WQC MEP

A local air conditioning system is a complete package that can contain cooling and heating source, a circulation fan, a filter, and control devices. There are three main types. Window air-conditioner. This system is a packaged device consisting of a vapour compression refrigeration cycle that contains a compressor, a condenser, an expansion valve, and an evaporator, in addition to a fan, a filter, control system and housing. Window air conditioners are mostly installed in a framed or unframed opening in building walls and in window openings without any ductwork and distribution the cooling or heating air effectively inside the conditioned space. The air conditioning consists of an evaporator and condenser where the condenser is located outside the space while the evaporate is inside the space, however, it serves the entire single zone with the thermal requirements. The heating process can be achieved by adding an electric resistance coil in the air conditioning or reversing the refrigeration cycle to act as a heat pump. Many feature designs are produced to provide aesthetical values and improve the quality and response. Unitary air-conditioner. It is similar to window air conditioners as far as the equipment is concerned but it is designed for commercial buildings. It is installed on the exterior wall of the building. There is a Horizontal hierarchy representation of the main types of local HVAC systems. A single zone will be having one unitary air-conditioner as in each guest room in many hotels. A packaged rooftop air- conditioner. It consists of vapour compression refrigeration cycle, a heat source such as heat pump and electric resistance; an air handler such as dampers, filter, and fan; and control devices. This system may be connected to ductwork and serve a large-size single zone that cannot be served by unitary or window air conditioners. Split systems. The split systems contain two central devices, the condenser, located outdoor, and the evaporator, located indoors. The two devices are connected by a conduit for refrigerant lines and wiring. This system takes care of small-scale single-zone systems since the location and installation of window, unitary or rooftop air conditioners may affect the esthetic value and architectural design of the building. The split systems consist of one condenser unit that is connected to multiple evaporator units to serve multiple zones as possible under the same conditions or different environmental conditions.

Smoke Detector is a device to fight against the smoke. By using ionization or photoelectric technique, the presence of the smoke is detected by the device. The components used include a photoelectric smoke detector, encoder, decoder, transmitter, receiver and siren. The relay is built in the smoke detector. On detecting the smoke, the relay is triggered. The relay then connects the transmit enable (TE) pin of the HT-12E encoder to ground causing the encoder to send a digital output to the transmitter. Apart from that, several smoke detector is one of the important things in placing them in the building. Even small buildings need more than one smoke detection system. The exact number depends on two things which are the number of levels in the building and the number of rooms. A house newly constructed requires a smoke alarm in each bedroom, one outside the bedroom area that is close enough to be heard through closed doors and a minimum of one on each level of the home. The objective of having a smoke alarm outside the bedroom area is to alert the sleeping occupants of a fire that starts outside of the bedrooms. Incase the bedrooms are located in different areas, then each area should have its smoke alarm. If a home is large, it is better to use more than one on each level. The closer the smoke alarm is the faster it will work. Moreover, the smoke detector should not be placed in garages for two reasons. First, garages are usually not heated or cooled. Sometimes, it is above or below the temperature range. Second, the smoke from engine exhaust fumes causes alarms and activates the smoke alarm. The HT12E is used for remote control application. It can encode N address bits and 12-N data bits information. The wireless smoke detection system is tested indoor and outdoor with smoke, noise, heat and flame itself. For the indoor test, a positive response is received for the first 70 meters because the signal fails to transmit over 80 meters onward. Even the distance between transmitter and receiver are tested in the building with the smoke and the presence of noise. Positive respond is recoded for the first 70meters. This result indirectly indicates that the noise is considered as a small interruption for signal transmission. On testing the system with heat and flame, negative results are recorded all over the range of distance due to the sensitivity of the smoke detector towards flame and heat. While for outdoor testing, the same procedures are used.

A well-designed return air strategy is essential for the performance of the HVAC system in an energy-efficient house with lower airflow requirements to meet the load. The return air must “see” a clear path from every room that has a supply outlet, except bathrooms or kitchens due to the potential for spreading odours through the house. A direct return from each room to the equipment is not desirable when trying to minimize duct lengths and pressure losses in the return system. Rooms without proper return air path tend to become pressurized, which will impede supply airflow and could result in comfort complaints. The usual door undercuts do not allow adequate return volume and are not appropriate for an energy-efficient house. Low resistance in the return air path has less than 0.05-inch water column (iwc) pressure loss. The pressure loss for a filter at the return grille must also be considered in the return air stream. The value for return capacity is two times the volume of the total supply air with an airflow velocity within the return at less than 500 feet per minute and the net free area that is sized 1.5 times the cross-sectional area of the return duct. The central return strategy is the simplest and effective way to get air back to the air handler. Each room that has a door to close it off from the central space except for the laundry and the hall both utilize an over-the-door method to transfer from that room back to the central return. turn, it Even with the proper net free area and sizing of the return duct, airflow can be restricted by turbulent air at the entrance of the return duct, causing poor performance and noise issues should be placed in a central hallway where it is adjacent to the main living space of the house. The selection and placement of the supply air outlets are essential to provide comfort in the space. The air must be delivered in a manner that mixes the supply air with the room air without introducing unacceptable noise or causing the sensation of a draft on the occupant. The distribution of air in the room is the function of the shape and size of the air outlet. At the same time, the placement of the air outlet is as important to the comfort in the room as is the type of air outlet that is selected.

Some buildings have multiple zones or have a large, single-zone, which needs central HVAC systems to serve and provide thermal needs. Few buildings have a single zone which needs equipment located inside the zone itself, such as small houses and residential apartments. This type of system is considered as local HVAC systems since each equipment serving its zone without crossing boundaries to other adjacent zones (e.g., using an air conditioner to cool down a bedroom, or using an electrical heater for the living room). Therefore, a single zone requires only one-point control point connected to a Thermo- stat to activate the local HVAC system. Some buildings have multiple local HVAC systems as proper equipment serving specific single zones and controlled by the one-point control of the desired zone. However, these local systems are not connected and integrated into central systems, but still part of a large full-building HVAC system. There are many types of local HVAC systems. Local heating systems. A single zone requires a complete, single package of heating system which contains heat source and distribution system. Some examples include portable electric heaters, electric resistance baseboard radiators, replaces and wood stoves, and infrared heaters. Local cooling systems include active systems as air-conditioning systems that provide cooling, a proper air distribution inside a zone, and control of humidification, and natural systems as convective cooling in open window, evaporative cooling in fountains. Local ventilation systems are forced systems using devices such as window fan to allow air movement between outdoor and a single zone without changing in the thermal environment of the zone. Other systems used for ventilation are air circulation devices such as desk or paddle fans to improve the thermal comfort of the space by allowing the heat to be transferred by conventional mode. A local air conditioning system is a complete package that can contain cooling and heating source, a circulation fan, a filter, and control devices. A Window air-conditioner is a packaged device consisting of a vapour compression refrigeration cycle that contains a compressor, a condenser, an expansion valve, and an evaporator, in addition to a fan, a filter, control system and housing. Window air-conditioners can be installed in a framed or unframed opening in building walls and in window openings without any ductwork and distribution the cooling or heating air effectively inside the conditioned space. The air conditioning contains both evaporator and condenser where the condenser is located outside the space while the evaporate is inside the space, however, it serves the entire single zone with the thermal requirements. The heating process can be achieved by adding an electric resistance coil in the air conditioning or reversing the refrigeration cycle to act as a heat pump. Many feature designs are produced to provide aesthetical values and improve the quality and response. The unitary air-conditioner is similar to window air conditioners from the equipment perspective, but it is designed for commercial buildings. It is installed on the exterior wall of the building and generally located in Horizontal hierarchy representation of the main types of local HVAC systems.

A well-designed septic tank must fix a minimum residual detention time at which it becomes necessary to dislodge the tank. Many standards usually specify 24 hours. A minimum residual depth per occupant corresponding to the chosen residual detention time should also be specified. The overall residual depth is a result of the product of the residual depth per occupant and the number of occupant’s.For good design and for practical purposes, the overall residual depth value should not be lesser than 10cm and not more than 75cm. A very low residual depth will help in washing out the sludge and also interfere with inlet and outlet fittings while too high residual depth will result in a tank that is of low length and depth ratio which will be inefficient. Narrow tanks are opted to provide quiescent hydraulic conditions which favour settling and thus solids removal determine the volume of sludge that will accumulate in that period of time. The depth of sludge in the tank at this time is then obtained by dividing the volume of accumulated sludge with the plan area obtained as described above. The total depth of the tank is considered as the sum of sludge depth. Dividing the volume of sludge by the plane area gives the depth of the sludge. Thus the total depth of the tank is the sum of sludge depth, overall residual depth and depth of reserve volume. The depth of the reserve space should be equal to the residual depth since it is based on 24 hours detention time. If the overall depth of the tank is much higher than the length, a lower overall residual depth should be chosen and the design repeated residual depth and the depth of the reserve space. The reserved space must be equivalent to the volume of 24 hours of detention time. At last, the ratio of length to width is chosen and thus the length and the width can be determined. The length must be longer than the width so as to provide for quiescent conditions. Every septic tank is unique and therefore should be designed taking cognizance of the number of users, desired desludging interval and expected wastewater flow which is a function of water availability. It is essential to know when to expect to dislodge their tanks. This should be an intrinsic aspect of the design. Septic tanks should have enough initial volume for long term storage of sludge to avoid frequent desludging. Tanks with small volumes will soon get silted up with sludge thus requiring frequent desludging. People should not wait for their septic tanks to be overflowing with sludge before desludging as this reduces the life span of the whole system and also reduces the efficiency of the drain field or soak pit.

The use of hot water heating systems can be seen in many types of buildings and facilities, especially for single-family houses and low rise multiple-dwelling buildings. Many HVAC systems use hot water systems as the primary source for heating the distribution air. The alternate chilled water cooling systems (hydronic cooling) are popular in certain large residential buildings, hospitals, and office buildings. The main components of a hydronic system are:

1. Boiler (heating source) or Chiller (cooling source)

2. Circulating pump(s)

3. Expansion tank(s)

4. Heating load (radiators, convectors, HVAC units, etc.) or cooling load (terminal units, fan-coil units, HVAC units, etc.)

5. Air separator

6. Connected piping system

7. Make-up and fill water system

8. Control system.

   The hydronic system consists of

• Operating temperature;

• Pumping and piping arrangement

• Operating pressure.

Depending on the particular application and the type of the facility, the proper selection of the boiler(s) or chiller(s), pumping systems, piping arrangement, and control system are essential for an effective and economical hydronic system. Temperature Classifications.—the temperature classifications of the hydronic systems
can be categorized as

1) Low-temperature water (LTW) system
2) Medium temperature water (MTW) system
3) High-temperature water (HTW) system
4) Chilled water (CW) system
5) Dual temperature water (DTW) system.

Low-Temperature Water (LWT) System: The maximum temperature limitation, in this case, is 250°F, The maximum allowable working pressure is 160 PSIG. The maximum working pressure depends on the static head of the building (height of the building) and the location of the system pump(s). It is recommended for working pressure of higher than 60 psi to use steam to water or water to water heat exchanger(s) so that the heating boiler and its closed piping loop can be separated and to operate at lower operating pressure without being affected by the high system working pressure. Separating the boiler by using heat exchanger(s) from the rest of the system minimizes boiler leaks and prolong the life of the boiler. Medium Temperature Water (MTW) System: In this case, the working temperature is ranged between 250°F and 350°F with an operating pressure of 300 PSIG. The maximum temperature is 400°F. Chilled Water (CW) System: In this case, the chiller(s) operates to provide a supply water temperature of 40 to 55° F, and a pressure of up to 120 PSIG. For temperatures below 40°F, mostly in process applications, antifreeze of brine solution may be used. Dual Temperature Water (DTW) System: In this case, both boiler(s) and chiller(s) are used with the common piping system to provide hot water heating and chilled water cooling. The maximum operating temperature of the heating water is limited to 180°F and
minimum 40°F for the chilled water.

 

Two basic types of evaporative cooling devices are used. The first of these, the direct- contact or an open cooling tower, exposes water directly to the cooling atmosphere, thereby transferring the source heat load directly to the air. The second one called a closed-circuit cooling tower, consists of indirect contact between heated fluid and atmosphere, essentially combining a heat exchanger and cooling tower into one relatively compact device. The most rudimentary of contact devices is a spray filled tower that exposes water to the air without any heat transfer medium or fills. In this device, the amount of water surface exposed to the air depends on the spray efficiency, and the time of contact depends on the elevation aid pressure of the water distribution system. To increase the contact surfaces and time of exposure, a heat transfer medium, or fill, is installed below the water distribution system, in the path of the air. The two types of fill-in use are splash type and film-type. Splash-type maximizes contact area and time by forcing the water to cascade through successive elevations of splash bars arranged in staggered rows. Film-type fill achieves the same effect by causing the water to flow in a thin layer over closely spaced sheets, principally polyvinyl chloride (PVC), that are arranged vertically. Either type of fill can be used in counter-flow and cross-flow towers. For thermal performance levels typically encountered in air conditioning and refrigeration, a tower with film-type fill is usually more compact. However, the splash-type fill is less sensitive to initial air and water distribution and, along with specially configured, more widely spaced film-type fills, is preferred for applications that may be subjected to blockage by scale, silt, or biological fouling. Closed-circuit cooling towers contain separate fluid circuits. An external circuit, in which water is exposed to the atmosphere as it cascades over the tubes of a coiled bundle, and an internal circuit, in which the fluid circulates inside the tubes of the coil bundle. In operation, heat flows from the internal fluid circuit, through the tube walls of the coil, to the external water circuit and then, by heat and mass transfer, to atmospheric air. As the internal fluid circuit never contacts the atmosphere, it +can be used to cool fluids other than water and/or to prevent contamination of the primary cooling circuit with airborne dirt and impurities. Some closed-circuit cooling tower designs with cooling tower fill to augment heat exchange in the coil.