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The volumetric thermal expansion coefficient (β) describes how much a fluid expands per degree of temperature rise. It is reported here in units of β × 10−5 1/K. The volume change is:
ΔV = V0 × β × ΔT
where V0 is the initial volume and ΔT is the temperature change in Kelvin.
In closed-loop heating and cooling systems, fluid volume changes with temperature must be accommodated by an expansion tank. Undersizing the expansion tank — by using water's expansion coefficient when the system actually contains a propylene glycol solution — can result in system overpressure, relief valve discharge, or pipe damage. Propylene glycol solutions expand more than water at equivalent temperatures, making accurate β values essential for expansion tank sizing calculations.
Note: β increases with both temperature and glycol concentration. Always size expansion tanks using the highest expected operating temperature.