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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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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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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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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Cooling systems

Cooling systems
Air conditioners come in many forms, from the massive boxes designed to cool an entire house to a portable window-mounted box that can be pulled out and used in cooler climates to handle short summers.
Many air conditioners can even be installed by the owner, with ductless mini split systems a popular choice. Installation is still a major project, as the interior and exterior elements of the system need to be properly connected, but they are relatively inexpensive to buy and run.
For dryer climates, evaporative coolers are a popular choice. They draw outside air into the system, passing it through water-saturated pads, which cool and moisten the air before pushing it into the living space and displacing the hot air.

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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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Heating, Ventilating, and Air Conditioning

Heating, Ventilating, and Air Conditioning
HVAC stands for Heating, Ventilating, and Air Conditioning, and HVAC systems are, effectively, everything from your air conditioner at home to the large systems used in industrial complexes and apartment blocks. A good HVAC system aims to provide thermal control and indoor comfort, and one that is designed using the principles of thermodynamics, fluid mechanics, and heat transfer.
The big air conditioner boxes that you might see on top of apartment blocks or offices are examples of (the visible part of) HVAC systems. They’re typically deployed in large industrial buildings, skyscrapers, apartment blocks, and large interior environments. They’re also an essential component of environments where there are health regulations requiring that temperature and humidity be kept at certain levels, using air taken from outside.
But heating and cooling systems you use in your home are also HVAC systems. They may take a different form, but many of the fundamental principles determining how they operate, as well as their efficiency, crosses over from the smallest of personal devices right through to the biggest commercial installations.

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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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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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