The Glossary of Geothermal Heating and Cooling provides definitions of many terms used within the Geothermal heat pump industry. The terms in this glossary may be used by industry professionals, for education materials, and by the general public.
Contents
- Active Borehole Length
- Ambient Air
- Ambient Ground Temperature
- Annual Ground Load
- Antifreeze
- As Built Drawing
- Auxiliary Heat
- Average Efficiency
- Balance Point Temperature
- Bend
- Bentonite Grout
- Best Practice
- Bin
- Bleed
- Block Load
- Blowers
- Brine
- Buffer Tank
- Building Management System
- Centralized Pumping System
- Circulating Pumps
- Closed Loop System
- Coaxial Heat Exchanger
- Coefficient of Performance
- Coil
- Combination GSHP Unit
- Condenser
- Compressor
- Deep Earth Temperatures
- Degree Day
- Delta P
- Delta T
- Demand DMD
- Design Loop Temperatures
- Design Outdoor Temperature
- Design Loads
- Design Temperature Summer
- Design Temperature Winter
- Desuperheater
- Dimension Ratio DR
- Direct Expansion DX Earth Coupled Heat Pump
- Distributed Pumping System
- Dual Circuit GSHP Unit
- Efficiency
- Energy Efficiency Ratio EER
- Energy Loads
- Energy Model
- Emergency Heat
- Entering Water Temperature EWT
- Equipment Loads
- Evaporator
- Expansion Valve
- Fan Coil
- Finish Tank
- Flow Center
- Flow Meter
- Flow Rater
- Fluid Factor
- Flush Cart
- Flow Regime
- Flushing Velocity
- Forced Air
- Fossil Fuel System
- Fusion
- Gauge Pressure
- GeoExchange System
- Geo Stab
- Ground Coupled Heat Pump
- GHX Circuit
- Geothermal Heat Pump
- Ground loop
- Ground Heat Exchanger GHX
- Ground Loads
- Ground Source Heat Pump GSHP
- Grout
- Grouting
- Header
- Heat Energy
- Heat Exchanger
- Heat of extraction HE
- Heat of Extraction
- Heat Fusion
- Heat Gain
- Heat Load
- Heat Loss
- Heat Pump
- Heat of rejection HR
- Heating Ventilation and Air Conditioning System
- Heat Sink
- Heat Source
- Heating Seasonal Performance Factor HSPF
- Heat Transfer Resistance
- Horizontal loop
- Hybrid System
- Hydronic
- Inhibitor
- Integrated Design Process IDP
- Internal Gains
- Joint
- Laminar Flow
- Latent Cooling Load
- Latent Heat
- Loop System
- Manual J
- Maximum EWT
- Minimum EWT
- Methanol
- Monitoring System
- Multi pipe Trench
- Multi source heat pump
- Non Pressurized Flow Center
- Open Loop
- PT Port
- Package System
- Passive Solar
- Percent of Load
- Performance Factor
- Pond Loop
- Positive Displacement Pump
- Power Flushing
- Pressure Drop
- Pressurized Flow Center
- Pressure Rating
- Pump Curve
- Pump and Dump
- Purge Pump
- Racetrack
- Radiant
- Refrigerant
- Return Air
- Reversing valve
- Reverse return
- Reynolds number
- Rule of Thumb
- Run Fraction
- Run Time
- Saturated Liquid
- Saturated Vapor
- Saturation Temperature
- Scaling
- Schedule
- Seasonal Energy Efficiency Ratio SEER
- Sensible Cooling Load
- Sensible Heat
- Sensible Heat Factor SHE
- Series System
- Short Looped
- Site derived renewable fraction SDRF
- Site Plan
- Slinky loop
- Solenoid
- SoilField Resistance
- Split System
- Standing Column Well SCW
- Supplemental Heating
- Temperature Lift
- Therm
- Thermal Conductivity
- Thermal Conductivity Test
- Thermal Energy Storage
- Thermally Enhanced Grout
- Throttling Valve
- Ton of Refrigeration
- Total Cooling Load
- Tremie Line
- Turbulent Flow Regime
- Ubend
- Unitary Heat Pump
- Valve Expansion
- Valve Reversing
- Variable refrigerant flow
- Vertical loop
- Vorizontal Loop
- Water Source Heat Pump
- Water Source Heat Pump Closed Loop
- Water Source Heat Pump Open Loop
- Water to Air
- Water to Water
- Zone Load
- References
Active Borehole Length
The length of the U-bend in the borehole below the header trench (usually 4 to 6 feet less than the total borehole length from the surface).Ambient Air
The surrounding air (usually outdoor air or the air in a specific location).Ambient Ground Temperature
The natural temperature of the earth in a specific location. This temperature will typically be quite stable at a depth of 30' (9 m) and is usually close to the annual average air temperature of the area and is influenced primarily by the average air temperature and secondarily by the thermal energy absorbed from the sun. While the ambient ground temperature is constant, as heat is extracted or rejected via the ground heat exchanger (GHX), the temperature will vary. Typically, a GHX is designed to operate at a minimum fluid temperature of about 32°F (0°C) and a maximum fluid temperature of 90°F (32°C)Annual Ground Load
Defined to be the difference between the annual amount of heat rejected to the GHEX in the cooling mode and the annual amount of heat extracted from the GHEX in the heating mode.Antifreeze
A variety of Antifreeze solutions are used in geothermal ground loops. The most common types are: Propylene glycol, Methanol, and EthanolAs-Built Drawing
A detailed drawing that shows everything included on the site plan in addition to the exact location, dimensions, and other pertinent details for a given GHEX installation after the installation is complete.Auxiliary Heat
A supplemental source of heating to provide additional heat to assist a geothermal heating and cooling system. Auxiliary heat can also be used as back-up emergency heat if heat pump goes into fault.Average Efficiency
Seasonal average versus peak Energy Efficiency Ratio (EER) or Coefficient Of Performance (COP).Balance Point Temperature
The outdoor air temperatures where internal heat gains from people, appliances, etc. offset the envelope heat loss to the atmosphere. It is at the balance point temperatures where no indoor heating or cooling will be required to maintain the temperature of the home at the thermostat set point.Bend
A fitting either molded separately or formed from pipe for the purpose of accommodating a directional change.Bentonite Grout
A common grout mix 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.Bin
In the bin method, a temperature increment, usually 5 F, into which the range of temperatures for an area are divided. Bins are used to produce a frequency distribution of hourly, monthly, or annual outdoor temperature occurrences for a specified location.Bleed
Discharge of water from a standing column well to maintain desired temperaturesBlock Load
Defined to be the sum of the zone loads. A block load calculation is necessary for a building with multiple zones served by a centralized heating/cooling system.Blowers
Fans used to force air across the heat exchanger. With a ground source heat pump, the only blower used is to force air through the central heating system.Brine
A mixture of water and antifreezeBuffer Tank
A storage tank for geo conditioned waterBuilding Management System
A computerized or digital control system that controls many or all of the systems in a building, including the HVAC system, lighting system, building access controls, etc.Centralized Pumping System
Flow centers located centrally in a ground source system that produce flow to all heat pump units in that system.Circulating Pump(s)
The pump(s) that circulates the fluid in the closed-loop system during normal operation.Closed-Loop System
The heat exchange loop in a GSHP system that consists of the ground heat exchanger, the circulating pump, and the water-source heat pump in which the heat transfer fluid is not exposed to the atmosphere.Coaxial Heat Exchanger
A tube in tube heat exchanger where water (or brine) is separated from refrigerant.Coefficient of Performance
A measure of heat pump efficiency. It is calculated by dividing the heating or cooling output of a heat pump (in BTUs/hr) and dividing it by the energy input (converted to BTUs/hr).Coil
A heat exchanger used to transfer energy from one source to another. In ground source heat pumps, water-to-refrigerant and refrigerant-to-air coils are used.Combination GSHP Unit
A GSHP that has the ability to heat or cool air at full capacity or to heat or cool water at full capacity, but not both at the same time.Condenser
A heat exchanger in which hot, pressurized (gaseous) refrigerant is condensed by transferring heat to cooler surrounding air, water, or earth.Compressor
The central component of a heat pump system. The compressor increases the pressure of a refrigerant fluid, and simultaneously reduces its volume, while causing the fluid to move through the system.Deep Earth Temperatures
Relatively constant temperature at a given depth which vary when heat is extracted or rejected by ground loops.Degree Day
A measure of the severity and duration of an outdoor temperature deviation above or below a fixed temperature (65 F), used in estimating the heating or cooling requirement and fuel consumption of a building for either summer or winter conditions.Delta P
Difference in pressure between two test pointsDelta T
Temperature difference between two test sites such as supply and return air or entering and leaving water in ground loop.Demand (DMD)
The electrical input required to operate a GSHP unit for space conditioning.Design Loop Temperatures
Temperatures that the ground loop is designed to stay above during the heating mode and below during cooling mode.Design Outdoor Temperature
Outdoor air temperatures that coincides with the peak seasonal heating or cooling load.Design Loads
The peak heating or cooling load used to select the equipment for a system (such as a heat pump) and to design the air distribution system (supply air diffusers, return air grilles, and the duct system). Design loads are based on standard or accepted conditions for a given locality (a design day).Design Temperature, Summer
A specific temperature used in calculating the cooling load of a building. The summer design temperature is typically the outdoor air temperature that is exceeded 0.4% or 1.0% of the time.Design Temperature, Winter
A specific temperature used in calculating the heating load of a building. The winter design temperature is typically the outdoor temperature that is exceeded 99.0% or 99.6% of the time.Desuperheater
A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating water. Also known as a heat recovery water heater.Dimension Ratio (DR)
A specific ratio of the average specified outside diameter to the minimum specified wall thickness (OD/t) for outside-diameter controlled plastic pipe.Direct Expansion (DX) Earth-Coupled Heat Pump
A heat pump system in which the refrigerant is circulated in pipes buried underground.Distributed Pumping System
A system made up of smaller, individual pumping stations (one flow center for each heat pump) each controlled individually by the operation of the specific heat pump unit that they serve.Dual Circuit GSHP Unit
A GSHP which utilizes two compressors (generally of different capacities) connected to two refrigeration circuits to allow multiple modes of operation. This unit may use one compressor in heating or cooling of ducted air only, one compressor to heat water only, one compressor heating or cooling air while the other is heating water, or both compressors either heating or cooling air.Efficiency
A measure of the useful output of a system divided by the input required to drive the system.Energy Efficiency Ratio (EER)
A measure of cooling efficiency for heat pump equipment, expressed as the cooling energy removed from the space (Btu) divided by the electric energy consumed to provide that cooling (W).Energy Loads
Used in predicting the energy necessary to operate the system for some prescribed time such as a month, year, or season. The calculation methodology may be the same as for the design load; however, the actual operating and weather data are used instead of design conditions.Energy Model
A detailed heat loss and heat gain calculation for a building. The calculation takes into account heat transfer to and from the space inside the building to the outside air. It takes into account the construction of the building walls and roof, including insulation values, mass of the structure, orientation of the different components to the sun, color of the material. An 8,760 hourly model is used to calculate the heat loss/gain based on the historical average temperature data (usually 20 years) for the building location. The modeler then overlays building occupancy schedules, lighting schedules, ventilation, etc. to account for internal heat gains, heat losses and gains from the mechanical system, etc. in detail, on a room by room basis. The software than calculates the actual heating and cooling loads required for every hour of the year. The detailed energy analysis allows us to calculate the energy consumption per day, month or year. This can be translated into energy cost based on local utility rates. It also allows us to calculate energy transfer to and from the GHX and size the system accurately.Emergency Heat
A backup heat source that is activated if heat pump shuts off. The most common form of emergency heat is electric resistance.Entering Water Temperature (EWT)
The temperature of the water entering the heat pump from the ground loop heat exchanger. Systems are designed so that the entering water temperature does not fall below the Minimum Entering Water Temperature during heating or rise above the Maximum Entering Water Temperature during cooling. Entering water temperature has a significant effect on heat pump operating efficiency.Equipment Loads
Loads served by the heating/cooling system that are not included in peak heating/ cooling block load calculations. These loads include duct and hydronic piping losses/gains as well as ventilation loads.Evaporator
A heat exchanger in which cold, low-pressure (liquid) refrigerant is vaporized to absorb heat from the warmer surrounding air, earth, or water.Expansion Valve
A device that reduces the pressure of liquid refrigerant entering the evaporator and meters and regulates the flow of refrigerant so that it can properly absorb heat.Fan Coil
A water or refrigerant coil through which air is circulated for conditioningFinish Tank
Water heater downstream of a buffer tankFlow Center
A packaged set of circulating pumps mounted in a cabinet, which often includes valves and ports for flushing/purging, antifreeze charging (if used), and loop pressurization (if a pressurized flow center is used).Flow Meter
A device 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
A factor, F, used in calculating geoexchange rate, G, in BTUs/hr.Flush Cart
A system which integrates the purge pump with the valving, hose connections, electrical connections, filtration, and reservoir tank on a hand cart for maximum portability and ease of use during operation. Flush carts fabricated for residential or light commercial use will typically utilize high-head, high-volume purge pumps from 1-1/2 hp to 3 hp in size.Flow Regime
A term used in fluid mechanics to define the nature of fluid flow in any situation. Flow regime can either be regarded as laminar, transitional, or turbulent.Flushing Velocity
Velocity of fluid (often stated in feet/second) required to force air out of any pipe in a ground loop heat exchanger, generally accepted minimum is 2 feet/sec.Forced Air
System that conditions a space by circulating air through a heat exchanger or fan coilFossil Fuel System
A home heating system that uses natural gas, liquid propane or fuel oil.Fusion
Method of joining loop pipes together. Most common are socket fusion, butt fusion or electro fusion.Gauge Pressure
Pressure reading directly taken from a pressure sensor or gauge (psi).GeoExchange System
A system that utilizes renewable thermal energy in the shallow subsurface to extract or reject heat.Geo Stab
Fusionless loop fittingsGround Coupled Heat Pump
See Ground Source Heat PumpGHX Circuit
Most GHX's are designed and built with one or more "supply and return runout pipe pairs". Connected to the runout pipe pairs are 2 or more GHX circuits that are installed in vertical boreholes, horizontal trenches or submerged in bodies of water. The GHX circuits are the primary heat exchange surface areas that absorb heat from the ground or water or reject heat to it.Geothermal Heat Pump
A refrigeration-based system that extracts or rejects heat (BTUs) from an open or closed loop systemGround loop
See Ground Heat Exchanger.Ground Heat Exchanger (GHX)
A heat exchanger buried in the ground around or under a building. Typically it is built by burying a continuous coil of high-density polyethylene (HDPE) or cross linked polyethylene (PEX) pipe in the ground. The pipe can be buried in excavated trenches 4' to 10' (1.3 to 3 m) deep, inserted into horizontal or vertical boreholes, or laid in the bottom of a pond, lake or the ocean.Ground Loads
Associated with ground source systems and related to the design of the GHEX. In principle, these calculations are similar to the energy loads except the ground load is heat rejected to the ground (cooling mode) or removed from it (heating mode).Ground Source Heat Pump (GSHP)
A heat pump system that uses the ground as a heat source and/or heat sink.In a closed loop system, the heat exchanger is typically coils of high-density polyethylene pipe installed in the ground under or around a building. A heat transfer fluid, usually water or water mixed with antifreeze (propylene glycol, ethanol or methanol), is circulated through this pipe, warming or cooling to the temperature of the earth or rock around it.
In open loop systems the pipe draws water from a well, lake or pond. After it is warmed or cooled the water is returned via a discharge well or back to the lake or pond.
The fluid from the open or closed loop is circulated through a heat pump. The refrigerant in the heat pump either extracts heat from the fluid or rejects heat to it, cooling or warming the refrigerant. When heat is absorbed by the refrigerant, the heat pump boosts its temperature and sends it to the air handler to circulate hot air to heat the home and (optionally) to a hot water heater to produce domestic hot water. The now cooled fluid goes back into the closed loop or, in an open loop system, is sent back to its source.
When the heat pump cools the building, the air handler transfers the heat to the heat pump's refrigerant, warming it and the heat transfer fluid. The now heated fluid circulates back into the closed loop for cooling back to the ambient ground temperature. In an open loop system is sent to the discharge well or back into the lake or pond.
Grout
A material used during the grouting process specifically designed to form a hydraulic barrier in the borehole and to promote transfer between the GHEX piping and the earth. Most grouting products are bentonite-based with fewer being cement-based.Grouting
The practice of making a conscious effort to form a hydraulic barrier in a borehole to protect the integrity of the deep earth environment. Proper grouting implies that an approved grouting material is used and that it is placed in the hole starting through a tremie line, filling it from bottom to top.Header
A manifold that joins parallel loops to a common header pipeHeat Energy
Thermal energy (often measured in BTUs) that is transferred from and to ground loop with the heat pump.Heat Exchanger
A device, often a coil, specifically designed to transfer heat between two physically separated fluids of different temperatures.Heat of extraction (HE)
Thermal energy removed from the ground loop and provided to the building during heating mode. This is commonly referred to as geoexchange and is recognized as renewable thermal energy. Commonly expressed in BTU/hrHeat of Extraction
The portion of a GSHP's heating capacity that is extracted from the earth in the heating mode. Heat of extraction is always smaller than the heating capacity of the heat pump because the electrical power consumption of the compressor, fan, and pumps add to the heating capacity of the GSHP.Heat Fusion
Making a joint by heating the mating surfaces of the pipe components to be joined and pressing them together so that they fuse and become essentially one piece.Heat Gain
When cooling a building the heat gain is the amount of btus a system must be able to reject elsewhereHeat Load
Heat load is a calculation that identifies both the heat gain and the heat lossHeat 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 resistanceHeat Pump
A mechanical device used for heating and cooling which operates by pumping heat from a cooler to a warmer location. Heat pumps can draw heat from a number of sources, e.g., air, water, or earth, and are most often either air source or water source.Heat of rejection (HR)
The amount of heat that must be rejected to the earth in the cooling mode to provide cooling to the space. The heat of rejection is always larger than the cooling capacity of the heat pump because the electrical power consumption of the compressor, fan, and pumps must also be rejected to the heat sink (ground connection).Heating, Ventilation and Air-Conditioning System
A building system designed to maintain the required temperature and air quality in occupied spaces in a building. It includes equipment that provides heating and cooling to the distribution system, which delivers this conditioned air to all parts of a building, as well as adequate air quality by ventilating and filtering the air. Often referred to as "HVAC."Heat Sink
The medium—air, water, earth, etc.—which receives heat from a heat pump.Heat Source
The medium—air, water, earth, etc.—from which heat is extracted by a heat pump.Heating Seasonal Performance Factor (HSPF)
A measure of heating efficiency for air source heat pump equipment on an annual basis, expressed as the heating energy provided to the space (Btu) divided by the electric energy consumed (Watt-hour) over the entire heating season.Heat Transfer Resistance
A system's resistance to heat flow resulting from the specific thermal properties and dimensions of the system.Horizontal loop
See description hereHybrid System
For residential systems, this typically refers to package units that can provide space heating and domestic hot water. In commercial applications, this typically refers to systems that consist of multiple types of heating/cooling systems.Hydronic
A heating or cooling distribution system using liquid piped throughout the house to radiators or convectors.Inhibitor
A fluid additive specifically designed to decrease the rate of oxidation in metal (rust) and promotion of microbial life (bacteria) in the closed-loop circulating fluid.Integrated Design Process (IDP)
A process used when designing a building in which all of the stakeholders in a project work closely together in an attempt to achieve the most efficient building and system possible. As an example, a lighting designer may determine that the energy cost savings from installing more efficient lighting in a building is not very cost-effective because the electricity saved by the lighting will not pay for the additional cost of installing the lights for more than 30 years...and would normally recommend against installing the lighting. But, when the reduced heat gain from more efficient lighting is taken into account, the capacity of the cooling system can be reduced enough to pay for the more efficient lighting, and savings resulting from both the lighting and cooling system are taken into account, it results in an overall saving for the owner.Internal Gains
In load calculations internal gains are things that contribute heat in a building such as lighting and other appliances.Joint
The location at which two pieces of pipe or a pipe and a fitting are connected.Laminar Flow
Fluid that flows in static layers with no intermixing. See Laminar flowLatent Cooling Load
The amount of moisture that must be removed to maintain the space at the desired humidity level.Latent Heat
The thermal energy required for water to make a phase change from vapor (humidity) to liquid (water condensate that runs down the drain) or liquid to solid (ice). See Latent heatLoop System
The ground heat exchange for a heat pump. It is either open or closed loop.Manual J
Among the most common load calculation formula.Maximum EWT
In loop field design, the maximum entering water temperature is what you size your loops not to exceed during the cooling seasonMinimum EWT
In loop field design the minimum entering water temperature (from the GHX) permitted throughout the heating seasonMethanol
Commonly used antifreeze. See MethanolMonitoring 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 heat pump
A heat pump with access to more than one source/sink element of thermal energy. Common elements include, ground, solar, air, biomass, waste heat. Often applied with a thermal battery or thermal energy storage devices.Non-Pressurized Flow Center
A flow center that maintains a flow of water into the suction side of the pump (maintaining a flooded volute and reliable pump operation) by having the pump located directly adjacent to a column of water (in a canister). As a result, the system can operate at "zero" or atmospheric pressure. Thus the term "non-pressurized" simply means a device that allows for reliable pump operation without the need to elevate the system pressure (typically 20-60 psig for pressurized systems). Non-pressurized does not mean that the system is open to the atmosphere, but simply a closed sealed system that operates at atmospheric pressure.