This section explains in basic terms the principals that are used to create the refrigeration effect. Graphics and animation's are used in an attempt to make it easy to understand the concepts involved.
First of all, did you know that there is no such thing as cold? You can describe something
as cold and everyone will know what you mean, but cold really only means that something
contains less heat than something else. All there really is, is greater and lesser amounts
of heat. The definition of refrigeration is
The Removal and Relocation of Heat.
So if something is to be refrigerated, it is to have heat removed from it. If you have a warm
can of pop at say 80 degrees Fahrenheit and you would prefer to drink it at 40 degrees, you
could place it in your fridge for a while, heat would somehow be removed from it, and you
could eventually enjoy a less warm pop. (oh, all right, a cold pop.) But lets say you placed
that 40 degree pop in the freezer for a while and when you removed it, it was at 35 degrees.
See what I mean, even "cold" objects have heat content that can be reduced to a state of "less
heat content". The limit to this process would be to remove all heat from an object. This
would occur if an object was cooled to Absolute Zero which is -273º C or -460º F. They come close to creating this temperature under laboratory conditions and strange things like electrical superconductivity occur.
How do things get colder?
The latter two are used extensively in the design of refrigeration equipment. If you place
two objects together so that they remain touching, and one is hot and one is cold, heat will
flow from the hot object into the cold object. This is called conduction. This is an
easy concept to grasp and is rather like gravitational potential, where a ball will try to roll
down an inclined plane. If you were to fan a hot plate of food it would cool somewhat. Some of the heat from the food would be carried away by the air molecules. When heat is transferred by a substance in the gaseous state the process is called convection. And if you kicked a glowing hot ember away from a bonfire, and you watched it glowing dimmer and dimmer, it is cooling itself by radiating heat away. Note that
an object doesn’t have to be glowing in order to radiate heat, all things use combinations
of these methods to come to equilibrium with their surroundings. So you can see that in order to refrigerate something, we must find a way to expose our object to something that is colder than itself and nature will take over from there. We are getting closer to talking about the actual mechanics of a refrigerating system, but there are some other important concepts to discuss first.
The States of Matter
They are of course; solid, liquid and gas. It is important to note that heat must be added
to a substance to make it change state from solid to liquid and from liquid to a gas. It is just as
important to note that heat must be removed from a substance to make it change state from a gas
to a liquid and from a liquid to a solid.
The Magic of Latent Heat
Long ago it was found that we needed a way to quantify heat. Something more precise than "less
heat" or "more heat" or "a great deal of heat" was required. This was a fairly easy task to
accomplish. They took 1 Lb. of water and heated it 1 degree Fahrenheit. The amount of heat that was required to do this was called 1 BTU (British Thermal Unit). The refrigeration industry has long since utilized this definition. You can for example purchase a 6000 BTUH window air conditioner. This would be a unit that is capable of relocating 6000 BTU's of heat per hour. A larger unit capable of 12,000 BTUH could also be called a one Ton unit. There are
12,000 BTU's in 1 Ton.
To raise the temperature of 1 LB of water from 40 degrees to 41 degrees would take 1 BTU. To
raise the temperature of 1 LB of water from 177 degrees to 178 degrees would also take 1 BTU.
However, if you tried raising the temperature of water from 212 degrees to 213 degrees you
would not be able to do it. Water boils at 212 degrees and would prefer to change into a gas
rather than let you get it any hotter. Something of utmost importance occurs at the boiling
point of a substance. If you did a little experiment and added 1 BTU of heat at a time to
1 LB of water, you would notice that the water temperature would increase by 1 degree each
time. That is until you reached 212 degrees. Then something changes. You would keep adding
BTU's, but the water would not get any hotter! It would change state into a gas and it would
take 970 BTU's to vapourize that pound of water. This is called the Latent Heat of Vapourization
and in the case of water it is 970 BTU's per pound.
So what! you say. When are you going to tell me how the refrigeration effect works? Well hang
in there, you have just learned about 3/4 of what you need to know to understand the process.
What keeps that beaker of water from boiling when it is at room temperature? If you say it's
because it is not hot enough, sorry but you are wrong. The only thing that keeps it from
boiling is the pressure of the air molecules pressing down on the surface of the water. When
you heat that water to 212 degrees and then continue to add heat, what you are doing is
supplying sufficient energy to the water molecules to overcome the pressure of the air and
allow them to escape from the liquid state. If you took that beaker of water to outer space
where there is no air pressure the water would flash into a vapour. If you took that beaker
of water to the top of Mt. Everest where there is much less air pressure, you would find that
much less heat would be needed to boil the water. (it would boil at a lower temperature than
212 degrees). So water boils at 212 degrees at normal atmospheric pressure. Lower the
pressure and you lower the boiling point. Therefore we should be able to place that beaker of
water under a bell jar and have a vacuum pump extract the air from within the bell jar and
watch the water come to a boil even at room temperature. This is indeed the case!
A liquid requires heat to be added to it in order for it to overcome the air pressure pressing down on its' surface if it is to evaporate into a gas. We just learned that if the pressure above the liquids surface is reduced it will evaporate easier. We could look at it from a slightly different angle and say that when a liquid evaporates it absorbs heat from the surrounding area. So, finding some fluid that evaporates at a handier boiling point than water (IE: lower) was one of the first steps required for the development of mechanical refrigeration.
Chemical Engineers spent years experimenting before they came up with the perfect chemicals for the job. They developed a family of hydroflourocarbon refrigerants which had extremely low boiling points. These chemicals would boil at temperatures below 0 degrees Fahrenheit at atmospheric pressure. So finally, we can begin to describe the mechanical refrigeration process.
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Here are Some of the Topics
Covered in the
Index
| 3 Phase |
| 4 way reversing valve |
| AB |
| Absolute Zero |
| AC |
| access valves |
| accessories |
| accumulator |
| Accurator |
| Add On Heat Pump |
| adiabatic |
| AEV |
| AFUE |
| AHU |
| air (components of) |
| Air Conditioning |
| air (conditions of) |
| air filtration |
| alkylbenzene oil |
| All Electric Heat Pump |
| Alternating Current |
| amperage, also |
| Annual Fuel Utilization Efficiency |
| anti-short-cycling device |
| anticipation |
| ASHRAE |
| atom |
| Automatic Expansion Valve |
| Azeotrope |
| Back Seated |
| Balance Point |
| barometer |
| bi-metal disk |
| Bourdon |
| Boyle's Law |
| British Thermal Unit |
| BTU |
| bull headed tee |
| burn outs |
| capacitor |
| Capacitor Start Capacitor Run Motor |
| Capacitor Start Induction Run Motor |
| capillary line |
| Celsius |
| centrifugal compressor |
| ceramic capacitor |
| charging |
| Charle's Law |
| check valve |
| Close Coupled |
| Class 1 conversion |
| Class 2 conversion |
| coalescing oil separators |
| compressors |
| compressor driver |
| Compressor Efficiency Test |
| condensate line |
| condensate pan |
| Condenser Dampers |
| condensing medium |
| Condensing Unit |
| conduction (electrical) |
| conduction (thermal) |
| conductor (thermal) |
| controls |
| Constant Cut In Control |
| convection |
| cooling anticipation |
| cooling load |
| cooling tower
|
| COP, also |
| Coulomb |
| CPRV |
| cracked |
| crankcase heater |
| CSIR |
| CSCR |
| current relay |
| cut in |
| cut out |
| Daulton's Law |
| DC |
| Defrost Termination Thermostat |
| design temperature |
| Dew Point |
| Defrost Termination Stat |
| dielectric |
| Direct Current |
| Discharge Service Valve |
| discharge temperature |
| distributor |
| drop in replacement |
| DSV |
| EER |
| EEV |
| electric defrost |
| Electro-Magnetism |
| electrolytic capacitor |
| Electromotive Force |
| Electronic Expansion Valve |
| EMF |
| energy |
| Energy Efficiency Ratio |
| enthalpy |
| enthalpy controls |
| entropy |
| EPRV |
| evacuation, also |
| Evaporative Condenser
|
| Fahrenheit |
| fan cycling |
| Fan Delay Thermostat |
| fan rotation |
| fan speed controller |
| filters (air) |
| filters (refrigerant) |
| Fixed orifice |
| flash gas |
| flammability |
| Fresh Air |
| Free Cooling |
| front seated |
| gases |
| Gas Laws |
| gauge |
| gauge manifold set |
| Hand Operated Expansion Valve |
| hand valve |
| Head Pressure Control |
| heat |
| heat anticipation |
| Heat of Compression |
| Heat Pumps |
| Heating Seasonal Performance Factor |
| helical oil separators |
| HEPA |
| hermetic compressor |
| Hertz |
| High Side Float |
| High Side Restriction |
| holding circuit |
| Hop Scotch Method (troubleshooting) |
| Hot Gas Bypass Regulator |
| hot gas defrost |
| Hot Wire Relay |
| HSPF |
| hygroscopic |
| hydrostatic pressure |
| human comfort zone |
| humidity |
| impedance |
| impingement oil separators |
| incremental unit |
| insulation (electrical) |
| insulation (thermal) |
| Kelvin |
| King Valve |
| Latent Heat |
| ladder schematic |
| lead-lag |
| Line Tap Valve |
| liquid/vapour interface |
| Liquid Line Filter/Drier |
| Liquid Line Solenoid Valve |
| liquid slugging
|
| LLSV |
| lock out circuit |
| Locked Rotor Amperage |
| Low Side Float |
| low voltage controls |
| LRA |
| magnetism |
| MAT |
| Mechanical Cooling |
| MegOhm |
| Mercury |
| mercury bulb thermostat |
| Metering Device |
| MFD |
| micron |
| micron gauge |
| Mid Seated |
| migration |
| mineral oil |
| Minimum Fresh Air |
| Mixed Air |
| MO |
| molecule |
| Mollier Charts |
| motor theory |
| motor types |
| muffler |
| multiple stages |
| Non-Recycling Pump Down |
| OAT |
| ODS |
| ODS conversions |
| OEM |
| off cycle defrost |
| Ohm |
| Ohm's Law |
| oil failure controls |
| oil separator |
| oil slugging |
| open compressor |
| ORD |
| ORI |
| OROA |
| Ozone Depleting Substance |
| Packaged Systems |
| PAG |
| Parallel Drop |
| Permanent Split Capacitor Motor |
| phosgene |
| piping |
| POE |
| polyalkylglycol oil |
| polyolester oil |
| potential relay |
| pressure |
| pressure control |
| Pressure-Enthalpy Diagrams |
| Pressure Temperature Relationship |
| PSC |
| PSIG |
| Psychometrics |
| P-Trap |
| PTC |
| PT Charts |
| PTCR |
| pump down |
| Radiation |
| Rankine |
| receiver |
| reciprocating compressor |
| reclaim |
| recover |
| recycle |
| refractometer |
| refrigerant leaks |
| refrigerant oils |
| refrigerants |
| Refrigerant Side Head Pressure Control |
| Refrigeration (definition of) |
| Refrigeration loop |
| relay |
| resistance |
| retrofitting ODS |
| reuse |
| reverse cycle defrost |
| rotary compressor |
| rotor |
| run capacitor |
| running burn out |
| safety |
| safety controls |
| saturated conditions |
| Schraeder Valve |
| screw compressor |
| scroll compressor |
| Seasonal Energy Efficiency Ratio |
| Secondary Refrigerant |
| SEER |
| semi-hermetic compressor |
| Sensible Heat |
| Service Valves |
| set back |
| Shaded Pole Motor |
| short cycling |
| sight glass |
| Specific Heat |
| Split Phase Motors |
| Split Systems |
| Squirrel Cage |
| Start Capacitor |
| stator |
| Subcooling |
| Suction Cut-Off |
| suction filter |
| suction/liquid heat exchanger |
| Suction Service Valve |
| Superheat |
| SSV |
| tackifed |
| Temperature |
| TEV |
| TD (Temperature Difference) |
| Thermal Starting Relays |
| Thermostatic Expansion Valve |
| thermostat - low voltage |
| three phase motors |
| time delay fuses |
| time delay relays |
| Ton |
| toxicity |
| transformer |
| troubleshooting |
| TXV |
| unloader |
| vacuum |
| vibration absorber |
| vibration loop |
| voltage |
| wall mounted thermostats |
| water cooled condensers |
| water cooled system |
| water regulator valve |
| Zeotrope |
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