5.17 Piping Systems
All piping systems shall be designed and sized in accordance with ASHRAE Fundamentals Handbook and the ASHRAE HVAC Systems and Equipment Handbook. Materials acceptable for piping systems are black steel and copper.No PVC or other types of plastic pipe are permitted.
Chilled Water and Condenser Water Piping. In general, HVAC systems shall utilize parallel piping systems with a two-pipe main distribution system arranged in a reverse return configuration. If applied, series loop piping for terminal or branch circuits shall be equipped with automatic flow control valves at terminal units (all types of heat transfer units).
Each terminal unit or coil shall be provided with isolation valves on both the supply and return and a flow indicating balance valve on the return line. Isolation valves shall be provided on all major branches, such as at each floor level, building wing or mechanical room.
For new chilled water HVAC distribution, a pumping and piping arrangement is generally appropriate, with constant volume primary pumping and variable volume secondary pumping. The primary and secondary circuits shall be separate, with neither having an effect on the pumping head of the other. The primary circuit serves the source equipment (chillers), while the secondary circuit serves the load. Refer also to Pumping Systems in this chapter for additional requirements.
Cathodic Protection. The need for metal protection for underground piping must be evaluated by a soils resistivity test. This is part of the Geotechnical Report. (See Appendix A.) Cathodic protection or another means of preventing pipe corrosion must be provided if required by the Geotechnical Report.
Piping Material. Table 5-5 cites which commercial standard should be used for piping material.
Isolation of Piping at Equipment. Isolation valves, shutoff valves, by-pass circuits, flanges and unions shall be provided as necessary for piping at equipment to facilitate equipment repair and replacement. Equipment requiring isolation includes boilers, chillers, pumps, coils, terminal units and heat exchangers. Valves shall also be provided for zones off vertical risers.
Provisions for Piping in Earthquake Zones. In Seismic Zones 2, 3 and 4, sleeves for pipes shall be at least 25 mm (1 inch) larger than the pipe, to allow for movement. Flexible couplings shall be provided at the bottom of pipe risers. Spreaders shall be used to separate adjacent pipes, unless the distance is large enough to prevent contact in an earthquake. See Chapter 4: Structural Engineering, SMACNA Seismic Restraint Manual and ASHRAE Application Handbook for more detailed information.
Piping Supports. Provide channel supports for multiple pipes and heavy duty steel trapezes to support multiple pipes. Hanger and support schedule shall have manufacturer’s number, type and location. Comply with MSS SP69 for pipe hanger selections. Spring hangers and supports shall be provided in all the mechanical rooms.
Flexible Pipe Connectors. Flexible pipe connectors shall be fabricated from annular close pitched corrugated and braided stainless steel. All pumps, chillers, and cooling towers shall have flexible connectors.
Piping System and Equipment Identification. All pipes, valves and equipment in mechanical rooms, shafts, ceilings and other spaces accessible to maintenance personnel must be identified with color-coded bands and permanent tags indicating the system type and direction of flow for piping systems or type and number for equipment. The identification system shall also tag all valves and other operable fittings. Gas piping and sprinkler lines must be identified as prescribed by NFPA.
Table 5-5 Commercial Standards for Piping Material
|Standard Piping Material
|ASTM Schedule 40
||Chilled water up to 300 mm (12-in) dia., Condenser water up to 300 mm (12-in) dia.
Natural gas, fuel oil
Steam (100 kPa (15 psig) to 1035 kPa (150 psi))
|1035 kPa (150 psi) fittings.
Standard weight pipe over 300 mm (12-in) diameter.
Test to 2100 kPa (300 psig)
Weld and test to 2100 kPa (300 psig)
|ASTM Schedule 30
||Chilled water over 300 mm (12 in) dia
Condenser water over 300 mm (12 in) dia.
|1035 kPa (150 psi) fittings.
Standard weight pipe over 300 mm (12-in) diameter
|ASTM Schedule 80
||Chilled water up to 102 mm (4 in) dia,
Condenser water up to 102 mm (4 in) dia.
Cast Iron Sanitary, waste and vent
|Builder’s option. Use type K below ground
and type L above.
Lead-free solder connections.