This is an extension of my question a while back out variable speed compressors.
(Does anyone make a residential variable speed compressor in the 4 tonn range) (Not 2-speed or multi-compressor, true multi-speed like some of the ductless, or commercial)
How does the expansion valve deal with variable liquid flow rates? I would thing that at one flow you would get good expansion, but at too higher or lower you might have problems. How do the commercial units deal with the change if flow rates through the expansion valves, as I thought the expansion valves were tied to the flow, which would be tied to the compressor....
I know that several manufactures make a big deal about their expansion "metering" values and was wondering how they fit into the grand scheme of the system.
A thermostatic expansion valve releases _stored_ liquid refrigerant as required to maintain a particular temperature at the sensing bulb, which would be placed, say, at the exiting vapor line of the evaporator. It says to itself, "That line is too warm, so I'll release more liquid" or it says "that line is getting colder than I want, so I'll slow or stop the supply." (anthropomorphizing the machine a _little_, but only a little. Some of the new systems are pretty smart)
When the system 'knows' to slow or stop the compressor, it's because there's a smaller demand for refrigerant. The expansion valve will release only as much as required. All the compressor has to do is "keep up".
LLoyd (you'd get better information by hiring a good tech for a couple of hours to explain by Show&Tell on an actual unit)
Copeland Scroll Digital technology provides infinitely variable capacity modulation and is ideal for commercial applications with widely varying loads and a need to maintain precise temperature and humidity control. It offers an innovative way to modulate the capacity of the compressor from 10 to 100 percent, so that the output precisely matches the changing cooling demand of the room, and it does this without changing the speed of the motor. This approach to capacity modulation is as much as 30 percent more efficient than traditional hot-gas bypass and is capable of holding a precise temperature to within half a degree Fahrenheit. The innovative design allows for a quieter, more efficient, and highly controllable unit, enhancing a system?s performance and providing a quality product for contractors and end-users alike.
"Extract from Copeland advertisement"
My opinion to what I can understand here manufacture came up with excellent
control of compressor pumping capacity, however they are neglecting to tell you
that by reducing pumping capacity it also reducing compressors efficiency
Air Condition utilize this compressor at 100% capacity "example" it has 18 SEER
by reducing pumping capacity to 10% will become now 5% SEER
Pay attention motor is running at constant speed capacity is control by closing
intake yes amperage drop some but far way from staying efficient to maintain
18 SEER
Unless you can cut power input, power consumption all this hypo about multi and
variable speeds is in plain language lots of crap unless you are looking
A Digital Scroll is not the best design... in my opinion. It has a solenoid valve that displaces the scroll (screw) enough that pumping capacity is reduced to 10 percent. It is NOT linear-modulated... you either get 100 percent or 10 percent... and nowhere in between. It's also a mechanical operation, and I'd rather rely on electronics these days.
Copeland claims the energy savings are at least 20 percent. Frankly, I don't buy that. The motor is energized and running constantly.. while the pump starts working and stops working on demand... something like a clutch on a vehicle.
I realize a lot of field techs have trouble with electronics, and solenoids are a lot simpler to diagnose than a VFD that takes analog inputs from microprocessor-processed data. However, I'm a big believer in VFD's because I seem them save huge amounts of money with fans and pumps using them... as well as screw air compressors. Fifty percent is not unusual.
Tony's claim that a VFD system only helps comfort is baloney. A properly designed and setup system is not ON/OFF... but usually variable from
40-100 percent capacity. It's true there is some loss of efficiency by the drive itself... but not much... for good drives less than 2 percent.
A VFD system might be more expensive... but it is worth it. We have several RTU's running VF coupled to our own SCADA system and the power cost is about 40 percent less than it would be with a traditional setup.
Electronics have come a long way, mostly due high current switching MOSFET (MOS transistor) advances. It opens a whole new world.
Reluctance to accept electronics is not unlike the auto industry when it switched from carburetors to electronic injection. Survivors will learn how to deal with electronics, just as the auto industry had to.
What is missing at the moment is a standard for diagnostic tools. Heck, with the automotive analogy, it is just recently the EPA specified a single standard protocol (CAN) for all diagnostic connectors on autos.
Why the heck these OEM's don't just use Ethernet for everything amazes me even today. It's fast.. and perfectly suitable for troubleshooting or SCADA applications.
It is a protocol not yet developed well enough for use as I/O control... but the layers A/B, Modicon and other have implemented work fine using Ethernet as the transport media.
You know, Modicon developed Modbus (a RS-485 protocol) long ago and made it an open communication standard. You'd be pretty hard pressed, even today, to find a industrial device that doesn't talk Modbus.
Allen Bradley, on the other hand... developed Data-Highway and DH+... and still refuses to make that 'open'. Stupid.
What would be wrong with having a E-net connection on stuff like this? Plug in a laptop or cheap portable/specific tool and the software would tell you virtually everything you needed to know... immediately. Whatever the 'system'... or mysterious 'board' knows... you can see.
We design new-technologies systems for industry like this every day. It's saved customers millions. No longer does someone wonder whether a limit is made, or a overtemp condition exists... or whatever else causes the equipment to refuse to run (or run improperly). Maintenance people can pinpoint the problems and fix it in minutes.
That's the model the autmotive's have taken.. and that's the one HVAC OEM's should be looking at right now.
Fujitsu ductless units use DC modulated VFD compressors. The indoor section sends the information through a data line to the outdoor section and 'modulates' the compressor to meet the indoor load. Exceptional. Their
12,000 btu model has a 21 SEER rating!
So why can't the USA Mfg.'s step up to the plate? Instead of cumbersome 2 speed compressors, why not VFD?
So the compressor is 2 stage. What are they *doing* with the second contactor on the Lennox 2-speed and the Goodman 2-speed if they aren't
*2-speed?* Like the CARRIER 24ANA1 Deluxe 2-speed or GOODMAN SSX16 2-speed.
Generally I've seen the term *stage* for gas unloaded compressor [15 ton or larger.] like on Carlyle Compressors. They either are electric unloaders or suction gas unloaders.
Ummmm....check out the Copeland 2 stage scroll..... a solonoid shifts the scroll plates to either run "unloaded" at 60% or "loaded" at 100% of its rated output.
The Copeland 'Ultratech'... which I think you're referring to... is a classic unloader. The Digital Scroll takes things a bit further... but it's still mechanical and I'm not partial to that....
There is no 'linear' control. 60 or 100 percent? Geeze....
I'm not 'dinging' you, Steve.... But please remember the manufacturers are not doing right by the consumers here. I don't blame Copeland, either.
The OEM's have a great concern the field techs out here have no ability to deal with complex electronics like VFD's and digital control.
I just want to know if that's justified, or not..
If they are looking at "Billy-Joe-Jim-Bob, its justified.... As far as I am concerned, just give me the additional training, and I am good to go. I already have a pretty good basic knowledge base for electronics, computers and controls. But then I am not the *average* HVAC technician, and neither are the majority of the folks on here.
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