Results 1 to 13 of 19
07-28-2012, 11:32 PM #1
Variable displacement compressor for home A/C?
I don't mean like two stage, but I mean 15-100% adjustable capacity.
Some cars use variable displacement compressor.
The displacement is controlled by moving the swash plate. The angle of swash plate determines the piston stroke and offers capacity variation down to about 15%.
In older designs, the adjustment target was to set the suction to a target pressure. As the compressor output increases (with the engine RPM increasing) compressor will cut back to reduce capacity.
If you're at idle, it will also adjust compressor in response to evaporator motor speed as that affects the evaporator load.
Some newer designs use an electronic valve which also monitors thermostat setting. So, if the cabin temperature is close to adjusted value, it can actually increase the evaporator temperature by throttling enough to cause evaporator pressure to go up.
The point of that is, rather than making air that is too cold and uncomfortable out the vent and reheating, it makes the air not as cold.
MVAC variable compressors are usually 5 cylinder axial type with pistons arranged in pentagon shape.
Why can't the same setup be used for stationary A/C?
07-28-2012, 11:43 PM #2
I'd rather have a mechanically simple compressor, with an inverter drive to vary its capacity.If more government is the answer, then it's a really stupid question.
07-29-2012, 12:07 AM #3
Carrier Green speed and now several WSHP use inverters and change the compressor RPM to go from about I think 30-150% capacity. The +50% I think is only unsed in heating. There are alos VRF system, which are multizone minispits with condensers up to 10 tons that cna alos be tied together for up to 30 tons of combined capacity. Those also have vairable speed compressors.
I'm waiting for cars to use heat pumps so you don't freeze your a** off the first 5 minutes in winter. Plus the extra load would warm-up the engine faster. Heck just a 2000Watt set of heat strips would help... especially with defrost.
07-29-2012, 09:54 AM #4
07-29-2012, 02:36 PM #5
07-29-2012, 03:24 PM #6
I suppose you could also combine 2 small scrolls with an inverter drive and get 20-150%... but it would be cost prohibative.
At some point, you have to consider what you're trying to accomplish with variable capacity, and you might find that using a chiller for example would be even better. Plus as mentioned in another thread, you could use chilled water for your refrigerator too and generate r at least preheat heat hot water with the condenser.
07-29-2012, 03:54 PM #7Regular Guest
- Join Date
- Jun 2001
- Oklahoma City
The problem with warmer evap temps during light load conditions is poor humidity control when you need it the most. However if you combine lower blower speeds with lower compressor speeds you are onto something. The thermostat could be a little computer constantly monitoring temperature and humidity and varying blower/compressor speed "on the fly".
But with these new systems comes high equipment costs, and proprietary systems. When the system goes down, it could be days before a replacement part comes in. Technicians would need significant training on the newer technology. Furnaces last for 20-30 years in our area, A/C units are good for 10-15 years. High tech system are rarely put in by a builder. When a unit suddenly goes down most customers are willing to spend the extra cash for a high tech system.
07-29-2012, 04:12 PM #8
07-29-2012, 04:20 PM #9
Besides some GM cars (not trucks) anybody else use the variable displacement comps? Why not? Too expensive? I like that over constantly cycling every few seconds at times.
07-29-2012, 04:42 PM #10
It's easier to diagnose constant output compressor like residential units, because obstructions and problems are visible through gauges.
When you have variable displacement, compressor will reduce stroke and hide symptoms.
You're stuck with either on or off with constant compressor. With variable displacement, you can actually change the load on engine by changing fan speed.
07-29-2012, 05:19 PM #11
Our summer class installed a 24.5 SEER iQ Drive in one of our class rooms. Compressor, condenser fan and air handler motor all modulate to load. We set the controller at 75 degrees and the humidity is constantly below 50%. It's the best humidity control that room has been since it was made in 2010.
Just have to love engineers that think bigger is better because they get paid by the tonnage. NOT.Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.
07-29-2012, 05:29 PM #12Professional Member*
- Join Date
- Jul 2006
After the severe thunderstorms and lighting we have been replacing v/s modules x13 motors and circuit boards ,think ill stick with my psc motors and single speed compressor
07-29-2012, 06:17 PM #13Regular Guest
- Join Date
- Sep 2010