[Equest-users] CFM/ton conflict issue for LEED projects

[Bishop, Bill]

Mustafa,
 
Short answer: No, you should not use the same system capacities or flow rates in your proposed and baseline designs.
 
The baseline system airflow rates are calculated using a supply-air-to-room-air temperature difference of 20°F, per ASHRAE 90.1, Appendix G, G3.1.2.8.
If the DESIGN-COOL-T of the zones is 75°F (the default), then the system MIN-SUPPLY-T should be 55°F.
Use a system COOL-SIZING-RATI of 1.15, per G3.1.2.2.
Make sure you have entered the minimum outdoor air ventilation rates and kept them identical between baseline and proposed models.
 
While I have not tried it before, you may get higher baseline capacities by using the design day sizing option described in G3.1.2.2.1 instead of using the weather file.
 
Usually, the cooling load in your proposed model will be less than the baseline, since your envelope will (hopefully) be improved and you will (hopefully) have a better lighting design.
 
If you still show higher fan energy in the proposed model, and you are doing LEED v3, see if you can take advantage of any of the pressure drop adjustments listed in Table 6.5.3.1.1B.
 
Regards,
Bill
 
William Bishop, PE, BEMP, LEED® AP | Pathfinder Engineers & Architects LLP
Mechanical Engineer
 
134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 Ext. 114
F: (585) 325-6005
wbishop at pathfinder-ea.com
www.pathfinder-ea.com
P Sustainability - less is more.
________________________________

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Mustafa Herzalla
Sent: Tuesday, July 20, 2010 3:47 AM
To: Equest-users at lists.onebuilding.org
Subject: [Equest-users] CFM/ton conflict issue for LEED projects
 
Dear eQuest users,
 
I calculate cooling load and design air flow using eQuest software then apply the  same design using HAP 4.3, the cooling load for the two designs in tonnage were the same, while the design air flow in CFM was in eQuest less than the design air flow in HAP.
For LEED projects, the proposed design should be model as the design documents, and many designers use HAP or other design software which is different than eQuest. and for LEED simulation we use eQuest , in this case the CFM/ton in the baseline design is less than the CFM/ton in the proposed design. The problem here that this case will reduce the energy savings in fans for the proposed design. 
My question is: is it ok to make the CFM/ton for the baseline design as in the proposed design? If NO, is there a solution to increase the design airflow for the baseline?
 
Best,
Mustafa Herzallah
 
 
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