- author "me"
- tags "Cooling 101"
- description ""
- fileName "Cooling terms"
- freezingBlueDBID -1.0
- Air conditioner
Device used to control temperature, humidity, cleanliness and movement of air in a conditioned space.
*** is oversize better?
No, b/c uncompotable, humidity control problem, system will be on/off too often.
Temperature of fluid (usually air) which surrounds on object on all sides.
- Pressure on low side of the refrigerant system;
- Also, called the suction pressure or low side pressure.
British Thermal Unit (BTU)
Quantity of heat requires to raise the temperature of one pound of water one degree fahrenheit in one hour.
Change of state
Condition in which a substance change from a solid to a liquid or a liquid to a gas due to addition of heat. Or the reverse, in which a substance change from a gas to a liquid or a liquid to a solid due to the removal of heat.
- - The absence of heat;
- - A temperature considerably below normal.
Pump of a refrigeranting mechanism which draws a low pressure on cooling side of the refrigerant cycle and squeezes or compresses the gas into high-pressure on the condensing side of the cycle.
The part of the refrigeration mechanism which receives high pressure, high temperature gas from the compressor and cools gasous refrigerant until it returns to a liquid state.
Part of the refrigerating mechanism in which the refrigerant vaporizes and absorbs heat.
Act of allowing a liquid to flow into a part of a system.
Pressure which exists in condensing side of refrigerating system. Also, called in Discharged or High side pressure.
- - Form of energy
- - Energy associated with random motion of molecules.
- - It cannot be created or destroyed, but can be transferred from one substance to another.
Heat added or removed from substance to change its state without changing its temperature. Also, called Hidden Heat.
Device used to regulate the flow of liquid refrigerant into the evaporator. It can be a capillary tube, expansion valve, or a piston.
- - Condition existing when a substance contains all another substance it can hold.
- Ex) sponge
- - presence of both liquid and vapor at any given temperature.
Vapor condition which will result into droplet of liquid if the vapor temperature is reduced lower than saturation.
- - Heat which causes a change in temperature of a substance.
- Ex) 32°F - 212°F. ; 180BTU
- - Measurement of intensity ( also definition of temperature).
Cooling of a liquid refrigerant below its condensing temperature.
- - Heat added to a vapor above its boiling temperature or saturation temperature.
- - temperature difference between the boiling temperature of a liquid and the vapor temperature.
- - the difference between the temperature at the evaporator outlet and the temperature of the refrigerant in the evaporator.
Ton of refrigeration
- - Refrigerating effects equial to the melting of one-ton of ice in a 24-hour period.
- 288,000 btu's/24 hr.
- 12,000 btu's/1 hr.
- 200 btu's/per min.
- - pressure lower than atmosphere
- - atmospheric pressure = 14.7 psi
- - vacuum allows moisture to boil at lower temperature.
Heat flows in three ways
- Is the transfer of heat from molecule to molecule through a substance by chain collision.
- In natural,
- In a space as cooling load,
- In equipment as cooling capacity.
The movement of heat from one place to another. Place by way of fluid or air.
Heat transfer by convection
Free convection and forced convection.
- Transfer heat by passing from a source to an absorbent surface without heating the space in between.
- - the transfer of heat by rays.
Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these methods.
What is refrigeration
Is cooling by the removal of heat.
Movement of heat
Refrigeration is the transfer of heat from where it is not wanted to a place where it is not objectionable.
- - Temperature indicates the average velocity of the molecules of a substance.
- - Temperature does not measure the spacing and arrangement of molecules within a substance.
- - any fluid or gas used as a medium to transfer heat.
- - has a pressure temperature relationship.
The mover of heat
A refrigerant is a fluid that picks up heat by evaporating at a low temperature and pressure and rejects heat by condensing at a higher temperature and pressure.
Total heat is equal to sensible plus latent heat.
- - energy impact on a unit area.
- - force or thrust on a surface.
- Top of atmosphere
- 14.7 psi @ sea level then
- The 1 sq.in. air = 14.7 lbs.
Latent heat of vaporization for water
970 BTU/HR PER LB.
Latent heat of fusion for water; ice 32° to water
144 BTU/HR PER LB.
The amount of heat, measured in BTU's, requires to raise one pound of a substance one degree fahrenheit.
Note: specific heat
- One pound of dry air = 13.3 cu.ft.
- 0.24 BTU/HR to raise 1 lb. of air 1°F
- 1 lb. x 0.24 (specific heat) x 60 min. = 14.4 specific heat per hour
- (14.4 specific heat/hour) / (13.3 cu.ft.) = 1.08 specific heat of 1CFM of air
- 1 ton = 2000 lb.
- 1 gal. = 8.34 lb.
- Blue side,
- Low side,
- Measurng pressure & vacuum
Storage tank that receives liquid refrigerant from the evaporator and prevents it from flowing into the suction inlet of the compressor.
Property of a nonconductor that permits storage of electrical energy.
A device that is a switch and a safety that automatically opens an electrical circuit if overload or short circuit arises.
Def. = prevents liquid migration in the off cycle.
- Device installed around the base or sump or the compressor.
- Adds heat to the compressor to keep the refrigerant in a vapor state to prevent slugging on start up.
- Ratio of the volume f the clearance space to the total volume of the cylinder.
- In refrigeration it is also used as the ratio of the absolute low-side pressure to the absolute high-side pressure.
A fluid formed when a gas is cooled to its liquid state.
Liquid or droplets that form when a gas or vapor is cooled below its dew point.
Device used to remove water condensate that collects beneath an evaporator.
The temp. or pressure at which he control circuit closes.
The temp. or pressure at which the control circuit opens.
Temp. at which vapor (@ 100% humidity) begins to condense and deposit liquid.
- A device used to remove moisture and debris from a refrigeration system.
- Made up of filtering screens and activated alumina used as the drying agent or dessiccant.
- Drier needs to be replaced every tme you open up the system.
Dry bulb temperature
Air temp. as indicated by an ordinary thermometer.
Fault in an electrical circuit allowing electricity to flow into the metal parts of a mechanism.
High pressure switch (R-22)
- Electrical control switch, mounted on the discharge or liquid line after the condenser coil (within he unit).
- normally closed-opens on a pressure rise.
- Opens @ approx. 400 PSIG ~ 450 PSIG.
- Automatic reset.
- Closes @ approx. 300 PSIG.
Moisture or dampness of air.
Locked rotor current
- Initial current when initially closing a circuit, normally atleast 3 to 4 times greater then the running amperage.
- Measured on the common leg of the compressor from a cold start with equalized pressure.
Low pressure switch (R-22)
- A switch located in the suction line/side or low side of the cmpressor that will de-energize the contactor during a low pressure condition.
- Normally open switch
- Opens @ approx. 25 PSIG.
- Closes @ approx. 50 PSIG.
PTCR / PTC = positive temperature coefficient resistor
- A thermistor installed in parellel with the run capacitor and in series with the start winding.
- Allow current to flow to the start winding until the PTC heats up to 260° F.
- Must have a time delay installed with.
Device embedded within a motor winding to shut the motor off should either the component develop a excessive temperature situation or intense heat via excessive current.
Permanent split capacitor motor
A motor with no relay in which current flows through boh the starting and running winding, making the motor sensitive to line voltage and resulting in low starting torque.
- Electrical relay that opens its normally closed contacts on an increase of BEMF from a motor and reclose contacts when the voltage drop.
- Wired in parellel with the start winding.
- Uses a starting capacitor to boost compressor starting torque.
Device used for measuring relative humidity and wet bulb temp.
Ratio of the difference between the amount of water vapor present in air to the greatest amount possible at the same temp.
- An electromegnetic mechanism used to operate a switch to control a device.
- Relay under 20 amps - general purpose.
- Relay over 20 amps - are called contactor.
Run winding (main windng)
Electrical winding of a motor that has current flowing through it during normal operation.
SEER (seasonal energy efficiency ratio)
The ratio of rated cooling capacity divided by the amount of electrical power used in watts during a season of operation.
- E.E.R. = the same ratio but at full load condition.
- Ex) 36,000 BTUdivided by 4000 watts = 9.0 S.E.E.R.
- Capacitor used soley for increasing the starting torque of electric motor.
- Wired in series with the start winding and is controlled by the BEMF of a motor on start up and drop out when the motor reaches 75% of its BEMF.
Winding in electric motor used mainly for starting the electric motor.
Time delay fuse
- A fuse that does not blow until the overload has persisted for a set duration of time.
- Normally about 10 seconds.
- Ignores the initial current surge or locked rotor current on a start up situation.
Time delay relay
- Usually a solid-state device wired in series with the contactor coil and after any pressure or temp. safties that will allow the compressor to start under the least amount of load.
- Normally set @ 5 min.
Wet bulb temperature
Temperature indication of the rate of evaporation of moisture in an air sample.
The removal of refrigerant from a system.
Steps for checking suction superheat
- 1. Put low side gauge on the low side of the system to read pressure
- 2. Find the corresponding saturation temp.
- 3. Put a temp. Probe on the suction line to measure temp.
- 4. Subtract the saturation temp. from the measured line temp. to find the amount of superheat.
Steps for checking subcooling
- 1. Put high side gauge on the high side of the system to read pressure
- 2. Find the corresponding saturation temp.
- 3. Put a temp. Probe on the liquid line to measure temp.
- 4. Subtract the liquid line temp. from the saturation temp. to find the amount of subcooling.
Methods of charging refrigerant systems
- Weighing method,
- Superheat method,
- Subcooling method,
Utilized any fixed orifice type metering device.
- There are two ways to charge a system using the superheat method:
- 1) using dry bulb return air temp.
- 2) using wet bulb return air temp.
- ** The wet bulb return air temp. method is the most accurate.
Used on equipment utilizing TXV type metering device.
- Add charge to lower superheat.
- Remove charge to raise superheat.
The boiling temp. of a liquid is affected by
Why suction is insulated?
- Prevent from condensate.
- Prevent from ambient heat absolve along the suction line.
Five different states of the refrig. in order between the discharge line to the liquid line.
- (Discharge line)
- Hi pressure/temp ; superheat vapor
- (Condenser coil)
- Hi pressure/temp ; saturated vapor/liquid
- (Liquid line)
- Hi pressure/temp ; sub cooled liquid
- (Evaporator coil)
- Lo pressure/temp ; saturated liquid/vapor
- (Suction line)
- Lo pressure/temp ; superheat vapor
Four major components of the refrigerant cycle
- Metering device
Only the size, style and arrangement of the four basic refrigerant components will change from system to system.
- Maintains a pressure differential between inlet(suction) and its outlet(discharge) that will cause refrig. to flow in sufficient quantities to meet coling requirements of the system.
- The function of a compressor is to take refrigerant vapor at low temp. and pressure and raise to a higher temp. and pressure.
Excessive liquids in compressor
- High power usage
- Motor overheating
- Compressor overheating
- Oil breakdown
- Improper compressor lubrication
- Noisy operation
- Compressor damage through deformity and breakage
- Inadequate capacity
- Changes high pressure, high temp. vapor discharged from the compressor to a high pressure sub cooled liquid.
- Rejects heat that was absorbed in system.
- The condenser is a device for removing heat from the refrigeration system.
Types of condensers
- Air cooled
- Water cooled
- Sub cooling increases system efficiency & capacity by 1/2 % per degree.
- Insures full column of liquid entering the metering device.
- Ex) 3 ton A/C = 36000 BTU/HR
- requires sub cooling = 15 degrees
- System that only has 1 degree of subcooling has a capacity loss of 2520 BTU/HR or 7%.
- Capacity reduced to 33480 BTU/HR
- ex) 4 ton A/C
- Requires subcooling 14 degree
- Actual subcooling 2 degree
- 14 - 2 =12
- 12 / (1/2 %) = 6% capacity loss
- 4 x 12000 = 48000
- 48000 x 6% = 2880 loss
- 48000 - 2880 = 45120 BTY/HR
Sub cooling coil
- Cools liquid refrigerant below its saturation temperature.
- Dirty condenser is number one cause of compressor failure.
Dirty condenser coils
- A dirty condenser restricts the ability to reject heat causing excessive head pressure and compressor temp.
- Excessive compressor temp. will cause the lubricating oil to break down, create sludge in oil, and acid formation can occur.
- Dirty condenser coils cause higher discharge pressure which causes higher compressor amperage which increases operating costs and reduces system capacity.
- This problem is greatly intensified when the outdoor ambient temp. is high.
Metering device ( function)
- Maintain an evaporator pressure that will result in a saturated vapor temp. in the evaporator below the entering air temp. so heat can be transferred from the air to the refrigerant.
- - meters refrigerant into the evaporator
- - provides a pressure drop which saparates the high side from the low side of the system.
Two types of metering devices
- Fixed type
- - capillary tube
- - fixed orifice
Adjustable type of metering devices
- Hand expansion valve (F)
- Lowside float valve
- Highside float valve
- Automatic expansion valve
- Thermostatic expansion valve
- Electric / Electronc expansion valve
Capillary tube design complications
- Too long and too small in diameter = starved evaporator
- Too short and too large in diameter = evaporator flooding
Capillary tube application
- Well suited for:
- - fairly constant load
- - Small capacity
- - less than equil 3 tons
- - residential comfort
- - household refrigeration
- - factory design
Poorly suited for capillary tube:
- - widely changing loads
- - large capacity
- - greater than 10 tons
- - commercial comfort
- - commercial / industrial refrigeration
- - field design
Metering device assembly
Body > piston (orifice) > retainer > flare nut
Thermostatic expansion valve (TXV)
A txv maintains a constant superheat of 10 degrees by modulating a needle valve allowing more or less refrigerant flow depending on the operating forces of the txv.
The three operating pressures of a txv are:
- Spring pressure
- Back(suction) pressure
- Bulb pressure
- Spring and back pressure tries to open the valve allowing more refrigerant to flow through the evaporator.
- Most txvs are hard shut off which means the pressures do not fully equalize on the off cycle. (For higher efficiency)
- For this reason if you are replacing an indoor coil with a fixed orifice with a coil that has a txv (all new indoor coils), compressor, a hard start must be installed.
Valve closing - superheat too low
E + S > B
Valve opening - superheat too high
E + S < B
Compressor will not start till the pressures are equalized.
To measure superheat
- Find suction pressure
- Find matching saturation temp.
- Read temp. leaving evaporator.
- Superheat = temp. leaving - saturation temp.
Common metering device problem
- Stuck expansion valve
- Oversized expansion valve
- Improper sensing bulb location
- Valve superheat setting too low or too high
- Wrong type valve
- plugged equalizer line
- Plugged distributor
- Improperly sized distributor nozzle
- Transfers heat from entering air to the refrigerant in the evaporator.
- Absorbs heat into system
Common evaporator problems
- Inadequate air flow through the coil
- Uneven air distribution over coil
- Inadequate refrigerant supply to coil
- Uneven refrigerant distribution to coil circuits.
Condensate pump in A/C inspection: 3 things need to be done
- Make sure safety switch is wired in.
- Take apart and clean condensate pump.
- Fill it up with water and make sure it works.
B&B water damage policy
- Attic air handlers, condensing furnaces, & horizontal coils will be hung as high as possible, suspended with heavy solid link chain & properly supported b uni-strust their entire length.
- We want as much pitch on the drain as possible.
- Coils installed in the upflow position must have an E-Z Tee installed in the high drain port.
- Air handlers installed in the upflow position will have an E-Z Trap and E-Z Tee installed.
- All condensate pumps must have a safety switch and it must be wired in to the control circuit.
Without prior permission from the homeowner, No water valves shall be turned ON/OFF (i.e. outdoor spigots, main water to water heater / home etc.)
- May have to offset the plenums for proper pitch. ( quote accordingly)
- Install a properly supported emergency drain pan (minimum depth 4" deep and tested for water leakage.) With separate drain line and pitched towards the drain.
- Emergency pan safety float switch to be installed.
- Primary drain will have an E-Z trap.
- The high drain will be piped into the emergency drain pan or have an E-Z Tee installed.
- All safeties are to be wired in series and shut down the system should a malfuction occur.
- On existing installations, we will automatically recommend the appropriate safety devices.
- Be sure to note on the ticket if the customer does not want them installed.
- the service ticket Should have the following statement:
- " customer refused water safeties. No guarantee on drainage. B&B is not responsible for water leak damages."
- Existing installations utilizing a free draining humidifier and a condensate pump must have a safety switch on the condensate pump.
- The safety switch shall be wired to break "R" power to the thermostat.
- Free draining humidifiers are not to be installed on condensate pumps.
- A gravity type drainage system must be available (i.e. floor drain or gravity drain to slop sink.)
- When no gravity drain is available install a circulating / wicking type humidifier.
- Humidifiers are not to be installed in attic or spaces exposed to temp. below freezing under any cicumstances.
Humidifier overflow drain
Any humidifier equipped with any overflow drain must have the overflow drain piped to the nearest drain system, (i.e. A/C drain, condensate pump, etc.) as a safety.