Hi,
Greetings!
We are doing the energy model for Office space which has registered under LEED ID+C v4. The overall floor area of the project space is 45,000 Sq.ft & the overall floor area is 1,20,000 Sq.ft. Conditioned area of project space is 38,000 Sq.ft & the overall conditioned area is 1,00,00 Sq.ft. This is G+4 Floors building.
As per Baseline Energy Model/Appendix G,
The baseline system is system 6 – PVAV with PFP Boxes & we have considered one system per floor. However, we have decided to consider exception of G3.1.1
c. If the baseline HVAC system type is 5, 6, 7, 8, 9, 10, 11, 12, or 13 use separate single-zone systems conforming with the requirements of system 3 or system 4 (depending on building heating source) for any spaces that have occupancy or process loads or schedules that differ significantly from the rest of the building. Peak thermal loads that differ by 10 Btu/h·ft2 or more from the average of other spaces served by the system, or schedules that differ by more than 40 equivalent full-load hours per week from other spaces served by the system, are considered to differ significantly.
For the above-mentioned exception, we have calculated the peak thermal load for all the conditioned spaces by considering the following energy model inputs/methods.
- Baseline system is 6
- Auto sized capacity (Cooling 1.15 & Heating 1.25)
- Supply air temperature difference is 20 deg F
Our software has provided the floor area and peak thermal load in KBTU/Hr. From these, we have calculated the BTU/Hr/Sq.ft. Also, we have compared each room’s BTU/Hr/Sq.ft with an average BTU/Hr/Sq.ft of rest of spaces.
Finally, we have found that which are the spaces are differing more than 10 BTU/Hr/Sq.ft.
Can this approach be correct?
Which system to be used for identified spaces? (System 3 or 4 or same 6)
Note:
80% of conditioned spaces are office, meeting & manager cabins
10% is corridors
10% - Elec, kitchen & storerooms.
We look forward to your kind response.
Thanks.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 2, 2019 - 11:46 am
If your calculations demonstrate that the exception applies then you must apply it. You must use the same fuel type so if it is a system 6 for the balance of the building then you use a system 4 for the spaces where this exception applies. So which spaces does the exception apply?
SSN Energy Model
Mechanical Engineer5 thumbs up
October 2, 2019 - 2:20 pm
As per the baseline simulation, 53% of the offices are differing more than 10btu/hr/sq.ft while comparing with avg peak load of other zones. Rest of the spaces are under 10btu/hr/sq.ft.
So, can I use the system 4 with CAV for 53 % of the spaces. System 6 for remaining conditioned spaces. Please let me know your reply.
Is there any CIR for the same. Thanks...
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 2, 2019 - 2:42 pm
Typically you will not have this degree of difference between similar or the same space type. You generally have this difference if the spaces have vastly different temperature set points or large internal loads. If you are claiming this exception for some office areas it will most definitely be questioned by the reviewer. I am not aware of a CIR on this subject.
SSN Energy Model
Mechanical Engineer5 thumbs up
October 2, 2019 - 2:51 pm
There is no highly use process equipments in the office spaces. Only plug load/EPD. The only difference between these office spaces are glazing area, orientation and location. So these factors only the reasons for the peak load.
Once again please refer below,
LPD, u values, shgc are as per ASHRAE.
Cooling capacity and supply air are auto sized.
Fresh air and no of people are as per ventilation calc.
Once again thanks....
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
October 2, 2019 - 2:57 pm
If you are going to try and claim this you will need to provide all your calculations to demonstrate this difference to the reviewer. What you are claiming is highly unusual.
Waleed AlGhamdi
Sustainability EnablerEskew+Dumez+Ripple
18 thumbs up
October 2, 2019 - 5:52 pm
Given the location of the project in the UAE this might be the case, and in my opinion, the 10 Btuh/SF in the exceptions is kind of a loophole for an extreme climate zone like this. I recall doing an exercise for a city in the Middle East where the difference was more than 50 Btuh/SF, all due to enormous solar gain through the glazing when compared to core zones. As a sanity check I removed all glazing and the difference in peak loads between the perimeter and core zones dropped dramatically.
I'd say before taking advantage of the exception take a look at unmet load hours and box flow rates.
SSN Energy Model
Mechanical Engineer5 thumbs up
October 2, 2019 - 8:49 pm
Thank you for the valuable guidance and support...