ASHRAE 90.1-2019, Section 6.5.1.1 / ASHRAE 62.1

ASHRAE 90.1-2019, Section 6.4.3.3

Night setback/setup is required by ASHRAE 90.1 for buildings with DDC. The heating setback to 55 degrees F prevents freezing while saving energy. The 90 degrees F cooling setup prevents extreme overheating while allowing the cooling system to rest. The 30-minute pre-start is an acceptable fixed lead time, though optimal start is preferred for larger buildings.

ASHRAE 90.1-2019, Section 6.4.3.3.3

Optimal start is not just allowed — it is required by ASHRAE 90.1 for systems with DDC controls. The algorithm must bring the space to occupied setpoint by the scheduled occupancy time using the minimum energy. Using outdoor temperature, space temperature, and historical data is the recommended approach per ASHRAE Guideline 36.

ASHRAE 90.1-2019, Section 6.5.1.1

In humid climates, dry-bulb economizer control can introduce excessive moisture. ASHRAE 90.1 and Guideline 36 require differential enthalpy or fixed-enthalpy control for climate zones where humidity is a factor.

ASHRAE 90.1-2019, Section 6.5.3.2.2

ASHRAE 90.1 requires static pressure reset for VAV systems with DDC. A fixed setpoint wastes fan energy during part-load conditions. The setpoint should reset down based on zone damper positions — when all dampers are less than 90% open, the static pressure setpoint should decrease. ASHRAE Guideline 36 specifies Trim and Respond reset logic for static pressure.

ASHRAE 90.1-2019, Section 6.5.4.4 (temperature reset) / Section 6.5.4.2 (variable-flow DP reset) / Guideline 36

This chiller plant sequence fails ASHRAE 90.1-2019 Section 6.5.4.4 (Chilled- and Hot-Water Temperature Reset Controls), which requires chilled water supply temperature reset for systems with DDC controls. A fixed 44 degrees F supply temperature forces the chillers to work harder than necessary during mild weather and part-load conditions — wasting significant energy (roughly 1-2% per degree F of potential reset). Additionally, the fixed differential pressure setpoint on the variable-flow pumps violates Section 6.5.4.2 (Hydronic Variable Flow Systems), which requires the DP setpoint on DDC variable-flow pumps to be reset downward based on valve positions. Best practice per ASHRAE Guideline 36 likewise resets DP based on the most-open control valve position, reducing pump speed when full design pressure is not needed. Both reset strategies — supply water temperature and differential pressure — are essential for energy code compliance and efficient chiller plant operation.

ASHRAE 90.1-2019, Section 6.5.4.4 / Guideline 36

This is a proper implementation of chilled water supply temperature reset per ASHRAE 90.1-2019 Section 6.5.4.4 (Chilled- and Hot-Water Temperature Reset Controls) and Guideline 36 Trim and Respond logic. Raising chilled water temperature when loads are low improves chiller efficiency significantly — roughly 1-2% per degree F of reset. The valve position-based reset ensures cooling capacity is available when needed.