BTU Capacity in Boiler Plants with Glycol Solutions

Glycol solutions are used for freeze protection in hot water systems. These solutions have a lower ability to hold and transfer heat. Because of this, adjustments must be made to the heating system to compensate for the glycol characteristics.

Question: How much will my boiler de-rate if I am using a glycol mix in my system?
Answer: A boiler’s ability to transfer heat is not changed by the fluid passing through it. The “de-rate” seen is due to the glycol mix having a lower specific heat than water. If no adjustments are made to the plant, the amount of BTUs supplied will need to be increased.
Q: What adjustments do I need to make?
A: The specific heat of glycol solutions is lower than that of water. In order to transfer the same amount of heat, the lower heat capacity can be compensated for by increasing the flow rate of the heating plant. To calculate this, divide flow rate by the specific heat of the glycol solution at a given mix percentage and working temperature.
Q: Can you provide the glycol de-rate factors?
A: No, these factors are specific to each glycol formulation, and must come from the glycol manufacturer directly. The tables given below are examples only and do not represent a specific formulation.

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