## HVAC

HVAC is used in both residental and commercial systems to controll air quality, humidity, and temperature in indoor spaces.

### abbreviations

• HVAC - Heating, Ventilation and Air Conditioning
• HVACR - Heating, Ventilation, Air Conditioning and Refrigeration
• HACR - Heating, Air Conditioning and Refrigeration

## HVAC Nomenclature & Symbols

• $$AC$$ = Air conditioning
• $$AC$$ = Alternating current
• $$Q_a$$ = Air flow rate
• $$AHU$$ = Air handeling unit
• $$AI$$ = Analog input
• $$AO$$ = Analog output
• $$p_a$$ = Atmospheric pressure
• $$BDD$$ = Back-draft damper
• $$B$$ = Boiler
• $$BTU$$ = British thermal unit
• $$BAS$$ = Building automation system
• $$CHW$$ = Chilled water
• $$CHWP$$ = Chilled water pump
• $$CHWR$$ = Chilled water return
• $$CHWRT$$ = Chilled water return temperature
• $$CHWS$$ = Chilled water supply
• $$CHWST$$ = Chilled water supply temperature
• $$FSD,\; SFD$$ = Combination fire and smoke damper
• $$CWP$$ = Condenser water pump
• $$CWS$$ = Condenser water supply
• $$CWR$$ = Condenser water return
• $$CWRT$$ = Condenser water return temperature
• $$CWS$$ = Condenser water supply
• $$CWST$$ = Condenser water supply temperature
• $$CV$$ = Constant volume
• $$CL$$ = Cooling load
• $$CT$$ = Cooling tower
• $$DP$$ = Dew point
• $$DC$$ = Direct current
• $$DA$$ = Discharge air
• $$LVDR$$ = Door louver with clear area
• $$UC$$ = Door undercut size
• $$D$$ = Drain pipe
• $$EH$$ = Electric heater
• $$EER$$ = Energy efficiency ratio
• $$H$$ = Enthalpy
• $$EF$$ =  Exhaust fan
• $$FW$$ =  Feed water
• $$FD$$ = Fire damper
• $$GPM$$ =  Gallons per minute
• $$q$$ = Heat
• $$C$$ = Heat capacity
• $$HX$$ = Heat exchanger
• $$Q_f$$ = Heat flow rate
• $$HC$$ =  Heat recovery
• $$HCU$$ =  Heat recovery unit
• $$Q_c$$ =  Heat transfer
• $$HPS$$ = High pressure steam
• $$HWP$$ = Hot water pump
• $$HWR$$ = Hot water return
• $$HWS$$ = Hot water supply
• $$H$$ = Humidity sensor
• $$IAQ$$ = Indoor air quality
• $$U$$ = Internal energy
• $$L$$ = Latent heat
• $$LL$$ = Low limit
• $$LP$$ = Low pressure
• $$LPS$$ = Low pressure steam
• $$MU$$ = Make-up water supply
• $$MA$$ = Mixed air
• $$MAT$$ = Mixed air temperature
• $$MZ$$ = Milti-zone
• $$NC$$ = Normally closed
• $$NO$$ = Normally open
• $$OA$$ = Outside air
• $$OAP$$ = Outside air percentage
• $$OAT$$ = Outside air temperature
• $$P,\; PWR$$ = Power
• $$PRV$$ = Pressure relief valve
• $$PRV$$ = Pressure reducing valve
• $$HP$$ = Pump horsepower
• $$RH$$ = Relative humidity
• $$RA$$ = Return air
• $$RF$$ = Return fan
• $$Q$$ = Sensible heat
• $$SHR$$ = Sensible heat ratio
• $$SP$$ = Set point
• $$SD$$ = Smoke damper
• $$SP$$ = Static pressure
• $$SA$$ = Supply air
• $$SF$$ = Supply fan
• $$T$$ = Temperature
• $$\Delta T$$ or TD = Temperature differential
• $$Q$$ = Thermal energy
• $$R$$ = Thermal resistance
• $$T$$ = Thermostat
• $$VAC$$ = Vacuum
• $$VAV$$ = Variable air volume
• $$VFD$$ = Variable frequency drive
• $$VSD$$ = Variable speed drive
• $$VSP$$ = Variable speed pump
• $$V$$ = Vent pipe
• $$VD$$ = Volume damper
• $$WC$$ = Water column

## HVAC Terms

### A

• Air cleaner  -  A device that removes allergents, pollutants
• Air conditioner  -  A device that changes humidity levels, temperature or air quality.
• Air diffuser  -  A device that distributes the air and balances the air flow in the system.
• Alternating current  -  An electric current that reverses its direction over and over.
• Ambient temperature  -  When outdoors the ambient temperature is the current surrounding environment air temperature.  This temperature has nothing to do with high or low forcasts.

• Amp  -  Amp is a unit of current.
• Atmospheric pressure  -  The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.

### B

• Blower  -  Pushes air through the system.
• Burner  -  A device that promotes the combustion of air and gas.
• Butterfly flat disk damper  -  Uses a blade on a hinge that completely fills the duct and is more efficient and requires less maintenance.

### C

• Carbon monoxide  -  A colorless, odorless, and poisonous gas that occures as a byproduct of burning fuel.
• Charging a system  -  Adding coolant or refrigerant to an HVAC system.
• Cold  -  Is when the temperature is less than normal or the lack of heat.  The faster atoms and molecules move the more heat they create, so the opposite also holds true, the slower they move the colder it becomes.
• Condensate  -  Vapor that is turned into a liquid as its temperature is lowered.
• Condensate Coil  -  A device remove heat from the refrigerant.
• Condensate fan  -  A fan that passes air over the condensate coils to remove heat from the refrigerant.
• Condenser  -  An outdoor part of the AC or heat pump that releases or collects heat.
• Cooling load  -  The rate at which heat must be exchanged from a space in order to maintain the desired temperature within the space.
• Current  -  The rate of flow of electricity in a circuit, measured in amperes.
• Cycling  -  The heating and cooling system cycles when it turns on and off.

### D

• Damper  -  A device that regulates and redirects the flow of air.  Also called duct damper and volume balancing dampener.
• Dehumidifier  -  A device used to draw moisture out of indoor air.
• Duct  -  Tubing that connects the air handlers to the air diffusers.
• Ductwork  -  A series of ducts that makeup the entire coolung/heating system.

### E

• Energy efficiency ratio  -  Determines the energy efficiency of an air conditioner.
• Enthalpy  -  Measures the sum of internal energy changes in heat under constant pressure of the system.
• Evaporative cooler  -  Also called swamp cooler, is cooling by exchanging of latent heat from the water spray or wetted material.

### F

• Fan  -  A device that has a motor and wheel with blades that creates air flow.
• Freon  -  A cooling agent used in most air conditioning systems.

### G

• Guillotine damper  -  It will completely block the duct.

### H

• Heat  -  , abbreviated as q, is a form of energy that causes physical change in what is being heated.  The lack of heat is cold.  This physical change comes from total amount of internal energy (kinetic energy and potential energy) possessed by an object or substance.
• Heat capacity  -  The ratio of heat transferred to raise the temperature of an object.
• Heat exchanger  -  A device used to transer heat from one medium to another at different temperatures.  The heat transfer can be air or a liquid such as water or oil.
• Heat flow rate  -  The rate at which heat moves from an area of higher temperature to an area of lower temperature.  Heat flow is generally used to quantify the rate of total heat gain or heat loss of a system.
• Heat loss or heat gain  -  The measure of the total heat transfer through your body, clorhing, building walls, etc.
• Heat pump  -  An outdoor unit that can both heat and cool indoor air.
• Heat transfer  -  The exertion of power that is created by heat, or the increase in temperature.  It is the transfer of heat from one system to another.
• Heat transfer by convection  -  Convection is the energy transfer of heat by air, water, or any other fluid to and object. It includes energy transferred by random molecular motion as well as energy transferred by the bulk motion of the fluid.
• Humidifier  -  A device that adds humidity.

### I

• Internal energy  -  The total of all energies associated with the motion of the molecules in the system.

### L

• Latent heat  -  The energy absorbed or released by a substance during a constant temperature or phase change from a solid to liquid, liquid to gas or vise versa.
• Led  -  Light emitting diode used to display the status of the system.
• Load  - The amount of cooling or heating a building requires.
• Louver damper  -  Uses flat blades on hinges and used for quick responce time.
• Low pressure steam  -  Is when the pressure is less than or equal to that of the atmosphere.

### N

• Normally closed  -  The circuit is closed when the switch is not open.
• Normally open  -  The circuit is open when the switch is not operated.

### P

• Package system or unit  -  All HVAC components are located in one cabinet outside.
• Power  -  The rate of doing work or the rate of using energy per unit time.
• Pressure balancing  -  The process of neutralizing pressure differences within a system.
• Programmable thermostat  -  A type of thermostat that can be programmed to be run only when needed.

### R

• R-22  -  A cooling agent commonly known as freon.
• R-value  -  A measure of a material's thermal resistance.
• Relative humidity  -  A measure of the amount of moisture in the air with respect to the temperature.
• Return air  -  Air that is returned to the evaporator coil from outside the building.
• Return duct  -  The duct through which warm air is drawn into the cooling system, cooled, then returned to the cooling system.

### S

• SEER  -  Stands for Seasonal Energy Efficiency Ratio.  The higher this number is, the more energy efficient the system is.
• Sensible heat  -  The heat added to a substance which increases its temperature but not the phase.
• Sensor  -  A device that reacts to any change in conditions.
• Single-speed  -  A motor that runs a full speed until it reaches the set temperature then shuts off.
• Space heater  -  A self-contained appliance used to heat enclosed spaces.
• Static pressure  -  The difference in air pressure between the suction side and pressure side of a blower.  The higher the static pressure or resistance, the more energy it takes to move air through the object.
• Swamp cooler  -  Also called evaporative cooler, is cooling by exchanging of latent heat from the water spray or wetted material.

### T

• Temperature  -  Normally described as the amount of heat or cold, but it is neither heat or cold.  Temperature is expressed as a number that is related to energy and porportional to a type of energy, but it is not energy.
• Temperature differential  -  The difference between two specific temperature points of a volume at a given time in a system.
• Temperature zones  -  Areas of a building or rooms where the temperature can be controlled seperately.
• Thermal energy  -  The exertion of power that is created by heat, or the increase in temperature.
• Thermal resistance  -  The temperature difference by which an object or material resists a heat flow.

• Thermodynamics  -   A branch of physics and an engineering science that deals with large scale reactions of a system that can be observed and measures and the relationship between properties such as energy, heat, pressure, temperature, work, etc. on a system.
• Thermostat  -  A wall mounted device uesd to monitor and control the HVAC system output.
• Tonnage  -  A unit of measurement in air conditioning to describe the cooling capacity of the system.

### V

• Vacuum  -  A contained space having little or no matter or a volume having a pressure lower than the outside atmospheric pressure.
• Vacuum test  -  Check to see if the refigerant lines are sealed before changing with refrigerant.
• Varactor diode  -  The capacitance varies according to the applied input voltage.
• Variable capacitor  -  Used in tuning the circuit to a required frequency.
• Variable indicator  -  Allows the value of the inductance to be changed.
• Variable-speed  -  A motor that has variable speeds to be choosen.
• Ventilation  -  A natural or mechanical process of moving air into or out of interior spaces.
• Ventilation Air  -  The total air brought from the outdoors and the air re-circulated inside the building.
• Ventilation Rate  -  The rate at which air enters or leaves a building.
• Vent pipe  -  A pipe or tube used to vent combustable gasses to the outside air.
• Volt  -  A unit of electrical pressure.
• Voltage  -  The amount of pressure that will cause one ampere of current in one ohm of resistance.

### W

• Weather-stripping  -  A material used to seal gaps around exterior doors and windows.
• Weatherization  -  Process of modifying a building/home to protect it from the outside elements.
• Wet bulb thermometer  -  Measures the relative humidity in the air.

### Z

• Zone  -  A space in a building under the control of a thermostat.
• Zoning -  Allows control of the heating and cooling system delivered to different parts of the system.

Display #
Title
Air Change
Air Changes Per Hour
Air Conditioning
Air Diffuser
Air Handler
Air Infiltration
Air Sensor
Air Vent
Airflow
Anemometer