Dear all,
I have a question regarding the core and shell proposed model. Here I use the HVAC main system designation to mean the main air loop, excluding terminal units. I summarized three scenarios for the proposed HVAC system for core and shell space. Please correct me if the summary is wrong or not complete.
1. The HVAC systems and terminal units have been designed for the core and shell project, but the function of the tenant space has not been determined yet.
The capacity, efficiency, supply fan power, and supply air flowrate should be hard sized for the HVAC system to be the same as what has been designed. The terminal unit type should be simulated to be the same as what has been designed, but the coil capacity and the airflow rate should be auto-sized.
2. The HVAC systems have been designed, but the terminal units have not been designed yet.
The proposed model simulates the tenant space terminal units to be the same as the baseline model. But the model simulates the main HVAC system to be the same as what has been designed, which includes hard- size for the capacity, efficiency, supply fan power, and supply air flowrate.
3. Neither the main HVAC system nor terminal units have been designed. The proposed model HVAC system should be simulated to be the same as the baseline model. The capacity, supply fan power, and supply air flowrate should be auto-sized for both the HVAC system and the terminal units. Additionally, the HVAC system efficiency should be calculated per ASHRAE 90.1 Appendix G.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
November 19, 2020 - 1:13 pm
1. If the whole system has been designed including coil capacity and airflows then that is what should be modeled. There should be no autosizing.
2. correct
3. correct
Ying Lindsey
6 thumbs up
November 19, 2020 - 5:20 pm
Thank you for your response, Marcus.
For item 1. Suppose the System leveled AHU is a DOAS, but the zone leveled terminal units are VRF fan coil units. The coil capacity and airflow for these terminal units have been designed already, but the zone function of the VRF served areas are not determined yet. This means that there might be three VRF fan coil units for the whole floor, but the branch ducts from the fan coil unit to the zone level and the internal walls are not designed yet. Under this condition, can the modeler auto-size the fan powers and the coil capacities for the terminal units? If the modeler cannot auto-size the terminal units, should the modeler combine three fan coil units to be a single fan coil unit to condition the whole floor? (If the modeler simulates three VRF fan coil terminal units as what has been designed, it is hard to determine which terminal unit conditions which zone.)
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
November 27, 2020 - 1:09 pm
If it has been designed then model it as such. If not designed then you can auto-size.
Ying Lindsey
6 thumbs up
December 1, 2020 - 6:09 pm
Thank you for your reply Marcus, but I am still confused so please let me clarify my question. For item 1, I don't know if it can be defined as "has been designed". Could you please clarify? The condition described in item 1 is that the VRF fan coil units per floor have been designed (coil size, fan power, and supply air CFM have been designed) but the branch ducts and diffusers for each VRF fan coil unit are not designed yet. What is more, we don't know if the tenant will use the VRF system or not since the tenant contract has not been signed yet. Under this condition, should I treat the VRF fan coil terminals like they have been designed or not designed?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
December 2, 2020 - 12:34 pm
Are they going to be installed in the building the way you have designed them? If so then it has been designed. It sounds like a part of the system has been designed and part has not yet been designed yet pending the space fit out. It makes no sense to me why you would design a part of a system and then the tenant would opt for a completely different system. Is that a likely scenario? Again if the VFR fan coil units are going to be installed then they have been designed.
Ying Lindsey
6 thumbs up
November 4, 2021 - 2:41 am
Hello Marcus, I would like your advice regarding one of my questions above. If the main HVAC system and the terminal boxes have been designed, but the branch ducts and diffusers for each terminal unit are not designed yet, and the tenant space is still a shell space. The proposed thermal blocks for the tenant space are determined through ASHRAE 90.1-2013 table G3.1 No.8(HVAC zone not designed) Under this condition how do I simulate the proposed terminal box? I am confused that although the terminal boxes have been designed already, I don't know which terminal box serves which part of the shell tenant space and I don't know if more terminal boxes will be added in the future either. I was thinking to simulate the proposed terminal box the same as the baseline terminal box (parallel fan-powered box) and ignore the terminal boxes that have been designed already. What about your opinion? Thank you.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
November 5, 2021 - 10:32 am
I think that if the terminal boxes have been designed then you have to model it with them included and not just ignore them.
Ying Lindsey
6 thumbs up
November 5, 2021 - 12:33 pm
Thank you Marcus. One more thing needs to clarify, in the future more terminal boxes might be added to the shell tenant space. In addition, the branches and diffusers are not designed for all terminal boxes. What confused me is, if I don't know the layout of the branches how should I decide which terminal box with designed CFM condition which thermal block?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
November 10, 2021 - 12:00 pm
Technically you could use the baseline parallel fan-powered box in the proposed as that is a conservative approach, just explain that to the reviewer.
To include the already designed boxes - Rather than specifying the design air flows for each zone, you could let the software autosize it. You would only specify the air flow for the entire unit.