APPENDIX

The frictional (e.g., dynamic) pressure drop created as cold (nominal 60ºF) water flow through copper tubing can be estimated using the Hazen-Williams Formula.

Formula B-1:

$$ \Delta P = {{0.000426(f)^{1.85}} \over {(d)_i}^{4.87}} $$

Where:
$\Delta P$ = pressure loss through copper tubing (psi/ft)
$f$ = flow rate of cold water (gpm)
$d_i$ = exact inside diameter of tubing (inches)

For example: Determine the pressure drop through 150 feet of 3/4” type L copper tube as water flows through it at 6 gallons per minute.

Solution: The exact inside diameter of 3/4” Type L copper tube is 0.785 inches. Putting this value and the other given conditions into Formula B-1 yields: 

$$ \Delta P = {{0.000426(f)^{1.85}} \over {(d)_i}^{4.87}}={{0.000426(6)^{1.85}} \over {(0.785)}^{4.87}} = 0.0381 {\text{psi} \over \text{ft}} $$

The final step is to multiply the pressure drop per foot by the total length (150 ft).

$$ \Delta P = \Bigg[0.0381 {\text{psi} \over \text{ft}} \Bigg] 150 \text{ft} = 5.72 \text{psi} $$