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Maximum Allowable Cooling Capacity. Bruce Wilcox, BSG Ken Nittler, Enercomp. 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
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Maximum Allowable Cooling Capacity Bruce Wilcox, BSG Ken Nittler, Enercomp
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
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
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
Exception 1 – Systems not Covered • No cooling system installed • Cooling system is not an electrically driven compression based system
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
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
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)
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
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
Standard Electrical Input Btu/Watt Cooling Capacity for Split Air Conditioners in the CEC Directory