[Bldg-sim] Altitude impact on airflow and fan power in eQUEST

[Zhen Tian]

Hi guys,

I faced an interesting situation when I used eQUEST to model a simple roof-top unit conditioned small one-zone building in Calgary, Canada. The Altitude of Calgary is 1050m (3444 ft). When I put the altitude value in the "site data", in the ASHRAE basecase, the autosized fan airflow rate was multified by 1.14, which is correct. However, I found the the fan power was not multiplied while it should be multiplied. Meanwhile, the outdoor airflow rate was also multiplied by 1.14 which should not be multiplied.

Some data for you reference,
1. Altitude factor included: system air flow rate by autosizing is 8830 cfm, according to Appendex G3.1.2.8 and G3.1.2.9, the fan powe should be 6.4 kW, the calculated fanpower by eQUEST is 5.61 kW (6.4/1.14) (SV-A report). I input the outdoor air flow rate as 1320 cfm, then the SV-A reports it as 1505 (1320*1.14).

2. If I did not input the altitude factor, the autosized system air flow rate is 7746 cfm, eQUEST calculated fan power is 5.62 kW, which matches with ASHRAE G3.1.2.9 value and outdoor air flow goes back to 1320 cfm.

Does any one knows what is the problem in the eQUEST calculation? I try to solve this problem by put the system sizing ratio as 1.14 and altitude as 0 to represent the altitude factor. Is this method OK for the  LEED requirement?

Thanks a lot.

Regards,

Zhen

       
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