Hello again eQUESTers,
For some zones, I want to set the min. allowable zone air supply flow rate
to a certain ACH. There is a zonal input for min. design air changes/hr
but I think eQUEST will go below this flow if possible. Sure I can
calculate the minimum flow as cfm.ft2 or ratio but would like to not do
this work if possible!
Is there a straight-up min. allowable ACH input for eQUEST?
Darryl,
There is no zone keyword for minimum ACH. But you can enter the zone design ACH (ZONE:AIR-CHANGES/HR) and set the minimum air changes as a percentage of this using ZONE:MIN-FLOW-RATIO. You can write a keyword expression that enters and calculates this based on other zone inputs if you wanted to. For example, the expression below modifies the default DOE-2 expression for MIN-FLOW-RATIO, adding a calculation step based on the zone input for AIR-CHANGES/HR. The sample calculation assumes you want a minimum ACH of 3, and calculates the MIN-FLOW-RATIO for any zones for which you enter a design ACH rate of 3 or more.
if (#P("MIN-CFM-RATIO") == unused)
then unused
else switch #SV(#P("TYPE"))
case 2 : unused
case 17 : unused
case 19 : unused
case 26 : unused
case 27 : unused
case 28 : unused
case 29 : unused
default : if (#RV(#P("MIN-CFM-RATIO")) == 0)
then #P("MIN-CFM-RATIO")
else if (#RV(#L("AIR-CHANGES/HR")) == 0
.AND. #L("AIR-CHANGES/HR") >= 3) then
3/#L("AIR-CHANGES/HR") else no_default endif
endif
endswitch
endif
Regards,
~Bill
William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer
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bbishop at pathfinder-ea.com www.pathfinder-ea.com
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Sorry to get off topic here but... Bill, is there a resource you can link
to that shows a list of commands that can be used in user expressions and
what they do?
The DOE-2 help files accessible within eQUEST are helpful for learning keyword expressions. Go to Volume 3: Topics -> Building Description Language, especially starting with the Keyword Expressions section. You can also look at the DOE-2 default expressions for each input within eQUEST to see common examples.
~Bill
Hello Bill,
Was going to ask you the following question but then I searched through BDLdft.dat. Very clever.
I am wondering how you determined that the MIN-FLOW-RATIO keyword is unused in the ZONE for systems where it is used in the SYSTEM? I am assuming that #SV(#P(?TYPE?)) refers to the system type. System 28 is PVVT and MIN-FLOW-RATIO is used in the System, no default is specified.
Christopher Jones, P. Eng.
Rowan Williams Davies & Irwin Inc.
Consulting Engineers & Scientists
901 King Street West, Suite 400, Toronto, Ontario, M5V 3H5
T: (519) 823-1311 ext 2052
M: (416) 697-0056
Hi Bill,
eQuest coding is over my head at this stage but I appreciate your
feedback. In my case, I do not know the design ACH but I do know design
flows (ZONE:ASSIGNED-FLOW) and want a min 6 ACH.
How would that change the expression you provided?? No worries if it's a
bit of a pain, I can always do some manual calcs for each zone.
Thanks
Darryl
Darryl,
You can enter the expression below as a custom default expression for zone MIN-FLOW/AREA based on the desired minimum ACH.
It will calculate the minimum cfm/ft2 based on 6 ACH, and use the smaller of that value or the equivalent value for zone AIR-CHANGES/HR if it is entered for that zone.
~Bill
if (#RV(#L("AIR-CHANGES/HR")) == 0 .AND. #L("AIR-CHANGES/HR") <= 6)
then #L("AIR-CHANGES/HR")*#LR("SPACE","HEIGHT")/60
else 6*#LR("SPACE","HEIGHT")/60 endif