Dear all,
I need your professional opinion about a project that I am currently working on.
The HVAC zones and zone groups tree is like: Group 1>A(5)>A.1(Master), A.2, A.3, A.4 and A.5. They are 5 different spaces (corridor, offices, conference, and storage). These five rooms are conditioned by one RTU. Room A.1 is the master room and where the thermostat is. The other rooms will only be conditioned when the master room is conditioned.
I have two questions.
First, can I treat these 5 zones as 5 different HVAC zones even though they are conditioned by one RTU?
HVAC zone definition from ASHRAE: a space or group of spaces within a building with heating and cooling requirements that are sufficiently similar so that desired conditions (e.g., temperature) can be maintained throughout using a single sensor (e.g., thermostat or temperature sensor)
If they are 5 different HVAC zones, this means that I have 5 different thermal blocks. Per ASHRAE 90.1-2013 Table G3.1 No. 7, each HVAC zone shall be modeled as a separate thermal block.
The proposed project uses over 30 RTUs. When creating the baseline for this project, system 6 should be utilized. My second question pertains to the RTUS. Can the RTUs be simply replaced by fan-powered boxes (which means one fan power box conditions multiple thermal blocks) or should one fan-powered box be assigned to one thermal block?
Thank you
Tyler Thumma
7GroupLEEDuser Expert
60 thumbs up
February 14, 2020 - 8:44 am
Your HVAC zones/thermal blocks should correspond to the thermostats in the design. So if your design only includes a single thermostat for these five rooms, they would be combined into a single HVAC zone/thermal block for modeling.
In the Baseline, all the thermal blocks on a given floor are served by a single System 6, with a fan-powered box for each thermal block.
Ying Lindsey
6 thumbs up
February 14, 2020 - 10:51 am
Thank you for your comment. Could you please clarify what do you mean by combining five rooms into a single HVAC zone/thermal block?
Tyler Thumma
7GroupLEEDuser Expert
60 thumbs up
February 14, 2020 - 11:09 am
I'm not sure how you would specifically do this in IES, that might be a question for their support team.
Ying Lindsey
6 thumbs up
February 14, 2020 - 11:47 am
Thank you, could you please clarify which software you are referencing for offering the method by combining five rooms into a single HVAC zone/thermal block, and how will you do it by using that software? The reason I asked since I might need to use the other software in future (it might be the one you are referencing) and I might need to deal with a similar design condition again.
Tyler Thumma
7GroupLEEDuser Expert
60 thumbs up
February 14, 2020 - 12:02 pm
This will be very software-specific so it is difficult to generalize the guidance. If the software creates individual spaces for each room shown on the drawings, there will be five spaces modeled which will need to be assigned to a single HVAC zone with a single thermostat in the control zone. If you are creating the spaces manually you could just combine all five rooms into a single "space" which is representative of the entire HVAC zone.
3 thumbs up
May 28, 2020 - 5:41 pm
Tyler, Your last comment "if you are creating the spaces manually, you could just combine all five rooms into a single space which is representative of the entire HVAC zone" doesnt' sound right. What if the five rooms are of varying space types? Perhaps two are the same space types, which could be combined, for argument's sake. But I don't believe you could combine say a classroom with a storage room, with a conference room, with an office for example? Please provide further feedback.