ASHRAE Fundamentals Handbook — Hydronic System Design
What it means on the job
The decoupler (common) pipe connections must be spaced at least 4 to 6 pipe diameters apart so primary and secondary loops are genuinely hydraulically decoupled; at 2 diameters the two loops interact and flow in the common pipe no longer reflects the true surplus or deficit. Note what is NOT the defect here: the absence of isolation valves on the decoupler is CORRECT as installed — valving the common pipe would defeat decoupling entirely.
Tested in 1 CraftIQ puzzle
- whats-wrongPrimary/Secondary Pumping System
Related ASHRAE sections
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 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.
ASHRAE Guideline 13, Specifying Building Automation Systems (advisory) — applied through the project BAS specification, Division 25
The installed sensors meet the specification. ASHRAE Guideline 13 (advisory, applied via the project BAS specification) 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.
CraftIQ explanations are original educational commentary written in trade language and verified against the cited standards. Always confirm requirements against the code edition adopted by your jurisdiction — this is training material, not a substitute for the code book or your AHJ.