ACTUATOR: A portion of a valve that a form of energy such as electrical or heat energy
into mechanical to open or close valve seats. An example would be your natural gas
furnace combination control valve.
AFUE: Annual Fuel Utilization Efficiency, the efficiency rating of a natural gas,
oil, or propane furnace in converting fuel to home heating. If your heating unit is
rated at 82% AFUE, this means approximately 82% of the fuel your furnace consumes
over a heating season is distributed into the ductwork.
BTU: British Thermal Unit: about the same amount of heat in the old 1" wood-stemmed
matchstick fully consumed. Burning this matchstick would raise one pound of water one
degree Fahrenheit. When a technician salesman refers to your heating or cooling system,
the term 'BTU' per hour (BTUH) is used. A typical furnace of a 1400 square foot 1980s
home would be about 80,000 BTUH. Your air conditioner would typically be about 36,000
BTUH for a home in Seattle but perhaps 48,000 in Los Angeles.
BLOWER FAN: A radial or axial flow component with metal blades to mechanically move air.
One is found in the furnace and one in the outside condenser unit. The Blower fan is
typically comprised of a motor, a control, and the actual fan blades. Today's blower
fans are typically direct-drive meaning they no longer use a 'belt' to transfer the motor
RPM to the fan component.
CFM: A measurement of airflow describing Cubic Feet (of air) per Minute. The furnace
in your home needs somewhere between 200-400 to make your furnace or A/C work properly.
With the A/C, 400 CFM is ideal.
CONDENSER: The condenser is the name we use for your outside unit of a 'split' air condition system.
It works on the same principles of the indoor evaporator although in reverse. When the
refrigerant gas enters exits the evaporator, it get's compressed by the compressor
greatly rising its' temperature from ~ 70 F to around 160 F. Boyles Law states that
the higher the pressure of any gas is, the higher the temperature. Then, the hot
refrigerant gas enters into the condenser coils.
With the outdoor blower fan moving
air over these coils, the refrigerant condenses. This is the same principle as when
you warm humid air reaches you window and you'll see the water forming on the glass
surface. In return, the condenser coils losses heat to the outside in preparation to
return to the evaporator.
DEFROST CYCLE: Heat Pumps during the winter often gather frost on the outside coils.
The heat pump will 'reverse' its cycle to melt the ice and restore the efficiency of the
system since ice will prevent the outdoor unit from absorbing heat.
EVAPORATOR: The evaporator is a component usually found in you air return
plenum that absorbs the heat out of your home's distribution air. It is
called an evaporator because its job is to evaporate the liquid refrigerant
gasses entering into it. The method it uses is to allow the refrigerant gasses
in the system to expand via a metering device. Remember that Boyle's Law state
that as the pressure of a gas goes down, the temperature does as well (if the
volume of the container does not change. So when the pressure past the metering
device dropped, so did the temperature of the refrigerant, usually to around 40
degrees Fahrenheit. The temperature of the air crossing over the evaporator will
drop off its' heat (or pick up 'cool') as a result.
A homeowner can check how well
it does this using a chart. Under typical summer conditions such as 74 F indoor
temperature, 90 F outdoor, and 50% relative humidity, the temperature drop across
the evaporator should range from 15F to 30F degrees. If it is a 'muggy' (high humidity), the drop
will be lower from 10F to 10F since the evaporator is also removing a fair amount
of humidity in the air.
Back to top
HSPF: Heating Seasonal Performance Factor is used in measuring the heating
efficiency of a heat pump. Like the SEER, it is based on the season it is designed to
be used in. If the unit is 7.2 HSPF, it will use 1 unit of electrical energy (to
deliver 7.2 units of heat energy) that the standard electrical heater would have
consumed.
IN-SHOT BURNER: Like the burner on your stove, natural gas needs to inject the gas
along with combustion air (O2) and a source of igntion. In-shot burners take advantage of aninduced-draft fan
to 'pull' the flames into the heat exchange. By doing so, the efficiency increases as well as
ensuring the proper flow of the combustion gases .
METERING DEVICE: Typically a TXV or capillary tube device/valve regulate flow of
liquid refrigerant entering the evaporator. The 'fixed' metering device and the 'TXV'
will both cause a pressure drop in the line that allows the refrigerant to go to a
state where it will 'boil' (evaporate) downstream of the device. Essentially, it
meters' the flow of refrigerant gasses to maintain the pressure difference.
MOTOR: A device to take an electrical energy and, through a magnetic field, turn an
axle and deliver kinetic energy (mechanical power). The basic two residential types
are the shaded-pole and the permanent split capacitor (PSC). The basic difference lies
within the way the motor is 'instructed' to operate. Choose a PSC whenever you need a
new one.
PSYCHROMETER: A device used to determine wet bulb temperatures to combine with dry
bulb to determine relative humidity. Combining the two is used to consider how much
TOTAL heat there is in the air and figure out how the (typically) effectively the air
conditioner is work to remove TOTAL heat from the home.
REFRIGERANT: A substance that uses the change of state between liquid and gas to
transfer heat energy from one location to another. Since matter such as the refrigerants
can absorb and release upwards of 10 times the energy to go from gaseous to liquid (and
vice-versa) than it does just rise or falling 10 degrees, it is a very effective fluid
to move heat energy to cool or heat your home. All heat pump/AC-based refrigerants will
change from liquid to gas if it leaks out of your system. It is most always non-toxic,
however.
THERM: A term to define 100,000 BTUs. Your Natural Gas company will often use this
term on your billing statement. They sometimes use CCF which is about 1000 BTUs or
1/100th of a therm. The current cost of a therm in the US averages about $1.20.
TON: A unit of measurement used for determining heat pump or air conditioner capacity.
One 'ton' equals 12,000 BTUs per hour. A typical 3-ton air conditioner will remove 36,000
BTUs per hour.
SEER: Seasonal Energy Efficiency Ratio is the term you will see on air conditioners that
basically states how efficient the AC is over the course of a cooling season (summer). If
the unit has a rating of 14 SEER, it will, under ideal conditions, deliver 14 units of
cooling 'energy' for every unit of electrical energy it consumed.
Back to top
