Solar heated hydronic or oil filled heaters for RV

jdmangum

Hello...........new to this board and glad for any and all help. Have been full-timing in a fifth-wheel for years, but now that I have one I am keeping would like to start becoming more energy independant. Looking for any information on a heating system that will allow me to use solar heating panels allong with a radiant element to heat my trailer. Think that a oil or coolant filled system may be best as I do not want to worry about freezing weather. Also considering using some sort of heat exchanger to warm/heat my hot water. Any input or direction would be greatly appreciated. Hopefully I posted in the appropriate forum.

Oh yeah....FYI...I am presently working at building one of the largest solar plants of it's kind in the world.....It is the Ivanpah Project near Primm NV. Approx.325 MW.

BB.

Re: Ssolar heated hydronic or oil filled heaters for RV

Heating with solar electric power is difficult to justify because of the costs (solar array, batter bank) to support the large electrical loads from general heating applications. There are people here who use microwaves and even induction cookers on solar. And one person that uses a 250 watt panel and a 250 watt 12 volt (or 24 volt?) hotplate for cooking (vs the whole fuel/wood/fire thing).

But for heating a home--It takes a lot of electricity when using a resistance heater. The typical portable electric heater is around 800-1,500 watts. You can use a Kill-a-Watt type meter to measure a few days of heating (genset, grid power when available) to see how many kWH per day you would need.

However--There are heat pump mini-split A/C units that can heat also--At 2-3x the efficiency of electric heating. And there are quite a few people that are using them these days--Even on solar in well insulated rooms/cabins/homes. Still need a fairly good sized system to power them--I don't know if you could have such an solar PV array for a portable RV/5th wheel or not--As I say, we can do the math and see what it would take.

As well as stand-alone heat pump water heaters--So far, working well for a few folks here.

Otherwise, solar thermal panels are not bad--They are 60-80% or so efficient--So the size of panel for heating thermally will be much smaller than the ~15% or so efficient solar PV panels (and their deratings do to losses of battery and inverter inefficiencies).

-Bill

Cariboocoot

Re: Ssolar heated hydronic or oil filled heaters for RV

Welcome to the forum.

Well I think direct solar thermal heating for an RV is entirely viable, but I haven't heard of anyone doing it yet.
The place to check out this sort of solar thermal project would be Build It Solar (to start with): http://www.builditsolar.com/
They have many such projects from people all over. Not sure if any of them are on RV's though. You could be a pioneer!

jdmangum

Re: Ssolar heated hydronic or oil filled heaters for RV

Not talking about heating with solar electric......................please read my thread......I am looking for info about using a SOLAR HEATED PANEL that will HEAT OIL OR GLYCOL instead of water. My father used a solar heated panel for water 35 years ago. I would think it would not be a giant leap to use oil or glycol as that is all that is used in any industrial facility I have ever been around. Just trying to adapt it to a home/rv inviornment(?). If there is nothing out there already I would be flabergasted......

BB.

Re: Ssolar heated hydronic or oil filled heaters for RV

Solar thermal links (to other threads/links):

BB. wrote: »

Solar Thermal can be a nice source for space heating and hot water... And usually is "cheaper" per kWhr/BTU vs Solar PV Electric. Also, Solar Thermal lends itself very well to do it yourself projects. Note, these are plumbing projects and have their own issues (leaks, pump failures, installation issues trapping air, anti-freeze, storage, heat exchangers, etc.):

Solar Shed and other Solar Thermal Links

A good place to start reading is Home Power Magazine... They have a free past issue online--and have a lot of articles you can read for free. I don't always agree with them and their reviews--but they are a fun and enlightening read:

Home Power Mag

If you are looking for standard amounts of hot water for a few people--The "new" heat pump water heaters such as the GE GeoSprong units are very interesting. About 2-3x more efficient than resistance heating, Less things to go wrong (water pumps, leaks, freezing, etc.) than solar thermal. And if you are in a warm area, heat pump will cool the room and dehumidify too.

If the room where the heat pump water heater is installed goes below ~55F--Then they become less efficient and can turn on resistance heater (not good for solar PV systems).

-Bill

icarus

Re: Ssolar heated hydronic or oil filled heaters for RV

Consider a small evacuated tube system. Quite efficient, and forgiving of off angle instllations, especially important on a mobil vehicle. Whqt I dont know is if they make them small enough to be practical. A small circ system and small tank, coupled with. Small demand Lp gas nit might b just the ticket.

Tony

PS. A couple of quick google searches reveals that they make ETs under a meter long,, 800mm, just bout right for n Rv.

T

inetdog

Re: Ssolar heated hydronic or oil filled heaters for RV

jdmangum wrote: »

Not talking about heating with solar electric......................please read my thread......I am looking for info about using a SOLAR HEATED PANEL that will HEAT OIL OR GLYCOL instead of water. My father used a solar heated panel for water 35 years ago. I would think it would not be a giant leap to use oil or glycol as that is all that is used in any industrial facility I have ever been around. Just trying to adapt it to a home/rv inviornment(?). If there is nothing out there already I would be flabergasted......

For any system other than a drain-back system which will be used in a cold climate, the common system is glycol or at least water-glycol mix. I expect that oil would cost a lot more than glycol and may not have as high a heat capacity nor be as easy to pump.

One drawback to using a fluid other than the water to be heated is that it then requires a heat exchanger to transfer the heat from the circulating fluid to the water. Almost all DHW systems will still require a heat exchanger, but for a pool heater, running with low temperature differences, avoiding the extra heat exchanger makes the system less complicated and more efficient.

If you are using the solar thermal panels for space heating (radiator or in-floor radiant, for example) then no additional heat exchanger would be necessary.

jdmangum

Re: Ssolar heated hydronic or oil filled heaters for RV

Thanks for the input............gives me some new specific components to follow up on. Still think that somewhere some boondockers are using a solar/h20 system. Will keep checking on new items to include in a final system.

westbranch

Re: Ssolar heated hydronic or oil filled heaters for RV

I dont know if it has been mentioned but with water systems there is also the problem of mineral deposits in the 'heat exchanger' area that can damage the unit if the water has too high a mineral (hardness) count.

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

I would second the suggestion of Evacuated tube collectors. They would fit the RV well. I would not use oil or glycol. I would use straight water. Evacuated tube systems are isolated from ambient temps and freezing by a vacuum, hence, if the manifold is well insulated or a small circ. pump used, they will not freeze. They also will not loose heat at night and work very well on cloudy days. Only problem you might have is if they get snow on them it will not melt off. You will need to manually clean them off.

They will provide water temps right up to boiling so make sure you have an expansion tank and pressure relief valve in the system. A 25$ transmission cooler coil from your local RV store with hot water circulated through it placed in your RV's furnace duct will provide heat without using electric resistance or propane.

Pure water is the most efficient heat transfer medium. Better than glycol or oil. Glycol will withstand a greater temp range than water but is less efficient. Oil is able to withstand higher temps but is less efficient at heat transfer and viscosity becomes an issue at low temp You would have trouble circulating the oil when it got cold out. Most suitable oils are also toxic if consumed and would cause severe illness in the event of a leak or cross contamination. (We are still trying to clean up PCB's from cooling oils in old transformers)

If you use a pure water based system, you do not need a heat exchanger for Domestic Hot Water. You can use it direct, Just make sure it goes through a final stage which ensures it is over 120 degrees to avoid legionnaires or bacterial contamination

Ralph Day

Re: Ssolar heated hydronic or oil filled heaters for RV

I drive by a 15mw solar development occasionally and am impressedby it's size, but 325Mw? That just blows my mind.

Ralph

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

I would second the suggestion of Evacuated tube collectors. They would fit the RV well.

I have a set of tubes here, and yes, the length of these units would fit on top of an RV nicely, you could even set up a tilting frame, to get a good angle on the sun . . it is not as improtant as with solar electric, but having it at the proper angle with the sun does heat it up more. . ..

Also, depending on the area you are in, do not fall for the sales man's story of "year round hot water" . . . that is what I was told, and it does not work, at least not with my system . . . during 3 of the coldest winter months, my system does not get over 70 degrees F. I have heard of a nursing home that has something like 1000 tubes on the roof, and their water is ALWAYS hot (so I have heard) . . . so if you get enough of these tubes, it should work . . you may just have to get 60 or 90 of them.... my system is a 30 tube.

Just as I am typing this reply, I am wondering what would happen if I did add another 30 tubes to what I already have . . , but then, I am warry since the first set didn't work as expected. . . so just how many WILL I have to get ?

So, Can anyone out there testify - dealing with (Apricus) High Efficiency Evacuted Tubes , that adding more tubes will give results and just how many are needed ?

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

Skippy wrote: »

I have a set of tubes here, and yes, the length of these units would fit on top of an RV nicely, you could even set up a tilting frame, to get a good angle on the sun . . it is not as improtant as with solar electric, but having it at the proper angle with the sun does heat it up more. . ..

Also, depending on the area you are in, do not fall for the sales man's story of "year round hot water" . . . that is what I was told, and it does not work, at least not with my system . . . during 3 of the coldest winter months, my system does not get over 70 degrees F. I have heard of a nursing home that has something like 1000 tubes on the roof, and their water is ALWAYS hot (so I have heard) . . . so if you get enough of these tubes, it should work . . you may just have to get 60 or 90 of them.... my system is a 30 tube.

Just as I am typing this reply, I am wondering what would happen if I did add another 30 tubes to what I already have . . , but then, I am warry since the first set didn't work as expected. . . so just how many WILL I have to get ?

So, Can anyone out there testify - dealing with (Apricus) High Efficiency Evacuted Tubes , that adding more tubes will give results and just how many are needed ?

Skippy,

We would need to know some other factors to know if an additional panel would help: What is the input temp of your water and what is the output temp from the collector at the collector manifold? How long are your runs to and from collector and how well are they insulated, are you using a heat exchanger and if so what type, how well insulated is your storage tank and what is the capacity, what is the distance form your storage tank to your taps, what is your flow rate through the collector, how much hot water are you using and what time of day are you using it? These are all factors which could effect your system and need to be taken into account. Obviously you cannot heat water with a solar collector at night. This means during the winter months in Ontario, unless you use very little hot water in the evening, or have a very large, well insulated storage tank, your water will tend to be on the cool side for a AM Shower.

I suspect there are some efficiency losses somewhere or defective tubes if you are seeing max midday water temps of 70. Your circ. pump may be running to fast or to slow, you may have a problem with insulation or a heat exchanger problem or inappropriately sized storage capacity.

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

Skippy,

We would need to know some other factors to know if an additional panel would help:

What is the input temp of your water and what is the output temp from the collector at the collector manifold?

I believe the input water temp is around 40 - 45 F off the street, but the heat exchanger recirculates the water in the tank, so once the tank is up to temp, thats the temp it works with. I have tried different temperature differentials, the last one I tried was a 20 degree temp diff. So whatever the tank temp is - say 70 F , then the manifold has to be 90 F to turn on the pump. . . lower diff's just make the pump run more, with not alot of gain in temp. Higher diffs and the pump just does not come on.

How long are your runs to and from collector and how well are they insulated,

The feed lines are 3/4 inch pipe, using the dealer supplied insulation (about 1 1/2 inches thick - dense foam). the lines drop from the top of the collector about 10 ' straight down, and then into the side of the house.... from there (near the peak of the house), they are run thru the 1 1/2 story house (air temp 70 - 75 F) down into the basement, everything is insulated with the same thick foam from the dealer.

are you using a heat exchanger and if so what type

I built 2 - 12 foot single walled heat exchangers that I seen in Home Power Magazine. The warm water goes into one end of both units (slows down going thru 2 pipes at once) , then the cooler water comes out into a "T" and comes back thru a seperate pipe . . all insulated with the same dealer supplied foam.

, how well insulated is your storage tank and what is the capacity,

40 gallon standard water tank, with an extra 18 inches of roxsol insulation all around (except bottom) Its sitting on a couple of inches of foam padding.

what is the distance form your storage tank to your taps,

not worried about that, as the temp in the tank never gets above 70 F

what is your flow rate through the collector,

Grundfos pumps set on low speed, have also tried medium and fast speeds. Both the glycol loop pump and the heat exchanger pump. - Next thing on my list is to switch to El-Sid pumps, to save hydro.

how much hot water are you using and what time of day are you using it?

same thing, does not matter, if I use no hot water all weekend or if I take a nice long hot shower, the tank never gets above 70 F, of course, the colder the water is, the more the pumps come on. . . but above 70 - nadda.

These are all factors which could effect your system and need to be taken into account. Obviously you cannot heat water with a solar collector at night. This means during the winter months in Ontario, unless you use very little hot water in the evening, or have a very large, well insulated storage tank, your water will tend to be on the cool side for a AM Shower.

I suspect there are some efficiency losses somewhere or defective tubes if you are seeing max midday water temps of 70. Your circ. pump may be running to fast or to slow, you may have a problem with insulation or a heat exchanger problem or inappropriately sized storage capacity.

Whatever I do, it can wait till this darn snow melts, I only asked about the extra tubes, since I have "heard" that the nursing homes hot water averages about 50 C in the winter - thats 122 F if you can believe it.

Got them pants on yet ?

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

Skippy,

I suspect there are some efficiency losses somewhere or defective tubes if you are seeing max midday water temps of 70.

Keep in mind, that the lower temps are only for 3 months of the year. As a rule, I turn on my on demand water heater in November, and turn it right off in March. During the summer months, I can do a load of laundry, using straight 170 F water every day if I need too. . .

It gets HOT !

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

Hey bill, how do you do muliple quotes ? It is easier to read that way. . . and thanks for fixin it

BB.

Re: Ssolar heated hydronic or oil filled heaters for RV

If you "edit" your post, you will see where I added the quote tags:

[HTML]

text to be quoted

[/HTML]

Will look like this:

text to be quoted

You can also select the text, and push the cartoon dialog button to put the tags at each end of the quote.

-Bill

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

Skippy,

A couple things are popping out at me.

1. Your runs from the collector to the tank are quite long IMHO. I suspect you are losing a significant amount of heat along that route especially after dark when the collector is not producing.
2. Put your circ. pump on a photo cell. ( see #8 for reason why)
3. Your water temps from the street are very cold and your tank is very small. Every time you open a hot water tap you are tempering the water with 40 F water and you have no buffer for a slow recovery. IMHO you need no less than a 120 gal. storage tank, maybe more, with no less than 2 in of poly iso or urethane foam insulation.
4. You should see water temps from the panel in the 180-200+ range if the input water temp is not too cold. (once again I suspect lengths of pipe are factor)
5. Was thermally conductive grease applied to heat pipes when they were installed in the manifold? Poor conductivity will decrease output.
6. Do you have a heat trap installed at the storage tank to prevent thermal loss from occurring
7. I suspect you may be circulating too fast... not sure.
8. Temp diff setting is a problem. Hard to explain in words but.. You want every degree you can get. If collector is 1 degree hotter than tank, that is gain you are losing if you do not circulate. Each pass should gain 1 degree. If it is not gaining you have too much line loss. Also, if you have your panel set at 90 trigger and you tank is at 70 and you have 30' of cold water sitting in the line, the line water will cool the panel to below set point causing the pump to shut off before you ever start to heat anything other than line water. (this is a type of short cycling)

Temp differential may be fine in summer but in winter when your lines get cold especially during night it can cause some real headaches in the morning. Check to make sure you are circulating any time the sun is shining regardless of what your collector temp sensor is telling you, especially with your long lines. (see#2)

A a second collector will not help until you can get these potential issues checked and solved.

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

Skippy,

A couple things are popping out at me.

1. Your runs from the collector to the tank are quite long IMHO. I suspect you are losing a significant amount of heat along that route especially after dark when the collector is not producing.

I agree. . .. Thinking about relocating the collector, but it will still be a ways from the tank, no way around it. . .

2. Put your circ. pump on a photo cell. ( see #8 for reason why)

The controller I picked up is fully adjustable from 0 - ###, so changing that is at the very bottom of the list . . although, the ElSid pumps are know to run off solar . .

3. Your water temps from the street are very cold and your tank is very small. Every time you open a hot water tap you are tempering the water with 40 F water and you have no buffer for a slow recovery. IMHO you need no less than a 120 gal. storage tank, maybe more, with no less than 2 in of poly iso or urethane foam insulation.

I don't see the point in getting a bigger storage tank, as it does not heat the stuff I have now . . . I can leave it sitting stagnant all weekend, and it does not get above 70 . . . Need to figure out if there is enough heat being generated, and where the heat is going first. . .

4. You should see water temps from the panel in the 180-200+ range if the input water temp is not too cold. (once again I suspect lengths of pipe are factor)

Don't think thats going to happen as it sits right now. . . Even with the pumps turned right off, it does not get near that hot - just sitting there. So its either not enough sun, or not enough grease on the pipes. . .

5. Was thermally conductive grease applied to heat pipes when they were installed in the manifold? Poor conductivity will decrease output.

I installed the tubes myself, and put lots of grease on the ends. . . when I relocate the unit, I will have to really lather it on so I know its done right . . .

6. Do you have a heat trap installed at the storage tank to prevent thermal loss from occurring

I have a spring loaded backflow preventer installed in the glycol loop. So when the pump shut off, nothing moves.

7. I suspect you may be circulating too fast... not sure.

That makes 2 of us . . .:p

8. Temp diff setting is a problem. Hard to explain in words but.. You want every degree you can get. If collector is 1 degree hotter than tank, that is gain you are losing if you do not circulate. Each pass should gain 1 degree. If it is not gaining you have too much line loss. Also, if you have your panel set at 90 trigger and you tank is at 70 and you have 30' of cold water sitting in the line, the line water will cool the panel to below set point causing the pump to shut off before you ever start to heat anything other than line water. (this is a type of short cycling)

I agree with you on the temp differential being a problem, as I have had it set at 5 degree difference, and it was staying on all day. . . the hydro bill went thru the roof ! And the tank was still at 70 . . turn it up to at 20 degree diff, and the pumps stay off, saves hydro, but does not do anything else. . . (see note at bottom)

Temp differential may be fine in summer but in winter when your lines get cold especially during night it can cause some real headaches in the morning. Check to make sure you are circulating any time the sun is shining regardless of what your collector temp sensor is telling you, especially with your long lines. (see#2)

A a second collector will not help until you can get these potential issues checked and solved.

I am already thinking about moving down off the roof, and putting it somewhere more acessable.

NOTE : I had this reply all typed out, and then I thought, "well, if it is supposed to be in the 180 - 200 range, lets see what the dealer has to say ! " So I called him on the phone. He has the same collector and storage tank as I do, just different exchanger. He says that on any given day in the winter, his collector is at 48 C which turns out to be around 118 F. . . so there is something wrong if I have 2 people telling me my system should be running at a hotter temp.

Come spring time I will have to disect this thing and see what I can do. . .

Thanks for the kick in the butt to get me going . . I don't mind finding out (and admitting it ! ) that I did something wrong if it helps someone else avoid the same mistake . .

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

Skippy, I think you may have misunderstood a couple things. I did not mean power you pumps with a PV panel. I mean use a photo electric sensor switch, like they type they use to turn street lights on and off only in reverse.

The point in the bigger tank is that you have more storage and make more hot water when you get a sunny period. This means you start at a higher temp and finish at a higher temp.

If the dealer has same collector and tank and is getting 118 then I would copy his setpoints and see what happens. If it still doesn't work, you may have an airlock or something wrong with your heat exchanger as that is the only difference.

Good luck.

Out of curiosity, why don't you use a de-superheater on your GSHP for hot water?

One more thing that it didn;t sound like you understood what I was saying. A heat trap is not a backflow preventer or one way valve, it is more similar to a sink trap. Short section of pipe forming a downward "S" (no less than 6") that carry's water downward at the outlet of the water storage tank before it travels horizontally or upward. This prevents the hot water in the tank from migrating upward or horizontally in the system and keeping the water in the tank from heating properly

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

You can see a heat trap in the following image. It prevents storage tank from trying to heat water in lines or more accurately, the lines from dissipating the heat in the tank to ambient air over their length. Convection and conduction heat migration should stop at the second elbow from the tank in this diagram.

Attachment not found.

inetdog

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

Convection and conduction heat migration should stop at the second elbow from the tank in this diagram.

I know of no physical mechanism by which an elbow can stop conduction. But conduction was never a major route for heat loss.
The heat trap will work fine to stop convection inside the pipe and may also inhibit thermo-siphoning, just because of the flow restriction of the elbows.

Cariboocoot

Re: Ssolar heated hydronic or oil filled heaters for RV

Elbow has plastic isolation perhaps? And how about a nice, common check valve to prevent thermal syphoning. Even my water system has that.

Personally I can see how elbows alone could be all that effective if there's enough temperature difference to increase the pressure.

But then I haven't had lunch yet.

inetdog

Re: Ssolar heated hydronic or oil filled heaters for RV

Cariboocoot wrote: »

Elbow has plastic isolation perhaps? And how about a nice, common check valve to prevent thermal syphoning. Even my water system has that.

Personally I can see how elbows alone could be all that effective if there's enough temperature difference to increase the pressure.

But then I haven't had lunch yet.

I have had lunch, and it was delicious.

The elbows are not, by themselves, the active element. If you leave out thermosiphoning and also forget conduction, the biggest heat loss involving the inlet and outlet pipes in a conventional hot water tank system is that you can have convection currents circulating entirely within one run of pipe that is either vertical or horizontal. But when the direction of "up" in the pipe changes from hot on the bottom to hot on the top, the convection loop cannot extend from one pipe section to another.
In that case, convection can heat the top of the inverted U, and even extend the convection loop along the short horizontal segment.
But cold water in the large pipe beyond the U will not rise up the U, down into the heater, and be replaced by warm water rising from the heater and going back down the U. It would take two pipes to allow that to happen.

The whole loss mechanism which the heat trap is designed to reduce is not dependent on an overall pressure difference between pipes. And if there were a pressure difference (as for thermosiphoning) the heat traps would not affect it at all.

Cariboocoot

Re: Ssolar heated hydronic or oil filled heaters for RV

I was just thinking about how there often is a pressure difference as the cold on the inlet can drop in psi every time someone opens a cold water tap. Hot water flows out to relieve the pressure in the tank, and then when the valve closes again the pressure builds up pushing cold back into the tank. Depending on circumstances it can be enough to turn the heating element on again. Simple check valve stops the problem.

So many problems that need solving, eh? Like; now what are we going to have for dinner?

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

Cariboocoot wrote: »

So many problems that need solving, eh? Like; now what are we going to have for dinner?

Your making me hungry

I will have to have a look at my system - looks like from top to bottom - although, I don't think losing the heat is the problem, I think its more like - not MAKING heat - to begin with. . .

I'll keep you guys updated as I go . . but yes, these tubes will fit on an RV rather nicely, and if its over 40 F , they will make lots of hot water - I think

inetdog

Re: Ssolar heated hydronic or oil filled heaters for RV

Cariboocoot wrote: »

I was just thinking about how there often is a pressure difference as the cold on the inlet can drop in psi every time someone opens a cold water tap. ... Simple check valve stops the problem.

So many problems that need solving, eh? Like; now what are we going to have for dinner?

Not a bad idea as long as you trust the overpressure relief valve on the tank.

I don't know about you, but I have sent the daughter out for pizza.

Skippy

Re: Ssolar heated hydronic or oil filled heaters for RV

thehardway wrote: »

Out of curiosity, why don't you use a de-superheater on your GSHP for hot water?

Sorry, missed that one. . .

At the time, I already had the solar water heater tied into the on demand water heater and had a full 40 gallon tank sitting at 170 F (summer time), so when the installer told me that the unit had a de-superheater already installed in it, and asked me if I wanted to hook it up, I asked just where is the heat coming from to heat the hot water ? Too which, he replied that the de-superheater takes so many percent off of the total output of the unit, so if its a 36,000 btu unit, it splits off 5,000 btu off of that too heat the domestic hot water. . .

1. Since this was a new install, I was not sure how much heat I would need to heat the house (going from a natural gas furnace with a 18 " flame in it ) so I wanted the whole output to heat the house - just in case . .

2. As stated, already had the water heaters installed, so I did not see the sense in a 3 rd way to heat the hot water. . .

3. Did not have the extra money at the time to worry about plumbing said extra piping. . .

So I didn't use it. It is there, not hurting anything, so if I do change my mind at some point, I can connect it. . .

thehardway

Re: Ssolar heated hydronic or oil filled heaters for RV

inetdog wrote: »

I have had lunch, and it was delicious.

The elbows are not, by themselves, the active element. If you leave out thermosiphoning and also forget conduction, the biggest heat loss involving the inlet and outlet pipes in a conventional hot water tank system is that you can have convection currents circulating entirely within one run of pipe that is either vertical or horizontal. But when the direction of "up" in the pipe changes from hot on the bottom to hot on the top, the convection loop cannot extend from one pipe section to another.
In that case, convection can heat the top of the inverted U, and even extend the convection loop along the short horizontal segment.
But cold water in the large pipe beyond the U will not rise up the U, down into the heater, and be replaced by warm water rising from the heater and going back down the U. It would take two pipes to allow that to happen.

The whole loss mechanism which the heat trap is designed to reduce is not dependent on an overall pressure difference between pipes. And if there were a pressure difference (as for thermosiphoning) the heat traps would not affect it at all.

Give inetdog a twinkie! His explanation is correct. There is no magic elbow or special properties its just a physical location where the heat migration tends to stop.

Convection occurs within the water. Conduction happens in the pipe, which that close to the tank should still be copper and is a very good heat conductor. It is all due to the fact that heat tends to rise, whether it be in air, water or copper pipe.

Inspectors in our area now require heat traps installed on all hot water storage tanks.

A thermal expansion tank of some kind is also required on pressurized systems if a one way valve is used.

BB.

Re: Ssolar heated hydronic or oil filled heaters for RV

You can get heat traps that are short sections of steel pipe and have a small check valve in them that blocks thermal siphoning. And now some hot water heaters have plastic (rubber?) disks with "fingers" that close if there is no water flow.

http://www.whirlpoolwaterheaters.com/learn_more/basicfeatures.aspx

Attachment not found.

-Bill