# =?iso-8859-1?q?Estimating_Energy_Consumption_Using_Spr?=

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Hello!

There is a good reason people don't use spreadsheet analyses very much
anymore for building modeling. I used bin models for many years to
estimate HVAC energy use and kept improving my technique until I arrived at
what was dubbed the Osama bin Model approach. In the end, I ditched this
to learn how to do things right in eQuest.

What was the big lesson? Bin models at best are big sloppy averaging
exercises that use first principals (read: "easy math") to determine
operation at any one point in time. This is cool for ventilation
calculations where the loads are instantaneous and related directly to
ambient conditions, but definitely not a good way to model the impacts of
anything that has time lags/delayed responses. How do you estimate the
benefit of commercial building envelope upgrades? Most savings arise
during unoccupied periods, primarily from reduced cycling of fans, pumps,
cooling systems, and boilers. Sure there are reduced heating/cooling
loads, but how do you estimate the heat loss when you can't estimate what
the average interior temperature is going to be?

Yeah, spreadsheet calcs definitely have their place and I still do use
them. I have found that eQuest is a whole lot faster and more accurate
than the ol' Osama bin Model when doing whole-building analyses.

Eric Studer, PE

FROM: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] ON BEHALF OF Daniel
Croisant
SENT: Monday, February 22, 2010 4:50 PM
TO: bldg-sim at lists.onebuilding.org
SUBJECT: [Bldg-sim] Estimating Energy Consumption Using Spreadsheets

Hello,

I?ve ?grown-up? in the time when energy modeling programs always existed.
I?m curious if anyone that has been in the business for awhile has any
experience using spreadsheets to estimate a building?s energy consumption,
and if so, would you be so kind as to share them with me? I?m not looking
to use it on any projects and would not try to hold anyone liable for any
results. I?m just curious as to how people tackled the issue of estimating
energy usage, other than degree days, before the popularization of DOE and
other energy modeling programs. Plus I think it would just be fun to play
around with what other people have used.

DAN CROISANT

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Joined: 2011-09-30
Reputation: 200

Hello Brent,

I agree that DOE2 does not perform the same degree of calculations as E+ or
other newer calculation engines, but it does allow us to get a reasonably
accurate estimate of savings for a wide range of design options without
having to wait hours for results. In addition, we can access intermediate
results to diagnose modeling problems or check to see if we are modeling
unique systems correctly. We will switch to E+ when it can run as fast as
eQuest and/or when there is a user interface that allows us to model a wide
array of HVAC systems and easily check intermediate results.

I am curious, do you or anyone else over at NREL have comparisons of
projected savings generated using DOE2 and E+ for the same base and proposed
case envelope designs calibrated to actual energy use of a real building?
We may switch from eQuest if there is evidence that there is a substantial
difference in the accuracy of energy savings estimates.

It is my understanding that the E+ FORTRAN code is an agglomeration of DOE
programming from the past 30 years that may not be operating as smoothly as
it could be. Do you know if there are any efforts underway to speed up the
processing time?

Eric

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Joined: 2011-09-30
Reputation: 200

I'd guess that, back when DOE2 took an hour to run, this sort of reasoning was often used to justify hanging on to spreadsheets.

Your understanding of the Fortran in E+ is incorrect. E+ is getting faster with each release.

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Joined: 2011-10-02
Reputation: 0

The 'hilarious' thing is that EnergyPlus was introduced with much fanfare in
2001. At the time it was described as a program designed to be used with an
interface (though I noticed that now they it's a "stand alone program
without a 'user friendly' graphical intrerface").
Nine years later we're still waiting for a fully functional interface!

Mike

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Joined: 2011-09-30
Reputation: 0

We always said it was an "engine" for calculations. Designed to be
the engine. Look at our documentation if you think otherwise.

And 3rd parties, at their request, were to step up to the plate and
provide those interfaces all the domain users love so much. The
Government has been highly criticized for any attempts to produce
full scale commercial software and step on others toes.

Go
to
http://apps1.eere.energy.gov/buildings/energyplus/interfaces_tools.cfm
to see how far private industry has progressed in terms of providing
interfaces.

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