spreadsheet includes rule-of-thumb velocity limits developed by a local acoustical consultant.7 Figure 3 shows the corresponding maximum allowable velocity for a given pipe size. As with erosion, these velocity limits can be enabled and disabled for each piping section and manually changed by the user. Economic Variables 30 ft Economic variables include: • Inflation rate; • Energy escalation rate (above inflation); 5 ft 8 ft • Electricity cost (effective 4 ft cost per kWh including 5 ft demand); Example 1: Simple Chilled Water System • Natural gas cost (for estiChiller 3 ft mating pump energy imFigure 4 shows a simple 3 ft Suction Diffuser pact on hot boiler cost); 500 gpm (32 L/s) chilled water • Discount rate; and system. The user must enter Figure 4: Example chilled water plant schematic. • System lifetime. the lengths of each pipe and Calculated annual energy costs are adjusted for inflation and the quantity of each type of fitting into the spreadsheet. On a escalation then discounted over the system lifetime. real project, pipe lengths are measured from drawings (typically directly from CAD files) while piping accessories are tabulated Examples from piping schematics. Each section of pipe that has a different Two examples are described in the following sections. The flow rate must be entered as a separate row in the spreadsheet. In first example is a simple chilled water plant. The example also this case, there is only one flow rate, so all data could be entered examines the same basic system but assuming the plant produces hot water rather than chilled water to demonstrate the impacts on pipe size. The second example describes a recently approved addendum to ANSI/ASHRAE/IESNA Standard 90.120078 that establishes maximum flow rates for chilled and condenser water system piping 6 ft based on the life-cycle calculations performed by the piping 3 ft spreadsheet. Similar pipe sizControl Valve 5 ft 3 ft ing limitations have been put forward in proposed ASHRAE 10 ft 5 ft Standard 189.1P.9 Figure 5: Example chilled water plant spreadsheet results. Figure 6: Example hot water plant spreadsheet results. 28 ASHRAE Journal ashrae.org October 2008
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