Freeze Point

The Freeze Point of liquids is defined as the temperature at which ice crystals first form. In the case of pure water, that point is 32° Fahrenheit. Water is unique in its property of increasing its volume by 9-10% as the freeze point is approached and achieved. Freezing water breaks pipes, pumps and containers unless there is adequate expansion room.

As glycol, glycerin, salt and other substances are dissolved in water, the volume expansion is generally reduced by the physical interaction among the various molecules in the solution. As the concentration of other substances is increased, the freezing properties of the solution changes in two ways: First, the solution may go through a longer phase change, turning into a slush before freezing hard. Second, the expansion of the fluid is reduced.

The freezing properties of Propylene Glycol are most interesting to our customers, as it offers protection in both freezing temperature and burst suppression. At a concentration of 35% PG, there is no expansion as the solution begins freezing at a temperature of 1° Fahrenheit. The solution will freeze hard and cannot be pumped or poured much below that temperature. Concentrations of PG about 60% will remain liquid at any temperature a normal facility would experience. Our ice melt and snow melt customers generally use PG concentrations of 45%-55% to insure the liquid can be circulated.

Side-Stream Filter

Most HVAC systems have pipes, pumps, fittings, valves and other components made of many different materials. There are many ways for dirt, scale and other debris to be present in the heat transfer fluid (HTF). Our staff has seen new buildings with significant debris in newly-installed HTF; for example, the steel pipe used in the construction is often stored outdoors and subject to an environment of dirt, and welding slag as the system is constructed. Neglected systems may show scale, chunks of iron oxide and other suspended substances.

Clearing a system of physical contamination is a fairly simple process: G2 can install a bag filter housing with isolation valves in the mechanical room, close to the circulation pumps. We have several different filter pore sizes, and generally start with a coarse filter to pick up the largest contaminants first.  By examining the debris and testing the HTF for inhibitors, we can assist you in improving the condition of the HTF in your system. This process may take as long as several weeks. The side-stream flow is low enough as to not degrade the heat transfer efficiency of your system while it is temporarily in place.

How HTF’s Age

Glycols age slowly, with some percentage of the molecules “cleaving” into glycolic and formic acids. As with most chemical reactions, heat expedites this process. If there are insufficient chemical inhibitors present in the HTF, this process can accelerate, creating a corrosive liquid.

We’ve seen pipes, zone valves and pump casings severely damaged by old, foul, neglected HTF’s. Annual testing of your HTF for pH, inhibitors and clarity is the best way to prevent expensive, unseen damage to your HVAC system.