BMS SYSTEMS PART-1

In This Article we are going to discuss about BMS systems complete working principles part 1

Air Handling Unit

What is BMS :

 

• BMS means Building Management Systems, that  provide control and monitoring of heating, air-conditioning, ventilation and other building services.

• BMS use programmable microprocessor based DDC (Direct Digital Control) Controllers communicating back to a Central Computer.

DDC CONTROLLER

• Each of the controllers is programmed to meet the specific requirements.

• Controllers can also be used stand-alone for small Installations.

• BMS save energy and ensure optimal working environments and can deliver significant time and cost savings.

BMS Save Energy 

How to achieve ?

• Using AHU that means Air Handling Unit. This is the graphical view of Air Handling Unit.

• It consist of ( Fresh air duct , Return air duct , Exhaust air duct , Filter , coil , water inlet and outlet pipes , blower and so on).

• This is the schematic view of Air Handling Unit.

 

AHU:

• An Air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating, ventilating and air-conditioning system. 

• The basic function of the AHU is to take in outside air, re-condition it and supply it as fresh air to a building. All exhaust air is removed, which creates an acceptable indoor air quality. 

• Depending on the required temperature of the re-conditioned air, the fresh air is either heated by a recovery unit or heating coil or cooled by a cooling coil.

• In buildings where the hygienic requirements for air quality are lower, some of the air from the rooms can be re-circulated via a mixing chamber and this can result in significant energy savings. 

• A mixing chamber has dampers for controlling the ratio between the return, outside and exhaust air.

• AHUs connect to duct work that distributes the conditioned air through the building and returns it to the AHU. 

• A heat and cooling recovery exchanger is normally fitted to the AHU for energy savings and increasing capacity. An AHU designed for outdoor use, typically on roofs, is also known as a Roof Top Unit (RTU).

 

VAV:

VAV means Variable Air Volume , this part of device is fitted inside the supply air duct on AHU unit.

 

Working Principle of VAV

• Temperature Control Loop (1) and Flow Control Loop (2) working simultaneously (in Cascade mode) to maintain indoor air quality.

• A VAV system maintains the air supply at a constant temperature while individual zone thermostats vary the flow of air to each space maintaining the desired zone temperature.

• Flow Control Loop controls the flow within the range, called as operating flow range V minimum and V maximum

 

V minimum: Minimal Air Change rate required to cover the hygienic condition

V maximum : Full Load or Full Cooling Demand

 

VAV - Pressure Dependent:

• A VAV is said to be pressure dependent when the flow rate passing through it varies as the system inlet pressure fluctuates.

• The flow rate is dependent only on the inlet pressure and the damper position of the terminal unit.

• The pressure dependent terminal unit consists of a damper and a damper actuator controlled directly by a room thermostat. The damper is modulated in response to room temperature only.

Siemens Room Thermostat

• Since the air volume varies with inlet pressure, the room may experience temperature swings until the thermostat reposition's the damper.

• Excessive air flow may also lead to unacceptable noise levels in the space.

 

VAV - Pressure Independent

 

• A VAV is said to be pressure independent when the flow rate passing through it is maintained constant regardless of variations in system inlet pressure.

• The pressure independent control is achieved with the addition of a flow sensor and flow controller to the VAV box.

• The controller maintains a preset volume by measuring the flow through the inlet and modulating the damper in response to the flow signal.

• The preset volume can be varied between calibrated limits by the thermostat output.

• Pressure independence assures the proper distribution of air to the spaces that need it.

• More specifically , it allows user to feel comfortable that the design limits specified will be maintained.

• Each pressure independent terminal unit has minimum and maximum air flow limits preset at factory.

 

VAV Box

Maximum air flow limits prevent over-cooling and excess noise in the occupied space.

Minimum air flow limits assure that proper ventilation is maintained.

1. How Chiller Systems Works? (Blog)

2. How BMS System Working? (Video)

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