FREEZE PROTECTION By Jonathon Harp
P
art I of this primer, in the November/December 2020 issue, dealt with glycol types, uses and mixtures. In Part II, we review how glycol affects the operation of HVAC systems and provide tips for contractors on key factors, that can ensure systems perform well throughout their usable lives. “Contractors play an important role in the use of glycol systems,” said Neil Bingham of Hood Chemical, a manufacturer of glycol. “Building owners know very little about glycol and its value to their equipment. Contractors who work with glycol systems can act as an information bridge and educate customers about the importance of protecting their investments.”
A primer on
glycol Part II
Glycol can have significant effect on performance and potential need for maintenance. The typical concerns are freezing and bursting of pipes in water-based systems; however, glycol also affects the way pumps, pipes and other components operate in systems. Consider the following when looking at system operations:
• While the right mixture of glycol in a system
can prevent freezing and bursting, too much glycol can affect its performance, efficiency and longevity. From a performance standpoint, it is important to understand that water is a much better heat transfer fluid than glycol. For example, a 50-50 water/glycol mixture has 16 per cent lower heat transfer capacity than water alone.
Keeping it clean Cleaning and flushing are essential when adding glycol to both new and existing systems. Existing systems accumulate a number of contaminants such as rust, scale and sediment that must be removed before glycol is introduced. In the case of large systems, professional industrial cleaning companies may be needed to ensure the cleaning process is done correctly.
• Performance and efficiency are going to decrease
This glycol primer is a general overview of the key factors associated with the use of glycol in waterbased HVAC systems. These articles are not intended as exhaustive field guides. The objective is to help contractors better understand glycol use and prompt you to obtain more specific technical information from wholesalers and/or glycol suppliers about specific systems. The more information you have, the better your design decisions will be.
76
M e c h a n i c a l
B u s i n e s s
Photo Adey Innovation, Morrison Mechanical, BC
as the amount of glycol in the system increases, and the ambient temperature at which the system is operating decreases. The glycol mixture must be carefully determined to ensure freezing and bursting will not occur and the glycol percentage used is not excessive, which can cause performance to drop unnecessarily. Excessive glycol in a system increases costs and may increase maintenance requirements.
With new systems, there are typically contaminants such as oil, grease and protective substances, as well as welding and pipe scale, that remain in the system from the fabrication or construction processes. Again, a thorough cleaning and flushing is needed to remove these contaminants. There are a variety of commercial cleaning products available to accomplish this task.
As evidenced by the magnetite capture here, installing a magnetic dirt filter is a vital step in protecting system components.
0 2 . 2 1
To protect against corrosion and degradation, glycol systems require inhibitors and buffers to be added to the mixture. These inhibitors are usually premixed with the glycol by the supplier. Inhibited glycol typically contains four to six per cent inhibitors. Many suppliers
