I know I'm resurrecting a dead thread, but I've been thinking about the idea of picking up the smallest used 3 phase condenser I can find (2 stage if possible), and then doing speed control with a standard VFD.
2 stage usually gets you 2/3-70% of rated output -so for a 5 ton that's 3.5 tons
3.5 tons at 60Hz, running at 50Hz is about 83%, which gets you down to about 3 tons. assuming you can probably turn it UP to 72Hz, that'd get you a 6 ton AC/heatpump with a 50% turndown ratio. a good bit better than stock, eh?
Not sure how far down you can go before oiling becomes an issue on a compressor not intended for low speed operation, but lets say you could get to 44Hz safely (based on the 3 phase 2 stage scroll compressors i've seen rated at 50/60Hz), that'd drop down to 2.5 tons.
|