Maximum Allowable Cooling Capacity

1. Maximum Allowable Cooling Capacity Bruce Wilcox, BSG Ken Nittler, Enercomp

2. Overview • Air conditioners operating on peak in California’s hot central valley climates typically draw 1.7 kW/ton of rated capacity • Field data indicates that oversizing is common • The most reliable way to capture peak electrical demand savings from envelope and duct measures required under the standards is to ensure that air conditioners are appropriately sized

3. Proposed Changes • Proposal expands current sizing requirements to include calculation of a Maximum Allowable Cooling Capacity • Goal is to prevent gross oversizing • Alternative Calculation Method software will be required to do calculations • Procedures allow calculations based either on whole building or for each separate cooling system • Tradeoff for systems with larger cooling capacity but same peak demand

4. Proposed Language • Standards • Section 150(h)3 establishing the maximum allowable cooling capacity • Two exceptions • ACM Manual • Appendix L - Procedure for calculating design cooling capacity • Appendix M - Procedure for calculating maximum allowable cooling capacity • Appendix N – Procedure for calculating electrical input exception

5. Exception 1 – Systems not Covered • No cooling system installed • Cooling system is not an electrically driven compression based system

6. Appendix L – Design Cooling Capacity • Follows ASHRAE 2001 Fundamentals Chapter 28 Residential Loads • Using • Region X Design Data • Block Loads either whole building or by cooling system • Specific Rules to select Tables • Title-24 U-factors, SHGC values, Infiltration, Duct Efficiencies, Radiant Barriers • Load is adjusted to rating conditions to get Design Cooling Capacity

7. Capacity at Standard Rated Conditions • 95 F outdoor dry bulb • 67 F indoor wet bulb • Capacity = Load / (0.88 – 0.002286 x T) Where: Capacity = Design Cooling Capacity (Btu/hr) Load = Sensible Design Cooling Load (Btu/hr) T = Outdoor Cooling Design Temperature (F) – 95

8. Appendix M – Maximum Capacity • Uses Design Cooling Capacity from Appendix L • Allows next largest size to be selected • For buildings with more than one cooling system that have the design cooling capacity calculated for the entire building Maximum Allowable Cooling Capacity = Design Cooling Capacity + (6000 x Number of Cooling Systems)

9. Maximum Allowable Cooling Capacity

10. Multiple Orientations • Maximum Allowable is the highest of the four cardinal orientations • For buildings with more than one cooling system, the orientation may be different for each system

11. Exception 2 – Electrical Input Exception Appendix N • Allowed to exceed maximum allowable cooling capacity if the proposed total electrical input of the oversized system is less than or equal to the standard electrical input • Standard total electrical input is equal to 0.117 x Design Cooling Capacity • Proposed electrical input includes compressor and fan energy • Proposed electrical input is from CEC Directories of Certified Equipment • Proposed fan energy is 0.017 W per Btu of design cooling capacity or may be measured as part of new duct measurement procedure

12. Standard Electrical Input Btu/Watt Cooling Capacity for Split Air Conditioners in the CEC Directory