What Is ASHRAE Guideline 36?

ASHRAE Guideline 36, "High-Performance Sequences of Operation for HVAC Systems," provides standardized control sequences for common HVAC system types — VAV (Variable Air Volume) air handling units, VAV terminal units, chilled water plants, and hot water heating plants. Published in 2018 with an updated edition in 2021, it represents the current best practice in HVAC control, encoding decades of building science research into implementable control logic.

ASHRAE Guideline 36 is increasingly specified by energy-conscious owners, required by some energy codes, and recognized by LEED v4.1 (under Optimize Energy Performance credit) as a pathway to demonstrate advanced controls.

Why Typical HVAC Controls Waste Energy

Most HVAC systems are controlled with simplified sequences that don't optimize system-wide efficiency. Common problems:

  • Supply air temperature set to a fixed value (e.g., 55°F) regardless of actual cooling demand — this causes over-cooling and simultaneous reheat
  • Duct static pressure maintained at a fixed setpoint (e.g., 1.5 in. w.g.) regardless of actual airflow needs — fans run faster than necessary
  • Chilled water setpoint fixed at 44°F rather than reset upward when cooling loads are low
  • No coordination between cooling plant operation and time-of-use electricity rates

Guideline 36 Key Sequences

Trim and Respond (T&R) for Static Pressure Reset — instead of fixing duct static pressure at a constant value, T&R adjusts it dynamically. At a defined interval, the system "trims" (decreases) the static pressure setpoint. If any VAV terminal unit requests more air (its damper is fully open), it sends a "respond" request, and the static pressure setpoint increases. The result: static pressure is always as low as possible while meeting all zone demands, saving significant fan energy.

Supply Air Temperature Reset — supply air temperature (SAT) is reset upward based on zone cooling demand. When all zones are comfortable with minimal cooling, SAT rises toward 65–68°F, dramatically reducing cooling energy and reheat energy.

Demand-Controlled Ventilation (DCV) — CO₂-based DCV adjusts outdoor air delivery to each zone based on actual occupancy signals, coordinated at the AHU level through the ventilation efficiency calculations of ASHRAE Standard 62.1.

Economizer Controls — precise logic for when to use outdoor air for "free cooling" versus mechanical cooling, with differential dry-bulb or enthalpy comparison and high-limit shutoff conditions.

Energy Savings Potential

Lawrence Berkeley National Laboratory (LBNL) research quantifies the savings. A California commercial building study found that implementing Guideline 36 sequences (versus conventional fixed setpoint controls) reduced HVAC energy consumption by an average of 29% in new construction and up to 35% in retrofits of existing VAV systems. Fan energy savings are typically the largest component (40–60% reduction), followed by cooling plant energy and heating energy.

Implementation Requirements

Guideline 36 requires a capable, open-protocol BAS (BACnet is preferred) and programmable DDC controllers at both the AHU and terminal unit levels. The sequences are complex — approximately 100 pages of control logic — and require experienced controls engineers to implement and commission correctly. Functional testing during commissioning is critical; improperly tuned T&R gains or incorrect CO₂ sensor calibration can negate the savings.