Exterior cladding on building walls
Siding or wall cladding is the protective material attached to the exterior side of a wall of a house or other building. Along with the roof, it forms the first line of defense against the elements, most importantly sun, rain/snow, heat and cold, thus creating a stable, more comfortable environment on the interior side. The siding material and style also can enhance or detract from the building's beauty. There is a wide and expanding variety of materials to side with, both natural and artificial, each with its own benefits and drawbacks. Masonry walls as such do not require siding, but any wall can be sided. Walls that are internally framed, whether with wood, or steel I-beams, however, must always be sided.
Most siding consists of pieces of weather-resistant material that are smaller than the wall they cover, to allow for expansion and contraction of the materials due to moisture and temperature changes. There are various styles of joining the pieces, from board and batton, where the butt joints between panels is covered with a thin strip (usually 1 to 2 inches wide) of wood, to a variety of clapboard, also called lap siding, in which planks are laid horizontally across the wall starting from the bottom, and building up, the board below overlapped by the board above it. These techniques of joinery are designed to prevent water from entering the walls. Siding that does not consist of pieces joined would include stucco, which is widely used in the Southwest. It is a plaster-like siding and is applied over a lattice, just like plaster. However, because of the lack of joints, it eventually cracks and is susceptible to water damage. Rainscreen construction is used to improve siding's ability to keep walls dry.
Thatch is an ancient and very widespread building material used on roofs and walls. Thatch siding is made with dry vegetation such as longstraw, water reeds, or combed wheat reed. The materials are overlapped and weaved in patterns designed to deflect and direct water.
Wood siding is very versatile in style and can be used on a wide variety of building structures. It can be painted or stained in any color palette desired.
Though installation and repair is relatively simple, wood siding requires more maintenance than other popular solutions, requiring treatment every four to nine years depending on the severity of the elements to which it is exposed. Ants and termites are a threat to many types of wood siding, such that extra treatment and maintenance that can significantly increase the cost in some pest-infested areas.
Wood is a moderately renewable resource and is biodegradable. However, most paints and stains used to treat wood are not environmentally friendly and can be toxic. Wood siding can provide some minor insulation and structural properties as compared to thinner cladding materials.
Wood shingles or irregular cedar "shake" siding was used in early New England construction, and was revived in Shingle Style and Queen Anne style architecture in the late 19th century.
Wood siding in overlapping horizontal rows or "courses" is called clapboard, weatherboard (British English), or bevel siding which is made with beveled boards, thin at the top edge and thick at the butt.
In colonial North America, Eastern white pine was the most common material. Wood siding can also be made of naturally rot-resistant woods such as redwood or cedar.
Jointed horizontal siding (also called "drop" siding or novelty siding) may be shiplapped or tongue and grooved (though less common). Drop siding comes in a wide variety of face finishes, including Dutch Lap (also called German or Cove Lap) and log siding (milled with curve).
Vertical siding may have a cover over the joint: board and batten, popular in American wooden Carpenter Gothic houses; or less commonly behind the joint called batten and board or reversed board and batten.
Plywood sheet siding is sometimes used on inexpensive buildings, sometimes with grooves to imitate vertical shiplap siding. One example of such grooved plywood siding is the type called Texture 111, T1-11, or T111 ("tee-one-eleven"). There is also a product known as reverse board-and-batten RBB that looks similar but has deeper grooves. Some of these products may be thick enough and rated for structural applications if properly fastened to studs. Both T-11 and RBB sheets are quick and easy to install as long as they are installed with compatible flashing at butt joints.
Slate shingles may be simple in form but many buildings with slate siding are highly decorative.
Wood clapboard is often imitated using vinyl siding or uPVC weatherboarding. It is usually produced in units twice as high as clapboard. Plastic imitations of wood shingle and wood shakes also exist.
Since plastic siding is a manufactured product, it may come in unlimited color choices and styles. Historically vinyl sidings would fade, crack and buckle over time, requiring the siding to be replaced. However, newer vinyl options have improved and resist damage and wear better. Vinyl siding is sensitive to direct heat from grills, barbecues or other sources. Unlike wood, vinyl siding does not provide additional insulation for the building, unless an insulation material (e.g., foam) has been added to the product. It has also been criticized by some fire safety experts for its heat sensitivity. This sensitivity makes it easier for a house fire to jump to neighboring houses in comparison to materials such as brick, metal or masonry.
Vinyl siding has a potential environmental cost. While vinyl siding can be recycled, it cannot be burned (due to toxic dioxin gases that would be released). If dumped in a landfill, plastic siding does not break down quickly.
Vinyl siding is also considered one of the more unattractive siding choices by many. Although newer options and proper installation can eliminate this complaint, vinyl siding often has visible seam lines between panels and generally do not have the quality appearance of wood, brick, or masonry. The fading and cracking of older types of plastic siding compound this issue. In many areas of newer housing development, particularly in North America, entire neighbourhoods are often built with all houses clad in vinyl siding, given an unappealing uniformity. Some cities now campaign for house developers to incorporate varied types of siding during construction.
A predecessor to modern maintenance free sidings was asphalt brick siding. Asphalt impregnated panels (about 2 by 4ft or 0.61 by 1.22m) give the appearance of brick or even stone. Many buildings have this siding, especially old sheds and garages. If the panels are straight and level and not damaged, the only indication that they are not real brick may be seen at the corner caps. Trademarked names included Insulbrick, Insulstone, Insulwood. Commonly used names now are faux brick, lick-it-and-stick-it brick, and ghetto brick. Often such siding is now covered with newer metal or plastic siding. Today thin panels of real brick are manufactured for veneer or siding.
Insulated siding has emerged as a new siding category in recent years. Considered an improvement over vinyl siding, insulated siding is custom fit with expanded polystyrene foam (EPS) that is fused to the back of the siding, which fills the gap between the home and the siding.
Products provide environmental advantages by reducing energy use by up to 20 percent. On average, insulated siding products have an R-value of 3.96, triple that of other exterior cladding materials. Insulated siding products are typically Energy Star qualified, engineered in compliance with environmental standards set by the U.S. Department of Energy and the United States Environmental Protection Agency.
In addition to reducing energy consumption, insulated siding is a durable exterior product, designed to last more than 50 years, according to manufacturers. The foam provides rigidity for a more ding- and wind-resistant siding, maintaining a quality look for the life of the products. The foam backing also creates straighter lines when hung, providing a look more like that of wood siding, while remaining low maintenance.
Manufacturers report that insulated siding is permeable or "breathable", allowing water vapor to escape, which can protect against rot, mold and mildew, and help maintain healthy indoor air quality.
Metal siding comes in a variety of metals, styles, and colors. It is most often associated with modern, industrial, and retro buildings. Utilitarian buildings often use corrugated galvanized steel sheet siding or cladding, which often has a coloured vinyl finish. Corrugated aluminium cladding is also common where a more durable finish is required, while also being lightweight for easy shaping and installing making it a popular metal siding choice.
Formerly, imitation wood clapboard was made of aluminium (aluminium siding). That role is typically played by vinyl siding today. Aluminium siding is ideal for homes in coastal areas with much moisture and salt, since aluminium reacts with air to form aluminium oxide, an extremely hard coating that seals the aluminium surface from further degradation. In contrast, steel forms rust, which can weaken the structure of the material, and corrosion-resistant coatings for steel, such as zinc, sometimes fail around the edges as years pass. However, an advantage of steel siding can be its dent-resistance, which is excellent for regions with severe stormsespecially if the area is prone to hail.
The first architectural application of aluminium was the mounting of a small grounding cap on the Washington Monument in 1884. Sheet-iron or steel clapboard siding units had been patented in 1903, and Sears, Roebuck & Company had been offering embossed steel siding in stone and brick patterns in their catalogues for several years by the 1930s. Alcoa began promoting the use of aluminium in architecture by the 1920s when it produced ornamental spandrel panels for the Cathedral of Learning and the Chrysler and Empire State Buildings in New York. The exterior of the A.O. Smith Corporation Building in Milwaukee was clad entirely in aluminium by 1930, and 3-foot-square (0.91m) siding panels of Duralumin sheet from Alcoa sheathed an experimental exhibit house for the Architectural League of New York in 1931. Most architectural applications of aluminium in the 1930s were on a monumental scale, and it was another six years before it was put to use on residential construction.
In the first few years after World War II, manufacturers began developing and widely distributing aluminium siding. Among them Indiana businessman Frank Hoess was credited with the invention of the configuration seen on modern aluminium siding. His experiments began in 1937 with steel siding in imitation of wooden clapboards. Other types of sheet metal and steel siding on the market at the time presented problems with warping, creating openings through which water could enter, introducing rust. Hoess remedied this problem through the use of a locking joint, which was formed by small flap at the top of each panel that joined with a U-shaped flange on the lower edge of the previous panel thus forming a watertight horizontal seam. After he had received a patent for his siding in 1939, Hoess produced a small housing development of about forty-four houses covered in his clapboard-style steel siding for blue-collar workers in Chicago. His operations were curtailed when war plants commandeered the industry. In 1946 Hoess allied with Metal Building Products of Detroit, a corporation that promoted and sold Hoess siding of Alcoa aluminium. Their product was used on large housing projects in the northeast and was purportedly the siding of choice for a 1947 Pennsylvania development, the first subdivision to solely use aluminium siding. Products such as 4,-6,-8-and-10-inch (100,150,200 and 250mm) by 12-foot (3.7m) unpainted aluminium panels, starter strips, corner pieces and specialized application clips were assembled in the Indiana shop of the Hoess brothers. Siding could be applied over conventional wooden clapboards, or it could be nailed to studs via special clips affixed to the top of each panel. Insulation was placed between each stud. While the Hoess Brothers company continued to function for about twelve more years after the dissolution of the Metal Building Products Corporation in 1948, they were less successful than rising siding companies like Reynolds Metals.[1][2]
Stone and masonry veneer is sometimes considered siding, are varied and can accommodate a variety of stylesfrom formal to rustic. Though masonry can be painted or tinted to match many color palettes, it is most suited to neutral earth tones, and coatings such as roughcast and pebbeldash. Masonry has excellent durability (over 100 years), and minimal maintenance is required. The primary drawback to masonry siding is the initial cost.
Precipitation can threaten the structure of buildings, so it is important that the siding will be able to withstand the weather conditions in the local region. For rainy regions, exterior insulation finishing systems (EIFS) have been known to suffer underlying wood rot problems with excessive moisture exposure.
The environmental impact of masonry depends on the type of material used. In general, concrete and concrete based materials are intensive energy materials to produce. However, the long durability and minimal maintenance of masonry sidings mean that less energy is required over the life of the siding.
Various composite materials are also used for siding: asphalt shingles, asbestos, fiber cement, aluminium (ACM), fiberboard, hardboard, etc. They may be in the form of shingles or boards, in which case they are sometimes called clapboard.
Composite sidings are available in many styles and can mimic the other siding options. Composite materials are ideal for achieving a certain style or 'look' that may not be suited to the local environment (e.g., corrugated aluminium siding in an area prone to severe storms; steel in coastal climates; wood siding in termite-infested regions).
Costs of composites tend to be lower than wood options, but vary widely as do installation, maintenance and repair requirements. Not surprisingly, the durability and environmental impact of composite sidings depends on the specific materials used in the manufacturing process.
Fiber cement siding is a class of composite siding that is usually made from a combination of cement, cellulose (wood), sand, and water. They are either coated or painted in the factory or installed and then painted after installation. Fiber cement is popular for its realistic look, durability, low-maintenance properties, fire resistance, and its lightweight properties compared to traditional wood siding. Composite siding products containing cellulose (wood fibers) have been shown to have problems with deterioration, delamination, or loss of coating adhesion in certain climates or under certain environmental conditions.
A younger class of non-wood synthetic siding has sprouted in the past 15 years. These products are usually made from a combination of non-wood materials such as polymeric resins, fiberglass, stone, sand, and fly ash and are chosen for their durability, curb appeal, and ease of maintenance. Given the newness of such technologies, product lifespan can only be estimated, varieties are limited, and distribution is sporadic.
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Siding (construction) - Wikipedia
Siding gives you a great way to add color and definition to your house. There are lots of options these days to help you create the perfect faade and you want to choose carefully. While aesthetics are always important, you also want to consider the material's durability, ability to resist water, ease of installation and versatility.
"From a functional point of view, siding gives you protection," says architect Amy A. Alper. "From an architectural point of view, there's an interest now in using a variety of materials to highlight special features on a home. For example, using stone or Western red cedar to highlight an entry."
The low cost, versatility and easy maintenance of vinyl siding has helped it become the most popular siding choice in the United States. While some design professionals and homeowners are turned off by the "plastic look" of some vinyl siding products, the variety of colors and styles available helps explain this siding's popularity.
"The technology has changed dramatically, even in the last five years," says Max Bumgardner, sales manager for Sutton Siding & Remodeling, Inc. "All the manufacturers are competing to offer the best product."
Requiring few tools to install and available at home improvement stores, this is an option for those looking for a do-it-yourself product. Since mistakes can be costly, make sure to follow instructions from the manufacturer and take advantage of online how-to videos.
Commonly used for bungalow, Cape Cod and cottage exteriors, wood siding offers a rich look and is durable if maintained properly. If you are attracted to this look keep in mind that it requires periodic maintenance (chalking and painting or staining to prevent weather damage) and is susceptible to insect or rodent attacks. Depending on maintenance, your rich wood siding can last from 10 to sometimes 100 years.
Wood siding comes in clapboard (also known as lap or bevel siding) as well as shakes and shingles. Clapboard siding uses planks of wood installed horizontally with an upper piece that overlaps the lower piece. Western red cedar and redwood, woods known for being attractive and durable, are considered the best choices.
More uniform in appearance but thinner than shakes, shingles give you a smooth and consistent look. They can be cut into different shapes to add visual interest to your exterior. Some manufacturers also offer shingles treated with fire-retardant chemicals, often a requirement in high-risk locations. Be sure to check into the local rules in your area.
Wood siding typically costs around $5 to $10 per square foot installed. That doesn't count additional cost for painting or staining.
Made from fired clay, genuine brick comes in different sizes and textures. Brick is commonly found on Colonial, Tudor and English cottage exteriors, providing a beautiful look that has been used for hundreds of years and has stood the test of time. These days brick siding is usually a veneer constructed outside of a home's wood frame structure, with mortar used to hold the bricks together.
Since water can penetrate brick veneers, a membrane installed between the brick veneer and house can protect the structure. Under normal conditions and when installed correctly brick siding can last the life of your house. Installing brick is labor-intensive, so the cost is on the higher end compared to other siding options.
Typically, brick siding costs around $6 to $15 or more per square foot installed.
Offering the look of masonry, stucco or wood at a lower cost, fiber-cement siding has become a popular siding choice for many homeowners. Fiber-cement siding is low-maintenance, non-flammable and termite-resistant. Available in a range of styles and textures, factory painting or finishes are highly recommended.
On the other side, fiber-cement siding could encounter possible moisture-related problems, and older homes built before the late 1980s may have siding that contains asbestos and requires a professional abatement contractor for removal.
The average cost is $6 to $12 per square foot installed (cost higher with trim), and the siding will last 25 to 50 years, depending on manufacturer.
Traditional stucco is made from building sand, Portland cement, lime and water. A waterproof barrier paper and galvanized-metal screening are applied over wood walls before stucco is added to provide a good base for the stucco and protect the walls underneath. While stucco can be applied to homes with brick and stone surfaces, the classic look is commonly found on Mediterranean, ranch and Spanish-mission exteriors.
Because stucco is very rigid, careful installation can help reduce the possibility of unwanted cracks. When stucco siding is properly installed and maintained, it can last the lifetime of the house.
Stone and stone-veneer siding
The natural beauty and durability of stones like granite and limestone are appealing to homeowners who want a siding that adds texture and visual interest to their exterior. Because stone is more expensive than other siding options and can be difficult to add to an existing home concerns about costs should be considered.
More lightweight and less expensive than natural stone, stone-veneer siding comes in natural and synthetic materials. There are many styles available that help enhance your home's curb appeal. Annual cleaning with a hose and inspection of the siding helps ensure it will last the life of the house.
The average cost of stone is around $10 to $30 per square foot installed, and if maintained properly, can last the lifetime of house.
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Top 6 Exterior Siding Options | HGTV
Technology of indoor and vehicular environmental comfort
Heating, ventilation, and air conditioning (HVAC)[1] is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).
HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.
Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Methods for ventilating a building are divided into mechanical/forced and natural types.[2]
The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments. HVAC systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.[3]
In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. For larger buildings, building service designers, mechanical engineers, or building services engineers analyze, design, and specify the HVAC systems. Specialty mechanical contractors and suppliers then fabricate, install and commission the systems. Building permits and code-compliance inspections of the installations are normally required for all sizes of buildings.
Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[4][5][6]
Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings, for utilizing renewable energy sources such as solar heat,[7][8][9] winter's cold,[10][11] the cooling potential in some places of lakes or seawater for free cooling, and the enabling function of seasonal thermal energy storage. By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods.
HVAC is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Rolla C. Carpenter, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, and many others.[12]
Multiple inventions within this time frame preceded the beginnings of the first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) for the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit the same year. Coyne College was the first school to offer HVAC training in 1899.[13]
The invention of the components of HVAC systems went hand-in-hand with the industrial revolution, and new methods of modernization, higher efficiency, and system control are constantly being introduced by companies and inventors worldwide.
Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.
Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire (see Nichrome). This principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump systems.
The heat pump gained popularity in the 1950s in Japan and the United States.[14] Heat pumps can extract heat from various sources, such as environmental air, exhaust air from a building, or from the ground. Heat pumps transfer heat from outside the structure into the air inside. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates, they can also operate in reverse by cooling an interior.
In the case of heated water or steam, piping is used to transport the heat to the rooms. Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system (as opposed to older gravity-fed systems). The heat can be transferred to the surrounding air using radiators, hot water coils (hydro-air), or other heat exchangers. The radiators may be mounted on walls or installed within the floor to produce floor heat.
The use of water as the heat transfer medium is known as hydronics. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.
Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is normally filtered through air filters to remove dust and pollen particles.[15]
The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects.[16]
Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[17]
Ventilation is the process of changing or replacing air in any space to control the temperature or remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide, and to replenish oxygen. Ventilation often refers to the intentional delivery of the outside air to the building indoor space. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.[18]
Mechanical, or forced, ventilation is provided by an air handler (AHU) and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates more energy is required to remove excess moisture from ventilation air.
Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. Direct drive fans are available for many applications and can reduce maintenance needs.
In summer, ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor.
Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and other planned building envelope penetrations, and as being driven by natural and/or artificially produced pressure differentials.[2]
In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.
An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which has thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[19]
Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.[20]
Natural ventilation [21] is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide the greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.[22]
An air conditioning system, or a standalone air conditioner, provides cooling and/or humidity control for all or part of a building. Air conditioned buildings often have sealed windows, because open windows would work against the system intended to maintain constant indoor air conditions. Outside, fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air. Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down, then be guided to the space creating positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent. Typical fresh air intake is about 10% of the total supply air.[citation needed]
Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle, or in a free cooling system that uses pumps to circulate a cool refrigerant (typically water or a glycol mix).
It is imperative that the air conditioning horsepower is sufficient for the area being cooled. Underpowered air conditioning systems will lead to power wastage and inefficient usage. Adequate horsepower is required for any air conditioner installed.
The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device, and evaporator.
In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.
Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.
Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.
Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.[23] (Minisplit ductless systems are used in these situations.) Outside of North America, packaged systems are only used in limited applications involving large indoor space such as stadiums, theatres or exhibition halls.
An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems. Split systems are preferred and widely used worldwide except in North America. In North America, split systems are most often seen in residential applications, but they are gaining popularity in small commercial buildings. Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern.[24] The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control, and quiet operation.[25] In space conditioning, the duct losses can account for 30% of energy consumption.[26] The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting.
With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.
Split systems are more efficient and the footprint is typically smaller than the package systems. On the other hand, package systems tend to have a slightly lower indoor noise level compared to split systems since the fan motor is located outside.
Dehumidification (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside.
A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. It is often employed in basements that have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.
The HVAC components that dehumidify the ventilation air deserve careful attention because outdoor air constitutes most of the annual humidity load for nearly all buildings.[27]
All modern air conditioning systems, even small window package units, are equipped with internal air filters. These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop airflow. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, which can result in damage to the system or even fire.
Because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) and the heat generated by the electric motor driving the compressor.
HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy.[28] Since the 1980s, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by increased awareness of environmental issues. Additionally, improvements to the HVAC system efficiency can also help increase occupant health and productivity.[29] In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.
In the past, water heating was more efficient for heating buildings and was the standard in the United States. Today, forced air systems can double for air conditioning and are more popular.
Some benefits of forced air systems, which are now widely used in churches, schools, and high-end residences, are
A drawback is the installation cost, which can be slightly higher than traditional HVAC systems.
Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.
Forecasting is another method of controlling building heating by calculating the demand for heating energy that should be supplied to the building in each time unit.
Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's 57C (70F) low temperature or cool a building in the highest temperature ever recorded in the US57C (134F) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A metre below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 1.8 metres (6ft) underground, temperatures generally only range from 7 to 24C (45 to 75F).
Photovoltaic solar panels offer a new way to potentially decrease the operating cost of air conditioning. Traditional air conditioners run using alternating current, and hence, any direct-current solar power needs to be inverted to be compatible with these units. New variable-speed DC-motor units allow solar power to more easily run them since this conversion is unnecessary, and since the motors are tolerant of voltage fluctuations associated with variance in supplied solar power (e.g., due to cloud cover).
Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy from the stale air inside the home to the incoming fresh air from outside.
The performance of vapor compression refrigeration cycles is limited by thermodynamics.[30] These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient of performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35C (95F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35C (95F) outdoor temperature. The current industry minimum SEER rating is 14 SEER.[31] Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce the electrical power required to move the air by a third.[32]
Demand controlled kitchen ventilation (DCKV) is a building controls approach to controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen. Traditional commercial kitchen ventilation systems operate at 100% fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings. By deploying smart sensing technology, both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy, increasing safety, and reducing ambient kitchen noise levels.[33]
Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation, and air conditioning. Air cleaning and filtration should be taken in account when protecting our building environments.[34]
Clean air delivery rate (CADR) is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 30 cubic metres (1,000cuft) per minute and an efficiency of 50% has a CADR of 15 cubic metres (500cuft) per minute. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. This depends on the size of the particle or fiber, the filter packing density and depth, and the airflow rate.[34]
The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI (Heating, Air-conditioning and Refrigeration Distributors International), ASHRAE, SMACNA, ACCA (Air Conditioning Contractors of America), Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement. (UL as an omnibus agency is not specific to the HVAC industry.)
The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions. However, before taking up the heat load calculation, it is necessary to find fresh air requirements for each area in detail, as pressurization is an important consideration.
ISO 16813:2006 is one of the ISO building environment standards.[35] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[36]
The building environmental design standard aims to:[36]
In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), EPA certified (for installation and service of HVAC devices), or locally engineer certified such as a Special to Chief Boilers License issued by the state or, in some jurisdictions, the city. ASHRAE is an international technical society for all individuals and organizations interested in HVAC. The Society, organized into regions, chapters, and student branches, allows the exchange of HVAC knowledge and experiences for the benefit of the field's practitioners and the public. ASHRAE provides many opportunities to participate in the development of new knowledge via, for example, research and its many technical committees. These committees typically meet twice per year at the ASHRAE Annual and Winter Meetings. A popular product show, the AHR Expo, has been held in conjunction with each winter ASHRAE meeting. The Society has approximately 50,000 members and has headquarters in Atlanta, Georgia.
The most recognized standards for HVAC design are based on ASHRAE data. The four volumes of most popular ASHRAE Handbooks are Fundamentals, Refrigeration, HVAC Applications, and HVAC Systems and Equipment. The current versions of the four handbooks are shown below:[37]
Each volume of the ASHRAE Handbook is updated every four years. The Fundamentals Handbook includes heating and cooling calculations. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.
American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.
An HVAC technician is a tradesman who specializes in heating, ventilation, air conditioning, and refrigeration. HVAC technicians in the US can receive training through formal training institutions, where most earn associate degrees. Training for HVAC technicians includes classroom lectures and hands-on tasks, and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period.[citation needed] HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration.
The Chartered Institution of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical, heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirements are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, engineers must also attain an Honours Degree and a master's degree in a relevant engineering subject.[citation needed] CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:
Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2%-3% of the GDP.
The Air Conditioning and Mechanical Contractors Association of Australia (AMCA), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Australian Refrigeration Mechanical Association and CIBSE are responsible.
Asian architectural temperature-control have different priorities than European methods. For example, Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people, as opposed to the Western focus, in modern periods, on designing air systems.
The Philippine Society of Ventilating, Air Conditioning and Refrigerating Engineers (PSVARE) along with Philippine Society of Mechanical Engineers (PSME) govern on the codes and standards for HVAC / MVAC (MVAC means "mechanical ventilation and air conditioning") in the Philippines.
The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was founded at New Delhi[38] in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India.[citation needed]
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