Guideline 36-2021: High-Performance Sequences of Operation for HVAC Systems
About this book
ASHRAE Guideline 36-2021: High-Performance Sequences of Operation for HVAC Systems, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), is the most significant advance in HVAC control specification to emerge in decades. The guideline provides fully detailed, vendor-neutral sequences of operation for the most common commercial HVAC system types, enabling consistent high-performance control implementation that is estimated to reduce energy consumption by 20-40% compared to conventionally specified and commissioned systems. Guideline 36-2021 recognises that the primary cause of poor HVAC energy performance in commercial buildings is not hardware limitations but inadequate control sequences — vague or incomplete specifications that leave implementation to building automation system (BAS) vendors who may optimise for lowest installation cost rather than operational performance.
By providing detailed, unambiguous sequences of operation that can be referenced by specification and verified during commissioning, the guideline addresses this fundamental gap. The sequences are organised by system type. Variable air volume (VAV) systems receive the most extensive treatment: detailed control logic for supply air temperature reset, supply static pressure reset, zone-level minimum outdoor air control (DCV with CO₂ sensing), occupancy-based setback, economiser operation, and supply fan speed control.
Each sequence includes state diagrams, setpoint calculation algorithms, and alarm logic. The guiding principle throughout is trim-and-respond logic: systems continuously adjust setpoints based on real demand signals rather than operating at fixed design setpoints that may be significantly above actual demand. Parallel sequences are provided for air handling units, fan coil units, dedicated outdoor air systems (DOAS), chilled water plants (with sequencing of multiple chillers and cooling towers), hot water boiler plants, and heat recovery systems.
The sequences explicitly address common energy waste sources: simultaneous heating and cooling, excessive outdoor air beyond code minimums, pump and fan operation at excessive speeds when demand is low, and unnecessary equipment running during unoccupied periods. Guideline 36-2021 is designed for implementation with BACnet control systems and uses BACnet-standard point naming conventions throughout. It is increasingly referenced in LEED commissioning documentation and by energy codes as a specification standard for high-performance HVAC control.