How Do HVAC Coils Freeze?
Frozen coils can wreak havoc on your HVAC system and building. It’s not just about repair costs – it’s about keeping your operations running smoothly.
How Do Fluid & Steam Coils Freeze?
What are Fluid HVAC Coils?
Fluid coils are a type of heat exchanger that can be used for both heating and cooling. They work by transferring heat from the water flowing through the coil to the air passing over it. Types of fluid coils include hot water coils, chilled water coils, and glycol coils.
How do Fluid Coils freeze?
At temperatures 32°F and below, water can freeze and expand, causing excessive pressures that result in coil damage within a matter of minutes. The ice that forms within the tubes of a hot water or chilled water coil expands and builds immense pressure causing a split that leaks fluid everywhere once thawed.
Water-damaged floors, walls, and equipment, mold and mildew remediation can all be the result of just one ruptured tube. And we often see multiple splits throughout a ruptured coil.
Understanding the mechanics of coil freezing in HVAC systems is essential for maintaining an efficient and functional heating, ventilation, and air conditioning system. One of the causes behind this phenomenon is stratification.
Stratification refers to the uneven distribution of temperature within the airstream entering a coil. Contrary to popular belief, the airstream is not usually isothermal or at the same temperature throughout its entirety. This disparity in temperature, coupled with the stark difference in air densities between outdoor air and return air, results in stratification.
The entire airstream does not need to be at 32°F to freeze a coil. If a select portion of a coil is consistently exposed to low temperatures, that portion of the coil can freeze and rupture while the remainder of the coil is exposed to standard mixed air temperatures.
What are Steam HVAC Coils?
A steam coil is a heat exchanger often found in the air handling units of commercial and industrial buildings. It works by warming up air that fans blow across fins made of materials like aluminum, copper, or stainless steel. These fins get heated up from steam moving through tubes.
There are two kinds of steam coils: standard and steam distributing. Standard steam coils are usually used for reheating, while steam distributing coils are needed when the air coming in is below 40 F degrees.
How do Steam Coils freeze?
How to Prevent Freeze Damage HVAC Coils
Freeze Block Coils
Freeze Block technology offers additional protection for both steam hot water or chilled water coils. It incorporates a pressure and temperature relief valve integrated with an expansion relief header. In freezing conditions, the Freeze Block valve releases a controlled amount of fluid from the coil, allowing ice to form without rupturing the coil. The valve reseats and once the coil is thawed it returns to normal operation. This technology has saved numerous coils from bursting. It is a power-independent, environmentally friendly freeze protection solution with minimal maintenance requirements.
Freeze stats are devices that monitor low-temperature limits. They primarily used to safeguard hot or chilled water coils in an air handler. They can be a useful tool in preventing freezing, but they also have a propensity for nuisance alarms. This often leads maintenance departments to lower the trip temperature. To prevent coil rupture, it is crucial that the freeze stat trips before the coil freezes. Annual calibrations and trip tests before the onset of cold weather are necessary to ensure the proper functioning of the freeze stat.
Draining Coils During the Winter
Draining HVAC coils in the winter is a preventive measure facilities can take against coil freezing or rupturing. The challenge lies in predicting the best time for draining due to fluctuating temperatures and extended warm weather into the fall season. The process requires adequate manpower and attention, especially considering labor shortages in facilities departments.
Recirculating pumps keep water moving in the coil, maintaining a temperature above freezing even when the outdoor temperature drops. Regular maintenance and inspection of these pump systems are essential to ensure their proper operation before cold weather sets in. Power failure can cause the water within the coil to cool and freeze, leading to coil bursts or rupture.