DC compressors are often called inverter drive compressors. In general, about the only difference from a regular compressor is that the stator is 3 phase since that is optimal for control purposes. (There are exceptions, such as the "Tesla Turbocompressor" prototype my friend is working on, which has a switched reluctance motor that runs as fast as 75kRPMs! It uses distilled water as a refrigerant due to the high flow rates and low operating pressures.) But in theory, it is possible to operate a regular compressor motor as a 2 phase motor.
Direct-to-line motors are difficult to optimize for efficiency under varying load conditions since the torque angle can never be optimized over a range of load torques. Inverter drive motors are therefore often more efficient. Then reductions in delta T in HVAC systems at partial capacity increase efficiency even further. In fact, it is possible to increase the efficiency of an A/C by downsizing the compressor, without changing the technology used.
How to Add or charge Freon or Refrigerant to your air conditioning equipment
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Simply put what makes one unit more efficient than another is bigger coils in relation to the compressor capacity. This is the dirty little secret that no one wants to talk about. Because if they did talk about it then it wouldn't be a secret.
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Note: This 3 ton coil had a leak and was replaced in the late 90s. It has since been repaired and donated to a needy family along with a Carrier 5 ton outdoor coil (no compressor at the time) and a 2.5 ton Rotorex rotary compressor in a house that had a 4 ton gas air conditioner and all the surrounding houses have 4 or 5 ton systems, this one cools just fine. No wonder the other contractors hate me!
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