Designing a 20kW Commercial System

What are the power requirements on the AC side of things.  Do you happen to know the LRA of the A/C units?

2 forklift batteries...are we talking 12v, 24v or 48v?

They haven't finalized the air conditioning but at this stage it look like there may be three 4 ton units. Those are typically under 120 LRA. I would also interlock the controls so that units can't start simultaneously. I'm also looking into DC solutions for air conditioning.

Batteries will be 48 volt. As far as AC loads, there is probably less than 1000 connected watts of lighting. A commercial refrigerator that pulls about 13 amps at start. A low heat dishwasher that pulls 11 amps continuous @120 volts. A 1 HP well pump @240 V. Two 3000 watt water heaters. I think I will interlock those as well. Besides air conditioning, I don't expect the instantaneous draw to be more than 10000 watts at any given moment, almost certainly less. 

Surprisingly, I haven't found a DC-powered A/C (all Chinese made) that's worth the expense--or for that matter, uses less power than a similarly sized AC version.  All of the Chinese 48v DC mini-splits I was checking on Alibaba...convert the power to 360vDC for a regular inverter A/C compressor in the first place.  They also used significantly more power than an off-the-shelf Pioneer mini-split of the same size (and less cost).

Absolute best bet would be inverter-based A/C units--the startup surge is completely eliminated, and you could technically power them on 360vDC.

Obviously, this project sounds like a job for 2 12kw GS inverters (whether split-phase or parallel...not sure yet)--that is once we finally get the design proofed and ready for manufacturing.  Awaiting a transformer test at the moment.

Ok, so how many say 6K's can be paralleled? If this has been covered somewhere else in forum, then my apologies.

My thoughts are to split the system up across several panels, each powered by its own inverter. That way, a single inverter failure won't black the whole place out. Two lighting and general purpose receptacle panels can be fed from one 6kW each. Then, maybe the mini splits share two parallel inverters and a control system staggers their start up.

Fair enough 😉

If you're using "inverter compressor"-based units, you do not need to be concerned about startup surges.  (It's just the old-as-dust synchronous AC compressors that have the ginormous startup surge.)  I have a Pioneer 1-ton mini-split (12kbtu)...and for startup, it literally starts at under 1A (120v)...and slowly ramps up to full 8A load if required over 30 seconds' time.

5 hours ago, Joe S said:

Ok, so how many say 6K's can be paralleled? If this has been covered somewhere else in forum, then my apologies.

Parallel functionality is (like I've told Sean) very difficult to handle...at least via the "no comm harness" method I've been trying to do.  At the moment, the theoretical limit for paralelling inverters would be your wallet...but this has not been tested.  Max testing has only been on 2 units thus far.

We may have to add a (hardwired) inter-inverter comm method, as much as I don't like to--but if properly implemented, that'd handle surge loads as well.  It would connect to an existing port on the control boards, so the only difficulty would be mounting said connector in the chassis (and as they're stainless steel chassis, that's easier said than done).

We may have to add a (hardwired) inter-inverter comm method, as much as I don't like to--but if properly implemented, that'd handle surge loads as well.  It would connect to an existing port on the control boards, so the only difficulty would be mounting said connector in the chassis (and as they're stainless steel chassis, that's easier said than done).

I  would  buy  2  GS 6kw  if  parallel  2  GS  240 vac  can  handle the surge of a  4 ton heat pump .   

Not at the current time...at least in parallel mode.  The 6k seems to be able to reach a 77A surge...which is a solid 3x surge.  (Limit there is a hardware limitation.)

If the 2 GS inverters are internally set to 120vAC single-phase output, and run in split-sync...they should be able to handle the startup surge of a 4-ton A/C.  (This has not been tested, however.)

2 hours ago, Sid Genetry Solar said:

Fair enough 😉

 

If you're using "inverter compressor"-based units, you do not need to be concerned about startup surges.  (It's just the old-as-dust synchronous AC compressors that have the ginormous startup surge.)  I have a Pioneer 1-ton mini-split (12kbtu)...and for startup, it literally starts at under 1A (120v)...and slowly ramps up to full 8A load if required over 30 seconds' time.

OK. That can be done. I suggested mini-split systems from the beginning. We'll use inverter based systems if the 6 kW will supply it comfortably. I think four 6 kW units will probably be sufficient.

As long as the full load is under 6kw, a 6kw GS inverter should do just fine.  There's no startup surges to be concerned with inverter-based A/C compressors; the water heaters are just instantaneous loads (no surge).

Balancing the loads out across the inverters would be kinda important so you can run everything without overloading any of them.  Another possibility would be running 2 6kw inverters in split-sync mode (one per AC phase) for a 12kw circuit.

OK so a hole punched out for a future connector might be worthwhile. 

OK so a hole punched out for a future connector might be worthwhile.

To  parallel  2 GS  6kw inverter by  punching  2 holes  to hardwired  is a lot cheaper than  buying  a 12kw  GS  inverter . 

Yeah...in the NEXT run of inverters.  Chassis are stainless steel, so drilling holes by hand is next to impossible.