HVAC system requirements

Image result for HVAC system requirementsFour requirements are the bases for any HVAC systems i.e. primary equipment, space requirement, air distribution, and piping. Primary equipment includes heating equipment such as steam boilers and hot water boilers to heating buildings or spaces, air delivery equipment as packaged equipment to deliver conditioned ventilation air with the use of centrifugal fans, axial fans, and plug or plenum fans, and refrigeration equipment that delivers cooled or conditioned air into space. There are cooling coils based on water from water chillers or refrigerants from a refrigeration process. Space is essential in shaping an HVAC system to be central or local. It requires five facilities like the following:


a. Equipment rooms: The total mechanical and electrical space requirements are between 4 and 9% of the gross building area. It is preferable to be centrally located in the building to reduce the long duct, pipe, and conduit runs and sizes, to simplify shaft layouts, and centralized maintenance and operation.


b. HVAC facilities: heating equipment and refrigeration equipment may perform their primary tasks of heating and cooling the building by using several facilities. The heating equipment requires boiler units, pumps, heat exchangers, pressure-reducing equipment, control air compressors, and miscellaneous equipment, while the refrigeration equipment requires water chillers or cooling water towers for large buildings, condenser water pumps, heat exchangers, air-conditioning equipment, control air compressors, and miscellaneous equipment. The design of equipment rooms for placing the equipment should consider the size and the weight of equipment, the installation and maintenance of equipment, and the applicable regulations to combustion air and ventilation air criteria.


c. The HVAC fan equipment and other miscellaneous equipment are found in the fan room. The rooms should consider the size of the installation and removal of fan shafts and coils, the replacement, and maintenance. The size of fans depends on the required airflow rate to condition the building, and it can be centralized or localized based on the availability, location, and cost. It is preferable to have easy access to outdoor air.


d. Vertical shaft: this is used to provide enough space for air distribution and water and steam pipe
distribution. The air distribution contains HVAC supply air, exhaust air, and return air ductwork. Pipe distribution includes hot water, chilled water, condenser water, and steam supply, and condenser return. It also has the mechanical and electrical distribution to serve the entire building including plumbing pipes, fire protection pipes, and electric conduits/closets.


e. Equipment access: the equipment room should be such that it allows the movement of large, heavy equipment during the installation, replacement, and maintenance

Pipe joints

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Pipes are connected with the help of joints. A variety of joints are used in an assembly of pipes. Fitting refers to the connecting of two or more pipes together. Various types of joints could be used in a pipe as per the requirement. Joints are also used for multiple pipe connections and are an important component of the plumbing system. Generally, the pipe joint fitted can easily sustain the pressure
created in the pipe. Various types of pipe joints are as follows. 1. Threaded joint 2. Welded joint (butt welded, socket welded) 3. Brazed joint 4. Soldered joint 5. Grooved joint 6. Flanged joint 7. Compression joint.
Threaded joint: When pipes are joined by screwing in threads which are provided in the pipe, it is called a threaded joint. Pipes usually have internal threads and threads externally. The threads are also made in various pipes like PVC, CI pipes, copper pipes and GI pipes, etc. Threaded joints are used for various diameter pipes. Welded joints: It is one of the most common methods of joining pipes used in large infrastructure like a commercial, institutional and industrial systems. Cost of material is low, but the labour costs are more due to the non-availability of trained welders and fitters.
Socket-welded joints. These are used when there is a high chance of leakage in the joints. Pipes are joined by putting one into other and welding it around the joint. Pipes having different diameters are suitable for this type of joint. Socket-welded joint gives good results as compared to other joints.
Brazed joints: When pipes are joined with the help of molten filler material at above 840°C, it is called brazing. Brazing is used for connecting copper pipes or copper alloy pipes. It is important to note that the melting point of the parent material (pipe material) should be higher than the filler material. Brazed joints usually have very less mechanical strength and are used in case of moderate temperatures.
Soldered joints: Soldering and brazing are similar activities. In soldering, the filler material melts below 840oC. With the help of soldering, copper and copper alloy pipes are joined. During soldering, flux or metal joining material is used to prevent oxidation due to the flame. Soldered joints are suitable for low-temperature areas and have low mechanical strength.
Grooved joints: When two pipes are joined together by making grooves (narrow cuts or depression) at the end of pipes with the help of sockets or couplings, such joints are called grooved joints. Due to the ease of assembly of the grooved joints, the labour cost is less. The piping system can be easily uninstalled and reinstalled frequently for maintenance. These are mostly used for fire protection.

Operating conditions – AC

In real-time, any A/C-R system experiences a narrow or wide range of imposed operating conditions, depending upon the application. The imposed operating conditions may change due to one or a combination of the following reasons:

o Ambient temperature/humidity variations

o Conditioned space cooling demand variations

o Controller commands (usually an on-off command from a thermostatic controller)

Ambient temperature and humidity continuously vary and affect the operation of almost all components of A/C-R systems. The conditioned space cooling demand varies due to peripheral heat transfer variations as well as indoor heat generation changes. Cooling demand variations can happen gradually or suddenly depending upon the application. For conditioned spaces with either a high rate of door/window opening/closing or a repetitive loading/unloading of thermal mass, the variations in cooling demand can be high; however, for most applications the variations are not significant and do not suddenly affect the A/C-R system, due to the thermal mass of the conditioned space. In addition to the variations in the ambient or conditioned space temperatures and cooling demand, all A/C-R systems are equipped with a controller that commands the components to turn on/off or change their capacity. Accordingly, the controller command is another imposed parameter that affects the operational characteristics of an A/C-R system. Due to the existence of such variations in the operating condition of an A/C-R system, a transient model is required to simulate the behaviour of the system during unsteady conditions. Accordingly, in this research, the transient model is also developed. In the quasi-steady state approach for modelling A/C-R systems, it is assumed that at any instant the A/C-R system is at a quasi-equilibrium condition that can be considered as a steady-state condition. By this assumption, the modelling of real-time operation can be condensed into a time-marching steady-state approach. Based on this approach, modelling of the transient behaviour of A/C-R systems is divided into two steps:

1) quasi-steady-state modelling
2) fully transient modelling.

The main advantage of a quasi-steady-state the modelling approach is its lower computational costs with acceptable accuracy for most of the smooth transitions taking place in reality.

HVAC

The major classification of HVAC systems is a central system and decentralized or local system. Types of a system depend on addressing the primary equipment location to be centralized as conditioning entire building as a whole unit or decentralized as separately conditioning a Specific zone as part of a building. Therefore, the air and water distribution system should be designed based on system classification and the location of primary equipment. The criteria mentioned above should also be applied in selecting between two systems.
Four requirements are the bases for any HVAC systems are primary equipment, space the requirement, air distribution, and piping. Primary equipment includes heating equipment such as steam boilers and hot water boilers to heating buildings or spaces, air delivery equipment as packaged equipment to deliver conditioned ventilation air by using centrifugal fans, axial fans, and plug or plenum fans, and refrigeration equipment that delivers cooled or conditioned air into space. It includes cooling coils based on water from water chillers or refrigerants from a refrigeration process. Space requirement is essential in shaping an HVAC system to be central or local. It requires the following:
a. Equipment rooms: The total mechanical and electrical space requirements range between 4 and 9% of the gross building area so It must be centrally located in the building to reduce the long duct, pipe, and conduit runs and sizes, to simplify shaft layouts, and centralized maintenance and operation.
b. Facilities: heating equipment and refrigeration equipment require many facilities to perform their primary tasks of heating and cooling the building. The heating equipment requires boiler units, pumps, heat exchangers, pressure-reducing equipment, control air compressors, and miscellaneous equipment, while the refrigeration equipment requires water chillers or cooling water towers for large buildings, condenser water pumps, heat exchangers, air-conditioning equipment, control air compressors, and miscellaneous equipment. The design of equipment rooms to host both pieces of equipment should consider the size and the weight of equipment, the installation and maintenance of equipment, and the applicable regulations to combustion air and ventilation air criteria.
c. The HVAC fan equipment and other miscellaneous equipment are kept in the fan room. The rooms should consider the size of the installation and removal of fan shafts and coils, the replacement, and maintenance. The size of fans depends on the required airflow rate to condition the building, and it can be centralized or localized based on the availability, location, and cost. It is preferable to have easy access to outdoor air.
d. The vertical shaft is required to provide space for air distribution and water and steam pipe distribution. The air distribution contains HVAC supply air, exhaust air, and return air ductwork. Pipe distribution includes hot water, chilled water, condenser water, and steam supply, and condenser return. It also includes other mechanical and electrical distribution to serve the entire building including plumbing pipes, protection pipes, and electric conduits/closets.
e. Equipment room must allow the movement of large, heavy equipment during the installation, replacement, and maintenance

Septic System

A septic system is an underground wastewater treatment system so as to hold, treat and dispose of household wastewater. When the liquid portion leaves the system, it can eventually reach groundwater or surface water, and be recycled back into your drinking water source. If wastewater is improperly treated, it can pollute local water sources that you and your community use for drinking water or recreational activities. Proper care and maintenance of your septic system will help prevent contamination of local water sources, protecting the health of your family, community and the environment. As wastewater leaves the plumbing system and enters the septic tank, the solids, oils and grease will separate into different layers. Over a short time, the solids will sink to the bottom and become sludge, while the oils and grease will float to the top of the tank and form the scum layer. A septic tank is designed so that the scum and sludge do not clog up the drain field. The middle liquid layer in the septic tank (called effluent), will flow through a filter and into the distribution box before it reaches the drain field. The drain field is a series of perforated pipes buried underground, sitting in
trenches of drain rock. When the effluent enters the pipes, it seeps into the soil, where natural filtration occurs and microbes help to remove or alter the pollutants and pathogens that may be remaining. Suitable soil and adequate separation distances from water tables, helps the effluent safely return to the
groundwater. Sufficient effluent treatment is possible with the help of a depth of suitable soil. Raised mounds of engineered sand are required in some systems in order to properly treat the final effluent.

Pressurization is at times employed to provide better distribution in the drain field. Other systems, commonly referred to as Type II or Type III systems, employ mechanical/electrical equipment to provide additional treatment due to environmental needs on your property. This equipment can include aeration blowers, filtration media within the tank, additional filters or ultra violet disinfection vessels. All septic systems require Regular inspection and maintenance of septic systems is must to ensure they function as intended.

Lightning Arrester

Several preventive mechanisms are used to avoid lightning hitting tall buildings or houses where lightning incidence is high, but no lightning rod can offer absolute protection. A lightning rod protection system consists of three main parts:

  1. The rods on the top of the secured structure.

  2. The wires which connect the rods together and run down the sides of the structure to the grounding arrangement.

  3. The grounding arrangement.

The high voltage transmission lines are protected from lightning by replacing the metallic rods and wire conductors with a system of wires suspended between tall towers arranged around the structure. These grounded wires are strung above the high voltage lines to intercept strokes that would otherwise hit the power lines. If a lightning stroke hits a power line, the only way to protect it is by using a lightning arrester (LA). The lightning arrester is a non-linear device that acts as an open circuit to low potentials but conducts electrical current at very high potentials. When the lightning strikes a line that has been protected with a lightning arrester, the non-linear resistance draws the current to ground. The best -known lightning arresters is the MOV (Metal Oxide Varistor). The MOV has a piece of metal oxide that is joined to the power and grounding line by a pair of semiconductors. The semiconductors have varied resistance dependent on voltage. When the voltage level in the power line is at the rated voltage, the electrons in the semiconductors flow in a way that creates a very high resistance. In case the voltage level in the power line exceeds the arrester rated voltage, the electrons behave differently and create a low resistance path that conducts the injected lightning current to the ground system. Selecting an arrester for a distribution system is based on the system’s line-to-ground voltage and the way it is grounded. The limiting condition of an arrester does not usually have anything to do with the magnitude of the surges (switching or lightning) that it might see. This is in contrast to the selection of arresters for transmission. An arrester usually has a limited protective zone of only a few meters to up to several ten meters, where the protective zone is defined as the maximum separation distance for which the insulation coordination requirements are fulfilled for a given arrester protective level and coordination withstand voltage. Arresters, therefore, should be installed as close as possible to the device to be protected.

Filter Drier

The function of a filter-drier in a refrigeration system is to remove harmful contaminants. If the contaminants are at a higher level, they will jeopardize the longevity of the system. Contaminants that are commonly found include moisture, acid, copper oxides, metal chips, wax-like compounds and others. Selecting a filter-drier for a particular application requires various technical factors to be considered. The major factors are the type of system, connecting line size, water capacity, flow capacity (size of system), filtration capability, acid capacity, the material of construction(steel vs. copper), and design pressures. Evaluation of each factor is necessary to ensure proper and economical filter-drier design. The capability to remove moisture from a refrigerant system is a fundamental function of the filter-drier. Moisture can come from a few sources like trapped air from improper evacuation, system leaks, and motor windings or due to improper handling of polyol ester (POE) lubricants, which are hygroscopic; that is, they readily absorb moisture. POEs can pick up more moisture from their surroundings and keep it much faster than the mineral oils which have been used for many years. This moisture can lead to freeze-ups and corrosion of metallic components. Moisture in the system can hydrolyze the POE lubricant, forming organic acids. These acids, if they exist in significant quantity, will react with materials within the system and can adversely affect component operation. To prevent the formation of acids, the moisture must be minimized. This is accomplished by the use of a filter-drier that utilizes molecular sieve and activated alumina. Molecular sieves are crystalline sodium alumino-silicates (synthetic zeolites)having cubic crystals which selectively adsorb molecules based on molecular size and polarity. The crystal structure is honeycombed with regularly spaced cavities or pores that are uniform in size. This permits molecules, such as water, to be adsorbed, while allowing other larger molecules, such as the refrigerant, lubricant and acids to pass by. The surface is charged positively with cations, which act as a magnet and will, therefore, adsorb polarized molecules, such as water, first and hold them tightly on the structure. The major differences in using steel vs.copper filter-driers are the system sizes and applications. Copper filter-driers are normally used in smaller, less complex applications, systems with fewer pressure fluctuations and lower vibration tendencies. Some smaller systems do not require high filtration capabilities; however, some of the smaller systems using the new refrigerants will require better filtration. In order to meet these requirements, a moulded core construction and filter-driers with additional fibrous media and screen should be considered. Copper is again the most economical option for smaller systems. Because copper driers are used for smaller applications, the refrigerant charge required will generally be smaller than in the steel filter-drier.

Kitchen Ventilation

The effectiveness of ventilation effectiveness is the ability of the ventilation system to achieve design conditions in the space (air temperature, humidity, the concentration of impurities and air velocity) at minimum energy consumption. The air distribution methods used in the kitchen should be one that provides adequate ventilation in the occupied zone, without disturbing the thermal plume. In the case of a commercial kitchen, the airflow rate required to ventilate the space is a major factor that contributes to the system energy consumption. Traditionally high-velocity mixing or low-velocity mixing systems are taken into consideration. An alternative that clearly demonstrates improved thermal comfort over mixing systems, is displacement ventilation. The supply of air (make-up air) can be delivered to the kitchen in two ways:

high velocity or mixing ventilation

low velocity or displacement.

The airflow and air distribution methods that are used in the kitchen should be one that provides adequate ventilation in the place where it is installed, without disturbing the surrounding air as it rises into the hood system. As per the standards states ventilation rate over 40 vol. /h effect on the basis of the heat load may influence to droughts. The location of the installed ventilation is also important for providing good ventilation. Ventilating systems should be designed and placed so that the ventilation air is provided equally throughout the occupied zone. Locating the supply and exhaust units too close to each other, causing ‘short-circuiting’ of the air directly from the supply opening to the exhaust openings are some common faults. Installation of supply diffusers of high velocity close to the hood system leads to a reduction in the ability of the hood system to give ample capture and containment (C&C) of the thermal plume. It is a known fact that the type of air distribution system utilised affects the amount of exhaust needed to capture and contain the effluent created in the cooking process. A properly designed and sized kitchen hood will ensure that effluents and convective heat (warm air) from the cooking process are captured; however, it is not sufficient to ensure the kitchen space temperature is comfortable. The radiation load from appliances under the hood, heat from appliances not under the hood, people, lights, kitchen shell (heat transfer through walls and ceiling), solar load, and implied heat and moisture from untreated makeup air are to be managed by the kitchen air conditioning system. It is recommended that a negative air balance be maintained in the kitchen. A simple rule of thumb is that the amount of air exhausted from the kitchen should be at least 10% higher than the supply air flow into the kitchen. This will guarantee that the odours from the kitchen do not spread to the adjacent spaces.

Prevention of fire and safety in buildings

fire-extinguisher-prevention - WQCMEP

A manual alarm system may be the minimum standard required in a building since there is no other risk. However, there are often circumstances in which an automatic fire detection system is needed. For example, this could be needed to compensate for some departure from the guidance in the local building code, or as a component of the operating system for a fire protection system. It is also required where a fire could break out in an unoccupied part of the building, which prejudices the means of escape from the occupied parts. The automatic fire detection system has to be designed, installed and maintained in accordance with the relevant standard. If maintenance of fire detection and fire fighting systems and equipment is contracted out, this should be under the terms of a clearly defined service level agreement (SLA) Automatic smoke vents are generally provided to assist in case of fire and escape from the building. By making smoke ventilation, the occupants can escape from the building underneath the smoke layer in reasonably safe conditions. Apart from that manually operated smoke vents are generally provided to aid the fire and rescue service with smoke clearance once the fire has been extinguished. In case both the sprinkler systems and smoke vents are provided in a building the interaction between them has to carefully considered. Studies showed that the provision of automatically operating smoke vents can cause delays in the operation of sprinkler systems. This is because of the automatic smoke vents open when triggered by smoke, whereas sprinklers operate when the heat is detected. Since smoke can be detected more quickly than heat, the sprinklers would perform more effectively if there were no vents because the building would fill with smoke; this, in turn, will create low oxygen conditions which limits combustion, allowing the sprinklers to extinguish the fire more effectively. However, where life safety is the predominant concern and a smoke control solution is used to protect the escape routes within a building, current guidance requires the smoke vents to operate automatically; the vents will thus start functioning before the sprinkler system. On the other hand, if the fire service response time is short, and the sprinkler system is provided with fast response, the smoke ventilation system can be activated by the flow switch in the sprinkler supply. Compartments that come under the category of the building are those enclosed in fire- resisting construction; this approach provides passive fire protection by inhibiting the spread of fire within the building. In order to comply with local building regulations, the size of individual compartments may have to be limited. The size of the Compartment is determined by the overall size of the building, the number of storeys, and whether or not an automatic sprinkler system is provided. Preventing fires from occurring is as important as having properly working fire safety systems to deal with a fire incident. The main objective is to create an operating environment in which fires are prevented from starting in the first place. In case of fire does the first option is to prevent it from developing beyond a very minor event.

fire-prevention-measures-for-high-rise-buildings - WQCMEP

What is a Surge Arrester?

Surge arrester generally uses the body and air gap, and surge arrester does not assume system operating voltage, without considering the long-running voltage electrical ageing, also the body failure does not affect operation. when a lightning flash directly strikes the tower, part of the lightning current flows through the grounding wire to the adjacent tower, the other part of the lightning flows into the earth through the tower, grounding resistance of tower manifested transient resistance characteristic, it is generally characterized by the impulse grounding resistance. The lightning current associated with the location and atmospheric conditions, reducing grounding the resistance of tower is the main measures for improving lightning withstand the level of transmission lines without the use of surge arresters. Especially ˈ it is very difficult to reduce grounding resistance in the mountains, which led to line tripping frequently struck by lightning.

After the installation of surge arresters, surge arrester is parallel with insulator. When transmission line being struck by lightning, part of the lightning current flows through the grounding wire to the adjacent tower, the other part of the lightning current flows into the earth through the tower. When there is an excess of lightning current than the action value of the arrester, the current will flow through the arrester. After lightning current pouring, continuous frequency current flowing through the surge arrester is only mA level, the arrester will cut off continuous frequency current in the first zero crossings of current, so dielectric strength fast recover. As such a surge arrester is capable of ensuring that the insulator string flashover does not occur, thus achieve the goal which prevents transmission line lightning trip. Effect of lightning protection with surge arrester on transmission line has been compared with other lightning protection measures. The surge arresters can to a great extent reduce lightning accidents for transmission lines in complex terrain and high soil resistivity area. Distribution network develops rapidly at the present time, a large number of the line put into operation each year, expanding the size of the line increases the probability of lightning trip and created a lot of difficulty in lightning protection work. From the technical economy view, not all towers can be installed by surge arresters, so we should selectively install arresters combined with the line being struck by lightning frequency and landform characteristics and so on. Thus it can be said that the line surge arrester effectively avoids the lightning trip accidents occurring by way of installing line surge arrester after correctly choosing the tower which easily is struck by lightning so that lightning withstands the level of transmission lines has been effectively improved.

Given the current situation in lightning protection work proposed to continue to promote the application of line surge arrester, the effect of line arrester depends on correctly selecting the section or the tower which has chances of stroke. At the same time, a lot of arresters hanging on the towers to a certain extent increase the pressure of maintenance of the line, it should be appropriately controlled the scale.