Heating using the hot water tank.

[aggie79]

If starting from scratch I would also check into radiators designed to water-cool computers. These have evolved tremendously over the years. They are sized and designed to work computer fans. Many have a built in shroud or stand-off to reduce turbulence and increase airflow. Many are "thicker" than transmission coolers and heater cores. This increased thickness is in the depth of the fins which allows air to be in contact longer and thus have greater heat transfer. Most have threaded female inlet and outlet ports so you can easily adapt them to whatever type of piping is used. And, because they fit in PC cases most are very compact.

Great discussion! Let's keep it going.

[lrrowe]

aggie 79,

Do you mean like these?

http://www.aliexpress.com/item/2x140mm- ... 22694.html

http://www.aliexpress.com/item/Computer ... 23958.html

[aggie79]

aggie 79,

Do you mean like these?

http://www.aliexpress.com/item/2x140mm- ... 22694.html

http://www.aliexpress.com/item/Computer ... 23958.html

Bob,

Yes, those are two good examples. Your examples show another quality of the PC water cooling radiators, that I hadn't mentioned before, that I think would make them effective to use to heat a CTC. Instead of a round tube, the water loop uses hollow flat plates. This gives more surface area for the fins to contact and should result in better heat transfer.

Here's example of a "thicker" radiator: http://www.frozencpu.com/products/16235/ex-rad-409/Alphacool_NexXxoS_Monsta_Single_120mm_Radiator_-_80mm_Thick.html?tl=g30c95s159. In fact, this site has more radiator possibilities that one could imagine would exist.

Take care,
Tom

[bdosborn]

I've got a couple of heater cores I got off eBay for cheap. I was planning on doing Don's experiment but lost interest. Maybe I'll dust them off and do a little bit of experimenting.

Bruce

[Shadow Catcher]

One of the concerns I have is that the system has to withstand water pressure that can come from either the camp ground or your pump. RV systems supposedly proof tested to between 100 and 120 psi. When I spec the hose I use, it will be food grade and stand 200F and 150 psi and I will hope it never comes close.

[lrrowe]

I've got a couple of heater cores I got off eBay for cheap. I was planning on doing Don's experiment but lost interest. Maybe I'll dust them off and do a little bit of experimenting.

Bruce

[lrrowe]

One of the concerns I have is that the system has to withstand water pressure that can come from either the camp ground or your pump. RV systems supposedly proof tested to between 100 and 120 psi. When I spec the hose I use, it will be food grade and stand 200F and 150 psi and I will hope it never comes close.

This example makes the heat exchanger model have the upper hand. You can keep the pressure of the heating loop separate and constant.

Another thought....wouldn't the pressure issue be there also even if you do not use this heating model? Pipes to the sink or shower could have the same pressure issue as the incoming campground pressure.

[lrrowe]

aggie 79,

D

Here's example of a "thicker" radiator: http://www.frozencpu.com/products/16235/ex-rad-409/Alphacool_NexXxoS_Monsta_Single_120mm_Radiator_-_80mm_Thick.html?tl=g30c95s159. In fact, this site has more radiator possibilities that one could imagine would exist.

Take care,
Tom

It is about 6 inches square and 3 inches deep (just rough calculations). Will this being smaller in size be better? And it is about three times the cost of some of the others I have seen. It is also not aluminum (to help with the potable requirement).

[MtnDon]

PEX has to meet ASTM standard F 877 which is the excessive temperature and pressure test of 150 PSI @ 200 degrees F for 30 days. And it has to pass a thermocycle test; being pressurized with 100 PSI nitrogen and then alternately immersed in 68 F water for 2 minutes, then in 180 F water for 2 minutes, 1000 times. Pretty rigorous requirements.



A big difference in our trailer and shadow catchers is that we opted to forgo the normal RV water system that connects to an outside pressurized water source. Our RV use with previous RV's hardly ever included campgrounds with water and power service. So I left out that part. We rely on water from the internal tank being pumped by the RV water pump at a limit of 40 PSI. If I did build with the direct hookup I would think about installing a pressure regulator of the type used for permanent installation in residential plumbing. The RV reducers are not all that well made.



The CPU coolers could be a nice simple radiator / fan solution. I do wonder what PSI they are good to? ATF coolers can run around 30 PSI or so. In it's previous incarnation the radiator tranny cooler I am now using in the trailer ran for several months with 40 PSI.

[MtnDon]

An earlier post about BTU's had some guesswork in it. I estimated the time off the top of my head and that is a slippery slope. (literally; I'm bald). Plus I thought the heater burner had just been shut off and there was still residual heat from the burner transfering to the water from the steel burner. So this AM I went out there ans got some better data.



Water heater burner on to heat water to 136 degrees then turned off.
Water pump and fans turned on and left to run to stabilize. (two 45 CFM fans)
Measured temperature every minute until temperature began to fall.
Started stopwatch.
Trailer interior at 46 F.
Hot line (surface of PEX pipe) from water heater measured just before radiator @ 131 F.
Let the pump & fans run for 15 minutes.
Hot line then measured @ 119 F, a difference of 12 degrees

Water tank volume is 6 gallons. I don't know how accurate that is or if the volume takes into account the space occupied by the burner heat exchange tube. 6 gallons @ 8.34 pounds per gallon = 50 pounds. I noticed Socal Tom used a weight of 48 pounds, so let's go with that to compensate for a possible reduction in water volume by the burner tube.

48 pounds with a 12 degree temperature drop, 48 lbs x 12 degrees = 576 BTU's.
(temperature change of 1 degree F on 1 lb.of water = 1 BTU by definition)

576 BTU per 15 minutes = 2304 BTU/hour, call it 2300 BTU/hour.

BTW, the interior temperature rose to 50.3 F in the 15 minutes. Call that 4 degrees and that works out to 16 degrees an hour, more or less.

Keep in mind that temperature change slows down as the difference between the hotter and the cooler decreases, so the interior temperature rise will slow down from the initial 4 degrees per 15 minutes. Also the transfer of heat from the radiator to the air will slow down as the interior warms. Slightly compensating will be that the water temperature will return to 131 and even higher when the burner is allowed to be turned back on by the water heater controller.

Next I think will be to change the fans to the higher output and retest tomorrow morning or late tonight. It's too sunny to get any really meaningful data during the day.


If anyone sees any holes in that data please speak up

[MtnDon]

An earlier post about BTU's had some guesswork in it. I estimated the time off the top of my head and that is a slippery slope. (literally; I'm bald). Plus I thought the heater burner had just been shut off and there was still residual heat from the burner transfering to the water from the steel burner. So this AM I went out there and got some better data.



Water heater burner on to heat water to 136 degrees then turned off.
Water pump and fans turned on and left to run to stabilize. (two 45 CFM fans)
Measured temperature every minute until temperature began to fall.
Started timing.
Trailer interior at 46 F.
Hot line (surface of PEX pipe) from water heater measured just before radiator @ 131 F.
I left the trailer and let the pump & fans run for 15 minutes.
Hot line then measured @ 119 F, a difference of 12 degrees

Water tank volume is 6 gallons. I don't know how accurate that is or if the volume takes into account the space occupied by the burner heat exchange tube. 6 gallons @ 8.34 pounds per gallon = 50 pounds. I noticed Socal Tom used a weight of 48 pounds, so let's go with that to compensate for a possible reduction in water volume by the burner tube.

48 pounds with a 12 degree temperature drop, 48 lbs x 12 degrees = 576 BTU's.
(temperature change of 1 degree F on 1 lb.of water = 1 BTU by definition)

576 BTU per 15 minutes = 2304 BTU/hour, call it 2300 BTU/hour. For the curious that converts to 675 watts. Not a high capacity heater for certain, but the trailer is a small enough space and insulated well. The interior volume of the trailer calculates to about 440 cu ft, BTW.

BTW, the interior temperature rose to 50.3 F in the 15 minutes. Call that 4 degrees and that works out to 16 degrees an hour, more or less.

Keep in mind that temperature change slows down as the difference between the hotter and the cooler decreases, so the interior temperature rise will slow down from the initial 4 degrees per 15 minutes. Also the transfer of heat from the radiator to the air will slow down as the interior warms. Slightly compensating will be that the water temperature will return to 131 and even higher when the burner is allowed to be turned back on by the water heater controller.

Next I think will be to change the fans to the higher output and retest tomorrow morning or late tonight. It's too sunny to get any really meaningful data during the day.


If anyone sees any holes in that data please speak up

[lrrowe]

Good work. I look forward to your reports and I appreciate your efforts and technical knowledge in this area.

[Socal Tom]

An earlier post about BTU's had some guesswork in it. I estimated the time off the top of my head and that is a slippery slope. (literally; I'm bald). Plus I thought the heater burner had just been shut off and there was still residual heat from the burner transfering to the water from the steel burner. So this AM I went out there and got some better data.



Water heater burner on to heat water to 136 degrees then turned off.
Water pump and fans turned on and left to run to stabilize. (two 45 CFM fans)
Measured temperature every minute until temperature began to fall.
Started timing.
Trailer interior at 46 F.
Hot line (surface of PEX pipe) from water heater measured just before radiator @ 131 F.
I left the trailer and let the pump & fans run for 15 minutes.
Hot line then measured @ 119 F, a difference of 12 degrees

Water tank volume is 6 gallons. I don't know how accurate that is or if the volume takes into account the space occupied by the burner heat exchange tube. 6 gallons @ 8.34 pounds per gallon = 50 pounds. I noticed Socal Tom used a weight of 48 pounds, so let's go with that to compensate for a possible reduction in water volume by the burner tube.

48 pounds with a 12 degree temperature drop, 48 lbs x 12 degrees = 576 BTU's.
(temperature change of 1 degree F on 1 lb.of water = 1 BTU by definition)

576 BTU per 15 minutes = 2304 BTU/hour, call it 2300 BTU/hour. For the curious that converts to 675 watts. Not a high capacity heater for certain, but the trailer is a small enough space and insulated well. The interior volume of the trailer calculates to about 440 cu ft, BTW.

BTW, the interior temperature rose to 50.3 F in the 15 minutes. Call that 4 degrees and that works out to 16 degrees an hour, more or less.

Keep in mind that temperature change slows down as the difference between the hotter and the cooler decreases, so the interior temperature rise will slow down from the initial 4 degrees per 15 minutes. Also the transfer of heat from the radiator to the air will slow down as the interior warms. Slightly compensating will be that the water temperature will return to 131 and even higher when the burner is allowed to be turned back on by the water heater controller.

Next I think will be to change the fans to the higher output and retest tomorrow morning or late tonight. It's too sunny to get any really meaningful data during the day.


If anyone sees any holes in that data please speak up

Looks good to me, and it aligns better with the previous calculations at the radiator side.
It's clear that it's enough BTUs to increase the temp, if you add a couple of bodies it will be about 3k BTUs.
Tom

[MtnDon]

New trial this morning; new data

I changed the fans to the twin 90 CFM models.

I repeated the warm up process as done yesterday.

Initial temperature at the pipe = 138 F
After a 15 minute run the temperature measured at the pipe fell to 113 F
Temperature difference = 25 F
48 lbs water x 25 degrees F = 1200 BTU per 15 minutes or 4800 BTU / hour

4800 BTU/hr = 1406 watts, call it 1400 watts.

The increased fan volume makes quite a difference!


I messed up with the before and after interior temperature readings so I do not have that data. However, that is of minor importance.


I also measured the temperature at the pipe after 7.5 minutes. At that point it was 119 F, a drop of 19 F. (The second 7.5 minutes saw a drop of only 7 degrees F. This reflects the faster rate of heat transfer that occurs with greater temperature differentials) 48 lbs x 19 degrees F = 912 BTU/hour. If we round that to 900 BTUH and then multiply by 8 we get 7200 BTUH or the equivalent of 2100 watts. That would be more or less what the output would be if the water heater burner was left turned on so as the water temperature dropped the burner would cut back in and bring the water temperature back up. (That water temperature is achievable with the heater control set on high. Depending on the weather or the need to heat quicker/slower the water heater could be used at a lower setting.)


The twin 90 CFM fans are noisier, but still not bad. We use an air filter device at home in the bedroom in part to act as a white noise when one of us goes off to bed earlier than the other. The twin 90 CFM are quieter than that bedroom unit so I don't see any potential issue there. Just in case, though, I am pondering whether or not I should wire the trailer fans up with the PWM speed controller I have. I did re-find it yesterday! And then that raises the question of slowing the pump as well, or not? ???

One more thing, the current draw increased from 0.67 amps to 0.77 amps with the twin 90 CFM fans. (Pump and fans total)

[lrrowe]

This testing reminds me of Myth Busters. In this case , the myth was proven to work.

Very encouraging!


Now, when the cabin temp is getting comfortable, would it be helpful, such as when you are trying to sleep, to use the PWM to slow the fans down? After all, the rate of temperature increasing slows down anyway.

NEW IDEA!
I have always considered the idea of infloor radiant heating. Now that MtnDon has shown that even the smaller 6 gal water heater can work as a "boiler" and since I have a 1 1/2" subfloor, it could handle some PEX tubes in it. This idea would have the floor tubes in series immediately after the radiator. Then if the floors were a little warmer, it would only help to compliment the radiator system.

I think I will get the ceiling insulated asap and add tubing to the floor. I have the pex leftover from my house system and if it does not work, so what! I then just leave the tubing there.