04-13-2020, 07:50 AM
Lecture Notes -
HVAC (Heating, Ventilation and Air-Conditioning)
for the student of architecture
https://frontdesk.co.in/building-service...ditioning/
Basic principles of refrigeration
Temperature
How Heat Flows
Conduction: the transmission of heat from one molecule to another within a material or from one material to another when they are held in direct contact.
Heat Energy
Latent Heat, specific heat
Refrigeration
Sensible and latent heats of water at different phases
Vapor Compression Refrigeration System
Vapor Compression Refrigeration System Major Components: (i) Compressor, (ii) Condenser Coil, (iii) Expansion Valve and (iv) Evaporator Coil. Chemical Refrigerants such as R-12, R-22 or R-134a are used to provide refrigeration effect.
Refrigeration cycle
The Vapor-Compression Refrigeration Cycle is comprised of four steps
Part 1: Compression : In this stage, the refrigerant enters the compressor as a gas under low pressure and having a low temperature. Then, the refrigerant is compressed, so the fluid leaves the compressor under high pressure and with a high temperature.
Refrigeration cycle
Part 4: Evaporation : The low pressure, low temperature refrigerant enters the evaporator, which is in contact with the cold reservoir. Because a low pressure is maintained, the refrigerant is able to boil at a low temperature. So, the liquid absorbs heat from the cold reservoir and evaporates. The refrigerant leaves the evaporator as a low temperature, low pressure gas and is taken into the compressor again, back at the beginning of the cycle
Refrigeration system Component
Scroll Compressor
Screw compressors
Screw compressors : use a pair of helical rotors or screws which mesh together to compress the refrigerant between them. They can produce high pressure for a small quantity of gas and consume less power than reciprocating compressors. They have low to medium initial and maintenance costs and few moving parts. However, they have difficulty in dirty environments, high rotational speeds, and shorter life expectancies than other designs
Rotary Compressors
Rotary compressors have two rotating elements, like gears, between which the refrigerant is compressed. These compressors are very efficient because the actions of taking in refrigerant and compressing refrigerant occur simultaneously. They have very few moving parts, low rotational speeds, low initial and maintenance costs, and are forgiving in dirty environments. However, they are limited to smaller volumes of the gas and produce less pressure than other types of compressors.
Centrifugal compressor
Centrifugal – The centrifugal compressor increases the refrigerant pressure by throwing it at high velocity (like an ordinary house fan throws air) using a rotating impeller inside a stationary housing.
Condenser
Air cooled condenser
Water cooled condenser
Air cooled condensers (coil condensers ) are used in small units like household refrigerators, deep freezers, water coolers, window air-conditioners, split air-conditioners, small packaged air-conditioners etc. These are used in plants where the cooling load is small and the total quantity of the refrigerant in the refrigeration cycle is small. Air cooled condensers occupy a comparatively larger space than water cooled condensers.
Condenser
Water cooled condenser :
Water is used as the heat transfer medium in place of air. Water flows through a heat exchanger where refrigerants contained in separate piping give up their heat to the water.
Evaporator
An evaporator is used in an air-conditioning system to allow a compressed cooling chemical to evaporate from liquid to gas while absorbing heat in the process. It can also be used to remove water or other liquids from mixtures. There are two types of evap.:
Forced Convection Type uses a fan or pump to force the liquid being cooled over the evap.
Natural Convection Type has the liquid being cooled flows naturally to the evap. due to the density differences of the chilled and warm liquid.
Expansion valves
Expansion valves are devices used to control the refrigerant flow in a refrigeration system. They help to facilitate the change of higher pressure of liquid refrigerant in the condensing unit to lower pressure gas refrigerant in the evaporator.
Types.
1. Automatic Exp. Valves
regulates the flow of refrigerant from the liquid line to the evaporator by using a pressure-actuated diaphragm. It maintains a constant pressure in the evaporator.
Refrigerant in Refrigeration
Chemical Refrigerant A refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back. The two main uses of refrigerants are refrigerators/freezers and air conditioners.
Refrigerant Properties: Special Thermodynamic qualities such as suitable
boiling point (somewhat below the target temperature),
high heat of vaporization, moderate density in liquid form,
high density in gaseous form,
Non-corrosive,
Non-toxic and safe.
Unit of refrigeration
A ton of refrigeration (TR), also called a refrigeration ton (RT), is a unit of power used to describe the heat-extraction capacity of refrigeration and air conditioning equipment. It is defined as the rate of heat transfer that results in the melting of 1 short ton of pure ice at 0 °C (32 °F) in 24 hours.
Unit of refrigeration Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. Prior to the introduction of mechanical refrigeration, cooling was accomplished by delivering ice. Installing one ton of mechanical refrigeration capacity replaced the daily delivery of one ton of ice.
Latent heat of ice (i.e., heat of fusion) = 333.55 kJ/kg = 144 Btu/lb
One short ton = 2000 lb = 907 kg
To Read more...
register as member and login to download attachment [pdf]
use for Educational Purposes Only
HVAC (Heating, Ventilation and Air-Conditioning)
for the student of architecture
https://frontdesk.co.in/building-service...ditioning/
Basic principles of refrigeration
Temperature
How Heat Flows
Conduction: the transmission of heat from one molecule to another within a material or from one material to another when they are held in direct contact.
Heat Energy
Latent Heat, specific heat
Refrigeration
Sensible and latent heats of water at different phases
Vapor Compression Refrigeration System
Vapor Compression Refrigeration System Major Components: (i) Compressor, (ii) Condenser Coil, (iii) Expansion Valve and (iv) Evaporator Coil. Chemical Refrigerants such as R-12, R-22 or R-134a are used to provide refrigeration effect.
Refrigeration cycle
The Vapor-Compression Refrigeration Cycle is comprised of four steps
Part 1: Compression : In this stage, the refrigerant enters the compressor as a gas under low pressure and having a low temperature. Then, the refrigerant is compressed, so the fluid leaves the compressor under high pressure and with a high temperature.
Refrigeration cycle
Part 4: Evaporation : The low pressure, low temperature refrigerant enters the evaporator, which is in contact with the cold reservoir. Because a low pressure is maintained, the refrigerant is able to boil at a low temperature. So, the liquid absorbs heat from the cold reservoir and evaporates. The refrigerant leaves the evaporator as a low temperature, low pressure gas and is taken into the compressor again, back at the beginning of the cycle
Refrigeration system Component
Scroll Compressor
Screw compressors
Screw compressors : use a pair of helical rotors or screws which mesh together to compress the refrigerant between them. They can produce high pressure for a small quantity of gas and consume less power than reciprocating compressors. They have low to medium initial and maintenance costs and few moving parts. However, they have difficulty in dirty environments, high rotational speeds, and shorter life expectancies than other designs
Rotary Compressors
Rotary compressors have two rotating elements, like gears, between which the refrigerant is compressed. These compressors are very efficient because the actions of taking in refrigerant and compressing refrigerant occur simultaneously. They have very few moving parts, low rotational speeds, low initial and maintenance costs, and are forgiving in dirty environments. However, they are limited to smaller volumes of the gas and produce less pressure than other types of compressors.
Centrifugal compressor
Centrifugal – The centrifugal compressor increases the refrigerant pressure by throwing it at high velocity (like an ordinary house fan throws air) using a rotating impeller inside a stationary housing.
Condenser
Air cooled condenser
Water cooled condenser
Air cooled condensers (coil condensers ) are used in small units like household refrigerators, deep freezers, water coolers, window air-conditioners, split air-conditioners, small packaged air-conditioners etc. These are used in plants where the cooling load is small and the total quantity of the refrigerant in the refrigeration cycle is small. Air cooled condensers occupy a comparatively larger space than water cooled condensers.
Condenser
Water cooled condenser :
Water is used as the heat transfer medium in place of air. Water flows through a heat exchanger where refrigerants contained in separate piping give up their heat to the water.
Evaporator
An evaporator is used in an air-conditioning system to allow a compressed cooling chemical to evaporate from liquid to gas while absorbing heat in the process. It can also be used to remove water or other liquids from mixtures. There are two types of evap.:
Forced Convection Type uses a fan or pump to force the liquid being cooled over the evap.
Natural Convection Type has the liquid being cooled flows naturally to the evap. due to the density differences of the chilled and warm liquid.
Expansion valves
Expansion valves are devices used to control the refrigerant flow in a refrigeration system. They help to facilitate the change of higher pressure of liquid refrigerant in the condensing unit to lower pressure gas refrigerant in the evaporator.
Types.
1. Automatic Exp. Valves
regulates the flow of refrigerant from the liquid line to the evaporator by using a pressure-actuated diaphragm. It maintains a constant pressure in the evaporator.
Refrigerant in Refrigeration
Chemical Refrigerant A refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back. The two main uses of refrigerants are refrigerators/freezers and air conditioners.
Refrigerant Properties: Special Thermodynamic qualities such as suitable
boiling point (somewhat below the target temperature),
high heat of vaporization, moderate density in liquid form,
high density in gaseous form,
Non-corrosive,
Non-toxic and safe.
Unit of refrigeration
A ton of refrigeration (TR), also called a refrigeration ton (RT), is a unit of power used to describe the heat-extraction capacity of refrigeration and air conditioning equipment. It is defined as the rate of heat transfer that results in the melting of 1 short ton of pure ice at 0 °C (32 °F) in 24 hours.
Unit of refrigeration Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. Prior to the introduction of mechanical refrigeration, cooling was accomplished by delivering ice. Installing one ton of mechanical refrigeration capacity replaced the daily delivery of one ton of ice.
Latent heat of ice (i.e., heat of fusion) = 333.55 kJ/kg = 144 Btu/lb
One short ton = 2000 lb = 907 kg
To Read more...
register as member and login to download attachment [pdf]
use for Educational Purposes Only