ASHRAE Guideline 36 — Redundant Equipment / high-rise office Mechanical Specification

ASHRAE Guideline 36 — Freeze Protection

A freeze stat alarm must automatically shut down the AHU fan, close the outdoor air damper, and open the heating valve. An alarm-only response without automatic action risks coil freeze-up and catastrophic water damage.

ASHRAE Guideline 36 — High-Performance Sequences of Operation

The DP sensor is located at the pump discharge instead of at the most remote coil or 2/3 of the way out in the system. Sensing DP at the pump header causes the VFD to maintain artificially high system pressure, defeating the purpose of variable flow. The sensor must be relocated to represent the actual system load point.

ASHRAE Guideline 36 — Monitoring Requirements

Temperature trend data should have at least 0.1 degree resolution. Whole-number-only resolution (e.g., 72 vs. 72.3) loses critical information needed for analyzing control loop performance, setpoint drift, and energy optimization.

ASHRAE Guideline 36 — Redundant Equipment Staging

Redundant CRAC units must have one designated as lead and one as lag. Setting both as lead causes both units to run at full capacity simultaneously, wasting energy and eliminating redundancy protection. The Liebert vNSA switch must coordinate lead/lag sequencing so only one unit operates at a time under normal conditions.

ASHRAE Guideline 36 — Section 5.18

The installed sensors meet the specification. ASHRAE Guideline 36 recommends space temperature sensors with accuracy of +/- 0.5 degrees F or better for zone control. The 10K thermistor is a standard sensor type for DDC systems, providing adequate accuracy for HVAC zone control.

ASHRAE Guideline 36 — Sensor Placement

Temperature sensors must not be placed in direct airflow from supply diffusers. The supply air temperature causes false readings, making the controller unable to maintain proper space temperature setpoint.