NATE Ground Source HP Loop Installer key terms

The resistance to heat flow between the circulating fluid and the borehole wall, combining pipe wall, grout, and borehole geometry effects. Lower values improve heat exchange and shorten the required loop length.

The drilled diameter of a vertical borehole, typically 4 to 6 inches for residential work. It sets annulus volume, grout quantity, and the spacing between the down and up pipes.

Center-to-center distance between vertical boreholes, commonly 15 to 20 feet. Spacing controls thermal interference between holes and long-term ground temperature drift in the bore field.

The arrangement of multiple vertical boreholes serving one heat pump system, defined by hole count, depth, and spacing. Field layout determines total ground loop capacity and long-term performance.

The reduction in heat exchange caused when adjacent boreholes or trenches compete for the same ground volume. It increases with tight spacing and unbalanced annual heating or cooling loads.

A design condition in which annual heat rejected to the ground roughly equals annual heat extracted. Balanced loads keep ground temperature stable and allow shorter loop fields than heavily unbalanced loads.

The rate at which soil or rock conducts heat, usually expressed in Btu/(h·ft·°F). It is the single most influential site property in sizing a ground loop.

A field test that circulates fluid through a test borehole and measures heat input and temperature response to estimate formation conductivity and borehole resistance. Results refine loop length calculations.

An industry method for sizing heating and cooling equipment from building envelope, orientation, and occupancy data. The resulting block load is the starting point for ground loop sizing.

The total peak heating or cooling load for a building at design conditions, expressed in Btu/h or tons. It drives heat pump selection and the required ground loop capacity.

The engineering process that converts block load, ground conductivity, borehole resistance, and operating temperatures into required pipe length or borehole count. It must account for the most extreme entering water temperature.

The fluid temperature returning from the ground loop to the heat pump. Design limits are typically 25 to 40°F in heating and up to about 90 to 110°F in cooling, depending on equipment.

The standard plastic for buried ground loop pipe, commonly PE 3408 or PE 4710, rated by dimension ratio and pressure. It resists corrosion and is joined by thermal fusion.

The ratio of pipe outside diameter to wall thickness, written as DR with a number such as DR-11. Lower DR means thicker wall and higher pressure rating.

The maximum allowable working pressure of a pipe or fitting at a stated temperature, derived from material, dimension ratio, and a design safety factor. It must exceed the loop's highest expected pressure.

A factory-fabricated fitting joining two lengths of loop pipe at the bottom of a borehole, turning the flow 180 degrees. It must be pressure rated and fused or mechanically sealed per manufacturer instructions.

A device that holds the two legs of a borehole U-bend apart at a set distance. Proper spacing improves heat transfer and helps grout fully surround both pipes.

A small-diameter pipe lowered to the bottom of a borehole to place grout from the bottom upward. It prevents voids and bridging by keeping the discharge end submerged in rising grout.

The ability of borehole grout to conduct heat between pipe and formation, commonly 0.4 to 1.4 Btu/(h·ft·°F). Higher-conductivity grout reduces borehole resistance and required depth.

The quantity of grout needed to fill the annulus of a borehole, calculated from hole diameter, pipe outside diameter, and depth, plus an allowance for overbreak and loss.

A joining method that heats squared pipe ends against a hot plate, then presses them together to form a homogeneous joint. Temperature, pressure, and cooling times must follow the procedure standard.

A joining method that heats the outside of a pipe end and the inside of a fitting with heated tools, then pushes them together. It is common for smaller-diameter headers and fittings.

The raised ring of displaced polyethylene formed at a fused joint. A uniform, continuous double bead indicates proper heating and alignment; a crooked or missing bead signals a defective joint.

A test that pressurizes the completed loop with water or air and holds it to reveal leaks before backfilling. Test pressure, duration, and allowable loss follow the project specification.

Documentation of test pressure, hold time, fluid temperature, gauge readings, and any makeup fluid added. It proves the loop was leak-free before concealment and supports warranty claims.

A manifold pipe that collects or distributes flow among multiple loop circuits. Headers must be sized for total flow and arranged so each circuit receives balanced flow.

An assembly of valves and ports that connects multiple ground loop circuits to a common supply and return. It allows isolation, flow balancing, and purging of individual circuits.

A header arrangement in which supply and return paths are mirrored so each circuit sees nearly equal pressure drop. It balances flow without relying solely on balancing valves.

A buried access chamber housing headers, valves, and fittings below grade. It must be structural, watertight, and sized for operation and service of the contained components.

The heat-transfer liquid pumped through the ground loop, typically water with antifreeze or a brine. Its freeze point, viscosity, and heat capacity affect pump energy and loop performance.

The percentage of methanol, propylene glycol, or similar additive in loop fluid, set to protect against the lowest expected temperature. Higher concentration raises viscosity and pumping power.

The margin by which loop fluid's freeze point sits below the coldest expected operating temperature. Adequate protection prevents ice formation and pipe damage during heating operation.

High-velocity circulation of clean water through the loop to remove construction debris, air, and contaminants before commissioning. Flow should exceed normal operating velocity and continue until discharge runs clear.

The process of forcing air out of loop circuits, often with a purge pump or flush cart, until no air bubbles remain. Trapped air causes poor heat transfer, noise, and pump cavitation.

A device that removes entrained air and gases from circulating fluid, often combined with an expansion tank. It protects pumps and maintains stable heat transfer in the loop.

Practices that protect workers in trenches and bore pits, including sloping, shoring, and keeping spoil back from the edge. Trenches five feet deep or more generally require a protective system.

The process of marking buried utilities before excavation, usually through a one-call notification service. It prevents striking gas, electric, water, and communications lines during drilling or digging.

A horizontal excavation holding loop pipe in a horizontal or slinky configuration. Depth, width, and backfill material determine heat transfer and protect pipe from damage.

A horizontal loop configuration in which pipe is coiled in overlapping rings within a trench to fit more pipe length into limited land area. Ring spacing affects thermal interference.