Refrigeration Fundamentals

• This module introduces refrigeration fundamentals, concepts, and terminology.
• The content aims to provide basic knowledge of refrigeration concepts and the refrigeration cycle.

What is Refrigeration?

• Refrigeration involves removing heat from a space or objects, and rejecting it where it doesn't matter.
• Refrigeration is used for food preservation and transport.
• Refrigeration aids in manufacturing commercial products and in medical research.
• The first closed vapor compression system was developed in 1834 by Jacob Perkins.
• Modern air conditioning was pioneered in 1902 by Willis Carrier.

Matter and Energy

• Matter has mass and occupies space.
• Matter is the substance of all physical objects in the universe.
• Four states of matter are solid, liquid, gas, and plasma.
• Refrigeration cycles involve liquid and gas states.
• Heat content and pressure decide the state of matter of a substance.

Volume

• Volume is the amount of space a substance occupies.
• Volume is important to gas study because it relates to pressure, temperature and number of molecules.
• Volume is three-dimensional and uses three measurements.
• The volume of a square or rectangle is calculated as: V = L x W x H.
• The formula for the volume of a cylinder is: V = πr² x h.
• π is 3.14.
• R = Radius.
• S = squared.
• H = height.

Mass and Weight

• Mass is a measure of the quantity of matter in an object.
• Mass is the property of matter that’s responsive to gravity.
• Weight is the physical force that matter applies to a surface when at rest.
• Earth's stronger gravitational force means a brick weighs more on Earth than on the moon.

Density

• Density describes the relationship of mass to volume in a substance or object.
• Mass enclosed in a particular volume defines the density for that substance.
• Density can be found by comparing an object's weight per unit, in lbs per cubic foot or lbs/ft³.
• Water has a density of 62.4 lbs/ft³.
• Wood can float on water because it weighs less than 62.4 lbs per cubic foot.
• Iron sinks as it weighs more than 62.4 lbs per cubic foot.
• Density = Mass / Volume.

Specific Gravity

• Specific gravity is the density of a substance relative to the density of water.
• The specific gravity of water is 1 because the density of water is 62.4 lb/ft³.
• If specific gravity is greater than 1, it will sink in water.

Specific Volume

• Specific volume is the amount of volume each pound of a specific gas occupies.
• Specific volume is different from total volume.
• Units are lb/ft³, not ft³.
• Air's specific volume at standard atmospheric conditions is 13.33 ft³/lb.
• Specific volume and density are inverses of each other, where specific volume = 1 / density and density = 1/specific volume.
• As gas pressure increases, specific volume decreases, and density increases.
• Compress = lowers volume = packing more molecules = increased density = increased pressure.

Additional Specific Volume Concepts

• The specific volume of air is 13.33 lbs/ft³.
• Density = 1/13.33 lbs/ft³ = 0.075 lbs/ft³.
• CFM is cubic feet per minute.
• 400 CFM equals 1800 lbs per hour.
• Dry air weighs more than humid air.
• Nitrogen Molecule = 28.014 g/mol.
• Oxygen Molecule = 32.00 g/mol.
• Hydrogen Molecule = 2.016 g/mol.

Pressure

• Pressure is the force exerted by a gas or liquid per unit area on the surface of a container.
• PSI means pounds per square inch.
• Pressure = force/area.
• A cubic foot of water weighs 62.4 lbs.
• 1 cubic ft of water exerts a downward pressure of 62.4 lbs on the bottom of a 1 cu.ft container with bottom of 144 sq.in.
• 62.4 lbs/144 in² = 0.433 PSI.

Vacuum

• Vacuum is a condition existing in a closed system, compared to atmospheric pressure.
• Atmospheric pressure is 29.92 inches of mercury (inHg) at sea level.
• A vacuum is created when pressure is lowered below atmosphere.
• Vacuums measured in microns are a measurement of distance.
• There are 0.0000001 meters in 1 micron.
• 1 inHg equals 25,400 microns.
• 14.7 PSI is atmospheric pressure.
• 759,168 microns equals Atmospheric pressure.
• Space being in a vacuum means there isn't any atmosphere, which makes it dark for light to scatter/reflect.
• Micron reading below 500 means a dry system.
• When the pump and hoses are shut off and a 30-minute decay test is performed, the final micron reading is take
• System needs to hold a micron reading below 500 for at least 30 minutes for degassing.

Critical Point

• Refrigeration requires the refrigerant to be in a liquid state.
• Critical point is the highest temperature at which a gas can still be condensable by pressure means.
• The pressure or enthalpy diagram critical temperature and pressure exists.
• Liquid refrigerant cannot be produced above a refrigerant's critical point.

Trans-Critical Point

• Trans-critical defines processes above a refrigerant's critical temperature.
• The refrigerant does not have a distinct liquid-gas phase transition.
• Refrigerant vapor cannot be condensed into a liquid.
• CO2 systems operating above 88 F are an example.

Triple Point

• Refrigerant exists in all three phases (vapor, liquid, solid) simultaneously.
• CO2 has a triple point of -70 F, equivalent to 75 PSIA or 60.3 PSIG.
• CO2 operating below its triple point transitions directly from a solid to a gas, known as sublimation.

Enthalpy

• Enthalpy is referred to as total heat content in a substance.
• Refrigerant enthalpy charts base at -40 F.
• • 40 F on the example chart means = 0 btu/lb.
• Heat is expressed in BTUs
• Enthalpy accounts for the energy that changes the temperature of a material, and the energy needed to change the state.
• Enthalpy is expressed in btus/lb.
• Sizing refrigeration systems to match product load uses enthalpy.

Entropy

• Entropy means reversibility.
• Ice to water, water back to ice are examples.
• Discharge gas to a liquid, liquid back to a vapor are examples.

Energy

• The conservation of energy explains that energy isn't created or destroyed.
• Energy can be transferred or converted between forms.
• Energy drives all physical processes/ 'work' to happen.

Energy and Types of Energy

• Energy wants to seek equilibrium.
• Energy sources transfer from high to low.
• High temperature goes to low temperature.
• High moisture content wicks away to the low moisture content.
• Kinetic energy means the energy an object contains based on its motion.
• Potential energy means the energy stored because of an objects position.
• Thermal refers to all the energy particles in a substance, related to temperature.
• Chemical energy is stored in the inter-atomic bonds of molecules.

Work and Power

• Work = force x distance.
• Work can be expressed as Work(lb.-ft) = 180 lb. x 100 ft = 18,000 ft-lb.
• Power is the rate at which work is being done, expressed in horsepower or watts.
• One horse can lift 33,000 lbs 1 ft in 1 minute.
• 746 Watts equal 1 HP.
• There are 3.413 btus in 1 watt.

Subcooled

• Subcooling is measured in degrees F or C.
• When a liquid's boiling point is lowered down, it is called subcooled.
• If water boils at 212 F, and its now 200 F, its now 12 F subcooled.
• The presence of subcooling indicates presence of of liquid refrigerant in the system.
• Refrigeration needs requires the presence of liquid.

Superheated

• Superheated describes a vapor heated above its boiling point.
• Units of measurment for superheat are degrees F or C.
• Liquids can never be compressed.
• If there is superheat, there's no liquid returning to the compressor.
• Measured steam temperature discharging at 220 F in a pressure cooker with 212F means there’s 8F.

1 Ton of Refrigeration

• A ton of refrigeration = 12,000 btu/hr.
• Btu's of heat melts a ton of ice (2000 lbs) at 32 F in 24 hours .
• Latent heat of fusion of ice = 144 btu per pound.
• 2000 lbs. x 144 btu = 288,000 Btu. -288,000 btu/ 24 hrs. = 12,000 btu. /hr. -A rate of heat transfer is created when a time period is added, replacing a quantity of heat.

Basic Refrigeration Cycle

• Vapor compression cycle.
• High temperature, superheated gas discharges to the condenser.
• At the condenser it superheats, condenses the substance to a liquid, and subcools.
• The subcooled liquid travels to an expansion device.
• It then is expanded to reduce pressure and temperature prior to entering the evaporator.
• The heat gets tansferred to the refirgerant raising temperature and pressure as it is colder than surrounding air.
• The refrigerant becomes superheated gas as it boils, and enters the suction/ 'intake' of compressor.
• During the compressor phase, the pressure and temperature is increase where it goes back to the condenser to repeat its cycle again.
• To move flow you need toconstantly changing the pressures and temperatures of a refrigerant.
• There has to be a presence of pressure difference to move flow.
• Liquids cant be compressed which helps keep refrigerants working.
• Refrigeration requires low boiling point temperature, and it requires a device to create the pressure difference in order to transform the energy into work.
• Hig boiling temperature refrigerants would not have a refrigeration effect, and you would need more energy to flow.