Carrier HAP 5.1 compliance with ASHRAE 90.1 VAV inconsistent automation

asked 2020-01-22 02:45:30 -0500

kaczjer's avatar

Dear Sir or Madame,

I am writing if HAP ver 5.1 is compatible with ASHRAE 90.1-2010 G3.1.3.13

Generally it is software approved by GBCi, but in my opinion the operation of System Type 7 - VAV minimum airflow is not correct and I am not sure if it can be correctly set.

G3.1.3.13 requires to set minimum airflow of 30% of Design Airflow based on automatic sizing. So if zone is in deadband temperature range the airflow should be set to 30% of max airflow in design cooling conditions.

However in HAP 5.1 we need to set Reheat Box Design Supply Temperature. If we set it as recommended - 35 C it calculates design heating airflow for each zone which is close to cooling max airflow in colder climates.

The problem is that in such case HAP uses sized heating airflow as a minimum airflow temperature instead of 30% of design airflow. That results in huge Baseline Energy Use for fan ( mainly) heating and cooling and GBCI Reviewer noticed it and wants a explain why is it so high.

As example... One of my system Design Airflow Rate based on Cooling Sizing is 6717 m3/hr and Airflow for Winter Design is 5617m3/hr, so minimum Airflow should be 2051 m3/hr when all zones are in deadband temperature range, however the minimum is 5617m3/hr.

My question is if there are some workarounds? or maybe it is acceptable but I cannot find how?

Many Thanks for Help

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