Exception b. of G3.1.1 states: “use separate single-zone systems (..) for any spaces that have occupancy or process loads or schedule that differ significantly from the rest of the building”. Are setpoint temperatures considered as “schedules”?
Consider a floor where there are a space with cooling setpoint temperature equal to 25°C and another space with cooling setpoint temperature equal to 40°C. They have similar process loads. During many hours the first space will need cooling while the second one won’t. Anyway, if the two spaces are connected with the same system they will both be supplied with cooled air. For the space that doesn't need cooling the air flow will be at the minimum level (see G3.1.3.13), but anyway supplying a space with cooled air when it doesn’t need cooling is an energy waste. What is correct for the baseline model?
Regards
P.S.: as supply temperature from the central AHU I’m going to use 25°C – 11°C = 14°C, and I’m going to “reset higher by 2.3°C under the minimum cooling load conditions”, based on the outdoor temperature (see G3.1.3.12)
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Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
October 23, 2014 - 3:49 am
Yes they are in my opinion. I've also come accross this issue. And yes, that is why there is a reset rule. The reset rule is basically trying to minimize the waste.
You can consider it differently. The rooms with the 40 C setpoints have very different loads than those with 25 C, and there is an exception for that. So don't hang a trash room on the same air circuit as the office spaces in the proposed design, for example.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 23, 2014 - 11:13 am
The temperature set points are certainly like schedules in that they need to be identical in both models.