[Bldg-sim] Cooling Load in EnergyPlus

[Ery Djunaedy]

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 
report.

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

On Fri, Mar 4, 2011 at 12:00 PM, Karen Walkerman <kwalkerman at gmail.com 
<mailto:kwalkerman at gmail.com>> wrote:

    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?

    Thanks.

    --
    Karen

    On Fri, Mar 4, 2011 at 12:26 PM, Ery Djunaedy
    <ery.mailinglist at gmail.com <mailto:ery.mailinglist at gmail.com>> wrote:

        Sandeep,

        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 explained.

        Cheeers,

        Ery


        On 03/04/2011 07:07 AM, Paul Raftery wrote:
>         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 [W]
>
>         Regards,
>         Paul
>
>         On 4 March 2011 13:50, Sandeep Kachhawa
>         <sandeep.kachhawa at gmail.com
>         <mailto:sandeep.kachhawa at gmail.com>> wrote:
>
>             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.
>             Regards
>             Sandeep Kachhawa
>


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