eQuest/DOE2 instantaneous loads

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Hi there,

Just joined the group and I am glad there are people out there as
curious about building simulations.

That said, I have a questions regarding getting instantaneous loads
from DOE2 using eQuest. Here in the University of Texas we are
currently trying to do a parametric study on effects of varying
temperature set-point and occupancy. Pretty much we are changing the
occupancy schedules and set points in the HVAC setup and see what
happens (for a specific test building).

While we are getting decent HVAC electricity consumption outputs
(which somewhat fit our expectations), we were not able to get the
simulated instantaneous loads for a zone... Say if I have a cooling
zone with the set point changed from 75F to 80F, the increased indoor
temperature should decrease the conduction load and ultimately reduce
the energy used for cooling.

We are seeing the energy reduction, but all the "loads" stay the same
no matter which parameters we are looking at in the report.

I believe I read it somewhere that all the "loads" in DOE2 are design
loads for a specific building material/weather then they modified for
the load for set points and occupancy, that's why when there is no
material changes, the loads stay the same, is that true?

The bottom line is we will need to somehow figure out how much the
external load reduction is when we adjust set point and occupancy.

Thanks for the help!

L. James Lo

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James,

There are two sets of loads in DOE-2, in both the LOADS and SYSTEMS
routines. Make sure you're looking at the SYSTEMS loads, not the LOADS
loads.

Joe Huang

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Is it also safe to say that the eQuest Loads are not the same as the
loads that would be calculated by a load calculation program (i.e.
Trane, Carrier, etc.)? The primary differences laying in the way that
eQuest calculates effective R-Values vs. nominal for assemblies and uses
a 30-year average weather file rather than degree days. And if I'm not
mistaken, coincident vs. non-coincident cooling-heating has a role in
the loads as well.

Matthew Higgins, Associate
LEED AP + ASHRAE-HBDP

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Joe,

Since we are only novice users here and only using the eQuest as our
interface, I am not familiar with the DOE2 output file well enough to
isolate the SYSTEM loads. (any pointers on the file definition will be great).

That said, from what we can tell, the system loads (making sure I am
not misunderstand you here), such as total cooling coil output, does
reflect the changes we make. That said, since I am trying to separate
them out into gains from walls/window, etc, I was looking into the loads side.

I assume there must be some outputs from DOE2 file which eQuest is
reading from which describe what I am looking for.

Any additional help will be awesome.

thanks everyone

- James

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"SYSTEMS" outputs will be labeled SV or SS.

"LOADS" outputs will be labeled LV or LS, in the upper left corner of the page.

"PLANT" outputs will be labeled PV or PS.

Jeff S. Haberl, Ph.D.,P.E., FASHRAE

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James,

Here is a DOE-list you will need-very useful.

Thanks,
Nikola

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Thanks Dr. Haberl and Nikola for the info, and it's clear now what
the DOE2 file definitions are

The big question remains tho:

1. LOADS loads are calculated based on components of the buildings
(window, wall, roof, etc) and these are design loads
2. SYSTEM loads are summarized loads subjected to the HVAC system, so
these are "operation" loads

SYSTEM loads are not separate back into components, only total loads
are present.

So my questions is really whether there is a way for me to break the
SYSTEM loads back into components?, ie, x% of SYSTEM cooling load for
month z is from wall conduction, y% is from window radiation, etc.

Is this even doable? hopefully I am making sense to you guys...

thanks!

- James

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James,

You can create an hourly report output for this and then sum the results in Excel. Go to the "projects and site" tab, double click on the hourly report, and add a new block. Make it look like the picture attached. Run the model and then go to file>export hourly results. You will then have a .csv file with the hourly loads. You can also do this for each thermal zone you created.

John Grando LEED AP

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John,

Thanks for the info, but the procedure you described IS what we have
been doing. The loads from the report you showed do NOT vary when
occupancy and set point change, hence the problem. These loads only
change (from LOADS described from others) when building geometry,
materials and other building envelope parameters change.

hopefully I am making sense...

thanks

- James

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The loads are calculated at a fixed temperature specified by the user
- usually between the heating and cooling setpoint. The loads report
uses this to report all the component breakdown. You might want to
change this temperature - but it is a single value and not a schedule
so probably not very useful in your case.
Not sure how you can have the breakdown at the system level - if you
find something, I will be interested in knowing.

-Rohini

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James,

It's good to see that you're getting a lot of help in answering your
questions. I'm sorry if my original answer was too brief to explain
the situation. Here are some additional thoughts:

1. The differences between LOADS and SYSTEM loads. You can think of
LOADS loads as the heat flows into and out of the space at a user
defined constant temperature. In SYSTEM, DOE-2 models the effect of
those heat flows, plus the actions of the HVAC system, to determine
the true temperature of the zone and the loads imposed or met by the
HVAC system. Thus, set point changes will not affect the LOADS loads,
but occupancy changes should have an effect by changing the internal
heat gain from occupants (but not the fresh air amount which is
considered a SYSTEM action).

2. Deriving the component loads at the SYSTEM level. This is something
I've looked into for many years. As you've mentioned in another e-mail,
component loads are available only for LOADS, since SYSTEM deals only
with the aggregated loads for the entire zone. The component loads in
LOADS, however, are calculated at the fixed reference temperature, and
not the true zone temperature. You can make a UA-delta T adjustment of
the LOADS loads for this difference in zone temperature, but this will
still not account for the pick-up loads in the morning, nor tell you
what to do with those loads when the HVAC system is off.

Joe Huang

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Erik,

I don't agree with your assumption that going to a heat balance model
will "make life easier" for James' needs. From my experience, getting
the "component loads" from EnergyPlus is even more difficult than with
DOE-2. About 8 years ago, there was a DOE project that tried to extract
component loads from EnergyPlus that found the task quite complicated
and convoluted.

In the final analysis, a "component load" is an abstraction,
since the HVAC system is responding to zone-level heat gains or losses
that have built up over many hours. For example, when the air
conditioner kicks
on in the midmorning, is that "load" due to the solar through the windows,
the lights that came on, or the fresh air supplied over the past three
hours?
On the flip side, when the heating comes on at night in the Fall, is that
"load" attributable only to the cumulative envelope heat losses and how
should it be offset by solar heat gain and internal loads built up during
the day?

These are bookkeeping problems that extend beyond simply switching to
a heat balance model.

Joe Huang

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Erik,

I've never used ESPr, so my comments refer just to DOE-2 and EnergyPlus.
Both programs use certain simplifications in their modeling of floating
conditions. DOE-2 calculates LOADS at a fixed reference temperature, and
then adjusts those loads in SYSTEMS while solving for the actual zone
temperature. EnergyPlus calculates loads at the zone temperature the
previous time step, and does not "look back" during the system solution.

When I compared the two programs for the California Energy Commission
a couple of years back, I found that EnergyPlus tended to produce lower
morning start-up heating loads. and thus lower annual heating energies,
than DOE-2. At this point, I'm not able to able to say which results
are more accurate.

Joe

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Joe,

I am willing to repeat the "complicated and convoluted" process of
defining "component loads" in EPlus. The peak load information that
we have in DOE2 is too important for the design process, that I
really need to have similar information in EPlus.

Is there any documentation/publication that came out of the DOE
project you were talking about? Anything at all that you can share?

Thanks,

Ery

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