Cooling Load in EnergyPlus

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Dear All

Can we get the individual break-up of cooling load in *EnergyPlus*? Internal
loads (People, Equipment & Lighting), Infiltration loads and Window gains
are available but the *gians from Walls and Roof is missing. *Surely EnergyPlus
does calculate all the above loads to size the Cooling Equipment but there
is no such specific output.

Sandeep Kachhawa

Sandeep Kachhawa's picture
Joined: 2011-10-02
Reputation: 0

Hi Sandeep,

A full list of the available output variables are given in the .rdd file (it
is one of the files output from the simulation). Simply copy the relevant
line from that file into your .idf (or .imf) file, rerun the simulation, and
the new variable(s) will be output to the .csv and .eso files.

e.g. Adding this line to the input file will give you the convective heat
gain from all interior surfaces in your model.
Output:Variable,*,Surface Int Convection Heat Rate,hourly; !- Zone Average


Paul Raftery's picture
Joined: 2011-10-02
Reputation: 0


This is what I call a legacy topic from the DOE2 era. You better search
the posts in EnergyPlus support mailing list. Search for "cooling load
component", and you will find an interesting discussion.

In summary, you will not find a cooling load component report in
EnergyPlus nicely formatted a-la LS-C report in eQuest/DOE2.

If you try to match the total gains v.s. the cooling load for every time
step, then you will be in for a long ride. Take the solar radiation
gain, for example. The GAIN for a particular time step is not
necessarily converted into cooling LOAD at the next time step. If your
building is thermally massive, then the delay plays an important role
and it could be hours before the solar radiation GAIN becomes an actual
LOAD as seen by the thermostat. Do not forget about this, if you try to
match the cooling load report with the total gains.

If you are talking about peak cooling load, then you will need to focus
on the zone sizing report. Calculating the gains component is easy
because the schedule is always 100% on. You just need to quantify the
ventilation load.

Please note that the report suggested by Paul below is the convection
report. I imagine that you would expect a conduction report? EnergyPlus
zones technically cannot see conduction through opaque surfaces, in the
sense of A*U*DeltaT. They can only see convection and radiation. In
fact, if you try to match A*U*DeltaT for external wall with this report
(Surface Int Convection Heat Rate) then you will have a hard time
explaining. If you keep this in mind, the differences can be easily



Ery Djunaedy2's picture
Joined: 2011-09-30
Reputation: 200

Thank you;
I am running the example file Supermarket_Detailed which has a 50m x 50m supermarket but the Electricity:HVAC [J](Monthly) for July in Tampa weather is 1.3 ? 10 9 .

To convert this into Kwh I multiplied it by 2.7778 ? 10 ?7 which gives 363Kwh only . I think it should be around 100 times this amount. Am I doing something wrong?
Thank you for any help

Abaza Hussein's picture
Joined: 2011-10-02
Reputation: 200

Hi Ery,

Thanks for this explanation. I have been struggling with this topic as well
as I do more modeling in Energy Plus. However, there is one thing that you
did not address above. While DOE2's LS-C report may not match exactly to
what systems are seeing as far as loads, it does give an easily readable
report which allows you to check your inputs. I review it quite often as a
quality control check for my models. It also allows me to target energy
saving measures, and helps me explain to clients why certain changes might
make sense for their building. For example, one client might be interested
in increasing roof insulation, but if they have a multi-story building with
a relatively small roof, and lots of wall area, it makes more sense for them
to reduce thermal bridging in their wall construction. Having a
model-generated report makes this process much faster for me.

Do you have any suggestions with regards to Energy Plus of ways to achieve
the above goals with the currently available reports?



No Username provide's picture
Joined: 2011-09-30
Reputation: 200

Hi Karen,
Same here, I always use LS-C when I use eQuest. Just adding the
ventilaton load, then you will have the peak load. Its always fun to
compare this number with what the mechanical engineer has.
I said earlier, in EnergyPlus it is not nicely formated like LS-C. It
does not mean you cannot have it. You can force EPlus to show the
numbers. The internal gains are the easy ones, the windows are also
relatively easy, the last pieces are the opaque "conduction" and the
ventilation load. Which is not difficult.

The problem is what peak to report? You will have the peak of the total
gains, which will happen at a different timestep then the peak of the
cooling load. And these two, in turn is different with the zone sizing

I personally use the zone sizing reports as the peak loads, and I will
get all the details by running the designday run with schedules
consistent with the design day schedule.

Hope this helps,


Ery Djunaedy2's picture
Joined: 2011-09-30
Reputation: 200

Thanks Ery.

It helps. It's just slow. What I love about LS-C is that it's fast. Do
you know of a way to get a grouped report for all walls within a particular
zone. So instead of having hourly output for every wall in a space, you
would have one for each: exterior walls, interior walls, etc? This would
make reviewing these outputs much faster!



No Username provide's picture
Joined: 2011-09-30
Reputation: 200

Nope, not that I know of. Before this kind of summaries is implemented
in EPlus, I think scripting is the way to get faster results. SQLite is
really a powerful result analysis tool. What you describe below can be
implemented relatively easily with some SQL statements.

We have been trying to come up with a better way to communicate this
kind of output to the client. I will share the results to this list once
we finalize how to do this in EPlus.



Ery Djunaedy2's picture
Joined: 2011-09-30
Reputation: 200

Hi Ery

I appreciate your suggistions. So its clear that we can't get the complete
break-up of coolong load in EnergyPus in terms of energy (joules), but we
can get the components of peak load in Watts.

You mentioned, "You can force EPlus to show the numbers... the last pieces
are the opaque "conduction" and the ventilation load. Which is not difficult".
Can you please elaborate, how?

Sandeep Kachhawa

Sandeep Kachhawa's picture
Joined: 2011-10-02
Reputation: 0