Blend program - cooling load

Hello,

I’m trying to figure out how blend program works. Test script attached. I blend one air-conditioned program and one non air-conditioned program (by setting the cooling setpoint to 100C), and adjust the ratio. It seems the annual cooling load does not vary proportionally with the ratio of the air-con program.

Blend program test.gh (90.0 KB)

Am i setting up something wrong? If i’m not wrong, what’s the use of the blend program then? I’ll still have to model AC and non AC spaces explicitly.

I don’t know how this is handled in LB, and if there’s any existing rules-of-thumb guiding setpoint blending. However from first principles, this assumption seems incorrect.

Specifically, I don’t think there’s a way to combine setpoints (to a scalar output) so that highly different setpoints (i.e 23C, 100C) reflect the resulting annual energy in a reasonable fashion since the annual energy is a nonlinear function of that setpoint temperature. In contrast, it makes sense to use weighted averages (based on program floor area) for properties like lighting/equipment loads since the combined lighting/equipment load is linearly related.

I agree with @SaeranVasanthakumar here and his intuition about how setpoints are “blended” or “averaged” is correct.

In the current “Blend Programs” component, there’s simply a linear averaging happening between the two setpoint objects that are blended. This is fine for most buildings where all of the spaces are at roughly the same setpoint or when blending a 23C setpoint with a 26C setpoint since this will give a 24.5C setpoint, which is probably “good enough” for this type of case. However, blending a 23C and a 100C setpoint will yield a 73C setpoint, which is functionally the same as a 100C setpoint since the temperature in the rooms isn’t likely to reach 73C.

Furthermore, if a program has no setpoints at all, it’s effectively ignored in the blending calculation with an assumption that the program is like a closet or plenum, in which case the low internal loads and conditioning of the surrounding spaces tends to keep it at relatively the same setpoint as the surrounding rooms. This is fine for most full-building blends of programs where the building is expected to be conditioned with the exception of a few outlier storage spaces. But it’s not appropriate for a hybrid building where you have one half of a building that is fully naturally ventilated and another half that is fully conditioned.

Thank you @SaeranVasanthakumar , let’s forget about blending multiple programs first, let’s say I have only one program. What puzzles me is why there is a reset set-point of say 26C at night by default, are buildings in U.S. all conditioned at night? Am I right that the only way to shut down the default night operation is by setting the set-point to 100C?
Do you know what Chris mean by “if a program has no setpoints at all”? How can a program be without setpoints?

No problem, I can try to clarify the single program behaviour as I understand it. But, I think you should first mark Chris’ post as the solution to your main question. It details the logic of multiple program blending very clearly.

If you don’t specify a program explicitly, then by default Honeybee uses a “Generic Office” program, which then provides a default setpoint schedule. I think this is why you are seeing the 26C reset setpoint. It’s not an assumption about setpoints for all buildings, it’s just the default program assumption.

I’m not sure if this is the only way, but its how I shut down HVAC systems in a schedule - set setpoints to +/- 100C. You can also disable HVAC systems completely by toggling _conditioned to False in the HB Room from Solid component.

Not sure if I follow this question. Aren’t your previous questions asking why there’s a night default setpoint temperature, and how to remove it? A program with no setpoints just means exactly that: an unconditioned space like a closet, plenum, or office space passively conditioned by natural ventilation.

Thank you very much @SaeranVasanthakumar ! It clears all my doubts so far.

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