Offgrid Air Conditioning

Started by Dave Sparks, June 22, 2009, 12:50:45 PM

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Dave Sparks

Okay I am new here but I have been lurking since Glen told me about it 4 years ago. So, it is time to give something back! I just finished 2 installs and testing on the Sanyo "mini split heat pumps"  These are the first units that the user can limit the power of the compressor. This means you can set it for 300 watts, 600, and on up to the rated power.  Most other units cycle the compressor on and off at full power.  This unit has a DC compressor that the controller pulses to allow this low energy usage. You can turn it on at sunrise at 300 watts and pre-cool the house with a small 3/4 ton or 9,000 BTU unit. This is a strategy to allow a small unit to cool a rather large home. Getting ahead of the heat gain early. It is perfect with a tracked array!

There is a full review on the Arizona wind and sun forum under  the energy section title "sanyo mini split". It has been tested for it's heating as well but this unit is really for air conditioning at 16 SEER. The billy goat building inspector that is up on Glen's hill would have a hard time sneaking up with this unit running. It is so quiet that when I first turned it on I thought the unit was defective!

Thanks again for all the great ideas over the years! [cool]
"we go where the power lines don't"

John Raabe

Interesting concept - PV powered air conditioning.

Here is Dave's thread on the Arizona solar site:
http://www.wind-sun.com/ForumVB/showthread.php?t=5104&highlight=mini+split+heat+pumps

If you are working this into a new house, you would be wise to first design in the basics of PASSIVE solar cooling to keep the load to a minimum and then make up the rest with the PV heat pump. This is the same strategy you want to use with solar heating - do the inexpensive or free PASSIVE things first and the high tech stuff after that.

Passive cooling strategies might involve:
• good insulation
• white roofs
• window placement and type of glazing
• external shading
• evaporative cooling
• solar chimneys
• ground contact floors
• earth berming

None of us are as smart as all of us.


Phssthpok

I have one of the smallest window AC units available...about 5000 BTU @ 520watts. Basically a bedroom sized unit. One of those $100 jobbies. I also have almost 1.3Kw of PV panels, an 800AH battery bank, and a 1000w continuous (3Kw surge) Heart inverter/charger (I've been gathering materiel in anticipation of moving for a few years now).

All this to say that on a really hot-n-sunny day, I should (if the maths hold true) be able to run that little window unit directly off of PV power (filtered through, but not affecting the charge level of the battery bank). 1000w in, 500w out...the batteries should remain full while I'm chillin' my cabin! [cool]

Even if start up surge is 5 times running usage, I should be just fine in my sub-200sf cabin since I can't foresee any other loads on the AC system during the day, when I'd need it (I'm trying to keep as many things 12vdc as possible  ;D).

If I find that the surge is too great on start up, I'll look into either some starting capacitors or a larger dedicated inverter just for the AC unit. ;)

Dave Sparks

Thanks John for the link! I was going to do that! Reducing the heat gain/loss is always the best way to keep a living space comfortable. There are choices however that are "cast in cement" and technology has evolved here to address existing conditioned spaces.  Big Time!

What I like about this stategy of running a small heat pump early in the day is it can work for non-optimum conditions and it is perfect for offgrid use where the solar panels are idling most of the time. Running the cooling or heating at 7 am on 300 watts and getting ahead of the buildings gain or loss was never an option with typical cooling/heating methods. Normal AC compressors have huge surges and are basically on or off. AC line surges and all that noise is not good for you or your other electrical users.  I monitored power on a logging meter and there just is not any surge or even a hint of it. You can not even hear the different settings change.

On really hot days you will need to run the power up to 600 to 800 watts but this will be after the batteries have charged.

Phssthpok, wish I could give you good news about using starting capacitors or different inverters! The good news is this technology will spread as it is cheaper to build electronics that soft start. It is also easier on compressors that do not have to be designed for brut forcce conditions. Maybe by the time you ar ready there will be less expensive options.  For now, it is amazing that there is this strategy! Hats off to Sanyo!
"we go where the power lines don't"

John Raabe

A great concept and a synergistic application for off grid PV which, like you say, may not be doing too much with the morning power anyway.

Thanks for the link.
None of us are as smart as all of us.


Windpower

Thanks Dave !

I was wondering what to do about air conditioning !

the heat pump is a real bonus too when it's chilly but not cold enough to fire up the wood stove

I think I will put it in the bed room of the 'barndominium'

it looks very practical

now there's another reason to build a tracker unit for the PV

Often, our ignorance is not as great as our reluctance to act on what we know.

glenn kangiser

Nice to see you here, Dave. 

Thanks for the information.  I may consider that myself but have to grow my system a bit more.  Seems we always want more. d*
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Pritch

Dave, welcome and thanks for the tidbit.  Areas that tend to have the best solar potential also seem to have the most need for AC!  I hope this works out. 

Quote from: Dave Sparks on June 23, 2009, 09:45:04 AM
What I like about this stategy of running a small heat pump early in the day is it can work for non-optimum conditions and it is perfect for offgrid use where the solar panels are idling most of the time.

Wouldn't your panels be busy recharging your battery bank from the night before? 

-- Pritch
"The problem with quotes from the internet is that they're not always accurate." -- Abraham Lincoln

Phssthpok

Quote from: Pritch on June 24, 2009, 01:43:41 AM
Dave, welcome and thanks for the tidbit.  Areas that tend to have the best solar potential also seem to have the most need for AC!  I hope this works out. 

Quote from: Dave Sparks on June 23, 2009, 09:45:04 AM
What I like about this stategy of running a small heat pump early in the day is it can work for non-optimum conditions and it is perfect for offgrid use where the solar panels are idling most of the time.

Wouldn't your panels be busy recharging your battery bank from the night before? 

-- Pritch

That would all depend on the size of your array and battery bank (BB), and how much power you consume after the sun goes down.

Consider that an AC unit will (most likely) be used exclusively during daylight hours in the summer time* when there probably isn't much actual charging going on past, say noon on any given day...the BB will generally be full in short order.

*Think: long sunny days. At my latitude (~45 N) the sky starts to get light around 4:30 am, is light enough to wake me up around 5:30 and stays fairly light until around 9-9:30 PM during the height of summer. Daytime power use for light would be minimal, and since off-griders tend to be super conscientious about ghost loads and other sources of waste, I can't foresee anything other than say a small fridge consuming power while not in direct use.

The two most common methods of charge control (preventing overcharge conditions in the BB) are Pulse Width Modulation (PWM) and 'dump' loads. PWM is basically a micro circuit that alternately opens and closes the circuit from the panels to the BB. The 'width' of the open 'pulse' is determined by the BB State of charge, and increases as it approaches float levels, to the point that the circuit will remain 'open' for 99+% of the time, thus 'idling' your array and wasting potential energy manufacture. 

'Dump' loading is where the charge controller is set up to switch on a 'load' (most commonly a resistance heater, but anything that uses power will do, so long as it uses ENOUGH power) to 'burn off' excess power when the BB reaches a set state of charge. This allows one to keep the batteries 'full', while at the same time still getting some 'work' out of your panels. Either way, when the batteries are 'full', the panels are no longer actively charging the batteries.







Dave Sparks

Pritch,

Thanks!  

"Wouldn't your panels be busy recharging your battery bank from the night before?"

With a tracked array, low energy usage, hi ratio of solar to battery capacity, most of the systems I design, and use are in float by 11 am this time of year. By running a 300 watt air conditioner at 7 am there is hardly a difference in when the system goes to float. In float, most systems are using less than 200 watts.

Offgrid is all about different strategies tailored to location and the owner.  This is just another one. The manufactures of Tracker's even now! leave out the best reason in the world to have one offgrid! If your sunny location can support one, they are the path to not using a generator. In winter, there are many days where the sun pops out for an hour in the am and then pops out again before sundown. If you are sized right you easily charge the batteries. If you can be flexible with energy usage there is no reason for a generator offgrid other than arc welding. The location does have to support a tracker!  It is my philosophy!


"we go where the power lines don't"

Dave Sparks

Phssthpok,

You guy's up North do have some long days! Another stategy for long days is reducing absorb times on batteries. If you are lucky enough to be able to measure specific gravity you can reduce the absorb time and finish the charge during the long hours of float. There definately is charging going on in float and the other positive is alot lower water usage by the cell.

"we go where the power lines don't"

Windpower

I was at the MREA Fair last weekend

attended a talk about 'Advanced PV"

pretty good

I asked about trackers

he said that a tracker would add about 30 % more energy captured (or more)

then someone asked about payback for the investment -- he said it would be a postive income payback -- but not much

So then I looked at trackers

wow are they expensive

I saw one that was $ 26,000 for 16 panels

you could just buy 5 or 6 KWatts more panels for that

got me to thinking there must be a cheaper way to home brew a tracker

from real cheap using a manual wind-up or weight system

or more automated geared motor/timer set ups

I have several ideas -- what do you recommend Dave ?


Often, our ignorance is not as great as our reluctance to act on what we know.

Dave Sparks

#12
First HI Glen,
I want to build a pond up on my hill but my wife says it will bring that bear over from your hill.  Did you make him go away?


Trackers....Glen has a home brew??? My old one still works but I just ran out of time and some aerospace company up here in the foothills actually wanted me after 12 years at sea with an equal but creatively filled resume gap from the old Hewlett-Packard company.

OK, I like the Wattsun AZ-125's ! You can get 1,800 watts of Sanyo's on them or 1,600 watts of most other brands. They are 6 inch pipe based and I have been to several islands in the caribbean where they have stood the ultimate test. If you buy one retail they are over 3 grand. If you have bought from them before and can tell good stories they are a lot less.  Times are tight right now and good stories can go a long way! nuff said except talk with Michael Reed at Array Technologies.

They are  simple and elegant and people who say they have alot of maintenance and you only get 30% more power just have never owned one. I turn down offgrid clients who do not want one.  I want happy customers and tracking up here in the Sierra and alot of other places is a no brainer offgrid.

Somebody has to tell me how to convince my better half on that pond!
"we go where the power lines don't"

Pritch

Dave and Phssthpok,

Excuse the brainfart!  I forgot to consider that a system would be designed to deliver sufficient power in the dead of winter so there is typically a surplus in the summer.   d*  Thanks. 

-- Pritch
"The problem with quotes from the internet is that they're not always accurate." -- Abraham Lincoln


Phssthpok

On a slightly different tangent, yet still (sort of) on topic:

I had teased with the idea of fabricating a solar powered evaporative ammonia ice maker not only for food storage, but also for space cooling. Homepower Magazine has an article about a trough collector evaporating ammonia, which then gets re-absorbed overnight (or after covering the collector) causing stored water to be frozen.




Use your ice (frozen water jug?) to make something similar to this and you're set! :D

Windpower

but....


I would need the $6000 az 225 for my 12 Evergreen 205's

for 6000 I could just buy another  10 panels almost double the energy instead of 40 %


no payback there

now if I could build a tracker for ~ $1000, and I see no reason why I can't ---that will give me a good return on investment

I have posted a topicabout this over at the Wind Sun forum und the PV section

I don't want to reinvent the wheel so to speak if someone has already done it


Often, our ignorance is not as great as our reluctance to act on what we know.

Phssthpok


Dave Sparks

Quote from: Windpower on June 24, 2009, 12:48:10 PM
but....


I would need the $6000 az 225 for my 12 Evergreen 205's

for 6000 I could just buy another  10 panels almost double the energy instead of 40 %


no payback there

now if I could build a tracker for ~ $1000, and I see no reason why I can't ---that will give me a good return on investment

I have posted a topicabout this over at the Wind Sun forum und the PV section

I don't want to reinvent the wheel so to speak if someone has already done it




When you say payback that means to me you are not offgrid but gridtied. All of my previous comments are based on the strategy of charging everyday offgrid in most all weather conditions. I do not know your situation but I will say that the Evergreens are one of the hardest sized panels to get up on a tracker. Just hard to get the square footage on the array. One strategy I use is a fixed and tracked array to get the best of both. I do not like the 10" pipe system AZ-225 because it is just too big. If you stand in front of an AZ-225 you will know what I mean.

To homebrew  the big AZ225 one would take a gut check on how good you are, not to mention risking the cost of solar panels in an unproven design. The smaller AZ125 is doable but someone else will have to help.

In your math remember that solar panels power output is alot less than the nameplate but the power that is up on a tracker is there always at the right angle to the sun. I would also consider growing trees of AZ125's for offgrid,
diversify the threat of lightning if you will! Anything is possible with your time! It was possible to buy old satellite trackers years back for this. All the people that I have read about doing this have alot more time to fuss with this and end up with a non repeatable fixed mount on a pole. I sure would like to spend a weeks time and 1,000 dollars to get what you want!

Good Luck!
"we go where the power lines don't"

Windpower

Thanks Dave

the idea I have in mind is based on the design innovation from a tracker at the energy fair

instead of using a suntracking sensor he recognized that the only difference from one day to the next is the length of the day --- the rate of travel is always the same (15 degrees per hour) I think he just pulsed the drive a degree every 4 minutes -- (If I did the math correctly)

so he just programmed a commercial timer to turn on at sunrise, pulse the drive a degree every 4 minutes and turnoff at sun set and then recycle to the east for each day of the year

I think I found the timer that will work for about $200


he also used a  motor driving a chain drive for rotation -- simple (maybe I will use a garage door opener chain drive geared way down with a smaller motor -- another  $200 or so )

the rest is just steel, concrete and sweat

he also had a linear drive for tilt -- I think a manual tilt change every month or so should be almost as good and not cost very much
 
Often, our ignorance is not as great as our reluctance to act on what we know.

Dave Sparks

Agree that automatic tilt is not worth it! Just remember how much loading is going on at the pivot point and the connection to it. It is a big sail and the wind loading is huge as the array grows. I would use big gears and avoid a chain for arrays over 100 square feet.
"we go where the power lines don't"


ToddSInGA

In the early '90's I lived in a upper level apartment whose wall mounted AC unit died in the middle of July, and it took a month for the apartment management to replace the unit. I opened the window and placed a box fan in it with the air flow going OUT and it kept the place bearable even during the 100 degree heat of high noon! The noise was a little bit annoying but after a while I didn't notice it.

Unless you want to be cold inside during the summer I think a permanently mounted system of several fans would do well to keep you comfortable, as well and keeping the air fresh as a side effect.

There's now a car on the market using PV panels to operate a internal fan system to do the same thing, so I'm sure this could be applied to a house.

Dave Sparks

Good point but it all depends on what you call comfortable! Most people like 75F and most do not like 85F and up. For a month I am sure you were fine. Try doing that year after year when there is an easy and free source of power that is just sitting there. Some climates work well with fans and some do not.

As for using a solar powered fan in an automobile that already has a power source I find the whole idea laughable and just more marketing for crazy people. just my opinion....
"we go where the power lines don't"

glenn kangiser

Quote from: Dave Sparks on June 24, 2009, 11:55:06 AM
First HI Glen,
I want to build a pond up on my hill but my wife says it will bring that bear over from your hill.  Did you make him go away?


Trackers....Glen has a home brew??? My old one still works but I just ran out of time and some aerospace company up here in the foothills actually wanted me after 12 years at sea with an equal but creatively filled resume gap from the old Hewlett-Packard company.

OK, I like the Wattsun AZ-125's ! You can get 1,800 watts of Sanyo's on them or 1,600 watts of most other brands. They are 6 inch pipe based and I have been to several islands in the caribbean where they have stood the ultimate test. If you buy one retail they are over 3 grand. If you have bought from them before and can tell good stories they are a lot less.  Times are tight right now and good stories can go a long way! nuff said except talk with Michael Reed at Array Technologies.

They are  simple and elegant and people who say they have alot of maintenance and you only get 30% more power just have never owned one. I turn down offgrid clients who do not want one.  I want happy customers and tracking up here in the Sierra and alot of other places is a no brainer offgrid.

Somebody has to tell me how to convince my better half on that pond!

I made a bear go away and I heard of another one that went away but I heard of another very interesting couple of bears between you and I.

I have dug 2 small ponds at my place and they have not seemed to attract bears, Dave. :)

My tracker works pretty good although I have a slight propane leak in the West side and every few months I have to add a pint or so.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Whitlock

Welcome to the fourm.
Dave you will have bears pond or no pond.
I have two ponds and have not seen a bear or a track at them yet.
Maybe the bears like my apple trees too much ???

There are a lot of good reasons to put in a pond, fire supresion,fish,wildlife,water storage for your plants animals, garden.

How well would a swamp cooler work on a solar set up?



Take care,W
Make Peace With Your Past So It Won't Screw Up The Present

Dave Sparks

OK, it is friday d* and I will schedule time this weekend to force (discuss) the better half into building a pond for next winter! Thanks guy's! I may have enough man cards to win now!

I think a rabbit fence around the pond might be good but fences have their problems with water I suppose?
I also seek advice on making my stream safely go into a pond with steep terrain. (hills) I suppose if I screw up and erode I may find gold.....

Whitlock,
I really wanted an evaporative cooler. They work great up here in the Sierra as we don't get much of the monsoon. They are low energy but they require water and maintenance which I am short on. The side benefit to having enough solar to charge just about every day in winter is too much solar for summer. The Sanyo mini split is a natural for this situation. We store 14,000 gallons but my wife, again, thinks that old sailors can become gardeners. Glen met her and may have an inkling to the "joy" that some of us enjoy or maybe endure..............I did get the USDA pond file from the forum so I can at least show her the pictures!
"we go where the power lines don't"