A/C that runs off a battery...

[Jimmyt]

Purely by seat of the pants... Paraphrasing what I've learned so far from you above, a good goal is 55F air from the return and that likely takes 45F fluid/coils/plates to achieve.

Just so we can all talk on the same page, air going into the unit is called return air. Air coming out of the unit is called supply air. In cooling/humidity limiting mode, a typical supply air target condition for comfort applications is 55 degrees and near saturation (over 90% RH). The cooling coil is condensing water out of the air as it passes through, leaving it in a nearly saturated state as it exits. Typically, the fan is placed downstream of the coil to add a touch of heat to get the air further away from saturation. As that 55 degree saturated air warms to 75 degrees, the resulting relative humidity becomes 50% RH (warm air can hold more moisture than cold air), so the overall room condition will be between 50 & 60% RH, depending on the space moisture load.

Today's psychometric 101 lesson...

[Jimmyt]

Here you've introduced a totally new concept... Internet didn't mention this. He doesn't mention this. In fact he seems to be cobbling together (as you so aptly noted) common, automobile evaporator parts.

I think you may have been referring to the expansion device statement. Yes. This is what makes the magic. Clarke probably got a 134a expansion valve as part of his auto evaporator-blower assembly. Problem is, the auto unit capacity would be so far beyond what the little D.C. compressor could support that the valve may not have been able to do its thing properly. If it was all properly matched, it would have been blowing air in the 50-55 deg range.

It would have been interesting to see him reduce the speed of the evaporator fan to achieve a better supply air temp. I'd be curious to see if the thermostatic expansion valve would modulate down to match the small compressor. Who knows? He may be one speed control setting away from the goal line... it's obvious that his airflow can be reduced significantly without losing the ability to cool the space (albeit a bit slower).

[PMake]

Very interesting and educational discussion. Living in south Florida, for sure AC is in my must-have list before I date to propose overnighting in boat to admiral. Though at the moment I am struggling with even “stepping onboard” part.

I did some googling, and my guess is that his compressor is from https://www.aspencompressor.com/product-documentation

Those seem to match his claims for USA made, high efficiency, small size, 12V and works with 134a. And being expensive when bough individually…

This discussion and Nick Calders book might make me reconsider my thinking about modifying window ac approach…(134a so. much easier to come up vs. 401a) when I get to that point.

[Inquisitor]

Unfortunately I can't devote as much time as I'd like to this project (Re-shingling my house is kicking my ass. I'm used to working a desk in a temperature/humidity controlled office).

I imagine quite a few people are OK with the shore powered / window unit. I tried that once on a B.E.E.R. cruise while at the dock the first night. Yeah! it worked great... if anything it was too cold. But it was real noisy and I felt it disturbed the other boaters and I felt guilty. It also kept me awake over the noise and maybe guilt. Also... in an M, even in a nice frame insert, its really in the way trying to go up/down the gangway. In an X, it makes for far nicer install!

Then... the next five days were on the hook at night. Can you say boat anchor? As, my style of overnighters is/will always be far more on the hook than in the slip, I only have the one option... on a battery. No way am I going to spoil the solitude with a generator.

So... reduce the cooled volume, super insulate, super seal and seek super expert guidance.

...
Just so we can all talk on the same page, air going into the unit is called return air. Air coming out of the unit is called supply air. In cooling/humidity limiting mode, a typical supply air target condition for comfort applications is 55 degrees and near saturation (over 90% RH). The cooling coil is condensing water out of the air as it passes through, leaving it in a nearly saturated state as it exits. Typically, the fan is placed downstream of the coil to add a touch of heat to get the air further away from saturation. As that 55 degree saturated air warms to 75 degrees, the resulting relative humidity becomes 50% RH (warm air can hold more moisture than cold air), so the overall room condition will be between 50 & 60% RH, depending on the space moisture load.

Today's psychometric 101 lesson...

... 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... (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.

Obi-Jim,

In the context of just de-humidification for this hypothetical 75 cu-ft... are these 2100/0.62 number significantly reduced? Imagine its a difficult calculation... outside 90% with two adults breathing/adding humidity. When gearing for humidity control, is the design significantly different - pressures / hardware?

Grasshopper

[Jimmyt]

So far I haven't found how this is used. There was no Wikipedia type explanation or flow chart. As the name expansion suggests, it goes just before the evaporator??? Clark just talks about a spray can nozzle. I did see in one datasheet https://sporlanonline.com/literature/10 ... Series.pdf the phrase superheat that you previously mentioned. So far, I'm not fathoming what the thermostatic variability provides. I don't recall seeing one of these in the last student fridge I dissected to be used as a vacuum pump. Maybe it was there... but I just needed the compressor.

Your posts are so rich with good questions, I have to read them several times just to get to them all. Completely missed this earlier.

There is a mechanical sensing bulb (actually liquid/gas filled but whatever) that is typically placed on the suction line leaving the evaporator coil. This opens and closes the thermostatic expansion valve [TXV] which regulates the refrigerant flow to maintain a certain condition in the suction line at that point, and to a lesser degree, maintains a somewhat consistent coil condition as the load varies. Think, variable speeds on the fan, adjustable cabin temperature settings, etc, and you can see that some sort of capacity control in the refrigeration system might be helpful - other than just cycling the compressor on and off as your only means of control. What you are actually controlling with the TXV is superheat. Now, at that point in the line it is desirable to have some superheat (the state of refrigerant is a tad higher temperature than the saturation temperature). This precludes the possibility of injecting liquid droplets into the compressor, subsequently draining off your extra money.

In your typical fashion, you astutely noted the refrigerator you cannibalized didn't have a TXV. A refrigerator gets plugged in and runs at almost constant conditions for 20 years until it breaks. Therefore, they can solder in a capillary tube to generate the pressure drop required to make the system function in lieu of the more expensive TXV. Now, there have been automotive systems that used fixed orifices, and refrigeration systems that use TXVs, so you really can't make too general a rule as to where you'll see which approach. Well, the low-priced, budget equipment may be more likely to have cap tube expansion devices. I would be shocked to see one on a student fridge.

It's a nice addition to a refrigeration system when you're rolling your own. Calculating the amount of cap tube you need is a bit of a noodle workout, and it's difficult to adjust after you put it in... An adjustable TXV, that's roughly the right size, can make a system a lot easier to dial in.

[Jimmyt]

Unfortunately I can't devote as much time as I'd like to this project (Re-shingling my house is kicking my ass. I'm used to working a desk in a temperature/humidity controlled office).

Obi-Jim,

In the context of just de-humidification for this hypothetical 75 cu-ft... are these 2100/0.62 number significantly reduced? Imagine its a difficult calculation... outside 90% with two adults breathing/adding humidity. When gearing for humidity control, is the design significantly different - pressures / hardware?

Grasshopper

Bless your heart! Roofing in the summertime... Hope you have a nailer. I'd loan you mine, but it's a long drive to drop it by.

The 2,100 btu/hr capacity figure was to comfort condition the v berth area to 75 deg F and approximately 50% RH. I assumed two resting adults. If you are at a different activity level, or take your 3 Rottweilers with you, you may need a bit more capacity...

So, if I read you, you want to know if dehumidification only will reduce your equipment capacity requirement. Possibly, but you get some cooling effect anyway (assuming you're talking mechanical dehumidification while rejecting heat outside). A mechanical dehumidifier is the same process as air conditioning (cooling cycle), with one significant difference. The condenser coil is located downstream of the evaporator coil, reheating the air after it is cooled and dried. The cooling coil is at roughly the same temp (some humidifiers can get air down to a dew point of 38 deg, so the cooling coil is a bit colder). The condenser heats the 38-50 degree air back up (typically slightly above room temp) so the air coming out of the unit is warm and dry.

So, we would still cool the air down to 50-55 deg to dry it, and you would still reject the heat to a water heat exchanger (or otherwise outside of the cabin). Pressures would be the same. I'll try to figure out whether you could get away with less capacity if you were willing to settle on a slightly warmer temp. Also, note that the capacity was based on 90 deg ambient, high humidity. If it's not that hot, less capacity is required.

[Jimmyt]

Very interesting and educational discussion. Living in south Florida, for sure AC is in my must-have list before I date to propose overnighting in boat to admiral. Though at the moment I am struggling with even “stepping onboard” part.

I did some googling, and my guess is that his compressor is from https://www.aspencompressor.com/product-documentation

Those seem to match his claims for USA made, high efficiency, small size, 12V and works with 134a. And being expensive when bough individually…

This discussion and Nick Calders book might make me reconsider my thinking about modifying window ac approach…(134a so. much easier to come up vs. 401a) when I get to that point.

I'd be interested to hear your Admiral's issues with stepping aboard. Did you heel over and spill her beer on your first trip?

No question that 134a is a kinder gentler refrigerant than 410A, but technicians work on 410A systems every day, so it can be done. But, if you want 12v D.C., low power operation, and don't want to mortgage your Ferrari, you'll probably be better off rolling your own with 134a.

I'll have to see what Nick Caulders book is about. Thanks!

[Jimmyt]

Then... the next five days were on the hook at night. Can you say boat anchor? As, my style of overnighters is/will always be far more on the hook than in the slip, I only have the one option... on a battery. No way am I going to spoil the solitude with a generator.

You're killing me... I was happy with the modified window unit idea until you threw that "cool on the hook with no gen set" idea in my face...

[PMake]

OFFTOPIC: “Stepping onboard” part is tricky as my admiral had long time ago bad experience with jet ski (nothing drastic, just little bit too much airborne) and she is not super comfortable in small floating things, eg smaller than cruise ships… we have been motoring in intracoastal, but due to bridges etc, that means I need to take mast down on the way. And she have to steer. And once motorboat made big waves turning boat towards sea wall. Not close call, but she panicked. And since that she has “steering freight”. Plus our dock is quite tight and we had few difficult approaches so that doesn’t make her happy either. So Admiral must be just a passenger. I am looking for my son to grow older so I get him as a deck hand and then we can actually go somewhere. But that is at least 5 years away as he is 5 now… OFF TOPIC ENDS


I had book name wrong, it is Nigel Calder : Refrigeration for Pleasureboats: Installation, Maintenance and Repair. It is old and speaks only R-12, but he explains step by step how to make ice box and all components. For you that is for sure too basic, but I can at least learn terms and components… (technically minded and crazy enough to want to learn this kind of stuff. And cheap, so if I buy 1500 usd system, I would really want to buy that only once. Or if I can build one with little less, I do not count value for my time.)

I am not in hurry, if I start building anything like this, it might be 2022, or 2024. But I enjoy following discussion around subject. Thank you for increasing my understanding of ac systems. Your explanations clarified few points that i have not thought earlier…

I also have obsession about energy efficiency, especially in boat as that is batteries, but also it beats me, why we do not use water cooled condensers In Florida much more. Almost every building is next to some water body, river, lake, sea, or swamp and still we have air condenser units in roofs with 100+ degree air, which can’t be optimal. small water pump and coaxial hex seems mechanically easier and more efficient for me even if you need filteration and regular maintenance there.

[OverEasy]

Hi

One of the reasons use of natural water bodies aren’t used for commercial building air conditioning is the dumping of the heat warms the water and eventually harms aquatic life either by becoming too warm or algae growth.

Some commercial applications utilize a sequestered water pond that is man made and managed. (Ever wonder about why some commercial buildings have a stand pond with fountains. ...well they are using the pond water as a heat sink for the air conditioning and heating via heat pumps.)

Most systems installed now for residential in warm climates are heat pumps.
It is often efficient enough as is using air. Those that want a higher efficiency can often use a ground loop heat sink which is burying a loop of fluid underground. It’s less hassle for a home owner to have a ground loop rather than the maintaining of a pond.

Hope this helps answer at least part of your concern.

Regards,
Over Easy

[OverEasy]

Hi Inquisitor

Banging away on your roof in this kind of weather
More power to ya!
I figure you just are using this as an excuse to slim down for the summer season

Hey, this thread has been really interesting. Thanks for all the great info and references.
A real eye opener as to the possibilities of battery A/C being a realistic thing!

Good luck and stay safe with the roofing in this heat.
I did it as a much younger me in much better shape and it was no picnic in this kind of heat even back in those long ago days!

Tricks of the trade:
1) Get out at predawn twilight to start.
2) Get and use a square or two of seat cushion foam to rest on instead of being directly on the shingles. Better grip and less mar of the shingles. Junk curb couch cushions are a good source less the fabric.
3) Gloves & sunglasses
4) As you already know..copiously hydrate and then some.

Good luck!
Over Easy

[Inquisitor]

Bless your heart! Roofing in the summertime... Hope you have a nailer. I'd loan you mine, but it's a long drive to drop it by.

Hi Inquisitor

Banging away on your roof in this kind of weather
More power to ya!
I figure you just are using this as an excuse to slim down for the summer season

You got that right... 15 lbs of winter/COVID flab... GONE! Farmer tan included for free. I now come by as a red-neck honestly!

Tricks of the trade:
1) Get out at predawn twilight to start.
2) Get and use a square or two of seat cushion foam to rest on instead of being directly on the shingles. Better grip and less mar of the shingles. Junk curb couch cushions are a good source less the fabric.
3) Gloves & sunglasses
4) As you already know..copiously hydrate and then some.
5) Forgot - LOT's of sunscreen!

Good luck!
Over Easy

Thank you for the kind encouragement. But I'm a big wuss and a follower of Tim the Toolman.

• Our retirement house is only 1200 sq-ft.
• Three bids - only one came back with labor. They can't find anyone to do this kind of work anymore and the one that did was $10K and would not do a tear off. I had some water damage and HAD to know the extent. So I did the tear off... and that WAS a b!+(#. Heat off the black felt was like a furnace. Removed felt also and replaced with the artificial (white) stuff. Reflects more, but way cooler.
• Lifetime / architectural shingles $1200, nailer $130, nails $40... a thorough inspection and repair of $100 of wood damage. It was an easy decision.
• Remember... mountains. A lot cooler than either of your all's places by at least 20F.
• Work from 7am till the sun reaches me. Comes over the mountain about 10. Sometimes cloud cover can keep me out till noon.
• Back out about 6pm as the sun goes behind the other mountains... till dark about 9pm.
• Got a big tractor... does all the heavy lifting. No way I can lift a 70 lb packet up a ladder.

[Inquisitor]

...
Your posts are so rich with good questions, I have to read them several times just to get to them all. Completely missed this earlier.

And I greatly appreciate your thoughtful responses. I know there will be many people now and over the following years that will learn greatly from your experience!

There is a mechanical sensing bulb (actually liquid/gas filled but whatever) that is typically placed on the suction line leaving the evaporator coil. This opens and closes the thermostatic expansion valve [TXV] which regulates the refrigerant flow to maintain a certain condition in the suction line at that point, and to a lesser degree, maintains a somewhat consistent coil condition as the load varies. Think, variable speeds on the fan, adjustable cabin temperature settings, etc, and you can see that some sort of capacity control in the refrigeration system might be helpful - other than just cycling the compressor on and off as your only means of control. What you are actually controlling with the TXV is superheat. Now, at that point in the line it is desirable to have some superheat (the state of refrigerant is a tad higher temperature than the saturation temperature). This precludes the possibility of injecting liquid droplets into the compressor, subsequently draining off your extra money.

Am I understanding this things purpose correctly? Going back to Clark's 3rd video at 16:25 and he's talking about how much to fill based on the moving of the frost line up his evaporator. Where the frost line ends is where the fluorocarbon is fully evaporated (no liquid left). He uses amount added to dial that in, but also comments how things have to reach steady state and takes hours. This gizmo's sensor part is placed at the end of the evaporator tubing and detects that frost line approaching it by its temperature. As it gets colder, it starts closing off the valve so the frost line (and more importantly the liquid) doesn't pass the sensor and into the compressor??? Since it's variable, it doesn't rely on Clark's "steady state" and it can deal with the wild swings of the room's environment???

Does the throttling valve portion also go at the end of the evaporator (radiator) or at the entry into the evaporator?

The one you have in mind... is it as small/cheap as the one pictured above? This was off Amazon https://www.amazon.com/UAC-EX-10006C-Ex ... B00CFQT1TI and only $16 for two of them. At that kind of price... I'd buy two just to have the spare (or next science project )

[Inquisitor]

You're killing me... I was happy with the modified window unit idea until you threw that "cool on the hook with no gen set" idea in my face...

Don't you hate that when it happens?

In a quiet cove and ten other boats. All is perfect silence. You can whisper and be heard by the boat 50 feet away. Then someone cranks up a generator. The picture is ...

Here is my simplistic (Thermodynamically ignorant) blue-sky concept.

As anyone who knows of even one of my projects... cutting and drilling in the boat doesn't bother me much, until... it goes from inside to outside. Through hulls freak me out. Water stays outside... good water. Water gets inside... bad water. No holes... no bad water.

Condenser
Some ages ago I saw a sailboat with a simple U-shaped loop of copper tubing under the hull. Stretched out it couldn't have been more than 2 feet long. It was obviously for cooling. Don't know if it was engine cooling or some kind of refrigeration cooling. But it instantly made sense in an ugly kind of way. In my speed freak days, I said no way am I going to have that dragging in the water. Now, I'm thinking how brilliant... no costly, maintenance prone, pump-driven water heat exchanger inside the boat... just hang the actual coil in the water. I would certainly need your guidance for length needed. If short enough, I can imagine going out the hull on the transom above the waterline and drape down below the engine. No bad water.


Compressor
Under the steps, next to the battery. Short electrical runs, insulate for quietness... easy peasy.

Evaporator, Expansion Valve
Place in M's floatation space around the anchor locker. Can drain out anchor locker drain... OR better yet, filter and drain into fresh water storage under V berth. Uses a couple of computer fans for air flow.

Lot's of insulated copper tubing running the length of the boat... but the loudest noise would be the compressor under the steps... IOW the whole system will be almost dead quiet.

Aft Berth Design
Those using the aft berth as the master have it easier. Could probably hang the whole kit and caboodle on the inside of transom and blow over your feet.


... OR... Did I just NASA this thing to death?

[Jimmyt]

Last post first. You are using a solid concept for your condenser strategy. Closed loop cooling with an in-water heat exchanger is a great way to go.

https://www.wekamarine.com/keelcoolers/

I've used these for water-source heat pumps at hydropower facilities where I had access to flowing river water. You still have to deal with fouling of the heat exchanger, but it's on the outside of the system. You're not trying to clean the gap between two concentric tubes... or pulling hoses off trying to scrub out a spiral tube.

All of your other concepts sound good. You can't over analyze in my opinion. Unless the design is very simple, there will always be a detail that gets missed on the first iteration - no matter how careful you are.