CHILLED SYSTEM

CHILLED  SYSTEM

Water cooled chillers: With water cooled chillers, the refrigerant is cooled with a shell and tube condenser that is part of the chiller package. The condenser water heat is then rejected to the cooling tower located outdoors.

Glycol cooled chillers: Glycol-cooled chillers look identical to the water-cooled chillers. With glycol-cooled chillers, heat removed from the returning chilled water is rejected to a glycol loop for transport to the outside atmosphere. The glycol flows via pipes to an outdoor-mounted device called a dry cooler also known as a fluid cooler. Heat is rejected to the outside atmosphere as fans force outdoor air through the warm glycol-filled coil in the dry cooler.

 Air cooled chillers: With air-cooled chillers, the heat of refrigerant is rejected to an air-cooled condenser that is typically integrated with the chiller. This type of chiller is known as a packaged chiller and can also be integrated into a cooling facility module. Air-cooled chillers are typically located outdoors.

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HVAC COOLING SYSTEM DESIGN

HVAC COOLING SYSTEM DESIGN

 Cooling and heat dissipation techniques are extremely important topics when it comes to designing and operating a data center. In many instances, system designs fall short of clients’ expectations in terms of reliability and availability. Perhaps naively, often too much importance is placed on the power and network availability without the same being applied to the air conditioning systems.

 Remember, ‘a chain is only as strong as its weakest link’. Infrastructure designs often fail to meet expectations because the same level of reliability/redundancy in many instances is not applied to all other components of the supporting infrastructure. While many people understand that only a short interruption in power supply to computer equipment can mean loss of data, what is often not considered is that an interruption in cooling system can be just as devastating.

This section includes:

1. Heat gains

2. Temperature and humidity requirements

3. Ventilation rates

4. Air quality

5. Cooling loads

6. HVAC equipment

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Condenser, Evaporator, and Compressor

Condenser, Evaporator, and Compressor

The condenser is one of three primary elements in your air conditioning system. The other two, the evaporator and compressor, are also important. To understand how the condenser works, it’s important to understand the other two as well.

• Evaporator: The system starts in home with inside air being blown over evaporator coils. These coils contain low-pressure refrigerant which absorbs the heat from the air and converts into a high-pressure gas.
• Compressor: The gas is transferred into the compressor, which is in the outside unit. Here, it’s compressed to help convert it back into a liquid so it can continue the cooling cycle. This produces extra heat.
• Condenser: The condenser is a set of coils, also located inside the outdoor unit. Here, a fan blows across the coils, dissipating the heat from the refrigerant inside them and allowing it to convert back into a liquid, at which point it’s sent back inside to start the process over again.

Without the condenser, the refrigerant would retain its heat and the process would not work. Therefore, it’s important to be able to tell if the condenser is malfunctioning or broken.


Diagnosing Condenser Problems

Often, the problem may not be with the condenser coils themselves, but with the fan or motor in the outdoor unit. The following signs can let you know if the condenser is broken:

• Air conditioner blows warm air inside.
• Outdoor condenser fan doesn’t run.
• Refrigerant leaks from outdoor unit.

Compressor Types

Compressor Types

Two types of compressor dominate HVAC systems in buildings: piston and scroll.
The piston type uses pistons attached to a motor-driven crankshaft to draw in and compress the refrigerant.

Scroll compressors use an orbiting scroll on an eccentric motor-driven crankshaft to suck in vaporized refrigerant and push it into a stationary scroll whose volume gradually decreases to compress the refrigerant. There are three forms of compressor construction. Hermetically sealed units have motor and compressor sealed within a welded steel casing. They can't leak, but they also can't be repaired. Semi-hermetic units put motor and compressor inside a steel shell whose halves are sealed with a gasket and bolts. These can be opened for repairs, but might leak refrigerant. Open compressors have motor and compressor as separate units linked by a coupling. This variety is found in very large HVAC systems.

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What Is the Function of a Compressor in an HVAC System?

What Is the Function of a Compressor in an HVAC System?

The compressor is the heart of the cooling function of heating, ventilation and air conditioning (HVAC) systems. The air conditioner component of a building's HVAC system essentially is a type of refrigerator that cools and dehumidifies the air in the building, ensuring thermal comfort for the occupants. Most HVAC compressors look like a black box with lines running to and from it.

Compressor Function
Air conditioners are devices that transfer heat from an enclosed space to the outside air. The motor-driven compressor in an air conditioning system powers the whole heat-transfer cycle. Air conditioners rely on two facts of nature. One is that heat flows from a high-temperature area to a lower temperature area. The other is that gases always flow from a high-pressure area to a low-pressure area.
Air Conditioning Cycle
The heat-transfer cycle starts as the compressor squeezes the refrigerant. This squeezing action raises its temperature well above that of the surrounding atmosphere. The squeezing action also pressurizes the refrigerant just to its liquefying point so it can flow through the system. The hot, pressurized, liquified refrigerant flows to a condenser coil where it gives up its excess heat to the cooler atmosphere. Typically, a fan blows air through the condenser coil to facilitate transfer of the excess heat.
Expansion Phase
After shedding its excess heat to the atmosphere, the refrigerant flows to an evaporator coil where it expands into a gas at the reduced pressure in the evaporator, which is located in the space to be cooled. This expansion requires heat, which is drawn from the air in the enclosed space that's being cooled. This warms the refrigerant. The cold evaporator also draws humidity from the air. A fan blowing across the evaporator coil facilitates this transfer of heat and humidity. As the compressor pushes hot pressurized refrigerant toward the condenser, it pulls the warm vaporized refrigerant from the evaporator to start the cycle all over again.

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What does the Expansion Valve do in an Air Conditioning System

What does the Expansion Valve do in an Air Conditioning System
The modern air conditioner is quite a marvel of engineering. The complex working of its components is the reason that only professionals can effectively diagnose and repair a malfunctioning air conditioner.
One of the key components allowing an air conditioner to work is a part called the expansion valve. Without this valve, an AC would not be able to draw sufficient heat from the inside of a home.

How the expansion valve helps cool down your home
In order to explain the purpose of an expansion valve requires first explaining the basics of how refrigerant works in an air conditioner. Refrigerant is a heat transference fluid that shifts between liquid and gaseous state, absorbing and releasing heat as it does so. When the refrigerant moves through the outdoor condenser coil, it releases heat to the outside. Cooled down, it then moves toward the indoor evaporator where it absorbs heat.
However, at the point after leaving the condenser, the refrigerant—which is in a high-pressure liquid form—is still too hot to effectively go carry out the process of evaporation that will draw heat out of the indoor air. This is where the expansion valve does its job: the valve is designed to remove pressure from the refrigerant and rapidly cool it down into a cold gas. The valve doesn’t remove heat, only pressure—but removing the pressure has the effect of lowering the temperature of the refrigerant. After it leaves the valve, the refrigerant will be at its the coldest. The refrigerant is now ready to move through the indoor evaporator coil, where it will meet warm indoor air and through evaporation lower the temperature of the air.
Live any component inside an air conditioning system, the expansion valve can malfunction, leading to an AC that won’t provide any cooling. Always call on professionals to look your air conditioner when it encounters trouble: a number of different malfunctions might lurk behind the problem, and it takes training to locate the actual cause. If a broken expansion valve is at fault, the technician will repair or replace it.

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Classification of Valves

Classification of Valves

Fluid control valves are classified in many ways. Following is the classification of valves.

Multi Turn and Quarter Turn Valves

Multi turn valves need many turns of actuator to bring closure member (disc) from fully open position to fully closed position. Examples of multi turn valves are gate valves, globe valves, needle valves, and diaphragm and pinch valves.
While quarter turn valves need only quarter ,0 to 900 degree, motion of closure member (disc) to bring it from full open position to full closed position.  Examples of quarter turn valves are butterfly valves, ball vales and plug valves etc. Quarter turn vales are quickopening valves.

Self actuated Valves

Self actuated valves don’t need actuator to operate them. These valves operate based on some property of fluid line like pressure or flow. Self actuated valves don’t need operator’s interference to control the fluid. Examples of self actuated valves are check valves and pressure relief valves or safety valves.

Linear Motion and Rotary Motion Valves

In linear motion valves, disc moves in linear or straight path to open, close or throttle the flow in valve. While in Rotary motion valves, disc rotates to open, close or throttle the flow. Examples of linear motion valves are gate valves, needle valves, globe valves, diaphragm valves and pinch valves. Examples of Rotary motion valves are ball valves, butterfly valves etc.


General Types of valves

In general following are the types of valves.
• Gate valve
• Globe Valve
• Pinch Valve
• Needle valve
• Diaphragm valve
• Ball valve
• Butterfly Valve
• Check valve
• Pressure relief Valve (safety or relief valve)

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Refrigerant Leak Detection

Refrigerant Leak Detection
Leak detection is an essential service practice. There are many old and new methods available to assist technicians' eyes and ears in finding leak sites.
All pressurized HVACR systems can eventually leak refrigerant. Therefore, it's the responsibility of the HVACR technician to monitor systems regularly and inspect for leaks.
Although a tight system — with minimal leakage that doesn't affect system performance — may not pose a problem, a more serious leak will do so, and could occur at any time.
Some leaks are plainly visible to the eye. These include a visible line break, the presence of oil, and quite possibly a refrigerant vapor cloud of escaping gas.
An audible leak might also be detected if a system is pressurized and large leaks are present.

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Electronic Refrigerant Leak Detectors and Methods

Electronic Refrigerant Leak Detectors and Methods
Other methods include portable, hand-held electronic devices, and fixed system monitors. These are recognized as the quickest, cleanest methods.
A question that's commonly asked is, “Are leak detectors helpful in detecting leaks with all of the new refrigerants and R-22 replacement blends?” With the influx of new refrigerants, following the Environmental Protection Agency-mandated phase-out of chlorodifluoremethane (R-22) and other mandates for CFCs, HCFCs and HFCs, detection products and methods continue to be a challenge. With that in mind, many instrument companies have developed and improved their products to meet the current and even future needs with the refrigerant evolution.
Superior Sensing Devices
State-of-the-art leak detectors are able to identify all CFCs, (those containing chlorine), HCFCs (those containing fluorine) and HFCs (non-ozone-depleting refrigerants and compounds), plus bromine gas (found in HBFCs) and halogens. A superior portable leak detection tool will accurately detect and may identify the smallest of leaks. The ability to target the gases and the severity of the leak is the key to a great detection device. Reliability, longevity, serviceability, and cost should also be considered, yet initial cost alone may not be the best deciding factor.

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HVAC Components

HVAC Components
Other important components of an HVAC system include:
Ductwork: This system of metal pathways allows for distribution of hot or cold air throughout your home.
Humidifier: Adds moisture back into the air before distribution throughout the home, ultimately making breathing easier.
Thermostat: This is what allows you to control the temperature in your home.
Filters: Ensures air in your home is free of dirt, allergens, and odors, and helps maintain your system.
In order to ensure that all aspects of your home’s HVAC system are running at peak performance, it is essential to perform seasonal and annual maintenance. Keeping filters and ducts clean of dust and debris helps make your system more efficient. It also ensures your HVAC systems keeps your family comfortable for many years.

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How Does HVAC Work?

How Does HVAC Work?

Understanding Heating, Ventilation, and Air Conditioning Systems, Components, and How They Work

Your home’s heating, ventilation and air conditioning (HVAC) system might be one of its largest components, but unless something goes wrong you probably give very little thought to it. However, understanding how a HVAC systems work helps homeowners troubleshoot potential problems and become a more informed homeowner.

Heating

The heating aspect of your home’s HVAC system is carried out by your furnace. Depending on the style of heat distribution in your home, you may either have electric baseboards, a gas forced air furnace, or radiant heat system (also known as a boiler) installed. For our purposes, we’ll focus on gas-powered forced air systems, as they are the most popular system installed in homes today.

All central heating systems consist of a burner, heat exchanger, blower, and a flue. The burner is what engages when the thermostat calls for heat, and it delivers the fuel to your heat exchanger to begin the heating process. The heat exchanger intakes air and turns the fuel and air mixture into heat that will ultimately be sent through your home’s ductwork. The heated air is then transferred to the air distribution system. The blower is part of this distribution system, and is what ultimately moves the heated air through your ductwork and into the various rooms of your home. We’ll discuss the flue in the next section, as it’s a significant part of the ventilation aspect of the HVAC system.

A boiler-based or hydronic heating system works in a similar manner as a gas-powered forced air system, heating water within the boiler for distribution via piping to radiators located in the various rooms of a house, which then give off heat. Electric baseboards or registers contain a heating element that heats up when the thermostat calls for heat. Some have a blower to help distribute the heat, but some simply give off radiant heating.

Ventilation

The ventilation aspect of your home’s HVAC system is comprised of the flue and vent pipes. It might also involve a fresh air intake pipe or vent. The fresh air intake helps to bring the heated air to the correct temperature before it is distributed throughout the house. The flue and vent pipe are responsible for keeping the air in your home safe to breathe. It works by exhausting harmful byproducts of the combustion process, such as carbon monoxide and other noxious fumes, outside the building. The flue will open and close accordingly in order to ensure there is no backup of dangerous exhaust into your home.

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Heating systems

Heating systems

Heating systems can take a couple of different forms. Some are furnaces that burn material to provide heated air through the ductwork, while another popular choice is boilers that heat water for steam radiators, or forced-water systems with baseboard radiators, electric heat, and heat pumps. A furnace will generally operate on natural gas or propane, while a boiler will use gas or oil to heat the water.

Another option is a radiant floor, also known as a hydronic heating system. These use piping under a floor, and are made up of flexible tubes that are filled with water or a glycol solution. These can heat any kind of floor, including concrete, and are an efficient method of providing warmth in a home. They can even be retrofitted into wooden flooring, though they need to be carefully installed in sheathing for wooden floors.

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How Aır Curtaıns Reduce Coolıng Costs

How Aır Curtaıns Reduce Coolıng Costs

Nearly all business owners are wary of costs and search for effective ways to save money. In warmer months, most businesses turn their thermostats down and make use of air conditioning systems. Maintaining an optimum temperature is essential for ensuring that customers enter the building- and that they wish to stay there.

However, controlling the climate of premises can be a costly affair. Air curtains can reduce cooling costs by preventing the amount of warm air that enters through an entryway. They will also prevent the loss of cooled air, by blocking the entry of hot air when a door is opened and closed. Both of these features mean that you can maintain a desired temperature, without needing to use air conditioning as often, or for as lengthy periods of time. This reduces the amount of energy used by air conditioning units, therefore saving your business valuable money spent on cooling costs. Air curtains also prevent outside contaminants- such as dust and insects – from entering an establishment. This can be invaluable for customers or employees with sensitivity to these contaminants, and can be particularly useful in months where hay fever is prominent.

Air curtains come in a variety models. Most are designed to fit above eight foot doorways; however, many companies have created models to fit in smaller or larger gaps. Air curtain length can also vary- some need only to be a little shorter than the width of the doorway, whereas other companies find that extra-long curtains, or several in a row, have a greater impact. You also choose the right strength to fit the requirements of your company. For example, air curtains made for walk-in freezers must work harder to account for the drastic difference in temperatures. Businesses that work in dusty or bug infested areas may look for air curtains that are best at filtering such contaminants.

Whatever your needs, air curtains are certain to save you money on the costs of climate control, and may even bring you a greater return as customers are happy to stay on site longer.

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Types of Gas Burners

Types of Gas Burners
Types of residential gas burners include atmospheric injection, yellow (luminous) flame, and power burner units. Their classification is determined by the firing method used. Gas burners can also be divided into two broad classifications based on whether they are specifically designed as integral parts of gas-fired heating equipment, are used to convert a furnace or boiler from one fuel to another. The latter are called conversion burners and, at least outwardly, resemble the gun-type burners used in oil- fired appliances. Gas conversion burners are commonly designed and manufactured with integral controls so that they can be installed as a unit in the existing furnace or boiler.
Note
The burner(s) producing the heat in a gas-fired appliance is some- times called the main gas burner. Do not confuse the main gas burner with the pilot gas burner. The function of the latter (where it is used) is to light the gas flowing to the main gas burner.

Gas burners may also be classified as inshot and upshot types, depending on the design of the burner tube. The burner tube of an inshot gas burner is commonly a straight, adjustable venturi that extends horizontally from the unit. An upshot gas burner is characterized by a burner tube that extends horizontally from the unit and then bends to assume a vertical position.

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Function of Condenser

Function of Condenser

In a cooling cycle of a refrigeration system, heat is absorbed by the vapor refrigerant in the evaporator followed by the compression of the refrigerant by the compressor. The high pressure and high temperature state of the vapor refrigerant is then converted to liquid at the cond. It is designed to condense effectively the compressed refrigerant vapor.

There are basically three types of condensing unit depending on how the heat is removed by the condensing medium which is usually water, air or a combination of both.

• Air-Cooled types are usually used in the residential and small offices applications. They are used in small capacity systems below 20 tons. The advantages of using this design include not having to do water piping, not necessary to have water disposal system, saving in water costs and not much scaling problems caused by the mineral content of the water. It is also easier to install and has lower initial cost. There isn't much maintenance problems. The disadvantages are that it requires higher power per ton of refrigeration, has shorter compressor life and on days when most cooling is required, the least is available. 

• The circulation of air-cooled type can be by natural convection or by forced convection (usually using blower or fan). Due to its limited capacity, natural convection is used in smaller applications such as freezers and refrigerators. In forced convection, air is circulated by using a fan or blower that pulls the atmospheric air through the finned coils. Internally, the refrigerant circulates through the coil and air flows across the outside of the tubes.

• Water-Cooled There are 3 types commonly being used. They are shell and tube, shell and coil, and double tube. The most commonly used is the shell and tube type and are usually available from two tons up to couple of hundred tons. This design has lower power requirements per ton of refrigeration and the compressors can last longer compared to the air-cooled type. A water cooling tower is frequently used for higher capacity application.

• Evaporative type which is a combination of water and air-cooled.

Air-Cooled and Water-Cooled Comparison Summary

• Air-cooled type operates at higher head pressure or condensing pressure, hence reducing the capacity of the compressor and increases the power intake. In general, a 2 hp water-cooled system will require the same refrigeration as a 3 hp air-cooled system.
• The maintenance costs of water-cooled type is about three to four times the air-cooled type. Air-cooled type maintenance is usually limited to regular lubrication of fan and motor bearings. Water-cooled type requires cleaning from algae and bacteria. Scales on the tubes are removed by using acid compound. Proper water treatment is also critical to the operation of the cond.

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Types of Filter

Types of Filter
There are basically two types in used today.
• Liquid Line Type
• Suction Line Type

Liquid Line Type is placed after the condenser coil and before the expansion valve. The liquid refrigerant that flows from the condenser to the expansion valve is filtered from particles and moisture before entering it. Good filter will filter out particles that are 20 micron or above from the system.
Some higher end device has sight glass that enables the technician to look into it to see the level of refrigerant. Some have chemical in it that indicate the amount of moisture in the system based on the color of it.
Suction Line Type is placed after the evaporator and before the compressor. This device is used to protect the compressor especially after any failure that contaminates the system.
Motor failure in the compressor usually cause acid and other contaminants to be introduced into the refrigerant system hence it is important to have the suction line filter dryer installed.

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Expansion Valves

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.

The term "low side" is used to indicate the part of the system that operates under low pressure, in this case the evaporator. The "high side" is used to indicate the part of the system that operates under high pressure, in this case the condenser.

Types of Expansion Valves

There are basically four types of valves that are in used. These valves are also refer to as metering devices.

• Automatic Exp. Valves
• Thermostatic Exp. Valves
• Capillary Tubes
• Float Valves

Automatic Expansion Valve 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.

The setback is that it is not efficient if the load fluctuates hence this type is not suitable for use in air conditioning as the load fluctuates a lot during its operation.

Thermostatic Expansion Valve uses a valve mechanism to control the flow of liquid refrigerant into the evaporator coil. The flow is controlled by the pressure in the evaporator.

This type of metering device is able to operate well when the load fluctuates and hence is suitable for use in air conditioning system. When the evaporator warms, the valve provides a higher flow rate amd when it cools, it reduces the flow rate.

It is also commonly refer to as TXV, TEV or TX valve. There is a sensing bulb which detects the temperature of the coil and is usually located at a higher temperature within the evaporator.

The bulb must be clamped firmly to the coil to ensure proper sensing. When the temperature of the evaporator increases due to the demand for cooling, the pressure in the bulb will also increase hence pushing the spring to open the valve.

Similarly, when the temperature of the evaporator reduces due to a lack of demand for cooling, the pressure in the bulb will drop hence causing the spring to close the valve.

Capillary Tube is a tube with small internal diameter and could be coiled for part of its length. It is installed to the suction line. A filter-drier is sometimes fitted before the tube to remove dirt or moisture from the refrigerant.

This device is simple, does not have any moving part and lasts longer. In order to use this device, the amount of refrigerant in the system must be properly calibrated at factory level.

Due to its lower cost compared to TXV, this metering device is used in units that are produced in large quantity such as room or window air conditioners.

Depending on the capacity design of the system, the capillary tube internal diameter that is commonly used range from 0.031" to 0.065" and the outer diameter from 0.083" to 0.130".

Float Valve is actuated by a float that is immersed in the liquid refrigerant. Both low-side float and high side-float are used to control the flow of liquid refrigerant.

The low-side float helps to maintain a constant level of liquid refrigerant in the evaporator. It opens when there is no liquid in the evap. and closes when there is liquid in the evap.

The high-side float is located at the high pressure side of the system and maintain a constant level of refrigerant in the condenser. When the compressor operates, the condensed refrigerant flows to the float chamber and opens the valve.

This causes the refrigerant to flow into the evaporator where it is stored. As the liquid level falls in the float chamber, the valve opening will close hence preventing the liquid from flowing to the evap.

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Evoporator

Evoporator
The evaporator works the opposite of the condenser, here refrigerant liquid is converted to gas, absorbing heat from the air in the compartment.
When the liquid refrigerant reaches the evaporator its pressure has been reduced, dissipating its heat content and making it much cooler than the fan air flowing around it. This causes the refrigerant to absorb heat from the warm air and reach its low boiling point rapidly. The refrigerant then vaporizes, absorbing the maximum amount of heat.
This heat is then carried by the refrigerant from the evaporator as a low-pressure gas through a hose or line to the low side of the compressor, where the whole refrigeration cycle is repeated.
The evaporator removes heat from the area that is to be cooled. The desired temperature of cooling of the area will determine if refrigeration or air con¬ditioning is desired. For example, food preservation generally requires low refrigeration temperatures, ranging from 40°F (4°C) to below 0°F (-18°C).
A higher temperature is required for human comfort. A larger area is cooled, which requires that large volumes of air be passed through the evaporator coil for heat exchange. A blower becomes a necessary part of the evaporator in the air conditioning system. The blower fans must not only draw heat-laden air into the evaporator, but must also force this air over the evaporator fins and coils where it surrenders its heat to the refrigerant and then forces the cooled air out of the evaporator into the space being cooled.

Fan Speeds
Fan speed is essential to the evaporation process in the system. Heat exchange, as we explained under condenser operation, depends upon a temperature differential of the air and the refrigerant. The greater the differential, the greater the amount of heat exchanged between the air and the refrigerant. A high heat load, as is generally encountered when the system is turned on, will allow rapid heat transfer between the air and the cooler refrigerant.
A blower fan turned on to its highest speed will deliver the most air across the fins and coils for rapid evaporation.
For the coldest air temperature from the evaporator, operate the blower fan at the lowest speed so the heat will be absorbed by the refrigerant from the air
Problems of Flooded or Starved Evaporator Coils
Changing the state of the refrigerant in the evaporator coils is as important as the air flow over the coils. Liquid refrigerant supplied to the coils by the expansion valve expands to a vapor as it absorbs heat from the air. Some liquid refrigerant must be supplied throughout the total length of the evaporator coils for full capacity.
A starved evaporator coil is a condition in which not enough refrigerant has been supplied through the total coil length. Therefore, expansion of the refrigerant has not occurred through the whole coil length, resulting in poor coil operation and too-low heat exchange.
A flooded evaporator is the opposite of the starved coil. Too much refrigerant is passed through the evaporator coils, resulting in unexpanded liquid passing onto the suction line and into the compressor.

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EVAPORATOR COIL

EVAPORATOR COIL
An evaporator coil is the part of an air conditioner or heat pump that absorbs the heat from the air in your house. It is located inside the air handler or attached to the furnace.
How the evaporator and condenser coils work together
The evaporator and condenser coils inside a central air conditioner or heat pump make it possible for these systems to complete the heat exchange process, which is the basis of refrigerated cooling and, in the case of heat pumps, heating. The coils form a loop and, even though they’re continuous, each has a different function.
The role of the evaporator coil
Located inside the blower compartment or air handler, the evaporator coil holds the chilled refrigerant that the compressor moves into it.
As the air from the blower fan moves over the coil, the cold refrigerant removes the heat from your home’s air. The refrigerant becomes warmer and travels to the condenser coil outdoors.
With a heat pump, the process reverses in the winter and the evaporator coil expels heat from the refrigerant into your home, instead of absorbing it and taking it outdoors. Most heat pumps have auxiliary heating elements that are part of the evaporator coil components to supply heat when temperatures fall below a certain point.

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HVAC FAN TYPES

HVAC FAN TYPES 
All types of fans are designed for the sole purpose of delivering air. In an HVAC unit, most furnaces contain one or more fans, and different fans are used for different applications. There are three basic fan types that are usually encountered in the HVAC industry. The Axial Fan, the Forward Curved Centrifugal Fan and lastly, the Backward Inclined Fan.

Axial Fan
Axial fans, also known as propeller fans, are engineered to move a low volume of air under low static conditions (static pressure is the resistance to air flow). These types of fans are low cost, and don’t work well when it faces resistance. Since propeller fans are low cost, most are built to run on Single Phase Voltages. These types of fans are more suited for applications with lower air volumes and pressures.

Axial fans can usually be found positioned on top of an HVAC Rooftop or home compressor that is outside a house. A basic HVAC system which doesn’t run a heat pump is designed with condenser coils which remove heat from an area. These coils have fins that need air to move through them so as to remove heat. Since these sections don’t require a high power fan, an axial fan is the best and most cost efficient solution.

Centrifugal Fan

Centrifugal fans look similar to hamster exercise wheels. These types of fans produce more pressure for a given air volume than axial fans. They are usually noisier as compared to axial fans and are suited for applications with higher air flow volumes and pressures. It has 3 types of drive mechanism: direct, belt, or variable drive. Inside the HVAC Rooftop system, you will find a centrifugal fan. These fans should be strong enough to overcome all the resistance of the room’s duct-work. This is where axial fans are inadequate. Centrifugal fans move a large quantity of air while overcoming all the resistance or static pressure of the duct-work so that it can provide adequate air flow throughout the facility.

Backward Inclined Fans

These types of fans are designed to handle large volumes of clean air as needed in heating, ventilating, and air conditioning systems. These are also used in many industrial air supply and exhaust applications. There are some HVAC Rooftop units and HVAC accessories that may contain one or a series of backward inclined fans.

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