Hi to all,
This multyfamily building has 10 floors and 4 residential apartments per floor. For each apartment, there is only air-conditioning units in the living room, but no air-conditioning units in the bedrooms.
Regarding the modeling protocol for the conditioned spaces, should I model just only the spaces that are conditioned or should I model the complete apartment as if it was full conditioned, considering the baseline HVAC system for both the baseline building as well as for the proposed building spaces that currently are not conditioned?
Thank you in advanced.
David Eldridge
Energy Efficiency NinjaGrumman/Butkus Associates
68 thumbs up
August 6, 2018 - 6:52 pm
One clarification might be that although the A/C unit may be located in the living room, the bedroom may still be cooled from that unit either indirectly or by allowing a duct between the rooms or transfer air.
What is the location (general description if you can't be specific) and maybe if you can describe the heating system we'll have a better feel for your building.
If the whole facility is heated, and the bedrooms might be indirectly cooled, I would still model the whole building as being conditioned but perhaps the bedrooms may have a higher temperature setpoint during the summer season.
The model may over estimate energy consumption then if some occupants shut their doors and prevent the bedrooms from being conditioned or if the occupants may tend to use operable windows for cooling.
Gustav Alfaro
Mechanical Engineer16 thumbs up
August 6, 2018 - 7:16 pm
Thanks for your response. The building is located in a mild weather location (1271 CDD and just 105 HDD), there is no heating for any space since wont be required.
I would like to understand if I have to model an air-conditioning system for those spaces that have no AC design, I am confused since an interpretation of ASHRAE 90.1 is that I should model the baseline HVAC system for those spaces, but dont know if my interpretation is correct.
Regards,
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
August 7, 2018 - 11:00 am
It sounds like the bedrooms are indirectly cooled, so they would be part of the HVAC zone that includes the entire apartment. The location of the unit does not really matter. The entire space is conditioned, so it needs to have a system for baseline. The system in the baseline will be sized for the whole zone. You might be able to justify the creation of a separate zone in the bedrooms, with a different temperature setting but I would think this would need to be backed up with some considerable study of how the temperatures would vary within the actual design.
How are the air conditioning units being sized?
Gustav Alfaro
Mechanical Engineer16 thumbs up
August 7, 2018 - 9:01 pm
Thanks Marcus.
The air-conditioning units are sized just only for the living room area, all of the other spaces are not conditioned so I am not sure if I can justify that the other spaces are indirectly cooled since they have partitions and doors.
My understanding is that the baseline case must be modeled with a single air-conditioning unit for the whole dwelling unit, is this correct? And my proposal for the proposed case is to model the as-designed air conditioning unit for the living room, and the baseline unit for the remaining of the spaces, does this make sense?
Regards
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
August 8, 2018 - 11:27 am
The nature of the partitions and the door opening will influence whether this is indirectly conditioned or not. This comes down to whether the bedroom spaces meet the definition of indirectly conditioned. So the first thing I would do is to look at the definition and make that determination. If it is not indirectly conditioned then it is unconditioned. If it is unconditioned then it will be unconditioned in both models. If it is indirectly conditioned and the unit is only sized for the living space you may run into unmet load hour issues. If you do you will probably have to increase the temperature settings until you get the unmet load hours below the limit. The temperature setting must be identical in both models.
As an aside if the whole unit is fully conditioned in the baseline and is not in the proposed this would not be fair comparison but it would increase the baseline energy use and therefore, increase your savings. So I agree that both models should include the bedrooms as indirectly conditioned or as unconditioned in order to generate a fair comparison.
Gustav Alfaro
Mechanical Engineer16 thumbs up
August 8, 2018 - 11:38 am
Thanks Marcus, as always your feedback is crystal clear.