Determination of Existing Heat Distribution Systems

Generally, any new distribution systems will have to connect to existing distribution systems at the installation. The first step for the designer is to determine what media are available at the installation. The media distributed in these systems are as follows:

• High-temperature hot water (HTHW) (201^50°F [94-232°C])

• Low-temperature water (LTW) (150-200°F [66-93°C])

• Low-pressure steam (LPS) (up to 15 psig [103 kPa])

• High-pressure steam (HPS) (over 15 psig [103 kPa])

• Condensate return (up to 200°F [93°C])

Selection of Heat Distribution Systems

After the medium type has been determined, the heat distribution system type must then be selected. There are four basic types of distribution systems that can be used:

1. Above ground (AG) (high and low profile)

2. Concrete shallow trench (CST)

3. Buried conduit (ВС) (preapproved type)

4. Buried conduit (ВС) (not preapproved type)

AG Systems

AG systems are the least expensive and lowest cost (for labor) maintenance sys­tems available. However, aesthetic reasons may prevent the use of AG systems. These systems are a good application in industrial areas where the entire piping systems are aboveground. The AG system design should include the following:

• Detailed piping layouts

• Pipe support design (low- or high-profile type)

• Piping insulation selection

• Jacketing selection (to protect against moisture)

• Transition details to buried systems

• Vent, drain, and trap designs

CST Systems

CST systems are the preferred buried system. These systems consist of concrete, at grade tunnels, that allow access along the entire route. These systems can be used for all the listed media. The CST design should include the following:

• Detailed piping layouts showing all support locations

• Clearances inside the trench system, insulation, and jacketing selection

• Concrete trench wall and floor design (cast-in-place)

• Concrete top design (precast or cast-in-place) complete with lifting devices

• All road crossings

• Grading to keep groundwater from ponding over the trench system

• Sealant types and locations

• System slope 1 in./20 ft [25 mm/6096 mm] minimum, to ensure the trench floor
will drain to the valve manholes)

• Vent locations

All drains and traps must be located in the valve manholes. Vents may be located in the trench system only if access is provided to them with manhole lids poured in the trench top.

The use of manholes in these systems to provide housing for drains and traps must be evaluated concerning confined space entry provisions.

Дата добавления: 2015-11-16