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NREL / EnergyPlus

EnergyPlus™ is a whole building energy simulation program that engineers, architects, and researchers use to model both energy consumption and water use in buildings.
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EMS actuators on utility-consuming internal heat gains objects (e.g. ElectricEquipment) allow negative values #9675

Open mitchute opened 2 years ago

mitchute commented 2 years ago

Issue overview

As per the description, some of these internal heat gain objects should not allow EMS actuators to set negative values.

For example: https://github.com/NREL/EnergyPlus/blob/1d22b9a61f7cd00b9e7b0ef27e4b24ffb6b849f3/src/EnergyPlus/InternalHeatGains.cc#L7112

I don't have an example file to post, but I was made aware by seeing someone use an EMS actuator with an ElectricEquipment object to extract heat from a zone...

Details

Some additional details for this issue (if relevant):

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

shorowit commented 2 years ago

We do this in our residential models -- both to allow negative heat gains (i.e., heat losses) as well as to increase/decrease fuel consumption, in order to comply with some standards. As far as I'm aware, this flexibility is intentionally allowed in EnergyPlus. If you are concerned that it is being misused, you could consider giving a warning if there isn't one already, but I'm pretty sure that changing this behavior would break our models.

mitchute commented 2 years ago

@shorowit I'm sure there's some reason why but it seems like an odd way to do it. I did assume others would also be using it that way, though, so I'm OK with adding warnings rather than explicitly prohibiting it.

rraustad commented 2 years ago

Um, no. A negative heat loss (e.g., a refrigerator door opening) is much different than negative electricity or fuel energy from any of these objects. Can we get an example of equipment that would have negative electricity or fuel consumption? If not then negative electricity/fuel should not be allowed.

shorowit commented 2 years ago

The ANSI 301 Standard requires us to multiply the water heater's energy consumption by a multiplier (above or below 1) to account for all sorts of hot water distribution technologies based on equations published in the standard. We currently use EMS to make this adjustment.

An alternative approach would be to adjust the thermal efficiency of the water heater, but EnergyPlus currently restricts it to be less than 1. We have considered proposing that EnergyPlus relax the inputs of water heater efficiency values to allow values greater than 1 (I think this would work for our use case), but I could see some EnergyPlus developers pushing back. I would actually prefer to switch to that because our EMS approach has some definite drawbacks.

rraustad commented 2 years ago

Maybe an ANSI301Standard object would be a better option? Can you post the table that shows these multipliers?