Page 70 - HVAC Pump Handbook

Rishel_CH03.qxd 20/4/06 5:35 PM Page 67

Piping System Friction
Piping System Friction 67

Figure 3.7 Loss coefficients for reducing ells. (Copyright © 1999. American Society
of Heating, Refrigerating and Air-Conditioning Engineers, Inc. www.ashrae.org
Reprinted by permission from ASHRAE Transactions, Vol. 105, Part 1.)

Tests were conducted on 6, 8, and 10 in fittings, and they can be
compared to tests on steel fittings that were completed under
Research Project 1116 RP.

It has been believed for some time that the friction loss in plastic
pipe fittings was less than for steel pipe fittings of the same nominal
size. These tests demonstrated that this is not the case. The reason is
the smaller radii of the elbows as shown in Fig. 3.8a, and the sharp
edges of the reducers, as shown in Fig. 3.8b. Comparable K factors for
steel and plastic pipe fittings are available from these tests. Figure 3.9
shows the piping arrangement for these tests.

3.5 Thermoplastic Pipe
Thermoplastic pipe is being used in the HVAC industry for cold water
services such as cooling tower and chilled water systems. It can offer
distinct advantages cost-wise on some installations. It has a decided
advantage on cooling tower water that may be laden with oxygen and
where steel pipe is susceptible to rusting. The pressure and temperature
ratings of plastic pipe and fittings are available from the principal

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2006 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.