). But that seems complex and I may connect the wrong connector to the panel. 

[HVAC-Novice]

Has anyone come across this issue? Is this a thing where Revit calculates the lighting power density wrong (since it uses apparent power, instead of W). 

My only (maybe) workaround would be to use 2 electrical connectors and assign one to lighting power density, and the other one to the actual connection to a circuit. but I would have to implement that to all my fixture families,  and i foresee accidental misuse of connectors when I create circuits. So this may not be the best solution. 

for right now I just enter the Wattage, and when creating the circuits. when sizing circuits , I just "keep in mind" that the VA is a about 10% higher. This obviously goes against the Revit way. 

Edit: I realize worrying about a power factor of 0.9 or so may seems silly. but it has quite some influence on on sizing inc. emergency lighting load. 

[sragan]

For light fixtures, the cut sheets list an "input power", and they typically don't list a power factor or VA.  So I don't know how you would know what power factor or VA rating to use.   With energy efficiency being so important now, I think the PF for a typical "commercial grade" LED fixture is probably very high.

So I just use the wattage they show on the cut sheets and I don't worry about the PF or actual VA.   I don't usually load lighting circuits to the max. though, either.  

[HVAC-Novice]

Correct, they list Watt. and every energy code also says "Watt". I would use a PF of 0.9 since that is an often quoted number and most fixtures don't list that. But I would have apparent power that is  shown 11% lower than it is. In some cases this could bring it to the next size conductor. 

You are right, with a 15A circuit, and todays high LED efficiency, it would be impractical to load up the circuit anyway. For this project our electrician wants each 277V lighting circuit fused at 5A to protect from arching. At 80%, this gives me 4A. that brings me closer to where the above 11% (if ignoring PF) inaccuracy can bite me. And I'm just not satisfied knowing it is wrong 🙂

[HVAC-Novice]

I added a second electrical connector. the one named " Space Load" is connected to real power (W) and is assigned to be space lighting load. The other connector " Space Load" is connected to apparent power (VA) and will be connected to the panel.

One issue is, when connecting to a power circuit, I have to select which connector. This goes against my laziness, and could inadvertently make me select the wrong connector. Is there a way to disable the " Space load" connector so it doesn't show up as an option to be part of a power circuit? 

I also found another reason why the seemingly small $ change is important. i try to keep voltage drop under 2%. Some circuits have 1.8% for example if I use real power. but now with using the more exact method, I see it is above 2%. I use a PF of 0.9 to be conservative. Every Google search says for LED it is 0.9 or higher.

[fabiosato]

Hello,

Regarding the connector selection, it will not show the window only when you have only one option to choose from.

[HVAC-Novice]

But it looks like I kind of need both if I want correct lighting power density and correct circuit load. 

I even set voltage of the connector for space load (real voltage) to 0V to no avail. 

Edit: here is another little hiccup. In the family I set the load classification " Lighting" (the one I connect to the panel)  to NOT be used for spaces. After reloading the family, this was reverted back to be used with spaces. So my model used both connectors (apparent + real power) for lighting power density). In the project electrical Settings I had to set this to NOT be used in spaces. and that seems to work. 

So whatever the setting for use in spaces we do in families seems irrelevant. 

I created an idea hoping Autodesk will fix this. Please vote on this if you think it has merit. 

[HVAC-Novice]

I talked to one of the manufacturers I use. They gave me the spec sheets of some of the specific drivers of some of the LED fixtures. If you want to use something higher than PF=0.9 you should investigate. 

They did not give me a blanket statement, they need to know the exact model number of each fixture since with different lumen packages etc. it can be different. I think that would be cumbersome to do in design and using a PF of 0.9 or 0.95 is more conservative. Note the below are excellent fixtures. I have some niche applications (like track lights, can lights etc.) where the LED performance is much worse and PF most likely not close to 1.0.

but it seems brand name drivers get close to a PF of 1 at full load