Hvac notes pdf free download

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Many sizeable single story buildings such as supermarkets, discount stores, can be effectively conditioned by a series of single zone systems. Large office buildings are sometimes conditioned by a series of separate single zone systems. In a multi-zone all-air system, individual supply air ducts are provided for each zone in a building.

Cold air and hot or return air are mixed at the air handling unit to achieve the thermal requirement of each zone. A particular zone has its conditioned air that cannot be mixed with that of other zones, and all multiple zones with different thermal requirement demand separate supply ducts, as shown in Figure 5.

Multi-zone all-air system consists of an air handling unit with parallel flow paths through cooling coils and heating coils and internal mixing dampers. It is recommended that one multi-zone serve a maximum of 12 zones because of physical restrictions on duct connections and damper size. If more zones are required, additional air handlers may be used. The advantage of the multi-zone system is to adequately condition several zones without energy waste associated with a terminal reheat system.

However, leakage between the decks of air handler may reduce energy efficiency. The main disadvantage is the need for multiple supply air ducts to serve multiple zones.

All-air HVAC system for multiple zones. A terminal reheat all-air system is a multiple zone, which considers an adaptation of single zone system, as shown in Figure 6. This can be performed by adding heating equipment, such as hot water coil or electric coil, to the downstream of the supply air from air handling units near each zone. Each zone is controlled by a thermostat to adjust the heat output of heating equipment to meet the thermal condition. The supply air from air handling units is cooled to the lowest cooling point, and the terminal reheat adds the required heating load.

The advantage of terminal reheat is flexible and can be installed or removed to accommodate changes in zones, which provides better control of the thermal conditions in multiple zones.

However, the design of terminal reheat is not energy-efficient system because a significant amount of extremely cooling air is not regularly needed in zones, which can be considered as waste energy. Therefore, energy codes and standards regulate the use of reheat systems. Single duct system with reheat terminal devices and bypass units. The dual duct all-air system is a terminal-controlled modification of the multi-zone concept.

A central air handling unit provides two conditioned air streams such as a cold deck and a hot deck, as shown in Figure 7. These air streams are distributed throughout the area served by the air handling unit in separate and parallel ducts. Each zone has a terminal mixing box controlled by zone thermostat to adjust the supply air temperature by mix the supply cold and hot air. This type of system will minimize the disadvantages of previous systems and become more flexible by using terminal control.

All-air HVAC dual-duct system. Some spaces require different airflow of supply air due to the changes in thermal loads. Therefore, a variable-air-volume VAV all-air system is the suitable solution for achieving thermal comfort.

The previous four types of all-air systems are constant volume systems. The VAV system consists of a central air handling unit which provides supply air to the VAV terminal control box that located in each zone to adjust the supply air volume, as shown in Figure 8. The temperature of supply air of each zone is controlled by manipulating the supply air flow rate.

The main disadvantage is that the controlled airflow rate can negatively impact other adjacent zones with different or similar airflow rate and temperature. Also, part-load conditions in buildings may require low air-flow rate which reduces the fan power resulting in energy savings.

It may also reduce the ventilation flow rate, which can be problematic to the HVAC system and affecting the indoor air quality of the building.

In an all-water system, heated and cooled water is distributed from a central system to conditioned spaces [ 4 , 5 ]. This type of system is relatively small compared to other types because the use of pipes as distribution containers and the water has higher heat capacity and density than air, which requires the lower volume to transfer heat. All-water heating-only systems include several delivery devices such as floor radiators, baseboard radiators, unit heaters, and convectors.

However, all-water cooling-only systems are unusual such as valance units mounted in the ceiling. The primary type that is used in buildings to condition the entire space is a fan-coil unit. Fan-coil unit is considerably small unit used for heating and cooling coils, circulation fan, and proper control system, as shown in Figure 9. The unit can be vertically or horizontally installed. The fan-coil unit can be placed in the room or exposed to occupants, so it is essential to have appropriate finishes and styling.

For central systems, the fan-coil units are connected to boilers to produce heating and to water chillers to produce cooling to the conditioned space. The desired temperature of a zone is detected by a thermostat which controls the water flow to the fan-coil units. In addition, occupants can adjust fan coil units by adjusting supply air louvers to achieve the desired temperature.

The main disadvantage of fan-coils is ventilation air and only can be solved if the fan-coil units are connected to outdoor air. Another disadvantage is the noise level, especially in critical places. All-water system: fan-coil units. Air-water systems are introduced as a hybrid system to combine both advantages of all-air and all-water systems [ 5 ]. The volume of the combined is reduced, and the outdoor ventilation is produced to properly condition the desired zone.

There are two main types: fan-coil units and induction units. Fan-coil units for air-water systems are similar to that of all-water systems except that the supply air and the conditioned water are provided to the desired zone from a central air handling unit and central water systems e.

The ventilation air can be separately delivered into space or connected to the fan-coil units. The major types of fan-coil systems, are 2 pipes or 4-pipes systems, as shown in Figure Air-water HVAC system using fan coil units with 4-pipes configuration. Induction units are externally similar to fan-coil units but internally different.

An induction unit induces the air flow in a room through cabinet by using high-velocity airflow from a central air handling unit, which replaces the forced convection of the fan in the fan-coil by the induction or buoyancy effect of the induction unit, as shown in Figure Air-water HVAC system using induction units.

Water-source heat pumps are used to provide considerable energy savings for large building under the extreme cold weather [ 6 ]. A building of various zones can be conditioned by several individual heat pumps since each heat pump can be controlled according to the zone control.

A centralized water circulation loop can be used as a heat source and heat sink for heat pumps. Therefore, heat pumps can act as the primary source of heating and cooling. The main disadvantage is the lack of air ventilation similar to the all-water systems as in fan-coil units. For a heating process, the boiler or solar collectors will be used to supply heat to the water circulation, while a cooling tower is used to reject heat collected from the heat pumps to the atmosphere. This system does not use chillers or any refrigeration systems.

If a building requires a heating process for zones and cooling process for other zones at the same time, the heat pump will redistribute heat from one part to another with no need for a boiler or cooling tower operation,.

Heating and cooling panels are placed on floors or walls or ceilings where can be a source of heating and cooling [ 7 ]. It also can be called as radiant panels. This type of system can be constructed as tubes or pipes impeded inside the surface where the cooling or heating media is circulated into the tubes to cool or heat the surface.

The tubes are contacted to the adjacent large surface area to achieve the desired surface temperature for cooling and heating process. The heat transfer process is mainly by the radiation mode between the occupants and the radiant panels, and the natural convection mode between the air and panels.

Radiant ceiling or wall panels can be used for cooling and heating process. The surface temperature should be higher than the air dew point temperature to avoid condensation on the surface during the cooling process.

The installation of such systems is often expensive compared to other types as mentioned above, but they can be useful and has a lower running cost mainly because of the surface temperature restriction.

A control signal is connected to the thermostat of each zone to manipulate the medium temperature to condition the space. The used medium can be refrigerant or water mixing with inhibited glycol anti-freeze instead of plain water to prevent icing inside the tubes for the cooling process.

The main advantage is no space required, only a few inches for the panels to be installed and no more collected dirt in the standard ceiling or the ductwork. Many designs are available to produce attractive panels. Some buildings can have multiple zones or have a large, single zone, which needs central HVAC systems to serve and provide the thermal needs [ 4 , 5 ].

However, other building may 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. Therefore, a single zone requires only one-point control point connected to a thermostat 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 to central systems, but still part of a large full-building HVAC systems.

Horizontal hierarchy representation of the main types of local HVAC systems. A single zone will require a complete, single package of heating system which contains heat source and distribution system.

Some examples include portable electric heaters, electric resistance baseboard radiators, fireplaces and wood stoves, and infrared heaters [ 8 ]. Local cooling systems can 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 [ 5 , 6 ].

Local ventilation systems can be forced systems by 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 thermal comfort of the space by allowing the heat to be transferred by conventional mode [ 5 , 6 ].

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 listed below [ 5 , 6 ]. This system is a packaged device consisting of a vapor 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 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.

It 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 near the floor-wall intersection, as shown in Figure Every single zone will contain one unitary air-conditioner as in each guest room in many hotels. Unitary air-conditioner package.

It consists of a vapor compression refrigeration cycle; heat source such as heat pump and electric resistance; an air handler such as dampers, filter, and fan; and control devices, as shown in Figure This system may be connected to ductwork and serve a large-size single zone that cannot be served by unitary or window air conditioners.

Packaged rooftop air-conditioning unit. The split systems contain two central devices [ 5 , 6 ]: the condenser, located outdoor, and the evaporator, located indoors. The two devices are connected by a conduit for refrigerant lines and wiring. This system solves some issues 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 can contain one condenser unit and connected to multiple evaporator units to serve multiple zones as possible under same conditions or different environmental conditions.

This chapter presents the types of HVAC systems. HVAC systems have several requirements including primary equipment such as heating equipment, cooling equipment, and delivery equipment; space requirement such as HVAC facilities, equipment room, and vertical shaft; air distribution; and piping.

This classification depends on zone types and the location of HVAC equipment. The central HVAC systems can serve multiple and single zones and locate away from the building, which needs distribution devices. They also can be sub-classified into all-air HVAC systems, air-water systems, all-water systems, water-source heat pumps, and heating and cooling panel systems. The local HVAC systems are mostly placed inside or adjacent to the living spaces and serve one single zone.

They consist of local heating systems, local air-conditioning systems, local ventilation systems, and split systems. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.

Edited by Mohsen Sheikholeslami Kandelousi. Published: November 14th, Impact of this chapter. Abstract HVAC systems are milestones of building mechanical systems that provide thermal comfort for occupants accompanied with indoor air quality. Introduction Heating, ventilation, and air conditioning HVAC system is designed to achieve the environmental requirements of the comfort of occupants and a process.

However, it is difficult for roof location due to bad weather Reliability Central system equipment can be an attractive benefit when considering its long service life Reliable equipment, although the estimated equipment service life may be less Flexibility Selecting standby equipment to provide an alternative source of HVAC or backup Placed in numerous locations to be more flexible. Table 1. Comparison of central and local HVAC systems.

All-air systems The thermal energy transfer medium through the building delivery systems is air. The publication contains numerous data charts and data tables, inspection checksheets, examples of the calculations, informative diagrams clearly illustrating the information making it faster and easier to understand.

The book will definitely answer most of the question the practicing engineer may have in the field. That is why it is recommended to all mechanical inspectors to be used as a reference source for their day to day work. Opening with the introductory chapter on the design quality control covering the specifications and plans, design analysis, structural and mechanical design checksheets, drawing checksheets, fire protection design, IBC Code requirements, electrical design and other relevant information, the content of the book proceeds to the ductwork including shop drawings, fabrication and installation, supports etc.

The next three chapters have been devoted to the installation, insulations and heating systems while the remaining chapters of the publication are dealing with the fuel storage tanks together with the associated fitting and equipment, inspections, cooling and heating equipment, ventilation, refrigeration, air conditioning and other matters.

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