Dakin refrigerant cooled Inverter is a great solution, especially for all those chillers operating at extremely high ambient temperatures. That is required in Middle East projects, for instance, where chillers are required to operate in extreme conditions that don’t really suit the use of air-cooled or water-cooled Inverter types.
The inverter technology also known as Variable Frequency Drive (VFD) or Variable Speed Drive (VSD), has been increasingly in demand over the last few years, as it is a technological solution which allows to considerably improve the efficiency of chiller units used in the widest variety of applications.
As the world is moving towards more environmentally friendly and sustainable technology, the HVAC sector needs the adjust to a larger demand of highly efficient products. The inverter technology, in this sense, is a reference technology. In fact, it has probably been one of the most revolutionary technologies.
The Inverter is an electronic power component that, by varying the frequency of the motor power supply, modulates the compressor rotational speed (RPM) and in such a way controls the compressor capacity. And that is very important. Especially in Air Conditioning applications, where we know chillers and heat pumps typically spend most of their operating time at part load. So, since the compressor of a chiller or a heat pump usually encounters many hours of off-design operation, it is important, that it can perform as efficiently and reliably as possible, even at part load conditions. The inverter is a great solution to allow the compressor to do that.
Of course, there are different types of inverters. The most commonly used are usually air-cooled Inverters. For this kind of Inverter, the cooling vector is clearly the surrounding air. But the capacity of the air to cool the VFD depends on air characteristics like temperature and density. So, conditions such as altitude and ambient temperature must be considered when using air-cooled Inverter. In fact, the power and the current that this Inverter can manage is subject to derating according temperature and altitude. For this reason, based on the ambient condition, some restrictions must be considered for air-cooled VFD.
Water-cooled using glycol, then, is another type of inverter. In this case the heat from the Inverter is removed by a water and glycol mixture moving into a loop between the electrical panel (where the VFD components are) and is rejected into the ambient through a heat exchanger in contact with the ambient air. The effectiveness of this system, though, is influenced by the ambient conditions as well, as it is not possible to have the glycol coolant below the air temperature. Also, the glycol mixture is pushed through the cooling loop by a dedicated pump which is a sensitive component requiring frequent dedicated maintenance.
In 2013 Daikin has introduced a new development for Screw Compressors – the refrigerant-cooled Inverter – which is available for centrifugal compressors as well since 2019.
Daikin refrigerant-cooled Inverter is in-house produced, in Italy, by the Power Electronic factory in Vicenza, where Inverter is designed and assembled. It differentiates from other VFD types for being directly integrated into the compressor’s body. This feature allows the electronics of the Inverter to be cooled by the refrigerant in the chiller’s circuit.
So, what is the difference with other Inverter types? A refrigerant cooled Inverter differentiates for not being affected by environment conditions such as ambient temperature, altitude or the presence of pollutants, dust or sand in the air. That is a great reason why the refrigerant cooled Inverter proves valuable in high ambient temperature applications like those in the Middle East area.
We are all aware of the fact that most of the times, HVAC projects executed in Africa or Middle East regions require chillers to operate in extreme conditions. That means units are usually required to operate in really very high ambient temperatures – typically 46+ C° – also being installed in very harsh environments, where chillers are often subject to the corrosive action of agents such as humidity, salt, sand and dust. All conditions that do not really suit the use of air-cooled and water-cooled Inverter types for the reasons previously mentioned.
Daikin refrigerant cooling system is specifically designed to be highly reliable, even during operations in extreme conditions such as high ambient temperature operation and desert installations. The fact that is directly integrated into the compressor, and it uses the refrigerant as a means of cooling, allows the inverter temperature to always be on point and be maintained at optimal conditions, regardless of the outdoor temperature and air quality.
All this allows chillers to operate at peak ambient conditions of Middle East, with the advantage of lower operating cost at reduced load conditions, which happens for more than 90% of the hours a chiller operates in a year.
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