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RE: [EnergyPlus_Support] Zone Level Airflows

Dear Celia,

The “Central Cooling Design Supply Temperature“ must be 11.1C below the zone cooling setpoint in order to achieve your goal. Since you supply the air at 13.3C and serve 20 zones, ALL of the zone setpoints must be ~24.4   � and they are not.

Similarly, the zone heating setpoints must be 11.1C lower than, in this case, the Zone Heating Design Supply Air Temperature (35C) in Sizing:Zone � and they are not.


For an ASHRAE 90.1 energy model, each zone on a particular system must use a uniform setpoint for heating or cooling!  The fact that the actual design may use somewhat different zone setpoints is not relevant, although I suppose that you are allowed to specify a delta T larger than 11.1C.  The purpose of the Baseline � Proposed model iss � the comparison between a “fictitious” Baselinne system and an almost-true Proposed system.  In order to make the comparison consistent and understandable, some variables (like setpoints and schedules) must be regulated.

I looked very quickly at your IDF and may have missed some things, but I think that you will see an improvement if you change these setpoints.



James V Dirkes II, PE, BEMP, LEED AP
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653


From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Celia King-Scott
Sent: Wednesday, June 26, 2013 5:17 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Zone Level Airflows





I was wondering if any can help me with an issue I am experiencing in EnergyPlus.

Initially when we looked at the User Design Airflow column under Zone Cooling Loads in the output I saw that the supply air-to-room air temperature was much less than 20F even though the room setpoint was at 75 and supply temperature was 55F. (Following ASHRAE 90.1 2007 Appendix G requirements for Baseline model). We corrected this by adjusting the design outside air at the zone level sizing parameter however now the undercooled hours are about 1000 (much more than allowed). This tells that without taking the outside air into account for zone sizing, there isn’t enough airflow to cool the space during the year. The outside air zone sizing parameter isn’t used for calculating the cooling capacity, only the airflow, which is what I think is causing difference in temperature differences in the zone. However how do we meet the supply air-to-room air temperature delta T requirement and have less than 300 unmet load hours as also required?


I have attached the Baseline idf and output for your review.

Thank you for your time on this. Any help is greatly appreciated. 






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