Problem in cooling load

[Helia Taheri]

Hi.

I have a problem in getting cooling load from energy plus!!!! 

I have simulate a 3x4x3m building with a vertical 2x1 window in the south facade. I get cooling load for July.

In the times between 8am to 8pm we have increase in cooling load non logically.

I don't know what mistake that I have in it.

Thanks.

Best Wishes,

Helia Taheri

[farhang.tahmasebi]

Hi,

Based on the limited information that you provided, it might be the case that you have some internal loads (like people, lights and electric equipment) during those hours.
So, check those objects and their schedules. If you need a more specific answer, upload your IDF file here.

Best,
Farhang

[Helia Taheri]

[farhang.tahmasebi]

Hi,

I checked the model and simulated it with Tehran weather data with constant set points of 21 and 24. The building never got warmer than 24 degrees during the nights of July. So I just got cooling load during the day and it was like 26 KWh/m2 for the whole month that doesn't look too high to me for Tehran.

But why you only have temperatures higher than 24 degrees during the day? Apart from the weather conditions, that's because the main heat gain source in your model is solar radiation and clearly it just warms your building during the day. But in a real building you have some internal heat gain sources (like people, lights, electric equipment) and it's more likely to have cooling demand even when the sun is not there!

Another problem in your model is that you are heating the building in July. Is that what you want? If not, you may change the heating set point schedule in a way that it returns a value like -60 during summer, so that the heating system doesn't get activated.

Best,
Farhang


On Friday, December 21, 2012 8:09:15 PM UTC+1, Helia Taheri wrote:

    Hi,
    I didn't have any people and light schedule, yet. Although I don't have any of them, I have a lot cooling load.
    Thanks
    Helia
    On Fri, Dec 21, 2012 at 9:18 AM, <BES...@googlegroups.com> wrote:

          Today's Topic Summary

        Group: http://groups.google.com/group/BES_fb/topics

            Problem in cooling load [2 Updates]

         Problem in cooling load

            Helia Taheri <helia.tahe...@gmail.com> Dec 20 05:15PM +0330  

            Hi.
            I have a problem in getting cooling load from energy plus!!!!
            I have simulate a 3x4x3m building with a vertical 2x1 window in the south
            facade. I get cooling load for July.

            In the times ...more

            "farhang.tahmasebi" <farhang....@gmail.com> Dec 20 06:18AM -0800  

            Hi,
             
            Based on the limited information that you provided, it might be the case
            that you have some internal loads (like people, lights and electric

            equipment) during those hours. ...more

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[farhang.tahmasebi]

Hi,

As we are in holidays something else came into my mind! If you remove the heating and cooling system, you can see the indoor air temperature gets as high as 41 degrees while the maximum outdoor temperature is like 33 degrees (based on Mehrabad Weather Data). So, your zone performs like a sunspace meaning that the room gets a lot of solar radiation and you don't ventilate it. So, without any cooling system, it gets warmer and warmer until 41 degree.

But, in reality, if the building has an operable window, the occupants will open the window, when the indoor temperature is higher than outdoor temperature. So, to make your model a better representation of the built environment you may add a simple ventilation object to your model like the following:

ZoneVentilation:DesignFlowRate,
    vent1,                          !- Name
    Main_Room,                !- Zone Name
    INFIL_SCH,                 !- Schedule Name
    AirChanges/Hour,         !- Design Flow Rate Calculation Method
    ,                                 !- Design Flow Rate {m3/s}
    ,                                 !- Flow Rate per Zone Floor Area {m3/s-m2}
    ,                                 !- Flow Rate per Person {m3/s-person}
    4,                               !- Air Changes per Hour
    Natural,                       !- Ventilation Type
    ,                                 !- Fan Pressure Rise {Pa}
    1,                               !- Fan Total Efficiency
    1,                       !- Constant Term Coefficient
    ,                         !- Temperature Term Coefficient
    ,                         !- Velocity Term Coefficient
    ,                         !- Velocity Squared Term Coefficient
    22,                      !- Minimum Indoor Temperature {C}
    ,                         !- Minimum Indoor Temperature Schedule Name
    100,                    !- Maximum Indoor Temperature {C}
    ,                         !- Maximum Indoor Temperature Schedule Name
    1,                       !- Delta Temperature {deltaC}
    ,                         !- Delta Temperature Schedule Name
    -100,                   !- Minimum Outdoor Temperature {C}
    ,                         !- Minimum Outdoor Temperature Schedule Name
    100,                    !- Maximum Outdoor Temperature {C}
    ,                         !- Maximum Outdoor Temperature Schedule Name
    40;                      !- Maximum Wind Speed {m/s}

Adding a ventilation like this to your model, the indoor temperature and the cooling load decrease. Of course, in this simplified ventilation model, we should just assume an air change rate and EnergyPlus doesn't calculate it for us.

But, this object offers you some temperature setpoints to control when the ventilation happens. I used 2 of them to ventilate the building when the indoor air temperature is higher than 22 and the outdoor temperature is at least 1 degree cooler than indoor air. You can play around with these values and also the ventilation schedule if you want.

Best,
Farhang