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# Model calibration, operative temperature measurement

Hey guys,

I am trying to calibrate in EnergyPlus a 20" container (low insulated) used for data center equipment that is located outside in a warm and sunny climate in southern europe. I have the data for total electric consumption and inside temperature. hvac for cooling is on all the time.

Analysing the hourly inside temperatures over a year I can observe that sometimes the sensor show similitarities to my simulated operative temperature profile and sometimes temperature is more stable , thus it represents more the simulated mean air temperature (almost constant all the time).

attached you can find the two plots to compare (august vs november, mean air vs operative).

there are sensors measuring indoor temperature (exact location is unknown).

does anybody have an idea why the difference in behaviour?

thank you very much!

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Hi @Soeren

Zone operative temperature is an average of the Zone mean air temperature and the Zone Mean Radiant Temperature. Since Zone Mean Radiant Temperature is a measure of the combined effect of the temperatures of the surfaces in a space, Zone Operative Temperature also gets affected by the surface temperatures. Did you take a look at the surface temperatures within the zone for these two months? The insulation levels of your envelope, outdoor air temperature, solar gains, internal gains etc. have an impact on the zone operative temperature. My guess would be that the outside air temperature difference (and also solar gains) is causing the zone operative temperature to vary for different months.

That aside, I am trying to understand the purpose of comparing the temp sensor measurements to the zone operative temperature. Are you trying to calibrate the model so that the sensor measurements match the zone operative temperature?

Raghu

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Hi Raghu,

thank you for your answer, really appreciating it. The internal gains are constant over time, so the only variation is in the HVAC power. Solar gains are in both time periods high (august, november), which explains the operative temperature curve. I am just trying to figure out, what could cause the sensor measurement being different. Shading from trees? Air velocity?

( 2017-07-14 10:28:01 -0600 )edit

Yes, the purpose is, I am trying to match the simulated temperature to the measured temperature. Thus in some times the operative temperature is matching more than the mean

( 2017-07-14 10:28:04 -0600 )edit

Thank you for your second answer, unfortunately I don't have acess to the sensors nor to the facility owners. I will read more to choose the right variable for calibration in the I/O reference

( 2017-07-14 10:31:53 -0600 )edit

Hi Raghu, one more question: Does it make sense for you that the simulated Mean Air Temperature is constant (only varying in the second decimal), as in the Setpoint Temperature determined? My model is a 1Zone, Small container, constant Internal IT Equipment, cooling Only (enough cooling capacity to meet the cooling Loads.), Infiltration Rate at 0.5ACH.. Thank you, Sören

( 2017-07-16 18:06:59 -0600 )edit

Hi @Soeren , The simulated mean air temp would be met by the simulated systems irrespective of the loads in the simulation if there is enough cooling capacity resulting in a constant temp. value. However, this may not be the case in real life due to various disturbances. If the aim of your study is to make sure your model matches the sensor data, then these disturbances would need to be introduced into the model. Schedules of occupancy, thermostats, other internal loads and mech equip sched. are the most important to be verified.

( 2017-07-17 08:22:09 -0600 )edit