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Old 12-30-2011, 10:52 AM   #57
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I'm in hot-water too - cached diesel burner and pumps etc. and still looking for cheap/free pieces... and ideas!

The physics of transferring heat BTUs from a solid to a gas rears its ugly head around this point; to get acceptable efficiencies a minimum 40F degree difference between air temperature and the heat sources point-of-contact is required.

If one graphs out the thermal transfer below 40F difference there'd have to be a turbine fan stuffing air like squalling madness past the heating component to make up for the lack of energy that a gas molecule can pick up then share with other gas molecules in a brief moment of contact.

That's where true on-floor-level baseboard radiators gain an advantage by capturing the coldest & heaviest air and circulating it in a loop. I'm leaning toward all baseboard heaters with extra insulation behind them except for one or two 'heat plates' to act as little pseudo-fireplaces for their radiant warmth.

A while back one of the true lost freight eBay liquidators had a run of McDonalds' style Bunn tea dispensers going begging for $20 each - narrow four gallon stainless tanks - that might've been ideal for my planned system if I could figure out how to seal the open top and put the exchanger tubing through-wall without too much trouble - keep the food grade anti-freeze in a closed loop and use plain water in the 4-gallon reservoir... And place it against a cabinet built-in or divider where it'd be broadside to seating or dining area.

An extension of this idea would be magazine racks or towel racks out of stainless that had circulation pipes backing them up - open bottoms to allow some air flow but mostly there for the radiant IR heat beaming off them. Okay, it'd play out badly touching them with the errant buttocks or thigh, calf or elbow but its just an idea to start.
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Old 12-30-2011, 02:49 PM   #58
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There are lost of options...

In the process of building my radiant system I have come across all sorts of information on various types of equipment that can be used other than just tubing loops in the floor. I would be happy to try to answer any specific question anyone has.

Here are some inexpensive fan forced hot water units. Some are 12 volt and some are 110 volt.

Check out the two Red Dot units at the bottom of the page - 12 volt units:
https://www.lfsmarineoutdoor.com/boa...n-heaters.html

More 12 volt units:
Radex Hot Water Forced Air Heater for Boats.* Manufacturer: Dickinson Marine

Good price on Beacon Morris 110 volt units - shown in above post:
Beacon Morris Twin-Flo III Kickspace Heater - Heaters Kickspace Hydronic made by Beacon Morris

Another 110 volt unit:
Myson Toe Kick Heaters. Kickspace Heater. Kick Space Heaters. Fan Convectors Space Heating. Replace Baseboard Heat - Hydronic or Electric. 5000 EZ / 9000 EZ

Some things to think about:

1.) I notice that some of the units above have an on/off switch on them for the fan and others mention that they have an aquastat that senses the water temperature and turns on the fan when it is high enough. For example the Beacon Morris one says something about water temps around 140 degrees but that a lower temp aquastat version is available.

2.) If you are going to use your domestic hot water for the heater keep in mind that your water temperatures will be around 110 to 120 degrees. Anything hotter and you run the risk of dangerous scalding at your faucets and shower.

3.) Depending on what exactly you have in your system you need to be careful to select a pump with enough capacity. That turned out to be a big problem for me. My first and second pumps were 12 volt pumps intended for solar applications or hot water but did not have enough capacity for my tankless water heater.

4.) Each of the units list BTU capacities but they are not all the same as each other so you might want to take that into account in your selection process.

5.) You will have to give some careful thought as to how to control your pump - whether by thermostat or just a switch. I found a really economical relay that can be switched from a 12 volt source and that can switch either 12 volt DC or 110 volt AC. Take a look at these two items here - I used the second one but the first one would also work fine:

ELK-912 | Relay Module SPDT 12 VDC | Home Security Store
ELK-924 | Sensitive Relay DPDT 12 or 24 VDC | Home Security Store

I was able to use a very simple 12 volt thermostat connected to the input side of the relay. I was first switching a 12 volt pump and now I am switching a 110 volt pump. Both work fine with the relay.

Malcolm
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Old 12-30-2011, 03:09 PM   #59
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An update on my system...

Over the holidays I was able to run some tests on my radiant heating system. I was actually using my Airstream as a guest room over the Christmas holidays.

Here are some observations and unresolved issues:

For my first test run the starting temp in the Airstream was about 37 degrees as I recall. It took perhaps 3 hours to warm the interior up to around 55 degrees. That is not very fast but it did get up there. Also it was really nice to feel how warm the floors were. My water pump and water heater ran continuously during that time without any apparent problems. What I discovered was that the water heater has issues with the input water temperature getting too close to the output water temperature. I do not yet know what the acceptable differential amount is but I will be looking into that. What happens is that at thermostat settings above 55 the water heater controller would sometimes show an error code and sometimes would just shut down and need to be reset. I could just stop the pump and the error code would reset or I could stop the pump and turn the controller back on for it to reset.

There are a couple of things that I am thinking at this point as follows:

1.) I think that I need to be pulling more heat out of the loops so that the water temperature going back to the heater stays lower.

2.) I would like to be able to heat up the inside of the trailer faster at start up.

3.) It might make sense to cycle the pump and water heater on and off now and then during initial warm up rather than running it continuously. This might help with the input water temperature issue too.

What I am contemplating doing is to add a fan assisted hot water blower unit in the system. This had been a back up plan anyway and it looks like it might indeed be a good idea. It would help with warming up the cabin a lot faster and it should be able to such more heat out of the water as it is pumped around. This may be enough of a solution to help with the water heater limitation. Secondly I ordered a relay timer from the same place that I bought my pump control relay. It has the ability to be set to run for a time amount when triggered. It can also be set to run 50% and be off 50% of a given time setting while triggered. I thought I could experiment with that as a way to help the water heater too. The timer relay I ordered is the following:

ELK-960 | Delay Timer Module | Home Security Store

I am at least happy that the system in general is working and that it has the potential for doing every thing that I have in mind for it to do.

I will update with my progress as I make any...

Malcolm
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Old 12-30-2011, 04:00 PM   #60
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Even better Beacon Morris prices...

I have purchased a number of my radiant heating supplies from Pex Universe. I see that they also carry Beacon Morris kick space heaters at an even better price than the site I mentioned above. Take a look below:

Search result

I am thinking strongly of ordering one of the K84 units for my Airstream. I intend to install it in the front of the living room pointing backwards toward the rest of the trailer. My thought is to install it close to the output of my water heater which is mounted outside on the front of the trailer.

Malcolm
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Old 12-31-2011, 09:26 AM   #61
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Barts, thanks for pointing out the truck cab heat exchanger. The reason I ended up looking at residential units is noise. I much prefer axial fans over the radial ones, they tend to be quieter and emit a more pleasant "whiter" noise.

WRT the Dickinson direct vent unit I just don't know where to mount it in a 23FB. The only spot where I could conceive mounting it would be in the entrance, but having a hot object protrude ~7" doesn't sound safe or comfortable. If we had a larger trailer with some space to "waste" I'd buy the unit in a heartbeat.
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Old 12-31-2011, 09:39 AM   #62
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Malcolm: when I designed the radiant hot floor system in our house a few years back I looked at instance hot water heaters and was baffled by the fact that everyone advised against using one. (I ended up using a relatively small high power 96% efficient stored water heater instead.) The explanation I got when I inquired is that most instant hot water heaters have a fixed flame, i.e. amt of heat added to the water. Some have a variable flame, but the low end of the range tends to be pretty high still. The result is that when the incoming water is just 10-20 degrees below the expected output temperature the amount of heat added is too much. Sounds like that's the problem you're hitting. I did see some expensive heaters designed for radiant systems that have the ability to pulsate the flame to crank down the heat output significantly.

If I recall correctly, a drop of ~10 degrees in steady-state is a typical design target for residential radiant floor loops, the main consideration is avoiding uneven heating between the start and end of the loops. You may not care about that in the trailer.

WRT timer, the way I regulate the heat in our house is by varying the duty cycle of the floor circuits. I timed how long it takes hot water to flow through a loop and that's the basic unit of time. If I set the heater to 10% the pump is on 1 time unit and off 9 time units, at 25% it's on 1 unit and off 3. This ensures that the heat output remains relatively even throughout the loops.

About the kick-space units, I'd look carefully at the dimensions. I don't know how they compare between manufacturers. Then the big question comes about the noise! I noticed that the slant/fin units have two speeds, that's already a big plus! Certainly worth an extra $100 to me, but everyone's priorities are different :-)

Best of luck with your design, it's already pretty darn cool (uh, hot) that your system works well down to almost freezing!
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Old 12-31-2011, 02:59 PM   #63
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My tankless water heater is too smart...

The tankless water heater that I am using has a relatively complicated electronic controller that may be a bit too smart for my application. It is supposedly able to modulate the flame as needed. It monitors the temperature of the incoming water versus the set point for the output and makes adjustments accordingly. Along with monitoring these temperatures it seems that it also has an error mode that kicks in when the temperature differential is too small. That is what I am evidently up against.

Since I wrote my last post I did have one other idea of something to do that might help. In working through all of the pumping issues I took out the temperature mixing valve that I suspected was allowing an alternate path for the pumped water. I think this still might be the case but that problem can be remedied by adding a one-way valve to prevent back flow. If I re-install the mixing valve I can set the temperature of the water heaters output to 140 degrees. It has been set at about 120 degrees for my tests since that is about the maximum safe temperature to prevent scalding danger in domestic water systems. That might even be a bit too high. My thinking is that if the water heater output is set to a higher temperature then the water in the floor loops can get to a higher temperature before the error mode kicks in. I can also set the domestic water temperature to something more like 110 degrees to for sure be on the safe side relative to scalding dangers. Since I already have the mixing valve and a spare one-way valve putting it back into the system should be a relatively easy experiment.

Malcolm
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Old 12-31-2011, 07:23 PM   #64
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I don't know the details of your design, but you do tend to need check valves ("one-way valve") at both inputs of the mixing valve. I would need to see the detailed schematic. In any case, be sure to buy quality check valves and to ensure they are designed for hot potable water use. I've had lots of trouble in my system, but I do have hard water. The check valves stop functioning properly after about a year. One version turned out not to hold up to the heat (I actually run at 160F out of the heater), another's piston stopped gliding. Many check valves are either not for hot water or not for potable water, so beware.

BTW, you should install some thermometer at the inflow and outflow of your heating circuit, if you haven't already done so. I have a dual thermometer that has probes that can easily be attached to a metal fitting called "digit-stat by azel". This way you can measure the temp differential. You may want to play a bit with the flow rate, I suppose lower flow rate means higher temp differential, which may help you with your issue, although it will also result in less heat output.

One thing I wondered from your description is about the efficiency. You mentioned that the heating ran for 3 hours to go from 37F to 55F. If the heater was running at full blast that would be horrible efficiency, if I compare to hot air furnace which would do the same in 20-30 minutes. So unless your heater was burning on low all the time, I'd be concerned about the propane use.
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Old 01-01-2012, 04:06 PM   #65
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For check valves I am using the type that has a swinging flapper gate. It is all brass construction and is for 3/4" pipe. It also has a removable top that could be opened to clean out the valve without removing it from the system if that were ever to be necessary. They are a standard product at Home Depot. I can understand the need for one 1-way valve on the hot water heater source side to keep water from getting pumped back through the valve instead of through the floor loops but what would having a 1-way valve on the cold water input side do I wonder?

Yes, I do need to add some thermometers into my system somewhere. That would help me better understand what the differential is. Do you happen to have a link or pointer to where I could buy the type of thermometer that you were describing?

I suspect that since the water heater monitors heat in and out that it has been adjusting the flame down to a lower level as the return water temperature increases. The system has run for a long time over the holidays and I have not used up one of my propane tanks so far. It would be useful to have some sort of flow meter on the propane too I guess.

Malcolm
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Old 01-01-2012, 07:14 PM   #66
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I've not had good luck with the flap-type, but that may have had to do with the water hardness. The flap stopped swinging properly and thus didn't shut easily enough. YMMV...

The thermometer I use is listed at Digital Temperature Gauge, Digital Temperature Gauges for Radiant Heat Systems, Digit-Stat DS-60P for Hydronic Heating Systems, not exactly cheap, but I didn't spend time to search for better prices. It came with my radiant heat kit.
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Old 01-02-2012, 03:12 PM   #67
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Price of sensors does not seem too bad...

Considering that there are two probes and a remote digital display the cost of the Digit-Stat ds-60p does not seem all that unreasonable to me. It does replace two thermometers and individual thermometers can run at least $15 each depending on how they are mounted. Mounting hardware can make them cost more too. Thanks for the pointer. I will give this unit consideration for adding to my system.

Malcolm
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Old 01-03-2012, 12:21 AM   #68
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The one thing to consider is that the probes have a rounded indentation so they can be pressed against a metal pipe and make good contact for heat transfer. But it does mean you need some metal pipe somewhere. Also, I found that putting some insulation around the probes (and pipe) to help.
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Old 01-03-2012, 06:15 PM   #69
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Temperature sensors and flow meters...

I did order the temperature sensor you suggested. I should be able to find something metal in my system to attach them too. Worst case I can add something in the middle of a PEX run that is metal. The installation guide I looked at also suggested adding insulation which I will indeed do.

In looking around for something else I discovered a flow sensor that I wish I had found earlier in my experiments. I have one of these on order - at the bottom of the page:

Flow Sensor

This gadget measures flow and can keep track of how much flow has passed through it. It has a nice digital display panel too. For $19.90 plus shipping this seem like a deal. The only issue that I might have is that it says the threads are 1/2 BPS which turns out to be a British standard - which I have not heard of before. I do not know yet if I am going to have any trouble connecting my PEX tubing to it. I hope not.

Malcolm
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Old 01-03-2012, 06:20 PM   #70
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I have ordered a fan assisted radiator...

After much deliberation I finally decided to order one of the following 12 volt fan assisted radiators:

https://www.lfsmarineoutdoor.com/boa...ry-heater.html

Note that the photo is actually for the dual fan unit. If you check out the dimensions you will see that the single fan unit that I ordered is actually closer to being square.

I have a good place under my stack of drawers in the kitchen area where I can install it within easy reach of both hot water and power.

I will post results when I have some about how it goes.

Malcolm
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