Central (or Built-Up) System
This system utilizes a number of separate components field-assembled and piped to serve the specific needs of an individual building. It typically serves a building with a heating and/or cooling medium (water and/or air) from a central mechanical room and includes several redistribution systems providing thermal comfort and ventilation for buildings with several zones of control. Systems may be all-air, all-water, or air and water, and be either constant or variable air volume. Air or water is ducted or circulated to the conditioned space. Depending on the design of zoning there may be some loss of year round individual room control.
Fuel is converted to heat energy in a boiler or cogeneration plant and is distributed throughout the building via a piping system as either steam, or hot water. In mild climates, electric resistance heat may be the most economical design.
Electricity is converted to energy for cooling using large chillers (although steam turbine drive or absorption chillers are also used in certain designs) and is distributed throughout the building via a piping system as chilled water or brine. Large systems are typically water-cooled using a cooling tower or from a body of water (lake, river, etc.). Smaller systems may be air-cooled or evaporatively-cooled.
Central system advantages include:
- Having all the mechanical equipment in one or a few machinery rooms for ease of maintenance and noise control,
- Well operated systems tend to have lower operating costs, better air filtration (essential in hospitals), better control electrical use and demand, more readily use heat recovery, use thermal storage to minimize peak use, and typically use longer life equipment.
Central system disadvantages include:
- Higher first cost,
- Need for skilled operators,
- Required space for the air ducts and the room fan-coil or similar units if chilled/hot water is circulated,
- And requires use of cooling tower and its associated considerations.
Unless sufficient redundancy is provided, loss of one or more large chillers or boilers could cause major disruption to the entire building's thermal comfort.
Links to Related Topics
Indoor Air Quality
Outside Air Control
Central Plant System
All-Air Central Systems
All-Air Central Reheat Systems
All-Air Central Dual Duct
All-Air Central Multizone
Air-Water Central Systems
All Water Central Systems
Two Pipe System
Three Pipe System
Four Pipe System