ASHRAE Guideline 36 / Crestline Controls Specification

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.

ASHRAE Guideline 36 / Manufacturer maintenance requirements

Dirty CRAH coils reduce heat transfer efficiency significantly, potentially losing 20-40% of cooling capacity. Regular coil cleaning is required per ASHRAE maintenance guidelines. Reduced capacity leads to higher server inlet temperatures and potential thermal shutdowns.

ASHRAE Guideline 36 / Manufacturer Requirements

Chillers require a minimum runtime (typically 15-30 minutes) and minimum off-time (typically 15 minutes) to prevent compressor short-cycling. Frequent starts damage the compressor motor and reduce equipment life.

ASHRAE Handbook — Fundamentals, Chapter 7

A thermostat behind a door that is typically held open will be in stagnant air and will not sense the true space temperature. It must be in an area with representative airflow of the occupied zone.