Tuesday, 5 July 2016

Energy Conservation in fans using inverter technology

Inverter technology uses a variable speed compressor motor similar to a car. It simply slows down and speeds up as needed to hold a selected comfort setting. Inverter technology provides a more precise room temperature without the temperature fluctuations of fixed speed systems.
Air Conditioners are a pain point for most people in our country who are concerned about their electricity bills. The moment an air conditioner is added to the list of appliances used in a household, the electricity bills increase significantly. Although it is difficult to significantly reduce the “big” impact of an air conditioner on your electricity bills, but still some of it can be managed by choosing the right technology, doing the right installation/maintenance/operation and by doing the right insulation of the room where the air conditioner is used (more details in our articles listed at the end of this article). When it comes to technology, there were not many available till sometime back. When BEE actively started analyzing and labelling the air conditioners, we got some good one in form of 5 star air conditioners. The latest and the most efficient technology that is available in market today is the Inverter Technology for air conditioners. Inverter technology is designed in such a way that it can save 30-50% of electricity (units consumed) over a regular air conditioner. How does an air conditioner work?
What is benefit of Inverter Technology?
Are Inverter technology air conditioners slow in cooling?
For most people, air conditioner just throws cool air at the temperature one sets it at. But does it really work that way? In fact air conditioner during cooling process, takes the indoor air, cools it by passing it through evaporator and throws it back in the room. It is quite opposite to how our good old air coolers used to work. Air coolers used to take outside air, cool it with water and throw it in. But air conditioners just work on internal air. Along with evaporator air conditioner also has a compressor that compresses the gas (refrigerant) in the AC to cool it that in turn cools the incoming internal air from the room.
The compressor is either off or on. When it is on, it works at full capacity and consumes full electricity it is designed to consume. When the thermostat reaches the temperature level set in the AC, the compressor stops and the fan (in AC) continues to operate. When the thermostat senses that the temperature has increased, the compressor starts again.
In an Air Conditioner with Inverter Technology:
The inverter technology works like an accelerator in a car. When compressor needs more power, it gives it more power. When it needs less power, it gives less power. With this technology, the compressor is always on, but draws less power or more power depending on the temperature of the incoming air and the level set in the thermostat. The speed and power of the compressor is adjusted appropriately. This technology was developed in Japan and is being used there successfully for air conditioners and refrigerators. This technology is currently available only in split air conditioners.
Every air conditioner is designed for a maximum peak load. So a 1.5ton AC is designed for a certain size of room and 1 ton for a different size. But not all rooms are of same size. A regular air conditioner of 1.5ton capacity will always run at peak power requirement when the compressor is running. An air conditioner with inverter technology will run continuously but will draw only that much power that is required to keep the temperature stable at the level desired. So it kind of automatically adjusts its capacity based on the requirement of the room it is cooling. Thus drawing much less power and consuming lesser units of electricity.
Although air conditioner with Inverter Technology adjusts its capacity based on the room requirement, it is very important to install a right sized air conditioner in a room. Please make sure that you evaluate the room and air conditioner capacity before you make a purchase. Keep watching for this space as we are in process of creating a comparator for electricity savings in various air conditioners.
Several people have concerns that Inverter Technology air conditioners do not cool well or cool slowly. However let us take this image as reference to understand how inverter AC works:
Non inverter ACs are fixed speed ACs, where as inverter ACs are variable speed ACs. Non inverter ACs have compressors that go “On” and “Off”. Whereas inverter ACs have compressors that are “On” all the time. As non inverter ACs are sized for peak summer heat load, they are over-sized all the other times (in fact most of the time people oversize even for peak summer season). The drawback of the same is that the AC “Over cools” most of the time. So if you set AC at temperature of 25, it will cool it down to 23 or 22. Now one would question: then what is the use of thermostat? Well the thermostat (in a non inverter AC) switches off the compressor when the outside temperature has reached 25. But a lot has happened before that. In an AC, refrigerant moves from liquid to gas (by taking heat from the room) and then back from gas to liquid as the compressor compresses it. But if the refrigerant is more and heat in the room is less (which happens in over sized AC), it does not get enough heat from the room to convert from liquid to gas and it keeps moving as liquid. Now when the thermostat detects temperature and switches off the compressor, the refrigerant still remains in liquid state and thus has capacity to take heat from room to convert to gas. And so it takes more heat from the room and cools the room below the set temperature.
In comparison, the inverter tech AC changes the flow rate of refrigerant based on the heat of the room. When heat is less, the flow rate is less, when heat is more, the flow rate is more. And it does not switch off the compressor ever. It just makes sure that if temperature setting is 25, it is maintained at that level.
So the difference is: non inverter AC would over cool as shown in the picture. Whereas inverter AC will cool optimum. And thus one may feel that inverter AC does not cool or is slow.
Lesser known benefits of Inverter Technology
§  Regular motors need 3-4 times more current (more than running current) at startup. So the inverter/generator size needed to run any AC or Refrigerator increases significantly. But Inverter Technology air conditioners and refrigerators have variable speed motors that start up gradually needing much lesser current at startup. Thus the size of inverter/generator required to startup is less. For e.g. A 1.5 ton fixed speed AC that runs at about 10 Amp current may need up to 30 Amp current at startup and thus a 5 kVA inverter/generator. But an inverter technology Air Conditioner needs about 6-7 Amp current and not much more at startup and thus a 1.5 kVA or 2 kVA inverter/generator is good enough to support it.
§  Regular motors have much lower power factor. In commercial and industrial connections there is penalty for low power factor and rebates for higher power factor. An inverter technology motor will have power factor close to unity (or 1) which not only results in lesser electricity consumption but also help get rebates on better power factor.
§  If you are planning to use Solar PV for air conditioner, then it is the best to use inverter technology air conditioner or refrigerator as it not only reduces the size of PV panels because it consumes lesser electricity, it also reduces the size of inverter to be put along with the PV panel.
Inverter ACs are 20-30% efficient as compared to same EER fixed speed AC model. So if you find an inverter AC with EER of 3.3 then it is comparable to a fixed speed AC of EER 3.3/0.8 = 4.12 …. now most inverter ACs are efficient than BEE 5 star rated ACs, but some are not. For e.g if you get an inverter tech AC of EER 2.9 then its equivalent AC would be one with EER of 3.63. Now that AC would be a BEE 5 star rated one, but still you can get BEE 5 star rated AC with EER as high as 3.9. So it is not always that inverter tech AC is efficient than BEE 5 star rated AC.
BEE star rated does get updated every year as the efficiencies improve. We hope that soon BEE will include inverter ACs in the star rating as well. And then it will remove all ambiguity (Inverter Tech Refrigerators are already included in BEE star rating). What sized model are you looking for? We can suggest you some models that have high EER.
ACs are designed to cool enclosed space. So when you use an AC in a room you should keep the doors and windows closed (unlike a desert cooler). Even when sizing is done, it is done considering the volume of air to be cooled. Now if your kitchen is connected to the hall the AC will also try to cool the air in the kitchen. So for sizing the AC you will also have to consider the volume of the kitchen. Also kitchen will involve cooking which will increase the heat load on the AC.
Now fixed speed ACs have constant Energy Efficiency Ratio …. while inverter ACs have variable energy efficiency ratio. Inverter ACs are more efficient when they are running at lower capacities and less efficient when they are running at capacities higher than the marketing capacity or tonnage. If you have sized your AC as per your hall without including the kitchen then the inverter AC will always run at capacity higher than the marketing capacity and thus it will not provide you electricity savings that you expect. And that is why we suggested you to go for BEE 5 star rated AC as it will run at constant energy efficiency.
Mostly when the AC is sized for peak summer, it is sized in such a way that it can bring down the temperature to 25 degrees. And 25 degrees is the temperature in thermostat which is there on the internal unit of the AC (some ACs from bluestar have ifeel technology in which the thermostat is in the remote instead of the IDU). Now if in peak summer it can bring down temperature to 25, other times in the year it should be able to bring it down lower. Now when temperature of the air near IDU is 25, the room temperature will be about 26 (with good air circulation). If the circulation is not good then it can be higher as well.
Now I did not understand what you meant by AC is throwing cooling in between 10-12 degrees. All I can say is as long as the AC is able to make your room comfortable, it should be good. If your expectation is that it should bring down the room temperature to 16 or 18, then it will be difficult. It can happen only at nights when the heat load is less. But it should certainly bring down the room temperature to 24-25 which is more than comfortable. If it is not doing that, then there is a problem in the AC.
As far as current is concerned, Inverter AC starts with 0 and increases to highest current (9 amp in your case) and then settles to a stable current (most probably 6.77 in your case). If it is continuously consuming 9 Amp then it means that the AC is not cooling properly or is undersized. Improper installation can also cause improper cooling.[Courtesy]

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