Solving Freeze Stat Trips: Advanced Diagnostics at NJ R&D Facility

As any facility manager can attest, failure of freeze protection systems can have serious and costly consequences. Designed to protect hydronic systems from freezing and subsequent pipe or coil ruptures, these systems serve as critical safeguards against damage during frigid weather. Over the past five decades, MSC has encountered numerous freeze-related issues, including HVAC coil breaks, frozen sprinkler lines, plumbing failures, steam condensate problems, and condenser water issues.

Case Study: Freeze Crisis at R&D Facility

A large research and development facility with multiple 100% outside air (OA) HVAC systems was experiencing repeated freeze stat trips during a prolonged cold spell, causing costly business interruptions. As is typical with 100% OA systems, the exhaust is interlocked with the supply, meaning all air circulation stops during a trip. This shutdown can affect critical pressurization requirements in airlocks and compromise lab hood functionality. Upper management needed the problem resolved immediately, especially since other contractors had already made several unsuccessful attempts to fix the issue.

Our Diagnostic Approach

After meeting with facility personnel directly involved with the systems to establish background on the freeze stat trips, MSC verified proper installation of freeze stats and related instruments, and confirmed all equipment was functioning correctly. Using NIST-calibrated instruments, our team verified that the systems met design specifications for preheat water temperatures and flow rates, AHU CFM airflow measurements, and pressure drops across equipment. We also performed temperature and velocity profiles throughout the air handling units and carefully trend-logged critical parameters, including outside air temperature and humidity, discharge air temperature, preheat water temperature, and preheat two-way control valve position.

Identifying the Root Cause

Analysis of the collected data revealed an issue with temperature profiles in some of the AHUs, particularly when control valve positioning dropped to approximately 25% or less. To investigate further, we incorporated a FLIR thermal imaging camera, which clearly revealed temperature variations across the coils, indicating significant temperature concerns at low control valve positions.

The Solution

After reviewing all collected information and evaluating various options, MSC recommended installation of freeze protection pumps at each laboratory AHU. These pumps would activate automatically when outside air temperature reached 40°F and below, maintaining proper coil circulation and temperature to prevent unnecessary freeze stat trips and associated business interruptions. While awaiting the arrival of the new pumps, we implemented a temporary measure: preventing preheat control valves from closing below 35% open and providing offset cooling to maintain proper discharge air temperature.

Results

Once the freeze protection pumps were successfully installed, controlled, and inspected using the thermal imaging camera, MSC was able to verify that the freeze stat problem was completely corrected, allowing the systems to operate properly without interruption.

Need freeze protection diagnostics for your HVAC systems? Please contact MSC to learn how our advanced diagnostic techniques and proven solutions can protect your facility from costly freeze damage and business interruptions.