Concept for cold weather use of rPod water systems - R-pod Owners Forum

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lostagain

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Location: Quaker Hill, CT
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Topic: Concept for cold weather use of rPod water systems
Posted: 29 Sep 2018 at 10:08am

Wow, only $500. That's puts it into a whole different category. How do you plan on attaching the closed cell foam on the bottom? I assume you also plan on using something like that to deal with the other heat loss areas, but maybe with something less costly.

Yes, dealing with snow in the west is different from the east. We lived in northern New Jersey for several years and, except after a fresh snow fall when everything was beautiful white, snow there isn't very pleasant. And yes, people drive without chains, indeed in some places they're forbidden, but there are a heck of a lot of ice caused crashes too. Speaking of snow removal, how do you plan on rinsing the salts they use on the roads if you're out an around after after a snow fall? That stuff is so insidious it eats away at everything it touches.

As for my axle, I don't think that we've ever come close to the GVW, even at our heaviest. Since I've taken stuff out of the trailer, such as tv and upper bunk and we have a minimalist approach to our trailer camping, it's something that I'm not too worried about. Water is is the biggest issue for us, and when we travel, we put a lot of it forward in the bed of the truck in jugs in milk crates. I guess that is one advantage of having a pickup truck as a TV, you can kind of spread the weight around. Some day, when I'm feeling really frisky, I'll call FR and ask them what axle they put in the trailer. They've been real helpful so far.

Never leave footprints behind.
Fred & Maria Kearney
Sonoma 167RB
Our Pod 172
2019 Ford F-150 4x4 2.7 EcoBoost

offgrid

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Posted: 29 Sep 2018 at 11:34am

I was going to lift the trailer, reroute lines through split plastic wire loom so I could access them and pull them through later, dress up in a moon suit, and spray the whole bottom of the trailer using the two part foam kit. I should have plenty in the kit to do everything. Can't use open cell hardware store type foam, that holds water. Anything left over I have some places in the attic to seal up.

Yep, idiots drive off the roads everywhere, they don't need an excuse. Especially common after the first major winter storm of the season, seems like they forget that they no longer have traction. Snow in the cities is dirty nasty stuff. Nice clean snow in the mountains, either in the west or east, is beautiful.

Get the road salt off? He he, least of my worries. I live on the Outer Banks. Salt water, salt spray, salty sand everywhere, all the time. I get under my vehicles, flush them with fresh water, dry, spray WD40 everywhere. WD stand for water displacement, if you can fill up all the little gaps and cracks with something else salt water can't get in there. It helps, but stuff still rusts.

I also use Fluid Film, a lanolin based water displacement material. Thicker, so stays on surfaces longer and fills bigger gaps. Good stuff. Gotta flush and recoat a couple times a year though. Basically I just try to do the best I can and avoid the salt as much as possible.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

offgrid

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Posted: 29 Sep 2018 at 2:56pm

mjrpod, that nupod looks very nice, thanks. But like the smaller rPods, its a little smaller than we'd prefer. We like the slideout on our 179. Makes it just a little bigger inside. My wife does some telecommuting while we're in the rPod, and the space created by the slide makes that quite a bit more doable.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

CharlieM

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Posted: 30 Sep 2018 at 8:45am

Originally posted by offgrid

CharlieM,

I read through your links and found them very useful. I have a couple of questions.

Looks like the solenoid part of your system is very similar to what I plan to do, other than I'm thinking of using a thermostat rather than a timer and will be dumping the water back into the fresh water tank. How did the timer work out for you, did you do any testing to determine your cycle times? Did you consider a thermostat and if so, what made you decide on the timer approach? Also, do you recall what solenoid you used?

I'm planning to use the solenoid only to heat the fresh water tank and the pressure pump suction line (because feedwater would return to the system through that line whenever the solenoid was energized).

For the hot and cold water lines as well as the gray and black tanks I'm planning a circulator pump, just connected between the hot and cold lines at the water heater. This is where the circulators are usually placed in residential instant hot water systems. The circ pump is left running in those (its tiny) and generally a temp sensitive wax valve is placed across the hot and cold lines at the farthest point in each plumbing loop. This keeps both hot and cold lines warm. I basically want to substitute the tank drain heat exchangers I plan to make for the wax valves and turn the pump on and off via a thermostat(s) to save energy rather than just leave it running.

Looking at the way the rPod's fresh water plumbing is laid out relative to your Camplite one benefit of the rPod is that all the hot and cold feed lines are inside the camper except for the two sets of low point drains. If I tee off the hot and return to the I think that should keep all the fresh water plumbing warm. Do you agree? My biggest concern was the low point drains themselves which would have to stick out of the insulation a little. It sounds like you had the same potential concern but never had a freezing problem at those points with your system?

Thanks again!

OFFGRID,

I did consider a thermostat but settled on the timer as simpler and adequate. The thermostat would need a remote sensor and I couldn't decide on where to put it. Simply sensing outside temperature would waste energy but I couldn't decide where in the network of insulated pipes would be the most vulnerable. Also the thermo controllers were more expensive; the timer was amazingly cheap.

My experience with subfreezing temps to date is very limited so I haven't experimented with cycle time. The timer has a minimum run time of one minute with 17 settable events. I set the timer to turn on every 45 minutes during the coldest pat of the night/early morning as a starting point.

The solenoid I used is https://www.amazon.com/12v-Normally-Closed-Brass-Solenoid/dp/B005EP0WAO/ref=sr_1_3?ie=UTF8&qid=1451588576&sr=8-3&keywords=duda+diesel+solenoid

Although adequately rated for pressure and temperature I think I have caught it not actuating several times. Not sure what's happening yet but it should be OK. The solenoid connects the HW pipe under the kitchen sink to the vent hose leading into the FW tank. Thus the heated water dumps back into the FW tank and heats it too. No wasted water. I did verify the one minute run time is adequate for HW to reach the solenoid and FW tank. Your scheme should work as well. One advantage of my end to end circulation path is I can run it manually for 20 seconds before showers when dry camping. This provide instant HW at the shower saving FW and gray storage space. No wasting either while waiting for the shower to warm up. Smile

Agreed the POD piping system is better. More enclosed piping makes it much easier. In fact the POD is better insulated all around and was a very cozy camper when we had one. The low point drains were a concern to me too. I hope the added insulation will allow conduction from the pressurized water above to keep the valves from freezing. Time will tell. Again, my goal was to protect from short overnight freezes, not long deep freeze storage. Let me know how you progress.

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

offgrid

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Posted: 30 Sep 2018 at 5:16pm

CharlieM, the thermostat I'm planning to use is crazy cheap too.

https://www.amazon.com/LM-YN-Thermostat-Fahrenheit-Temperature/dp/B076Y8RBJ6/ref=asc_df_B076Y8RBJ6/?tag=hyprod-20&linkCode=df0&hvadid=198093463189&hvpos=1o2&hvnetw=g&hvrand=51075119854268219&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9009728&hvtargid=pla-578924223832&psc=1

I already used one to have an actual adjustable thermostat on the gas side of the water heater to save wasting water adjusting while taking showers. So far it works well but I don't have much experience yet.

My thought was to just via trial and error (at temps above freezing) to add as many temp sensors and thermostats as needed in as many places as required. They use normally open relays so putting several in parallel is going to trigger the circ pump or solenoid to start whenever the coldest one calls for heat, as well as provide for redundancy.

I too was thinking to add a manual switch to run the circ pump for 30 seconds to avoid water waste showering too. Looks like we both dry camp a lot and are always looking for ways to save water.

Your use of just a solenoid is triggering me to take another look and my heat transfer calculations. The reason I am planning both a circ pump and a solenoid is because while the heat transfer rates between the copper tubes immersed in the two tank drain lines will be pretty good, it will never be as good as just dumping a little hot water directly in the fresh tank is. So in order to not overheat the fresh tank I've been planning separate systems. I'll go through those numbers again and see how bad the imbalance will be.

I really want to try the internal drain line heaters because I've done a few thermosiphon heat transfer systems in the past and they're a lot of fun. They're also very hard to predict via calculation, even fluid dynamicists have trouble with them. If it works it will eliminate the need for antifreeze in moderate freezing conditions without having to waste huge amounts of energy on electric tank heating pads.

I actually think the pod plumbing and low point drain design lends itself to this type of freeze protection system, we'll see how it turns out and I'll keep you posted.

Thanks again, you've been very helpful.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

CharlieM

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Posted: 30 Sep 2018 at 7:30pm

Offgrid,

Sounds like you're on a roll. I'm an engineer and approach such tasks with prelim calcs too. However, with all the variables in your project I'd expect huge uncertainties...like +/- 100% LOL

A few thoughts: Your thermostat is dirt cheap and it would be a more precise solution than my timer. I didn't find that or it wasn't available when I started my job. I really like the idea of using HW from the heater with the onboard pump and dumping back to the FW tank. Consumes no water, does heat the tank and the manual mode for showers really works even in non freezing weather. For the waste tanks I really think some antifreeze is the easy solution, especially for the few times I camp in sub freezing WX. The black tank should take care of itself with all the microbial action and the gray tank shouldn't take much. For the cost of a few gallons of AF it saves a lot of work. BTW this system also works for nights when the trailer is at home, unwinterized, and temps drop. It means I don't have to winterize/dewinterize during the shoulder seasons. The FW system is the only vulnerability since the waste tanks would be empty and open. A small electric heater keeps the interior above freezing and the circulator takes care of exposed plumbing.

That said, I wonder if you could glue a coil of copper tubing to the bottom of each waste tank near the exit ports. Circulate the HW through them via thermostat. I think the waste tanks are ABS so you could use a conductive epoxy ABS. Cover them with spray foam insulation. No tank penetrations or fittings required and all work can be done on the bottom of the tanks. . No such solution for the FW tank 'cause it's polyethylene.

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

offgrid

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Posted: 01 Oct 2018 at 11:58am

Yes, I agree that an overall modelling uncertainty of 100% is in the right range. As you know, lots of engineering has uncertainties like that and the solutions still work out just fine. The main sources of error here are the heat loss rates in the tanks and plumbing, and the heat transfer rates in the heat exchangers. The heat losses in the tanks and pipes are a matter of surface area and r values, so pretty well understood, so I think those are maybe +-30-50% at worst. Those will govern how much total propane or electric energy is required from the water heater. There is plenty to spare so not a big deal if I get that wrong.

The heat exchange transfer rates are less well understood, those probably are actually about a factor of 2. Those govern how long the circ pump is on. So I plan to design for worst case and if the transfers are more efficient, great. The power requirement for the circ pump is so low that it really doesn't matter much.

Actually it turns out after some more research that ciculators use less power and are more reliable than solenoid valves. The reason looks like it is because the circulators aren't trying to fight against water pressure, they just pump a small amount of water at very low head pressure from the hot to the cold side of the water heater. I would prefer to use a circulator for everything except that I can't figure out how to transfer heat to the fresh water tank that way, without putting more holes in the tank. As you say polyethylene isn't the best material to try to adhere stuff to.

The other reason I like the idea of using a circulator in the rPod 179 is because the hot and cold low point lines are adjacent and at the far ends of the plumbing run so by recirculating between the hot and cold lines you are guaranteed to heat all the pressure lines.

You could adhere copper tubing to the waste tank bottoms but it would require much more tubing than a immersion heat exchanger, and I would be concerned about how to heat the drain lines that way. The drain lines and gate valves are going to be more prone to freezing than the tanks themselves. I don't plan on inserting anything into the waste tanks themselves, the Cu heat exchange tubing would be inside the drain lines, so no new holes in the tanks. I've done horizontal tube immersion heat exchangers before and as you might expect, copper ones work quite well. I used to heat my hot tub that way from my gas water heater, silent and almost zero electrical requirements.

I did take a look at flow rates though the heat exchangers vs just running hot water into the tank and the duty cycle I get for running hot water into the tank is well under 1%, so it sounds like its about where you set your timer. The duty cycle for the heat exchangers/circulator is between 25 and 50%., so they are not a good match. So I can't simply dump water from the heat exchangers back into the fresh water tank.

Maybe I should just go ahead and install a couple of blind bulkhead fittings in the fresh water tank install a heat exchanger through it, and dispense with the solenoid valve. I could route one of the lines from that exchanger next to the pressure pump suction line to heat that. Then I could probably just leave the circulator on all the time when its below freezing, that would really simplify things. It would still only use well under 20Ah per day, not a big deal.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

SkiPod

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Posted: 22 Jan 2019 at 8:50am

Although a lot of work, this thread is an interesting concept and would be a good solution for extreme temps. We just went up to Taos Ski Valley from Dallas for the long weekend to go skiing in our 2016 176 Rpod. I wanted to have access to water and shower so I put heating pads on the three tanks, 12V self-regulating heat tape on the exposed fresh water line from tank and wrapped in the pipe insulation with aluminum tape going on before and after. I also put the heat tape around the grey water valve. Last weekend it was subzero, around -6 at night in the ski valley but was warming up to near freezing during the day. The only trouble we had was that in the morning each day the hot and cold water to the shower as well as the toilet water was frozen. We left the electric heater on high all day (took a generator with us) and when we got back the lines were no longer frozen. The lines are not exposed but run through the floor. So I suspect that just being adjacent the bottom layer of the floor was enough to freeze the lines at these temps. Not sure what can be done about that except maybe putting insulation under the Rpod or adding a skirt? Anybody else have this issue and figure out a simple solution? The electric heater would keep up with keeping the RV warm inside, even too warm. We didn't add any extra insulation anywhere.

offgrid

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Posted: 22 Jan 2019 at 9:07am

Yes I think the water lines in the floor are subject to freezing because there is no insulation under them. I think the water recirc method would be a pretty easy fix for that. By running hot water out the hot line and back through the cold line you will catch the whole system. The cold line doesn't really need to be cold anyway if you adjust the water heater temp to something comfortable.

If you skip doing my proposed heating system for the waste tanks and just use some extra antifreeze in them as CharlieM suggests then that would save most of the effort. I think that some type of insulation on the fresh water tank would probably still be required in the temps you're experiencing to keep propane use down but you could try it first without it. I'd also be tempted to just remove the low point drains, they're really only there to reduce antifreeze use and create an unnecessary freeze sensitive spot. You should add interior cutoffs for the outside shower or you'll probably be replacing that come spring.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

texman

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Posted: 22 Jan 2019 at 11:23am

great information here, thanks for posting. i was considering installing the pads on the tanks and water lines prior to reading this. the antifreeze for waste tanks makes the most sense instead of heating. I dont plan to camp at sub zero ever, more like just be able to camp when it dips into the teens at night for a few hours. I am thinking that a heater pad for the fresh water and heat pads for the fresh water runs may suit my needs. Very interesting project and i will stay tuned.

TexMan 2015 182g
2018 Sequoia
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