Just to clear some things up: This is not in anyway a hot gas bypass, to make this simple to understand it's kinda like a hydraulic clutch. The solenoid sends high pressure hot gas to a "piston" which in turn pushes away the base plate much like a pressure plate getting the "fingers" pushed in and releasing the pressure plate "off" the disc. In this case the scroll is partially separated causing decompression or "dumping back into compressor vessel". It never gets to full compression making true hotgas which if it did would cause the stator to build heat and overheat. Hotgas bypass even needs "liquid injection" or a limit to hotgas injection or it WILL overheat the stator and eventually the stator overtemp switch would open and the compressor would shutdown. Second item: digital compressor vs frequency drive controlled. Bitzer/ Copeland / Carlyle / Bristol I could go on and on. All are excellent compressors and all have the same issue, they need the oil to come back. Compressors with drives all have one problem that shows it downfall. If oversized or load is light running at minimal Hz for long without a "oil return" written into the unit the compressor with the lowered velocity for an extended time it can't bring the oil back. AAONs I have worked on for years this is a problem as it is with other manufacturers. In refrigeration we use oil separators, something I have expressed with my engineering buddies. This is costly and adds programming etc to a build as you have to have solenoids etc etc. I have some years now with both types for me I'd much rather the digital unloading as I have a lot more failures with frequency drive controlled compressors. Especially in splits where the oil can easily be stuck downstream.
It's many years since I made this video and haven't watched it myself in recent years. However I don't believe I ever said it was a hot gas by pass. It lifts the top scroll and therefore stops pumping momentarily which is a completely different process. The only comparison with hot gas by-pass would be that it is a method of capacity control. While we did not use oil separators and didn't have a failure rate that could be blamed on oil return, we always felt a little nervous. So we used program that put the compressor on full speed for a few minutes if it has been sat below 40% capacity for a period of time. That way we could sleep at night!
I would agree with your observation that inverter units are generally built to a low price because it is a very competetive world these days and some would have a very short lifespan. I would say Copeland digital scroll compressors would be more sturdy and have a longer lifespan especially if built in to units that are more robust. That can only be my opinion.
Where I work we have Aaon split systems with 4 compressors each, and 1 is a digital, and the digital constantly cycles on and off depending on load, compared to the others that run constantly. So instead of changing noise and movement it just cycles on and off.
A very well put explanation of the off loading/capacity control function. Its a bit like the slide controlon the screw compressors but offering fully off loading on a selectable time base. I'm fitting a system that has 6 x mid temp evaporators individually controlled, and I'm considering using EPR valves so that when the individual evaporators are satisfied, they don't pump down into a vacuum. This type of compressor is on the condenser unit, I've looked on the Emmerson pdf for this compressor and I couldn't find an understandable explanation until I came across this vid. To be honest a name like digital scroll suggested to me that it was designed for operation with a VVF drive. But it refers to the square wave-pulse width modulated signal to switch the sol valve on and off. Regarding oil return though, it states on the pdf for this compressor that it is undesirable to use an oil collector for some reason? But I am concerned that when the velocity reduces right down to maybe 10%, it won't be sufficient to return the oil that has already carried over. So I am planning on using a double suction riser and adding a shot of oil to compensate for trapped oil carried over from when tbe compressor is at full load. What actually controls the modulation on this type of capacity control, is it varying suction pressure or pipe temperature?
The modulation control of the solenoid is done by a variable voltage from a controller based on a thermostat giving a distance from set point. So it could be that at 1°C from set point zero volts, at 0.5°C from set point 5 Volts and at set point it could be 10 Volts, or something similar.
This system doesn't work with exv, if you set the exv to 6k SH and low protection to 3k SH this system just showed well in truly beyond 0k ! Even tho there is no flooding of evap but due to pressure increasing during unloading the valve will pump down and showes LOW SH protection and this has happened in a case I've worked on and had to set it to 12k SH with 2k low protection for it to work and this is not power efficient at all. Use a vsd for constant load and SST for capacity control use the PID function from 50% to 140% of capacity control also increasing power factor and no start up inrush current
@Threadbone Yes but the don't the inverters usually go bad after just a few years? I thought that these compressors would pase out inverter driven compressors
was wondering what causes comp burnout in our units we build ? what effect does using type L water tube insted of ACR tube in a reefer system ? and we dont have a top solinoid on the one digital comp in a tandum type setup ? zptd 364 tfe tw5
I am suspecting that when you charge a copeland scroll with liquid through high side while under vacuum causes internal damage with the result being equalized pressure while running....If so why?...
@@Threadbone thank you for sharing your knowledge. Do you know if Copeland has put any memos out about this or anyting. I'm pretty old school and was always taught on an empty system you start to add refrigerant from the high-side and liquid form at first. I shan't do it anymore perhaps there are others that might be helped. Also I am assuming you are referring to the check valve inside the compressor since there are no valve or valve plates used in the process of compression
@@LongTrout I made this video initially because Copeland had not issued one. I did my own test in Temperzone's R & D Lab so our customers could understand. I believe that some time later Copeland did do their own version because I had perhaps had embarrassed them! I've been retired now nearly 4 years so getting a bit removed from the industry!
what temp range should the compressor shell be? I can not find this info anywhere. My compressor is running very hot, is this normal for this type of compressor? any info would be appreciated
its normally to find the compressor surface hot when you touch but inside compressor the ways to cool compressor by the cooling refrigerant that returns from the suction pipe and the oil inside compressor
The thing you need to know is this: Discharge superheat between 40-50F. Inlet superheat 10-22F with the shell result around 58-65F. Keep in mind the return refrigerant (superheat) is your cooling for the motors stator. The discharge superheat getting past 50F is telling you the compressor is getting starved of refrigerant which results in higher temps in the compressor. The top of course will be hot, so for example: R410a 320psig discharge pressure with a measured temp @ discharge being 150F that's fine no problem here because that's 49.5F discharge superheat.
Very, not to say there are no failures but they are rare. Generally the coil needs replacing after a few years but the valves themselves are very long lasting.
it is really simple... it called hot gas bypass, nothing new, and this is the worst way for energy saving, try to use inverter like the Bitzer varispeed 25 to 87 Hz and get the best possible energy consumptions.
According to the animation in the video, the solenoid valve doesn't bypass discharge vapor into the suction. It allows the orbital scroll to separate which stops the vapor compression.
בני דורון Hot Gas By-Pass is very inefficient. This is not Hot Gas By-Pass, as Jim B has noted it essentially stops compressing when the scroll lifts. There is energy saving but agreed not as much as an inverter compressor. Digital scroll has a wider range of control than inverter and come in to their own for close control and very accurate control. They have also generally been cheaper than inverters especially the larger sizes as they don't require the driver boards. They have their place. Some believe that Inverters will replace digital scroll completely but I believe they will both exist for a long time yet.
Threadbone unfortunatly this is exactly hotgas by pass it is written in copeland documentation, no secret. with varispeed you can go higher than 50 Hz and get from 0.5 to 1.7 times of the compressor capacity. here you can go from 0 to 100% by using bypass on the compressor and still running almost the same motor consumtation. if you are getting free electric so this is a great solution.
בני דורון This is definitely not the same as HGBP, you are completely unloading the scroll and motor leaving the motor spinning at near zero energy consumption. It is varying the capacity by adjusting the loaded/unloaded time accordingly, similar to the pulse width modulation in an AC power circuit, like the one that drives the variable speed units.
