Hello,
Addendum bl for ASHRAE 90.1-2010 provides a methodology (with equations) for removing fan energy from packaged equipment efficiency ratings for the baseline, which is very useful. However, when using the provided equations and the mandated EER from Table 6.8.1A for air-cooled air conditioners, I get a pretty substantial equipment efficiency increase for larger equipment sizes. For example, if the provided equations are used for air cooled air conditioners with "all other" heating type for different sizes, this is what I get for COPnf:
- 100 kbtu/h: 11.0 EER, 3.80 COPnf
- 200 kbtu/h: 10.8 EER, 3.82 COPnf
- 500 kbtu/h: 9.8 EER, 3.70 COPnf
- 760 kbtu/h: 9.5 EER, 3.78 COPnf
- 10,000 kbtu/h: 9.5 EER, 10.66 COPnf
For the 10,000 kbtu/h system, the mandated EER is 9.5, but the COPnf is 10.66, which is a higher efficiency than what a centrifugal water-cooled chiller of a similar size would need to be (COP 6.17). This seems like an oversight when the formulas were created and provided in the addendum.
Has this been encountered before? And is there an acceptable way to get a more sensible COP for larger sized baseline HVAC systems with DX cooling?
Thank you!
Joanne Choi
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
September 14, 2018 - 12:16 pm
You appear to be correct. I am not certain what went into the creation of the formula and if this was intended or not. Perhaps they are trying to encourage the use of more efficient central plants equipment in the larger size ranges?
In most cases the size of the baseline system will never get this big without having to use a chilled water system. This may happen in a single story building that is just under 150,000 square feet but those are rare.
We are not aware of another acceptable way to apply this calculation.
Gayathri Udhayakkumaran
EngineerEnergy Management Services Emirates
April 27, 2020 - 1:51 am
Hi Joanne/ Marcus,
I am stuck at the same point mentioned above. My project is just under 150,000 Sqft and a two-storey building. Baseline design auto-sized cooling capacity for the System 6- packaged VAV with PFP boxes is coming up to 4000 kBtu/hr (1 system per floor). And the adjusted COPnf is coming to 6.06. This is not allowing the project to achieve the minimum energy savings required by LEED.
Any updates from your side on the above discussions?
Tyler Thumma
7GroupLEEDuser Expert
67 thumbs up
June 10, 2020 - 2:59 pm
I don't see any updates on this issue, and checked the 90.1-2013 user's manual just to make sure. If you are using 90.1-2010 there is no requirement to apply Addendum bl and these formulas. Most simulation programs are capable of adjusting the efficiencies automatically, so that would be my first recommendation.
Alternatively, you could limit the cooling capacity in the formula to 760,000 Btu/h, since this is the size category capacity listed in Table 6.8.1A for the larger systems and could be a reasonable interpretation of the language in Addendum bl, which defines "Q" as "the AHRI-rated cooling capacity."