DC Powered A/C...hmmmm

Wanderman

http://www.dcairco.com

Since I am stuck inside and can't do too many things in the snow, I revert to planning and R&D in the winter. Now that I have around 500 Watts on my small RV with a Tristar MPPT 45 AMP controller, I find myself with spare power very early in the day. The new US made panels are performing MUCH better than the old, failed China sourced ones.

I have a couple (2) of new Trojan SCS225 batteries (~130amp/hr [20hr rate] each) so I am ahead of my old capacity a little bit (~25 a/hrs+) So...now what? Until LiFePO3 get's to economical feasibility and I can quadruple my storage in the given physical space, I'd like to explore the possibility of running some type of Air Conditioning on excess solar after my batteries are charged in the AM (Usually by 10 or 11AM).

Toward that end I have researched Mini-splits (way to difficult to install in the RV and 12 Volt (24/48 as well) units designed for trucks, the military, and telecom industries. Recently I stumbled upon the link above. Here are the stats:

Cooling Capacity 30/359.000 BTU / 2650 WattCooling Capacity 27/357.650 BTU / 2250 WattAirflow in the cabin388 CFM / 660 M3/hPower Consumption 100% duty cycle720 WattPower Consumption 50% duty cycle360 WattVoltage VDC12 - 24 -74 Vdc (other voltages on request)Max allowable temperature 43 (celsius)Indoor noise fan low/high41/52 dB(A)Outdoor noise56 dB(A)Size indoor ceiling plate600 x 600 x 3 mmSize outdoor unit966 L x 700 W x 280 H mmRefrigerantR134AWeight65 Kg

The other concept would be too remove the existing 120V compressor and fan assembly from existing RV air conditioning units and swap in a 12V system (Boyard)

They have several units that purport to put out a decent amount of cooling btu's at a seemingly low draw.I'd like to get some opinions on the basic feasibility of this project before I get too deep.

What say you???

Rich "The Wanderman"
www.thewanderman.com

Photowhit

Re: DC Powered A/C...hmmmm

500 watts of panels will not do much...

If you are really wanting to do something, which will add minimal cooling in the under 300 watts (actual available power) you might look at a Danfross compressor and an all refrigerator type 'A' coil. Been a while, but years ago I had an idea to build a sleeping coffin, 4x4x8 insulated with and be able to AC it for sleeping 8 hours on a minimal system. NOT a cheap experiment, I think the compressor was $200 and a sailboat refrigerator only parts kit(including most of what I needed including a compressor) was around $500...

jimindenver

Re: DC Powered A/C...hmmmm

I use 720w of portable panel tracking the sun to power a Frigidaire 5000 BTU window air conditioner. It is rated at 446w and on a Kill a Watt the highest I have seen is 410w. The system tracking the sun at 10,000 ft in the Rockies is good for 50a once the haze has burned off but we only need cooling mid summer for a few hours mid day. It never will run off of the battery because even if it becomes partially cloudy, it cools down.

So it can be done but you will need more than you have. If you have a big enough bank you could let your 500w assist in running it and then recharge what it didn't cover afterwards. That's how we run a 1375w microwave for 10 minutes off of a 8-D.

jonr

Re: DC Powered A/C...hmmmm

Photowhit wrote: »

... years ago I had an idea to build a sleeping coffin, 4x4x8 insulated with and be able to AC it for sleeping 8 hours on a minimal system.

I have a theory that such a thing could be cooled by antifreeze being pumped from a freezer. Ie solar panels would power the freezer during the day and it would chill antifreeze. Then a very small pump would pump this through a radiator at night - almost no off-hours power needed.

Wanderman

Re: DC Powered A/C...hmmmm

All interesting info, however it seems no one looked at the link in the first post. Their A/C shows 360 watts! According to the square footage of space that needs to be cooled and the output a 50% duty cycle is on the upper end of the needed scale to cool the volume of space I have.

After fully charging the batteries, and having 500+ watts of solar, seems to me it would work fine. Perhaps I am missing something?

Also, their specs show soft-starting, so no large draws for motor starts. (maybe?)

Rich

westbranch

Re: DC Powered A/C...hmmmm

I looked at their site, which model are you looking at?

Photowhit

Re: DC Powered A/C...hmmmm

Wanderman wrote: »

All interesting info, however it seems no one looked at the link in the first post.

Your link goes to their main page, I followed it, found you wanted me to figure out which unit, you were referring to, so I used your figures.

Wanderman wrote: »

After fully charging the batteries, and having 500+ watts of solar, seems to me it would work fine. Perhaps I am missing something?

Yes! my post! You won't have 500 watts of power, but the NOCT value of your array, less any loads, NOCT value runs about 75% of panel rating. Add to that that RV mounted solar arrays are typically not at optimal angle for 'solar noon' and I'd guess 300 watts of available DC power was stretching it.

Wanderman wrote: »

Their A/C shows 360 watts! According to the square footage of space that needs to be cooled and the output a 50% duty cycle is on the upper end of the needed scale to cool the volume of space I have.

So where is the power coming from for the first hour or 2 when you will need 720 watts to cool the place down so it can run at the 50% cycle rate? From your batteries? you will need to charge them back up! better turn off the A/C so you can charge them! RV have gotten better, but tend to be poorly insulated, adding to your problem. as you needing to park your typically poorly insulated RV in the sun to use your solar panels...

Wanderman wrote: »

Also, their specs show soft-starting, so no large draws for motor starts.

Should help you start it...

Photowhit

Re: DC Powered A/C...hmmmm

I guess, perhaps you don't understand 'duty cycle'. Duty cycle has to due with the % of time the unit runs, so a 720 watt unit running at 50% duty cycle, means it will run at 720 watts for 50% of an hour giving you an effective draw of 360 watthours.

The unit will run longer when first cooling down the area.

Wanderman

Re: DC Powered A/C...hmmmm

The unit is:

http://www.dcairco.com/product/trucks-airconditioning/dc-9001-12-24-vdc-rooftop-air-conditioner

My panels put out more than 500 watts. Usually I see north of 450 watts into the batteries before mid day. I am not calculating based on panel rated size. I'm not that guy. No matter how you slice 50% it's still 50%. Aggregated over the course of a full day it works out as an average. Since the space is so much smaller than what they rate it out...it will likely be less. Also, depending on the day, it could be started earlier to maintain reasonable temps, instead of cooling down the entire rig.

My RV is many things, but not typical. I have excellent insulation and typically can maintain early morning temps into midday with just an exhaust fan.

Rich

Blackcherry04

Re: DC Powered A/C...hmmmm

One thing for sure can be done, Step up, Buy it, Install it, Use it and Log the data and share it.

Wanderman

Re: DC Powered A/C...hmmmm

Blackcherry,
I don;t usually take the "scream and leap" approach. Rather an appropriate research phase combined with fact finding and opinion gathering. If the concept and theory lends it self to success only at that point will I purchase expensive non-returnable goods.

Safer that way. And more practical.

Rich

Photowhit

Re: DC Powered A/C...hmmmm

Wanderman wrote: »

No matter how you slice 50% it's still 50%. Aggregated over the course of a full day it works out as an average.

Well, you might check your math! Since you will use stored energy, even just DC, the batteries will require more energy input than what you take out. FLA will require 15-20% more energy in than out.

Wanderman wrote: »

Since the space is so much smaller than what they rate it out...it will likely be less. Also, depending on the day, it could be started earlier to maintain reasonable temps, instead of cooling down the entire rig.

Sounds like you want t to work, heck give it a try and let us know! When I AC'd a small cabin, I had a window AC that used @460 watts and once cooled down had a duty cycle of around 50% on all but the hottest of days. Then again, my cabin was 'parked' n the shade and had 6" thick walls.

Wanderman wrote: »

My RV is many things, but not typical. I have excellent insulation and typically can maintain early morning temps into midday with just an exhaust fan.

This makes no sense. If you run and exhaust fan, the air must be replaced. The 'new air' would have to come from outside. It would make more sense to circulate the cool air inside. Moving air lets our bodies natural cooling work better.

westbranch

Re: DC Powered A/C...hmmmm

Thanks for the link, I have Bmarked it for reference, great that it is 24v.

For a bit I thought you might have been looking at the mini split version for cooling only in one space (sleeping) and let it circulate as it will , but the all in one unit is easier to install and keeps the hardware outside the RVs shell.