Heating using the hot water tank.

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Heating using the hot water tank.

Postby Socal Tom » Tue Apr 14, 2015 8:48 am

MtnDon wrote:
I might consider using a different water pump if the noise from teh RV pump was too much


The typical RV water pump uses a lot of power... like 7.5 amps @ 12 VDC for a Shurflo 4008. And they are noisy. I would suggest a serious look at a small "solar" pump such asthis.

I don't know if this is a concern or not, but RV pumps are built with the use of pumping cold water in mind. The Shurflo specs do not list an operating temperature range. The circulation pump I linked to has a rating of up to 212 F. And it is quiet. I don't see amps listed but the one I have is less than 24 watts; about 18 watts, IIRC.


My design is theoretical, since I don't have the water heater and I rarely camp when I "need" a heater. But after further consideration for the " on demand" version I think the solar pump is a better idea. I would probably install my heater core with some quick connect fittings, either under the cabin or through the bulk head. The water heater would probably hang from the side of the TD. A small ice chest could provide the reservoir for the system. The insulation would increase the efficiency. One question to consider is how big the reservoir and volume of water need to be. Odds are that some systems will allow the water to drain back into the bucket, so there would be a change in water level when the system was running. The only risk I can come up with is that if the water level drops too low the pump will run dry, but could continue to run.
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Re: Heating using the hot water tank.

Postby daveesl77 » Tue Apr 14, 2015 5:33 pm

After a bit more thought and some internet detectivation work, I think my solenoid actuation idea to divert flow is a bit too pricey, like crazy expensive and a major power hog. It would require two 3-way solenoid water valves (like $150 each) So, instead I'll use two 3-way brass ball valves with the two handles linked, so both must always operate to the same system. The reason this is needed is there must be an absolute diversion from pressure/washing water to high temp/cabin heater water. There must not be any way that the super heated cabin water can get into the normal use lines. This means that when the cabin heat is available, the pressure system is not. So one valve shift supply from normal to reservoir and the other shifts output from normal to cabin heat.

The reason for using these two system linked through a single water heater is because the water heater, doing a recirculation for cabin heat, has the ability to very quickly raise the water temp to a very high level, like 140-150 F. But those are levels you cannot have the chance of getting into the normal system. As an additional safety level, I may also add in a small solenoid valve (single action, $15 brass, 1.5amp, N.O.) into the supply side of the pressure system, so if the cabin heat is on, the solenoid activates and closes the supply side for normal water. This can be controlled by a leg of the relay operated by the thermostat. Thermostat calls for heat, solenoid disconnects the main, pump activates for the cabin heat.

So, my pump takes 1.5amp, my heater takes 0.1 amp, relays and such .5am, solenoid 1.5, fan(s) 1 amp = about 5 amp when running. Not sure what the duty cycle would be, and way to hot in Florida now to test, but with a well insulated and small cabin, I cannot see it going 20% after warmed up. Maybe I'm wrong and it is not efficient at all, but I'll build it and test it.

I checked my pump and it is rated for 200F and my heater's built in high limit is 160. I'd put my actual control limit at probably 140.

dave
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Re: Heating using the hot water tank.

Postby lrrowe » Tue Apr 14, 2015 8:21 pm

Dave, I am curious why you say that there should be no chance to get the 140 degree water into the normal system. If you are using PEX tubing, it can stand up to 180 degrees or more (source...several sites in google). One reason may be that you do not want that hot temp coming out of your faucet; but that really is controlable.
When I go the hot water tank heater method, I will adjust the output to as high as it will go and I expect that to be at 140 degrees for my Suburban water heater. I am going to start off my model with the thought that 140 degrees is not too hot for both the circulating heat system and then the shower line.
Bob

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Hot water infloor and radiator heating project:[url]http://www.tnttt.com/posting.php?mode=reply&f=54&t=62327[/

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Re: Heating using the hot water tank.

Postby daveesl77 » Wed Apr 15, 2015 7:05 am

Yeah, my concern wasn't the plumbing side, but the temperature of the water coming out of the faucet. In my case, with the tankless I have, I only run a single water line to the sink / shower. If I want cold water I simply turn off the burner igniter switch, all water is thus cold. For hot water I leave it on and the water temp control on the unit sets the proper temperature that comes from the faucet/shower head. Makes it real easy and a simple operation. One of the beauties of and on-demand heater, turned off- water is cold, turned on- water is warm/hot - 8 seconds from cold to hot.

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Re: Heating using the hot water tank.

Postby Shadow Catcher » Wed Apr 15, 2015 1:09 pm

In working with a closed loop while maintaining the use of the hot water function at the sink and shower may require a check valve to keep cold water from the water heater inlet back flowing.
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Re: Heating using the hot water tank.

Postby lrrowe » Wed Apr 15, 2015 1:39 pm

daveesl77 wrote:Yeah, my concern wasn't the plumbing side, but the temperature of the water coming out of the faucet. In my case, with the tankless I have, I only run a single water line to the sink / shower. If I want cold water I simply turn off the burner igniter switch, all water is thus cold. For hot water I leave it on and the water temp control on the unit sets the proper temperature that comes from the faucet/shower head. Makes it real easy and a simple operation. One of the beauties of and on-demand heater, turned off- water is cold, turned on- water is warm/hot - 8 seconds from cold to hot.

dave



Thanks...I understand what you are referring to now. Thanks.
Bob

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Re: Heating using the hot water tank.

Postby Socal Tom » Thu Apr 16, 2015 6:22 pm

daveesl77 wrote:Yeah, my concern wasn't the plumbing side, but the temperature of the water coming out of the faucet. In my case, with the tankless I have, I only run a single water line to the sink / shower. If I want cold water I simply turn off the burner igniter switch, all water is thus cold. For hot water I leave it on and the water temp control on the unit sets the proper temperature that comes from the faucet/shower head. Makes it real easy and a simple operation. One of the beauties of and on-demand heater, turned off- water is cold, turned on- water is warm/hot - 8 seconds from cold to hot.

dave


I've been doing a little research on the tankless heaters. It seems that many of them have a 20 minute cut off for the heater. If water flow is sensed for more than 20 minutes then it will shutdown the heater, so if you do this with a tanklesss heater then you need to make sure that it either doesn't have that safety feature, or build a timer into the system that doesn't let the pump run for more than 20 minutes at a time. ( apparently shutting off the shower head resets the timer).

There also appear to be two main sizes a 5L and a 10L version. In the 5L version the system is supposed to be capable of heating 5L ( 1.3 gallons) of water 25C (about 35F) ( works out to 820 BTU/min or 49K BTU/hour). You can adjust the flow rate to increase the temperature increase, but that means the flow rate is lower.
The 10L version would have double the BTU, but otherwise the same story. Interestingly, the 10L systems I looked at didn't mention the 20Min timer.
Tom

Edit I originally go the conversion from degrees C to F wrong ( damn google!) an increase of 25C is an increase of about 35F
Last edited by Socal Tom on Sun Apr 19, 2015 11:42 am, edited 1 time in total.
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Re: Heating using the hot water tank.

Postby daveesl77 » Thu Apr 16, 2015 6:40 pm

I have the Triton 5l and to be honest, I cannot say if I have ever run it continuously for 20 minutes. I think I did once when testing with a 1 lb propane canister.

I turn the faucet on and off as needed. With my shower setup I made a foot switch to control the pump, so get wet, water off, soap up, water on, etc. However, even if that time limit was there, using the recirculating system you'd never get a run of over 3-4 minutes, as the water temp would be insane and the normal safety of 160 would kick in. Remember, with the recirculation you are raising that temp 20-30 degrees every time it recirculates. On my original test it was 70-140 in 105 seconds. I just got my laser heat sensor, so I'll test again this weekend and not have to use a meat thermometer again. :-)

With my Triton, at full heat and full water flow (which also depends on supply pressure) rises about 30 degrees from ambient water temp in 8-10 seconds. If the water is real cold, then I reduce the flow rate which provides a much higher heat but longer time. In Texas back in early March of last year the outside temp was about 40 F, supply water temp was probably around 50. Within 15 seconds of having the shower running I had to reduce the temperature as it was getting too hot, and was running water flow at about 1/2 full rate. I absolutely love my Triton, it has never failed me and just works.

I just got in my heater core, so maybe next week I'll steal you guy's idea on the box and put it together with computer fans and see how it feels. As I said earlier, I can't really test it well because the daytime temps are now about 90 in Florida, but at least I can see how it kind of feels.

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Re: Heating using the hot water tank.

Postby Socal Tom » Thu Apr 16, 2015 7:52 pm

daveesl77 wrote:I have the Triton 5l and to be honest, I cannot say if I have ever run it continuously for 20 minutes. I think I did once when testing with a 1 lb propane canister.

I turn the faucet on and off as needed. With my shower setup I made a foot switch to control the pump, so get wet, water off, soap up, water on, etc. However, even if that time limit was there, using the recirculating system you'd never get a run of over 3-4 minutes, as the water temp would be insane and the normal safety of 160 would kick in. Remember, with the recirculation you are raising that temp 20-30 degrees every time it recirculates. On my original test it was 70-140 in 105 seconds. I just got my laser heat sensor, so I'll test again this weekend and not have to use a meat thermometer again. :-)

With my Triton, at full heat and full water flow (which also depends on supply pressure) rises about 30 degrees from ambient water temp in 8-10 seconds. If the water is real cold, then I reduce the flow rate which provides a much higher heat but longer time. In Texas back in early March of last year the outside temp was about 40 F, supply water temp was probably around 50. Within 15 seconds of having the shower running I had to reduce the temperature as it was getting too hot, and was running water flow at about 1/2 full rate. I absolutely love my Triton, it has never failed me and just works.

I just got in my heater core, so maybe next week I'll steal you guy's idea on the box and put it together with computer fans and see how it feels. As I said earlier, I can't really test it well because the daytime temps are now about 90 in Florida, but at least I can see how it kind of feels.

dave

I'm not sure that the overtemp would restart the timer. The manual just says restarting the flow would do it.
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Re: Heating using the hot water tank.

Postby FLFLYIN » Sat Jun 13, 2015 6:12 pm

I have decided to add this to my build once I have begun construction. Since I plan to use it primarily for boondocking, water conservation was part of the design consideration. Here is my design schematic for the system with the cold water from a potable water tank entering at the lower left (after the main water pump). Please forgive me for using a Diode Symbol for a check valve, but I think you get the Idea.
132970
The water circuit serves two main purposes in this design. First, when the heater is "ON" the thermostat controls the water pump, and the case fans blow air continuously over the heater core. Second, when the heater is "OFF", the Intermittent Push Button is used to move the "cold water" slug through the system past the sink and shower faucets to avoid wasting water. If using a tankless system, this could be used to maximize the water temp before use. Although this system would allow the Heater Core to heat up when selected off, the lack of airflow across the core should minimize the heat gain in the cabin in warm weather. Lastly, I forgot to depict a drain at the lowest part of the circuit to purge the system when not in use.

On a different note, has anyone who built a Hot Water "Heater" figured out how much LP this type system used on a cold (30's i guuess) night? (does yours use a tank or tankless heater) I understand insulation and selected temp are definite variables in the equation. I remember reading about a test with a 1# propane can, but I guess I missed the results. Just trying to get an idea how much (or little) propane I need to plan for in my design since weight is critical.
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Re: Heating using the hot water tank.

Postby lrrowe » Sat Jun 13, 2015 8:37 pm

I cannot get your link to do anything. And maybe MtnDon or Shawdow Catcher will step in and let you know what their tests showed. I have all the equipment to build mine very similar to theirs. I will be simply recirculating hot water from the 6 Gallon Suburban heater. I am close to installing my water heater now, but the connection and test process will take the back seat to all the other work I have to do. And to some extent, I expect the flow process of heated water to take place even when the heater is not running. I do not think you need 140 degree water running thru the raditor all the time. So that condition would result in heat to the CT without using propane for some period of time.

One poster, Bruce, stated earlier that his pilot alone does a good job keeping the water warm, so that too would lessen the propane used.

As an added experiment, I put pex tubing in the subfloor. I will experiment with getting heat thru the tubes and into the flooring. I am sure it will not result in much, but I wanted to do it anyway (could be because of my bias as I installed radiant heat in my house).
Bob

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Re: Heating using the hot water tank.

Postby Shadow Catcher » Sat Jun 13, 2015 8:54 pm

Ours will not be installed until this fall (long story). One of the things I realized is that we need a check valve to keep hot water from back flowing into the cold water line.
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Re: Heating using the hot water tank.

Postby MtnDon » Sun Jun 14, 2015 9:12 am

Shadow Catcher wrote:..... I realized is that we need a check valve to keep hot water from back flowing into the cold water line.


If I am on the same wavelength as you I believe you are over thinking that. When there is no water being drawn out of the system there is no problem in our system. The circulation pump pushes water from the water heater tank to the radiator and the water returns to the water heater cold inlet pipe.

Even with the recirculation heating system operating when we draw cold water at the sink or shower the pressure pump sends us cold water.
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Re: Heating using the hot water tank.

Postby Shadow Catcher » Sun Jun 14, 2015 1:20 pm

I had thought of that but what happens when you want to use the cold water tap when using the heater, this just insures none of it flows back. I am really jammed for space it is all behind this panel under the cook top. The cold water line T's off going to the tap and water heater at the bottom of the water heater where there is an existing check valve, the hot water from the heater core/solar pump will T just before where that check valve is now. I may eliminate that one and move it back.
114210 100406

"Typically there are three check valves in the fresh water system; one at the city water inlet (to prevent pump pressure from forcing water out the entry), one at the outlet of the water pump (to prevent city pressure from backing through the pump and filling the water tank and one at the cold inlet to the water heater. It’s there to prevent hot water from migrating back into the cold water system. If a branch cold line, say to the toilet, is plumbed (tee’d) into the cold line too close to the back of the water heater, it could siphon hot water out of the tank and into the toilet when it is flushed. It’s happened before! As long as you have no branch cold lines tee’s near the inlet to the water heater, you shouldn’t experience that problem. Having a check valve at the cold inlet to the heater also prevents mineral deposits and residue from backing into the cold system from inside the water heater. As long as you flush the water heater out once or twice a year, this too, shouldn’t be a problem. But to be safe, it might be wise to reinstall one when you get a chance." http://www.rvdoctor.com/2010/02/rv-water-heater-check-valve-what-for.html

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Re: Heating using the hot water tank.

Postby MtnDon » Sun Jun 14, 2015 3:26 pm

Well, I guess my distances work in my favor as we have had no loop-back issues.
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