Trane Trace Energy Modeling Ventilation OA hourly amount

Hi. I am working on energy modeling with Trane Trace 700, so I have proposed model and baseline model. Based on the code, I am using the minimum OA for thermal zones in both models with same amount. However, the result from Trane Trace shows me different outdoor air amount in hourly. The total amount of OA is same in Airflow report however, in hour Ventilation chart shows me dramatic difference between baseline model and proposed model. How that hourly OA amount is calculated? Is that space peak? or coil peak?

Thank you.

KLim

asked 2020-02-12 15:51:15 -0500

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__AmirRoth__

updated 2020-02-12 17:25:47 -0500

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Hi KLim, I would suggest you contact CDS support.

cdshelp@trane.com 608-787-3926

Since you are speaking of a specific project file you are working on it would be useful to send in the archived (.taf) file attached in your email so we can understand your question better. Also if you have screen shots showing the differences in your reports that would also be helpful.

tj.olson

answered 2020-02-12 21:03:26 -0500

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Hello, I am not sure if you were able to contact CDS support. If you haven't I would still recommend you reach out so they can look into your question at a deeper level. In TRACE 700 the VRF system is allowed to modulate down to 10% airflow for low load operation. PTHP systems are constant volume only. This more than likely explains the large difference in cfm between the two. However, to answer the question with more confidence it would be best to see your file. That way the ventilation schedules and any ventilation settings at the system level can be reviewed.

tj.olson (2020-02-18 08:46:44 -0500) edit

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Since OA is controlled based on HVAC operation, it might be that the OA differs because the air loop operation is different (e.g., building loads are different). You should also include information about the type of HVAC system to better understand possible reasons for the difference you see.

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rraustad

answered 2020-02-13 07:53:49 -0500, updated 2020-02-13 07:55:20 -0500

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Hi. Thank you for answering. The project is about residential building and proposed model has VRF system for residenatial area. In baseline model, obviously having PTHP. The loads for both model are different based on different construction set. I believe HVAC system operates based on the setpoints in the model and ventilation schedule. But still do not get why different amount of outdoor air hourly.