rgrace
Sawhorse
Keeping in line with baffling consistency questions brought on by ever changing energy code requirements, I will venture into this arena in an attempt to gain some logical explanation to specific demand control ventilation code language and try to decipher exactly what the intent is. Note the thread title code section reference; the code section in the 2018 IECC is C403.7.1 and in the 2021 IECC is not yet known. This requirement has not been in the same location since it's birth in the 2009 IECC and I suspect will continue to relocate every time we have a new edition.
Without going into too many details, I am trying to apply Exception 4 and I am struggling with the term "supply airflow rate." My understanding of "supply" is that it is a combination of outdoor air mixed with recirculated air.
That being said - scenario - A2, dining area and kitchen area only. RTU provides 8,000 supply air. 3,800 of this is outdoor air delivered to dining area (required by IMC). 3,500 is transferred into the kitchen for use as makeup air for the Type I hood system (permitted by IMC and encouraged by IECC). If my "supply airflow rate" is 8,000 and I subtract my "outgoing transfer air" being used for makeup air (3,500), my total is 4,500 which is greater than 1,200 and would require DCV.
If the DCV reduces the outdoor air significantly based on the actual occupancy of the space (see DCV definition), there would not be sufficient makeup air for the hood system. This conundrum would require that the design professional provide a dedicated outdoor air makeup unit for the hood exhaust system. This is in direct conflict with what C403.2.8 is attempting to achieve, which is to eliminate the practice of providing dedicated outdoor air units which sole purpose is to provide makeup air to hood exhaust systems (and of course, waste energy).
Soooooo, if the term "supply airflow rate" was actually meant to be "outdoor airflow rate," the equation would look like this; If my "outdoor airflow rate" is 3,800 and I subtract my "outgoing transfer air" being used for makeup air (3,500), my total is 300 which is less than 1,200 and DCV would NOT be required.
Think it's just been wrong from it's birth and nobody (code officials that is) has paid any attention to it? Thoughts? Comments? Corrections?
Without going into too many details, I am trying to apply Exception 4 and I am struggling with the term "supply airflow rate." My understanding of "supply" is that it is a combination of outdoor air mixed with recirculated air.
That being said - scenario - A2, dining area and kitchen area only. RTU provides 8,000 supply air. 3,800 of this is outdoor air delivered to dining area (required by IMC). 3,500 is transferred into the kitchen for use as makeup air for the Type I hood system (permitted by IMC and encouraged by IECC). If my "supply airflow rate" is 8,000 and I subtract my "outgoing transfer air" being used for makeup air (3,500), my total is 4,500 which is greater than 1,200 and would require DCV.
If the DCV reduces the outdoor air significantly based on the actual occupancy of the space (see DCV definition), there would not be sufficient makeup air for the hood system. This conundrum would require that the design professional provide a dedicated outdoor air makeup unit for the hood exhaust system. This is in direct conflict with what C403.2.8 is attempting to achieve, which is to eliminate the practice of providing dedicated outdoor air units which sole purpose is to provide makeup air to hood exhaust systems (and of course, waste energy).
Soooooo, if the term "supply airflow rate" was actually meant to be "outdoor airflow rate," the equation would look like this; If my "outdoor airflow rate" is 3,800 and I subtract my "outgoing transfer air" being used for makeup air (3,500), my total is 300 which is less than 1,200 and DCV would NOT be required.
Think it's just been wrong from it's birth and nobody (code officials that is) has paid any attention to it? Thoughts? Comments? Corrections?