Central Distributed Equipment

Central vs. Distributed Equipment

The decision to use a central or distributed water heating system impacts requirements for on-demand heaters, pipe insulation, application and building design.

Example: Central vs. distributed application
If a central hot water system is employed and hot water is needed in a bathroom that is 50 feet from the natural gas hot water storage tank, the 50 feet of water volume in the pipe will have to be drained in order to get to the hot water. If the pipe has a 3/4-inch diameter it will hold 4.6 gal in 50 ft. If the water heater is set at a level of 120ºF and incoming water is 50ºF, the 4.6 gal of wasted water will also waste 2,682 BTU when it is heated. One option around this loss would be the installation of tankless heaters adjacent to the hot water applications. This would avoid the loss of 4.6 gal as well as the 2,682-BTU loss. However, if there is a large capacity need, the instantaneous demand for energy could lead to electric cost penalties or difficulty meeting large delivery needs. (Adapted from Stein, Mechanical and Electrical Equipment Buildings 9th ed. Page 601–603.)

Additional information

For U.S. and California appliance efficiency standards see:
• Appliance Efficiency Regulations. Dec 2006. CEC-400-2006-002-RE V2. Accessible at http://www.energy.ca.gov/2006publications/CEC-400-2006-002/CEC-400-2006-002-REV2.PDF
For an introduction to facilities water management, see:
• James Piper, Maintenance Solutions. “Water Use: Slowing the Flow.” 2003. Accessible at http://www.facilitiesnet.com/ms/article.asp?id=1969&keywords
For a technical reference on hot water systems, see:
• Benjamin Stein and John Reynolds. 2000. Mechanical and Electrical Equipment for Buildings, Chapter 10, Water Supply. Sections 10.5, 10.6 and 10.7 containing Water Sources, Hot Water Systems and Equipment, and Fixtures and Water Conservation. Accessible at http://www.facilitiesnet.com/ms/article.asp?id=1969&keywords

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