Hi All,
I am working on a model where the baseline system type is Packaged Single Zone with a Fossil-Fuel Furnace (System Type 3) and the proposed system type is Chilled Water VAV with a Gas-Fired Steam Boiler. When I take the proposed model, save as, and then just change the system type to the DX CV system, the cooling loads in the SS-D report change. They are less when the DX CV system. How can the loads change? These should stay the same and the energy used to meet these loads should change. Has anyone run into this before?
Kristy M. Walson, PE, LEED AP BD+C, BEMP
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For space loads - see the LS reports. LS-B & C for Peak loads, and LS E & F for monthly loads.
The way eQUEST works is the thermal loads are reported here. This is not the load seen by your system because this does not include ventilation loads.
So thermal loads are reported in LS reports, system loads are reported n the SS reports, and plant loads are reported in the PS reports.
Hope this helps.
Vikram Sami, LEED AP BD+C
Thanks, Bruce. I ended up figuring this out yesterday. After going through everything and comparing different system types, I discovered that if I used the Equest system type "Packaged Single Zone", the software would add heating energy for the reheat used to control humidity, but did not add any additional cooling energy in order to overcome the additional heat from the reheat. The cooling kWh was literally the exact same with or without the reheat.
I then changed my system type to "Packaged VAV", set the fan control to be constant volume, and the cooling energy responded more appropriately when I added reheat to the zones. I hadn't run into this issue before, though I rarely use ASHRAE System Type #3 (Packaged single zone, CV, furnace), so it was a huge "aha" moment for me. Equest doesn't operate well using the Packaged Single Zone system (similarly, it also does not operate well using the WSHP system type), so it's better to use the Packaged VAV option when your baseline is ASHRAE system #3 and you have humidity control.
I've been spreading this information like a public service announcement, but I'm sure others have run across this before. Thanks again for your help!
Kristy M. Walson, PE, LEED AP BD+C, BEMP