Recently manufacturers of air conditioners are producing units equipped with inverter compressors. They claim that this type of compressor is a variable speed one and being so a remarkable saving in energy could be achieved.
Yes, AC units with a variable speed compressor is more advantageous than the conventional fixed speed type.
The variable speed motor saves energy and is more compatible with the smart homes where AC is dependent on the number of occupants in a given zone/ room.
Professor Yehia Khalil, Yale University, USA
Fellow of the University of Oxford, UK
Very interesting project related to this question, by the way.
The inverter design can be used in outdoor and indoor motors, allowing both the outside compressor and the internal fan to be variable speed, as opposed to always running at maximum speed or no speed at all. This should permit the system to remain on for a more ideal amount of time, irrespective of outdoor conditions. This allows proper air circulation inside, making it comfortable and evenly distributed. Otherwise, let's say the outside temperature is closer to normal room temperature than usual, your heating or air conditioning might run for such a short time that the air handler inside does not get a chance to circulate air everywhere evenly enough.
If air is not evenly distributed, the natural reaction is for users to raise or lower the thermostat more than it should be, to make different parts of the home comfortable. And another effect, when using air conditioning in humid climates, is that you might get inadequate dehumidification, if the air handler does not remain on for a certain amount of time.
Saving energy can be a subtle process of balancing many different factors. One might think that running outdoor and indoor units for the shortest possible time is all it takes. But that may not always be the case.
Inverter air conditioner utilizes DC brushless motor to drive the compressor, indoor fan and outdoor fan. DC brushless motor compressor is quiet in operation, compact, having long life time, consumes less energy and can provide better capacity control that ensure a more comfortable environment. Also, speed control of motors can be easily done with simple electronic controls. In contrast non inverter (conventional) air conditioners are equipped with induction motors which are relatively less efficient and speed control is possible only with VFD (variable frequency drive).
Due to the facility of speed control available with the inverter A/C, at the start when the cooling load is high, the compressor and fans run at a faster speed to achieve the controlled state in less time. Once the system get stabilized, then the cooling load will be low and the compressor and fans runs at low speed. This does not mean that the air conditioner is running continuously without cut off. As in conventional A/C, the compressor cut-in and off through a thermostatic control. But, in such intermediate switching on, the compressor will only run at lower speed. All these features ultimately provide increased energy efficiency. As in the foregoing discussions, the variable speed drive also provides some minor improvements in air distribution and dehumidification.
In some other inverter technology, the compressor is driven by the same conventional induction motor with a variable frequency drive (VFD) for speed control and fans are driven by DC motors. These systems are relatively less efficient than compete DC motor driven systems. Similar is the case with heat pumps also.
Yes I to agree The variable displacement compressors will deliver power according to the requirement hence saves the considerable amount of power
Very good and wide explanations have already been given. I would like to add that variable speed drivers can be applied to a vast variety of equipment, with the aim of adapting the power requested to the actual load: compressors, heat pumps and chillers, but also standard hydraulic pumps. One example where the operation of the compressor is particularly efficient is in the solar loop of solar thermal systems: when a variable speed pump is used, the excessive cooling of solar collectors is avoided and hence the efficiency of the system is increased.
I am really grateful to all of the above contributions. As a matter of fact we did some experiments to compare the performance of two 18 kBtu/hr split air conditioners one driven by an inverter drive and the other by a constant speed drive. The out door units containing the compressors are kept in an adjacent controlled temperature room.The units were tested at variable out door temperatures( 30,35,40,45,50oC ) while the indoor temperature was kept constant at 24oC. . The units were run for 8 hours and the power consumption was measured by a cumulative power meter . It was found that the inverter driven air conditioner saves energy most when the out door temperature was low ,but when it got higher say at 50oC no significant saving is found.
Quite natural. Here the problem is with the decrease in heat rejection in the condenser. As the condenser cooling fluid (ambient air) temperature increases, complete phase change of the refrigerant from gaseous to liquid phase is seldom possible and the compressor has to run continuously at higher speed without cut off to meet the cooling load. Thus, at some higher ambient temperature, in effect both constant speed conventional and inverter variable speed functions almost in the same manner. So, the difference is only in the slightly higher DC motor efficiency. .
An inverter compressor runs at lower speed when the setting temperature is reached. At lower speed, the compressor needs less energy to run
https://www.researchgate.net/publication/325680933_Experimental_study_on_comparison_of_energy_consumption_between_constant_and_variable_speed_air-conditioners_in_two_different_climates
Above linked paper can give you some ideas.
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