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## How to Calculate HVAC Pump Head for Open and Closed Systems

If you are working on a HVAC project that involves pumps, you need to know how to calculate the pump head. Pump head is the total resistance that a pump must overcome to move fluid through a system. It consists of static head, friction head, pressure head, and velocity head. Knowing how to calculate pump head can help you select the right pump for your system and optimize its performance.

In this article, we will explain what each component of pump head means and how to calculate it for open and closed systems. We will also provide some useful resources where you can download HVAC design calculations formulas pdf files that can help you with your calculations.

Pump head is measured in units of pressure or feet of head. One foot of head is equal to the pressure required to lift a column of water one foot high at sea level and standard temperature. Pump head is also related to the flow rate and power of the pump by the following equation:

Where P is the power in horsepower, Î is the specific weight of water in pounds per cubic foot, Q is the flow rate in cubic feet per minute, and H is the pump head in feet.

Static head is the difference in elevation between the highest and lowest points of the system. It represents the potential energy of the fluid due to gravity. Static head applies only in open systems, where the fluid is exposed to atmospheric pressure at some point. In closed systems, where the fluid travels through a continuous loop of pipes, the static head is zero because the fluid on one side of the system pushes the fluid up the other side of the system.

To calculate static head, you need to know the elevation of the highest and lowest points of the system relative to a common reference point. The static head is then given by:

Where Hs is the static head in feet, Z2 is the elevation of the highest point in feet, and Z1 is the elevation of the lowest point in feet.

Friction head is the loss of pressure due to friction when fluid flows through pipes, fittings, valves, heat exchangers, coils, and other system components. It represents the energy dissipated by viscous forces in the fluid. Friction head depends on several factors, such as pipe size, pipe material, pipe length, flow rate, fluid viscosity, fluid density, and pipe roughness.

To calculate friction head, you need to use empirical formulas or charts that relate friction factor to Reynolds number and relative roughness. Reynolds number is a dimensionless number that measures the ratio of inertial forces to viscous forces in a fluid flow. Relative roughness is a dimensionless number that measures the ratio of pipe roughness to pipe diameter.

One common formula for friction factor is the Colebrook equation:

Where f is the friction factor, Îµ is the pipe roughness in feet, D is the pipe diameter in feet, and Re is the Reynolds number given by:

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