HVAC Terminology



A geothermal heat pump or ground source heat pump is a central heating and/or cooling system that transfers heat to or from the ground.  It uses the earth as a heat source in the winter or a heat sink in the summer.  The design takes advantage of the moderate temperatures in the ground to boost efficiency and reduce the operating costs of heating and cooling systems.


SEER RATING (Seasonal Energy Efficiency Rating)

SEER Ratings are used to describe the cooling efficiencies of an air conditioning system.  The higher the SEER Rating, the less power is consumed to run the A/C unit.  Air conditioning equipment install 15 or so years ago probably have SEER Ratings between 6 and 10 while newer A/C systems installed today range from 13 to 21 SEER.


VAV SYSTEM (Variable Air Volume System)

An HVAC system capable of serving multiple zones.  The equipment controls the temperature in each individual zone by controlling the amount of heated or cooled air supplied to the zones.



An HVAC units economizer can significantly reduce energy by cooling buildings with outside air rather than using the units compressor(s) to cool the air.  This method is also referred to as "free cooling."  An economizer consists of electronic controls, an actuator, sensors and dampers that together decide on much outside air is needed in the building.  As the building heats up due to lighting, people and equipment, while the outdoor temperature is cool and comfortable, the economizer measures the outdoor air temperature and humidity.  If the economizer system determines it is cool and dry enough outdoors to keep the occupants comfortable, the economizer will use the outside air for cooling rather than operating the compressor(s).



A cooling tower is a heat rejection device, which extracts waste heat from the building and rejects it to the atmosphere through the cooling of a water stream to a lower temperature.  The process is achieved by moving air in the tower and water over the condenser coils until the desired temperature is obtained.



This control is used when high building heat loads dictate the operation of the cooling cycle during cold outdoor temperatures.  This control is useful with computer room, data centers, and IT room applications.  Extended operation  of the compressor in the cooling mode when outdoor temperatures drop below 50 degrees Fahrenheit can cause the indoor evaporator coil to freeze up.  The low ambient control cycles the outdoor fan motor in response to refrigerant pressures.  This keeps the system pressures from reaching the point where icing would occur.



A program of equipment maintenance implemented to reduce the probability of problems, usually through periodic inspection, cleaning, lubricating, adjustments, and replacement of  functioning, questionable parts of the HVAC system.


EMS - (Energy Management System)

An EMS system is a fully functional control system which includes controllers, communication devices, and operational software necessary to maintain control over a building's HVAC system.  It is designed to control and regulate the energy consumption of a building by the controlling the operation of the energy consuming systems.  An EMS control system  may control other mechanical systems within a building, such as lights, etc.


DDC - (Direct Digital Control)

Direct digital controls (DDC) form a loop in which a digital controller periodically updates the operating function of the HVAC systems, according to preset (desired) parameters, for conservation of energy in a commercial building.  DDC systems can be remotely accessed by building owners/managers.  Direct digital controls are used as part of the buildings energy management (EMS) system.


AFUE (Annual Fuel Utilization Efficiency)

The AFUE number represents how efficiently a furnace converts fuel to energy.  The greater the AFUE number, the more efficient the furnace is.  This translates to a higher savings on the fuel bills.  This value is intended to represent the heat transferred to the conditioned space by the fuel energy supplied over one year.


VFD - (Variable Frequency Drive)

A VFD is a drive that changes the actual speed of a motor by creating a new AC line voltage at any frequency.  Due to this, a motor will ramp up and down as required to supply increased or decreased airflow as required by the controlled temperature changes.  Significant energy savings can be realized through power consumption, which is why many utilities offer energy rebates for VFD installations.