NATE GS Installation key terms

The temperature rise of refrigerant vapor above its saturation temperature at a given pressure, measured at the evaporator outlet to confirm the expansion valve is feeding the coil correctly.

The temperature drop of liquid refrigerant below its saturation temperature at a given pressure, measured at the condenser outlet to confirm the coil is fully condensing and liquid reaches the metering device.

The temperature at which a refrigerant changes phase at a given pressure; on a gauge manifold it is read as the boiling or condensing point corresponding to the measured pressure.

A table or graph listing saturation pressures and temperatures for a specific refrigerant, used to convert gauge readings into the temperatures needed for superheat and subcooling calculations.

A metering device that regulates refrigerant flow into the evaporator by sensing suction line temperature and evaporator pressure, maintaining a set superheat across the coil.

Any restriction that drops refrigerant pressure between the liquid line and evaporator, controlling flow and creating the low-side pressure that drives boiling in the coil.

The outdoor coil where high-pressure refrigerant vapor rejects heat to ambient air and condenses into liquid, rejecting both sensible heat and the heat absorbed by the evaporator.

The indoor coil where low-pressure refrigerant boils and absorbs heat from air moving across it, producing the cooling and dehumidification delivered to the conditioned space.

The pump that raises refrigerant vapor from low-side to high-side pressure, creating the pressure difference that circulates refrigerant and drives the entire refrigeration cycle.

The fluid that circulates through the sealed system, absorbing heat as it boils at low pressure and releasing heat as it condenses at high pressure.

The outward force per unit area exerted by air against duct walls, expressed in inches of water column and used to size blowers and evaluate duct and filter resistance.

The total resistance to airflow measured across the air handler, including supply and return ducts, coils, filters, and grilles, used to verify blower performance against its rating table.

The pressure created by air in motion, equal to total pressure minus static pressure, used with a pitot tube or flow hood to determine air speed in a duct.

The volume of air moved per unit time, typically stated in cubic feet per minute, which must match equipment capacity and duct sizing for proper system performance.

Selecting duct dimensions so that airflow is delivered within acceptable friction loss and velocity limits, commonly done with friction-rate or velocity-based sizing methods.

A boxed chamber connected to the air handler that distributes supply air to branch ducts or collects return air before the unit; it must be sealed and sized to avoid turbulence.

A duct layout in which a large main trunk carries air from the air handler and smaller branches deliver it to individual outlets or rooms.

An adjustable plate inside a duct that is set during air balancing to restrict flow in one branch so that all outlets receive their design airflow.

Air drawn back from conditioned spaces to the air handler for reconditioning; undersized or restricted returns raise static pressure and reduce total system airflow.

Heat energy absorbed or released during a phase change without a temperature change, such as water vapor condensing on a cooling coil; it drives the dehumidification portion of the load.

Heat that changes the dry-bulb temperature of air or a substance without changing its phase, making up the portion of the load that a thermostat can directly sense.

The temperature of air measured by an ordinary thermometer, unaffected by moisture content, and the value most thermostats use to control space temperature.

The temperature reached by air when water evaporates into it until saturated, indicating the evaporative cooling limit and used with dry bulb to determine humidity and enthalpy.

The amount of water vapor in air expressed as a percentage of the maximum the air could hold at that temperature; it falls as air is heated and rises as it is cooled.

The temperature at which air becomes saturated and water vapor begins to condense; surfaces colder than the dew point will sweat or collect condensate.

The pipe and trap assembly that carries water removed from the cooling coil to a drain, requiring a trap to overcome cabinet pressure and a slope to prevent standing water.

Removing airborne particles by passing air through a filter media, rated by MERV, which also adds static pressure that must be accounted for in blower selection.

Minimum Efficiency Reporting Value, a 1-to-16 scale describing how well a filter captures particles of given sizes; higher ratings capture finer particles but add more resistance.

Deliberately introducing outdoor air into a building to dilute pollutants and control humidity, required by code for occupied spaces and often provided by an economizer or dedicated outdoor-air unit.

A colorless, odorless gas produced by incomplete combustion that can cause illness or death; combustion appliances must be vented and tested to keep levels within safe limits.

The air supplied to a fuel-burning appliance for burning fuel, required by code in adequate volume and often drawn from outdoors to avoid depressurizing the building.

Reversal of normal vent flow that spills combustion products into a building, typically caused by depressurization or a blocked flue; a serious carbon monoxide hazard.

The passage that carries combustion gases from an appliance to the outdoors, which must be properly sized, sloped, and terminated to prevent spillage and condensation damage.

A safety procedure that de-energizes equipment and places a personal lock and tag on the disconnect so it cannot be re-energized while someone is working on it.

The intentional connection of electrical equipment to earth, providing a low-resistance path that lets overcurrent devices clear faults and protects people from shock.

Connecting metal parts together so they remain at the same electrical potential, preventing dangerous voltage differences and ensuring fault current has a reliable return path.

A fuse or circuit breaker that interrupts current above its rating, protecting conductors and equipment from overheating caused by shorts or overloads.

A switch or breaker that removes all power from a unit for service, required within sight of the equipment and sized to the circuit's ampacity.

The motor-driven fan in an air handler that moves air through the duct system; its speed taps or ECM settings are selected to deliver design airflow against the system's static pressure.