Models for energy audits

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I've been working on a couple models for an energy audit project and am
coming up a bit stumped for issues with both buildings. I'd appreciate
any insight folks can provide.

Attached are 2 zip files with the .pd2 and .inp files for each project
as well as the utility analysis spreadsheets for each project. Year 1
in the spreadsheet is the output from the energy model for comparison to
the actual utility bills (2.5 years of bills). Here are my primary
issues for each project.

Carterville Intermediate

- The winter electric use is greater than the modeled values
while the summer is much higher. The shape of the curve is about right
but the values are off. I think the winter electric is low because I'm
not sure we're seeing fan energy associated with heating. The system is
DX coil unit vents (condensers on the roof) with hot water coils for
spaces and HW radiators in the halls. Gym is heating only. I think the
cooling electric is high because I think the teachers turn off the units
because of noise and they open windows. The District reports they open
corridor entry doors for airflow and teachers are supposed to keep
classroom doors closed. Do I have the HVAC system configured correctly
for the installed system? What can we do to adjust operation of the UVs
in cooling?

- I haven't entered a value for the size of the boiler. eQuest
has input in MBH and my photos show the label at 2603 MBH but that
increases gas use by a factor of 100. Am I mixing up units here?

- I haven't figured out how to do anything for exhaust fans.

Carterville TriC Elementary

- The peak summer electric demand is higher than actual but the
kWH curve is a good fit to actual but just needs more hours. The HVAC
system is ground source heat pumps per space with 6-7 ERVs (wheel only
no mechanical cooling/heating) feeding OA to the return air inlet. There
is one ERV for a 4 room addition that also has an electric heater in
addition to the wheel. There is no supplemental boiler for the condenser
loop. We haven't been able to learn any data on the actual geology of
the site but by plans we have the correct number of wells in our grid. I
think the high demand means we need a larger well field to keep
condenser water temps down and compressor load down but I may be missing
something. It might also be tied to increase OA load. I've tried but am
just not comfortable with my efforts to set up the ERVs in the system to
temper the OA before the GSHPs.

- When I go into Detailed edit it appears that my heat pumps
all become equipped with VFD supply fans. This concerns me that I've
really screwed up something in the HVAC system set up.

- Gas consumption is driving me nuts. The shape of the curve
is a great match but their summer consumption is 4 times the modeled
value. The only gas loads I have in the building are the DHW and the
kitchen and they've told me the kitchen is closed during the summer.
I'm a little concerned by the up/down nature of the model curve. With
DWH and kitchen only the loads should be pretty smooth shouldn't they?

- The majority of the classroom wings have pitched metal roofs.
I've walked through my selections with Mark and Cliff but I'm not sure
we have accurately modeled the thermal performance of the roof for most
of the building.

Ian T. Hadden, PE, LEED AP BD+C

ihadden's picture
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Ian,

Equest thermal inputs use the convention of Mbtu = million btus, while
common usage in the US is still generally Roman numerals with btus: mbtu =
thousand btus, mmbtu = million btus. You should be entering 2.603 Mbtu for
the boiler capacity in equest.

However, I'd recommend looking at load hours not met in the BEPS report
before and after entering that value. If the usage is going up when you
enter the 2603 Mbtu value, that may mean something else is going on. Do
teachers and staff report problems maintaining temperature in the winter, or
does the boiler spend a lot of time in winter running? Is it possible the
existing boiler is undersized, or is there something else going on?

For the elementary gas consumption, it looks like you have a pilotless
domestic water heater set up in the model. Are you sure that there's no
pilot on the domestic water heater or the boiler? Do they completely shut
the boiler off during the summer?

How is the domestic hot water recirc pump controlled? If it does not have a
timeclock or temperature control to shut it off when there's no system
demand, it may be causing the domestic water heater to cycle more frequently
during the summer when there's no load, especially if the HW & HWR piping is
not adequately insulated. If this is the case, you can do a side
calculation to estimate the HW & HWR piping UA and enter that in the
domestic water loop as a SUPPLY-UA to get a closer match in your baseline.

Thanks,

Steven

Steven Savich's picture
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Joined: 2011-09-30
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Thanks very much Steven. I know eQuest has some idiosyncrasies for units
and +/- entry but I don't know where they are. I've always hated MBTU
for the very point you make. The building has 2 equally sized boilers
but only on rare occasion do they run both boilers at the same time (2-5
days a year with steady overnight temps below 0 deg F). The boiler runs
a lot during the winter but I don't have reports of comfort problems
that aren't attributed to the single pane, aluminum frame glazing system
in many of the classrooms (1950s window wall design).

I'll look at the DWH set up (pilot light and recirc) for the elementary
school as well. The DHW was replaced/installed in 2009/2010. There is
no boiler in the elementary school to support the GSHP loop unless
someone cross connected the DHW with the condenser loop (admittedly that
wouldn't be the first time something like that has happened in a
building) but I don't have reports of unexpectedly high condenser loop
temps in the winter.

Please forward any other thoughts.

Ian T. Hadden, PE, LEED AP BD+C

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