Question on unmet load hours

[AllenMei]

Hi,

I have a question regarding unmet load hours in IESVE 2017.

In ApacheHVAC, I model HVAC as zone groups.

When calculating unmet load hours, IESVE looks at each space/room.

There are some unmet load hours and I just can't get rid of it after trying some typical methods.

Please correct me if I am wrong. Is it an issue that IES looks at spaces instead of zones?

Let me know what you think.

Respectfully,
Allen

[bbrannon4]

It's an interesting question. Typically when we are talking about unmet hours (like for LEED models) it's under the assumption that thermal zones have a mixed tank assumption with one temperature. However when IES added the ability to combine multiple rooms into a single controlled zone, that means that one thermostat zone could actually have multiple temperatures, and the ones that don't actually have the thermostat in them probably won't be controlled as well, which more accurately represents the real world. I'd say you should check the unmet hours on all the spaces, not on all the zones. If you have issues, then it's probably a good prediction that the building would have issues once occupied and might suggest a different zoning strategy.