[Bldg-sim] ASHRAE 90.1 unmet load hours

Jim Dirkes jim at buildingperformanceteam.com
Fri Dec 2 06:32:32 PST 2011


Dear Forum,
Feedback requested, please!  I've looked at some past posts on this general
topic and think I am asking about aspects not previously discussed..

>From previous posts and my own understanding:

.         If one or more zones is not meeting its setpoint in a given hour,
you have 1 unmet load hour.  If 500 zones all fail to meet their setpoint in
one hour, it's till one unmet load hour.

.         Add all such hours in a year to obtain your total unmet load
hours, which cannot exceed 8,760.

I am now modeling a hotel with:

.         "Massive" wall elements in the lower floors with moderate amounts
of glass, "lightweight" construction in the upper floors with a lot of glass

.         Occupancy schedules that are all over the map for Office, Assembly
/ Meeting Rooms, Kitchen & Restaurant, and Guest Rooms

.         Individual HVAC systems for almost every occupancy type.

.         Presentation to all points of the compass, especially the Guest
Tower, which is a 16-sided (roughly cylindrical) tower

This model is making my life very difficult trying to get unmet load hours
below 300!  As I think about why that is happening, it strikes me that the
combination of mass, schedules and orientations are spreading the unmet
loads around to different hours than is normal for many buildings.  Can any
of you share your thoughts about that perspective?

Thanks!

ASHRAE 90.1-2007

unmet load hour: an hour in which one or more zones is outside of the
thermostat setpoint range.

 

 

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