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
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
Mustafa,
I thought of a few more things that may affect the system airflow rate - don't forget to turn off self-shading (SHADING-SURFACE = "no") on all exterior surfaces and remove shading projections in the baseline, and set your WIN-SHADE-TYPE in both models to "No shade", as required in Table G3.1.
Bill
I might also suggest doing a sensitivity analysis (trying a couple different
control options) ---on the air-side systems tab (under "Basic") there is a
sizing option, look in the bottom left corner where you can choose air
sizing based on "conincident" or "non-coincident" loads. I'm guessing
yours is set to coincident which I believe is not the 'sum of the peaks'
option that your HVAC designer has based thier airflows on... hope this
helps.
pkg