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Old 09-21-2011, 10:13 AM   #43
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I keep my tankless WH unit at home set at 120 degree max and do not get scalded. It is uncomfortably hot using unmixed hot water only, but not scalding.
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Old 09-22-2011, 01:01 PM   #44
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Originally Posted by A W Warn View Post
I keep my tankless WH unit at home set at 120 degree max and do not get scalded. It is uncomfortably hot using unmixed hot water only, but not scalding.
That's a good information point. I will have to do some experimenting to see how the system does with water in the 110 to 120 degree range. I am still not yet sure how well the heating system will do and whether or not I will have to add extra radiators to the system. At least the weather around here is starting to cool down some so I will be able to do some testing with cooler temperatures.

Thanks,

Malcolm
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Old 10-17-2011, 04:26 PM   #45
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Pumping issue still not resolved...

I have completely removed the mixing valve and tried the system again. Still the pump does not seem to be doing what it is supposed to be doing. I am at a bit of a loss now as to why it does not seem to be able to operate as advertised. I am wondering now if using it in a circulation mode like I am is somehow causing an air bubble around the impeller of the pump keeping it from being effective. I don't know if there is something that I can add to the loop that would take care of this problem. Also it is hard to believe that this is in fact what the problem is. All of my hot water flows through the same plumbing so it is very easy for me to bleed the air out of the hot water line by just turning on the kitchen faucet. I am going to try consulting with the manufacturer before I decide to switch to a different type of pump.

Malcolm
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Old 12-04-2011, 08:12 PM   #46
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Pumping issue has finally been resolved!!!

After much hair pulling, several experiments and actually trying a couple of other pumps I have finally figured out what was wrong and have the water circulation problem fixed! The bottom line is that I was very naive about just how much resistance to water flow was caused by my system of 1/2" PEX tubing and the tankless hot water heater. The original pump that I started out with was nowhere near capable enough of pushing water around the system.

Resistance to the flow of water in the system is measured in feet of head - which can be translated to psi. I eventually found out that there was a way to measure how much head of resistance a system has. What you can do is to add two pressure gauges into the system - which I did. One pressure gauge is just past the pump and the other one is at the end of the whole heating loop after the water flows through the PEX tubing and the water heater. This location is almost back at the input side of the pump. What you do then is to turn on one or more a hot water faucets and measure the difference in pressure between the two pressure gauges. In my case I still had the flow meter installed in the system so I could also see what the flow rate was with the faucets turned on. With the kitchen faucet, bathroom sink and shower faucets all turned on I was getting close to 1.76 gallons per minute of flow. As the flow rate increases the head resistance to flow will dramatically increase by the way. When I subtracted the pressure reading of the output pressure gauge from that of the input pressure gauge and converted that value from psi to feet of head I found that I had about 29 feet of head at 1.1 gpm and about 46 feet of head at 1.76 gpm. I picked a pump that could handle up to about 39 feet of head at low flow rates. To see more details about the pump I picked check it out at the following link:

Taco 009 Circulator Pump (Stainless Steel), Taco 009-SF5 Pump

The pump is bigger and more expensive than I had originally hoped it would be. It also runs on 115 volt AC power rather than on 12 volt DC power. The important point here though is that it is able to pump water around my system at about 1 gpm or so. This is fast enough to reliably trigger turning on the hot water heater. I still have to do some testing on the system to get some sense as to how long it would take to heat up the trailer and just how warm I can get things when it is cold outside. As I think I have mentioned before the system may or may not provide enough heat all by itself to not need any other help. Time will tell on this part of the testing. The weather around here is fairly cold right now with temps dropping to just below freezing at night. I might be able to run some tests to see how it does. I did just fill up my water system with anti-freeze though so I have to decide if I want to do the testing with anti_freeze installed instead of water or what. When I first got the pump installed I did run the system for about 1 hour and I raised the temperature inside the Airstream from 40 degrees to only 44 degrees. I was going in and out some though so that did not help. I suspect that I would want to make sure that I turned on the heater early to get the system up to temp for when I needed it. I might even want to consider running it while I am driving. I don't know if that would be any kind of an issue for running the water heater or not though.

I am going to be installing an inverter that will allow me to supply 110 volt power to my water pump from the battery when I am not hooked up to shore power. The pump takes about 161 watts of power at 115 volts which does not seem too bad. My water heater also has a fan forced combustion system that runs on 115 volt AC but that is a relatively small fan compared to the pump. I expect to be hooked up to shore power more often than not but I would still like to be able get heat from the system even when I am not. Also this would help allow me to run the system when I am driving too.

Malcolm
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Old 12-04-2011, 11:46 PM   #47
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Do you have radiators in the system or are you just using the PEX tubing?
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Old 12-05-2011, 11:24 AM   #48
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Malcolm,

You have a blockage or kink somewhere. At 1 GPM you should have 1 foot of head for every 125 feet of 1/2" PEX. Or maybe there's a flow restriction device in the water heater that you could remove.

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Old 12-05-2011, 11:34 AM   #49
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Do you have radiators in the system or are you just using the PEX tubing?
Right now I am just using the PEX tubing in the floor. I can add radiators later if I decide that I need to. That has been a backup plan right along.

Malcolm
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Old 12-05-2011, 11:41 AM   #50
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Malcolm,

You have a blockage or kink somewhere. At 1 GPM you should have 1 foot of head for every 125 feet of 1/2" PEX. Or maybe there's a flow restriction device in the water heater that you could remove.

Jammer
Jammer,

No doubt the larger part of the flow resistance is in the tankless water heater rather than in the PEX tubing. I was told by a radiant heating consultant that it was not unusual to have a lot of head resistance in a tankless water heater. I suppose there could be some intentional resistance in the water heater to slow down the water long enough to get it heated. At this point I am OK with how the system is working and the rate of flow with the new pump. I just wish I had known sooner about the high head. It would have saved me a lot of hassle.

Malcolm
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Old 12-05-2011, 02:19 PM   #51
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Quote:
Originally Posted by Jammer View Post
Malcolm,

You have a blockage or kink somewhere. At 1 GPM you should have 1 foot of head for every 125 feet of 1/2" PEX. Or maybe there's a flow restriction device in the water heater that you could remove.

Jammer
Is this calculation for straight line resistance or including the great number of 180deg bends. There is a much higher flow resistance in a 180deg bend.
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Old 12-29-2011, 02:12 AM   #52
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Very interesting thread, please keep posting updates on your experience in the field!

We've just come home from a trip in the desert with night time temps around freezing. We hate the furnace with a passion due to its noise and only tolerate it briefly when the trailer is cold and we want to heat it up quickly. We had the luxury of an electrical hookup (we usually boondock) and ended up using two small electrical heaters. Not that we ran them both at the same time, we simply alternated using them to change the character of the noise every now and then. Sigh.

I concluded that the most quiet form of heat is the water heater. It's barely audible when running. So I'm now exploring options to use the hot water for heating purposes. The full-on radiant floor is too much to retrofit to our new trailer, but I'm wondering about making a semi-portable 3/4" to 1" thick "heat mat" that I could place under the dinette for the season to provide some extra comfort. It wouldn't heat the trailer on its own, but could make lounging during the cold evenings more comfortable.

For main source of heat I'm looking for fan assisted radiators, i.e. something like an automotive heater block. But I want potable water materials and a really quiet axial blower. Does anyone have suggestions for where to find something suitable? I suppose all the automotive stuff is out due to the potable water requirement.

From my experience with the electric heater we need 1000-1500 watts to keep a reasonable temperature through the night. That translates to 3500-5000 BTU/hr, which shouldn't be too difficult to put together, I hope.
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Old 12-29-2011, 02:58 AM   #53
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I've considered this myself.... you could do this with:

* a small 12V (or 120V + inverter) centrifugal circulating pump that can handle 140F or so water. An "El Cid" pump designed for solar heating systems has the lowest power consumption I've seen, and is designed for use in potable systems.

* 1/2" copper tubing soldered to copper sheeting as a radiator. With some thought, these could be finished nicely to match your Airstream.

I'd plan on making a large enough radiator so you could avoid the power draw and noise of a fan; you can put more than one of these in a larger trailer. You could even have heated towel racks...

If you use lead-free components & solder as you would for household plumbing, you'll have no problems w/ potability.

- Bart
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Old 12-29-2011, 11:57 PM   #54
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Barts, thanks for the suggestions. Yes, I was also thinking of copper. Maybe I can find some baseboard radiator type of pieces that I can reuse, they have nice fins around the copper. I do believe that I have to use forced air somewhere. In a 23FB there isn't much floor space I could take away from to mount radiators. Specially the entire bed area is tight enough as it is.

I took a look at some baseboard radiator ratings and with water @140F and 1-4 GPM flow you can expect around 300 BTU/HR per foot of radiator. So I'd need 12-17 feet, which perhaps doesn't sound like much until you actually try to cobble that amount of space together in a trailer and picture all the pipe and fittings. And then there's the question whether 140F is even realistic. At 120F the heating drops to ~200 BTU/HR/ft and then I'm looking at 20-25 linear feet.

I think I found what I'm looking for, it's called a kick-space heater. For example the slant/fin TK-70 or TK-90 which seems to be available in the $200-$300 range.
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Old 12-30-2011, 03:54 AM   #55
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Yup - ran some numbers; got the same kind of results.. hmmm. Forced air is noisy, though, unless speeds are kept down; it takes a lot of power, which makes boondocking hard. Here's a truck cab heater w/ a speed control:

Single Fan Heaters

A thermostat could be connected to the blower...

I guess I still like the ambiance of the Dickinson heaters best, although that's certainly not an inexpensive solution.

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Old 12-30-2011, 10:14 AM   #56
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try this pump..

I entertained this system a few years ago. decided I would roll the tires when temps got below 40 F.
My Dickenson direct vent works just fine. can be seen in my old Heaters,Heaters Heaters thread.
anyway the pump system in this system is the KISS approach.
good luck.
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