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Old 07-16-2020, 04:09 PM   #1
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Cooling your RV at night with DC and recharging during the day

The title indicates the holy grail of dry campers in warm environments: How to keep their coach cool during the night with only DC power from batteries and just as importantly how to recharge those batteries during the day.

To make this even possible you need to limit the coach area to the immediate sleeping area which will be curtained off during the night. Also the running time will be 1 hour of 100% to cool it down and 8 hours of 50% to stay cool.

I am basing this analysis on a Winnie View Class C with a Guchen 12V roof mounted truck air conditioner of 2,400 watt cooling capacity or about 8,000 btu/hr. The Guchen is reasonably efficient, about a 2.75 COP and since it runs on DC it doesn't require a large inefficient inverter.

That much cooling capacity will easily cool a medium size room but since RVs have poor insulation I feel we need to limit it to an 8'x10' sleeping area.

The Guchen uses 860 watts of power to produce that much cooling. So that is 860 watt hours for the first hour and .5*8*860= 3840 for the overnight period or a total of 4,700 watt hours each day. That will take a pretty big battery bank to run it but 4 Battle Born 100 Ah 12V lithium batteries should work, but lets go with 5 to give us some slack and keep it down to 80% of capacity.

Replacing those 4,700 watt hours will be the challenge. You could just run your generator during the daytime if allowed. That could also allow you to run the main A/C and keep you cool during the day. But if just for mostly replacing those 4,700 watt hours, a 3,200 watt Onan diesel generator that is available on most Views could do it in 10-11 hours using the standard 45 amp converter or 6 hours with an upgraded 80A converter. This is doable but will use a fair amount of diesel, probably 4-5 gallons a day. You couldn't do that for too many days even if you started with your View's diesel tank full (generators don't operate below 25% of the chassis' tank capacity). And forget a propane generator. The typical 13 gallon propane tank that is installed on a View won't last but two days.

The other way is solar. Solar panels roughly put out 30 amp hours at 12V for a 100 watt panel on an average mostly sunny day. So dividing through gives you 1,300 watts of panels. Most View's roofs will only handle a fraction of that so you will have to stake your panels out away from the RV. And where do you store all of those panels and cabling when you move, not to mention that the panels will weigh about 200 lbs?

How much will all of this cost? Here are some very rough numbers, installation labor excluded:

Guchen A/C $2,000
Batteries- 5 BB 100Ah, $5,000
Upgraded 80A RV converter for generator use $350
Solar panels $1,300
Solar controller $600
Wire $300

Not many RV dry campers are going to shell out more than $10,000 to make this happen, but it can happen with enough $$$$.

David
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Old 07-16-2020, 04:56 PM   #2
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Does your plan include replacing the 13,500 BTU A/C unit in the View with the 8,000 BTU Guchen or is it in addition to the existing A/C unit? And, won't that limit even more the space for solar panels?

And, are there any examples of an RV with this Guchen A/C unit in usage in the USA? I'd love to see the details of it.
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Old 07-16-2020, 05:49 PM   #3
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Well, it was a theoretical case and if I were installing it on my View I would put the 8,000 btu Guchen unit in the back over the sleeping area and keep the main A/C in place for shore power or generator use. I agree there wouldn't be much room on the roof for solar afterwards, but even if you pulled out the existing A/C you couldn't fit even half of the required wattage of panels on the roof. Most would have to go on the ground.

No I don't have any specific examples. Guchen claims to be one of the biggest suppliers of bus air conditioning systems in the world and has shipped more than 50,000 units. I based my analysis on their new 12/24 Parking Truck AC which I learned about in a boating forum. See https://www.guchen.com/.

I suspect you may see them installed in the sleeper cab on 18 wheeler tractors soon.

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Old 07-16-2020, 07:00 PM   #4
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And, David... would you also modify your View to be a 50-amp coach to accommodate the extra A/C unit?
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Old 07-16-2020, 08:27 PM   #5
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And, David... would you also modify your View to be a 50-amp coach to accommodate the extra A/C unit?
Since the two A/Cs would never run at the same time, well no. But if you upgraded the converter to 80 amps, just be aware of the extra amperage it will draw and manage your power usage accordingly. But I doubt it would trigger an upgrade of the main supply to 50 amps.

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Old 07-18-2020, 02:57 PM   #6
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That is an interesting look at cooling but if we need to stay cool at night in the summer here in Arizona we normally just camp in the mountains or, if that is not possible, make sure we stay someplace with shore power.

One alternative that you did not mention is to use a "swamp cooler" instead. They are generally good for up to perhaps 20 degrees of cooling and since they are a low power alternative they would not require more in battery power than we currently have. They consist of nothing more than a simple fan and a water pump that sprays water through filters. The fan pulls the air through the filters, losing the heat of evaporation, and then pushes the cooler air out. The drawback, of course, is that they cool by adding moisture to the air.

I used to live in Salt Lake City and used one of these to cool the house I had and it worked reasonably well up to about 90 degrees F, even if everything was wet in the morning.
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Old 07-22-2020, 06:25 PM   #7
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You stole my thunder :)

The whole time I’m reading this I’m thinking

A. Wow what a great disection of electrical use for cooling. Well done.
B. I wonder how I could build a little swamp cooler for the bedroom window of our 29r sightseer. And, how much power would I need tp pump water and a small fan?

Soooo, not trying to steal ( wrong term but my brain won’t bring up the right one) this thread but what about using swamp coolers when boondocking?

Do they build on for 12 volts?
How much energy might we use for a small fan and a slow GPM water pump?
Can you afford the water use?

??????
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Old 07-22-2020, 06:58 PM   #8
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Originally Posted by 7997redtail View Post
The whole time I’m reading this I’m thinking

A. Wow what a great disection of electrical use for cooling. Well done.
B. I wonder how I could build a little swamp cooler for the bedroom window of our 29r sightseer. And, how much power would I need tp pump water and a small fan?

Soooo, not trying to steal ( wrong term but my brain won’t bring up the right one) this thread but what about using swamp coolers when boondocking?

Do they build on for 12 volts?
How much energy might we use for a small fan and a slow GPM water pump?
Can you afford the water use?

??????

They are already out there and cost between $10 to $50 however they are also humidifiers so only really suitable for arid locations. Many are battery powered and have USB charging capabilities.

Not that great in Humid Deep South States like Florida.

$7.69: https://www.amazon.com/Personal-Port...s%2C201&sr=8-3





$21.98: https://www.amazon.com/Portable-Cond...s%2C201&sr=8-4





$31.25: https://www.amazon.com/Fmingdou-Cond...01&sr=8-9&th=1
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Old 07-22-2020, 10:12 PM   #9
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DavidM,


You may find that 1300 watts of panels won't have the harvest you hope--unless they can be tilted. Look at SiO2 batteries to reduce the costs.
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Old 07-22-2020, 10:14 PM   #10
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The ones listed are pretty much a joke. There are serious swamp coolers that do an excellent job and fit on the roof of an RV.



Quote:
Originally Posted by NeilV View Post
They are already out there and cost between $10 to $50 however they are also humidifiers so only really suitable for arid locations. Many are battery powered and have USB charging capabilities.

Not that great in Humid Deep South States like Florida.

$7.69: https://www.amazon.com/Personal-Port...s%2C201&sr=8-3





$21.98: https://www.amazon.com/Portable-Cond...s%2C201&sr=8-4





$31.25: https://www.amazon.com/Fmingdou-Cond...01&sr=8-9&th=1
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Old 07-22-2020, 11:08 PM   #11
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Yaaaa I think he is ...

Just pointing out that I didn’t know they even made them. At Oshkosh air show they have large 4’x4’ coolers. I’ve never seen one in western Canada.

Interesting to see however I don’t know how well a 7”x7” cooler will do.

But if it does well or others made for an RV. Might be a solution to the power problems mentioned earlier.
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Old 07-23-2020, 12:57 AM   #12
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Boondocking with AC

What works for us: Use the AC for 1 hour just before bedtime to take the edge off the heat and to lower the humidity, then interior fans in the bedroom area all night. This uses about 1-1.5kWH - easily replenished with solar the next day. We don't have (or want) a genny, but use a Victron Orion DC to DC to charge from the TV as a backup.
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Old 07-23-2020, 04:15 AM   #13
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DavidM,

You may find that 1300 watts of panels won't have the harvest you hope--unless they can be tilted. Look at SiO2 batteries to reduce the costs.
The 30 amp hours daily from a 100 watt panel on a mostly sunny day figure was first proposed by a fellow boater and I confirmed it over a year of full time cruising with no generator.

I averaged about 60 Ah of daily use and with 200 watts of panels on my boat could keep up on sunny days. This data came from a Xantrex battery monitor. A very efficient keel cooled DC fridge was my biggest single load, probably 2/3.

That factor holds up pretty good and is based on fixed mount panels. Yes you can get 40 Ahs in Arizona in the summer and only 20 Ahs in the winter in New England. Cloudy days cut the output significantly.

David
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Old 07-23-2020, 06:25 AM   #14
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Quote:
Originally Posted by 7997redtail View Post
The whole time I’m reading this I’m thinking

A. Wow what a great disection of electrical use for cooling. Well done.
B. I wonder how I could build a little swamp cooler for the bedroom window of our 29r sightseer. And, how much power would I need tp pump water and a small fan?
Swamp coolers can do a wonderful job in cooling at a much lower operating cost than compressor Air Conditioners, but you need to keep their limitations in mind.

1) They work by pumping water through filters and drawing outside warm air through the filters and pumping it into the house/building/RV. The air passing through the filters evaporates some of the water thus cooling the air (if I remember my Physics correctly it loses the heat of evaporation) and then passes that cooler air for cooling.

2) This works best if the outside air is dry and does nothing at all if the outside air is too humid to begin with. Thus swamp coolers work well in places like Utah, Nevada and Arizona in the Spring and Fall and work poorly, if at all, in places like Florida, Alabama and Louisiana where the outside air is too humid for the swamp cooler to pick up more moisture in the air drawn into the unit.

3) There is perhaps a 20 degree maximum of cooling that can generally be provided by a swamp cooler. Thus they work in southern Arizona in April and May, but not well in June, July and August because the outside air is often 110 and thus they may only cool to 90, not much of an improvement.

4) They make the inside of the house/building/RV much more comfortable if the temperature difference is not too great, but they will make everything damp due to the high humidity in the cooler air.

5) Unlike AC you need to keep an inside window open because they generally pump a lot of air into the house/building/RV and that wants to push a lot of air out.

I used one of these when I lived in Salt Lake City and it was a great way to cool - low cost compared to compressor AC and very effective because the hottest SLC generally got in the summer was perhaps 90, but I would not try to use them here in southern Arizona for reasons I mentioned above. It is just too hot and the swamp cooler can not drop the temperature enough to make the inside cool.

They can be a great alternative to compressor air conditioning under the right circumstances and in the right places, but a waste of money in other locations. I think that is why they are not generally offered as a standard for RVs. They just don't work well in many places and not at all in others.
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Old 07-23-2020, 06:36 AM   #15
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More great information.

I notice a few of you talking about roof fans or fans in your bedroom. I have a spare fantastic fan I’ve been meaning to cut into the bedroom. Just chicken so haven’t yet.

I’d think a fantastic fan would eat a good chunk of battery power. I’ll have to open the box next time I’m in the crawl space and see what the W ratting is.

If putting in standalone fans what have you found to be economical power wise?

Thanks
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Old 07-23-2020, 07:26 AM   #16
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I notice a few of you talking about roof fans or fans in your bedroom. I have a spare fantastic fan I’ve been meaning to cut into the bedroom. Just chicken so haven’t yet.

I’d think a fantastic fan would eat a good chunk of battery power. I’ll have to open the box next time I’m in the crawl space and see what the W ratting is.

If putting in standalone fans what have you found to be economical power wise?

Thanks
We just use simple small generic 110 fans. We turn on the inverter and plug them into an extension cord. We run them most of the day and at night until it cools off, and then we shut them down.
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Old 07-23-2020, 09:58 AM   #17
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This this thread is kind of about "pie in the sky" "maybe someday" stuff. I read a report this week that scientists are working on a way to combine solar panels and batteries into one device - the Solar Flow battery. The idea being the solar panel would charge the internal battery and provide excess power during sunlight hours and provide power during nighttime.

https://arstechnica.com/science/2020...-battery-tech/

https://www.chooseenergy.com/news/ar...rd-efficiency/
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Old 07-26-2020, 07:25 PM   #18
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The ones listed are pretty much a joke. There are serious swamp coolers that do an excellent job and fit on the roof of an RV.

The request was for a small 12 volt unit that used little power while the "Serious Swamp Coolers" are not small nor are they inexpensive and use more power to run the larger fans along with pump systems. Be that as it may Swamp Coolers are not effective in areas with high humidity.

In motor homes which are prone to mildew issues by nature a swamp cooler in a already humid area is not a very good a match.

As for the Swamp Coolers that bring in outside air that also brings in a second issue in humid areas which is introducing Mold Spores from the Outside Environment into the conditioned space which requires additional Hepa filtering along with de-humidification of the air being brought in from the outside which increases power consumption and operating expense due to the additional consumables.


For those that are unaware - Once you've been involved in the Mold Remediation of a structure that requires all the siding, wall board, ceilings, carpeting, and insulation in a structure along with all furnishings/personal items to be removed so that what remains can be cleaned with Ammonium Chloride and dehumidified by a work crew wearing full DecTam Suits before the structure can be rebuilt you are very cautious about using any technology that raises humidity levels to cool. Books, furnishings, family photos and other absorbent/porous items are very costly to restore afterwards so most may have to be destroyed. Family photos at times will need to be copied before the originals are destroyed with only the most precious conserved to maintain the originals. After an event such as is now occurring in Texas with Hanna, waiting a day before drying out a home that has had water get into it can make the difference between dry out/clean up and a Mold Remediation which can cause a greater loss than the Hurricane itself. Note that similar damage and remediation can also be required from having a pipe drip or any other situation that raises humidity levels to a point where mold/mildew growth is triggered,
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Old 07-26-2020, 08:19 PM   #19
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For those that are unaware - Once you've been involved in the Mold Remediation of a structure that requires all the siding, wall board, ceilings, carpeting, and insulation in a structure along with all furnishings/personal items to be removed so that what remains can be cleaned with Ammonium Chloride and dehumidified by a work crew wearing full DecTam Suits before the structure can be rebuilt you are very cautious about using any technology that raises humidity levels to cool. Books, furnishings, family photos and other absorbent/porous items are very costly to restore afterwards so most may have to be destroyed. Family photos at times will need to be copied before the originals are destroyed with only the most precious conserved to maintain the originals. After an event such as is now occurring in Texas with Hanna, waiting a day before drying out a home that has had water get into it can make the difference between dry out/clean up and a Mold Remediation which can cause a greater loss than the Hurricane itself. Note that similar damage and remediation can also be required from having a pipe drip or any other situation that raises humidity levels to a point where mold/mildew growth is triggered,
Tell me about it. We have a rental (home) in Ohio and the tenant wondered why it was so moist in the home, so to "dry" it out, she just turned up the heat (it was winter).
Problem was, the water heater, right next to the HVAC system, failed, and water was leaking into the duct work of the heater, sending warm moist air into the home.
Within days in was uninhabitable, and has been since taken down to the studs for remediation.
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