problem with energy consumption results

katerina · Posts: 11

hi,
i am modelling an office building of 300 m2.The building is mainly heated & cooled by 10 wall mounted aircondition of 5 kwh (10 devises,electricity consumption).

The problem is that the simulation results of DB do not correspond in the reality.

estimating of real cooling consumption (summer):
5 kwh x 10 devices x 5 hours per day x 22 days per month x
5 months per year =27500 kwh per year

estimating of real heating consumption (winter):
6 kwh x 10 devices x 5 hours per day x 22 days per month x
4 months per year =26400 kwh per year

electricity consumption per year = 27500+26400=53900 kwh per year

DB simulation results :24528 kwh per year

As you can see the result is far away from the reality.
what can i do about it?

AOG · Posts: 79

Katerina,

I couldn’t open the file because I’m using last release version. However, I wonder if you are taking into account the “real” operating time. In manual calculations you are assuming fixed operating periods, while in simulations you define setpoint temperatures (targeted temperatures into the space) and the software assumes devices are active only when it is necessary to maintain those temperatures. In fact, it is possible that your building requires less energy consumption than indicated by manual calculations.

I hope I’m not misunderstanding your question.

Best regards

katerina · Posts: 11

Hi,
thank you for your quick answer.
The schedule of a typical work day in my office building is 8 hours per day.In my calculations i am taking into account that the devices do not work 8 hours per day ,because of the reason you have already mentioned,but for 5 hours per day which is a realistic scenario,because of the insufficient insulation of the building and the very hot summer of Greece.
What else I might not take into account?

AOG · Posts: 79

Katerina,

Sorry for the delay. Finally I installed last beta version and took a look into your model. It seems that results are congruent with data assigned to the model. Some points:

The model has constructions with relatively good insulation and thermal mass, so the requirements of heating and cooling could not be as high as you are expecting.
You are using an Athens hourly weather data file which contains not extremely high temperatures in summer (maximum in some days is about 37ºC).
High CoP (2.5) are defined for heating and cooling systems. This reduces energy consumptions.
HVAC systems are active only during 6 hours (operate with occupancy), and not during the 8 hours work period you mentioned.

I think some little adjustments to the model data could offer more reliable results.

I hope it helps,

Arturo

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