Author Topic: Thoughts on air conditioning  (Read 7559 times)

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cardamon

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Thoughts on air conditioning
« on: September 04, 2013, 01:20:00 AM »
I figured this must have come up in the past, but i couldnt find anything on it.  I will have lots of extra PV capacity in the summer and would like to run a 120V window air conditioner.  I am off grid and will be charge controlling with diversion.  Anyone have any ideas on the control logic for this?  I do not want to cycle my batteries, just run the AC when there is enough surplus power.  My first thought was if the classic can control a relay at a certain amount of power input.  My battery bank is small and in the summer I have hardly any loads so I thought if I could tell the classic to  close the AC relay when It hit AC power + say 5 amps or so just to run the fridge and keep the batteries floated, that should keep the batteries from ever running the AC.  I currently have TRi stars running my diversion so another thought was to somehow get a reference off the amount of current being diverted.  Maybe get a SSR and  connect it in parallel with the diversion leads but how to get it to close at the right average voltage and then I would need some sort of latching relay or another relay to open once the diversion current went to zero... Anyone doing this or have some ideas? 

SparWeb

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Re: Thoughts on air conditioning
« Reply #1 on: September 04, 2013, 11:58:30 PM »
Ghurd built that for me a couple of years ago.

I call it the "auxiliary" diversion controller.  It basically sends a "sniffer" wire to the diversion load resistor.  If the main charge controller dumps through the resistor, the sense line to the Aux triggers its power circuit, which activates a relay, turning on any heavy AC load I want.  The relay is held "on" for an adjustable period of time, then drops out.  I use it to dump wind energy to the horses' water troughs, to keep them thawed in the winter.  I live in Calgary.  Minus 20 degrees.  Regular 1500W 120VAC heater.  It works.

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kitestrings

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Re: Thoughts on air conditioning
« Reply #2 on: September 05, 2013, 10:28:04 PM »
cardamom,

You might also try searching on the midnite forum (and/or the Outback forum).  Try aux. diversion or opportunity loads, "waste not" diversion loads, etc.  Quite a few articles on this topic.  We preheat water when extra - would be wasted  - energy is available.  AC would seem like another logical load to divert to.  I agree with SparW - it works - it is like having extra storage capacity (in the form of BTU's rather than kWh's.

~ks

hydrosun

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Re: Thoughts on air conditioning
« Reply #3 on: September 07, 2013, 01:02:36 PM »
Check out the forum at Arizona wind and sun. They have over 50 pages of discussions on air conditioning wirh surplus solar energy. Some are using a Sanyo inverter split heat pump at low speed to batter match small amounts of extra power. I have two   heat pumps i use for heating in the winter that are turned on by the Outback inverter aux relay. I have figured out that the thermostat is a thermistor that triggers when the resitance goes lower when the temp goes up ( it may be the opposite) So I put in a resitor in parralel that is connected when the battery voltage triggers the aux relay. That lowers the resistance to the thermistor circuit and turns on the heat pump. When the battery voltage goes back down the ristor is takenout of the circuit and the heat pump shuts off. Originally i had the relay cut the power to the heat pump, but thought that might shorten the life of the heat pump with such an abrupt cutoff many times a day. Which isone reason I    got the Sanyo heat pump so I can put it on th eslow speed and it only uses 300 watts at low speed, to better  match the available  power. But i have to maually change the speed settings. So I still use the older one speed heat pump that uses 700 watts to give a range of power usages from 300 to 1000 without my supervision. Then I can add 500 more watts manually. In the summer we sometimes use the dehumidfier function but the only automatic controll is the power relay unless I reverse the controll logic on the thermistor circuit. We don't use it enough for me to play with that yet. On the sanyo the thermistor circuit is in the remote and the Bonaire has the circuit in the indoor unit. I just connected wires on both sides of the thermistor without cutting any wires so it can be put back to normal usage easily.
Chris

dnix71

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Re: Thoughts on air conditioning
« Reply #4 on: September 07, 2013, 10:40:15 PM »
http://www.walmart.com/ip/15162429 There is a guy on Youtube who runs one of these tabletop icemakers from 2 HarborFreight 45-watt panel sets.

If you make ice with your excess capacity you can do two things with it. Make cool drinks and use the ice in a swamp cooler like this one:



Bruce S

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Re: Thoughts on air conditioning
« Reply #5 on: September 10, 2013, 02:54:03 PM »
When my batts are topped off and my 18volt NICDs are charged I do something similar to that but the ice is for my freezer :). Then for me :). Can normally only get about 8 lbs of ice but is a nice way to make use of excess power while waiting for my next batt bank to get finished.
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Deveak

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Re: Thoughts on air conditioning
« Reply #6 on: June 28, 2016, 05:00:28 PM »
Why go through all that effort when a simple AC switch will do? run it full blast while in float and turn it off when it gets around 3-4pm.

If you have a midnite classic you can use a relay to shut it on and off.

For air conditioning choices I would not go over 5000 btu unless its a mini spit with a high seer.
A 5000 btu wall unit is a cheap way to try it out. You can also go smaller but I am not sure what the efficiency of the smaller sub 5000 units will be. They make one thats designed for dog houses and kiosks, its a 2500 btu i think. Good for cooling you as you sleep in a small bedroom.

Sunfrost has a page up for a mini dc air conditioner designed to cool you in a small bunk space but I have yet to see anyone sell it or a price. It uses about 80 watts.

hell a simple DC air conditioner would be a real money maker if someone can build it. A mini split dc version exists but its a 1 ton 48 volt unit. a 4000-5000 btu dc air conditioner with a decent price tag (under 600) would sell like hotcakes. The rv/boat industry alone would love it.

Bruce S

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Re: Thoughts on air conditioning
« Reply #7 on: June 29, 2016, 08:36:44 AM »
Deveak;
YOU do know these are just short of being 3 years old. Besides , with my batt bank the 5000BtUs units wouldn't even start, where using the ice maker it'll run a few batches.
PLEASE try to read the entire post(s) and notice to dates on these, before giving your opinion(s).

Cheers
Bruce S
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dnix71

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Re: Thoughts on air conditioning
« Reply #8 on: June 30, 2016, 09:02:24 PM »
I installed a 5k BTU window a/c in my van after the vehicle a/c quit and the van was so old it wasn't wasn't worth investing more money in it.

Just starting a small window a/c required 2 boost caps. One on the a/c and another on the inverter. Keeping the a/c running required almost all of the van alternator output (450 watts). If you have that much excess solar you could do it, but even a momentary cloud would require a 3 minute lockout before a restart unless you have a variable speed scroll compressor, and those don't come on small cheap a/c's.

That small an a/c doesn't do much cooling, either. It made the van usable in hot weather, but was nowhere near the quality of cold as the original.

A vehicle a/c driven by a d/c motor would probably be easier to run.

Johann

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Re: Thoughts on air conditioning
« Reply #9 on: July 03, 2016, 08:34:38 PM »
http://www.walmart.com/ip/15162429 There is a guy on Youtube who runs one of these tabletop icemakers from 2 HarborFreight 45-watt panel sets.

If you make ice with your excess capacity you can do two things with it. Make cool drinks and use the ice in a swamp cooler like this one:


You would think that you end up with cold humid air.
But in a dry climates that could help to cool a place even more.

MattM

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Re: Thoughts on air conditioning
« Reply #10 on: July 04, 2016, 09:34:17 AM »
I keep thinking there has to be a way to cool air in the attic by mounting a passive unit on the ridge.  There is a small temperature delta of around fifteen to twenty degrees F between the ridge inside and outside on sunny days.  Too bad there isn't a way to use that temperature delta to generate power.  You only need that small delta to use thermoelectric techniques, right?   Bonus is that as you use it heat is reduced in the attic.

DamonHD

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Re: Thoughts on air conditioning
« Reply #11 on: July 04, 2016, 01:27:59 PM »
Thermoelectric is VERY inefficient if temperature differences are small, see "Carnot engine efficiency".  Fraction of 1% of energy at those sorts of differentials at a WAG...

Rgds

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joestue

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Re: Thoughts on air conditioning
« Reply #12 on: July 04, 2016, 09:27:17 PM »
Can you imagine?! Sterling engine in every attic, hybrid car in every garage.
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Johann

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Re: Thoughts on air conditioning
« Reply #13 on: July 07, 2016, 10:00:26 PM »
Can you imagine?! Sterling engine in every attic, hybrid car in every garage.
You could pre-heat the water in the attic before it goes to the water heater and winter time switch it to take a different rout.