ASHRAE 90.1-2019, Section 6.5.4.4 / Guideline 36

ASHRAE 90.1-2019, Section 6.5.1.1 / ASHRAE 62.1

This economizer setup is code-compliant on multiple fronts. The 75 degrees F dry-bulb lockout aligns with ASHRAE 90.1 Table 6.5.1.1.3 for most climate zones. The enthalpy limit adds humidity protection per ASHRAE 90.1 Section 6.5.1.1. The 20% minimum outdoor air damper position during occupied hours ensures ventilation compliance with ASHRAE 62.1 — the damper never fully closes when people are present. The CO2-based demand-controlled ventilation above 1,000 PPM is an accepted method per ASHRAE 62.1 Section 6.2.7 for adjusting ventilation based on actual occupancy. This is a well-programmed, energy-efficient, code-compliant sequence.

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, Table 6.5.1.1.3

ASHRAE 90.1 Table 6.5.1.1.3 specifies fixed dry-bulb high-limit shutoff temperatures by climate zone. For Climate Zone 4A, the fixed dry-bulb limit is 75 degrees F. This setup correctly locks out the economizer when outdoor air is too warm to provide free cooling. Differential enthalpy is an alternative method.

ASHRAE 90.4 / TIA-942

Branch circuit monitoring is required for capacity planning and to detect load imbalances. ASHRAE 90.4 mandates metering of electrical distribution in data centers, and most Tier III+ designs require per-circuit monitoring.

ASHRAE Fundamentals Handbook — Hydronic System Design

The decoupler pipe should not have isolation valves — this is correct as installed. However, the decoupler pipe connections are spaced only 2 pipe diameters apart. Connections must be spaced at least 6-10 pipe diameters apart to prevent flow turbulence and ensure proper hydraulic separation.