Glossary Terms

Name Description

Mixed with water to make brine. Most common are ethanol, methanol and propylene glycol

Auxiliary Heat

Secondary source of heat employed when conditions are at or below balance point.

Average Efficiency

Seasonal average versus peak EER or COP

Balance Point

Outdoor temperature at which auxiliary heat is required


A common grout used to protect aquifers from ground or cross contamination and ensure good contact between loop and surrounding soil

Best Practice

Commonly accepted practices among industry professionals.


Discharge of water from a standing column well to maintain desired temperatures


A mixture of water and antifreeze that operate near or below freezing

Buffer Tank

A storage tank for geo conditioned water

Closed Loop

A network of pipes underground through which water or brine is circulated to collect or reject heat energy

Coaxial Heat Exchanger

A tube in tube heat exchanger where water (or brine) is separated from refrigerant


Coefficient of performance. A heat pump is operating at 4 COP if one unit of energy nets 4 units of heat

Deep Earth Temperatures

Relatively constant temperature at a given depth (which vary when heat is extracted or rejected by ground loops)

Delta P

Difference in pressure between two test points

Delta T

Temperature difference between two test sites such as supply and return air

Design Temperature

Temperature that represents most of the seasonal heating or cooling load


A coaxial heat exchanger that uses superheated discharge gas from the compressor to preheat domestic hot water


Domestic hot water

Direct Solar

Solar energy collected directly such as heat or light through a window


Direct exchange or direct expansion system that circulates refrigerant instead of brine or water in ground loops


Entering air temperature


Energy efficiency ratio is the output of a cooling unit divided by the units of electricity used

Emergency Heat

Full emergency heat generally speaking is when auxiliary heat systems are sized for the entire building load to maintain set point in the event of heat pump failure


Entering Water Pressure


Entering water temperature

Fan Coil

A water or refrigerant coil through which air is circulated for space conditioning

Finish Tank

Water heater downstream of a buffer tank

Flow Center

Circulator for water or brine in a closed loop system

Flow Meter

For open loop systems a component that indicates water flow (often in gallons per minute)

Flow Rater

Component that reduces fluid flow to a specified rate (such as 4 gpm)

Fluid Factor

Used in calculating heat of extraction/rejection. Water is 500, antifreeze is often 485.

Flush Cart

A pump system used to purge air from a loop system and introduce water or brine

Flushing Velocity

GPM required to force air out of parallel ground loops

Foot per Foot

Number of feet of pipe per foot of trench in a horizontal loop field.

Forced Air

System that conditions a space by circulating air through a heat exchanger or fan coil

Fossil Fuel System

Generally refers to gas or fuel oil heating systems


Method of joining loop pipes together. Most common are socket fusion, butt fusion or electro fusion.


Ground coupled heat pump (see geothermal heat pump)

Geo Exchange System

A system that uses the earth to extract or reject heat

Geo Stab

Fusionless loop fittings

A trade organization and advocate for Geo pros

Geothermal Heat Pump

A refrigeration system that extracts or rejects btus from an open or closed loop system


Ground heat exchanger (such as a loop system)


Material (often Bentonite) used to prevent cross or surface contamination of aquifers and ensure loop has good contact with surrounding soil

Grout Pump

literally a pump that injects grout into boreholes


Ground source heat pump (see geothermal heat pump)


determines the nature of liquid flow through pipe. The higher the number the more turbulent the flow


A manifold that joins parallel loops to a common header pipe

Heat Energy

Btus in this context moved around by the heat pump

Heat Gain

When cooling a building the heat gain is the amount of btus a system must be able to reject elsewhere

Heat Load

Heat load is a calculation that identifies both the heat gain and the heat loss

Heat Loss

When heating a building the heat loss is the total number of btus that a system needs to extract from elsewhere or produce through combustion or resistance

Heat of Extraction/HE

Btus extracted by a GSHP are determined by multiplying the difference in entering and leaving water temperatures by gallons per minute times the fluid factor

Heat of Rejection/HR

Btus rejected by a GSHP are determined by multiplying the difference in entering and leaving water temperatures by gallons per minute times the fluid factor

Heat Pump

A system that moves heat energy from one location to another.

Heat Sink

A place that heat energy can be rejected for dissipation

Horizontal Loop

Closed loop buried horizontally in beds or trenches


In this context generally refers to a package unit that warms both air and water (excludes DSH)


Literally means water. A hydronic fan coil may be employed to heat or cool with hot or chilled water while radiant floors would be another way to deliver hydronic heat


A trade organization for geo pros. The International Ground Source Heat Pump Association offers certifications for installers, well drillers and designers

Indirect Solar

The suns energy collected indirectly perhaps through circulated brine in solar hot water or through the earth with a ground source heat pump or by conversion to usable electricity.

Internal Gains

In load calculations, internal gains are things that contribute heat in a building such as lighting and other appliances.

Laminar Flow

Fluid that flows in static layers with no intermixing


Leaving air temperature. Generally a measurement with entering air temperature to determine a systems performance

Latent Heat

In the context of cooling a building’s latent heat refers to the humidity load. More specifically it is the Btu’s required for a phase change such as vapor (humidity) to water (condensate that runs down the drain).


A condition in which a heat pump’s control system determines continued operation could be damaging to the appliance. Common causes are poor water flow or low air flow due to insufficient maintenance.

Loop System

The GHX for a heat pump. Can be open or closed loop


Leaving water pressure


Leaving water temperature

Manual J

Among the most common load calculation formulae

Maximum EWT

In loop field design, the maximum entering water temperature is what you size your loops not to exceed during the cooling season

Minimum EWT

In loop field design the minimum entering water temperature (from the GHX) permitted throughout the heating season

Monitoring System

Monitoring systems in the context of a geothermal system are used to monitor efficiency and operation. Some also give notices for maintenance such as filter changes and alerts for trouble such as excessive auxiliary use. This system could be linked to the internet for remote monitoring, could be in the form of an electric meter, an hour counter or a web based monitor or thermostat.

Multi-pipe Trench

A horizontal loop generally consisting of 2, 4 or 6 pipes. Pipes may be pinned to trench walls for separation or may have one course on the bottom of the trench and a second course after a foot or two of backfill.

Multi Source System

Also MSHP. A system that combines air source, solar or ground source technologies.

Open Loop

A system that uses well water that is discharged to a drain, re-injected into a return well or returned to the same well it was extracted from.

Operating Models

A software program that factors building load, weather averages and utility costs to help size systems and predict operating costs.

P/T Port

Generally at or close to where water or brine enters and leaves the geothermal unit, a P/T port is an opening where one may insert a gauge to measure pressure (P) or temperature (T).

Package System

In geothermal terms a self-contained forced water to air system. Both the refrigeration and air handling systems are in one unit.

Passive Solar

A system that extracts energy from the sun through an intermediary (also indirect solar). In the context of geothermal, the sun warms the earth and the loop system collects that solar energy for space conditioning.

Percent of Load

In the geothermal context the percent of load is usually the amount of seasonal btus provided by each of the geothermal stages. This is not the same as percentage of the actual heat loss/gain. Peak loads happen very infrequently so 60% of peak load may be 98% of seasonal demand.

Pond Loop

Loop system placed in a pond or lake instead of buried under ground.

Pressure Drop

In geothermal pressure drop most commonly refers to a measurement of entering and leaving water pressures at the unit to determine gallons per minute of flow through the coaxial heat exchanger. In general hydronics including loop fields it is also a factor in design that must be overcome with pumping power to deliver desired GPM.

Pump and Dump

Open loop system adds heat to or removes it from water and then discharges it.


Multi pipe trench of generally 2, 4 or 6 pipes


In the context of geothermal, hydronic radiant floors walls or ceilings are one way to deliver/extract heat

Reversing Valve

On closed loop headers the parallel loop that is closest to the heat pump on one header would return farthest from the heat pump on the other

Reverse Return

A refrigerant valve that reverses refrigerant flow to determine whether system is heating or cooling

Reynolds Number

Determines the nature of liquid flow through pipe. The higher the number the more turbulent the flow

Rule of Thumb

In geothermal “rules of thumb” are generally not considered best practice


Standing column well. An open loop system that returns water from the geothermal, into the same well it was extracted from. Usually a designer includes a bleed off to keep from adding or extracting too much heat. Bleed water is replaced by fresh water from the aquifer the SCW is drawing from.

Sensible Heat

Sensible heat changes the temperature of water or air

Short Looped

In geothermal a “short looped” system is one which fails to maintain minimum and maximum entering water temperatures due to inadequate design.

Slinky Loop

A type of loop that is coiled much like a flattened child’s toy of the same name. Generally laid flat in the bottom of a trench, vertical slinkies have been used as well.


Used for several things in geo a solenoid is generally used to interrupt flow of water when an open loop system is not running.

Split System

A heat pump that has an air handler and fan coil separate from the refrigeration components


Thermal conductivity. For our purposes the rate at which heat energy can move through soil surrounding ground loops. In geothermal we factor the TC of the soil into our loop design.

TC Test

In commercial applications a TC test often allows for GHX reduction if conditions are determined better than average

Thermally Enhanced Grout

High performance grout with a greater TC than more commonly used products

Throttling Valves

Most commonly used to restrict flow between desuperheaters and buffer tanks, throttling valves allow an operator to achieve higher delta T between entering and leaving water by slowing the GPM flow.

Tremie Pipe

Pipe used with a grout pump to inject grout into boreholes.

Turbulent Flow

Fluid passing through pipe with no discernable layers. Generally preferred in geo loop design to get best contact between all water or brine with pipe walls.

Vertical Loop

In geothermal a vertical loop is generally installed by a well driller and goes straight up and down versus horizontally

Vorizontal Loop

Generally installed by a directional boring machine this loop travels both horizontally and vertically.


Variable refrigerant flow. The next generation in technology that allows a compressor to only use what is required to satisfy demand versus multi stage or single stage systems that sometimes use more energy than is required


Water source heat pump. Generally in geothermal, water to air or water to water.


Water to air


Water to water