[Equest-users] Pump and Flow sizing issue
DEldridge at grummanbutkus.com
Thu Aug 14 11:23:49 PDT 2014
If the parameters were autosized before and aren't supposed to be...then you can forget you ever had those results before, they aren't valid. All you can do is move forward with the correct method...so starting only from the baseline vs proposed cases with 0.627 kW vs 11 kW and 57 gpm vs 141 gpm. (Right away we can see that 2.5x the gpm results in 17x power…?)
1. Is there an inconsistency with the hot water •T? That would be one reason why flow rate is higher in the proposed case…if proposed •T is less than the baseline •T then you should expect a penalty on pumping energy.
2. Any penalty resulting from #1 above would be compounded if there might be some challenge to overcome in the proposed design that adds pressure drop to the system, beyond what a normal baseline system would encounter…or it might be oversized/safety factor/future capacity. Any of these will inflate the proposed design comparison to baseline.
3. Review the assumptions in the baseline that generate a heating load – AHU coil sizing, OA quantities, and reheat control strategy, other heat consuming components of your model – you may not be using enough heating energy in the baseline, resulting in a lower gpm than expected. Compare the baseline system heating capacity per building area to ASHRAE rules of thumb, and to the proposed building…one or the other must be varying quite a bit from the typical building. This will let you know if you should question your baseline model sizing, or review the assumptions for the proposed case with the design team.
The energy penalty may not be the full value if this system has variable flow capability and operates at part-load most of the time, but you should investigate at least these three possibilities that could cause the values to diverge…two that inflate the proposed value, and one set that deflates the baseline.
David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Direct: (847) 316-9224 | Mobile: (773) 490-5038
Grumman/Butkus Associates | 820 Davis Street, Suite 300 | Evanston, IL 60201
Energy Efficiency Consultants and Sustainable Design Engineers
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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jacob Goodman
Sent: Thursday, August 14, 2014 11:50 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Pump and Flow sizing issue
I am working on a model using the DES option 1 for supplying steam to my building (district heating only so system 3). The baseline and proposed have working steam meters and all looks well. My problem arose when I went to fill in the new Section 1.4 tables for the pumping which brought my attention to the fact that both models had auto-sized gpm flow and pump size.
The auto sized values are WAY lower than the values on the mechanical schedules! Auto-sized proposed model = 23gpm and .325kW...designed proposed model = 141gpm and 11kW! Auto-sized baseline = 33 gpm and 0.467kW. If I input corrected pump size as per G188.8.131.52 this will give me a baseline pump of 0.627kW. I'm worried that if I correct the proposed pump size and flow to the designed numbers it will destroy my energy cost savings.
Attached are the files for both models.
Thank you all,
Jacob Goodman, LEED AP
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