With the winter weather upon us and the cold spell we had at the end of December, we took the time to review some of the means for freeze protection of piping and equipment with our staff. Our goal of continuous quality improvement turned into more of a round table discussion with various team members giving tips and lessons learned over decades in the industry.
We discussed several topics, including proper determination of heat trace sizing, differences between propylene and ethylene glycol, and the advantages and disadvantages of using a glycol solution. We also reviewed the benefits of recirculation pumps at hydronic preheat coils, the operation of specialty freeze-proof coils, and the practicality of using an energy recovery ventilator for preheating. We discussed which equipment needs to be on emergency power to keep pipes from freezing, from common items like heat trace and circulation pumps to overlooked items like control panels and network routers.
One of the specific items we touched on is freeze stat sensor alarms in air handling units. Generally, freeze stats should either be located on the downstream side of the first heating coil or the upstream side of the first non-heating coil to be protected. Freeze stats are mechanical devices that shut down the air handling unit upon detection, requiring a manual restart; the setpoint is often 40 degrees F. If repeated nuisance alarms are received, shutting down the unit when nothing seems amiss, do not assume the freeze stat is malfunctioning or incorrectly set. Experience tells us that a properly installed freeze stat is exceptionally reliable and typically alerts you to an actual condition. While some devices have an adjustable setpoint, investigate any potential freeze issues that would lead to a burst coil or pipe before changing the setpoint. Note that it would take a sustained freezing temperature to burst the coil, which may not be apparent in a control system sensor reporting an average temperature.
We all deal with freezing conditions this time of year, and knowing the proper means to combat those conditions helps us prevent broken pipes and coils. Not only does this prevent costly water damage, but in the current marketplace, it ensures that supply chain issues don’t leave you out in the cold for several months. If you have questions about what method of freeze protection is suitable for your application, please do not hesitate to contact Douglas Barnhart, PE, at 717-845-7654 or dcb@ba-inc.com.