Tuesday, April 21, 2015

The More Efficient Solar Water Heater Concept

I'm going to talk about some ready-made and also a home-made alternative to having enough hot water when out boondocking. The first relies on propane, the next one on free solar power.

Typical RV water heaters...

Most mobile travelers wish they had a reasonably efficient water heater on their RV, especially if out boondocking, where there are no hookups. Most RV's solve that problem by using a propane powered water heater, which works quite well...if you have room for one...and don't mind the huge hole for it in the side of your RV. They have to be there in order to vent the burned propane fumes to the outside.

In special circumstances where you may not want to have a huge hole in the side of your vehicle, such as in conversion vans or other "stealth" vehicles, there is an alternative that can be mounted totally within the vehicle, but still requires venting down through the floor. There's a site called RV550 (http://rv550.com) that has a "down-draft" propane water heater. However, it still requires power and may be cost prohibitive for some "would be" users (around $1100). And you still have to cut a hole in the floor and get wiring to it, as well as plumbing.

All of these ready-made water heaters are great...for some things. They still require propane bottles larger than you may want to put in your nice conversion van. If you don't have room for the water heater, you probably don't have room for the propane bottle that needs to go with it. Plus, if you are boondocking, you need to be somewhat "power conservative", so you don't really want an exhaust fan running if you can get around using it.

Many vandwellers and other travelers with small RV's need to conserve all the space they can inside their vehicles, as well as conserve any power or fuel on board. And since many of them travel in the Southwest at least part of the year, where there is abundant sunshine, why not use "free fuel and power"?

A factory-made solar water heater...if you have room for it...

It was brought to my attention after writing this, through a Facebook comment, that there is a small company who makes solar water heaters for RV's. You can find it at http://bhasolar.com. (I make no commission from that referral.) I looked the site over and they do have some interesting points, but because of the type of panels and the fact that they need a storage tank, it appears to be more for larger RV's. A conversion van, cargo conversion or Class B has limited roof space as it is, most of which would be taken up with solar panels if they are really serious about boondocking.

Solar power is far more important and complicated, due to the wiring and batteries, than supplying temporary hot water. Anyone can can hang a black bag camp shower on a tree and get hot water for showers or doing dishes. Not so with solar electric power.

Also, storage space is already limited in a small RV, and there's little space for fresh water, so finding additional space to put a hot water storage tank is next to impossible.

It looks like they recommend utilizing their system with an existing water heater, which is fine...if you have one to begin with. But if you have that, then you don't need solar, either, except as a conservation means of saving propane or electric, rather than necessity. My concept is more for creating a hot water system where none existed before, and without putting holes in the side of the RV to do it.

Theirs is also a ready-made $349 kit...supposedly. It's not something you can just plug in and use, though. It still has to be installed. The components for my home-built system should cost less than $100, and parts are obtainable at any hardware store. You still have some installation involved, but at least you don't have a big cash expenditure all at once. You can buy the parts a little at a time if you need to.

The difference between their ideas and mine is that in mine, I am assuming you have no means of hot water at all, nor a place to put panels or a tank. My concept is only eight inches wide and the same height, by a little over 5 feet long, although you can make it any length you want. It will fit in places a panel won't. For my own purpose, it will be mounted to the roof rack next to my solar panels for electric power. Also, the solar collector is the tank, so no additional space is taken up on the inside of the RV, other than for a small one-gallon expansion tank, which can fit almost anywhere.

Mine also does not require additional power to run a circulating pump. The fresh water pump is the only thing that runs, and only when you use water at the sink or shower. In fact, if you don't want the system on the roof at all, it could even be mounted on a bumper rack...as long as you face it toward the sun when parked. So in practical usage, power requirements, space, cost, and ease of building it and installing it, my concept still has the advantage on all counts.

But every product has a use...somewhere...so you make your own judgment as to what works for you. After all, I am only suggesting an idea...a concept. I'm not trying to sell you a product that I created. Wise consumers will know why that is important.

Let's go solar...

Those who watch videos on YouTube regarding what other vandwelling "self-builders" are doing, may have seen several different types of black pipes (or, more correctly, white PVC pipes painted black) mounted in various ways...either on a roof rack or on a ground-mounted slant-board. These all work...to a point. So even though it starts out as white PVC pipe, we will refer to it as "the black pipe" in future references.

One problem with nearly every one that I have seen is that they aren't as efficient as they "could" be. They heat up fairly quickly, but then after the sun starts going down, they also cool off just as quickly. Anyone hoping for a shower before bed time after a day of hiking, is going to be out of luck! And an early morning shower is going to be equally as cold. Also, a windy day is going to take away half your heat before you even get a chance to use it, even in the middle of the day! The efficiency is also going to drop exponentially as the outside temperature drops, AND/OR the wind speed increases, because there is nothing there to conserve the energy!

The other problem with roof mounted units is that nearly every one I have ever seen relies on getting up there with a stepladder, taking a cap off, filling it by hand, and then letting gravity provide whatever shower pressure you get. You have to leave the fill cap off all this time to serve as a vent, so it doesn't get air-locked from vacuum, but that can also introduce dirt into the pipe. The amount of water you get is limited by the size of the pipe that is being used. It's just a poorly designed system!

The circular hose types mounted to a slant-board that sets on the ground has to have a water supply to keep it filled. Trying to fill that type by gravity is nearly a lost cause. And even worse, they typically hold even less water than the roof-mounted types.

Think about this for a minute...what do you see on nearly every solar collector on the market?

They all have a glass or Plexiglass cover over them to hold the heat in! On house mounted solar water heaters, they are also fed from the water pump in the house. There are reasons for the way they are built, and yet nearly every home-built system for RV's that I have seen overlooks those simple principles!

What about the weight issue?

The other thing that roof-mounted units have to be careful of is inertia. If you gravity fill the tube, and then don't use it all, what happens if you make a sudden start or stop? The force of that water all goes rushing to the opposite end of the pipe, putting far more force against it than a solid weight would.

People put 100 pounds of weight on roof racks every day...solid weight, that does not shift. Think about what would happen if they put a 20 pound bowling ball inside a long pipe and then drove down the road with it! It would go crashing through the end of the pipe or rip the entire assembly off the roof with their first panic stop! And it is capable of it with far less weight involved, simply because of inertia!

In other words, if you FILL a tube with water, and keep it under pressure, it acts as a solid weight. It can't shift because it has nowhere to go! There's no air space to fill! That is far safer than a half-filled tube in which the water sloshes from one end to the other, building up momentum in the length of its travel due to the air space in the tube!

My design concept...

So my system concept, that I will be adding to our cargo trailer conversion will be a roof-rack mounted 6-inch diameter PVC pipe filled by pressure from the 12-volt demand water pump in the trailer. Even if the pump is off, there will be check valves in the system to prevent the water from gravity draining out, but yet be capable of a manual over-ride, so that the tube could be drained...such as for storage or for below freezing weather.

The other part of the system I will build, will be an enclosure around the water filled black pipe, just as every other efficient solar device has. I had originally thought about simply a larger, and yet clear tube, with the black pipe inside of it. But after checking sources, it is VERY difficult to locate, and when checking prices it is EX-PENS-IVE!

The reality is that is doesn't need to be round. It's not holding pressure like the black pipe, so the outer covering can be square. The bottom isn't going to receive any sunlight, so it can be solid. Based on the weight of the black pipe, I suggest something like a piece of treated 2 x 8 as a base. When mounting it to the roof rack, the U-bolts that secure the black pipe can go all the way through the 2 x 8 and be nutted on the bottom of the roof rack. This will add extra safety to the unit and also prevent the black pipe from sagging, especially after it gets hot.

After getting all the necessary piping and parts in place on the black tube, and the piping extended through holes in the bottom of the 2 x 8,  the top of the 2 x 8 can be sprayed flat black (or paint it prior to installing it) to attract more heat, and then the assembly can be enclosed.

For the two sides and the top, I suggest sheets of 1/4-inch Plexiglass. The corners can be joined using stock 3/4-inch aluminum angle running lengthways. Only two pieces are needed, as long as they are as long as the case for the tube. The bottom edges can be secured right into the edges of the 2 x 8. The length of the case wants to be about an inch past the ends of the black pipe, just for "wiggle room". The ends of the case can be made out of anything handy...wood scraps, sheet metal or even more Plexiglass, if you have pieces left over. It's not going to get enough sun on the ends to worry about it being clear, so any solid material will work just fine.

The outer case doesn't want to be sealed up tight. Leave a couple of small vent holes, preferably in the 2 x 8 base, so that a little bit of air can circulate. This will relieve any pressure buildup as well as keep the unit from steaming up the Plexiglass and ruining the efficiency of it. The main thing is that it keeps the wind off the pipe, so that it retains its heat much longer by acting as insulation.

That's what every solar collector ever made does! It can't be efficient if the wind is cooling it off as fast as the sun is heating it!

Mechanical factors...

As with any hot water or hot air device, there are going to be fluctuating temperatures and also fluctuating pressures...all of which must be allowed for in a closed system. But it's not rocket science.

The first thing you have to consider is where to put the water in. Because this unit is elevated above the rest of the RV, you have to consider the weight of that water. At an approximate weight of 8.34 pounds per gallon of water, a ten gallon black pipe is already pushing nearly 84 pounds of water "down", if you try to fill it from the bottom of the black pipe. If you only have a water pump capable of putting out 35 pounds of pressure, it may not be able to fill the pipe all the way, because the more water you put into the pipe, the heavier that water is going to get! It could create a back pressure that hits a balancing point, and you won't get more than that 35 pounds up there!

In pump terms this is called the "head" pressure. All pumps are rated in head pressure. They can be only 35 gallons in system pressure, but not be able to pump the weight of the water much higher than the height of the pump. OR...they can also provide plenty of head pressure to drive that water up hill.

So the answer is to fill the pipe from the top, so that the fill point is above the weight of the water. Now, you will only have the weight of the water in the fill pipe going to the roof. Depending on what size pipe you use (3/8-inch should be more than enough), you are only pushing against the weight of the water in the fill pipe.

I will show a diagram of the entire system as soon as I can draw it up, but I want you to understand it first. I will also add photos of the various parts involved, along with sources for those parts.

The other thing is that you don't want to introduce water to the middle of the pipe, as that would dilute half your hot water right off the bat. ALL residential water heaters introduce the cold water at the bottom of the tank. Cold "anything" sinks, while hot "anything" rises. Very logical.

Even tall water heaters that have the two pipes on the top, will have a dip tube on the cold water side to force the cold water to the bottom of the tank, while the hot water side comes straight off the top of the tank. This is how you manage to get somewhat close to 30 gallons of hot water from a 30-gallon water heater. The cold water rises as the hot water is taken off the top of the tank, but since the heat source is at the bottom of the tank, that cold water is also being heated as it rises. But that doesn't happen quickly. It takes awhile. Only at the very last of the hot water do you feel it start to go cold, and then it goes completely cold very quickly if the water heater can't recover fast enough. We've all been in showers and watched (or should I say, felt) that happen.

So our black pipe on the roof creates a slightly different problem...by being horizontal rather than vertical, the diameter of the pipe itself is hardly enough to justify a dip tube only a few inches long. So the next best thing is to introduce the cold water at one end. It's not going to go gushing into it and mix up all the water immediately because it is under pressure. It's only going to put in an equal amount to what is being taken out, no matter how large the fill pipe is. So the logical thing is to put the water in at one end of the black pipe and take it out at the other.

Keeping in mind that cold water will tend to stay toward the bottom, anyway, it is also logical to take the hot water off the top of the pipe, only at the opposite end of where the cold water is entering. So to make it simple, the cold water goes in at the top on one end, and the hot water is taken off the top at the opposite end. A slight tilt of the vehicle one way or the other isn't going to matter much.

Even though part of the cold water fill pipe is going to be enclosed in the outer Plexiglass case, it will still absorb some heat while getting to the other end. It may not be much, but can work to our advantage, so it should also be painted black, and zip-tied tight to the main black pipe, both for heat absorbtion and to keep it from rattling around.

In that same line of thought, you want to get the hot water back down to your sink or shower as fast as you can. So run the cold fill pipe all the way to the farthest end of your black pipe, and take the hot water side off the end closest to your sink, which will make the system that much more efficient. You can even wrap the hot water tubing with some insulating material to keep it warmer until it gets to the faucet.

Adding fittings...

OK, so what is the safest way to add the fittings and what kind of fittings should be used? I recommend a couple of brass 90-degree fittings, with no less than 3/8-inch NPT (stands for National Pipe Thread, an industry standard) male threads on one end and whatever you want to use for tubing on the other end. There is no need to use larger than 3/8-inch fittings, as under your sink are only 3/8-inch, and for water conservation, you really don't need to go any bigger.

What kind of tubing should I use for the water lines? For tubing, I recommend copper tubing, rather than plastic. Remember, the parts up on the roof are going to be subject to UV damage from sunlight, so unless you can find UV resistant tubing that is also suitable for drinking water...you should go with copper. In that case, the other side of the 90-degree fittings should be either compression fittings or flare fittings. Compression fittings are easier as they don't require special tools. For flare fittings, you need a flaring tool...not overly expensive...just something you'll have to store afterwards.

So how do I get the fittings attached to the black pipe? You will thread them into the top side of the pipe where the end caps and coupling overlap with the pipe to provide a double thickness, for more strength. First, I suggest using plain end caps on the large plastic PVC pipe, with a coupling near one end. You want the coupling to be as close to the end cap as possible. It doesn't matter whether you put it on the cold water end or the hot water end.

I don't recommend using adapters and screw in plugs on the end, because those large threads on the plugs of that size are hard to seal, even with Teflon tape. Just use the plain old rounded end caps and glue them on. It's a tank. You shouldn't ever have to get into it again if you assemble it properly.

You'll be buying a pipe tap for making internal threads for 3/8-inch NPT pipe. Any hardware store should have one. You don't need a tap handle. If you are careful, you can use a small wrench to turn the tap, as long as you can keep it straight. Drill a pilot hole first, using the recommended size pilot drill for the tap you will be using. Most taps will have the pilot drill size stamped on the side of them, or else look up that information. Never trust a hardware store clerk, unless you know that they know what they are talking about! They should have a chart to tell you the correct pilot hole sizes.

Install one cap only at one end, and then the coupling on the opposite end, with a short piece of pipe between it and the other end cap, but don't install the second cap yet! On the very top of the pipe (with it laying horizontally), drill through the area where the pipe cap overlaps with the pipe itself on one end, and through the coupling and pipe near the other end. Then on the opposite side (bottom side) of the pipe from one of the other fittings, drill and tap another hole for the drain fitting. We'll explain about that further down.

The reason for doing this before the last end cap is glued in place is so that after drilling and tapping, you can clean out any shavings before gluing the last end cap onto the pipe...otherwise you won't be able to get in or out of it. By drilling through the fittings and the pipe it will give you double thickness and plenty of thread depth to hold the pressures involved.

By using the coupling, you don't have to worry about drilling through the cap, then taking it off to clean out the pipe and then trying to line up the holes again. The second cap is just a cap, with no need to drill through it.

You'll want to do all your drilling before you install the pipe on the roof, so you can upend it and dump the shavings out. Make sure you do ALL your drilling and tapping first. Don't try to add something after it is all glued together, as the shavings can get into valves and faucets and cause all kinds of problems!

By the way, 6-inch schedule 40 PVC pipe used for drinking water has walls nearly a quarter-inch thick and will hold pressure of 180 pounds PSI. Your water pump is only going to be rated for about 35 pounds, so don't worry. You won't blow a gasket. Well..."you" might, but the pipe won't.

A one-foot length of 6-inch PVC pipe holds 1.47 gallons of water. A 5-foot length of pipe will give you 7.35 gallons, which is already bigger than most standard RV water heaters (at 6 gal.). We can get two "Navy" showers out of a 6-gallon water heater, so you be the judge. You can make the pipe as long as you need it to be, but for a small RV, or van, don't go overboard. That five-foot length of water will also weigh 61.4 pounds, plus the pipe itself, the 2 x 8, the clamps, fittings and enclosure. So you can already figure that you'll be up around 80-90 pounds on the roof rack. Don't over-do it!

Screw one of the 90-degree fittings into each end of your black pipe, on the top side, and then the third fitting on the opposite side, using Teflon tape. Put about three wraps around the fitting threads and that's all. Don't over tighten it. Hand tightening should be enough. When you have about two threads left outside the pipe, or can't turn it any more by hand, stop.

Make sure the outgoing part of the 90 is headed the right direction. They should all point toward the end that has the two fittings on it. That will be your hot water "out" end. If not, tighten it slightly more. NEVER back a fitting off to position it, as that loosens the thread seal. Then attach your smaller tubing for your cold and hot water lines to the other sides of the fittings. You want to leave enough tubing to reach the floor of the RV after you pass through the roof opening.

OK, so how do you get the water lines into the RV? What I recommend is a small plumbing vent cap, like RV's use over the bathroom plumbing vent pipe. Install it with proper roof sealant for RV's over the place that is easiest to get the tubing down to below your sink, and preferably near the edge of the roof, closest to the outside wall.

You might be able to hide the tubing in a cabinet, or if not, you can buy white plastic stick-on Wiremold at most builder stores. It is normally used as a chase for mounting surface wiring when you can't get through a wall or ceiling. The larger size will accommodate a 3/8-inch copper tube, as long as you keep it straight.

The cover of these roof vent caps snap off, and there's usually some "scalloped" openings around the inside. The 3/8-inch copper tubing should bend easily enough to go under the cap and down through the roof. Don't kink it! Borrow a tubing bender if you have to! And when finished, make sure the cap will snap back on. If you lose it, you will have rain coming into your RV, so be careful!

BTW, these vent caps are also good for wiring, such as for an antenna or solar panels, as are the Wiremold plastic chases. The latter usually has self-stick strips on the back, and the cover can be snapped on after the wires or tubing are laid into them.

Where should the water lines attach within the RV? The cold water side should go to an expansion tank first (mentioned later) and then a check valve, then to a tee with a snifter valve in the side opening, then to a manually operable valve (used when winterizing) and then to the outgoing side of your water pump, as the pump needs to supply water to both the cold water side of the faucet as well as to the solar water heater on the roof. It's better to put the expansion tank on this side (rather then the hot water side) so that the hot water coming in from the roof can go straight to the hot water faucet without being wasted or diluted with cold water before it gets there.

The hot water side from the roof needs to go through a check valve (allows flow only one direction), then a manually operable valve (for winterizing), then to the top of a tee (the side opening goes to the drain from the bottom of the roof-top tank) and then can go straight to the hot water side of your sink. This way you get the hot water as fast as possible with little waste waiting for it to warm up.

The third line is the the one from the bottom of the roof-top tank and will go to a manually operable valve before entering the tee mentioned in the last paragraph. All of these small manual valves are for the purpose of draining the roof top tank in case of freezing, or when winterizing for longer times.

Safety concerns...

As with any pressurized system, and especially one involving heat, there are going to be pressure fluctuations. Some will be caused by the pump or water supply, while others are going to be caused by the changing temperatures. ALL must be allowed for!

Another factor is that in a sealed system, you have to have a way to drain off the air trapped inside the pipes as the water replaces it. Since this system will have the hot water (outgoing) side coming off the top of the black pipe...and air rises above water...simply opening any hot water faucet will bleed the air out, just as in any other RV. No big deal.

However, water itself can expand and contract with temperature. In a normal RV system, once the water is heated to temperature, it usually remains fairly constant, and normal usage of hot water at the sinks relieves any slight difference in pressure. Even so, every water heater is required to have a temperature and pressure safety relief valve, just in case a thermostat sticks and causes the heat source to remain on...while constantly building up more and more heat and pressure.

I've seen instances where water heaters have "blown up", (usually the bottom goes first, but not always), and caused the entire water heater to break through floors above it and go shooting out the roof of a building, just like one of those water rockets that kids play with. That is because someone failed to install that safety relief valve on it. Safety is nothing to fool around with. Exploding water heaters have also killed people!

One major difference with solar water heaters is that the source of heat is limited in both time and temperature. Sure, the pipe may get VERY hot to the touch at the peak of the day, but the sun doesn't stay shining on it forever, either. There is a very limited amount of time when maximum energy is transferred. This is the reason for the expansion tank. Still, it pays to not ask for trouble.

For under $30, you can buy an expansion tank in a small size (one to two gallons is all you need) just like they use on hot water heat systems in commercial buildings. Inside the tank is a rubber bladder, with pre-pressurized air behind it. When the water enters the tank it pushes that bladder and the air behind it to a "mid-point" based on your water pump pressure, where it always has a little more to go if it needs to. This trapped air pressure allows the water to expand and contract as the sun heats the water, and then cools and contracts at night as the sun goes down.

It doesn't matter whether the tank is before the water heater or after it, as the pressure will equalize, as long as there are no check valves in the line between them. But if you put it after the heater, then any hot water you could have had will get diluted by the cooler water in the tank, and take longer to get to the faucet.

So you may ask, why the rubber bladder and not just air behind the water? The answer is that it would work for awhile, but eventually the air in the tank is absorbed by the water and depletes itself. The only way to add more air is to have what is called a "snifter valve" on the top of the tank, just like tires use. Then you have to use an air compressor to put air back in the tank occasionally. They use to do that, until someone figured out a way to put a sealed bladder inside the tank, so that the air and water can't mix. These systems are used on both cold water lines where pumps are involved, as well as hot water lines.

If you've ever noticed your RV water pump, it starts and stops very quickly as faucets are opened and closed. That is because it is a demand pump and reacts very quickly to water pressure. Many RVers have added expansion tanks to their water lines. This allows the pump to run longer when it does come on, but it may not come on at all for small amounts of water. This reduces the number of times the switch must turn the pump on, and also makes it work more like a water pump at home, which (on water well systems) usually pumps water to a storage tank (which also has this air cushion in it). When you hear a water pump cycle very quickly, every time the water is turned on or off, that over-works the switch and pump, sometimes causing over-heating of the motor and can cause early failure of the parts. Of course on city water, no tank is needed, as the city regulates the water pressure and any expansion problems.

The expansion tank in our case wants to be between the black pipe on the roof, and any check valves in the system below the roof. A gallon-sized tank is not that big, so you could easily fit it under the kitchen sink. It must be mounted vertical, with the pipe connection fitting on the bottom.

And it's doubtful you would ever need it on this type of system, but you could always add a temperature and pressure relief valve on the hot water out end of the black pipe on the roof. That would have to be drilled into the end of one of the caps, as the device has a probe on the back of it that will not fit crosswise in the pipe. You will also need a 3/4-inch NPT pipe thread tap to make the threads in the pipe to accept the fitting, and then it screws in, Always use Teflon tape on all pipe threads for water, and check everything once you get the pressure up. You don't want something to leak and leave streaks on the side of your vehicle.

The emergency cold weather drain...

For boondockers, conserving water is a fact of life. The other fact of life is finding themselves in sudden temperature drops. Even in the Desert Southwest it can occasionally drop below freezing during winter months, and then come right back to bright sunshine and 60 degrees during the day. They also get a lot more wind than many parts of the country, which is why any solar water heating system has to be behind a clear cover in order to work efficiently.

The last thing you want to do is deal with adding pink anti-freeze just to protect your system from freezing, when the freezing may only last a few hours. But you still have to deal with emptying it. You also don't want to dump all that perfectly good water out on the ground, when you may need it again later.

Since the other water lines are on the top of the black pipe, introducing air to the system won't push the water out of the black pipe. All it would do is push air out of the other water line at the other end. So a small bypass line is going to be needed that comes off the bottom of the black pipe. For this, you will want another one of those 90-degree fittings, along with a couple of tee fittings (to fit your water line tubing) and three small shut-off valves, the locations of which have already been mentioned.

(Don't worry, I'll work up a full parts list, along with diagrams and post everything on here as soon as I get time.)

The 90-degree elbow will be installed in the bottom of the black pipe at the same end that your hot water line comes off the top. A length of tubing will go from there to a valve under the kitchen sink, and then to the side of a tee installed in the hot water line below the kitchen sink. Right above that tee you need to install another valve in the hot water line. If you don't, the air will seek the path of least resistance, and blow back down through that pipe instead of pushing the air out of the black pipe tank on the roof. You will have a total of three 3/8-inch tubing lines from your black pipe tank to the inside of the RV.

In other words, this is no different than the valves you find on most RV's that are used to bypass the water heater. And there's no reason to use a stepladder to get to any of it. All valves will be under your kitchen sink.

So how do I push the water out of the black pipe and water lines? Below the kitchen sink, you will install the other cut-off valve in the cold water line going to the roof. Just above that, you will also install a tee in the line, with a "snifter valve" in the side opening. This can be right under the expansion tank. The snifter valve will be used to introduce air into the line going to the water heating pipe on the roof. It will push the air out of the bottom of that pipe, clearing it completely of water.

When winterizing your roof-top black water pipe, you simply close the water line from the pump to the tank just below the snifter valve, open the valve in the water line that comes off the bottom of the roof-top tank, to allow the water to drain out from the bottom of the tank to your sink faucet, while introducing low pressure air into the line going up to the black pipe tank. You also need to close the valve in the hot water line coming from the tank, until all the water is blown out of the tank. Then you need to open this same valve to allow it to blow the last bit of water out of the hot water line. The air will clear both the tank as well as ALL three water lines going to the roof.

You can use any kind of air pump to attach to the snifter valve fitting under the sink to put a LOW amount of pressure into the water line (under 50 PSI). A bicycle pump or hand pump works just fine for this. 

You can use a motorized tire pump, but be very careful of pressure. You don't want to add more pressure to the system than what the water pump normally provides. In other words, keep it under 50 PSI. It's not going to take much pressure to push the water out of the lines. Even 10 PSI will be sufficient. If the water starts coming out faster than it would under normal pump pressure, then stop putting air in until you need it again.

What happens to the water being drained out? How do I save it? That water is going to go right back into the hot water line under the sink, and to the hot water faucet. You can use an aerator attachment on the faucet to a white drinking water hose, and store that water in any kind of storage bottles or tanks that will hold that much. I suggest two (possibly collapsible) 5-gallon water jugs made for drinking water. They should hold all the water that you are blowing out of the lines, based on the five-foot pipe length I have recommended.

Keep in mind, the valve to get cold water up to the black pipe has been shut off...and you want to leave it off until such time as you feel safe adding water back into the black pipe. In other words your hot water faucet will be temporarily useless, and once you remove the air pressure, there won't be any pressure on it. The cold side will still work normally.

As long as all your water systems are inside your heated RV, you don't have to worry about anything else freezing, and you can function normally...just without hot water. But you can always heat some on the stove if you need to. That's what most RVer's do when winter camping, such as in ski areas. Unless they have heated tanks, they get by with what can be used, even down to bottled water.

To add the water back into the system, you first open the valve to the roof-top tank from the water pump, open the valve from the hot water line to the faucet, and close the valve from the bottom of the roof-top tank to your faucet, and you're all set. Just use the line from your pump to your water supply and dunk it into your storage bottles. The pump will do the rest. Open your hot water faucet to bleed the air out until the roof-top tank refills.

Don't worry about having to prime the pump. RV-type demand water pumps are a diaphragm and check valve style pump and are self-priming. They can even run dry until such time as they suck the water in.

Keep in mind, this is based on using a similar system as I will be using, with portable fresh water storage for one sink. In my case, my fresh water will be supplied by 8-gallon Reliance Hydrollers, which are on wheels. Once it is rolled under the sink cabinet and secured, a hose will be inserted into the top of the container, and the water pump will pump the water to the system. For additional water, I simply swap out the empty Hydroller to a filled one and put the hose back into the new one.

I never have to move the RV to obtain fresh water. I can take the containers in the van when we leave the campsite, refill them wherever convenient, and have a fresh batch of water every day. The same is true of dumping the porta-potty and obtaining propane. It all becomes really simple when you get away from factory mounted tanks! For the convenience, I don't mind paying a little more for one-pound propane bottles. And I can even refill those from a larger tank if I should choose to. I love choices!

Using portable fresh water tanks also has the side advantage of preventing "crud buildup" from letting fresh water tanks sit empty for long periods of time. Even fresh water treated with chlorine goes bad after awhile. Chlorine loses it effectiveness over time, and eventually bacteria will build up in the stagnant water. And trying to clean a permanently mounted fresh water tank with no openings is a royal pain. We will never have that problem with our way of doing it. 

If you have a permanently mounted fresh water tank, you can always rig something up to pump some of the water from the solar water heater back into that...if you don't mind the warm water going into your fresh water tank. There are a lot of ways to adapt the concept to whatever works best for your situation. You may have to use a tee and a couple of valves to create a way to switch from sucking the water from portable tanks or from your fresh water tank, back into your water system, but nothing is impossible. Just think it through and figure it out on paper if you have to, and then do it.  

When you are out in the desert, and trying your best to keep from moving your RV to go into town and refill your water containers (or dump, or get propane), the last thing you want to do is dump nearly eight gallons of perfectly good water out on the ground and waste it. By using this system, you can winterize the exterior portion of your system in minutes and still save the water removed from it, while continuing to use the water system that is NOT outside your RV. As long as you keep it above freezing on the inside, you can keep using your water pump and fresh water. It's a win/win situation.

Keep in mind, this will NOT winterize the interior portion of your system for longer term storage. For that you will have to also drain the lines under your sink and any other places not already drained.  

An added feature you might want...

Another thing that I will be adding to my solar water heater, is a remote theromometer. It isn't necessary, but I would like to monitor the temperature of my heater on the roof. It will give me an indication of when it is hot enough for showers, or even to do dishes. It will also tell me when it has cooled off too much to try to shower! I hate cold showers! And I certainly don't want to drag out a stepladder to get up there and feel it, or to waste water by feeling it at the sink!

In our case, we will be taking the hot water side to the high-rise faucet on the kitchen sink, so we can control the temperature of the water we use. That also applies to the "emergency" shower, which was described in an earlier post.

Our Bivouac Buddy shower stall can be used inside the trailer, right in front of the couch and the kitchen cabinets, with the drain water being pumped (with a small condensate pump) right back into the sink drain, to either drain out on the ground, OR be diverted to the gray water tank in the back storage compartment. We have choices. We LOVE choices!

We found a shower wand attachment at Walmart that attaches to the aerator on any standard faucet. So we can adjust the water temperature with the sink faucet, and then turn the shower wand on and off at the shower head without screwing up the temperature.

Granted, as long as we have other facilities available, we will use them, but just knowing that we "can" take a shower when boondocking, and do it in the privacy of our own unit, where we can keep it warm, is a very comforting thought!

Normal usage...

Even though solar will work better and much more consistently in the Southwest, it will also work well enough in other parts of the country. It's nice to have water close to 100 degrees for a shower, but for doing dishes, it doesn't have to be that hot, nor do you need as much of it. And even if it only works "well enough" for 50% of the time in the rest of the country, think how much that saves in either electric or propane. And the best part is that it works nearly anywhere. With the enclosure around it to hold the heat in longer, we should have enough hot water for dinner dishes or a late afternoon shower. Even if we're just pulling up at a rest park for lunch and cleaning up dishes afterward, even a little "totally free" hot water will be nice to have.

For showers, we will simply plan to shower at the end of our day, rather than in the mornings. Only time will tell how long the hot water will stay hot in the tank, but it's certain to be longer than in an open tube on the roof! Also, it's dependent on how intense the sun is during the day. Cloudy days aren't going to create much heat!

We aren't too concerned about having it hot enough for showers in the Midwest or the Eastern states. There are also less boondocking spots there, too, so we will figure on using campground showers when they are available. What we will save by boondocking for free during the winters out west will balance out what we may have to pay for campgrounds when we travel farther east.

It will be a learning experience, but we're sure it will all work out just fine.

I was hoping to have photos and sources for this article, but will have to come back and add those later. This technique is important enough that I wanted to get it out there while it is fresh in my mind, but I may edit it as needed if I think of anything else.

As always, let me know what you think, and thanks for reading.

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