Future Needs for Air Conditioning.

Changes are taking place in the living habits of people, in the air environments of the cities, in the requirements for industrial production, and in many other facets of modern society. These changes make it necessary to give more attention to air conditioning requirements.

The outdoor air in cities will continue to contain large amounts of undesirable foreign matter, such as dust, pollen, smoke, automobile exhaust gases, chemical fumes, and odors. Extensive use of air conditioning equipment will be one factor in providing a desirable air environment for urban dwellers. With the trend toward urban living, there will be greater concentrations of people in smaller areas and more apartments. Air conditioning will help to provide a. comfortable environment in apartments.

By using air conditioning, industries can move to regions that have desirable raw materials, labor supplies, or transportation.

The demand for manufactured goods of consistent quality can be met by close control of the environment. For example, a high-speed printing press must position overlapping colors precisely on a moving sheet of paper. This operation requires close control of the humidity to avoid expansion and contraction of the paper.

Modern architecture tends to use large amounts of exposed glass and large, flat roof surfaces. These practices accentuate the building heat gains from the sun and make air conditioning more necessary. Also, as air pollution becomes more widespread, the air introduced into buildings must be treated to obtain pure air.

If year-round school operation becomes necessary to handle a larger school population, the first provision that has to be made is to cool the classrooms. If public transportation is to compete with the individual's automobile, adequate heating and cooling of public vehicles is a necessity. In spite of high costs, hospitals and nursing homes will require complete air conditioning.

Text 5.

Exhaust ventilation systems

Exhaust ventilation is required to remove odors, fumes, dust, and heat from an enclosed occupied space. Such exhaust may be of the natural variety previously described or may be mechanical by means of roof or wall exhaust fans or mechanical exhaust systems. The mechanical systems may have minimal ductwork or none at all, or may be provided with extensive ductwork which is used to collect localized hot air, gases, fumes, or dust from process operations. Where it is possible to do so, the process operations are enclosed or hooded to provide maximum collection efficiency with the minimum requirement of exhaust air.

Because of the possibilities of re-circulated or external air pollution, it is customary to remove dust and fumes where practical or where required by means of ordinary ventilation filters, more efficient washers or centrifugal collectors, or chemical scrubbers.

Where dust is conveyed in the exhaust ducts, the velocities must be adequate to lift and move the dust particles. Velocities of 3000-6000 ft/min (914-1828 m/min) are required for this purpose. Lower velocities are tenable for fume removal, but corrosion protection must be provided by selection of duct and equipment materials. The round duct is used in most dust and fume systems because of its lower friction and because of its better dust-handling characteristics.

Fans for ordinary ventilation exhaust or heat removal may be similar to supply fans. Fume and dust exhaust fans must be more rugged and are frequently of the radial-blade (paddle-wheel) type for this reason. Axial flow and conventional centrifugal fans are also used in these applications.

Text 6.

Room Air Conditioner.

The lowest–cost cooling device is the room air conditioner. The indoor portion of the unit consists of an air filter, a fan, and a cooling coil. The warm, humid indoor air is drawn through the filter and into the fan. The fan blows the warm, humid air over the cooling coil, which cools and dehumidifies the air before it is blown into the room.

The cooling coil contains a refrigerant fluid. The refrigerant fluid changes from a liquid state to a gas state because heat from the warm air passing over the coil causes evaporation of the refrigerant fluid. This process takes heat from the warm, humid room air.

The outdoor portion of the unit consists of a compressor, a fan, and a condenser. The compressor receives low–temperature, low–pressure, refrigerant gas from the cooling coil. The compressor delivers high–temperature, high–pressure refrigerant gas to the condenser. The fan blows outdoor air over the condenser. Inside the condenser the high–temperature, high–pressure refrigerant gas is converted to refrigerant liquid. The cooler outdoor air passing over the condenser takes heat from the hotter refrigerant gas. This process causes the refrigerant gas to change to the liquid state. The refrigerant liquid is delivered to the cooling coil.

The refrigerant fluid constantly circulates in a closed path through the cooling coil, the compressor, and the condenser. The fan for cooling the condenser sucks in relatively cool outdoor air, passes the air over the condenser, and blows the hotter air back outdoors.

In the room air conditioner the compressor and the two fans are driven by electric motors. Smaller units use 110–volt–line supplies, and larger units use 220–volt–line supplies. Some room air conditioners have sufficient capacity to cool an entire small residence.

Text 7.