3.3.2
Horizontal Well Fields and Header Piping
Horizontal trenches for ground heat exchanger piping may be dug with a
chain type trenching machine or a backhoe. The piping shall be buried a
minimum of 1.2 m 48 inches deep or as indicated. Make joints while pipe is
laying beside the trench. If the soil contains rocks, dig the trench 152 mm
6 inches deeper than required and install a base of 152 mm 6 inches of
fines or sand before placing the pipe. [Buried piping in systems
containing antifreeze and installed within 1.5 m 60 inches of any building
wall, structure, or pipe shall be insulated with R-2 minimum closed cell
insulation.] After the piping is installed, tested, and flushed, purged,
inspected, and approved while still under pressure, backfill 152 mm 6 inches
above with fines or sand. Complete backfill in accordance with IGSHPA
21020 recommended procedures.
3.3.3
Polyethylene [and Polybutylene] Piping
Install piping in accordance with manufacturer's written instructions.
During installation, keep trash, soil, and foreign objects out of the pipe.
Tape or cap ends of the pipe until the pipe is joined to the circuit. The
vertical loop take-off tee fittings may be made using tee fittings or the
saddle fusion process on header piping 32 mm 1.25 inches diameter and
above. Completely remove the cutout on the saddle tees. Use bell
reductions at pipe reductions. Use reducing socket tees when fabricating
socket type reducing headers. Avoid sharp bends in piping. Consult pipe
manufacturer for minimum bend radius. Install elbow fittings at changes in
pipe direction that are tighter than the minimum recommended bend radius.
Use only continuous pipe in vertical U-bend loops.
3.3.4
Heat Fusion Process
Joining shall be either by butt, socket, or saddle (for sidewall
applications only) fusion in accordance with the manufacturer's Heat
Qualification Guide. Use socket fusion joints for pipe 50 mm 2 inches
diameter and less. Use butt fusion joints for pipe greater than 50 mm 2
inches diameter. Different plastics or grades of plastic shall not be
fused together.
3.3.5
Pressurizing
After assembly of the entire ground loop system, fill the system with water
and pressure test to 689 kPa 100 psi. Visually inspect welds prior to
backfill of the trenches.
3.3.6
Pipe Identification
Install metalized (detectable) warning and identification tape above each
horizontal pipe run. Install tape a minimum of 152 mm 6 inches below
finish grade. Install mechanical identification of vertical bore holes and
connecting headers.
3.3.7
Threaded Fittings
Threaded joints shall be sealed with a sealant compatible with the
circulating fluid; use of lubricating tape for sealing is not permitted.
Do not thread metal pipe into plastic pipe or vice versa. Direct buried
threaded joints are not permitted. Use threaded joints above grade, within
mechanical spaces, or within valve pits.
SECTION 15741N
Page 32
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