Wednesday, May 20, 2015

Variable Refrigerant flow Air conditioning; VRV System

Variable Refrigerant Flow (VRF) Systems
Variable refrigerant flow type Air conditioners also known as Variable Flow Volume i.e. VRV, Where variable refrigerant means the ability of the system to control the amount of refrigerant flowing to multiple evaporators i.e. indoor units. Actually VRV consists of multiple Indoor units and all are connected to one single outdoor unit.

VRV also provide the individual settings of all Indoor units and it can handle both heating and cooling in different zones simultaneously. VRV were originally manufactured by Diakin, Japan. These are more widely used for Industrial applications where ducting isn’t possible.

 There is one problem that Design of VRF systems is more complicated and requires additional work compared to designing a conventional direct expansion (DX) system.
Let’s how VRV is different from other Air conditioning systems:-
Split Air-conditioning
Split type air conditioning you have often seen which consists of one indoor unit along with one oudoor unit i.e. every indoor unit and outdoor unit will constitute a single split AC.
Split air conditioning

Few advantages and Disadvantages of Spilt AC’s
Advantages:-
1.    These AC’s have low initial cost
2.      Ease of installation
3.      No ducting required
4.      Each system have own control.
Disadvantages
• Distance between indoor and outdoor unit should not be greater than 100- 150 ft otherwise the performance will suffer.
• Limited air throw.

Multi-Split Systems
This system operates similar to split type air- conditioning system however difference is that in this case there are ‘multiple’ evaporator units connected to one external condensing unit.  These type of systems were designed mainly for small to medium commercial applications. These are basically used where ducting isn’t possible.
Each indoor unit has its own set of refrigerant pipe work connecting it to the outdoor unit.


Multi-Stage Air conditioning system

Advantages of Multi-splits
      No need of duct work installation.
·         System efficiency improves then individual Split unit
      Multi-splits are suitable for single thermal zone applications i.e. either for cooling mode or heat mode.

Drawbacks
• Main Drawback is that Individual system control not possible.
• In this systems whole system will turn OFF or ON completely in response to a single thermostat. These systems are therefore not suitable for areas/rooms with variable heat gain/loss characteristics.
Variable Refrigerant Flow Or VRV
These type of air conditioners are similar to the multi-split systems which connect one outdoor section to several evaporators main difference is that in multi-split systems there is only one controller which turns OFF or ON completely in response to one master controller. But in VRV systems can adjust the flow of refrigerant to each indoor evaporator.
The control of refrigerant is achieved by continually varying the flow of refrigerant through a pulse modulating valve. Opening of Pulse modulating valve is done by the microprocessor receiving information from the thermistor sensors in each indoor unit.

The indoor units are linked by a control wire to the outdoor unit which responds to the demand from the indoor units by varying its compressor speed to match the total cooling and/or heating requirements.

VRV

VRV systems are efficient than air conditioning options and usually save 10- 20% electricity. But they have some high initial cost. Today in modern technology  when there is inverter controlled technology has arrived which will leads to as many as 48 or more indoor units to operate from one outdoor unit .

With VRV refrigerant piping runs of more than 200 ft are possible, and outdoor units are available in sizes up to 240,000 Btuh.

VRF systems are engineered systems and use complex refrigerant and oil control circuitry. The refrigerant pipe-work uses a number of separation tubes and/or headers.A separation tube has 2 branches whereas a header has more than 2 branches. Either of the separation tube or header, or both, can be used for branches. However, the separation tube is NEVER provided after the header because of balancing issues