Are Inverter (Low-Consumption) and Regular Split Air Conditioner Units Only Different in Power Consumption?

What are the differences between an inverter and a regular split Air Conditioner (AC) and how is an inverter unit distinguished from a regular one?

To find out the difference between inverter (low-consumption) and regular AC units, one must begin by considering their functional mechanisms. When comparing the inverter with regular AC, it is essential to note that the two are similar in their mechanical and refrigeration cycles and that their only difference lies in the electric circuits.

A digital thermostat is integrated into the circuit of the regular AC unit (triggering to switch the AC on or off). The thermostat measures the temperature of the return air from the space, triggering the compressor when the adjusted temperature is reached. In regular AC units, the compressor turns on at maximum power and continues until the desired air temperature is attained.

split ac unit
A compressor in AC units (and all other electric motors) need to overcome the inertia of motion on start-up, which requires more force than when the motor is operative, resulting in a spike in power consumption on compressor start-up. Under such circumstances, energy consumption is increased two or three-fold instantaneously.

Therefore, on start-up, power consumption is instantaneously increased two-fold in a regular AC unit. For example, a unit powered by 10 amps, demands 20 amps at the start-up. Now, given the dimension of the power mains in most households, often 25 amps, power consumption can easily exceed the allowable limit should other equipment be plugged in at the same time.

split ac unit

The Functional Mechanism of the Regular AC Unit and its Drawbacks :

The regular AC unit has a high power demand and starts at maximum refrigeration capacity and turns off after a while when the desired room temperature is reached. There are two things to note as regards this mechanism:

  1. Repeated on/off cycles create power fluctuations, depreciating the compressor (switching on or off is highly strenuous on mechanical equipment).
  2. It is necessary for controlling and improving the on/off switching time that the equipment is adjusted at convenient switching temperatures, separated by a 1–3 °C difference, to prevent the unit from switching on or off at the slightest temperature change. Therefore, the regular AC unit provides a constantly-changing room temperature.

As it was discussed earlier, inverter and regular AC units are only different in their electric systems with practically identical mechanical cycles and other components a few of which have been improved in inverter models.

Inverter AC units, also referred to as low-consumption units, are regular AC units with different electrical systems.

Before discussing the low-consumption AC unit, we first take a look at the inverter technology.

All AC electric motors with ratings complying with the local power grid in Iran (220 V – 50 Hz) rotate at 2900 rpm. The motor speed depends on voltage and frequency. The inverter, or drive, tunes the electric motor speed by manipulating the two parameters, and the AC compressor with an electric motor in its shell can easily adapt to the inverter.

But how does changing the compressor speed help the AC unit? And how does it help manage power consumption?

As earlier discussed, AC units have much higher power demand on start-up, which increases power consumption and exerts stress on the power grid.

In low-consumption AC units, the inverter installed at the power input helps the compressor start at a lower speed. The start-up speed of the compressor or motor is lowered by reducing the voltage and frequency of the power input that are raised sufficiently after the compressor starts.

Accordingly, inverter ACs do not cause a voltage drop on start-up, thus exerting minimal stress and damage to the internal wiring system of the building. As a result, this type of AC unit is the best fit for buildings with fragile wiring—in particular, older buildings with a worn-out wiring system.

split ac unit

However, the difference between the inverter and regular AC units does not end at the start-up. Inverter-equipped ACs provide much better control over temperature as their compressors do not switch off after reaching the set temperature but lower the speed and the refrigeration load.

After reaching the set temperature, low-consumption split AC units do not switch off but bring down the refrigeration load by changing the speed, establishing an energy balance, that is, by offsetting the thermal energy generated in the room by the heat absorption by the unit, thus eliminating the need for operating the compressor at full capacity. Under such circumstances, the power consumption of the AC unit is lowered, falling even below the typical swamp cooler.

The inverter air conditioner compressors are available in AC and DC types. DC compressors are more expensive but much more adaptable to the inverter system as the inverters, to change its frequency and voltage, have first to transform AC power (mains) to DC and then back to AC. However, DC compressors do not require the second transformation. DC electric motors are also superior to their AC counterparts in terms of efficiency.

split ac unit

However, it must be noted that, at its peak operational capacity, the inverter AC has similar power consumption to a regular one as the two are only different in compressor capacity control and start-up. By the same token, the considerable price tag difference is not easy to justify, and one must be careful not to be tricked by advertisements claiming the ability of the units to reduce power consumption by up to 60%.

Pros and Cons of Inverter Air Conditioners and Mini-Split Units :

Small room temperature variation, gentle and gradual compressor start-up, and lower power consumption for attaining the desired temperature are the top advantages of an inverter AC unit. However, such drawbacks as their higher price tag and maintenance costs must also be taken into account.