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VA Design Manuals (PG-18-10) - Steam Heating, Hot Water, and Outside Distribution Systems - Volume 3 - Distribution Systems >
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VA Design Manuals (PG-18-10) - Steam Heating, Hot Water, and Outside Distribution Systems - Volume 3 - Distribution Systems, 0
- 1.1 Outside heat distribution work includes all heating hot water (HHW), steam supply and steam condensate piping and equipment located underground, in tunnel, or aboveground outside of buildings. Systems located 5 feet outside the building exterior w...
- 1.2 Design the outside heat distribution systems to comply with this design manual, and the current editions of VA design guides, VA design and construction procedures, and the VA master specifications. The design shall also comply with the provision...
- 1.3 Show outside heat distribution plot plans on drawings using a minimum scale of 1:250 (1”= 20’). Manhole piping plans and sections shall be drawn with a minimum scale of 1:30 (3/8" = 1').
- 1.3.1 Existing work shall be identified in a way which easily distinguishes this work from the new work. Points of connection between new and existing work shall be identified.
- 1.4 Outside steam and heating hot water distribution systems shall be designed to provide the required flow and pressure at the point of use as defined herein. All condensate shall be returned to the boiler plant unless the design of steam-using equi...
- 2.1 Outside heat distribution work shall only be indicated on "MS"-series drawings (see VA Design and Construction Procedure, “Drawings”).
- 2.1.1 “MS"-series drawings shall include symbols and schedules, details, plot plans and profiles with interference from other utilities located and identified, manhole plans and sections, tunnel and trench plans and sections, location of expansion loo...
- 2.1.2 Only symbols and abbreviations shown on VA Standard Details (PG-18-4) division 00 and 23 may be used on the drawings.
- 2.1.3 Pipe sizes shall be indicated on plot plans and on manhole plans and sections.
- 2.1.4 Equipment and piping systems shown on the drawings shall be generic and not the configuration of a particular manufacturer.
- 2.2 Major options and alternatives shall be evaluated utilizing the life cycle cost analysis methods using Department of Energy mandated discount factors.
- 3.1 Pre-engineered, factory-fabricated, direct buried distribution systems: These are systems of various manufacturers which include the carrier pipes, pipe insulation, protective enclosures, and accessories. The systems may be “drainable-dryable-tes...
- 3.2 Concrete Shallow Trench Distribution Systems: These are either precast or field-built systems designed specifically for each project. The tops of the trench covers are slightly below or at grade and the trenches are sized only for pipe, insulatio...
- 3.3 Concrete Tunnel Systems: These are either precast or field-built systems designed specifically for each project and are sized to permit personnel walk-thru. They can often be justified on the basis of life cycle costs when other utilities, such a...
- 4.1 The design engineer shall recommend the type of system primarily based on a comparison of the life cycle costs of the types of systems.
- 4.2 The analysis shall also include an environmental impact (potentially NEPA) as applicable to the past work on the site. Life cycle cost analysis shall include removal of any portion of an existing system that may pose an environmental hazard if le...
- 4.3 In making the selection, the engineer shall also consider the service record of existing types of systems at the site. Consideration shall be given to the extent of the new systems, the ability to combine various utility services into one trench ...
- 5.1 Steam and HHW load calculations:
- 5.1.1 Loads may include HVAC, domestic hot water, kitchen, laundry, sterilizers, other process loads, and line losses.
- 5.1.2 Load profiles shall include diversity factors and credits for heat recovery systems which are in operation during the peak load conditions.
- 5.1.3 Existing loads should be determined by reviewing boiler steam flow rate data for winter periods when the outside temperature approaches ASHRAE design conditions. Loads may be apportioned among separate buildings by analysis of major steam-using...
- 5.1.4 Consider future loads for new or upgrade construction projects which are programmed. A minimum of 10% additional capacity shall be provided in the sizing of the distribution system piping.
- 5.2 Steam/heating hot water distribution pressure:
- 5.2.1 Distribution shall be the same as the plant header pressure unless existing conditions make this impractical.
- 5.2.2 It is recommended that operational pressure not be increased on existing distribution systems. Pressures on existing systems may be increased only if a complete engineering analysis of the system is performed and stamped by a registered enginee...
- 5.3 Connecting to existing steam/heating hot water distribution systems:
- 5.3.1 Calculate steam flows and pressure drops on the portions of the existing system which are affected by the new steam loads. The new steam loads shall not impose excessive pressure drops or velocities (velocity shall be below 7000 fpm) on the exi...
- 5.3.2 Calculate water flows and pressure drops on the portions of the existing system which are affected by the new loads. The new loads shall not impose excessive pressure drops or velocities (velocity should be below 7 fps or 1psi/100ft) on the exi...
- 5.4 Sloping and dripping of steam lines:
- 5.4.1 Steam lines shall pitch down 50 mm in 12 meters (two inches in 40 feet) in the direction of flow. Provide drip pockets and steam traps at all risers and immediately ahead of all isolation valves that would collect condensate if the valves are c...
- 5.4.2 Steam traps for steam line drip service shall handle normal steady state radiation and convection heat loss condensate and also high levels of condensate and air flow when the steam line is being warmed-up. The preferred trap type is the invert...
- 5.4.3 Trap monitoring shall be supplied in critical locations on all mains and major traps.
- 5.4.4 Provide adequate access to all traps and other appurtenances for maintenance and inspection. See also para 5.11.11
- 5.5 Condensate Return:
- 5.5.1 Generally, all condensate should be collected at condensate return pump sets and then be pumped to the boiler plant. Exceptions include existing systems being replaced which have other types of condensate returns such as vacuum or gravity. Also...
- 5.6 Installation of HHW Lines
- 5.6.1 Indicate piping slopes on drawings. Piping shall be installed free of sags and bends. Design for fittings for changes in direction and branch connections. Design and installation of piping shall allow application of insulation. Groups of pipes s...
- 5.6.2 Reduce pipe sizes using eccentric reducer fitting installed with level side up.
- 5.6.3 Indicate branch connections to mains using tee fittings in main pipe, with the branch connected to the bottom of the main pipe. For up-feed risers, connect the branch to the top of the main pipe.
- 5.6.4 Show shutoff valve immediately upstream of each dielectric fitting.
- 5.6.5 Indicate sleeves and/or seals for piping penetrations of concrete walls and slabs with specific detail as to design and construction requirements.
- 5.7 Thermal Expansion:
- 5.7.1 Locate and design the anchors and the expansion joints, bends and loops so that piping will not be overstressed. The locations shall be shown on drawings. Sizes of bends and loops need not be shown on direct buried systems because the system m...
- 5.7.2 Pipe anchors shall be provided within 0.6 to 1.5 meters (two to five feet) outside of manhole and building walls to minimize pipe movement through the manhole and/or Building. For piping passing through the manhole, do not anchor on both sides o...
- 5.7.3 All anchoring and expansion joints, bends and loops shall be completely designed including the civil structural component and specified in the contract documents except for anchors and expansion loops and bends being furnished as part of a direc...
- 5.7.4 Design steam systems for boiler plant header pressure and temperature (150 psig, 370 (F) minimum, and design condensate systems for (100 psig, 200 (F) minimum. Pipe stresses must not exceed allowable stresses calculated in accordance with ASME ...
- 5.7.5 Vertical deflection shall not exceed 2.5 mm (0.1 inch) between supports when system is filled with fluid normally carried. Deflections due to seismic shock shall be restrained as necessary to prevent overstressing the supported system or the co...
- 5.7.6 If vertical angle of hanger rod exceeds four degrees, rollers or sliders are required.
- 5.8 Fiberglass Reinforced Plastic (FRP) Pipe for Condensate is prohibited.
- 5.9 Pipe Material
- 5.9.1 The following table reflects acceptable carrier pipe material. Outside HHW distribution, including distribution in tunnels and/or shallow trenches shall be all welded construction. Alternate systems may be considered based on specific needs and ...
- 5.10 Insulation:
- Comply with EPA and VA specification requirements.
- 5.10.1 Factory Applied Insulation: Prefabricated pipe and fittings shall be insulated in the factory. Foam insulation for prefabricated insulated pipe and fittings shall be polyurethane (polyisocyanurate) foam meeting the requirements of ASTM C591 ...
- 5.10.2 Field Applied Insulation: Steam Systems: Field applied insulation for fittings, and field casing closures, if required, and other piping system accessories shall be polyurethane (polyisocyanurate) matching the pipe insulation. Thickness shal...
- 5.11 Underground warning tape:
- Design for the provision of underground warning tape to be buried above the piping during the trench backfilling and shall be buried approximately 3T123T inches below grade. Tape shall be polyethylene tape with metallic core. Tape shall be six inch...
- 5.12 Manholes:
- 5.12.1 In direct buried systems and in concrete trench systems all devices requiring access for operation and maintenance shall be located in manholes. These devices include valves, steam traps, expansion joints, flanged and threaded joints, unions.
- 5.12.2 Manholes shall be cast-in-place reinforced concrete. Prefabricated manholes are prohibited due to difficulty of properly locating underground pipe openings in the manhole walls. Concrete floor slabs shall be of sufficient weight to prevent fl...
- 5.12.3 Do not locate manholes in roads or parking areas because of access and ventilation problems.
- 5.12.4 Manhole structure and mechanical layout shall be completely designed by the A/E. Allow adequate working access and headroom.
- 5.12.5 Provide a minimum of two separate entrances from grade with full-size manhole covers dependent on safety/operational requirements. One shall be for access with grab-bars or ladder set in the manhole wall, the other shall be for ventilation whil...
- 5.12.6 Provide 760 mm (30 inch) square (minimum) by 915 mm (36 inch) deep sump in floor and slope manhole floor to the sump. Provide duplex submersible sump pumps when electricity is available otherwise a drop-down pump shall be used. Where feasible,...
- 5.12.7 The designer shall review the “confined space” regulations of the facility and design the manholes to allow maximum possible access convenience. The designs shall be reviewed and approved by the appropriate facility officials regarding these re...
- 5.12.8 Show all pipe supports on drawing. Completely design all pipe anchors to withstand the applied forces.
- 5.12.9 Place waterproof membranes in or below the concrete bottom slabs and continue them up the outer sides to the top of the sidewalls.
- 5.12.10 Provide ventilation pipes through the top of the manhole. Terminate one, 12” above grade and the other 12” below the bottom of ceiling slab. Both pipes shall terminate 18” above finish grade in a gooseneck configuration.
- 5.12.11 All piping, fittings, valves, etc., in the valve manholes shall be insulated. Insulation shall be pre-molded, precut, or job fabricated to fit and shall be removable and reusable. Thickness of insulation shall be in accordance with VA specif...
- 5.12.12 Site Investigations:
- 5.12.13 The designer shall determine the most economical and practical locations for the system and accessories. In addition, the determination of soil conditions is necessary when direct buried systems are selected.
- 5.12.14 The designer shall perform the following:
- 5.12.15 Field work by the A/E or their consultant shall be administered under the terms of the contract between VA and the A/E.
- 5.13 Design of Direct Buried Systems:
- 5.13.1 The manufacturer is responsible for the design of the system within the parameters of the VA specification. This responsibility includes insulation types, pipe guides and anchors, end seals, corrosion protection, expansion bends and loops, and ...
- 5.13.2 The condensate return piping shall not be included in the same conduit as the steam piping. This will prevent condensate piping failures from affecting the steam piping. Typically, condensate pipes have a much higher failure rate than the ste...
- 5.13.3 Depth of burial of the systems shall be 0.6 to 1.5 meters (two to five feet) to top of conduit casing.
- 5.13.4 The designer shall be completely responsible for the manhole design including manhole structure, ventilation, and piping.
- 5.13.5 Provide cathodic protection for all steel casing systems and all buried exposed metal. Assume that a minimum of 25 percent of the exterior of the system is exposed metal. Submit design life calculations for the cathodic protection system, sta...
- 5.14 Design of Concrete Shallow Trench Systems:
- 5.14.1 The designer shall be completely responsible for the entire design including concrete trenches, pipe anchors, sizing of expansion loops and bends, sizes of expansion joints, pipe supports and guides, manhole structure and piping, system locatio...
- 5.15 Design of Concrete Tunnel Systems:
- 5.15.1 The designer shall be completely responsible for the entire design including concrete tunnel, pipe anchors, sizing of expansion loops and bends, sizes of expansion joints, pipe supports and guides, tunnel structure and piping, system locations,...
- 5.15.2 The tunnel shall include ample walking space with height for persons to stand erect, and drain system to handle ground water and piping leaks.
- 5.15.3 Tunnel access shall be provided every 350 feet of tunnel length and every change of direction. Provide a minimum of two separate entrances from grade and at least one every 350 feet of tunnel with full-size manhole covers. Access entrance shall...
- 5.15.4 Provide ample lighting and electrical receptacles designed for high temperatures per OSHA 1926.56 and NFPA 101. Lights must be connected to Life Safety branch of the EES, if it is practical or feasible (or have 1-1/2 hour-emergency power packs ...
- 5.15.5 Provide ventilation systems to allow personnel to work safely. A minimum 6 air changes per hour (ACH) are recommended or as required by IBC/IMC, whichever is more stringent for tunnel ventilation. Provide ventilation (exhaust) fans every 700 fe...
- 5.16 Design Details:
- 5.16.1 Provide pressure gages at the outlet side of all main steam valves so that personnel can observe the gages while warming-up the steam line.
- 5.16.2 Provide steam drip traps and manual drains on steam lines at all low points and upstream of all valves and pressure reducing stations. Spacing shall not exceed 150 meters (500 feet).
- 5.16.3 Provide HHW air vents, vacuum breakers and drains to allow the system to be purged of air and drained if required. The vents and vacuum breakers shall be placed at all high points and sized to accommodate the calculated drain rate and anticipa...
- 5.16.4 Provide isolation valves (gate valves) on all branch connections to the main piping runs.
- 5.16.5 Provide gravity drainage along the length of the tunnel and to the storm sewer in the vicinity. When not possible to drain by gravity provide 760 mm (30 inch) square (minimum) by 915 mm (36 inch) deep sump in floor and slop tunnel floor to the ...
- 5.16.6 The designer shall furnish thermal expansion calculations for the supply and return piping using the following design characteristics and installation temperature. The system design conditions supply and/or return shall be a temperature of 450 ...
- 5.16.7 Assure that proper chemical treatment for the site distribution system is provided and included with the design of systems and equipment in the Heating Power Plant (refer to Volumes 1 and 2 of this manual). If not, make provisions for a chemica... [Go to Page]