A/C that runs off a battery...

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A/C that runs off a battery...

Post by Inquisitor »

Highlights...
  1. Emily and Clark's Design
  2. Just for one cabin (not whole boat)
  3. 100 A-hr usage overnight in the tropics
https://www.youtube.com/watch?v=xF113aUlZgo
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Re: A/C that runs off a battery...

Post by Lee Ward »

This would be the holy grail indeed. Following.
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Re: A/C that runs off a battery...

Post by Inquisitor »

Clark is willing to have them assembled if there are at least 50 takers as...
  1. DIY kit where we do all the soldering / charging
  2. Sled like some built-in boat fridge systems that needs charging
  3. Complete, pre-charged, ready to couple up like a mini-split heat pump system.
... the thing is, he hasn't said prices (even ballpark)... don't know if its $200 or $2000.

We'll see
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Re: A/C that runs off a battery...

Post by Jimmyt »

Thanks for sharing that. Hadn't watched any of their videos before. Seems like an interesting guy.

I would like to see more detailed measurements of room conditions than just the dry bulb temperature though. With an 80 deg F room temp, he was showing 78 deg F supply air. Normally, the air leaving an air conditioner is very near saturation conditions, which would imply that the room relative humidity will be about 93%.

The reason your air conditioner at home discharges air in the 53-55 deg F range is, its lowering the dew point (by condensing water out of the air at a low temperature), so that when that air warms back up to room temperature (while reducing the room air temp), the resulting room relative humidity will be around 50-60%. He makes a brief statement that he only cools the air enough to cool the room instead of climbing up a big wall... However, with mechanical dehumidification, over-cooling the air is how you extract the moisture.

Now, what he did was very cool. I'm sure that 75deg F and 90% RH is better than 90 deg F and 90% RH. But, when he tries to Cycle it based on room relative humidity (his future control discussion), he may not see the unit cycling off at all.

A combination of desiccant dehumidification and mechanical cooling might be able to give you dry conditions with a small amount of refrigeration energy, but I don't know that you'll be able to do it with his rig.

Now, if he slowed his air handling fan down to give a 55 deg F leaving air temp (and more appropriately match his total cooling capacity), the unit would not cool the space as quickly, but would dehumidify a whole lot better - and might actually result in better comfort. I prefer 79 deg F at 50% RH over 75 deg F at 90% RH. This will likely increase his run time also, though.

Ah, the lure of a free lunch.
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Re: A/C that runs off a battery...

Post by Inquisitor »

Jimmyt wrote: Mon Jun 07, 2021 6:50 pm Thanks for sharing that. Hadn't watched any of their videos before. Seems like an interesting guy.
He does seem to fly by the seat of his pants sometimes. :)
I would like to see more detailed measurements of room conditions than just the dry bulb temperature though. With an 80 deg F room temp, he was showing 78 deg F supply air. Normally, the air leaving an air conditioner is very near saturation conditions, which would imply that the room relative humidity will be about 93%.
I was wondering about that. I know my home A/C is far cooler right out of the vents. It seemed like he was intentionally going for that small differential. At the very end when he was actually throttling it was interesting.
The reason your air conditioner at home discharges air in the 53-55 deg F range is, its lowering the dew point (by condensing water out of the air at a low temperature), so that when that air warms back up to room temperature (while reducing the room air temp), the resulting room relative humidity will be around 50-60%. He makes a brief statement that he only cools the air enough to cool the room instead of climbing up a big wall... However, with mechanical dehumidification, over-cooling the air is how you extract the moisture.

Now, what he did was very cool. I'm sure that 75deg F and 90% RH is better than 90 deg F and 90% RH. But, when he tries to Cycle it based on room relative humidity (his future control discussion), he may not see the unit cycling off at all.

A combination of desiccant dehumidification and mechanical cooling might be able to give you dry conditions with a small amount of refrigeration energy, but I don't know that you'll be able to do it with his rig.

Now, if he slowed his air handling fan down to give a 55 deg F leaving air temp (and more appropriately match his total cooling capacity), the unit would not cool the space as quickly, but would dehumidify a whole lot better - and might actually result in better comfort. I prefer 79 deg F at 50% RH over 75 deg F at 90% RH. This will likely increase his run time also, though.

Ah, the lure of a free lunch.
I'm glad you chimed in with your background. Can you touch on his wording about the "special" circumstances of his compressor? He referenced some number (80 something?) and talked about high versus low pressure units. That high are needed for fridges and low needed for A/C. Is there a more lay/intuitive explanation of this?

Also, his wording about it being geared for cooling of military equipment and that it was (I think he said) 2 to 3X more efficient than any other compressor. I installed one of the high-efficiency mini-splits (SEER 23) some years ago. I noted as the units got bigger their efficiencies went down. This being so tiny, does the opposite hold true and a 2 to 3X might be accurate fore something so small?
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Re: A/C that runs off a battery...

Post by Jimmyt »

Inquisitor wrote: Mon Jun 07, 2021 7:28 pm
I'm glad you chimed in with your background. Can you touch on his wording about the "special" circumstances of his compressor? He referenced some number (80 something?) and talked about high versus low pressure units. That high are needed for fridges and low needed for A/C. Is there a more lay/intuitive explanation of this?

Also, his wording about it being geared for cooling of military equipment and that it was (I think he said) 2 to 3X more efficient than any other compressor. I installed one of the high-efficiency mini-splits (SEER 23) some years ago. I noted as the units got bigger their efficiencies went down. This being so tiny, does the opposite hold true and a 2 to 3X might be accurate fore something so small?
First, the guy put together a functioning air conditioner with working controls. While it's not rocket science, it does take a fair amount of game. So, I congratulate him on his accomplishment.

Most of the chatter about low pressure and high pressure is either gross generalization or antiquated jargon. For any given application, you have to absorb heat on one side and reject heat on the other. The pressures in the system are a function of the refrigerant you use and the temperatures that you are working with. For a given refrigerant, air conditioning a house (absorbing heat from a 75 degree source but over-cooling to 55 deg F and rejecting it to 90 deg F); will require different operating pressures than a freezer (absorbing heat at 20 deg F and rejecting it to 75 deg F). Which isn't really relevant since you would likely be using different refrigerants for those applications... but I digress.

I will have to look into the claims of compressor efficiency that he states. I have no immediate response, but am somewhat skeptical. The original application was to make cooling water for a water-cooled electronics application in hot climates. Disclaimer: he did not specify the parameters of the military system the compressor served. But, just spit-balling... If he was absorbing heat at 80 degF in the electronics chassis and rejecting it to 130 deg F, that's a 50 deg F differential. If you compare that to a house system absorbing heat at 45 deg and rejecting it at 120, that's a 75 deg differential. So, it stands to reason that the overall cycle could be more efficient for the electronic cooling system (generally - refrigeration cycles tend to be more efficient as the heat source temperature and heat sink temperatures get closer - the smaller the hill, the easier the climb). As to the compressor itself, I don't intuitively see that making it smaller would make an appreciable difference in efficiency in either direction, but I don't know right off. My gut says he saw the cycle efficiency - not the compressor efficiency.

Bottom line, to maintain the condition of the air in a space, given known sensible and latent loads (dry heat and moisture), you need a specific refrigeration capacity. If I have some spare time earlier in the day, I can rough something up for a space similar to what he was cooling. Pulling the moisture out is a lot of what air conditioning needs to do in most areas. If you're lucky enough to live somewhere really dry, evaporative cooling can offer very low energy improvements in comfort. Otherwise, you've got to pay the piper.
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Re: A/C that runs off a battery...

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Jimmyt wrote: Mon Jun 07, 2021 8:42 pm If you're lucky enough to live somewhere really dry, evaporative cooling can offer very low energy improvements in comfort. Otherwise, you've got to pay the piper.
Having grown up in the South East, I was not prepared for a swamp cooler. I lived in Utah for a while and ours wasn't working. Had no idea what principle it worked under and wondered if it was going to require someone certified and with special knowledge. Having a DIY moment, I went up on the roof and opened it up. Imagine my surprise as seeing nothing but some filters made of some kind of plant reeds a water float switch and a big fan. :D I instantly understood what was going on, but couldn't conceive of how adding more water to air (in the SE would be lunacy) could make things enough cooler to be useful. Although skeptical, I thoroughly cleaned all the scale, replaced the valve and filters... and WOW! I could not believe how COLD that air was... down-right frigid if standing under the thing. We never wanted for a real air conditioner while there. Amazing what you can do with a relative humidity of 15%. :D
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Re: A/C that runs off a battery...

Post by Tomfoolery »

Inquisitor wrote: Tue Jun 08, 2021 5:06 am
Jimmyt wrote: Mon Jun 07, 2021 8:42 pm If you're lucky enough to live somewhere really dry, evaporative cooling can offer very low energy improvements in comfort. Otherwise, you've got to pay the piper.
Having grown up in the South East, I was not prepared for a swamp cooler. I lived in Utah for a while and ours wasn't working. Had no idea what principle it worked under and wondered if it was going to require someone certified and with special knowledge. Having a DIY moment, I went up on the roof and opened it up. Imagine my surprise as seeing nothing but some filters made of some kind of plant reeds a water float switch and a big fan. :D I instantly understood what was going on, but couldn't conceive of how adding more water to air (in the SE would be lunacy) could make things enough cooler to be useful. Although skeptical, I thoroughly cleaned all the scale, replaced the valve and filters... and WOW! I could not believe how COLD that air was... down-right frigid if standing under the thing. We never wanted for a real air conditioner while there. Amazing what you can do with a relative humidity of 15%. :D
And that's exactly how cooling towers work on commercial A/C systems. Still have a compressor and refrigerant, but instead of a heat exchanger that uses a fan directly, hot water is rained down through the slats of the cooling tower with a fan pulling air through, and that water, which has been cooled via convection and evaporation, is sent back to condense the refrigerant. Those giant cooling towers at nuke plants do the same thing, but without a fan as natural convection moves the air through the hot water rain storm with a bit of nearly pure steam escaping out the top and condensing.

So evaporation to the surrounding environment is what indirectly does the cooling, or at least the condensing of the cooling medium.

More or less.

Sort of. :wink:

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Re: A/C that runs off a battery...

Post by Jimmyt »

My nose would be bleeding instantly, my skin would start flaking off, and my gills would dry out if I were exposed to 15% RH. Wow! I bet the swamp cooler was magic in those conditions. :D

Looks like he would need about 6,000 btu/hr or 1.76 kw of cooling capacity to properly condition a 10ft x 10ft x 7 ft high cabin on a 90 degF 90% RH day if the space design is 75 deg F and 50 % RH. This is roughly the capacity of the small, one room, ac units you can get at the big box stores.

Air leakage (infiltration) is a big part of the equation, so sealing the space up to prevent large amounts of infiltration is a good idea. You can have a small amount, just not a 3 ft x 3" gap like my cabin hatch has...

At any rate, that's roughly the capacity required to do it correctly. Matching of system components is required for good performance also. He appeared to be using an automotive evaporator blower unit with his home-brew compressor-condensing section. The automotive unit was probably oversized by a factor of 2 or 3 minimum. That's why his leaving air temp was so high. He had a lot more fan and evaporator than his refrigeration could support.

It is confusing when you see the room temperature coming down fast, indicating that you seemingly have plenty of capacity. However, that is only the "sensible" heat (or dry air portion). Removing the "latent" heat (moisture component) is what appears to be missing with his setup. He will get some condensation if it's really humid (dew point above his leaving air temp), but not nearly as much as a unit blowing 50-55 deg F air.

Again, I'm largely speculating based on one or two data points and his verbal descriptions. So, take this with a grain of salt. I would just advise you, that if the system can't do at about 6,000 btu/hr total capacity, and give you a leaving air temperature at least 20 degrees lower than room temp, you might want to look carefully before you buy.

If you're in a hot, moderately dry area, his system might do fine as there would be little latent load. But, if that's the case, the swamp cooler could do it without costing you power for a compressor. :wink:
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Re: A/C that runs off a battery...

Post by pleb222 »

I use the Zero Breeze in my Mac26m. It's a mini compressor AC unit, about 2500 btus, has it's own lithium battery, has dual hoses for air exchange to the outside, very easy to use. It works very well to take the edge off at night, we can get quite a few degrees down.

https://www.zerobreeze.com/products/zer ... 2MQAvD_BwE
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Re: A/C that runs off a battery...

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Jimmyt wrote: Mon Jun 07, 2021 8:42 pm Most of the chatter about low pressure and high pressure is either gross generalization or antiquated jargon. For any given application, you have to absorb heat on one side and reject heat on the other. The pressures in the system are a function of the refrigerant you use and the temperatures that you are working with. For a given refrigerant, air conditioning a house (absorbing heat from a 75 degree source but over-cooling to 55 deg F and rejecting it to 90 deg F); will require different operating pressures than a freezer (absorbing heat at 20 deg F and rejecting it to 75 deg F). Which isn't really relevant since you would likely be using different refrigerants for those applications... but I digress.
Here is my summary of the videos and key points that Emily & Clark made so far on this subject. It doesn't appear that they have a playlist for this yet, but here is the series.
  1. https://www.youtube.com/watch?v=jTKT3w-6Bl0 - Basic boat refrigeration concepts.
  2. https://www.youtube.com/watch?v=HJpQn2gL0Aw&t=658s - Fixing a boat refrigerator. I see this as his way of getting us DIY minded individuals comfortable with the idea of unwrapping the black box* that is refrigeration.
    1. 4:05 - Water cooled condenser - pipe within a pipe heat exchanger.
    2. 9:10 - Refrigerant filter dryer
    3. 10:25 - Sled - What kind to buy - Don't get hung up on brand since they all use the same compressor (Danfoss BD35 or BD50)
    4. 27:15 - Charging the system up to actually adding the fluorocarbon.
  3. https://www.youtube.com/watch?v=tc3N6lzZIjY - Recharging a refrigeration system.
    1. 3:00 he talks about "calculating" the steady state pressure. This is the high versus low pressure I was questioning above. He says at 11.7 psi, it is ideal for a fridge that will freeze meat, but not ice-cream. If you want ice cream freezing, you need more pressure, but that takes more electricity to run. He's trying to optimize for efficiency.
    2. 16:25 - Having too much pressure is also bad. At this point the evaporator hasn't evaporated all the liquid and it passes back into the compressor pump. If you're lucky the electronics shut it down. If you're not the compressor seizes trying to compress the liquid.
In 3a and 3b is where I had the question about low versus high pressure. This is the reading on the low pressure side. He's talking about refrigeration at this point and I'm trying to rationalize how to adjust this reasoning for the pressure needed for an A/C unit. I'm trying to extrapolate this 3rd video information for an A/C unit. As the evaporator isn't in an ice box, it probably won't frost in an A/C unit. So how do you know you're filled properly when charging up the A/C system? Will it be a higher or lower pressure than 11.7 psi and what do you do as a "you're done" gauge?
Last edited by Inquisitor on Tue Jun 08, 2021 8:14 am, edited 1 time in total.
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Re: A/C that runs off a battery...

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Jimmyt wrote: Tue Jun 08, 2021 6:22 am My nose would be bleeding instantly, my skin would start flaking off, and my gills would dry out if I were exposed to 15% RH. Wow! I bet the swamp cooler was magic in those conditions. :D
I remember times with the swamp cooler going full blast the humidity inside the house might get to 35 to 40%. It was great for working outdoors. I could mow lawn in 110F, in the sun and feel just fine doing it. Here... 85F+/80% just kills me. :cry:
Looks like he would need about 6,000 btu/hr or 1.76 kw of cooling capacity to properly condition a 10ft x 10ft x 7 ft high cabin on a 90 degF 90% RH day if the space design is 75 deg F and 50 % RH. This is roughly the capacity of the small, one room, ac units you can get at the big box stores.

Air leakage (infiltration) is a big part of the equation, so sealing the space up to prevent large amounts of infiltration is a good idea. You can have a small amount, just not a 3 ft x 3" gap like my cabin hatch has...

At any rate, that's roughly the capacity required to do it correctly. Matching of system components is required for good performance also. He appeared to be using an automotive evaporator blower unit with his home-brew compressor-condensing section. The automotive unit was probably oversized by a factor of 2 or 3 minimum. That's why his leaving air temp was so high. He had a lot more fan and evaporator than his refrigeration could support.

It is confusing when you see the room temperature coming down fast, indicating that you seemingly have plenty of capacity. However, that is only the "sensible" heat (or dry air portion). Removing the "latent" heat (moisture component) is what appears to be missing with his setup. He will get some condensation if it's really humid (dew point above his leaving air temp), but not nearly as much as a unit blowing 50-55 deg F air.

Again, I'm largely speculating based on one or two data points and his verbal descriptions. So, take this with a grain of salt. I would just advise you, that if the system can't do at about 6,000 btu/hr total capacity, and give you a leaving air temperature at least 20 degrees lower than room temp, you might want to look carefully before you buy.

If you're in a hot, moderately dry area, his system might do fine as there would be little latent load. But, if that's the case, the swamp cooler could do it without costing you power for a compressor. :wink:
At the moment, all this is more academic and a hobbyist challenge in making it work. Although $1000+ for pleb222's systems is well into the threshold of pain region. Thus, from a mental exercise standpoint...
  • I've estimated the volume of my forward berth with the extension viewtopic.php?f=8&t=28028 I'm planning. Volume is about 75 cu-ft. The entire bottom will be the mattress, so 4-5" of insulation. I can make it air tight enough that I'd be more worried about us suffocating. :? Is your calculation above for 700 cu-ft WRT volume? If so, can I get away with 600 btu/hr or 0.2 kW?
  • I'm thinking tearing apart one of these cheap, 12VDC, car fridges (compressor type not thermal plate) Something like $190 https://www.amazon.com/AstroAI-Portable ... B088FDTTY4
  • It'll have all the 12VDC problems handled and computer controlled.
  • Replace the condenser with simple copper tubing run under the hull for some determined length. No additional fan or pump needed.
  • If the evaporator can be dissected, use computer fan(s) blown across it to cool the space.
  • You brought up an interesting concept above. Even if this isn't powerful enough to cool the volume, won't it still cool the plate way down to the point that it condenses the water out and even if the flow warms back up... it'll be far dryer. As you pointed out...
    Jimmyt wrote: Mon Jun 07, 2021 6:50 pm I prefer 79 deg F at 50% RH over 75 deg F at 90% RH. This will likely increase his run time also, though.

    Ah, the lure of a free lunch.
How about just a free snack? :D
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Re: A/C that runs off a battery...

Post by adudinsk »

Are you referring to a swamp cooler? Will not work in high humidity.. only in VERY dry locations (ie: not on the water ..).
Will also make it very humid in the boat.
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Re: A/C that runs off a battery...

Post by Jimmyt »

Volume is about 75 cu-ft. The entire bottom will be the mattress, so 4-5" of insulation. I can make it air tight enough that I'd be more worried about us suffocating. :? Is your calculation above for 700 cu-ft WRT volume? If so, can I get away with 600 btu/hr or 0.2 kW?
Volume is not a primary driver. The fiberglass hull exposed to the outside temperature; the fiberglass deck (with liner) exposed to the sun; single wall hatch; air infiltrating at 90 deg F, and two humans burning calories and exhaling steam are the driving factors.

If you could seal off the vberth and just condition that space, you could probably get away with 2,100 btu/hr or 0.62kw (according to the napkin I'm scratching numbers on... :wink: (actually using a spreadsheet, but a napkin and pencil is cooler)

I checked my assumptions against a whole boat model and it came up pretty close to what I estimated for the Emily and Clarke load. RIS uses one of the small window units in his 26x boat and I believe he said it was satisfactory - giving me a fair gut check.
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Re: A/C that runs off a battery...

Post by Jimmyt »

adudinsk wrote: Tue Jun 08, 2021 10:39 am Are you referring to a swamp cooler? Will not work in high humidity.. only in VERY dry locations (ie: not on the water ..).
Will also make it very humid in the boat.
Agree. I was referring to locations such as Inquisitor referenced with 15% RH ambient. Even using the swamp cooler he said his house interior only got up to 30-40%... I'd still be reaching for the chap stick. :D
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