Propylene glycol, 30 % by volume
A 30 % by volume propylene glycol solution, freeze protection to about −13 °C — the usual charge for a snowmelt or make-up air loop that only has to survive a Canadian shoulder season.
| Phase | Liquid |
| Temperature range | -10 to 100 °C |
| Freeze protection | about -13 °C |
| Source | ASHRAE Handbook—Fundamentals, Ch. 31 (Secondary Coolants), interpolated from published tables |
Validated from -10 to 100 °C.
| Density | 1,024 kg/m³ |
| Dynamic viscosity | 3.4 mPa·s |
| Specific heat | 3.87 kJ/(kg·K) |
| Thermal conductivity | 0.445 W/(m·K) |
| Kinematic viscosity ν = µ/ρ | 3.3203 mm²/s |
| Prandtl number Pr = cpµ/k | 29.57 |
Every fluid property in these opens already filled, all from the same state — so a density and a viscosity in one calculation always describe the same fluid at the same temperature.
Glycol Loop Heat Transfer (Capacity Derate)
ρ = 1,024c = 3.87
Reynolds Number
ρ = 1,024μ = 3.4
Prandtl Number
μ = 3.4cₚ = 3.87k = 0.445
Learning zone
Thirty percent propylene glycol by volume protects to roughly −13 °C for freezing and rather lower for bursting, which is the number that actually matters in a closed loop: a slush of ice crystals in glycol expands far less than pure ice and usually will not split a pipe. It is the lightest charge worth mixing — below about 20 % the inhibitor package is too dilute to protect steel, and the fluid turns acidic within a few seasons.
The penalty is modest at this concentration and easy to carry. Specific heat drops from 4.18 to about 3.87 kJ/(kg·K), roughly 7 %, so the same ΔT moves 7 % less heat per kilogram. Viscosity at 20 °C is 3.4 mPa·s against water's 1.0 — more than triple — and at 0 °C it is 7.4. Since Reynolds number scales as 1/µ, a coil comfortably turbulent on water can sit in the transition region on cold glycol, and the film coefficient falls away with it.
Propylene rather than ethylene glycol wherever the loop could contact potable water, food or people: propylene glycol is the one used in food processing and is broadly non-toxic, while ethylene glycol is sweet-tasting and seriously poisonous. The trade-off is that propylene is the more viscous of the two at the same freeze protection, so an ethylene loop pumps easier — which is why chillers and process cooling still use it where the risk is controlled.
The constants library carries these at a single stated temperature, with their uncertainty and provenance. The table above is the same substance as a function.