Heating using the hot water tank.

[lrrowe]

I do not remember enough of my old physics classes to start to approach this question.
With all other conditions remaining equal, is it better to move air over the fins of the raditor faster or slower?

I have found fans that move 60, 80, or 100 CFM. Is there an optimum air flow? Or are there many other variables to think about? Such as overall surface area of the radiator, depth of the fins, number of fins, amount of surface area that the fan covers and so forth? This sort of goes along with the speed of the heated water through the raditor.

Or for we camper's needs, is it adequate to use a combo that someone says gives good results and let it go at that. More of a trial and error approach?

[Socal Tom]

I do not remember enough of my old physics classes to start to approach this question.
With all other conditions remaining equal, is it better to move air over the fins of the raditor faster or slower?

I have found fans that move 60, 80, or 100 CFM. Is there an optimum air flow? Or are there many other variables to think about? Such as overall surface area of the radiator, depth of the fins, number of fins, amount of surface area that the fan covers and so forth? This sort of goes along with the speed of the heated water through the raditor.

Or for we camper's needs, is it adequate to use a combo that someone says gives good results and let it go at that. More of a trial and error approach?

Though this may contradict what I posted earlier, I believe the maximum BTU transfer will be with the highest CFM. I think it becomes more about the noise, and the energy use.
The greatest heat transfer will be when the difference between the temps is greatest. ( 40F air and 120F water will warm faster than 80 degree air with 120 degree water). So as the inside of the trailer warms up, the heat transfer will become less efficient.
Tom

[lrrowe]

Perhaps adding a rheostat would not be a bad step. Would slowing down the fan when you want a maintenance phase be a good thing?

[MtnDon]

An electronic speed control, rather than a rheostat. Rheostats waste power as heat. A PWM controller is actually an electronic switch that turns the power on and off extremely rapidly, leaving it on for short or longer durations and as such does not waste so much. Theire is an operating loss but it is insignificant when compared to a rheostat.

ebay has a bunch
I'm thinking that a speed controller might be handy if the fan used had a high enough volume to make slowing it down worthwhile.

I'm also beginning to wonder if there are some small squirrel cage fans in 12 VDC that might be better suited than the axial flow computer cooling fans? I have not looked. The nice thing about computer fans is their low current draw. That comes with lower flow and lower ability to push air through an obstruction like a radiator.

[Socal Tom]

My bad.... That night the outside temperature dropped to 41, the interior was at 72. That was with the water heater set at medium, and the pump and fans running continuously. A difference of 31 degrees.


Last night I set the water heater to the lowest setting and let it run all night. The outside low was 36. The interior temperature was 64 degrees, a difference of 28 degrees. Again, the pump and fans ran continuously.


... I need to dig out another fan set. These are 45 CFM; I have one that moves 90 CFM, with a little more noise, but still quieter than the pump. I ordered a second unit so I will change them out and run a test with them mounted in a pair in place of the first set. It is scheduled to arrive next Thursday as are the temperature controller and my new IR thermometer. A higher rate of air flow through the radiator should put more heat into the trailer interior.


My approach to this is start with simple basic equipment and then make changes driven by what is observed.
Thoughts? Comments?

Any idea what the difference in water temp was in the water heater at the different settings?

Personally this looks like a successful test to me. What expectations do you have that these results don't meet?
Tom

[MtnDon]

Any idea what the difference in water temp was in the water heater at the different settings?

Personally this looks like a successful test to me. What expectations do you have that these results don't meet?

No idea on the temperatures right now. However, my new IR thermometer arrived yesterday.

From that initial test I believe the concept has been proven sound. I guess I'm curious about what fans with 2x the CFM will do. The one new fan arrived in this mornings post. Probably tomorrow I'll do a test measuring water temperature across the radiator a the Low - Medium - High water heater settings. That'll be with the original fan set. Then I'll change the fans and do another set of temperature drop tests.

The temperature controller may arrive in a few days. Or may not. It's a direct China shipment. When that arrives it may be interesting to compare the energy use to maintain the selected temperature with both the low and the higher capacity fans. Or if I can find where the un-used PWM controller is I may try slowing the speed of the higher capacity fans.

But for now I'd say what I have works. Add a temperature controller and it should be viable for any TD and small insulated CT.

I'll be back with temperatures and energy use later. Just can't say when for certain. Then we can all compare results and maybe others can refine the system. All I want is to have some heat without spending the big bucks for something like a Propex. Some other heaters that others have used require wall space we do not want to give up.

[Shadow Catcher]

I am working on the design of the box for the radiator core. The 200MM fan dictates the width as it is slightly wider than the core. I am going to test the fan to see how much air it flows and how loud. Tested the fan using a 12 spare battery for my UPS, virtually silent.

[lrrowe]

Shadow Catcher,
How does one measure air flow?

[lrrowe]

An electronic speed control, rather than a rheostat. Rheostats waste power as heat. A PWM controller is actually an electronic switch that turns the power on and off extremely rapidly, leaving it on for short or longer durations and as such does not waste so much. Theire is an operating loss but it is insignificant when compared to a rheostat.

ebay has a bunch
I'm thinking that a speed controller might be handy if the fan used had a high enough volume to make slowing it down worthwhile.

I'm also beginning to wonder if there are some small squirrel cage fans in 12 VDC that might be better suited than the axial flow computer cooling fans? I have not looked. The nice thing about computer fans is their low current draw. That comes with lower flow and lower ability to push air through an obstruction like a radiator.

Thanks. I suspected I was using the wrong description, but I was in a hurry to type and get on the road this morning and I did not do the necessary verification.

[Shadow Catcher]

This is a 200 mm Cooler Master and advertised specs. 700 RPM 110 CFM 0.595 mmH2O 19dB-A. So not a lot of pressure. The 80mm fans we have in place of a Fantastic Fan put out 34 CFM at 30 dB on high at 2600 RPM and 18 dB on low which is where we have them most of the time.

[MtnDon]

Shadow Catcher,
How does one measure air flow?

That is difficult w/o specialized equipment. Good fans will list the CFM in their specs along with the amps, RPMs, dBA,

[Socal Tom]

Mythbusters has used a ping pong ball in a tube to measure relative air flow
Tom

[aggie79]

MtnDon,

I appreciate your research and findings. Things are looking very positive on using a water heater to heat a CT.

Another crazy thought came into my head last night that could increase heat transfer. The idea is not space efficient though. If the cooler/radiator is wide enough to accomodate two computer fans my thought was to use only one fan and have a "U" flow arrangement using a custom made plenum. The intake would be half of the width of the radiator. The exhaust side would then be routed back through the other half of the radiator and exit the same side as the intake. Of course you'd have to take extra steps so the the cool side and hot side don't mix.

Anyway, those are my musings.

Take care,
Tom

[aggie79]

MtnDon,

I appreciate your research and findings. Things are looking very positive on using a water heater to heat a CT.

Another crazy thought came into my head last night that could increase heat transfer. The idea is not space efficient though.

If the cooler/radiator is wide enough to accomodate two computer fans my thought was to use only one fan and have a "U" flow arrangement using a custom made plenum. The intake would be half of the width of the radiator. The exhaust side would then be routed back through the other half of the radiator and exit the same side as the intake. The air would be heated in two stages this way.

The fan could be mounted in the "U". Of course you'd have to take extra steps so the the cool side and hot side don't mix.

Anyway, those are my musings.

Take care,
Tom

[lrrowe]

Perhaps there has been some recent change but the manual for our 6 gallon pilot light Suburban water heater states, on page 12... "CAUTION: Temperature setting on control was factory set at low (120F/49C) to reduce risk of scald injury. Setting the temperature dial past the low position will increase the risk of scald injury......."

There is a black plastic adjuster that has settings with Low at one end, Medium in the center and High at the other end of the quadrant range of movement. That does permit adjustment of temperature to quite high temperatures. That's for the basic pilot light model. I have no idea about the other models. Ican easily get the water hot enough to cook fish by immersion.

~~~~~~~~~~~~~~~.

I did contact Suburban about the knob and this is their answer.
"Our pilot models have an adjustment knob on the “thermostat gas control” that allows you to adjust the temp. to 120,130, and 140 degrees F.".
So that ends the mystery so to speak.