[Bldg-sim] Doe2 Loop Sizing

[Kris Raj]

Hello,
            I am trying to determine how equest/doe2 sizes loop design flow. I 
would assume that that the program looks at the max coil load and divide it by 
the loop deltaT to obtain the loop design flow and the capacity. However in my 
case the program is over sizing the loop by more than two times. I have attached 
the PS-H report and it is evident that the peak load is only 2.7 MBTU. The SS-D 
report also confirms that the peak load is 2.7 MBTU. However the cooling 
capacity of the loop is 6.9 MBTU! The loop gets loaded to a max of 50%. I did 
not enter any values for loop/pump flow and let the program auto-size. The 
deltaT on the loop is set to 12 F with a supply temperature of 44 F.
 
I see a similar problem if I have primary only or a primary-secondary looping 
configuration. Also, I set the system sizing option to coincident. If the loop 
size ratio is set to 0.3 run again, I do not get any significant increase in the 
unmet hours, proving that the loop can meet the system demand at 1/3rd the 
flow!.
 
The only place that hints us about how the loop is being sized is in the 
definition of LOOP-SIZE –RATIO
 
“LOOP-SIZE-RATIO
The safety factor for loop sizing. (Note that safety factors could have already 
been specified within the secondary HVAC systems attached to this loop). This 
keyword is used only when SIZING-OPTION = SECONDARY-EQUIP; it is ignored for the 
PRIMARY-EQUIP sizing method. When primary equipment is to be auto-sized by the 
program, this keyword modifies the default capacity assigned. Note that this 
keyword affects only the auto-sizing of the primary equipment based on secondary 
loop loads. It has no effect on the design loop flow;  the loop flow is based on 
the sum of the coil flows or other loads attached to the loop. However, the 
design pump flow can be modified via keywords in the PUMP command.”
 
I am puzzled why it is not using the sum of coil loads to size the loop.
 
Thanks for your inputs.
 
Raj.


      
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