[Equest-users] Unmet Load hours in corridors & Max Flow ratio

[Fred Betz]

All,

I have again run into that issue where an interior corridor has hundreds of unmet load hours for no apparent reason.

I noticed the "Max Flow ratio" value on the "Air Flow" tab at the zone level.

The "Max Flow ratio" is defined as "the ratio of the maximum heating airflow to the cooling airflow".

The way I interpret this is:
-if a space has a maximum cooling air flow of 100 CFM, then the maximum supply of heating airflow is 50 CFM. Not sure if ventilation air flow is included in this or not.


Given that corridors could easily be a heating dominated zone given the few internal gains, it is entirely possible that the heating flow rate would need to be greater than the cooling flow rate.

I set the "Max Flow ratio" to 1.0 and eliminated nearly all of the unmet load hours in the corridor.


Here is a sample of the hourly airflow data before and after:

"Max Flow ratio" = 0.5 (default)
Air flow (cfm)  Unmet load (btu/hr)
71.0369

0

71.0369

0

71.0369

0

91.6157

-3248.37

91.6157

-1852.04

91.6157

-62.291

91.6157

0

91.6157

0

91.6157

0

91.6157

0

73.7393

0

71.0369

0

71.0369

0


Max airflow rate for the year is 114.158 cfm.


"Max Flow ratio" = 1.0
Air flow (cfm)  Unmet load (btu/hr)
71.0369

0

71.0369

0

71.0369

0

183.231

0

183.231

0

162.112

0

148.446

0

137.97

0

133.187

0

130.599

0

91.221

0

71.0369

0

71.0369

0


Max airflow rate for the year is 183.231 cfm.


The only other airflow related variable input in the zone is a 0.06 cfm/ft2 outside air flow requirement per ASHRAE 62.1. There are no system level inputs related to airflow.


Am I interpreting/using this "Max Flow ratio" value properly?

Thanks,

Fred


Fred Betz  PhD., LEED AP
Sustainable Systems Analyst



AEI | AFFILIATED ENGINEERS, INC.
5802 Research Park Blvd. | Madison, WI  53719

P: 608.236.1175 | F: 608.238.2614
fbetz at aeieng.com<mailto:fbetz at aeieng.com>  |  www.aeieng.com<http://www.aeieng.com/>



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20110523/2fc25ec8/attachment.htm>