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Wattage assumption for 'efficient' lights

Greetings all. I feel like this should be a simple question - but am having a hell of a time finding the answer...

What is the assumed wattage for lamps when you mark them "efficient" in RemRate? Does anyone know?


  • Lots of potential answers here. Efficacy of light bulbs is generally accepted as 50 lumens per watt. 100 Watt incandescent are generally accepted as 1,600 lumens. I have seen 23 - 32 watt CFLs rated at 1600 lumens. The LED is about 15 watts for 1600 lumens. That definition includes Halogen Bulbs.

    Energy Star Standards differ between lamp types.

    https://www.energystar.gov/products/lig ... t_criteria

    REM on the other hand does not rate lamps. Translation: Bulbs. Lighting has it's own terminology. On the Lights and Appliance page, hit the contextual help Icon in REM and Scroll down. It is very clear that you count fixtures that qualify. They must have specific controls. REM is not looking for bulbs, it is looking for qualifying fixtures. Lighting terminology: Luminaries.
  • Thanks John - but let me ask the question differently if I can be indulged for a sec.

    Let's say I have a home design that is all LED lamped. I can put the count in Rem - but only say tell it % 'efficient.' So - I am curious. Is there a delta between the watts Rem thinks I am spending and the watts I will have installed? I figured I would do a quick calc - but I have no idea what to use for watts for the Rem model. Does this information exist anywhere? Should I assume that Rem is assuming a 15 watt cfl lamp?

    (really appreciate your answers)
  • David ButlerDavid Butler Posts: 3,889
    @Prescott, I don't know the answer but I think any changes you make to the appliance and miscellaneous load section are treated differently for HERS than for energy consumption estimates. What exactly are you trying to do?
  • I think you are right that the two sections are treated differently...
    I have 2 objectives:

    1. Global Objective: I am trying to understand the Remrate model a bit better. In every other model I have worked with, I could tell you the wattage for every lightbulb in the building model. I was surprised to learn that this is actually kind of a hard question to ask when dealing with RemRate. I thought maybe that someone else had gotten curious and gotten to the bottom of this.

    2. Specific Objective: I am working on a Net Zero project. The Rem model is 'stuck' in a HERS 4. I am trying to get information to the HERS Provider on our specified lights (all LED) and compare them to the (seemingly broad) designation in Rem of "100% efficient) lights which has not changed as far as I know since the lamps were assumed to be all CFL. I would like to do some of the math here - but I really need to know what Rem is assuming about the lamps.

    Does anyone know this?
  • If you design a house in Rem with 1 lightbulb. Call it "100% efficient."
    Does anyone know how many watts the model will assume that one lightbulb is rated at? 15w cfl?
  • David ButlerDavid Butler Posts: 3,889
    @Prescott, first you need to realize REM is unlike other modeling software you may have used. The reason you're having trouble may be that your question presumes a certain way of modeling lights that may not apply to REM/HERS. For HERS, it's more of a broad brush than precise audit.

    In years past I could be more helpful but I no longer maintain a current edition of REM. As I recall, HERS and other compliance reports are based on a pre-defined miscellaneous energy loads (MEL) for the reference home, solely driven by conditioned floor area. For the rated home, you could adjust a handful of specific loads (e.g., refrigerator, % of efficient lighting, etc) but the impact was pretty small, especially for lighting.

    For specifics on the algorithms, check out the appropriate paragraphs under Section in RESNET 301 (http://bit.ly/2bgqYA6). Then work back through the contextual help file @ REM.

    You can enter a detailed lighting audit in REM but it has no impact on HERS.
  • David ButlerDavid Butler Posts: 3,889
    BTW, I would be very careful about making design decisions to get to net zero based on REM (or any other modeling tool for that matter). Energy modeling tends to fall apart as you move further down the scale.

    Here's an ad-hoc case study on my own home that demonstrates how far off REM can be in some cases: http://bit.ly/1p0xO9t.

    In general, when you specify a net zero solar array based on what REM says you need to get to net zero, in most cases you'll end up significantly oversizing the array, especially for homes that (a) are super efficient, (b) have a heat pump with low supplemental fraction, or (c) have lots of mass and/or were designed as passive solar.