Mini split amount revisited

[GlennWest]

Ok, guys. Been saying I need a 36k unit. I have read many post of others using just 2 12k units and staying cool. Even one, the mission cargo trailer, that uses just 2 12k. I have posted to him on Facebook and he has no problem cooling that trailer. It isn't insulated nowhere as good as my Teton. I must confess something also. Found mini splits are very sensitive to dirty filter. Ours wasn't moving much air. Raised cover, filter looks ok. Removed it and air greatly increased output. Fine dust in filters. Cleaned and night and day difference. So my bad for not checking fiter enough. So I may rethink my entire inverter needs. 2 of those 110v units are very efficient. Also opens up possibility of 48v units. Also considering mounting mini split in spare tire area. Only challenge would be flex lines to allow raising for traveling. Thinking simple pivot and using tire cable to crank up or down. Parker makes flex lines. Might be worth call to see if they can put on flare ends on their lines. Ok, so kick my butt if you want to. I am. 

[Daveh]

Where is your spare tire area?

[GlennWest]

It is near rear of Teton underneath. Large area. But just measured and not wide enough for two units, perfect for one. So scrap that idea. There is room at back for two with 10" clearance between them. So my thinking now go with that. Now whether to go 48v or 110v. The 48v units are twice the cost to buy. Just over 500 watts each to operate. Opens me up to lower wattage inverter. Decisions.

[sushidog]

You know my thoughts on the matter, Glenn. But I'm just planning on buying one. Two is a hefty price tag, as is a suitable 48v bank to power them. I assume you're going with lithium as lead acid is as heavy as, well, lead.

I plan on mounting above my rear bumper on a hitch mounted rack that can be removed to access my spare tire located just behind it. A pair of 48v mini-splits is a lot of money, and unless you plan on living off grid half of the year, would be hard to justify as a cost saving measure alone, even considering campground fees saved. It would give you ultimate independence though, which is why (along with cost savings) I'm going with a 48v native system with a single 12k btu heat pump, gaining all the inherent advantages the higher voltage system offers. I'm also planning on keeping a pair of GC-2s for all my 12v native gear such as my slide motor, fridge board, lights, fantastic fan, water pump etc. With a single 350 watt panel to keep them full and about 1800 watts tied into my 48v bank for all the heavy lifting (heat pump and 110v power.) I figure for the rare occasions I need to run my other roof mounted RV AC I can run my 5.5kw genny a little - heck it will probably need the exercise anyway and I can fully load it, topping off both battery banks too.

My DW and I went full time the first of the year, but have to tie up some loose ends at work before I leave Louisiana the end of next month. Look forward to seeing you down the road.

Chip

[GlennWest]

The 48v 12k unit is 500w cooling mode and 600w heating mode. My Pioneer unit is 960 watts cooling, 1120w heating. That is right close to the 48v units.  That would be less inverter to buy but I would need to buy 2 of the 48v units and only 1 110v unit as I have 1 now. That is $900 now or #4k . 3K will buy a second inverter. So it is a wash in upfront cost. Do believe I will have enough battery, chevy volt, for either. It is a few more years for full retirement for me so I likely go with the 1 110v unit. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[sushidog]

Yes, the power consumption of your single pioneer mini-split is about the same as two 48v super high efficiency mini-splits, (especially when you consider the power lost through inverter inefficiency - making the 110v power from your DC source) but the BTU output is doubles to 24k btus with the pair of 48v units. Or do you plan on keeping your current 110v mini-split?

Each  2kw 48v Chevy volt battery module is 41.6 amp hrs at 48v. You'll probably need 6 or more of these for the task at hand. Or do you have a complete battery module? If so, which one? The complete battery packs ranged from 16 kwh for the 1st generation 2011, 2012 year models (333ah at 48v), to 18.4 kwh (383 ah) for the 2016 models.  Either full module will be more than adequate for the task at hand. What kind of BMS do you plan on using?

Chip

 

[GlennWest]

No bms. Just use upper and lower cut off and in charging. Steve Dixion doing same with no problems. I will get the 17 year battery likely. They going for 3k now. If I stay 110v, yes will keep existing. Nothing to say can't have one of each. May do that.

[Daveh]

Glenn you have probably covered this previously but isn't your bottom mount position going to make the dust in the filter problem worse?

[GlennWest]

I have had no problems with dust in the unit. Now I have always, even when in stick and brick, washed out the outside unit every year. Just like I did the Dometic units. I also have not pulled down any dirt roads either. But my unit not running going down the road so it isn't sucking in dirt.

[sushidog]

3 hours ago, GlennWest said:

No bms. Just use upper and lower cut off and in charging. Steve Dixion doing same with no problems. I will get the 17 year battery likely. They going for 3k now. If I stay 110v, yes will keep existing. Nothing to say can't have one of each. May do that.

Absolutely. No judgement my friend. That is definitely the most cost effective solution since you already have it installed. It is twice as efficient as a standard rooftop RV unit. I'll be keeping my front rooftop Duotherm heat pump and replacing my rear unit with the 48v mini-split. Not in the same hole with a cassette, but with the inside unit that comes with the mini-split. I might plug the hole with an insulated plate, and leave the duct open to work with the front AC unit. I can then use the front AC in blower only mode to circulate air from the bedroom mini-split better rather than trying to mount a fan or blower on the hallway ceiling. I intend to attach the inside mini-split air handler to the rear bedroom ceiling, right in front of my mirrored closet, blowing down the hall.

I wish I could afford $3k for a battery bank, but it's a little more than I want to spend, right off the bat. I'd rather add more solar first and more and better batteries a few years down the road.  But with over 300 usable amp hrs in your lithiums, I'm drooling. Plus it's a pretty doggone big T-shaped battery bank. I don't know where I'd put it. I sure hope it comes apart. You probably have more basement space on your 5er than I have in my MH. I barely have enough room for 8 GC-2s. They probably weigh as much or more than your lithium bank and only hold 1/3 the energy. They are far less efficient to charge and discharge too - but they're only about $700 bucks and I don't have to worry about keeping them in a temp controlled environment. I think they will be my "learner set." I'm sure I will be upgrading down the road, as the prices of lithium continue to drop, but for now I'll probably be running my generator from time to time. Heck it needs exercise once a month anyway, right?  (Certainly if I need to run my front AC off grid.)

Chip

 

[GlennWest]

Sounds like a great plan. Think you will learn to hate that Dometic once you "hear" the quiet of the mini split. I know mine loud, but not until we quit using Dometic did I realize how loud. You can pick up the earlier 17kw Volt battery for 2k. You do disassemble it and use just the batteries. Shape it anyway you need.

 

[GlennWest]

Also you do know, you can buy a 12k,15k, 18k 48v mini split? Jfyi

[lockmup68]

Glenn, I was thinking of the area behind the rear jack, mounted vertically, but in parallel to the framerail. It could go up outside the frame rail a few inches, the fan would be clear of the framerail and it fits without removing the spare tire. Make sense? Might be able to get one on each side, depending on the slide side clearance. Would have to figure out a fender or something to keep the dift off the tires from hitting the unit in transit. 

[lockmup68]

Also, I am really trying to figure out how to mount the mini-split inside handler to blow into the existing air ducts in the ceiling in the Teton. I'm thinking if I give up the top center cabinet (very rear of trailer in middle), I can hook in right there in the rear. In the front, don't want to give up that much closet in the nose, and can't really have anything hang down in front of the closet or would hit your head going around the bed. Cassette in the middle would work, maybe in the same area the current roof mount unit is. But that would be really long lines to run. Watching what y'all do with interest. 

On another note, if I can't get my bunk AC to work in the truck relatively cheaply this spring, I'm going to drop in a mini-split on the truck and be done with it. 

[GlennWest]

Cassettes are only 230v. Jfyi. I think that area would be a good place. I had not considered mounting it pararrel. Could it hang to low? Looked to me that it would. Did not measure how deep it is though. That area is right at rear of camper. My unit is roughly a 1' behind that. My support has touched asphalt a time or two. 

[Daveh]

I have been thinking of doing this also but with the 120 volt.

[GlennWest]

I do believe you would enjoy them. So quiet and economical.

[sushidog]

On 1/29/2019 at 5:53 AM, GlennWest said:

Also you do know, you can buy a 12k,15k, 18k 48v mini split? Jfyi

Yes, but the efficiency drops on the bigger units. The 12k btu has an unbelievable EER of 21.43. (The SEER is not listed but I'm sure would be around 35. ) However when you just go to 15k btu the eer EER to  19.48 and at 18k btu it drops to 13.16.

Efficiency is everything when running off batteries.  For comparison, the 15k model uses 37.5% more electricity to produce 25% more cooling, while the 18k btu model uses a whopping 144% more electricity to produce only 50% more cooling . Plus if you are dealing with lead acid technology there's Peukert to take into account with that kind of heavy current draw. The small, 12k btu model only sips 11.5 amps at 48v which is close to the 20 hr rate of the cheap FLA batteries I'm considering initially. Anything larger would necessitate lithiums. Of course during the day the battery bank is only a buffer, as I'll have over 30 amps coming from the planned 2kw of solar at full sun which is more than adequate to power the mini-split directly plus provide sufficient extra power to both charge the batteries that were depleted the previous night and have a tad left over for inverter use for my 110v needs.

Chip

[GlennWest]

Yes, I noticed that too. But of you needed 2 of them and could get by with one 15 or 18k it would be less wattage used. 

[lockmup68]

is 48v that much more efficient than 24v? Tesla 5.5kw pack is $1600 at 24v. Would need two to go 48v. The cost of inverters and such seems to go up from 24 to 48v as well. 

[sushidog]

7 hours ago, GlennWest said:

Yes, I noticed that too. But of you needed 2 of them and could get by with one 15 or 18k it would be less wattage used. 

Two 12k btu mini splits producing 24k btus of cooling would consume 1120 watts, while one 18k btu unit would consume 1368 watts. Plus most times you are nowhere near capacity making the scalable power of 2 smaller units much more efficient, when less cooling is needed (which is most of the time) though at higher initial cost.

Chip

[sushidog]

Lockmup68, all the 24v systems I've seen are bus type systems that are very expensive and not very efficient.

Fortunately, my older 35 ft. motorhome is very well insulated, with dual pane windows, reflectix for the windshield, etc. I find that 2, 1,500 watt heaters keep it a comfortable 70+ degrees inside when it gets down to freezing outside, which is the coldest it has gotten so far. 2, 1500 watt electric heaters produce a total of 10,240 btus/hr.. A human being who is reasonably active produces another 650 btus/hr (about 300 btu's/hr when sleeping). Assuming no heat assistance from sunlight (as the observation of the heater's performance was over night) this means that 11,540 btus are responsible for a 38 degree delta T, or roughly 300 btus per degree change. Therefore a 12,000 btu air conditioner (minus 1,300 btus of body heat for 2) = 10,700 effective btus divided by 300 =  35 degree change in temp. theoretically possible.

So a single AC should theoretically be able to maintain a 70 degree inside temp at up to 105 degree ambient temperature (again assuming no heat load from direct sunlight, as under a heavy shade or at night). This computation ignores relative humidity factors which will minimally affect the outcome and more importantly, temperature load from sunshine. I plan on racking roughly 2,300 watts of solar about a foot off the roof, to act as shade, minimizing heat load on about half of my roof. My large awning and slide topper will also help provide some shade to.  Practically, if I a single mini split could produce a 20 degree temperature change from outside, taking into account heat load, this would still allow me to keep it a comfortable 75 degrees inside in 95 degree heat, without having to fire up my generator and run my rooftop heat pump for supplemental cooling when required. Any hotter than this and it's not fun to spend much time outside anyway, so I plan on moving before this point.

Of course night time is when a system like this will perform its best, with no solar heat load and falling ambient temps, allowing a good night sleep practically anywhere (especially if the bedroom door is closed, so only it is cooled). Obviously I couldn't camp at death valley in the summer, relying on a single 12k btu mini split,  but who would want to anyway? Nevertheless, I think it is a practical way of extending my off grid camping season/range while keeping my total solar climate control system (as it's also an efficient cool weather heat-pump) initial cost under $6,000, with minimal supplemental generator or furnace run time, which is my goal.

Chip

[GlennWest]

We been heating our Teton with the mini split and fireplace. Have seen teens in Tyler. Now in Freeport so not very cold here. Both keeps us cozy. But that single 12k would not cool this Teton in south Texas heat last year. It and the one remaining Dometic did. Now it was easier to cool that it was with both Dometics. So the mini split cools better. 

[lockmup68]

to summarize, to make sure I'm understanding correctly about mini-splits.

• 24v or 48v D/C units are more efficient vs. a 110v or 240v a/c units going through an inverter
• takes more solar/battery storage to run 110/240 a/c vs. d/c assuming same efficiency

My question still remains, what, if any, advantage of going 48v vs. 24v for the whole system when switching over to lithiums? I know Steve and David run 48v systems. Just curious. 

Thanks, 

[sushidog]

The main advantage of the higher voltage DC is that lower current is needed, thus smaller wires can be used. Also the highest efficiency mini split available runs off 48v dc. Here's a link:  http://www.geinnovations.net/HSAC_Productline.html

Remember, do not confuse SEER with EER. EER is simply the number of BTUs produced vs watts used. 12,000 BTUs / 560 watts = 21.4 EER.  For comparison, an excellent Fujitsu 12,000 btu mini split has an SEER of 29.3 but an EER of only 15.2 meaning it draws 790 watts to produce the same cooling power of the previous unit. To make matters worse you must buy a 220v inverter resulting in another 20% loss in efficiency meaning you now have about 986 watts coming out of your batteries. This means you need 75% more solar panels and battery capacity if you select this unit over the first one mentioned. The first mini split costs about $600 more than the second, but after you add in the cost of the inverter needed plus a 75% bigger system you can see, it it is more economical and you save much more weight by going with the 48v native mini-split and a 48v battery bank to match if at all possible.

Anytime you convert from AC to DC, step up or reduce voltage there is an efficiency penalty. The goal is to maximize efficiency so the smallest, lightest system can be utilized, since weight is at such a premium on an RV.

Chip