Variable Capacity vs. Variable Speed Compressor
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- Опубліковано 13 гру 2021
- In this video, we discuss the difference between a Copeland Digital Scroll Compressor and a Danfoss Variable Speed Compressor. These two HVAC modulating scroll compressor technologies accomplish similar results but are constructed differently.
Video Description:
The Copeland Scroll Digital offers compressor modulation from 10-100 percent, allowing cooling systems to automatically adjust capacity as needed while reducing energy consumption. This scroll technology allows for precise HVAC system control, is more efficient than on/off compressors, and allows for almost continuous operation during dehumidification modes. Variable-capacity control is accomplished by timing the compression by engaging and disengaging the top scroll while motor speed remains constant. Advantages are efficiency, precise control, very low turn down to 10%, and constant velocity refrigerant allowing for effective oil return. For some of the compressor sizes, the "modulating" can produce unwanted noise. Special considerations for location and attenuation are recommended.
Emerson’s Copeland Scroll Variable Speed compressors are designed with AC drive controls that modulate the compressor speed. This compressor speed modulation allows for precise capacity control. Advantages are efficiency, low acoustical characteristics, and precise control. Special considerations are required to ensure oil return which usually prohibits low turndown capabilities. Usually, the minimum allowable turn down is in the 10-25% range.
Thank you for watching and please let me know if you have any questions!
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Great video, very informative, thanks for comparing the two compressor types so thoroughly. We've had issues with acoustics of the VCC when located on the roof of a residential building.
Thanks for watching!
It's a very simplified and illustrated way of explanation. Hats off, sir.
Do we need a minimum charge quantity of refrigerant in both VCC and VFD Scroll compressor ?
I’m not sure if there is a minimum charge. Thanks for watching!
Extremely helpful! Thank you.
You’re welcome!
Great presentation!!
Thank you!
It was really a helpful video
Variable capacity is a more generic term. Variable speed is a type of variable capacity. Digital compressors do it by PWM over a 15 - 20 second cycle. Variable speed does this by changing the speed of the motor.
Can you explain how a variable speed compressor in a car works without having any of the fancy communication and control systems that are needed when VRF is used for residential and commercial buildings? The compressor in a car is usually directly driven from the engine. The engine speed typically varies somewhere between 500 RPM and 3,500 RPM under normal conditions. A receiver and expansion valve appear to be all the equipment necessary to keep the system in balance even when there are wild swings in load and capacity (compressor speed). The cabin is maintained at a comfortable temperature and humidity level even with massive swings in heat and humidity demand over short periods. Thanks
The car A/C will cool more the faster the engine spins. If this would result in overcooling the heater is often at the same time. This is obviously inefficient but nobody cares.
Any job opportunity in Houston? I am a Sustaining Design Eng at Daikin…
If you are looking for good efficiency at lower system purchase cost, two speed compressor is best compromise.
With new utility smart meters, more attention and regulations on appliance power factor, digital VCC compressors will not be around long as they are difficult to impossible to control utility grid load power factor.
Oil circulation is an issue with both variable and VCC compressors. The short compression on-off duty cycle of VCC is not long enough to make an impact to average oil circulation. The critical oil circulation is determined by suction line vapor mass flow and by the time vapor exits evaporator, the VCC pressure pulses have smoothed out to an average (lower) mass flow rate. If the liquid pressure pulses of VCC are too great it would also cause problems for the EEV expansion valve refrigerant regulation into evaporator. The pressure pulses of VCC are pretty much smoothed out by gas compression in first part of condenser.
It takes 10-30 minutes at full run speed to flush system distributed oil back to compressor. On most residential systems, when you drop below about 50% of capacity you end up with a net loss of oil in compressor. During low capacity run time you are running on compressor oil sump reserve. This is a primary reason why two speed compressors only drop to 60-65% capacity level.