Types of Chillers

Chiller Types have been designed to cater to the diversified requirement of industrial chillers.Water chillers have evolved due to the variety in availability of type of energy at industry or small level.Types of chillers have made the use of the chillers flexible in terms of energy input.

Water chillers

Industrial research in the field of chiller has eased the selection of chillers in an economical and robust manner.There is no need of worry whatever type of energy you have available with you.

Each type of chiller targets the specific users classified on the basis of type of energy they have.

HVAC systems employ different types of chillers within the available resources of clients or users.

A chiller may be the best option for particular application while the same chiller may costly or less feasible for another application or plant.

Hvac water chillers are classified primarily on the basis of cycle on which they work.

• Vapor compression chillers or compression chillers or electric chillers
• Vapor absorption chillers or absorption chillers or ammonia chillers or lithium bromide chillers

HVAC chiller types

Vapor compression chillers are further classified on following basis.

• Type of compressor i.e reciprocating compressor,rotory compressor or screw compressor type vapor compressor chillers
• Type of condenser i.e air cooled condenser or air cooled chillers OR water cooled condensers or water cooled chillers

While Vapor absorption chillers are further classified as following:

• Direct fired absorption chillers (Natural gas, Diesel or Kerosene Oil Operated)
• Indirect fired absorption chillers

  
  

   
  

Tips for HVAC System Engineers

As HVAC system engineer, one has to keep an eye on all factors and areas that can decrease the efficiency of system or increase downtime or HVAC system unavailability or increase the maintenance cost of heating, ventilation and air-conditioning system. The responsibility starts from very beginning, when you decide to install HVAC system and start working on it in any way.

Following are the tips for smooth, trouble free and economical operation/working of hvac system.

1. Start your working from the very early stages of hvac system selection, procurement and tendering. Don’t ignore all these pre-installation steps as it would become difficult at later stages to alter any pre-done work. Complete your home work in selection of type of chillers you are going to install for your building or space or for other purposes. Consult hvac experts for getting pros and cons of different types of chillers and select the one which suits your resources and priorities. Then select the renowned and reliable manufacturer for purchasing the hvac system components. Get involved in tenders to ensure transparency in whole process.
2. HVAC Installation is very important phase for hvac engineers. Include all essential items and accessories in hvac contract BOQ and monitor the activities of hvac contactor so that all goes in accordance with boq or terms and conditions written while awarding contract. Ensure that all installation is carried out in accordance with drawings and all components meet the specifications mentioned in BOQ. Your saving at any stage could lead you to spend more in later stages. Never compromise the material of all items being installed in hvac system. Low quality material would finally take you to problems in coming days/years. Commissioning is as important as its installation so adhere to commissioning procedures at all times and don’t ignore any thing in courtesy.
3. Training of hvac personnel is very important in operation and maintenance point of view. So include training of your personnel in contract or arrange it separately. Your expenditure on manpower training would pay back you in future so never overlook it.
4. Prepare all hvac procedures related to operation and maintenance of each and every component of hvac system and implement it strictly. Adhere to maintenance program for your water chillers, air handling units, cooling towers and fan coil units .Your adherence to maintenance programs would never let you face any problem regarding the unavailability of hvac system. Always try to complete maintenance work timely in the best available resources or with the support of hvac supplier
5. Adopt hvac pro-active approach regarding critical and heat transfer interfaces/surfaces or to operate hvac system at maximum efficiency, focus on heat transfer interfaces/surfaces. In this regard condenser is most important, keep it at optimum conditions. Scaling, corrosion and high pressure in condenser would get you in trouble finally so be pro-active before your condenser lets you down. Heating and cooling coils are also equally important as these would directly affect cooling or heating in hvac spaces/zones. Get all coils cleaned and keep them in best heat transfer condition. Ensure timely maintenance of cooling towers to operate them at maximum efficiency/effectiveness.

Water Cooled Chiller vs Air Cooled Chiller in HVAC System

• Initial cost of air cooled chillers is lower than water cooled chillers as air cooled systems don’t require cooling towers,condenser water pumps and associated HVAC components.
• Small systems are almost always air-cooled since the extra requirements of water treatment and maintenance are capital intensive and will not be offset quickly by the lower operating costs.  Larger HVAC water chillers are almost always water cooled .HVAC engineers and technicians feel easy with maintenance free or less maintenance equipment.
• Water cooled chillers may be preferred because of  better heat transfer properties of water as compared to air cooled chillers.The primary advantage of water is that the film coefficient is 10-100 times better with water than air.Film coefficient controls heat transfer with given constant area and temperature difference.
• Water-cooled HVAC units make less noise and give more cooling per square foot.While air cooled chillers have comparatively less cooling per square foot and are more noisy HVAC machines.Noisy machines are annoying especially for occupants of nearest offices or zones.
• While comparing  air and water cooled chillers, an overall system cost (both running and installed) has to be worked out. Size of HVAC unit matters when selecting the water cooled chiller or air cooled chiller.Smaller HVAC units are usually air cooled, larger are water cooled.
• HVAC engineers have to evaluate air cooled and water cooled chillers keeping in mind various factors.Refrigeration engineer has to consider the ambient conditions (wet bulb and dry bulb), number of hours of operation, part load pattern and cost of maintenance etc.
• HVAC experts have no single answer to when asked “water cooled chiller is better or air cooled chiller?”. The fact is that “It all depends”. Water-cooled chillers will normally condense at an average lower pressure than air-cooled chillers.  This is because the water temperature will usually be less than the air temperature.If your condenser is operating at lower pressure then it is directly reflected and translated into lower operating costs or KW /TR(Ton of refrigeration).
• The difference between the wet-bulb temperature and the dry-bulb temperature gives the available difference between the condensing temperatures of water-cooled and air-cooled condensers respectively.  
• Cooling towers and/or evaporative condensers have main disadvantage of maintenance and water treatment costs. This running cost is not present in air cooled chillers.
• Despite the advantages of lower IKW/TR of a water-cooled system or water cooled chillers, sometimes, air-cooled systems are preferred for various applications.
• For example in 24 hour application of HVAC chillers,the night time dry bulb temperature are generally much lower than the day time dry bulb temperature, as compared to the difference in wet bulb temperature between day and night.  This advantage is best capitalized by an air-cooled system or air cooled chillers.
• Other examples could be where the wet bulb temperatures are very high, especially coastal areas. 
• When comparing water cooled and air cooled chiller,scarcity of water and hence cost of water is another issue which is a point to be considered while deciding on the system.  This happens in many countries .
• Space is also of importance in some applications. Air cooled chillers can utilize open space, such as a parking lot, roof or ground level area. Although smaller in size but Water cooled chillers require a mechanical room and cooling towers.
• Air recirculation is very important for air cooled chillers.Any obstruction in the circulation of air near water chillers would adversely affect the performance of air cooled chillers.Air cooled chillers can have problems with recirculation if there are walls higher than the unit or too many units to close together. If there is a situation where outside walls are required for building code and the unit will not be receiving enough fresh air, then a water cooled application may be the best option.
• Water cooled chillers have longer life,higher efficiency,large capacity and also refrigerant containment.While looking on disadvantatges of air cooled chillers,they have lower efficiency,comparatively short life span and available in low capacity range.

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

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

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.

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 ):

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 .

Must Read : Absorption Chillers vs Electric (Compression) chillers

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 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.

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.

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.