[Bldg-sim] Cooling Load in EnergyPlus

[Sandeep Kachhawa]

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?

Thanks
Sandeep Kachhawa




On Sat, Mar 5, 2011 at 5:22 AM, 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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