This is one of three articles in our series on water quality for your district energy loops, which focuses on your building’s hydronic cooling system. There are two distinct connection methods to District Energy’s chilled water supply, direct connection and connection through a heat exchanger. Heat exchangers are a preferred and recommended connection approach that separates your building water from the cooling supply water. They are an important element of internal mechanical systems that allow you complete control of your own water chemistry and mitigate the risks to the cooling system and your building loop.
This month we will concentrate on the differences in treating your chilled water loop based on whether you are a direct connect customer or a customer with a heat exchanger.
Direct connect customers: If you are a direct connect cooling customer, your building takes water from the district cooling plant and distributes it directly to all terminal cooling devices in your building (fan coils, air handling units, etc.). Because you are circulating treated district cooling water, the water chemistry in your building cooling loop should not need special care if your system is in use all year round.
If your system is not in use all year round, freeze protection can be a concern during Minnesota’s long winters. While your cooling system is idle for the winter, we recommend circulating the water in your coils to keep them from freezing. Alternatively you may choose to carefully drain your coils absolutely dry. This can be achieved by ducting warm air from the discharge side of the heating coil back to the lower drain of the drained cooling coil and allowing it to blow through the coil and out through the air release for several weeks until dry. If the coil is not dry, microbial induced corrosion (MIC) can cause pitting and premature coil failure.
Do not, however, add glycol (antifreeze) to your coils to keep them from freezing. Our district cooling system does not contain glycol; therefore you should never add glycol to any part of your directly connected loop as this contaminates the main distribution system’s water. Even if you flush your coils of the glycol in the springtime, there is residual glycol that ends up in the district cooling water. All district cooling water is carefully monitored and regularly treated, and contaminants such as this add cost for maintaining the distribution system, which can affect demand rates.
Customers with heat exchangers: If you have a cooling heat exchanger, your water treatment schedule will be different since the heat exchanger separates the district cooling water from mixing with your building’s chilled water loop. You will need to perform annual water quality testing to make sure that the pH and corrosion inhibitors are at their appropriate levels and biologicals are not growing in the cooling loop. If you have glycol in your cooling loop, it needs to be maintained at its appropriate concentration. Less than 30% glycol is not lethal to bacteria and can actually become food stimulating bacterial growth. Biological growth and dead biological matter can significantly reduce the efficiency of your system and can be costly and difficult to correct.
If you have questions about your building’s water treatment program or switching to a heat exchanger connection, please contact the District Energy team at 651.297.8955, email firstname.lastname@example.org, or support request form.