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Standard 90.1 prototyping building models

asked 2020-09-15 19:29:12 -0500

bitaph gravatar image

My research is based on green roof design and I'm using EnergyPlus ecoroof to model my green roof. However, I'm not designing the whole building and have decided to use the prototyping models offered in the EnergyPlus library tool. I'm using secondary school buildings under the Toronto weather climate, but I'm not sure how to validate the heating and cooling loads I'm getting for my simulations.

I found a webpage: https://www.energycodes.gov/developme..., in this source all the prototyping models for all versions (2004, 2007, 2010, 2013, 2016 and 2019) and for all different climate zones along with the html results for each prototyping model of EnergyPlus is provided.

I used Buffalo, NY prototype model which is a climate zone 5A (same as Toronto city) and compared the results of my simulations to the html file provided on the web page for Buffalo city for secondary school (I used version 2013).

I compared only the total energy consumption of the building along with the heating and cooling loads. My results were not the exact values, however they were very close.

I got cooling, 974.65 GJ, and heating, 990.12 GJ for my simulations.

The html file provided on the webpage had cooling: 972.35 GJ and heating 922.42 GJ for the secondary school in Buffalo city version 2013.

I have two questions:

I used IDFversionupdater to update the IDF files as they were older versions, could this be the reason due to the small difference in result values?

Is this a correct method to validate my simulations and model my building base in Toronto city under the Toronto weather climate?

I would really appreciate it if anyone could help me or direct me to a source where I could find information regarding this matter.

Thank you!

Bita

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answered 2020-09-15 23:38:41 -0500

The 90.1-prototype models are under continual maintenance. There are also some known differences between EnergyPlus versions. If you are trying to exactly match the published values, make sure to use the same version of EnergyPlus used to generate the results. I suspect that is the source of the discrepancy you are seeing.

Buffalo and Toronto have a similar climate. However, Canadian building code is somewhat different from ASHRAE 90.1. If you intended to model how your green roof model interacts with building code, you will need to use the NECB version corresponding to Toronto. However, if you are just trying to validate your model and come up with comparative savings estimates in this climate, then using a 90.1 prototype model is fine. The differences you show in your model are within the noise typical of weather and variability among buildings of a similar type.

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Thank you so much!

bitaph gravatar imagebitaph ( 2020-09-16 10:34:26 -0500 )edit
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answered 2020-09-16 12:43:40 -0500

updated 2020-09-16 12:50:46 -0500

Regarding validation of the Green Roof Model, I would point you to the EcoroofOrlando.idf example file, which demonstrates the use of the Material:RoofVegetation object. The roof construction (ASHRAE 90.1-2004_Sec 5.5-2_Roof) has the BaseEco material as the outside Layer. Running this model with and without this BaseEco material in the roof construction demonstrates the impact of that material on the zone loads, particularly the top floor zones which are most impacted by changes to roof construction. Looking at the htm output file, there is a table called "Zone Sizing Information" which shows the calculated Design Loads {Watts} for each zone. Design loads are a much better indicator than annual energy consumption to assess the impacts of envelope constructions. To see the material's impact on the roof construction's thermal performance (i.e. u-factor and reflectance), look at the Envelope Summary table which summarizes the performance of all the constructions used in the model.

The results show that this green roof reduces heating loads on the top floor zones between 4-11%, and cooling loads from 11% to 29%. Repeating this exercise on the SchoolSecondary model in Buffalo should yield somewhat similar results, but keep in mind that zone cooling/heating loads are impacted by many components other than just envelope performance (e.g. internal loads, roof-area-to-zone-volume ratio, ventilation requirements, ambient weather conditions, space setpoints etc.), so your results may vary widely depending on the specifics of your model, in addition to any differences you may be assuming in your base roof performance and your Material:RoofVegetation definition.

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Asked: 2020-09-15 19:29:12 -0500

Seen: 44 times

Last updated: Sep 16