Question on AC condensers and off grid

dbarnard67

I am currently powering a traditional 3.5 ton ac compressor for my central ac.  Has anyone swapped these out with the new DC inverter models.  Currently pulls 3,400 watts and about 88 amp on my 48v system.  Would like to get that down with out installing mini splits all over.  I have a timberframe with *' and 10" thick SIP's so it does not run constantly but that our compressor really sucks the energy.  Thanks in advance.

Dave Angelini

I know a refrigeration guy who lives offgrid. He adapted a forced air unit for variable speed.
What you propose would not have any warranty and you would have to do the design. 

 Seems to me far easier to use a split. At least you could take a split back if it was DOA.  I think he used the guts from a Carrier but really off the top of my head. Maybe someone else will chime in. Not many people on this forum from the old days when alot of service people were on here.

Maybe some kind of addition to your existing forced air with a good sized split feeding it thru a big duct? The Rheem's seem to have the room in the manifold that I have seen.

dbarnard67

Good thoughts Dave.  Most of the time when they find out I am off grid the warranty never matters, lol.  I put my current Goodman furnace in and it does the trick just would like to get that big condenser out there from hogging so much energy.  Was thinking I could braze in the newer dc condenser version AC only and the initial start up on the Locked Rotor would not be as bad as well as the big ole motor cranking.  

Dave Angelini

More good thoughts on the big gain you get by losing the ducting in forced air. Even perfect ducts can lose 30%. Bad ducts Whoa!

 I went to a home out in the desert last month that had the crawl space pressurized for cooling/heating. No ducting loss but what a huge total loss for that system. Just holes in the floor wherever you wanted

waynec

I used a Bosch 20 seer inverter compressor outdoor unit which requires their air handler. their 18 seer condenser also inverter compressor can be used with your air handler. both can be used with your present thermostat. The start up amps  is near 0 and slowly ramps up.
I know this does not compare with the top tier mini splits but we did not want the wall hung units and when the mini splits are used with a central air handler the efficiency tumbles   

dbarnard67

Good to know Waynec.  That is what I am thinking.   Swapping that big condenser out for a better more efficient than I have currently.  Will look into the Bosch. Thanks

Dave Angelini

It brings up why not use any mini-split in this fashion. What size & what was special about the Bosch?

waynec

Nothing special about the Bosch there are many other brands out there, its just what I had knowledge of and what my local supply house carried and was far cheaper than the top brand mini splits with air handlers for duct work. The important thing is the inverter compressor and a high seer.  

Dave Angelini

Thanks !  What specifically did you do to interface the air handling? My post #2 was basically fitting the split air handler into the existing forced air manifold. I think he used a ceiling air handler. You do not have to us the wall split handlers as there are floor and ceiling handlers that "might" fit.

Splits are approaching 40 SEER in the smaller sizes. Not cheap but if you need to run offgrid at night, it is cheaper than batteries and the ability to charge them.

waynec

Referring to your #2 post I did not have to  adapt or modify any thing. the outdoor unit is designed to operate with a horizontal or vertical air handler. and varies compressor speed according to the load ( pressures ) so does not require a communicating thermostat. The wife and I did not like the idea of the wall mounted  air handlers and of the information I could find at the time the ceiling distribution manifold took a big hit on efficiency and wound require a lot additional installation. The vertical or horizontal air handler for the mini split, which no one stocked, took an even bigger hit.
I do agree the hi end mini splits is the way to go some provide full rated heat BTU output at very low temps I believe I have seen some
 claiming as low as 5 f .
I had water source heat pump for over 20 years, worked great until the spring began drying up so the duct work already there had a lot to do with my decision.