ASHRAE Fundamentals Handbook — Hydronic System Design

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.

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 Guideline 12 — Minimizing the Risk of Legionellosis

Without automatic blowdown control, condenser water cycles of concentration are unmanaged. Manual blowdown is unreliable and either wastes water (over-blowing) or allows mineral concentration to build (under-blowing). An automatic conductivity controller with a motorized blowdown valve is required to maintain proper cycles of concentration (typically 3-6 cycles).

ASHRAE Guideline 13 — Alarm Management

Alarms must be prioritized based on severity. A freeze stat alarm (life-safety) should be higher priority than a dirty filter alarm (maintenance). Without prioritization, critical alarms get lost in nuisance alarms, a condition called 'alarm flooding'.

ASHRAE Guideline 13 — Data Management

Storing trend data only in field controllers risks data loss when controllers are reset or lose power. Trend data should be archived to the BAS server or a dedicated historian. Controller memory is limited and will overwrite oldest data.