Heating using the hot water tank.

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Re: Heating using the hot water tank.

Postby Shadow Catcher » Fri Apr 10, 2015 11:32 am

I just finished wiring the thermostat. I am using a Radio Shack project box, and as you can see I followed Dons idea of poking the thermocouple through next to the thermostat. I did however leave all of the wire attached to it in case I want to put it some place else. One reason I can see for that would be that the thermostat and switch LED are bright and would not be conducive to sleep. I protected the edges of wiring holes with rubber grommets.
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Well the other Tom (I am also a Tom) gave me another idea. The campfire heater. One of the original ideas I had was to use an exterior boiler or even coils in a camp fire. My big concern was a boiler explosion potential, scalding etc. having it all external and ducting through the side of the trailer is an idea that has possibilities. My philosophy is to not have things like AC or heat or... as a fixed part of the teardrop, that way they can be left home. We have an Espar diesel heater that uses the same ducts I use for AC so I will not pursue this as an Idea but I can see all sorts of possibilities.
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Re: Heating using the hot water tank.

Postby Socal Tom » Fri Apr 10, 2015 11:46 am

Socal Tom wrote:
daveesl77 wrote:I think I have read all the posts in this thread, so please forgive me if this has been asked and answered...

This is really interesting using the Rv water heater for cabin heat and it makes perfect sense. Has anyone done this using an on-demand type heater? My thought is that if you had a secondary pump system, on a recirculating flow line, you would then use the thermostat to activate a relay which would in turn activate the pump. Water flowing then tells the heater to fire up. As you guys note on a tank type system, if you do a closed loop, then the feed water temp will keep rising. This would also happen with the on-demand, but I think much faster. With my little 5L, it raises the incoming water about 30-50 deg F at 3/4 heat/flow rate in 10 seconds. You could then put a high temp shut down in the circuit to cut out the burner ignition once the water got to say 150 degrees or so. It wouldn't be a pressurized system, just a free flowing pump dumping heated water back into a storage unit.

Circuit would be 1) Storage Tank - 2) secondary pump - 3) Heater core - 4) return to tank with high temp cut off on igniter, but not the pump. Thermostat turns off pump and igniter.

So, is this viable or am I missing something. I ask because I already have the on-demand and will happily add the heater system if it looks doable. Unfortunately, can't really test much on the cabin temp rise now, as it is 90 in Florida.

dave

I'm missing how this is really different from the current system? The HW heater heats the water based on the demand ( low temp). The pump and fans are activiated by the thermostat in the cabin. When the temp falls in the HW heater then it turns on and raises the temp back above the cutoff.
Tom

I think I get it now, you meant a tankless on-demand water heater.... I think it could work, if you had a reservoir to recirculate back to and you had a pump that met the minimum requirements of the heater then I don't see why it wouldn't work. There might be some safety issues to look into, so I would proceed with caution.
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Re: Heating using the hot water tank.

Postby bdosborn » Fri Apr 10, 2015 1:08 pm

Socal Tom wrote:I think this method makes perfect sense if you already have a hot water heater. If you don't, or lack the space to add one another option would be a RV type furnace.


I like the water heater approach much better. An RV heater isn't much smaller than a RV water heater and it's hard to get hot water out of one. ;)

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Re: Heating using the hot water tank.

Postby MtnDon » Fri Apr 10, 2015 1:18 pm

My reason for avoiding a std RV furnace was mainly that to install one in the CT required having an exterior wall for the intake and exhaust. It was not convenient. If it turns out that we need more heat, like for Dec - Jan cold weather I would do a Propex. The Propex has superb efficiency and has a low current draw.
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Re: Heating using the hot water tank.

Postby daveesl77 » Fri Apr 10, 2015 5:02 pm

With me, I already have the tankless, on-demand heater, the pump and storage system. I would only need to add a solenoid to control the feed water to shift from potable pump/city pressure to recirculating pump. Yes, it is almost identical to the standard water heater design you guys are working on.

The tankless systems work by using flow control. Now something I added to mine in my standard hotwater system is where the normal unit uses D cell batteries to operate the ignition, I have the "fake" D cell battery cases into which I put a small voltage regulator to drop it down from 12v to 3.3v. This allowed me to use both trailer power and a control switch. Control switch on - power is provided to the igniter and water can be heated. Control switch off - water flows at normal temp and system doesn't fire. That gave me the ability to run a single supply line from tank to faucet, switch on - hot water, switch off- cold water. It worked great in both my truck camper and tent camping.

I cannot see any downside to this system. In my use of the heater as a standard hot water system, I did a test and at full operation it would burn through about 1 lb of propane in an hour, non-stop operation. That was literally with an open water hose, running at full blast just to see how it worked. As the recirculating water temps rise, the burner runs less and less. At 150 it shuts off the burner with built in high temperature cut off, but the water can still recirculate. At 130 it can restart heating cycle. When internal cabin temp gets to thermostat limit, the pump shuts down. The burner cannot start without an appropriate water flow, built in safety factor.

This thing raises water temps fast, like in seconds. If looking at recycling water for temperature rise, if say bringing the initial water temp from 40-70 takes 15 seconds, then the second run of 70-100 would be the same, next run to 130, final run to 150 (shut down). So, conceivably, it could raise the water temp from 40-150 in under 2 minutes. I'll actually give it a try this weekend. I have the heater out anyway, measuring for it's location in the galley box, so I'll fire it up with the 12v pump system and recirc the water into a 5 gal tank. Now, it is almost 90 in Florida now, so not a real test of the extremes, but I can test the heat rise.

This will be interesting and boy I hope it works!

dave
Last edited by daveesl77 on Fri Apr 10, 2015 6:20 pm, edited 1 time in total.
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Re: Heating using the hot water tank.

Postby bdosborn » Fri Apr 10, 2015 5:54 pm

MtnDon wrote:My reason for avoiding a std RV furnace was mainly that to install one in the CT required having an exterior wall for the intake and exhaust. It was not convenient. If it turns out that we need more heat, like for Dec - Jan cold weather I would do a Propex. The Propex has superb efficiency and has a low current draw.


That seems odd that you didn't want an RV heater since the RV water heater has the same requirements? I agree that Propex is a slick package but it's easily 2 times the cost of an RV type at $800 and you'll need exterior access as well. I wonder how easy it to get parts and repair since I think it's only imported from the UK by a single US vender. AND, you can't get hot water out of a Propex. ;) I still think your water heater mod is the slickest approach, assuming it keeps you warm.
Bruce

P.S. I have a Espar heater that is just as efficient as the Propex, has about the same footprint but runs on diesel. One 2 gallon tank of fuel lasts a season. It works very well and it's the only reason I haven't started putting your mod together.
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Re: Heating using the hot water tank.

Postby MtnDon » Fri Apr 10, 2015 6:13 pm

bdosborn wrote:
That seems odd that you didn't want an RV heater since the RV water heater has the same requirements?


:) I agree that it is odd, as in, I am odd - weird - strange at times. :shock: I ran out of wall space where I would want to fit an RV furnace because of placing a higher priority on some other things; shower, wheel boxes, water heater and internal under the bed storage, storage under the sink / kitchen counter for chairs, etc.. The Propex OTOH would fit nicely centered under the bed in an unused area. But no wall access. The fresh air intake and exhaust for the Propex can be ducted through the floor and the interior air circulation could be ducted with relative ease. But yes, it is a pile of cash.

I do believe this hot water heater will do us nicely in the places we like to visit and at the times of year we prefer. Probably wouldn't do too well in February in Montana, but that is fine with us.

I have a change almost completed that will help with the trailer thermal efficiency too. I'll post that soon in the trailer build topic. For now it is a secret that can be pondered by those interested. ;)
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Re: Heating using the hot water tank.

Postby lrrowe » Fri Apr 10, 2015 9:56 pm

Hmmmmmm :thinking: :shhh: :crazy:
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Re: Heating using the hot water tank.

Postby daveesl77 » Sun Apr 12, 2015 3:53 pm

Just did a sample test run using a bucket of water (3 gals), the Triton 5L tankless water heater, a 12v pump. Base water temp was 75 degrees (sorry it is Florida). Pump is a cheap 1.5 gpm at 25psi. No heater core yet, just letting the water recirculate.

From start it took 105 seconds for water temp on 3 gals in an open bucket to go from 75 to 140. Hi temp override kicked in on the heater, not sure what the hose temp was, but I expect around 160. Pump, of course, kept running as I had it on just a standard switch and not on a thermostat, but in the real world this is exactly what you want - reservoir water gets up to temp, heat shuts down, thermostat tells pump to continue circulating water until such time that cabin temp reaches desired point. Assuming reservoir water temp drops below 130 (or whatever the low limit threshold you want to set), then the heater reignites, but only runs for a few seconds after initial warm up.

When I get time I'll build a prototype to add into my hotwater system, but yeah, this is a definite working system. By using a recirculation system, the actual water pressure is very, very low and having a venting reservoir means little to no internal "tank" pressure. You would want an external fill system, but in reality you would not lose much water through steam.

Please forgive the shaky video, shot it handheld with my little Mobius camera



Thanks to all that came up with this idea.
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Re: Heating using the hot water tank.

Postby MtnDon » Mon Apr 13, 2015 4:11 pm

Q. How do you see incorporating this into a hot water system so you can still use hot water at a sink or shower and at the same time use the hot water with a space heater (radiator)? I understand how a separate loop and reservoir system would have almost no pressure or at worst very low pressure. I will admit I have not given much thought to this with an on demand heater. I like the system that ShadowCatcher, lrrowe and I have as it lets us use water for space heating and use water for a shower, both at the same time. I would like lower pressure though as that would open the door to a wider choice of radiators (from the PC cooling world).
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Re: Heating using the hot water tank.

Postby Socal Tom » Mon Apr 13, 2015 4:35 pm

MtnDon wrote:Q. How do you see incorporating this into a hot water system so you can still use hot water at a sink or shower and at the same time use the hot water with a space heater (radiator)? I understand how a separate loop and reservoir system would have almost no pressure or at worst very low pressure. I will admit I have not given much thought to this with an on demand heater. I like the system that ShadowCatcher, lrrowe and I have as it lets us use water for space heating and use water for a shower, both at the same time. I would like lower pressure though as that would open the door to a wider choice of radiators (from the PC cooling world).


My water system is pretty small ( 6 gallons). What I would do it run a hose to the demand heater and open my hose bib. On the outlet of the water heater I would have a solenoid valve that was controlled by the thermostat, and I would use a heater core from a car for my "radiator", the return would go back to my water tank ( its not intended to be potable water, cleaning only). When triggered by the thermostat, the valve would open, the pump would sense lower pressure, and start pumping, the heater would kick on because of the water flow and my toes would start to warm. I would disconnect the heater system during the day, as this system would only come into service on rare occasions.
Tom

I might consider using a different water pump if the noise from teh RV pump was too much, or I was too concerned with putting the water back into my tank after going through the heater core.
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Re: Heating using the hot water tank.

Postby MtnDon » Mon Apr 13, 2015 7:33 pm

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.
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Re: Heating using the hot water tank.

Postby Shadow Catcher » Mon Apr 13, 2015 7:54 pm

RV water pumps are very noisy and not meant for continuous use, I went to some effort to silence mine. The solar hot water pumps a couple of us have do not have much head pressure but can operate in a pressurized closed loop system. I will be installing PEX T's to tap off of existing goes into and comes out of water lines.
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Re: Heating using the hot water tank.

Postby daveesl77 » Mon Apr 13, 2015 8:56 pm

For MtnDon and others, the idea on shifting between the normal water heat system (shower/sink) and the heater system is to use a electric solenoid valve. I think this will work, but haven't tested it yet. Anyway, the way I see it is that when the cabin thermostat calls for heat, it activates an electronic relay (I've got a few of these laying around for whatever reason). The relay activates the solenoid valve which would shift the water from the pressure/normal side to the heater side and at the same time activate the pump. I would also have a manual cutoff kill switch to turn off the cabin heat side if I need the pressure side during cabin heating.

I found what looks to be a pretty good, all aluminum heater core (new) and a hi/lo electronic temp control for burner control and have ordered both. Heater core will be here in a couple of days, temp control in a couple of weeks (yeah, China). The water heater also has its own built in hi/low limit, so if the secondary fails, there is an automatic safety shut off.

The cabin thermostat therefore operates both the solenoid, water pump and heater fan. The hi/lo sensor controls the burner. Pump runs as long as the thermostat calls for heat, sensor shuts down burner at a pre-determined high temp and restarts it at a lower limit.

The water pump is a bit noisy, but I will mount it with some decent vibration dampers. It would be the same whether using the tank or tankless system. Hopefully it isn't too objectionable to me, but we'll see. The amp draw isn't that bad with the small pump I have and is less than normal, since I'm not needing to fully pressurize the system. During my test, I let the system go up to the full 160 degree top limit and run for 30 minutes continuous. The pump had no problem with it, but we'll see how it goes in further testing.

This is fun!

dave
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Re: Heating using the hot water tank.

Postby Shadow Catcher » Mon Apr 13, 2015 9:42 pm

Dave, if the whole system is pressurized you can use the hot water as normal and still circulate through the heater core as a closed loop, the solar pump and fan operated by the thermostat. What you are planing on will work maybe, depending on how much heat the pump meant for cold water can stand, and for how long. Does that make sense :?
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