Maximum Allowable Cooling Capacity

1
Maximum Allowable Cooling Capacity

• Bruce Wilcox, BSG
• Ken Nittler, Enercomp

2
Overview

• Air conditioners operating on peak in
  Californias 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