Saturday, June 30, 2012

HVAC Quiz # 1

HVAC practice test

Following Quiz is related to ,HVAC ,vapor absorption cycle (single effect and double effect)and Lithium Bromide Chillers.

(Should you require quiz in pdf /ms word form,write down your email address in the comments below)  

  1. Expansion device in refrigeration machines is also sometimes called

  2. Condenser
    Throttle valve

  3. Solution in absorption chiller consists of

  4. Refrigerant only
    Rrefrigerant and water
    Refrigerant & absorbent
    None of above

  5. Heat in the lithium bromide chiller generator releases_________ from solution.

  6. refrigerant vapors
    water (in liquid form)
    absorbent vapors
    None of them

  7. The maximum refrigerant vapors from evaporator are absorbed in the absorbent in the ___ .

  8. Evaporator
    Heat exchanger

  9. A solution with relatively high % of absorbent and relatively low % of refrigerant is called

  10. Weak solution
    Strong solution

  11. A solution with relatively low % of absorbent and relatively high % of refrigerant is called

  12. Weak solution
    Dilute solution
    both A & B
    None of above

  13. Generator in single effect absorption chiller receives strong solution from

  14. Evaporator
    LT/HT hx
    invalid question

  15. In the absorption process, refrigerant (water) is absorbed into a(n) _____

  16. absorbent
    solution in absorber
    strong solution
    All of above

  17. Common heat sources for absorption system generator are________.

  18. Steam
    Hot water
    All of above

  19. Conversion of the strong solution into solid or slushy mass is called

  20. Condensation

Thursday, June 28, 2012

What is an Air-Conditioning System

HVAC airconditioning

Air-conditioning is a process that simultaneously conditions air, distributes it combined with the outdoor air to the conditioned space or zone. 


HVAC Air conditioning  at the same time controls and maintains temperature,humidity, air movement, air cleanliness, sound level and pressure differential  for the comfort of its residents ,workers,process requirements or preservation of goods/items placed in it. 

HVAC airconditioning system

 An air-conditioning system or HVACR (heating,ventilation ,airconditioning and Refrigeration) system consists of components and equipment arranged in sequential order to heat or cool, humidify or dehumidify, clean and purify air to conditioned space.


Functions of air-conditioning system also include to attenuate objectionable equipment noise, transport the conditioned outdoor air and recirculate air to the conditioned space, and control and maintain an indoor or enclosed environment at optimum energy use. 

Applications of Air-Conditioning

Air-conditioning systems in its simplest form are sometimes also called ac air conditioning or windows air conditioning.Some of applications / buildings where air conditioning systems are used ,are listed below.

  • Institutional buildings, air conditioned in buildings such as hospitals and nursing homes
  • Commercial buildings, air conditioned in buildings such as offices, stores, and shopping centers
  • Residential buildings, including single-family and multifamily low-rise or high rise buildings
  • Manufacturing buildings, which manufacture and store products
  • Process related buildings,air conditioned in buildings or spaces where there is need to supply conditioned air for process cooling or background environment cooling for machines

Friday, June 22, 2012

Absorption Chiller in HVAC system

Absorption chiller  occupies vital position in an HVAC system.Absorption chiller is an equipment which uses a heat source, a refrigerant and an absorbent for producing chilled or hot water. In the types of chillers,along with vapor compression water chiller or electric chiller ,absorption cooling system is also used in many applications.Absorption chillers produce chilled water under vacuum conditions for the purpose of air-conditioning and technology process.

Basic components of Vapor absorption chillers

Absorption chillers in its simplest form (single stage) consist of following main parts:

Steam absorption chiller
  • Generator
  • Condenser
  • Evaporator
  • Absorber
  • Heat exchanger
  • Refrigerant Pump
  • Solution pump

Working Principle of Absorption Chiller

1. Function of Generator in absorption chiller

In generator of absorption chillers weak solution is heated by operating steam (steam absorption chillers),hot water or flue gases in indirect fired absorption chillers.While direct fired absorption chillers are Natural gas, Diesel or Kerosene Oil Operated.After heating in generator solution is concentrated and high temperature refrigerant vapors are produced.After generator process in a chiller high temperature and pressure refrigerant vapors travel to condenser. A strong solution enters absorber through heat exchanger in exchanging heat with weak solution .

2. Function of Condenser  in absorption chiller

water chiller
vapor absorption cycle
Refrigerant vapor from generator is condensed in condenser by cooling water.Condensation is constant pressure process where refrigerant (water) gives off its heat to cooling water .In this way refrigerant heat is carried to atmosphere.In water cooled chillers , cooling water recycles after exchanging heat with air in cooling towers of same HVACsystem.

3. Function of Evaporator in absorption chiller

Refrigerant from condenser flows to evaporator .In this compartment of absorption chiller,refrigerant gets vaporized by taking heat from chilled water.Refrigerant from evaporator refrigerant pan is pumped over the evaporator tubes with the help of refrigerant pump.Flow of refrigerant over evaporator tubes evaporates the refrigerant thus producing refrigeration effect, and evaporates to form vapor by absorbing heat of chilled water flowing through tubes.In this way,evaporation takes place at constant pressure process where refrigerant gets latent heat from chiller water.Chiller absorption takes place here in absorber.Chilled water is cooled and return to the system of customer.

4. Function of Absorber in absorption chiller

simplified diagram of  absorption chiller works
Produced refrigerant vapor enters absorber, and absorbed by strong solution in the absorber.In this way,strong solution is diluted by absorbing refrigerant vapor in absorber . Heat generated is carried to atmosphere by cooling water.

5. Function of HVAC Solution Pump in absorption chiller

This weak solution is transferred by solution pump to generator for concentration.Pumps are components in absorption cooling systems which require electric energy for its operation.Weak solution from the absorber is pumped into the generator through heat exchanger. This process is continued, and refrigeration effect is repeated.

Must Read : Absorption Chillers vs Electric (Compression) chillers

Try here HVAC quiz related to absorption chillers or vapor compression cycle.

Sunday, June 17, 2012

Water Chillers

Water chillers are backbone of HVAC cooling systems.Water chiller is a refrigeration machine which produces chilled water ( Approx 7 Degree C ~ 12 Degree C).The primary function of a chiller is to lower the temperature of water to such value such that it can be used for producing cooling effect in integration with other HVAC components. A water chiller is just like a other refrigerator machine but instead of keeping your food cool or making ice,it produces chilled water.The output of chiller is a water at lower temperature usually around about 10 o C depending upon the Chiller design.

HVAC water chillers play vital role in any HVAC systems along with other basic components. Chillers have got much attention in recent years for its new designs and performance improvement in existing designs. New designs have resulted in hvac chiller with better efficiency and less operation and maintenance costs. Another desirable features is energy saving and precise load or capacity control  for new chillers. We see the chillers with above features in market but as engineering professionals we hope to see more with design improvements with less O & M cost. It is essential part of HVACsystem to have a chiller. Chiller manufacturers have also expanded their production as well design capabilities to cater to the diversified demands of  HVAC chillers.
HVAC Chiller Basics

Working Principle of Vapor Compression Chiller

An HVAC chiller works on vapor compression or vapor absorption cycle.In vapor compression cycle, refrigerant circulates in evaporator ,compressor, condenser and expansion valve of a chiller. A thermodynamic process occurs in each of above chillers.Theoretical working of Vapor compression or compression chillers is explained below.

Heat addition to refrigerant in evaporator ( 1-2):

Refrigerant gets vaporized by taking heat from chilled water in evaporator thus serving its prime purpose. Refrigerant comes out of evaporator as vapors but on other side chilled water is produced. Thus heat is added to refrigerant at constant pressure but is extracted from chilled water. Both refrigerant and chilled water don’t get mixed and are separated by some solid wall in between them in evaporator like shell and tube design.

Compression of refrigerant vapors in compressor (2 - 3 ):

Vapor compression Cycle
Working Principle of Water Chillers

Refrigerant vapors come out of evaporator and then compressed by chiller compressor to high pressure and temperature. Compressor requires energy input for its working and hence electric energy is supplied to it.

Heat rejection by refrigerant in condenser ( 3 - 4 ) :
Similar to evaporator ,but reverse is happening here. Refrigerant rejects its heat to outside cooling liquid or air .In this way, refrigerant gets condensed and outside media is heated. outside media e.g. cooling water may be cooled by cooling tower and recycled again into condenser.
Expansion of refrigerant in expansion valve ( 4 -1 ) :
Refrigerant in condensed form coming out of condenser is expanded in expansion valve and its pressure and temperature is reduced to level of evaporator so that above cycle is repeated again.
In above four components of hvac chiller ,evaporator is the part where we get chilled water after exchanging heat with refrigerant .

Friday, June 15, 2012

HVAC System

HVAC system is basically an assembly of various types of equipments installed together to provide heating and cooling alongwith indoor climate control. HVAC systems involve mechanical, electrical and I & C components to provide comfort to the occupants of building/space or to preserve goods,products or items placed in space.

HVAC water chillers
HVAC System,HVAC water chillers

HVAC cooling systems may be integrated with HVAC heating systems or these may be installed separately depending upon HVAC design  .HVAC system also serves on industrial scale to keep the machinery running by maintaining the temperature of space/hall/room where machines are installed.HVAC water chillers have become essential for any industry for its various needs.

HVAC System Basic Components

An HVAC System may include the following basic components or units.
  • HVAC water chillers and heaters
  • Hot water generator (if chiller does produce chilled water only) or furnace
  • Chilled water pumps
  • Cooling water pumps
  • Electrical power supply control or Motor control center (MCC)
  • Cooling towers
  • Piping for chilled water and cooling water or condenser side water
  • Valves for chilled water and cooling water sides
  • Air handling units (AHUs) , heating coils and cooling Coils
  • Ducts in ventilation system (supply ducts and return ducts)
  • Fan Coil Units (FCUs) and thermostats
  • HVAC Diffusers and grills
  • HVAC controls (instrumentation & Control components)  installed at various locations
  • HVAC software for building HVAC control or building management system (BMS)
An Assembly of all above components forms an HVAC system.

HVAC system working principle is explained as below.

In the background of HVAC system ,an HVAC water chiller produces chilled water which is then circulated throughout the building or space upto cooling coils in air handling units.Blowers move air on cooling coils which is then distributed into various portions of space or building for providing comfort or preserving goods/items as per HVAC design.Air is distributed through supply ducts and return air is collected in air handling units with the help of return ducts.Chilled water and cooling water pumps provide energy to keep the chilled and cooling water moving.

HVAC Valves are also installed at various points in piping to ease the maintenance of HVAC system or for the sake of system control.Heating of air may be done with the help of HVAC heat pump ,hot water generator or simply by furnace.Some industrial chillers also serve as heaters in winter season.Heating coils take the place of cooling coils in case of heating mode.

HVAC system cost may vary for different applications as heating and cooling space or environment  varies. Looking for cheap hvac systems may involve little research in types of HVAC systems and HVAC suppliers otherwise you would be lamenting over waste of millions of dollars for selecting wrong HVAC designer & contractor.

Saturday, June 2, 2012

What is an HVAC ?

Acronym HVAC stands for heating ,ventilation and air conditioning. Sometimes Refrigeration "R " is also added and it becomes "HVACR".HVAC is basically climate control of confined space with respect to requirements of persons or goods in it.HVAC system is not only heating and cooling of air but also concerned with mainatining the indoor air quality (IAQ).Heating of air is done usually in winter and similarly cooling of air is done in summer season.

What is an HVAC?

HVAC system works on the principles of thermodynamics ,fluid mechanics and heat transfer.

All these fields come into play in various components of HVAC.IAQ Indoor air quality is the quality of air inside the building or structures as mostly related to health and safe keeping of its occupants or items/goods placed.IAQ is changed with inclusiion or contamination with gases  and uncontrolled mass & energy transfer.

HVAC systems are used for heating and cooling  & air condition in homes, building, industry, vehicles, aquariums and many more.With the passage of time application of HVAC are increasing and more research is in-progress in this field.HVAC business is also increasing at the same pace as field of application is broadening.

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