[Equest-users] ASHRAE Bldg_Modeling Comparisons

[David Eldridge via Equest-users]

eQUEST should be referred to as DOE2.2 and isn't part of the national laboratory/DOE system...but aside from that, it would be normal in eQUEST that you can go back and size an airside or waterside system based on the observed loads in the model or from the design documents if they are available.

Did you use design day sizing for all three programs, or are you sizing from the TMY simulation? How did annual energy end-use compare between programs?

One thing to check is the airflow requirements specified at the zone level. I see HAP gave you 0.51 cfm/sf and 0.09 cfm/sf of outside air and an output of 17 cfm/person - make sure eQUEST is being given the same instructions at the zone level.

You can open the simulation file viewer and look the L-series of reports for results on the loads to the space and then a report for the whole building (LS-C or LS-D?). These reports are not including the system loads for outside air, they are the load calculations for zone heating/cooling so they won't add up to the SV-A report which includes OA.

You can also check the system report for each of the RTU's and see if the fan is operating at high levels often, or if it maxes out at a much lower airflow even though the sizing was for a larger capacity...this will tell you that the mix-up is in the sizing and not the model inputs, i.e. the loads aren't driving the sizing up, the sizing algorithm has selected the units to be larger than the load for some reason, or vice versa.

I'm not sure for RTU's about the sizing method - there may also be an option to size on modeled load vs capacity of zone equipment. Normally I'm working from design documents and don't use the auto-sizing feature for AHUs so I'm not sure if that could be one issue for you. You can cross-check this by summing the zone airflows and comparing to the total for both programs to see if the sizing algorithm is different, for instance eQUEST may be sizing at 15% more than calculated requirement while HAP includes diversity and sizes at 15% smaller. Speaking of which, there is also a safety factor input for sizing in eQUEST, make sure this is consistent between programs or you'll be higher by 15% capacity off the bat.

David



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates



From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Mike Schaefer via Equest-users
Sent: Monday, May 08, 2017 7:29 AM
To: equest-users at onebuilding.org
Subject: [Equest-users] ASHRAE Bldg_Modeling Comparisons


I'm running an office building with three different energy programs (Trane Trace, Carrier HAP, and DOE's eQUEST to compare and contrast each energy modeling programs output. Two of my programs Trane Trace and Carrier HAP have similar rooftop unit sizing, however, my eQUEST model is producing rooftop unit sizes (RTU-1 & RTU-2) that greatly exceeds the other two programs. I believe that this difference is the ventilation load. CFM's and building sensible loads are similar, however. There is a large discrepancy between the total cooling capacity (defined by "cooling capacity" in eQUEST's SV-A reports. My eQuest model is reporting a much higher than expected total "Cooling Capacity" for my rooftop units. All models have two VAV rooftop units (one for each floor of a two story office building). The ventilation rates, internal loads and envelope are identical between my models. The models have air side economizers w/integrated dry bulb with an upper cutoff of 75 deg. F with the non-economizer outside air turned off during unoccupied hours. All programs are using KC, MO TMY2 weather data.



Can anyone explain, or find my error, in the eQUEST modeling that is causing the unusual load in ventilation? It seems obvious that the three programs would produce similar outputs, however, there must be an eQUEST modeling error that I've created.



Also, does eQUEST have a load breakdown that describes (lists) the values that make-up the "SV-A cooling capacity"?



I've attached the Carrier RTU-1 (1st floor office load) system report and the eQUEST model.



Thanks,




Michael Schaefer - P.E.*, LEED AP

Licensed in Kansas, Missouri, and Colorado
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