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Psi conversion6/2/2023 ![]() If the test and balance technician uses the correct multiplier from the glycol table above, the multiplier would be 2.18.Ĥ0 PSI X 2.18 multiplier = 87.2 ft of head This would indicate we are flowing 950 GPM or 5% below the design flow rate. If concentration is unknown, we recommend you use a refractometer to measure current glycol concentration.Īssume the pump differential pressure was 40 PSI.Ĥ0 PSI x 2.31 multiplier = 92.4 ft of head The glycol concentration is known because the system fluids were purchased premixed with deionized water (DI water) from Go Glycol Pros. The heat transfer fluid is 50% Dowfrost HD (propylene glycol) at 40☏. In this example, we have a design condition of 1000 gallons per minute (GPM) at 90 feet. Table of Multipliers for Glycol Systems Propylene Glycol (DOWFROST or DOWFROST HD)ī) Chart is based on the % by volume of DOWFROST mixed with waterĬ) ®™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dowĭoes it Make a Difference in the Test and Balance Report? In this article, we will explore an example to illustrate the importance of adjusting the multiplier based on type of heat transfer fluid.įormula to Calculate Feet of Head for Water Systemįeet of Head (Ft of Water) = (PSI X 2.31 Multiplier) / Specific Gravity Formula to Calculate Feet of Head for Glycol Systemįeet of Head (Ft of Glycol) = (PSI X Multiplier from Table Below) Since specific gravity is normally close to one for water but is not so in glycol systems, pump differential pressure gauge readings from a hydronic glycol system require an adjusted multiplier to account for the change in specific gravity.įailing to adjust the multiplier for glycol fluid may result in an assumed flow rate that doesn’t match the design, and when temperatures become really hot or cold, you may not be able to meet the occupants’ temperature requirements. However, there are times when the multiplier for the conversion of PSI to feet of head (PSI to ft head) changes. It is a simple conversion we learn early in our careers. Although the pascal is more widely used in scientific contexts, psi is more often used in everyday contexts, particularly in countries like the United States as well as others under the US customary or imperial systems of units.ġ5 bar = 15 × 14.503773773 psi = 217.How to Read Out the GPM of a Centrifugal PumpĪsk any HVAC test and balance technician in the hydronic system world to convert PSI to feet of water (or feet of head), and a multiplier of 2.31 is the immediate response. As such, the prototype pound at the time was known as the avoirdupois wool pound.Ĭurrent use: The psi is fairly widely used to measure numerous pressures, such as tire pressure, scuba tank pressure, natural gas pipeline pressure, among others. The system is believed to have come into use in England around 1300 and was used in the international wool trade. It is based on the avoirdupois system, a system that uses weights in terms of the avoirdupois pound, which was standardized in 1959. History/origin: Pound-force per square inch is a unit that originated in the imperial and US customary systems of units. One psi is approximately 6,895 pascals (N/m 2). It is defined as the pressure that results when a force of one pound-force is applied to a one-square-inch area. Pound-force per square inchĭefinition: A pound-force per square inch (symbol: psi) is an imperial and US customary unit of pressure based on avoirdupois units. Meteorologists and weather reporters worldwide often use this unit for convenience, since working in pascals would result in much larger values. Millibars (symbol: mb) are also commonly used when referencing atmospheric air pressure, where atmospheric pressure equals 1013.25 mbar (101.325 kPa). The International Bureau of Weights and Measures has specified the bar as a unit that authors should have the freedom to use but has chosen not to include the bar in the list of non-SI units accepted for use with SI. The term "bar" comes from the Greek word "baros," which means weight.Ĭurrent use: Although the bar is a metric unit of pressure, it is not accepted within the International System of Units (SI) and is even deprecated within certain fields. ![]() ![]() History/origin: The unit, bar, was introduced by Vilhelm Bjerknes, a Norwegian meteorologist who founded modern weather forecasting. It is equal to 0.987 atmospheres (101,325 Pa), the unit often used as a reference of standard pressure. Definition: A bar (symbol: bar) is a metric unit of pressure that is defined as exactly 100,000 pascals (symbol: Pa).
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