5-06M
must have passed tests required by the current Unified Facilities Guide
Specification, UF 02546. Currently, no system has passed these tests.
Caution: The design of direct buried systems must adhere strictly to the
VA Master Specification, Section 02710. Numerous failures of
manufacturer's standard systems have been experienced.
3.2 Concrete Shallow Trench Distribution Systems: These are field-built
systems designed specifically for each project. The tops of the trench covers
are slightly above grade and the trenches are sized only for pipe, insulation,
and pipe supports with no provision for personnel access other than the
removable covers. These systems can be applied only where site conditions
(such as water table below maximum trench depth, lack of surface water, level
or continuous grades) permit. Refer to Master Specification Section 02710,
Appendix I for acceptable conditions for application of shallow trenches.
3.3 Concrete Tunnel Systems: These are 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 as chilled water, share the tunnel.
4. SELECTION OF TYPE OF SYSTEM:
4.1 The design engineer shall select the type of system primarily based on a
comparison of the life cycle costs of the types of systems.
4.2 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 or tunnel, and maintenance requirements.
4.3 VA and DOD have experienced short service life with the direct buried
systems. Constant supervision of the installation work is necessary to avoid
damage to the protective coatings on the casings, to obtain sound welds of
carrier pipes and casings, and to obtain proper installation of the cathodic
protection system, including the dielectric connections at manholes and
buildings. Because of this, the concrete shallow trenches are favored over
direct buried systems in situations where concrete shallow trenches can be
applied.
5. SYSTEM DESIGN:
5.1 Steam Load Calculations:
5.1.1 Loads include HVAC, domestic hot water, kitchen, laundry, sterilizers,
other process loads, and line losses.
5.1.2 Load profiles must 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 can be apportioned among separate buildings by analysis of
major steam-using equipment and comparing building floor areas, whichever is
most accurate.
5.1.4 Consider future loads for new construction projects which are
programmed.
5.2 Steam Distribution Pressure:
5.2.1 Distribution should be at the boiler plant header pressure unless
existing conditions make this impractical.
5.2.2 It is recommended that existing pressures not be increased on existing
distribution systems. Pressures on existing systems can be increased only if
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