28.3 Geothermal Loops, Surge Protectors, Phase Monitors & Plastic Pipe

28.3 Geothermal Loops, Surge Protectors, Phase Monitors & Plastic Pipe

Trade D’s remaining numbered items in this chapter are geothermal systems, surge protectors, phase monitors, and the plastic pipe those loops (and condensate) are made of. Chapter 22.4 already taught geothermal as a Trade C heat-pump install (closed horizontal, closed vertical, closed pond, open well). Chapter 25.3 already made the negative refrigerant point: PVC is not Table 1107.4 ACR. This section is the component side: fuse the HDPE, purge and charge the loop, clamp transients, watch three-phase power quality, and hang plastic only where plastic is legal. The 2026 CBT stack is Refrigeration & Air Conditioning Technology, 9th Edition (2021), Florida Building Code — Mechanical, 2023 (hydronic and condensate chapters; Table 305.4 hangers; 301.10 electrical), and F.S. 489.105 for license scope. Pipefitters Handbook, 3rd Edition (1967) still supports fusion-adjacent layout judgment; it will not list a PE4710 print.

Quick Answer: Closed geothermal loops are fused HDPE, equal-length circuits, 2.25–3 gpm/ton, purged, glycol if the listing wants freeze protection. SPDs clamp surges; they do not replace a ground. Phase monitors stop phase loss and reversal on three-phase compressors. Plastic = loops and condensate, not refrigerant. Class B still stops at 25 tons / 500,000 Btu in any one system.

Geothermal loops — flow, fusion, and what the heat pump actually sees

A ground-source heat pump (GSHP) is still a reversing vapor-compression machine (Section 20.2). The outdoor coil is replaced by a refrigerant-to-water heat exchanger (often coaxial) piped to the loop. Size capacity from expanded data at entering water (or loop) temperature, not from an air-source SEER sticker. Florida ground and pond water are warm; cooling-mode EWT is not a 45°F wish, and heating-mode EWT is not a Minnesota 30°F story. Class B may install a 20-ton GSHP; a 40-ton plant on one loop is Class A (F.S. 489.105(3)(g)).

Closed-loop pipe is high-density polyethylene (HDPE) — typically PE4710 (or the older PE3408 designation on drawings), DR11 or DR13.5, heat-fused (butt, socket, or electrofusion), never solvent-welded PVC. Circuits should be equal length so flow balances without a forest of undocumented balancing valves. Headers and purge ports (a flush cart with a powerful pump) belong at the flow center. Purge until the stream is clear and air-free; air trapped in a vertical U-bend is a permanent insulator. Pressure-test the loop per the listing and the mechanical code hydronic test (commonly a water test above operating pressure — use the spec; do not “air test HDPE to 150 psi because that is what we do on copper”). Fill with water or a listed antifreeze (food-grade propylene glycol is the usual HVAC fill). Do not dump automotive silicate coolant or ethylene glycol into a loop that can leak toward a wellhead.

Flow. Closed-loop design is commonly about 3 gpm per ton at a 10°F loop rise, with many listings happy in a 2.25–3 gpm/ton band. That is not the 2.4 gpm/ton evaporator chilled-water figure and not the ~3 gpm/ton condenser-water heat-of-rejection figure from Chapter 23, even though the arithmetic looks related — you are moving loop water through a coaxial exchanger, not tower water. Too little gpm and the heat pump trips on high head (cooling) or freeze protection (heating). Too much gpm and you pay pump watts for no capacity. The flow center (one or two circulators, isolation flanges, flush ports) is HVAC hydronic equipment. A new potable well, a sanitary injection, or building potable plumbing is outside F.S. 489.105.

Open loop (pump-and-dump or supply-and-return wells) runs groundwater through the exchanger and away. Water quality (iron, sulfur, sand) fouls coaxial tubes. Discharge must be legal — not a storm drain you invented, not a sanitary tap, not a neighbor’s ditch. Open loop is not a Class B plumbing license. Direct-exchange (DX) geothermal puts refrigerant copper in the earth; that is a different listed 608 circuit, still inside capacity limits, and not HDPE.

Electrical on a GSHP is the same fence as 28.1: single-phase dedicated existing disconnect and low-voltage controls are HVAC; three-phase power wiring is typically an electrician. The compressor still wants a phase monitor on three-phase. The loop pumps are often 120/240-volt circulators on HVAC control power or a dedicated HVAC circuit with a breaker lock.

Surge protectors

Florida is a lightning state. A surge-protective device (SPD) clamps a transient (lightning-induced or utility switching) before it punches through a control board, an ECM, or a communicating thermostat. It is parallel protection: it does not carry the motor load. Match the voltage (240-volt single-phase versus 208/480 three-phase), the listing, and the installation location. A Type 2 SPD at the HVAC disconnect or panel is the common equipment-level device; Type 1 lives on the line side of the service disconnect; Type 3 is point-of-use. You do not need to memorize a UL-number table the open-book list does not print — you need to install a listed SPD on the circuit the listing names, with short, straight leads (long pigtails add inductance and let the spike through), on a circuit that is actually grounded.

An SPD supplements the equipment grounding conductor; it does not replace it. It does not replace a phase monitor, a breaker lock, or LOTO. A fried board after a storm with the ground hanging in the air is not an SPD failure, it is a grounding failure. Whole-building service SPDs are often electrical-contractor work; the listed device at a dedicated HVAC disconnect on a single-phase changeout can sit inside the 489.105 disconnect grant when it is part of that dedicated HVAC circuit. When in doubt on a three-phase service SPD, subcontract.

Phase monitors

A phase monitor (phase-loss, phase-reversal, and often undervoltage / voltage-unbalance relay) watches the three line voltages feeding a compressor or fan. It opens the contactor coil when:

• One phase is lost (single-phasing),
• Two phases are swapped after a utility or electrician change (reverse rotation — lethal to many scrolls),
• Voltage is low or unbalanced enough to overheat windings.

NEMA’s teaching point is that a small voltage unbalance produces a much larger current unbalance (on the order of eight times — a 1 percent voltage unbalance can mean about 8 percent current unbalance). A 2–3 percent voltage unbalance is already a motor-killer. Set the monitor to the manufacturer’s dropout and restart delay so a two-cycle glitch does not chatter the compressor, but a lost phase does not sit there cooking windings. Manual-reset or an adjustable delay-on-make after a fault is the usual HVAC package. Wire it in series with the contactor coil, downstream of HP/LP/oil failure so those safeties still work.

On a VFD, put the phase monitor on the line side of the drive unless the drive’s own protection is listed as the phase-loss device. Drive output is pulse-width modulated and will confuse or destroy a standard phase-sequence relay. Three-phase GSHP scrolls, RTU compressors, and tower fans are the usual Florida homes for this device. Single-phase residential splits do not get a three-phase monitor; they get a run capacitor and an overload.

Plastic pipe — loops and drains, not refrigerant

Chapter 25.3 already parked the refrigerant negative: PVC, CPVC, ABS, and PEX are not Table 1107.4 refrigerant metals. This cluster’s plastic is the positive list:

Table 305.4 hanger spacing (PVC 4 feet horizontal, and the PEX/CPVC rows) applies only where that plastic is the right material. Hanging PVC every 4 feet does not make it a geothermal loop (use fused HDPE) and does not make it a suction line. Fusion joints on HDPE are heat joints: facing, alignment, melt pressure, and cool-down under the fusion machine’s procedure. A glue joint on HDPE is a leak waiting for the first purge-cart pressure.

F.S. 489.105 still does not grant potable water, sanitary sewer, or pool piping. Plastic condensate to an existing safe waste is inside the grant. A new sanitary tap is not. Open-loop well work that is a water-well contractor’s ticket is not an HVAC bonus because the water happens to go through a heat pump.

Florida HVAC scenario

A certified Class A shop in Alachua County installs a 15-ton closed-loop vertical GSHP on a clinic — tons a Class B shop could also take — with fused HDPE U-bends, equal circuit lengths, a flow center set near 3 gpm/ton, propylene glycol, and a purge until the sight stream is solid water. The heat pump is 208-volt three-phase. The HVAC crew lands low-voltage controls, a Type 2 SPD at the dedicated equipment disconnect with short leads, and a phase monitor in series with the compressor contactor coil (line-side, because the pumps are across-the-line, not VFD). The 208-volt three-phase feeder from the building switchgear is an electrical contractor. Condensate from the indoor coil is 3/4-inch PVC, sloped, not into a sanitary wye. The helper who wanted to solvent-weld Schedule 40 PVC for the buried loop “because plastic is plastic” fails the fusion item and the 25.3 refrigerant-adjacent item at the same time. If the clinic had asked for a 40-ton geothermal plant on one loop, Class B would have been the first “no,” before any fusion iron was plugged in.

Traps: (1) PVC solvent-weld as a geothermal loop. (2) Automotive coolant in the loop. (3) Skipping the purge cart. (4) SPD with long pigtails or no ground. (5) Phase monitor on VFD output. (6) Treating open-loop discharge as a plumbing-free dump. (7) Class B on a 40-ton GSHP because HDPE ‘is just plastic pipe.’