vrf aircontioning system

vrf aircontioning system

Variable Refrigerant Flow (VRF)


Central Government Offices Pretoria - Mitsubishi Electric Variable Refrigerant Flow (VRF) system


Project brief:

The total area air conditioned was approximately 26 000 m2. The system selected to undertake this task was the Mitsubishi Electric City Multi system explained below. The system summary is as follows:
  • 913 indoor units (Evaporators)
  • 81 outdoors units (Condensers)
  • An average of 11.3 indoor units (evaporators) connected to one outdoor unit (condenser).
  • 3455 kW of effective cooling has been installed.
  • Significantly, each outdoor unit will only consume 8 Amps of current when starting up. This industry leading advantage is unique to the Mitsubishi Electric City Multi VRF system.
City Multi VRF explained:

Mitsubishi Electric Airconditioning Distributors have established themselves as a world class brand for the past thirty years in South Africa backed by continuous research and development to meet a wide range of end user needs. This motive stimulated the introduction of the City Multi brand as a sub brand to the Mitsubishi Electric family of air conditioning equipment, offering class leading innovation to suit various markets and their ever changing requirements - from installation space to electrical efficiency. The City Multi product has been well received internationally and has found phenomenal success here in Southern Africa.

The main feature of the product is its high energy saving capability, consuming up to less than 40% electrical energy than a typical constant volume air conditioning system available today. This efficiency is achieved using inverter technology throughout the system combined with simultaneous heat recovery.

Briefly, inverter technology relies on variably controlled inverter compressors and fan motors that adjust their speed to various demands put on the system during differing peak loads on any a given day. For example in common applications the air conditioning systems when in operation will run at maximum output. Once the desired temperature is reached it will switch off, as the temperature increases the constant volume system will need to re-start at which time it will draw a large amount of current to start to meet the desired temperature. Each time drawing amperages of around six to eight times higher than the systems running current, forcing the electrical demand curve to move sharply up and down during varying levels of operation. Notably, this continuous switching off and on will be happening all day and the more individual systems you have the higher the demand for electrical power.

However with regard to Inverter technology reliance on high energy consumption to start the compressor is not necessary, rather than instantaneously starting up at its maximum power the City Multi system will instead start by drawing a very low 8 Amps of current slowly winding up to its peak demand without the need to draw high amperages to get the compressor to its maximum output effectively. In other words, as the temperature within the space is met rather than switching off, the compressor slows down, maintaining its set point without the need to restart every time additional cooling or heating is required. This operation flattens out the electrical demand curve resulting in lower energy consumption.

Furthermore, the biggest technological advantage the systems has to offer is its ability to recover heat energy from certain areas that is either in the cooling or heating mode, it uses this same energy rejected to either heat or cool other areas. Traditionally, when an airconditioning system is in the cooling mode it will absorb the heat energy contained within the space it's trying to cool down, using the basic principles of refrigeration. Once this heat energy has been contained it will then reject the heat outside via its outdoor unit. However, with the Mitsubishi Electric City Multi VRF system we can recover this heat energy in a sense employing the principles of reusable energy that can be used elsewhere rather than wasted. For example this contained heat can be used to heat another part of the building, which is very common during winter months and or early morning and late afternoon applications or even better heating water to 70oc. There are many applications today that need heating, cooling and hot water all at the same time from hotels, gyms to hospitals to mention a few.

In summary, the Mitsubishi Electric VRF system can heat, cool and heat water off one system simultaneously; this is an industry first and unique to the Mitsubishi Electric brand.

Another significant advantage, the City Multi VRF system is simple and flexible as was the case with this project. During building up grades where for example a chilled water plant has reached the end of its usable life and needs to be replaced the practicality and costs of installing new water tanks and water reticulation piping can be a massive challenge in its self. However with the City Multi product the equipment is light and can easily be maneuvered into position and the connection between indoor and outdoor is simple using light copper piping components resulting in the lower labour hours resulting in lowers over all costs.

In closing there are many more advantages to the Mitsubishi Electric products on offer from simple internet connectivity to off site monitoring making air conditioning management an absolute pleasure for the service engineers and building owner and or developers. Mitsubishi would welcome any opportunity to present many more added feature and benefits if required.