In the primary purpose of ensuring the comfort of occupants, heating refers to raising the temperature inside an enclosed space by increasing its temperature. The heating system in a Brooklyn’s building keeps the building’s structural, mechanical, and electrical systems in good repair by regulating the ambient temperature.
Thermoelectric generators are powered by a source of energy – generally coal, oil, or gas – that converts water into high-pressure steam. A turbine converts the expanding steam into electricity by turning its blades, which are connected to an armature that drives a generator. Steam is converted to water by a condenser, and water is returned back to the boiler by a pump.
Heat is converted from water to high-pressure steam by using a thermoelectric generating system, which is powered by coal, oil, or gas. When the steam expands, it turns the blades of a turbine which, in turn, turns the armature of a generator, converting it into electricity. Any remaining steam is converted into water by the condenser and returned to the boiler by a pump.
As early as the 10th century, open fires were used to provide interior heating. A direct heating source such as this and similar methods, such as fireplaces, cast-iron stoves, and contemporary space heaters operating on gas or electricity, is one that takes place at the place to be heated as the energy is converted to heat. In modern times, indirect heating is a more common form of heating. During the process of heating, energy is converted to heat in a source located outside of the site or sites to be heated, or located within the site or sites to be heated; the resulting heat is passed to the site by a fluid medium such as air, water, or steam.
Direct heating was a common practice for most cultures except ancient Greeks and Romans. In China, Japan, and the Mediterranean, wood was the earliest fuel used, though charcoal (which is made from wood) was used in areas where heat was not required, like China and Japan. A chimney was first a simple opening in the roof and then rose directly from the fireplace in medieval Europe. This chimney effectively eliminated the smoke and fumes produced by a fire in the living space. In 600 BC, Chinese enclosed stoves were used, and from there, they spread through Russia into northern Europe and across the Atlantic to the Americas. The Franklin stove, an improved design, was invented in 1744 by Benjamin Franklin. Heat is wasted much less when it is absorbed by the stove walls, which heat the surrounding air instead of passing up the chimney as hot combustion gases.
The roman hypocaust system became the greatest heating engineering achievement of ancient times. However, it is believed that central heating was invented in ancient Greece. The Roman streets were covered with mosaic tiles supported by columns that created air spaces called ducts. The heat was generated by burning charcoal, brushwood, or coal at a central location beside all the rooms to be heated; at the same time, the gases heated the floors beneath them. As the Roman Empire declined, hypocausts ceased to be used, and central heating was not introduced until approximately 1,500 years later.
It was not until the Industrial Revolution increased the size of industries, homes, and offices in the early 19th century that central heating was again introduced. By using steam as a power source in factories and mills, steam could be conveyed in pipes and could be used to heat the buildings. The steam generated by coal-fired boilers was distributed via standing radiators to the rooms. North America’s cold winters made steam heating the most popular heating method. From about 1830, warm water was recognized for its advantages over steam because it is cooler on the surface and has a milder effect. In twentieth-century central heating, warmth is conveyed primarily by air or hot water. Warm air ducts have replaced steam in most newly constructed American homes and offices, but in the United Kingdom and on most of the European continent, hot water has long been the preferred method of heating; warm air ducts have never been common. There is a preference in heating methods in North and South America, and in Europe.
Heating systems consist of three primary elements—a burner that can burn fuel to generate heat, a piped or ducted medium for moving the heat to different parts of a structure, and an emitting device releasing heat via convection, radiation, or both. Through a series of ducts and fans with which pressure differentials are produced, forced-air distribution delivers heated air to the building. In contrast, radiant heating involves sending heat directly from a source to the walls, ceilings, or floors of an enclosed space, independent of the temperature of the surrounding air. The heat generated sets up a convection cycle and warms the inside of the space uniformly.
Heating systems are designed in part by considering the air temperature as well as the effects of solar radiation, relative humidity, and convection. Physical activity is another important consideration in any given setting. The human body produces more heat under conditions of strenuous activity. This extra heat is dissipated by keeping the air temperature lower. Sedentary workers and domestic living rooms should have a upper temperature limit of 24° C (75° F), while heavy manual workers should have a lower temperature limit of 13° C (55° F).
In a mixture of air or water, carbon, hydrogen, and oxygen are burnt together to generate heat. That heat is transferred from the combustion chamber to the exterior.
By continuously removing the heated medium and removing cooler supplies, or by circulating, the heated medium is replaced. A furnace is a device that burns air, and a boiler or thermal energy unit is a device that burns water. Boilers in the definition of “water heaters” are vessels that heat water by heating it to a lower temperature; water heaters make steam as a result of heating water.
Heat is generated in boilers and furnaces by burning natural gas or fuel oil. The burners are completely automatic and do not require maintenance, although they must be cleaned occasionally. Their temperature may also be automatically controlled. There is no retained ash product left after coal and coke are used, unlike their predecessors. It is not necessary to store natural gas at all, but oil is pumped into storage tanks that may be located far from the heating equipment. Increased availability of natural gas from underground pipeline networks, the reliability of underground gas distribution, and the cleanliness of gas combustion have all contributed to the growth of natural-gas heating. As a result, natural gas consumption in residences has been growing rapidly as warm-air heating systems have become popular. Gas fuel is particularly well suited to these heating systems, so most natural gas consumption in residences is for these purposes. Fuel delivery is not dependent on motorized transport, the user does not require a storage tank or pay for fuel before using it, gasoline burns more efficiently, and the user can simply turn on the gas dispenser. Oil burners have more moving parts and are generally simpler than gas burners.
A gas heater must be vented to the outside since it produces noxious fumes. Whenever natural gas is not available in an area, liquefied petroleum gas (propane or butane) is delivered by a special tank truck and stored under pressure in the house until needed, just like in the case of natural gas. A large part of the convenience of oil and gas fuels is due to their automatic heating systems. Automation is based on a thermostat, which activates the furnace or boiler when space’s temperature drops below a predetermined threshold. A thermostat will anticipate and control nearly every conceivable danger for an automatic heating plant.
A low density makes air more energy efficient than steam or hot water over short distances. In American homes and offices, air is the primary heat carrier, although hot-water systems have been popular in European countries for some time. Through ducts, furnace heat is transferred to air, which is then discharged at registers in rooms above. Up until the 1930s, the warmth from a furnace could be carried by gravity in ducts directly to the rooms since it is lighter than the air it is replacing. However, gravity systems require ducts of very large diameter (20–36 cm [8–14 inches]) to reduce air friction, thus filling up the basement with ductwork. The lower pressure difference between heated supply air and cooler air returning to the furnace also caused rooms far from the furnace to be underheated. In order to overcome these difficulties, motor-driven fans were used, which forced heated air through small, rectangular ducts to the most distant rooms in the building. Registers, grilles, or diffusers of various types are used to introduce heated air into individual rooms, including those that look like baseboards. By opening doors and returning air vents, you can distribute heat evenly. After the room is heated, the warm air from the furnace is drawn back into it. A thermostat controls the whole system; it samples temperatures, activates the burners, and circulates the warm air through ducts. Forced warm-air heating offers a number of advantages, including the ability to clean the air as it circulates through the system. By installing a cooling coil in the ductwork and connecting it to appropriate refrigeration equipment, you can easily turn the system into a year-round air-conditioning system.
In addition to air, other systems work together. Heat is propagated by convection (movement of air) when the primary heated medium is steam or hot water. Convection is a more important source of heat than radiation for the common steam radiator.
Because of its high density, water is an ideal medium for central-heating systems because it can hold more heat and its temperature can be easily controlled. Radiators, pipes, or other heat emitters in the room to be heated are connected to the boiler through the pipes. Radiators or convectors receive heat from pipes, which are usually made of steel or copper. In order to reheat the water, now that it has cooled, it is returned to the boiler. For a hot-water system to function, there are two essential components: (1) a means of expanding the water in the system, which fills the boiler, heat emitters, and piping, and (2) any way to release air by a manually or automatically operated valve. The earliest hot-water systems worked based on gravity, with the cool water, which is denser, dropping back to the boiler while the lighter heated water rises to the radiators. Heating rooms below the furnace or boiler would not be possible with either gravity warm-air or gravity hot-water systems. Therefore, hot water is now driven through pipes by motor-driven pumps, allowing the boiler to be placed at any elevation relative to the heat emitters. When fluid is pumped, it can be pumped using smaller pipes than when gravity is used.
It consists of evaporating water that has been heated to about 35 kilopascals (5 pounds per square inch) in a boiler and then carried through steel or copper pipes to the radiators. Heat is transferred from the steam to the radiator, which operates to heat the room, and the steam cools to form water. In the boiler, condensate can either be pumped back or returned by gravity. In order to prevent steam from entering a radiator, the air valve needed on each radiator must allow air to escape. A single pipe is used to convey both steam and condensate in this system. Two separate streams of steam, condensate and water are transported in sophisticated systems using a two-pipe distribution system.
Although steam has a number of advantages and disadvantages, its main disadvantage is its high heat-carrying capacity. Due to the high temperature (about 102°C [215°F]) of the steam in the system, it is difficult to control the amount of steam fed into the rooms and needs to be adjusted regularly. Compared to warm-water or warm-air systems, steam systems require more apparatus, and the radiators they use are bulky and ugly. Thus, heating homes built in the 1930s and 40s has generally been replaced by heated air and hot water.