CENTRAL HYDRONIC AIR CONDITIONING SYSTEMS

     Central hydronic air conditioning systems are also called central air conditioning systems. In a central hydronic air conditioning system, air is cooled or heated by coils filled with chilled or hot water distributed from a central cooling or heating plant. It is mostly applied to large-area buildings with many zones of conditioned space or to separate buildings. Water has a far greater heat capacity than air. The following is a comparison of these two media for carrying heat energy at 68°F (20°C)

The heat capacity per cubic foot (meter) of water is 3466 times greater than that of air. Transporting heating and cooling energy from a central plant to remote air-handling units in fan rooms is far more efficient using water than conditioned air in a large air conditioning project. However, an additional water system lowers the evaporating temperature of the refrigerating system and makes a small- or medium-size project more complicated and expensive. A central hydronic system of a high-rise office building, the NBC Tower in Chicago, is illustrated in Fig. 1.1. A central hydronic air conditioning system consists of an air system, a water system, a central heating/cooling plant, and a control system. 

Air System

are the air-handling units, supply/return ductwork, fan-powered boxes, space diffusion devices, and exhaust systems. An air-handling unit (AHU) usually consists of supply fan(s), filter(s), a cooling coil, a heating coil, a mixing box, and other accessories. It is the primary equipment of the air system. An AHU conditions the outdoor/recirculating air, supplies the conditioned air to the conditioned space, and extracts the returned air from the space through ductwork and space diffusion devices. A fan-powered variable-air-volume (VAV) box, often abbreviated as fan-powered box, employs a small fan with or without a heating coil. It draws the return air from the ceiling plenum, mixes it with the conditioned air from the air-handling unit, and supplies the mixture to the conditioned space. Space diffusion devices include slot diffusers mounted in the suspended ceiling; their purpose is to distribute the conditioned air evenly over the entire space according to requirements. The return air enters the ceiling plenum through many scattered return slots. Exhaust systems have exhaust fan(s) and ductwork to exhaust air from the lavatories, mechanical rooms, and electrical rooms. The NBC Tower in Chicago is a 37-story high-rise office complex constructed in the late 1980s. It has a total air conditioned area of about 900,000 ft2 (83,600 m2 ). Of this, 256,840 ft2 (23,870 m2 ) is used by NBC studios and other departments, and 626,670 ft2 (58,240 m2 ) is rental offices located on upper floors. Special air conditioning systems are employed for NBC studios and departments at the lower level. For the rental office floors, four air-handling units are located on the 21st floor. Outdoor air either is mixed with the recirculating air or enters directly into the air-handling unit as shown in Fig. 1.2. The mixture is filtrated at the filter and is then cooled and dehumidified at the cooling coil during cooling season. After that, the conditioned air is supplied to the typical floor through the supply fan, the riser, and the supply duct; and to the conditioned space through the fan-powered box and slot diffusers

Water System 

        The water system includes chilled and hot water systems, chilled and hot water pumps, condenser water system, and condenser water pumps. The purpose of the water system is (1) to transport chilled water and hot water from the central plant to the air-handling units, fan-coil units, and fan powered boxes and (2) to transport the condenser water from the cooling tower, well water, or other sources to the condenser inside the central plant.

    In Figs. 1.1 and 1.2, the chilled water is cooled in three centrifugal chillers and then is distributed to the cooling coils of various air-handling units located on the 21st floor. The temperature of the chilled water leaving the coil increases after absorbing heat from the airstream flowing over the coil. Chilled water is then returned to the centrifugal chillers for recooling through the chilled water pumps.

    After the condenser water has been cooled in the cooling tower, it flows back to the condenser of the centrifugal chillers on lower level 3. The temperature of the condenser water again rises owing to the absorption of the condensing heat from the refrigerant in the condenser. After that, the condenser water is pumped to the cooling towers by the condenser water pump.

Central Plant 

    The refrigeration system in a central plant is usually in the form of a chiller package. Chiller packages cool the chilled water and act as a cold source in the central hydronic system. The boiler plant, consisting of boilers and accessories, is the heat source of the heating system. Either hot water is heated or steam is generated in the boilers.

    In the NBC Tower, the refrigeration system has three centrifugal chillers located in lower level 3 of the basement. Three cooling towers are on the roof of the building. Chilled water cools from 58 to 42°F (14.4 to 5.6°C) in the evaporator when the refrigerant is evaporated. The refrigerant is then.

    compressed to the condensing pressure in the centrifugal compressor and is condensed in liquid form in the condenser, ready for evaporation in the evaporator. There is no boiler in the central plant of the NBC Tower. To compensate heat loss in the perimeter zone, heat energy is provided by the warm plenum air and the electric heating coils in the fan powered boxes.

Control System 

        Modern air conditioning control systems for the air and water systems and for the central plant consist of electronic sensors, microprocessor-operated and -controlled modules that can analyze and perform calculations from both digital and analog input signals, i.e., in the form of a continuous variable. Control systems using digital signals compatible with the microprocessor are called direct digital control (DDC) systems. Outputs from the control modules often actuate dampers, valves, and relays by means of pneumatic actuators in large buildings and by means of electric actuators for small projects.

CLASSIFICATION OF AIR CONDITIONING SYSTEMS ACCORDING TO CONSTRUCTION AND OPERATING CHARACTERISTICS

Clean-Room Air Conditioning Systems

     Clean-room or clean-space air conditioning systems serve spaces where there is a need for critical control of particulates, temperature, relative humidity, ventilation, noise, vibration, and space pressurization. In a clean-space air conditioning system, the quality of indoor environmental control directly affects the quality of the products produced in the clean space. 

    A clean-space air conditioning system consists of a recirculating air unit and a makeup air unit—both include dampers, prefilters, coils, fans, high-efficiency particulate air (HEPA) filters, ductwork, piping work, pumps, refrigeration systems, and related controls except for a humidifier in the makeup unit (refer to Chap. 30). 

 Space Conditioning Air Conditioning Systems 

    Space conditioning air conditioning systems are also called space air conditioning systems. They have cooling, dehumidification, heating, and filtration performed predominately by fan coils, water source heat pumps, or other devices within or above the conditioned space, or very near it. A fan coil consists of a small fan and a coil. A water-source heat pump usually consists of a fan, a finned coil to condition the air, and a water coil to reject heat to a water loop during cooling, or to extract heat from the same water loop during heating. Single or multiple fan coils are always used to serve a single conditioned room. Usually, a small console water-source heat pump is used for each control zone in the perimeter zone of a building, and a large water-source heat pump may serve several rooms with ducts in the core of the building (interior zone, refer to Chap. 28). 

    Space air conditioning systems normally have only short supply ducts within the conditioned space, and there are no return ducts except the large core water-source heat pumps. The pressure drop required for the recirculation of conditioned space air is often equal to or less than 0.6 in. water column (WC) (150 Pa). Most of the energy needed to transport return and recirculating air is saved in a space air conditioning system, compared to a unitary packaged or a central hydronic air conditioning system. Space air conditioning systems are usually employed with a dedicated (separate) outdoor ventilation air system to provide outdoor air for the occupants in the conditioned space.

     Space air conditioning systems often have comparatively higher noise level and need more periodic maintenance inside the conditioned space

Unitary Packaged Air Conditioning Systems 

    Unitary packaged air conditioning systems can be called, in brief, packaged air conditioning systems or packaged systems. These systems employ either a single, self-contained packaged unit or two split units. A single packaged unit contains fans, filters, DX coils, compressors, condensers, and other accessories. In the split system, the indoor air handler comprises controls and the air system, containing mainly fans, filters, and DX coils; and the outdoor condensing unit is the refrigeration system, composed of compressors and condensers. Rooftop packaged systems are most widely used (refer to Chap. 29). 

     Packaged air conditioning systems can be used to serve either a single room or multiple rooms. A supply duct is often installed for the distribution of conditioned air, and a DX coil is used to cool it. Other components can be added to these systems for operation of a heat pump system; i.e., a centralized system is used to reject heat during the cooling season and to condense heat for heating during the heating season. Sometimes perimeter baseboard heaters or unit heaters are added as a part of a unitary packaged system to provide heating required in the perimeter zone. 

    Packaged air conditioning systems that employ large unitary packaged units are central systems by nature because of the centralized air distributing ductwork or centralized heat rejection systems. Packaged air conditioning systems are characterized by the use of integrated, factory-assembled, and ready-to-use packaged units as the primary equipment as well as DX coils for cooling, compared to chilled water in central hydronic air conditioning systems. Modern large rooftop packaged units have many complicated components and controls which can perform similar functions to the central hydronic systems in many applications

CLASSIFICATION OF AIR CONDITIONING SYSTEMS ACCORDING TO CONSTRUCTION AND OPERATING CHARACTERISTICS

CLASSIFICATION OF AIR CONDITIONING SYSTEMS ACCORDING TO CONSTRUCTION AND OPERATING CHARACTERISTICS

Air conditioning systems can also be classified according to their construction and operating characteristics as follows.

Individual Room Air Conditioning Systems

Individual room, or simply individual air conditioning systems employ a single, self-contained room air conditioner, a packaged terminal, a separated indoor-outdoor split unit, or a heat pump. A heat pump extracts heat from a heat source and rejects heat to air or water at a higher temperature for heating. Unlike other systems, these systems normally use a totally independent unit or units in each room. Individual air conditioning systems can be classified into two categories:

 Room air conditioner (window-mounted)

 Packaged terminal air conditioner (PTAC), installed in a sleeve through the outside wall

    The major components in a factory-assembled and ready-for-use room air conditioner include the following: An evaporator fan pressurizes and supplies the conditioned air to the space. In tube and- fin coil, the refrigerant evaporates, expands directly inside the tubes, and absorbs the heat energy from the ambient air during the cooling season; it is called a direct expansion (DX) coil. When the hot refrigerant releases heat energy to the conditioned space during the heating season, it acts as a heat pump. An air filter removes airborne particulates. A compressor compresses the refrigerant from a lower evaporating pressure to a higher condensing pressure. A condenser liquefies refrigerant from hot gas to liquid and rejects heat through a coil and a condenser fan. A temperature control system senses the space air temperature (sensor) and starts or stops the compressor to control its cooling and heating capacity through a thermostat. 

    

    The difference between a room air conditioner and a room heat pump, and a packaged terminal air conditioner and a packaged terminal heat pump, is that a four-way reversing valve is added to all room heat pumps. Sometimes room air conditioners are separated into two split units: an outdoor condensing unit with compressor and condenser, and an indoor air handler in order to have the air handler in a more advantageous location and to reduce the compressor noise indoors. 

    Individual air conditioning systems are characterized by the use of a DX coil for a single room. This is the simplest and most direct way of cooling the air. Most of the individual systems do not employ connecting ductwork. Outdoor air is introduced through an opening or through a small air damper. Individual systems are usually used only for the perimeter zone of the building.

CLASSIFICATION OF AIR CONDITIONING SYSTEMS ACCORDING TO CONSTRUCTION AND OPERATING CHARACTERISTICS

 Evaporative-Cooling Air Conditioning Systems

    Evaporative-cooling air conditioning systems use the cooling effect of the evaporation of liquid water to cool an airstream directly or indirectly. It could be a factory-assembled packaged unit or a field-built system. When an evaporative cooler provides only a portion of the cooling effect, then it becomes a component of a central hydronic or a packaged unit system.

    An evaporative-cooling system consists of an intake chamber, filter(s), supply fan, direct-contact or indirect-contact heat exchanger, exhaust fan, water sprays, recirculating water pump, and water sump. Evaporative-cooling systems are characterized by low energy use compared with refrigeration cooling. They produce cool and humid air and are widely used in southwest arid areas in the United States.

Desiccant-Based Air Conditioning Systems

    A desiccant-based air conditioning system is a system in which latent cooling is performed by desiccant dehumidification and sensible cooling by evaporative cooling or refrigeration. Thus, a considerable part of expensive vapor compression refrigeration is replaced by inexpensive evaporative cooling. A desiccant-based air conditioning system is usually a hybrid system of dehumidification, evaporative cooling, refrigeration, and regeneration of desiccant (refer to Chap. 29).

    There are two airstreams in a desiccant-based air conditioning system: a process airstream and a regenerative airstream. Process air can be all outdoor air or a mixture of outdoor and recirculating air. Process air is also conditioned air supplied directly to the conditioned space or enclosed manufacturing process, or to the air-handling unit (AHU), packaged unit (PU), or terminal for further treatment. Regenerative airstream is a high-temperature airstream used to reactivate the desiccant.

    A desiccant-based air conditioned system consists of the following components: rotary desiccant dehumidifiers, heat pipe heat exchangers, direct or indirect evaporative coolers, DX coils and vapor compression unit or water cooling coils and chillers, fans, pumps, filters, controls, ducts, and piping.

Thermal Storage Air Conditioning Systems

    In a thermal storage air conditioning system or simply thermal storage system, the electricity-driven refrigeration compressors are operated during off-peak hours. Stored chilled water or stored ice in tanks is used to provide cooling in buildings during peak hours when high electric demand charges and electric energy rates are in effect. A thermal storage system reduces high electric demand for HVAC&R and partially or fully shifts the high electric energy rates from peak hours to off-peak hours.

    A thermal storage air conditioning system is always a central air conditioning system using chilled water as the cooling medium. In addition to the air, water, and refrigeration control systems, there are chilled-water tanks or ice storage tanks, storage circulating pumps, and controls.

COMFORT AND PROCESSING AIR CONDITIONING SYSTEMS

 COMFORT AND PROCESSING AIR CONDITIONING
SYSTEMS

Air Conditioning Systems

An air conditioning, or HVAC&R, system is composed of components and equipment arranged in
sequence to condition the air, to transport it to the conditioned space, and to control the indoor environmental parameters of a specific space within required limits.

Most air conditioning systems perform the following functions:

1.  Provide the cooling and heating energy required
2. Condition the supply air, that is, heat or cool, humidify or dehumidify, clean and purify, and attenuate any objectionable noise produced by the HVAC&R equipment
3.  Distribute the conditioned air, containing sufficient outdoor air, to the conditioned space
4. Control and maintain the indoor environmental parameters–such as temperature, humidity, cleanliness, air movement, sound level, and pressure differential between the conditioned space and surroundings—within predetermined limits

Parameters such as the size and the occupancy of the conditioned space, the indoor environmental

parameters to be controlled, the quality and the effectiveness of control, and the cost involved determine the various types and arrangements of components used to provide appropriate characteristics. 

    Air conditioning systems can be classified according to their applications as (1) comfort air conditioning systems and (2) process air conditioning systems. 

 Comfort Air Conditioning Systems

        Comfort air conditioning systems provide occupants with a comfortable and healthy indoor environment in which to carry out their activities. The various sectors of the economy using comfort air

conditioning systems are as follows:

1. The commercial sector includes office buildings, supermarkets, department stores, shopping centers, restaurants, and others. Many high-rise office buildings, including such structures as the World Trade Center in New York City and the Sears Tower in Chicago, use complicated air conditioning systems to satisfy multiple-tenant requirements. In light commercial buildings, the air conditioning system serves the conditioned space of only a single-zone or comparatively smaller area. For shopping malls and restaurants, air conditioning is necessary to attract customers.
2. The institutional sector includes such applications as schools, colleges, universities, libraries, museums, indoor stadiums, cinemas, theaters, concert halls, and recreation centers. For example, one of the large indoor stadiums, the Superdome in New Orleans, Louisiana, can seat 78,000 people. 
3. The residential and lodging sector consists of hotels, motels, apartment houses, and private homes. Many systems serving the lodging industry and apartment houses are operated continuously, on a 24-hour, 7-day-a-week schedule, since they can be occupied at any time. 
4. The health care sector encompasses hospitals, nursing homes, and convalescent care facilities. Special air filters are generally used in hospitals to remove bacteria and particulates of sub micrometer size from areas such as operating rooms, nurseries, and intensive care units. The relative humidity in a general clinical area is often maintained at a minimum of 30 percent in winter.
5. The transportation sector includes aircraft, automobiles, railroad cars, buses, and cruising ships. Passengers increasingly demand ease and environmental comfort, especially for long-distance travel. Modern airplanes flying at high altitudes may require a pressure differential of about 5 psi between the cabin and the outside atmosphere. According to the Commercial Buildings Characteristics (1994), in 1992 in the United States, among 4,806,000 commercial buildings having 67.876 billion ft2 (6.31 billion m2) of floor area, 84.0 percent were cooled, and 91.3 percent were heated.

Process Air Conditioning Systems

    Process air conditioning systems provide needed indoor environmental control for manufacturing,
product storage, or other research and development processes. The following areas are examples of
process air conditioning systems:

1. In textile mills, natural fibers and manufactured fibers are hygroscopic. Proper control of humidity increases the strength of the yarn and fabric during processing. For many textile manufacturing processes, too high a value for the space relative humidity can cause problems in the spinning process. On the other hand, a lower relative humidity may induce static electricity that is harmful for the production processes.
2.  Many electronic products require clean rooms for manufacturing such things as integrated circuits, since their quality is adversely affected by airborne particles. Relative-humidity control is also needed to prevent corrosion and condensation and to eliminate static electricity. Temperature control maintains materials and instruments at stable condition and is also required for workers who wear dust-free garments. For example, a class 100 clean room in an electronic factory requires a temperature of 72  2°F (22.2  1.1°C), a relative humidity at 45  5 percent, and a count of dust particles of 0.5-m (1.97  105 in.) diameter or larger not to exceed 100 particles/ft3 (3531 particles/m3).
3. Precision manufacturers always need precise temperature control during production of precision instruments, tools, and equipment. Bausch and Lomb successfully constructed a constant temperature control room of 68  0.1°F (20  0.56°C) to produce light grating products in the 1950s.
4. Pharmaceutical products require temperature, humidity, and air cleanliness control. For instance, liver extracts require a temperature of 75°F (23.9°C) and a relative humidity of 35 percent. If the temperature exceeds 80°F (26.7°C), the extracts tend to deteriorate. High-efficiency air filters must be installed for most of the areas in pharmaceutical factories to prevent contamination.
5. Modern refrigerated warehouses not only store commodities in coolers at temperatures of 27 to 32°F ( 2.8 to 0°C) and frozen foods at  10 to  20°F ( 23 to  29°C), but also provide relative-humidity control for perishable foods between 90 and 100 percent. Refrigerated storage is used to prevent deterioration. Temperature control can be performed by refrigeration systems only, but the simultaneous control of both temperature and relative humidity in the space can only be performed by process air conditioning systems.

AIR CONDITIONING

AIR CONDITIONING

Air conditioning is a combined process that performs many functions simultaneously. It conditions the air, transports it, and introduces it to the conditioned space. It provides heating and cooling from its central plant or rooftop units. It also controls and maintains the temperature, humidity, air movement, air cleanliness, sound level, and pressure differential in a space within predetermined  limits for the comfort and health of the occupants of the conditioned space or for the purpose of product processing. The term HVAC&R is an abbreviation of heating, ventilating, air conditioning, and refrigerating. The combination of processes in this commonly adopted term is equivalent to the current definition of air conditioning. Because all these individual component processes were developed prior to the more complete concept of air conditioning, the term HVAC&R is often used by the industry

Basics of Air Conditioning

 Basics of Air Conditioning

Basics of Air Conditioning Most people don’t realize how their central air conditioner actually works. They think that an air conditioner functions by pumping cool air into their home. But your air conditioner actually removes warm air and recirculates it as cool air. An air conditioner is basically a refrigerator. It uses the evaporation of a refrigerant, like Freon, to provide cooling. An central air conditioning system includes both the cooling and heating of air and cleans the air as well as controls the moisture level. There are a number of ways you can cool our home, but with any central air conditioning system the basics are the same; you will have a method of removing warm air to create cool air, a way to distribute the air to all of the rooms in your home, typically your duct system, and a way to control or regulate your system (thermostat). The first component of your air conditioning system is temperature control. When the air temperature rises above a preset level on your thermostat, the thermostat sends a signal to the air conditioner. This signals the air conditioner that it is time to turn on. The compressor (which is controlled by the thermostat) is the "heart" of the system. The compressor acts as the pump, causing the refrigerant to flow through the system. Its job is to draw in a lowpressure, lowtemperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant. This highpressure, hightemperature gas then flows to the condenser coil. The condenser coil is a series of piping with a fan that draws outside air across the coil. As the refrigerant passes through the condenser coil and the cooler outside air passes across the coil, the air absorbs heat from the refrigerant, which causes the refrigerant to condense from a gas to a liquid state. The high-pressure, high-temperature liquid then reaches the expansion valve. The expansion valve is the "brain" of the system. By sensing the temperature of the evaporator, or cooling coil, it allows liquid to pass through a very small opening, which causes the refrigerant to expand to a low-pressure, low-temperature gas. This "cold" refrigerant flows to the evaporator. The evaporator coil is a series of piping connected to a furnace or air handler that blows indoor air across it, causing the coil to absorb heat from the air. The cooled air is then delivered to the house through ducting. The refrigerant then flows back to the compressor where the cycle starts over again. Most central air conditioning units operate by means of a split system. That is, they consist of a "hot" side, or the condensing unit—including the condensing coil, the compressor and the fan—which is situated outside your home, and a "cold" side that is located inside your home. The cold side consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler. The furnace blows air through an evaporator coil, which cools the air. Then this cool air is routed throughout your home by means of a series of air ducts. Heat pumps and geothermal systems are other options for cooling your home. The basic principle of removing warm air and replacing it with cool air applies to these systems as well. It is important to understand how air conditioning systems are rated for efficiency. They are rated by what is known as S.E.E.R., Seasonal, Energy Efficiency Rating. Air conditioners with a higher SEER are more efficient, less costly to operate and more environmentally friendly. The current government minimum is 13 SEER. So those are the basics of your cooling system, the thermostat for control, the central air conditioning unit to remove warm air in order to create cool air, and a duct system to move the air through your home. And that how your central air conditioning system keeps you cool!

 

A Ton of Refrigeration | 1 Ton Air Condition

A Ton of refrigeration (TR), Amount of heat require to melt a ton of Ice over 24 Hr period, that much of energy is called ton of refrigeration

A Refrigeration Ton is approximately equivalent to 12,000 BTU/Hr British thermal unit / Hour

one ton of refrigeration capacity can freeze one short ton of water at 0°C (32°F) in 24 hours.

Another unit of measure is the calorie which is the amount of heat removal required to raise or lower the temperature of one gram of water by one °C. A kilo-calorie is the amount of heat required to raise or lower 1 kg of water by 1°C. One ton of refrigeration is equal to 3024 kilo-calories per hour. This is 12,000 BTU/ h divided by 2.204 (pounds per kilogram) divided by 1.8 (°C to °F).

 

1 Ton of Air condition , Then you need to pick an air conditioning unit that has more BTU/h of heat removal than your room has coming in, ton” of cooling capacity is 12,000 BTU/hour.

Example : An air conditioner of 1 ton can make 1000 Kg of ice in 24 hours from water at 0° C