Glycol Fluid Factor and Solution Properties (Propylene Glycol)
The number that replaces 500 in Q = 500 x GPM x dT when the loop is propylene glycol, with the specific heat, density.
Example
You enter
- Propylene glycol concentration (% by volume, 30 to 60) 40
- Average fluid temperature (°F, 40 to 325) 40
- Load (BTU/hr, 0 to skip) 240000
- Fluid temperature difference (°F, 0 to skip) 10
You get
- Specific heat btu lb f 0.847
- Density (lb/ft³) 66.03
- Fluid factor 448.58
- Flow (GPM) 53.5
Checked against published worked examples from: The Dow Chemical Company.
Details, formula, and sources
ScopeViscosity and freeze point, from the manufacturer's published properties by volume percent and temperature. A 40% solution at 40 F has a factor of 449, so a load takes 11% more flow than water, and it is about six times as viscous. For 30 to 60% glycol between 40 and 325 F. The fluid maker's data governs.
Formula or tableFluid factor = 60 min/h x density (lb/ft3) / 7.4805 gal/ft3 x specific heat (BTU/lb F), in BTU/hr per gpm per degF (500 for water); flow multiplier = 500 / factor; GPM = Q / (factor x dT). Properties interpolated linearly in percent and temperature between the printed 30/40/50/60% columns and 40/180/325 degF rows, viscosity on its logarithm; specific gravity = density / 62.37.
Source and editionThe Dow Chemical Company, DOWFROST HD Heat Transfer Fluid, Engineering Specifications for Closed-Loop HVAC Systems, Form No. 180-01273-402AMS (April 2002), section 4.2 Typical Properties of Aqueous Solutions (glycol percentage by volume) and 4.3 Freezing and Boiling Points, cited by name.
Free accessThe manufacturer's specification sheet is distributed free by Dow and its distributors; the twelve printed specific heat and density values are reproduced exactly at the table's own concentrations and temperatures.
What governsEstimate. AHJ and licensed professional govern.
API field namesglycol_pct, fluid_temp_f, load_btuh, delta_t_f, specific_heat_btu_lb_f, density_lb_ft3, fluid_factor, flow_gpm
- Concentration basis percent by VOLUME, 30 to 60Dow Form 180-01273-402AMS, 4.2
- Water reference factor 500 (8.34 lb/gal x 60 min/h x 1.0 BTU/lb F); gravity against 62.37 lb/ft3 at 60 degFhydronic design practice
- Freeze point 8 / -7 / -28 / -60 degF at 30 / 40 / 50 / 60%, interpolatedDow Form 180-01273-402AMS, 4.3