USER EXPRESSION

2 posts / 0 new
Last post

Hi all Modelers,

This question is for all those 'user expressions' prodigies.

Can anyone guide me on how can user expression be used for MIN-FLOW RATIO
in Air side sytem as ASHRAE states to keep MIN-FLOW RATIO as 0.30 or equal
to Design outdoor air value whichever is greater.

I am in need of a user expression which i should be able to put in MIN-
FLOW RATIO Keyword such that it
*1) takes the Value as '0.30'* *when outdoor design ratio is less than 0.30
and *
*2) takes the Value same as design outdoor ratio** when design ratio value
is greater than 0.30*

*Thanks and regards,*
*Tejas*

equest user's picture
Offline
Joined: 2017-12-18
Reputation: 0

Hi Tejas,
I believe that eQUEST/DOE-2 always gives priority to outside air flow, so that hourly outdoor air requirements are always satisfied, consistent with the zone and/or system OA cfm values and control method. Therefore, the ?minimum outdoor air flow rate? requirement in ASHRAE 90.1-G3.1.3.13 is automatically met.
So you enter 0.30 for the SYSTEM:MIN-FLOW-RATIO and you meet the 30% minimum flow requirement. (You can also enter minimum flow at the zones using ZONE:MIN-FLOW-RATIO, but the default expression copies the system-level value if it is entered.)
HOWEVER, if you still wanted an expression that sets the MIN-FLOW-RATIO to the greater of 30% or SYSTEM:MIN-OUTSIDE-AIR, you could use this expression for SYSTEM:MIN-FLOW-RATIO:
if (#RV(#L("MIN-OUTSIDE-AIR")) == 0)
then MAX(#L("MIN-OUTSIDE-AIR"),0.30)
else 0.30
endif

Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

[https://upload.wikimedia.org/wikipedia/en/thumb/9/96/The_Prodigy_Spitfire.jpg/220px-The_Prodigy_Spitfire.jpg]

134 South Fitzhugh Street Rochester, NY 14608

T: (585) 698-1956 F: (585) 325-6005

bbishop at pathfinder-ea.com www.pathfinder-ea.com

[http://png-5.findicons.com/files/icons/977/rrze/720/globe.png]Carbon Fee and Dividend - simple, effective, and market-based.

Bill Bishop's picture
Offline
Joined: 2012-02-25
Reputation: 7