good afternoon everyone,
We are modelling a 2 story multi-family structure in eQuest that contains
four 3 bedroom apartments side by side. After simulating the model, we have
found that the eQuest estimate for TOTAL gas consumption (space heating +
DHW + misc. equipment) is very close to our spreadsheet calculation. The
model indicates a total annual gas consumption of 413.14 Million Btu's. We
calculated 414.01 Million Btu's. Very close! However, the proportions of
Btu's dedicated to space heating, DHW, and misc equipment is very different
in our eQuest model and our spreadsheet. Does anyone know a simple way to
manipulate the proportions of Btu's dedicated to each of these three
categories without affecting the TOTAL annual gas consumption which is
nearly dead on? We would like to divy it up based on our calculated usage
patterns. We understand that this might be accomplished by adjusting the
numbers in the Space Heating/DHW boiler diagrams. Also, that changing the
daily/weekly schedules might affect this. Are these the only ways to
approach this or is there a more simple solution without having to crunch
such numbers?
Thanks.
Vaughn Slovak
Vaughn,
Rumor has it that eQUEST v4.0 will have an "Autotweek" tool. You tell
the program what the output should be, and the inputs are automatically
adjusted accordingly. :-)
Kidding aside, why do you need eQUEST to tell you what you already
"know" from your spreadsheet? Matching the total BTUs does not mean much
if the individual values for space heating, DHW and process loads are
all way off.
You can adjust the DHW by adjusting the Process Flow (gpm) for the DHW
loop or by adjusting the process load schedule.
You can adjust the Input Power (Btu/h) and schedules for any gas loads
that you enter as Internal Energy Sources in your spaces.
If gas loads are entered as Direct - Interior or Direct - Exterior loads
on your fuel meter, then change the load (MBtu/h) or schedule in the
Utility & Economics module for the meter.
Space heating gas consumption is not so direct. There are many things
that affect this, including thermostat schedules, boiler efficiency,
building envelope, miscellaneous loads, lighting power, occupancy,
outside air, economizer operation, and nighttime fan operation, just to
get you started. Many of these also affect your electrical consumption.
Hopefully that's not on your spreadsheet too.
Long story short - model calibration is not so simple. Start crunching!
Regards,
William Bishop, PE, BEMP, LEED(r) AP
As Bill is saying, there is no fast/simple way to make your broken-out
consumptions match. That you came up with the "right" total consumption
is arbitrary. It will still be equally "right" if you correct the
individual consumptions one by one. Allow yourself a margin of error
and go to town! I'd follow Bill's advice, and first hammer out the
"easy" ones, as they may inadvertently affect "space heating": DHW and
misc equipment.
Also echoing Bill: Ask yourself the overall purpose of the model and
whether it really needs to be calibrated to this degree - is it really
so different from the expected "known" figures, or is your model
accurate enough to be functional for the task at hand?
NICK CATON, E.I.T.