[Bldg-sim] Cooling Load in EnergyPlus

Karen Walkerman kwalkerman at gmail.com
Fri Mar 4 16:04:31 PST 2011


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!

Thanks!

Karen

On Fri, Mar 4, 2011 at 6:52 PM, Ery Djunaedy <ery.mailinglist at gmail.com>wrote:

>  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>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> 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>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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>>
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