Humidifiers

Armstrong conditioned- steam Humidifiers Controlled humidification at the required level. They do not spit, drip, cause wet ducts, cor­rosion or add significant amounts of particulate matter to the air. The scheme shows how humidifiers work:

1. Steam supply

2. Steam jacket or distribution manifold at supply pressure and temperature

3. Condensate in steam supply or formed in manifold jacket knocked down by baffle

4. Separating chamber engineered to provide volume required for optimum velocity reduction and maximum separation

5. Condensate from supply and radiation and a substantial portion of the micron particulates in the steam collect in the drain and are discharged through the drain trap.

Steam from separating chamber flows around and through the metering valve which is positioned precisely by the operator in re­sponse to the demand signal from the controlled. Steam flows downward from metering valve into the drying chamber and is subjected to a abrupt change in direction of flow.

6. Drying chamber is completely jacked by the separating chambers. Steam entering drying chamber is at supply temperature and atmosphere pressure, so there is no condensation. Any remaining mist is re-evaporated.

7. Three- fourths of the circumference of the distribution pipe is jacked by steam at supply pressure and temperature to prevent condensation.

Central-heating system and fuel

The essential components of a central-heating system are an appliance in which fuel may be burned to generate heat: a medium conveyed in pipes or ducts for transferring the heat to the room to be heated; and an emitting apart from those spaces for releasing the heat either by convection or radiation or both. Following distribution moves heated air into the room by a system of ducts and fans. Radiant heating by contrast, in­volves the direct transmission from an emitter to the walls, ceiling or floor of an enclosed space independent of the temperature between them; the emitted heat sets up a convection cycle throughout the space, producing a uniformly warmed atmosphere within it.

Air temperature and the effects of solar radiation, relative humidity, and convection all influence the design of a heating system. An equally im­portant consideration is the amount of physical activity that is antici­pated in a particular setting. In a work atmosphere in which strenuous activity is the norm, the human body gives off more heat. In compensa­tion, the air temperature is kept lower in order to allow the extra body heat to dissipate. An upper temperature limit of 24°C is appropriate for sedentary workers and domestic living rooms, while a lower temperature limit of 13°C is appropriate for persons doing heavy manual work.

In the combustion of fuel, carbon and hydrogen react with atmospheric oxygen to produce heat, which is transferred from the combustion chamber to a medium consisting of either air or water. The equipment is so arranged that the heated medium is constantly removed and replaced by a cooler supply - i.e. by circulation. If air the medium, the equipment is called a furnace, and if the water is the medium, a boiler or water heater. The term "boiler" more correctly refers to a vessel in which steam is produced, and "water heater" to one in which water is heated and circulated below its boiling point.

Natural gas and fuel oil are the chief fuels used to produce heat in boilers and furnaces. They require no labour except for occasional automatic burners, which may be thermostatically controlled. Unlike their prede­cessor, coal and coke, there is no residual ash product left for disposal after use. Natural gas requires no storage whatsoever, while oil is pumped into storage tanks that may be located at some distance from the heating equipment. The growth of natural-gas heating has been closely related to the increased availability-of gas from networks of underground pipelines, the reliability of underground delivery, and the cleanliness of gas combustion. This growth is also linked to the popularity of warm-air heating systems, to which gas fuel is particularly adaptable and which accounts for most of the natural gas consumed in residences. Gas is easier to burn and control than oil, the user needs no storage tank and pays for the fuel after he has used it, and fuel delivery is not dependent on the vagaries of motorized transport. Gas burners are generally sim­pler than those required for oil and have few moving parts. Because burning gas produces a toxious exhaust, gas heaters must be vented to the outside. In areas outside the reach of natural-gas pipelines, liquefied petroleum gas (propane or butane) is delivered in special tank tracks and stored under pressure in the home until ready for use in the same manner as natural gas. Oil and gas fuels owe much of their convenience to the automatic operations of their heating plant. This automation rests pri­marily on the thermostat, a device that, when the temperature in a space drops to a predetermined point, will activate the furnace or boiler until the demand for heat is satisfied. Automatic heating plants re so thor­oughly protected by thermostats that nearly every conceivable circum­stance that could be dangerous is anticipated and controlled.

I. Запомните значение следующих слов:

1.nevertheless — однако, тем не менее

2.preference - предпочтение

3.employ - применять

4.friction - трение

5.resemble - походить на, иметь сходство

6.rectangular - прямоугольный

7.grill -решётка

8.evenly - ровно, равномерно

9.sample - образец, пример

10. conjunction - соединение

11. propel - приводить в движение

Warm-air heating

Because of its law density, air carries less heat for shorter distances than do hot water or steam. The use of air as the primary heat conveyor is nevertheless the rule in American homes and offices, though there has been a growing preference for hot-water systems, which have been used in European countries for some time. The heat of the furnace is trans­ferred to the air in ducts, which rise to rooms above where the hot air is emitted through registers. The warm air from a furnace, being lighter than the cooler air around it, can be carried by gravity in ducts to the rooms, and until about 1930 this was the usual method employed. But a gravity system requires ducts of a rather large diameter (20-36 cm [8-14 inches]) in order to reduce air friction, and this resulted in the basement's being filled with ductwork. Moreover, rooms distant from the furnace tended to be underheated, owing the small pressure difference between the heated supply air and cooler air returning to the furnace. These difficulties were solved by the use of motor-driven fans, which can force the heated air through small, compact, rectangular ducts to the most distant rooms in building. The heated air is introduced into indi­vidual rooms through registers, grilles, or diffusers of various types, in­cluding arrangements resembling baseboards along walls. Air currents through open doors and return air vents help distribute the heat evenly. The warm air, after giving up its heat to the room, is returned to the fur­nace. The entire system is controlled by thermostats that sample tem­peratures and then activate the gas burner and the blowers that circulate the warm air through ducts. An advantage of forced warm-air heating is that the air can be passed through filters and cleaned as it circulates through the system. And if the ductwork is properly sized, the addition of a cooling coil connected to suitable refrigeration machinery easily converts the system to a year-round air-conditioning system.

Air also works in conjunction with other systems. When the primary heated medium is steam or hot water, forced air propelled by fans distributes heat by convection (air movement). Even the common steam ra­diation depends more on radiation of heat emission.

1. favor - поддерживать, благоприятствовать

2. provision - снабжение, обеспечение

3. escape - избегать, бежать, уходить

4. manually - ручным способом

5. gravity - сила притяжения, тяжесть

6. consequently - следовательно, значит

Hot-water system

Water is especially favoured for central-heating systems because its high density allows it to hold more heat and because its temperature can be regulated more easily. A hot-water heating system consists of the boiler and a system of pipes connected to radiators, piping, or other heat emit­ters located in rooms to r e heated. The pipes usually of steel or copper, feed hot to radiators or convectors, which give up their heat to the room. The water, now cooled, is then returned to the boiler for reheating. Two important requirements of a hot-water system are (1) provision to allow for the expansion of the water in the system, which fills the boiler, heat emitters, and piping, and (2) means for allowing air to escape by a manually or automatically operated valve. Early hot-water systems, like warm-air systems, operated by gravity, the cool water, being more dense, dropping back to the boiler, and forcing the heated lighter water to rise to the radiators. Neither the gravity warm-air nor gravity hot-water system could be used to heat rooms below the furnace or boiler. Consequently, motor-driven pipes are now used to drive hot water through the pipes, making it possible to locate the boiler at any elevation in relation to the heat emitters. As with warm air, smaller pipes can be used when the fluid is pumped than with gravity operation.

1. sophisticated - сложный, усложнённый

2. capacity - способность

3. adjustment - регулировка, регулирование, исправление

4. bulky - громоздкий

Steam heating

Steam systems are those in which stem is generated, usually at less than 35 kilopascals (5 pounds per square inch) in the boiler, and the steam is led to the radiators through steel or copper pipes. The steam gives up its heat to the radiator and the radiator to the room, and the cooling of the steam condenses it to water. The condensate is returned to the boiler ci­ther by gravity or by a pump. The air valve on each radiator is necessary to allow air to escape; otherwise it would prevent steam from entering the radiator. In the arrangement of a simple one-pipe system, both the steam supply and the condensate return re conveyed by the same pipe. More sophisticated systems use two-pipe distribution system, keeping the steam supply and the condensate return as two separate streams.

Steam's chief advantage, its high-carrying capacity, is also the source of its disadvantages (about 102°C) of the steam inside the steam makes it hard to control and requires frequent adjustments in its rate of input Lo the rooms. To perform most efficiently steam systems require more ap­paratus than do hot-water or warm-air systems, and the radiators used are bulky and unattractive. As a. result, warm air and hot-water have generally replaced steam in the heating of homes built from the 1930s and 40s.

1.relatively - относительно

2.decrease - понижать(-ся)

3.excess - излишек

Electric heat

Electricity can also be used in central heating. Though generally more expensive than fossil fuels, its relatively high cost can be offset by the use of electric current when normal demand decreases, either at night or in the wintertime - i.e., when lighting, power, and air-conditioning de­mands are low and there excess power capacity in regional or local electrical grids. The most common method of converting electricity to heat is by resistors, which become hot when an electric current is set through them and meets resistance. The current is automatically acti­vated by thermostats in the room to be heated. Resistors can be used to heat circulating air or water, or, in the form of baseboard convectors, they can directly heat the air along the walls of an individual room, es­tablishing convective currents.

Heat pump

Another method for heating with electricity involves the use of the heat pump. Every refrigeration machine is technically a heat pump, pumping heat from an area of lower temperature (normally the space to be cooled or refrigerated) to an area of higher temperature (normally, the out­doors). The refrigeration machine may be used to pump heat, in winter, from the outdoor air, or groundwater, or any other source of low temperature heat, and deliver this heat at higher temperature to a space to be heated. Usually, the heat pump is designed to function as an air conditioner in summer, then to reserve and serve as a heat pump in winter.

A heats pump operations can be explained using the following example. The typical window-mounted air-conditioning unit has a heat-rejection unit (condenser) mounted outside. This unit discharges the heat removed by the indoor coil (evaporator) to the outside air. Therefore the evaporator subtracts heat from the residence and transfers it to the refrigerant gas, which is pumped to the outside condenser, where by means of a fan the heat is dissipated in the air outside. This cycle can be inverted: heat is subtracted from the outside air and is transferred via the refrigerant gas to the indoor coil (evaporator) and discharged into a residence's ductwork by means of the evaporator fan. This is a basic heat-pump system. Where winter climates reach freezing temperatures, however, the system is limited by the freezing of the condenser (outdoor coil); this, heat pumps work best in mild climates with fairly warm winter temperatures. The complexity of their machinery also makes them un­economical in many contexts.

Types of emitters

Types of emitters. There are many variations in the method of trans­ferring the heat from hot water, steam, or electric resistors to the space to be heated. The most familiar heat emitter in older buildings is the common radiator. Steam or hot water circulates through its hollow sections, which can be connected to each other to produce varying lengths. Radiators are usually placed along the external walls of a room. Ambient air enters from below and in rises vertically between the radiator section and discharges at the top. The warmed air, being less dense than the cooler air further away in the room, rises and displaces the cooler air, which falls, setting up a current о fair.

Convectors differ from radiators in their smaller heat-transfer surface and their placement at the bottom of a cabinet whose inlets and outlets are designed to property direct a stream of warmed air through the room using the same "chimney" effect. The typical convector is an arrangement of finned pipes or coils through which the heated air or water circulates at the base of an enclosure open at the top and bottom; air flows upward over the heating surface and is discharged at the top of the enclosure; cooled air drops to the floor and reenters the convector. Such convectors are often in­stalled along windows or along an external wall to counteract drafts and the loss of heat through those cold surfaces.

Many industrial buildings arc heated using a special form of emitter called a unit heater, which consists of an arrangement of finned tubes through which hot water or steam circulates and an electric fan that forces air over the tubes. The forced convection results in a rapid rate of heat transfer. Unit heaters can be mounted in units either above the floor or on it.

Radiant heating systems usually employ either hot-water pipes em­bedded in the floor or ceiling, warm-air ducts embedded in the floor, or some form of electrical resistance panels applied to ceiling or walls. Panel heating is a form of radiant heating characterized by very large radiant sur­faces at modestly warm temperatures. With many such systems there is no visible heating equipment in the room, which is an advantage in decorat­ing. A disadvantage is the extent to which a ceiling or floor might be ru­ined in case of corroded of faulty hot-water piping where this method is employed.

Domestic hot-water supply. In houses, a small hand-fired coal boiler was formerly the common means of heating water for cooking, bathing, and washing. This was superseded by a separate gas, electric, or oil-fired water heater in which the heating burner or element is included in the same unit as the hot-water storage; when hot water is drawn off, cold water enters, affecting a thermostat that turns on the heat until the tank temperature again reaches the predetermined level. Alternatively, a device known as a heat exchanger can be connected to the house-heating boiler, extracting heat from the boiler water to heat the service water.

Solar energy. Solar energy frequently works on a storage basis, in which water coils placed beneath heat-absorbing panels collect the radiant heat of the sun. This water may then be stored in a tank for use in heating lines or to provide hot water for washing and bathing. See solar energy; solar heating.