Inverters are coming, stay tuned.

Nordyne already markets an inverter controlled ASHP under 4 brandnames including Frigidaire and Maytag. If memory serves compressor speed is controllable down to 25% and load down to 40%

Daikin and Mitsu have similar capability in high end mini-split models

That's good news and would like to see them in geo compressors. They say it's good for an extra 20% in efficiency (I  assume over a single speed  - perhaps less gain as compared to a two stage).

I would expect such an efficiency improvement if the inverter is suitably high efficiency. The whole system would have to get much smarter to realize the full potential efficiency improvement. Zones would have to be individually weighted and humidity separately monitored and controlled. Compressor load and blower CFM would need to modulate together, with a trim on CFM per ton for dehu.

This kind of thing is routine for industrial regulatory control systems, and when it trickles down to resi HVAC it will result in considerable efficiency, comfort and noise improvements as well as being a substantial value add for contractors who embrace the additional expertise required.

I wasn't particularly impressed when I read about Digital Scroll several years ago. At the time it consisted of running the compressor at constant speed but rapidly valving refrigerant flow on or off to vary the average refrigerant flow. That would be an evolution of the present bypass staging valve used to provide low stage in the Ultratech line now widely deployed.

However, continually rapidly cycling a refrigerant valve while keeping the compressor at full RPM strikes me as inefficient, inelegant, and possibly vulnerable to early failure, so I'm not displeased that Digital Scroll isn't slated for resi HVAC.

I'm not all that jazzed about multiple compressor solutions owing to cost and complexity, so that leaves variable speed. Nordyne seems to have done it, (Google IQ Drive) but time will tell.

One of the big advancements towards variable capacities is electric metering devices.
Speaking with folks at Nordic and Daiken both I heard that these have been a real problem solver in multi and vari stage equipment.

20% efficiency increases (if that's the boast) over single stage equipment doesn't strike me as much more than 2 stage equipment currently offers.
j

Quite true. I'd expect a 20% boost over present two stage equipment; any less and it isn't worthwhile, but to get it in actual field use will likely require all the smarts I described and then some.

By electric metering devices are you referring to refrigerant metering? If so, I agree that's another area we'll see change, and there's always the issue of keeping refrigerant oil where it belongs.

Posted By engineer on 10 Mar 2010 10:31 AM

By electric metering devices are you referring to refrigerant metering? If so, I agree that's another area we'll see change, and there's always the issue of keeping refrigerant oil where it belongs.

Yep,
electric metering devices that replace mechanical TXV's have nearly infinate settings. it is a big step toward variable flow and true usefulness of variable speed compressors.
j

I agree, given the low prices on electronic inverters (VFDs), they make more sense to me. From Copeland:

"The high-efficiency Copeland Scroll UltraTech™ compressor can help reduce energy use by 20-60 percent in residential air conditioning units... Copeland Scroll Digital compressors are typically 30 percent more efficient than hot-gas bypass units" {ie, the UltraTech}.

Sounds like quick payback potential.

Are Ultratech models are considered "hot gas bypass" ?