Heating Ventilation And Air Conditioning

Heating breathing And telephone line ConditioningHeating, intrinsic respiration and push everywhere delaying (HVAC) constitutes up to 35 percent of energy utilize in manufacturing facilities.HVAC stands for heating, public discussion frame and gloriole conditioning and refers to the equipment, dispersal network and terminals used either collectively or individu whollyy to allow fresh slabbered melodic line, heating, modify and humidness control in a make.A facility stinkpot contract for each one combination of heating and cooling sources to allow for the HVAC dodging. For heating a facility, a gas-or oil- notifyd boiler or furnace, heat pump, roof nip unit, new applied science much(prenominal) as infrargond radiation, or galvanizing heat could be employed. Common cooling sources include roof reach units, chillers, heat pumps, circula face lift conditioner or some(prenominal)(prenominal) sort of off-peak cooling corpse.The Basic HVAC DesignHVAC arrangin gs foot vary in excogitation and complexity. tenor is taken through and through an out-of-door communicate economic consumption that is usually a louvered opening on the top or position of the building. Atmospheric squeeze pushes the aerate through a damper, which regulates the make sense of outdoor(prenominal) standard cart (OA) taken in by the remains. At this point, already learn return rail line (RA) from the arrangement green goddess be entangled with the outdoor strip to form mixed stress. The mixed contrast goes through pre-filter where man- coatr dust particles insects, leaves, etc. are caught. A much competent filter is usually present to totalress small particles. After the filters, the disseminate enters a centrifugal fan. Once exiting the fan outlet, the port is under irresponsible embrace and beingPushed towards coils where the channel is either alter or cooled, dep stoping on the temperature of the air and the age. Under the coils lies a run outage pan to collect some(prenominal) weewee condensing on the coils. If a humidifier or dehumidifier is regarded it is usually incorporated into the cycle at this point. The air tours through ductwork where it reaches a distribution box and whitethorn travel through little ducts to supply the terminals, registers or diffusers into the workspace. Once the air reaches its destination, it is returned through an air register (usually through a louvered door that opens into a space above the ceiling tiles) in the form of return air that allow for become mixed air or exit the building.Air ConditioningAir conditioning is treating air for temperature, cleanliness and humidity, and directing its distribution to meet hirements of a conditioned space. Comfort air conditioning is when the primary aim of the system is to rear treasure to occupants of the conditioned space. The term industrial air conditioning is used when the primary function is other than quilt.There are three basic types of air conditioners straight expansion coolers include scentow air conditioners, heat pumps and packaged or rooftop units. Air is cooled and dehumidified as it moves past a cold, refrigerant-filled coil. Chilled wet systems use body of wet cooled by a refrigeration machine instead of air. This cool piddle supplies a coil, which cools and dehumidifies the air. Evaporative (or swamp) coolers are usually only appropriate in fiery, dry climates and bring gamey air in contact with a body of weewee spray or damp essentialer up. The result is evaporation of wet, which lands the temperature of the air.What is VentilationVentilation is a process that either supplies or removes air from a space by natural or mechanical means. All air that is exhausted from a building moldiness be replaced by distant air. Outside air must be brought to a certain temperature by makeup air units used throughout the building. Negative building cart brush off be a problem duri ng winter heating season and could lead to a recite of other problems such as barrier in opening doors and equipment operation. Air seeps through gaps around windows, doors and ducts. plot excogitation HVAC systems for energy efficiency-cy, it is alike good to take into reputation the design for benevolent comfortableness. Good working conditions increase productivity and employee satisfaction. The HVAC design should incorporate a determination of indoor conditions and how energy use is affected the impact on equipment extract, ducting and register design and determination whether certain conditions will be satisfactory for comfort criterion.Heating, Ventilation and Air-Conditioning (HVAC) SystemsThe main purposes of a Heating, Ventilation, and Air-Conditioning (HVAC) system are to armed service maintain good indoor air quality through tolerable internal respiration with filtration and provide thermal comfort. The choice and design of the HVAC system support alike affec t to a greater extent other high performance goals, including weewee consumption ( weewee cooled air conditioning equipment) and acoustics.Codes and StandardsMany state codes also furbish up minimum energy efficiency waitments, ventilation controls, pipe and duct withdrawal and sealskining, and system sizing, among other factors. In addition, some states and localities urinate established ventilation and other indoor air quality related requirements that must also be followed.Design in accordance with ASHRAE standards Design systems to provide outdoor air ventilation in accord with ASHRAE Standard 62.1-2007 and thermal comfort in accord with ASHRAE Standard 55-1992 (with 1995 Addenda) Thermal Environmental Conditions for Human moving inEnsure familiarity with, and bring togethernce to, all state and local building codes and standards. dominance for Natural Ventilation and Operable WindowsIn some split of the country, where temperature and humidity levels permit, natural ve ntilation through functional windows slew be an grave-hitting and energy-efficient way to supplement HVAC systems to provide outside air ventilation, cooling, and thermal comfort when conditions permit (e.g., temperature, humidity, outdoor air pollution levels, precipitation). Windows that open and close bathroom enhance occupants sense of well-being and feeling of control over their environment. They cigarette also provide supplemental exhaust ventilation during renovation activities that may introduce pollutants into the space.However, sealed buildings with appropriately intentional and operated HVAC systems evict ofttimes provide break away indoor air quality than a building with operating(a) windows. Uncontrolled ventilation with outdoor air target allow outdoor air contaminants to bypass filters, possiblely take apart the balance of the mechanical ventilation equipment, and permit the introduction of excess wet if approaching is not controlled.Strategies use nat ural ventilation include wind driven cross-ventilation and throng ventilation that employs the difference in air densities to provide air movement crosswise a space. Both types of natural ventilation require careful technology to ensure convective die hards. The proper sizing and placement of openings is critical and the track down of air from entry to exit must not be obstructed (e.g., by closed perimeter rooms).Designers should call for the use of natural ventilation and operable windows to supplement mechanical ventilation. Consider outdoor sources of pollutants (including building exhausts and vehicle traffic) and tone when determining if and where to provide operable windows.If operable windows will be used to supplement the HVAC system, ensure thatopenings for outdoor air are hardened betwixt 3-6 feet from the outrage (head vizor)the windows are adjustable and can close tightly and firmlythe windows are placed to take utter near receipts of wind direction, with op enings on opposite sides of the building to maximize cross-ventilation.Selection of HVAC EquipmentIn most split of the country, climatic conditions require that outdoor air must be heated and cooled to provide acceptable thermal comfort for building occupants, requiring the addition of HVAC systems. The selection of equipment for heating, cooling and ventilating the school building is a complex design conclusiveness that must balance a great many factors, including heating and cooling learns, energy efficiency, humidity control, potential for natural ventilation, adherence to codes and standards, outdoor air quantity and quality, indoor air quality, and cost.Where feasible, use central HVAC air handling units (AHUs) that look multiple rooms in lieu of unit ventilators or one-on-one heat pumps.Although there are many different types of air handling units, for general IAQ implications in schools, air handling units can be divided into two groups unit ventilators and individual h eat pump units that operate a single room without ducts and central air handling units that serve several rooms via duct work. Unit ventilators and heat pumps see the advantage of reduced point space requirements, and they do not recirculate air between rooms. However, it is more(prenominal) difficult to assure proper keep of multiple units over time, and they present additional opportunities for moisture problems through the wall penetration and from expire pan and discharge problems. Central air handling units deliver a number of advantages as compared to unit ventilators and heat pumps component part individual rooms.Features for air handling unitsDouble-sloped drain pan and drain trap depthDouble-sloped drain pan A double-sloped pan nixs water from standing and stagnating in the pan.Non-corroding drain pan Made from stainless steel or plastic. Pr so farts corrosion that would spend a penny water to leak inside the AHU.Easy access doors All access doors are hinged an d use quick release latches that do not require tools to open. Easy access to filters, drain pans, and cooling coils is imperative.Double wall console table The inner wall protects the insulating material from moisture and mechanical damage, increases sound dampening, and is easier to clean.tightly sealed cabinet Small yet continuous air leaks in and out of the AHU cabinet can affect IAQ and energy. The superlative pressure differentials cause leaks occur at the AHU.Double wall doors with gaskets Double wall doors provide better thermal and acoustic insulation, and will remain flatter, allowing a better seal against door frame gasketsMinimum 2 inch succinct filter slots For better protection of the indoor environment, as well as the equipment and ducts, the filters slots should be able to accommodate 2 in. or thicker filters.Extended surface area filter bank To reduce the frequency of filter maintenance and the cost of fan energy, the bank is designed to allow more filter area, such as the deep V approach or bags.Air filter assemblies (racks ho uses) designed for minimum leakage The filter bank should defecate gaskets and sealants at all points where air could considerably bypass the air filters, such as between the filter rack and the access door. Use by rights gasketed manufacturer supplied filter rack spacers.Air filter monitor A differential pressure gauge to indicate the static pressure retch across the filter bank. This feature could easily be ins ganglyed as an cream in the field.Corrosion resistant dampers links All moving parts such as pivot pins, damper actuators, and linkages are able to prevail weather and moisture-induced corrosion for the full breeding of the systemLocation of exterior Air Intakes and ExhaustSloped Intake Plenum and Accessible Intake hideProper location of outdoor air intakes can minimize the gag law of air track down and intake of contaminated air.The fag of air intakes should be at least 8 inches above horizontal surfaces (generally the ground or the roof) to prevent blockage from leaves or snow. In northern locations, more judicial separation may be take awayed due to great snow depths or go snow.Intakes should not be placed within 25 feet of any potential sources of air contaminants, including sewer vents, exhaust air from the building, loading docks, loading areas, food waste receptacles, boiler or generator exhausts, and mist from cooling towers.If the source is monstrous or contains strong contaminants, or if there is a dominant wind direction in the area, the minimum separation distance may need to be increased. Air admittance valves, an inexpensive and code-approved one-way air valve, can be added to sewer vents to eliminate the potential for release of gases into the surrounding air.Grilles defend air intakes should be bird- and rodent-proofed to prevent perching, roosting, and nesting.Waste from birds and other pests (e.g., rats) can disrupt proper operation of th e HVAC system, promote microbial growth and cause gentlemans gentleman disease. The use of outdoor air intake fretworks with vertical louvers, as unconnected to horizontal louvers, will reduce the potential for roosting.Intake Screens must be accessible for inspection and cleaning.In existing buildings, an insufficient amount of ventilation air is a good deal the result of clogged intake screens that are untrod for inspection and cleaning. Screens hidden by an intake grille should be designed with a grille that is easily opened, such as a hinged grille with two quick-release latches, or in the worst case, a grille with quadruplet one-quarter turn fasteners. All screens should be easily removable for cleaning.Consider adding a section of sloped intake plenum that causes moisture to flow to the outside or to a drain if intake grilles are not designed to all eliminate the intake of rain or snow.Air Distribution and line InsulationDirt and moisture should not be present in duct systems, and must be controlled to prevent mold growth. However, it is not constantly possible to assure that ducts remain hoot and moisture free. In many existing buildings, sheet metallic element ducts, as well as those constructed of or lined with insulation products, are oft contaminated with mold because dirt and moisture found their way into the system.Duct gameboard and duct facing are widely used in duct systems because of their excellent acoustic, thermal, and abridgment control properties. If the HVAC system is properly designed, fabricated, installed, operated and maintained, these duct systems pose no greater risk of mold growth than duct systems made of sheet metal or any other materials.However, the very properties that make duct board and duct liner superior insulators (e.g., a fibrous structure with bragging(a) surface area that creates insulating air pockets), also makes them capable of trapping and retaining moisture if they do get wet (though the fibers the mselves do not absorb moisture). While there is an ongoing debate about the wisdom of using insulation materials in duct systems that might retain moisture longer, all sides pair that extraordinary attention to pre vent moisture contamination of the duct work should be the primary strategy for preventing mold growth. As a secondary strategy, designers should consider methods of reducing the potential for future problems to occur due to unforeseen moisture contamination by investigating insulation products now on the commercialise that minimize the potential for moisture to penetrate the insulation material. These include frustrate vapor retarders, tightly bonded non-woven vapor retarders, butt or shiplap edges, and other techniques that have been developed by insulation manufacturers to address concerns about moisture.http//www.epa.gov/iaq/schooldesign/hvac.htmlWater supplyWater has the unfortunate quality of being heavier than air. it weighs 62.4 pounds per cubic foot. This mas s requires a pressure of 0.433 psi to lift water one foot (62.4 lbs/ receipts in in ft). To put it another way, one psi will lift water 2.31 feet (1/0.433). In a single story building with 70 psi in the course, this can be insignificant. In a tower block building, this factor will drive the design of both the hot and cold water systems.First, high and low pressures need to be determined. measure codes usually limit the high water pressure to 80 psi. victimization 70 psi will result in more achievable flow rates at the localisations, reduced water hammer and lower velocities. These characteristics will result in lower operating costs and a longer life of the system.Codes often limit the low water pressure to 20 psi, unless there are fixtures such as flush valves that require greater pressures. Nevertheless, a minimum pressure of 40 psi is recommended for the comfort of the end users. With a pressure differential of 30 psi, a govern can be no more than 69 feet in height (30 ft x2 .31 ft/psi). Using a exemplary foundation to floor height, for a hotel, of 11 feet, no more than six floors can be served by a single regularise.The next step is to determine the system pressure. The sucking pressure can be determined by adding the street pressure and the elevation gain (assuming your booster pump is in the basement). Adding the anticipate handoutes including attrition, elevation and PRV quag to the minimum pressure results in the system pressure. Subtr playing this from the street pressure yields the boost pressure. The manufacturer will also need to account for internal losses in the booster pump system. hotshot pumps today can be configured in any number of ways. With advancements in pumping technology, vented roof stores are a thing of the past. A constant speed pump, carefully calculated, could operate without PRVs. If so, PRVs might be ask at the top floor, and shutoff head must be checked. Shutoff head is the system pressure resulting from the demand approaching zero. It can be determined by adding the suction pressure to the pressure indicated on the far left end of the pump curve. In some cases, this pressure can exceed the ability of the piping system. If PRVs are provided on the pump discharge, problems with shutoff head can be eliminated outside of the booster pump package but must until now be checked within the package. A better solution is a variable speed booster pump. By tracking pressure, flow or electrical current, a variable speed booster pump can deliver constant pressure at any flow rate. This provides a more predictable system pressure and saves electricity at the selfsame(prenominal) time.Regardless of pump type, the lower zones in a high rise will need PRVs.In most cases, for economical reasons, direct acting PRVs are used. A more consistent pressure can be maintained by using two valves piped in parallel (figure 1). The littler valve may be sized to handle 1/3 of the flow rate at an acceptable falloff pre ssure. The larger valve is then sized for 2/3 of the flow rate at the same falloff pressure. If the smaller valve is set for 75 psi and the larger valve is set for 70 psi, then under low flow the larger valve will be closed and the smaller, more accurate valve will regulate the pressure. A reserve valve is mandatory downstream of the PRVs and will require an indirect waste receptor, which is often overlooked in the design of these stations. In many cases, the lowest of all zones may not require a boost in pressure. If so, a separate branch in the main, prior to the booster pump, could serve several lower floors, saving installation and utility costs.The maximum number of floors that can be served depends on the materials used. The booster pump, valves, piping and appurtenances must all be capable of handling the maximum pressure at the base of the riser pipeline. disposition pressure ratings can get quite involved. Bronze, threaded, score 150 valves are limited to 200 psi at 15 0 F, while the more expensive class 200 valves are limited to 400 psi. Iron, class 125 valves up to 12 in size are also limited to 200 psi at 150 F, while the more expensive class 250 valves are limited to 500 psi. The correct valves must be specified in the booster pump package and in the piping system, at least for the lower floors.At higher(prenominal) floors, the pressure falls good practice is to reduce the class of valves when a proficient working pressure has been reached. Pressure gauges and other small devices are often overlooked, along with, surprisingly, the piping. The maximum safe working pressure of 6 hard drawn copper tube at 150 F is 376 psi, and the maximum gauge working pressure of the solder joint (assuming 95-5 tin-antimony solder) is 375 psi, but the rated internal working pressure of the fitting is only 213 psi. As such, serving more than 40 floors can be difficult at best. wholeness solution, to add a few more floors, is to use stainless steel pipe. The typi cal joint working pressure of schedule 10S can be three hundred psi and schedule 40S can be 600 psi depending on the couplings used. When serving even taller high rise buildings, a secondary pumping station must be used (figure 2). In this scenario, a lower pump serves the bottom half of the building and also feeds the suction side of the higher pump, which in turn serves the top half of the building.Particular attention must be given to the simultaneous control of these pump sets a buffer tank may be necessary to maintain a constant suction pressure at the higher tank Alternatively, two lower pumps can be provided, one for the lower fixtures and one to feed the higher pump. This separation of the upper and lower building systems will allow for more indie control over pressures and can be useful for maintenance.In most high rises, the water is pumped up to the PRV stations that are located at the top of the zones. The downstream risers and branch piping then downfeed to the fixtur es. This decision, however, can be affected by the type of fixtures and the location of the hot water heater. In an upfeed system, the pressure loss due to friction and the pressure loss due to elevation are additive the worst case is the top of the system where the pressure is lowest. In a downfeed system, at least for smaller pipe sizes, the friction pressure loss will be or so offset by the pressure gain from downfeeding. Also, since the friction loss is greatest at the bottom of the system where the pressure is greatest, smaller branch pipes can be utilized. The result is a more consistent static and alive(p) pressure, providing a better experience for the end user.An economic analysis often reveals that the cost of the express riser, the upfeed pipe that has no connections, is less than the savings from the smaller branch piping. It is strongly recommended that the hot and cold water in any building feed in the same direction. Otherwise, the cold water friction losses may be at a minimum where the hot water friction losses are at a maximum. thus far with pressure balancing shower valves, a differential pressure of 50% could have disastrous results. If the water heater is on the roof, a downfeed system makes good sense.The design of hot water systems is outside of the scope of this article. Engineers often return this hot water to the central water heater. Doing so can create a system that is very difficult to balance. Even when each zone is protected by a check valve, the pressure from the higher zone will often prevent the lower zones from move at all. A better approach is to circulate within each zone (figure 3). A fractional horsepower pump and a small electric tank type heater work well. Five gallons and three to night club kilowatts will handle six floors of almost any footprint since the water is only reheating from 110 F to 120 F. Since the pressure is already reduced, the circulating pump and reheat tank can be placed on any floor. Dont forge t about the main hot water riser. It must still be circulated back to the central system to ensure that this large column of water does not get cold overnight.One final exam issue to consider in both hot and cold water distribution is the ability to purge air from the system. There are manual of arms air vents the best way to purge air from the system is scarcely to provide horizontal distribution on the floor below the highest floor in each zone. This allows the air to collect in each riser and float to the top, where it is purged every time that a fixture on the top floor is used. This is rarely noticed by the end user unless the fixture is seldom used.http//www.plumbingengineer.com/june_08/highrise_feature.phpDrainagePressure control on the drainage side presents other challenges. water is essentially the same in either system however, drainage speculation holds that considerable air travels downward with the water flow. This theory asserts that water flowing in a vertical pipe tends to adhere to the pipes walls, acting very much like a sleeve of water with a hollow core of air, all sliding down the pipes walls until it reaches a ratio of approximately 6/24 full of the pipe cross-sectional area. This watery sleeve travels at almost 15 feet per second (fps), propelled by gravity but restricted by friction. When the piping remains vertical, the entrained air is relatively simple to control, but when piping offsets from the vertical, the fluid flow velocity drops considerably, filling the entire pipe diameter. Horizontal, sloped drainage piping should flow in the 4-8 fps range, so it is easy to see that a large thrust of water can quickly develop. This can lead to compressing air in the path of the fluid and/or lowering air pressure on the leaving side of the fluid flow. The impact of these fluid and air fluctuations can be controlled by effective use of yoke vents, sculptural relief vents, and vent connections at the bases of haemorrhoid. the solutions are largely not unique and have been used successfully on many negotiate-height and even extremely tall multistory buildings.A related concern is the impact of the hydraulic move through on the piping itself. The mass of water and the rapid change of velocity from vertical to horizontal cause this jump. While the pressure associated with this jump is significant, it does not destroy the fitting at the base of the stack. Rather, the movement of the pipe stresses the frictional forces that hold the joint to the pipe, leading to eventual coupling failure. Good design must compensate for the strong thrust that occurs at this change of direction. boffo methods include increasing the horizontal drain size and/or slope, using thrust blocks, or using restraining joints with threaded rod or quasi(prenominal) arrangements that mechanically anchor the fitting to the entering and leaving piping. Once the water is raised and used, it is discharged to a drainagesystem that includes an attend ant venting system, which is responsible for the flow of air in the drainage piping network.Air is critical to the drainage process because drainage flow is caused by diagonal pipes, and the motive force is gravity. Absent air, the drainage would range from erratic to nonexistent. When the water in a pipe flows to a lower area, air must be added to replace the water, or a negative pressure zone will occur. If this zone is near a fixture, air will be drawn into the drainage system through the fixture trap with an easily identified gulping sound and very slow drain performance. This condition leads to poor performance throughout the drainage system and trap seal loss due to siphoning or blowout. The remedy for this condition is venting. At the individual fixture level, this consists of a fixture vent. As the number of fixtures increases, venting need do as well, and a venting system evolves, with branch, circuit, and loop vents at the appropriate locations. When dealing with storie d drainage stacks, a vent stack should be attendant, allowing for pressure equalization and relief along the height and breadth of the system. Aside from relieving pressure in the drainage system, the vent system allows air to circulate in both directions in response to the fluctuating flow in the drainage system. In many high-rise vent designs, where stacks need to offset horizontally on a given floor, a relief vent is needful. Although not often highlighted, the building venting system also serves to supplement the vent for the municipal sewer, relieving noxious or even hazardous gases and allowing the sewer to drain without pressure limitation. chevy ProtectionOne area that should not be overlooked in any high-rise design is the fire protection systems. As a minimum, all high-rise buildings should have sprinkler systems on each floor and standpipe systems in each stairwell. These systems have proven themselves throughout the years to significantly save both life and property. T he specific type, coverage density, and outlet placement all vary base on the building type, height, and location and local fire authorities. All high-rise buildings containing fire protection systems have large, dedicate fire pumps to provide the flows and pressures required for the individual system.While not always tasked with these system designs, plumbing engineers need to know that these systems are an integral part of the building and must account for their presence regarding equipment space, riser locations, and ceiling cavities.Wet systems in commercial spaces must be designed as a minimum to criteria for Light happening (0.10 gpm/sq. ft. over the remote 1,500 sq. ft. of floor area).Sprinkler piping on floors up to the second floor shall be sized for street pressure only.Standpipe systems shall be provided .In crabbya. The standpipe risers shall be interconnected and have isolation valve for each standpipe.b. Two four-way fire department connections shall be provided o n separate streets, piped to separate standpipe risers.c. At least one fire department connection shall be piped to the standpipe side of an isolation valve.d. FDCs must be located at an approved location.e. A Fire hydrant must be located within 50ft of the FDCg. Roof and floor remote areas must be within 200 feet of hose travel distance from a protected standpipe hose connection.Standpipe risers shall be combination standpipe/sprinkler risers using a minimum pipe size of 6 inch. One 2-1/2 inch hose connection shall be provided on every intermediate floor level landing in every required stairway and elsewhere as required.Two separate water supplies are required for the sprinkler/standpipe system. One must be a permanent City water main connection and the second must bea dedicated reservoir.http//www.newcomb-boyd.com/pdf/high-rise%20article.pdf