Design Brief: Integrated Design for Small Commercial HVAC

November 1, 2003
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Table of ContentsBy using recommended design methods for rooftop heating, ventilation, and air conditioning (HVAC) systems, significant improvements in operational savings, energy efficiency, and indoor comfort can be achieved.

Small HVAC systems are the workhorses of the light commercial building market, which represents more than half of the annual commercial new construction floor area in California. Design, installation, and operations issues can prevent these systems from performing up to their full potential. This design brief focuses on actions that the architects, engineers, and design/build contractors can take to improve the energy efficiency of small HVAC systems, reduce operating costs, and improve indoor comfort and environmental quality. These actions include:

  • Practice energy-efficient design strategies such as reduced lighting power, high-performance glass and skylights, cool roofs, and improved roof insulation techniques in the overall building design.
  • Size units appropriately using American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) approved methods that account for the energy efficiency strategies implemented in the design, and use reasonable assumptions on plug load power and ventilation air quantities when sizing equipment.
  • Select unit size and airflow based on calculated sensible loads without oversizing. Consider increasing unit flow rate to improve sensible capacity in dry climates.
  • Specify units that meet the Consortium for Energy Efficiency Tier 2 efficiency standards; and incorporate premium efficiency fan motors, thermostatic expansion valves, and factory-installed and run-tested economizers.
  • Design distribution systems with lower velocities to reduce pressure drop and noise. Seal and insulate duct systems located outside the building thermal envelope.
  • Operate ventilation systems continuously to provide adequate ventilation air. Incorporate demand-controlled ventilation to reduce heating and cooling loads.
  • Specify commercial grade thermostats with the capability to schedule fan operation and heating and cooling setpoints independently.
  • Commission the systems prior to occupancy through a combination of checklists and functional testing of equipment control, economizer operation, airflow rate, and fan power.
  • Develop clear expectations of the services provided by HVAC maintenance personnel.
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