תגית: PLC

בקרה ואוטומציה ליט"אות -HVAC / AHU control

HVAC stands for Heating, Ventilating and Air Conditioning. AHU stands for Air Handling Unit.

HVAC and AHU control systems provide centralized monitoring and control of these systems, designed to maintain selected rooms in research and production facilities within specified pressure, temperature and humidity levels. This is achieved by operating and monitoring active components or actuators, and by monitoring environmental conditions, such as pressure, temperature and humidity, using corresponding sensors located in the HVAC and AHU system and the selected rooms.

Smartlogic has an extensive knowledge and experience in HVAC & Ahu systems.

The monitored values in HVAC and AHU systems and rooms are analyzed and processed by one or more controllers, such as programmable logic controllers (PLCs) or direct digital controllers (DDCs), which control the system accordingly in conjunction with an HMI installed on a PC connected to the PLCs or DDCs. The levels of the environmental conditions are compared to set-points (SPs) that are displayed and can be determined using human-machine interface (HMI) screens.

The level adjustments of the environmental conditions, such as pressure, temperature and humidity are performed using temperature control valves, electrical chillers and heaters, blowers, differential pressure switches, motorized flow dampers, etc. Fault switch, such as temperature, pressure and humidity switches, and fire alarm switches in HVAC/AHU systems provide alarm indications in case of failures.

The PLCs or DDCs currently used to control HVAC and AHU devices, such as valves, and heaters, receive analog and digital inputs from the sensors and devices installed in HVAC and AHU systems and, according to control logic, provide analog or digital outputs to control the devices.

An example of a device installed in HVAC and AHU systems, and controlled by PLCs or DDCs is a chiller.

Example – Chiller Control

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment, as required.

Use in Air Conditioning

In air conditioning systems, chilled water is typically distributed to heat exchangers, or coils, in HVAC and AHU systems, or other type of terminal devices which cool the air in its respective space(s), and then the chilled water is re-circulated back to the chiller to be cooled again. These cooling coils transfer sensible heat (heat exchanged by a body thermodynamic system that has as its sole effect a change of temperature) and latent heat (heat released or absorbed by a body or a thermodynamic system during a process that occurs without a change in temperature) from the air to the chilled water, thus cooling and usually dehumidifying the air stream.

Use in Industry

In industrial application, chilled water or other liquid from the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. They are often used in the plastic industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum systems, X-ray diffraction, power supplies and power generation stations, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines and lasers, and in hospitals, hotels and campuses.

Chillers for industrial applications can be centralized, where a single chiller serves multiple cooling needs, or decentralized where each application or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of both centralized and decentralized chillers, especially if the cooling requirements are the same for some applications or points of use, but not all.

Decentralized chillers are usually small in size and cooling capacity, while centralized chillers generally have larger capacities.

Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional facilities. Water chillers can be water-cooled, air-cooled, or cooled by evaporation. Water-cooled chillers incorporate the use of incorporate cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. Chillers cooled by evaporation offer higher efficiencies than air-cooled chillers but lower than water-cooled chillers.

Water-cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.

Chillers cooled by air and evaporation are intended for outdoor installation and operation. Air-cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Machines cooled by evaporation are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air-cooled machine.

Smartlogic has an extensive knowledge and experience in HVAC & Ahu systems.