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Central HVAC - Coggle Diagram

- - - - Disadventages
        
        serving a single thermal zone when improperly applied.
      - Adventages
        
        simplicity in design and maintenance
        
        low first cost compared to other systems.
      - Scheme
        
        consist of AHU, heat & cooling source, distribution ductwork, appropriate delivery device
        
        AHU can be
        
        integrated
        
        where heat and cooling sources are available
        
        most commonly a rooftop unit and connected to ductwork to deliver the conditioned air into several space
        
        separated
        
        where heat and cooling source are detached
        
        thermostat (located in the zone) controls the operation of the system
        
        control may be either modulating or on/off to meet the required thermal load
        
        adjusting the output of heating and cooling source
    - - Adventages
        
        zone system is to adequately condition several zones without energy waste associated with a terminal reheat system.
      - Disadventages
        
        need for multiple supply air ducts to serve multiple zones
        
        leakage between the decks of air handler may reduce energy efficiency
      - Scheme
        
        individual supply air ducts are provided for each zone in a building
        
        cold air and hot (or return) air are mixed at the AHU
        
        to achieve the thermal requirement of each zone.
        
        a particular zone has its conditioned air that cannot be mixed with that of other zones (different thermal requirement demand)
        
        consist of heating & cooling coil and internal mixing dampers
        
        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
  - - - Scheme
        
        some spaces require different airflow of supply air due to the
        changes in thermal loads.
        
        consists of a central AHU which provides supply air to the VAV terminal control box that located in each zone
        
        to adjust the supply air volume
        
        temperature of supply air of each zone
        
        controlled by manipulating the supply air flow rate
      - Adventages
        
        suitable solution for achieving thermal comfort.
      - Disadventages
        
        the controlled airflow rate can negatively impact other adjacent zones with different or similar airflow rate and temperature.
        
        reduce the ventilation flow rate
    - - Scheme
        
        a terminal controlled modification of the multi zone concept
        
        a central AHU provides two conditioned air streams (a cold deck & a hot deck)
        
        air streams are distributed throughout the area served by the AHU 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
        
        Adventages
        
        minimize the disadvantages of terminal heat system
        
        become more flexible by using terminal control
    - - Adventages
        
        flexible and can be installed or
        removed to accommodate changes in zones (provides better control)
      - Disadventages
        
        not energy efficient system
        
        because a significant amount of extremely cooling air is not regularly needed in zones
      - Scheme
        
        a multiple zone, which considers an adaptation of single zone system
        
        add heat equipment (hot water/electric coil) to the downstream of the supply air from AHU 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 AHU is cooled to the lowest cooling point, and the terminal reheat adds the required heating load
- - - - the use of pipes as distribution containers
      - the water has higher heat capacity and density than air
    - - include several delivery devices such as floor radiators,
        baseboard radiators, unit heaters, and convectors.
    - - unusual such as valance units mounted in the ceiling
  - - - considerably small unit used for heating and cooling coils, circulation fan, and proper control system
      - Installation
        
        can be vertically or horizontally
        
        can be placed in the room or exposed to occupants
        
        it is essential to have appropriate finishes and styling
      - the fan coil units are connected to
        
        boilers
        
        to produce heating
        
        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
      - occupants can adjust fan coil units by adjusting supply air louvers
        
        to achieve the desired temperature
    - - lack of ventilation air and only can be solved if the fan coil units are connected to outdoor air
      - noise level
- - - - the supply air and the conditioned water are provided to the desired zone from a central air handling unit and central water systems (e.g., boilers/chillers)
      - the ventilation air can be separately delivered into space or
        connected to the fan coil units
      - the major types
        
        2 pipes systems
        
        4 pipes systems
  - - - externally similar to fan coil units but internally different
      - induces the air flow in a room through cabinet by using high velocity airflow from a central AHU
        
        replaces the forced convection of the fan in the fan coil by the induction or buoyancy effect of the induction unit
      - can be performed as mixing the primary air from the central unit and the secondary air from the room
        
        to produce a suitable and conditioned air
  - - - to provide considerable energy savings for large building under the extreme cold weather
      - 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
        
        heat pumps can act as the primary source of heating and cooling
      - 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
        
        a cooling tower is used to reject heat collected from the heat pumps to the atmosphere
      - 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.
    - - lack of air ventilation