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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Central Heating Systems

Central Heating Systems

Central heating systems have been considered a necessity in our homes and businesses for many years. When comparing available systems, consumers should carefully consider safety, installation cost, operating costs, maintenance costs, and comfort.

Types of Heating Systems

There are two basic types of systems - those that require a flame to operate (i.e., combustion based), and those that do not. Most central systems presently installed create heat by combustion, just as they did in the early part of the century. These systems use a furnace to burn a fossil fuel (such as oil, natural gas or propane) or, in some instances, wood. More advanced, non-combustion systems operate by transferring or moving heat from one location to another.

Combustion Based Systems

Until the last few years, combustion-based systems have been the preferred heating systems for home and business owners because of their moderate installation and operating costs, and wide availability in the market place. Unfortunately, there are a number of serious safety and related maintenance concerns with these systems.

Some combustion-based systems present an explosion hazard if the storage or delivery of their fuel is not carefully controlled. Explosions due to improperly installed or maintained gas pipes and delivery systems are often in the news. Since these systems require a flame to operate, failures or improper installation of system components (for example, heat exchanger, damper, chimney, or flue) can result in property loss to fire. Fortunately, smoke detectors have saved many lives that might have been lost to fires caused by combustion-based heating systems.

In addition to heat, combustion-based heating systems also create by-products such as carbon monoxide. Carbon monoxide is a result of the incomplete burning of fuel in combustion-based systems. Incorrectly installed systems, chimneys that are blocked by birds nests, or downdrafting can cause carbon monoxide to remain inside of buildings. This is especially dangerous in modern, well-sealed buildings, where it is difficult for outside combustion air to reach the furnace, and where carbon monoxide can be trapped and build up over time. Furnaces, water heaters, and other appliances must be properly vented outside.

Combustion-based systems that deliver heat through ducts present occasional "blasts" of hot air. This not only reduces comfort directly, but tends to dehumidify the air. The addition of a central humidifier (with its associated installation, operating, and maintenance costs) can correct this humidity problem.

Combustion based central heating systems are often coupled with low-efficiency central air conditioners. This raises installation and operating costs significantly, while adding an entirely separate unit to be maintained.

Heat Transfer Systems

Non-combustion or heat transfer systems include heat pumps and geoexchange systems. Heat pumps operate by capturing heat from outdoor air and transferring it inside of a home or business. geoexchange systems capture and transfer heat from the earth.

Nearly all heat transfer systems can be reversed, providing central cooling as well as heating. Some heat pumps and most geoexchange systems also provide domestic hot water at low operating costs.

Heat Pumps

Beginning in the 1970s, air-source heat pumps came into common use. They have the advantage of no combustion, and thus no possibility of indoor pollutants like carbon monoxide. Heat pumps provide central air conditioning as well as heating as a matter of course. And they are installation-cost competitive with a central combustion furnace/central air conditioner combination.

Heat pumps operate by moving or transferring heat, rather than creating it. During the summer, a heat pump captures heat from inside a home or business and transfers it to the outdoor air through a condensing unit. During the winter, the process is reversed. Heat is captured from outdoor air, compressed, and released inside.

Much less electricity is used to move heat rather than create it, making heat pumps more economical than resistance heating. However, in all but the most moderate climates, the heating ability of the heat pump is limited by freezing outdoor temperatures. So electric resistance heat is used to supplement outdoor-air-source heat pump during the coldest weather, preventing "cold blow."

Depending on climate, air-source heat pumps (including their supplementary resistance heat) are about 1.5 to 3 times more efficient than resistance heating alone. Operating efficiency has improved since the 70s, making their operating cost generally competitive with combustion-based systems, depending on local fuel prices. With their outdoor unit subject to weathering, some maintenance should be expected.

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Types of Cooling Systems

Types of Cooling Systems
Air conditioning, or cooling, is more complicated than heating. Instead of using energy to create heat, air conditioners use energy to take heat away. The most common air conditioning system uses a compressor cycle (similar to the one used by your refrigerator) to transfer heat from your house to the outdoors.
Picture your house as a refrigerator. There is a compressor on the outside filled with a special fluid called a refrigerant. This fluid can change back and forth between liquid and gas. As it changes, it absorbs or releases heat, so it is used to “carry” heat from one place to another, such as from the inside of the refrigerator to the outside.

 And the process gets quite a bit more complicated with all the controls and valves involved. But its effect is remarkable. An air conditioner takes heat from a cooler place and dumps it in a warmer place, seemingly working against the laws of physics. What drives the process, of course, is electricity — quite a lot of it, in fact.

Central Air Conditioners and Heat Pumps
Central air conditioners and heat pumps are designed to cool the entire house. In each system, a large compressor unit located outside drives the process; an indoor coil filled with refrigerant cools air that is then distributed throughout the house via ducts. Heat pumps are like central air conditioners, except that the cycle can be reversed and used for heating during the winter months. (Heat pumps are described in more detail in the heating section.) With a central air conditioner, the same duct system is used with a furnace for forced warm-air heating. In fact, the central air conditioner typically uses the furnace fan to distribute air to the ducts.

Air conditioners and heat pumps use the refrigerant cycle to transfer heat between an inside unit and an outside uint. Heat pumps differ from air conditioners only in the special valve that allows the cycle to reverse, providing either warm or cool air to the inside.

Room Air Conditioners
Room air conditioners are available for mounting in windows or through walls, but in each case they work the same way, with the compressor located outside. Room air conditioners are sized to cool just one room, so a number of them may be required for a whole house. Individual units cost less to buy than central systems.

Evaporative Coolers
Evaporative coolers, sometimes called swamp coolers, are less common than vapor compression (refrigerant) air conditioners, but they are a practical alternative in very dry areas, such as the Southwest. They work by pulling fresh outside air through moist pads where the air is cooled by evaporation. The cooler air is then circulated through a house. This process is very similar to the experience of feeling cold when you get out of a swimming pool in the breeze. An evaporative cooler can lower the temperature of outside air by as much as 30 degrees.
They can save as much as 75% on cooling costs during the summer because the only mechanical component that uses electricity is the fan. Plus, because the technology is simpler, it can also cost much less to purchase than a central air conditioner — often about half.
A direct evaporative cooler adds moisture to a house, which could be considered a benefit in very dry climates. An indirect evaporative cooler is a little different in that the evaporation of water takes place on one side of a heat exchanger. House air is forced across the other side of the heat exchanger where it cools off but does not pick up moisture. Both types begin to lose their effectiveness with increasing humidity, because humid air is less able to carry additional moisture.
For evaporative coolers to do their job, they must be the right size. The cooling capacity of an evaporative cooler is measured not in the amount of heat it can remove (Btu), but in the fan pressure required to circulate the cool air throughout the house, in cubic feet per minute (cfm). A good rule is to figure the cubic square footage of your house and divide by 2. For example, a 1,500-square-foot house with 8-foot-high ceilings would require a 6,000 cfm cooler.

Ductless Mini-Split Air Conditioners
Mini-split systems, very popular in other countries, can be an attractive retrofit option for room additions and for houses without ductwork, such as those using hydronic heat (see the heating section). Like conventional central air conditioners, mini-splits use an outside compressor/condenser and indoor air handling units. The difference is that each room or zone to be cooled has its own air handler. Each indoor unit is connected to the outdoor unit via a conduit carrying the power and refrigerant lines. Indoor units are typically mounted on the wall or ceiling.
The major advantage of a ductless mini-split is its flexibility in cooling individual rooms or zones. By providing dedicated units to each space, it is easier to meet the varying comfort needs of different rooms.
By avoiding the use of ductwork, ductless mini-splits also avoid energy losses associated with central forced-air systems.
The primary disadvantage of mini-splits is cost. They cost much more than a typical central air conditioner of the same size, where ductwork is already in place. But, when considering the cost and energy losses associated with installing new ductwork for a central air conditioner, buying a ductless mini-split may not be such a bad deal, especially considering the long-term energy savings. Talk with your contractor about what option would be most cost-effective for you.

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Selecting Heating and Cooling Systems

Selecting Heating and Cooling Systems

Heating and cooling system selection is very important to a home. Read on for some tips in selecting the right one for your needs.

 This is a very important decision with many variables. These systems are components to a building that will last for a long time and can be costly. They play a big part in a house's energy efficiency and comfort level. There is not a "one size fits all" answer; it will depend on the region of the country a home is built in, the homeowners' budget and individual preferences. Every heating and cooling system has pros and cons. Here are some things to think about:

- Forced Air Styles: The new technology utilized in forced air units is much more efficient than in the past. They can be run from a variety of energy sources such as gas, electric, oil and propane. A downside is that they may produce spotty heat and coolness. Those that are equipped with blowers may expose allergy sufferers to more dust.

- Heat Pumps: Heat pumps are quite efficient in terms of energy use. Both the AC and the warmth can be piped through the same ventilation pathways, cutting down on installation costs. Some of these units are split into inside/outside locations. Filters which trap debris from vents must be changed every month or a breakdown in the system could occur.

- Duct-free: Systems that are duct-free are those that either hang from the wall or set on the floor. A positive of this type of unit is that it costs less in terms of installation as there are no ducts to position. The duct-free devices are best used in small areas or temperate climates. If temperatures drop well into the freezing zones, these models won't provide enough warmth in the home.

- Radiators with Steam: These are also called boilers and can be comfortable because they emit moisture along with heat. Some downsides include that they can rattle, clank, make lots of noise and the warmth may be spotty through the home. This is kind of an old-fashioned method of warming up one's abode, but it may make a comeback.

- Solar Energy: Solar technology is great for energy efficiency because it harnesses warmth from the sun. Solar systems can be passive or active. Panels on the roof or thermal mass holders are options.

- Wind Energy: Harnessing the power of the wind may also be an ecologically sound method of using natural sources of energy.

- Radiant Heaters: These devices are installed beneath the flooring of one room or an entire house. Pipes with hot water warm surfaces. No ductwork is requiredPsychology Articles, so no allergens will blow around. Efficiency is quite high.

There are many options in heating and cooling systems. Each of their goals is to provide comfortable temperatures inside of a home with as low a utility consumption as possible.

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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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How is humidity controlled with an AC system?

How is humidity controlled with an AC system?
Humidity is becoming more of a concern to building operators and owners. High indoor humidity leads to mold and mildew growth inside the building. The are several methods of controlling indoor humidity. The simplest (and most expensive) method is to connect a humidistat to an electric heater. When the humidity inside the building rises above the humidistat set point, the heater is turned on. The additional heat causes the air conditioning system to run longer and remove more moisture.
A more efficient method of controlling humidity is to use the waste heat from the refrigeration cycle itself. Instead of rejecting the waste heat outdoors, the heat is directed inside when humidity control is required. One form of heat reclaim is called hot-gas reheat or “refrigerant desuperheating” where refrigerant is passed through a heat exchanger located downstream of the cooling coil. The hot high pressure vapor leaving the compressor passes through this heat exchanger prior to entering the condenser coil. This in turn heats the indoor air and again causes the AC system to run longer to meet the thermostat set point. Although more energy is used, this is much more efficient than turning on an electric heater. Another form of heat reclaim is called sub-cool reheat. This strategy takes the warm liquid refrigerant from the condenser and passes it through a heat exchanger located downstream of the cooling coil. Less heat is available using this method because the majority of the heat has already been rejected at the condenser. Since more energy is used to pump liquid (as opposed to a gas) through the heat exchanger it would appear that this method is less efficient than the hot-gas method, however, the liquid in the heat exchanger is sub-cooled in the cold supply air stream which increases the capacity of the air conditioner. Since more capacity is available, the AC units is able to meet the thermostat more quickly.
Heat pipe heat exchangers or run-around coils perform a similar function when humidity control is required. Two heat exchanger are placed in the air stream, one upstream of the cooling coil and the other downstream of the cooling coil. These heat exchangers are connected together with piping. A heat transfer fluid, whether it be water or refrigerant, is either pumped or gravity fed from one heat exchanger to the other. The heat exchanger down stream of the cooling coil (re-heat coil) cools the liquid medium inside the heat exchanger and heats the air passing over the heat exchanger. The cold liquid inside the heat exchanger is moved to the heat exchanger upstream of the cooling coil (pre-cool coil) where it pre-cools the air passing over the heat exchanger and warms the liquid passing through the heat exchanger. The affect of a heat pipe or run-around coil is to reduce the sensible heat capacity of the AC system. The latent capacity of the AC system increases if direct-expansion equipment is used or remains relatively constant if chilled water equipment is used. Since the sensible capacity of the AC system has been reduced, the system must run longer to meet the thermostat set point thereby removing more moisture.

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What type of AC systems are available?

What type of AC systems are available?

Cooling Only Split-System
A split system is a combination of an indoor air handling unit and an outdoor condensing unit. The indoor air handling unit contains a supply air fan and an air-to-refrigerant heat exchanger (or cooling coil), and the expansion device. The outdoor condensing unit consists of a compressor and a condenser coil. Split-systems are typically found in residential or small commercial buildings. These systems have the highest energy efficiency rating (EER) of all the available AC systems. Manufacturers are required to take the EER rating a step further and provide a seasonal energy efficiency rating (SEER) for use by consumers. SEER ratings vary widely and range from 10 to 20. The higher the SEER rating, the more efficient the AC system operates. If heating is required, an alternate method of heating the interior of the building must be used, usually in the form of electric or gas heating.
Cooling Only Packaged-System
A packaged system is a single unit combining all the components described in the split system. Since the unit is a package, it must be placed outside the building and indoor air is “ducted” from the building to the packaged system and back through an air distribution system. These units typically have SEER rating from 10 to 18. If heating is required, an alternate method of heating the interior of the building must be used, usually in the form of electric or gas heating.
Heat Pump
Heat pumps are similar to cooling only systems with one exception. A special valve in the refrigeration piping allow the refrigeration cycle to be operated in reverse. A cooling only system cools the indoor air and rejects heat to the outdoors. A heat pump can also cool the indoor air, but when the valve is reversed, the indoor air is heated. A supplementary electric resistance heater may also be used to assist the heat pump at lower outdoor temperatures. In colder climates, heat pumps require a defrost period. During defrost times the electric heater is the only means of heating the interior of the building. These units are manufactured as either split or packaged systems.
Chilled Water System
In a chilled water system, liquid water is pumped throughout the building to “chilled water coils”. Since the liquid water needs to be at a cold temperature, a “cooling plant” is required. The plant is typically referred to as a chiller plant. Vapor compression equipment in the plant, similar to that described in “How does my AC work”, cool water to a cold temperature and pump the cold water to air-to-water heat exchangers where needed.
Window Air Conditioners
As the name implies, a window air conditioner is typically installed in a window or custom opening in a wall. The Window AC can only cool small areas and are not intended to provide cooling to multiple rooms or zones. These air conditioners are manufactured as cool only or can provide both cooling and heating. An optional damper in the unit can provide fresh outdoor air if necessary.
Packaged Terminal Heat Pump
Packaged terminal heat pumps (PTHP) are are similar to a window-mounted air conditioner. These units are typically installed in a sleeve passing through the outdoor wall of an apartment, hotel, school classroom, etc. PTHPs are completely self contained and require only an electrical connection in addition to the opening in the building shell. They use the outdoor air as the heat source in winter and as a heat sink in summer. They also can provide ventilation air. Flexibility and lower installed cost are the primary advantages of the PTHP. Disadvantages include in-room maintenance, higher operating cost, relatively short life, imprecise "on-off" temperature control, and they can be rather noisy.

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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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What does a condenser in an ac unit do?

The condenser does just what the name says: in the condenser the hot gaseous refrigerant coming from the compressor is cooled which causes it to condense into a liquid. Compressing a gas makes it much hotter, enough hotter than the outside air on a hot day that it can transfer its heat to that hot outside air  which makes the hot air even hotter, and cools the high pressure gas enough to make it condense into a fairly warm liquid.

The pressurized liquid refrigerant flows to the evaporator, where it is sprayed through a small nozzle into the evaporator (which is kept at low pressure because the refrigerant pump is constantly sucking on this part of the AC unit.)

When the warm high pressure refrigerant liquid sprays into the low pressure evaporator, it - you guessed it - evaporates. This lowers it temperature a lot, to near or below 0 degrees C. The air you wish to cool is blown over the cold evaporator, and the refrigerant gas gets somewhat warmer.

The warm low pressure refrigerant gas is sucked up and compressed into the condenser. And once it has transferred that heat to the outside air, it condenses, and the cycle repeats.

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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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Types of Valves

Types of Valves

Various types of Valves have been developed to cater to the diversified requirements of fluid control in various applications. These types of valves match the systems, fluids, and environments to accomplish their intended function.

Each type of valve has been designed to meet specific needs. Some valves are capable of throttling flow, other valve types can only stop flow, others work well in corrosive systems, and others valves handle high-pressure fluids. Each valve type has certain inherent advantagesand  disadvantages. Understanding these differences and how they affect the valve’s application or operation is necessary for the successful operation of a facility.

Although all valves have the same basic components and function to control flow in some fashion, the method of controlling the flow can vary dramatically.
Each method controlling flow has characteristics that make it the best choice for a given application of function. One valve may be best fit for one application but may not be fit for other at the same time.

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Types of Heat Exchangers used in Hvac system

Types of Heat Exchangers used in Hvac system
Heat exchangers are essential part of any kind of HVAC system nowadays. Heat exchangers contribute substantially towards energy conservation and reduction in energy bills.So what are the different types of heat exchangers that a HVAC system can use? 

The main function of a heat recovery system is to increase the energy efficiency by reducing energy consumption and also by reducing the cost of operating by transferring heat between two gases or fluids, thus reducing the energy bills.

The heat exchangers are the best known devices for this purpose. In heat exchangers, as the name suggests, there is a transfer of energy from one fluid to another. Both these fluids are physically separated and there is no direct contact between the fluids. There are different types of heat exchangers such as shell and tube, U tube, shell and coil, helical, plate etc. The transfer of heat can be between steam and water, water and steam, refrigerant and water, refrigerant and air, water and water. Now let’s take a look as to what are the different types of heat exchangers.

Rotary wheel type heat exchanger

A rotary wheel type heat exchanger has a large surface cylinder which is attached to the shaft. It has got a gas permeable material inside it. When the cylinder rotates, both the gases move in a counter flow pattern axially to the shaft. The heat from the warm gas is absorbed by the gas permeable material and then it is transferred to the colder gas. Sometimes hygroscopic material is put on the gas permeable material to absorb the moisture from the gases. Thus the moist gas becomes dry and transfers the moisture to the dry gas. Both latent and sensible heat is transferred in this system.

Fixed Plate heat exchangers

These types of heat exchangers do not have any moving parts. They have fixed plates that are alternately arranged and are separate from each other. Both the gases and fluids flow separately in these alternate plates and the transfer of heat takes place between them. The flow can be counter flow, parallel flow or cross flow.

Heat pipe exchangers.

This type of heat exchanger has an evaporator and a condenser separated by a plate. It has tubes running parallel and separated from each other. On the evaporator side the hot air transfers its energy to the liquid refrigerant and thus boiling it. The vapor refrigerant now passes through the pipes to the condenser side. The opposite process takes place. The cold air now passes over the vapor refrigerant. The vapor refrigerant after transferring its energy turns to liquid and flows though the pipes to the evaporator side. This type of heat exchanger generally uses parallel flow patterns.

Run- around system

In this type of system, a pump circulates water or any other liquid through the system. There are coils that are mounted in either series or parallel to facilitate maximum amount of heat transfer. This type of system is beneficial in any season. This means that if the outside air is warmer than the exhaust air, the exhaust air pre cools outside air. And if the outside air is cooler than the exhaust air, the exhaust air pre heats the outside air, making the system more and more energy efficient.

Hot gas heat exchanger

The HVAC system’s compressor generates heat by compressing refrigerant. This heat can be captured and used for heating domestic water. For this purpose a heat exchanger is placed in between the compressor and the condenser. The water that is to be heated is circulated though this heat exchanger with the help of a pump whenever the HVAC system is on.

Double bundle condenser heat exchanger

This heat exchanger consists of two sets of water tubes in the condenser shell. The superheated gas is forced into the shell where the transfer of heat to the water takes place through the tubes.

Heat jackets

Water jackets are kept at the sides of a reciprocating engine or a gas turbine to absorb the heat generated. This heat can be used for generating steam or for heating water or fuel oil.

Hot flue gas heat exchangers

The hot flue gases from the boiler exhaust can be used to heat water or fuel oil. An arrangement consisting of a series of pipes or water jackets are made in the boiler exhaust for the transfer of the heat. It can mainly be used to preheat the boiler feed water.

Hot drain heat exchangers

Heat from the hot condensate used in the kitchen, bathrooms or laundry system can be used for boiling water.Condensate is continuously formed when the release of heat takes place. A heat exchanger placed in the condensate return can take the condensate heat for heating water.

Heat pump water heater

The atmosphere of kitchens and laundries is extremely hot. This heat can be used to heat water or for other purposes. This can be done by using a dedicated heat pump that mechanically concentrates the heat in the atmosphere and bring it to the temperature where it can be used.

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Types of compressors

Types of compressors
The compressor is the component at the heart of a refrigerant circuit based on the so called “vapour compression cycle”.

This thermodynamic cycle exploits the evaporation of a refrigerant inside a closed loop piping circuit.
Specifically, evaporation occurs in a heat exchanger called the evaporator, which absorbs energy from the surrounding air; this is then delivered to the food storage compartment or air-conditioned space by natural or fan-forced convection.
The same also applies when using water as the medium, which is pumped through the heat exchanger and then flows into the storage tank for use by the terminal units.
Once having evaporated, the refrigerant can no longer absorb considerable amounts of energy, and consequently it needs to be returned to the liquid state by condensation.
The problem thus arises of having an environment that’s “cold” enough to absorb energy from the refrigerant, which naturally cannot be the same compartment or space that’s just been cooled.
The compressor is then used to compress the refrigerant to a pressure that’s higher than in the evaporator (up to 8-10 times!) so that the condensation process can take place at a temperature that’s compatible with a readily available “cold” source, typically the outside air.
Condensation thus occurs at a high temperature (usually 35-55°C) inside a heat exchanger where the two fluids are outside air and refrigerant. The latter condenses and returns to the liquid state, while the outside air will be heated. The liquid refrigerant is still at high pressure when it leaves the condenser. An expansion device is thus needed to expand the liquid refrigerant and reduce its pressure to the value at which evaporation occurs. The refrigerant has now returned to its initial state (liquid at low pressure and temperature) and can once again absorb energy from the air or water.

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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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Air Conditioning

Air Conditioning

Central air conditioning systems have become a must-have for year-round comfort, and are frequently installed in conjunction with a central heating system. The two must work together for optimal temperature control, and even share the same ductwork. Most central air conditioners are two-part or split systems, which contain:
• An outdoor unit with compressor, fan, condenser coil, and electrical components.
• An evaporator coil, typically situated on top of your furnace.
• Piping which connects the indoor and outdoor components.
• Refrigerant for cooling.
• Ductwork for air distribution.
• A thermostat for temperature control.

These components work together to provide your home with cool air when the thermostat indicates. When engaged, the air conditioner pulls warm air from the home into the ductwork. At the same time, the refrigerant circulates between the indoor and outdoor components. It absorbs the heat from the air as it passes into the interior evaporator coil from the exterior compressor coil. The cooled air then travels back through the ductwork and is distributed to the various rooms of your home. The cycle continues in order to maintain the desired temperature.

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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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How Hvac Systems Work

How Hvac Systems Work

The following diagram illustrates the basic function of a HVAC system:

•          The building automation device (computer or wall-mounted gadgets usually) can be used to determine whether to heat or cool the space, and to what temperature

•          The system then either heats or cools the coils inside

•          When air brought in from the outside is pushed through these coils, it is either heated or cooled before being pushed into the living space

•          At the same time, air will be displaced from the room back into the system.

Smaller air conditioning systems may operate in the reverse, however, where they collect heat from within a space and push it out in order to cool a room down. We can see these kinds of systems in places like cars. Here’s how these types of HVAC systems work:

This diagram reveals how a system will collect heat from within a space, soak it up like a sponge, and push it back out into the air.

There are five key parts in this system that allow it to operate:

•          Expansion valve: This device creates a restriction in the liquid line of a system, which in turn creates a pressure drop.

•          Evaporator: This device is what removes heat from the space by exchanging it for a boiling refrigerant.

•          Compressor: Think of this component as the system’s heartbeat - it creates the energy and thrust to move refrigerant around the system.

•          Condenser: This is the device that pushes the heat that has built up inside the refrigerant into the outside air.

•          Receiver drier: In order to preserve the air quality, this storage area for excess refrigerant contains a drying agent and a filter that removes contaminants from the system.

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