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Old 07-31-2011, 07:26 AM   #29
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Malconium,
Yesterday I was driving home around 5pm the temp showing outside on the truck was bouncing between 98 and 99 F. When I read your post, that you might need heat in your TT this week, it made me envious. Wish I was there!
Enjoy your trip this week! Let us know how it goes!
Alan
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Old 07-31-2011, 09:12 PM   #30
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Living31,

I think that's a fair summary for the most part although I would add that the physics of radiant heat dictate a specific maximum output level in BTUs per square foot for a particular surface temperature.

The other alternatives that are out there are to increase the area of the radiant surface by putting coils in the walls or ceiling, or to provide supplemental heat of some kind, such as the fan-forced solutions others are proposing.
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Old 08-03-2011, 12:41 PM   #31
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Thank you

Thanks for squaring me away.
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Old 08-09-2011, 02:57 PM   #32
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Back from the first trip with our Airstream...

Well I am back from the first trip ever with our Airstream. My wife and I spent a week in Central Oregon at the Thousand Trails campground just south of Sun River. Three of our four kids along with two spouses and 8 grand children also camped out there with us. In general we were very pleased with out Airstream even though a few details are not yet finished in my remodel.

I did get an unpleasant surprise though with the radiant heating part. I mentioned above that I had hoped this would be a great experimental time with the heating system. Indeed the weather got down to about the mid 40's at night so it would have been a good first test. I found out however that the water heater that I had chosen has a very specific problem relative to its use for radiant heating that I did not anticipate. I called the factory rep for debugging from the campground and we finally concluded that the unit will not work for what I want to do. The problem is that the burner is triggered on by water pressure - not water flow. At least 20 psi of pressure is required to trigger the system. That seems to be fine for the domestic hot water requirement but not fine for pumping water around in a loop. If I set the water flow limiter in the water heater to the lowest setting the heater would come on for anywhere from a few minutes to a max of 9 minutes. If I increased the water flow or even if I increased the temperature setting on the water heater it might turn off right away. This is even though the thermostat still has the water pump turned on. It seems that water pumping in a loop does not have sufficient back pressure to consistently reach 20 psi so as to keep the heater turned on.

I am currently examining other inexpensive tankless water heaters as a replacement. There are a couple that specifically say that they work well with even very low water pressure. I am seeing values around 3 psi advertised. My guess is that this would work since the current unit seems marginal at 20 psi. I am also speculating on perhaps using a smaller unit - and less expensive - for my system. Here are the current contenders:

Larger size:

~RV Tankless Hot Water Heater No Electricity Needed 10L | eBay

The EZ202 Tankless Water Heater by EZtankless.com

Smaller size:

~Marey Tankless Water Heater for Campers & RVs 5L | eBay

The EZ101 Tankless Water Heater by EZtankless.com

It is interesting to note that he first vendor listing Marey brand water heaters shows a picture of an Airstream in some of their adds. I might give them a call and see out of curiosity what they are recommending for installation with an Airstream. Marey water heaters are made in Puerto Rico and the EZTankless ones are made by a very large manufacturer in China. Both at least have people in the US that I can talk to.

My hot water pump is adjustable and can pump from 1 to 5 gpm. The smaller hot water heaters listed above range from 1.3 to 1.6 gpm capacity with about 34k to 42K BTU. The lager ones range around 2.7 gpm at 79k BTU to 3.2 gpm at 84k BTU.

Any thoughts on what size I should consider going with would be appreciated at this point.

Malcolm
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Old 08-09-2011, 03:40 PM   #33
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Old 08-10-2011, 09:05 AM   #34
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Quote:
Originally Posted by malconium View Post

Any thoughts on what size I should consider going with would be appreciated at this point.

Malcolm
Before buying a new water heater, why don't you experiment with restricting the flow to build pressure in they system that you already have? If the pump is sufficent, it could be that something installed just downline from the water heater with enough restriction to get just above 20psi would work. Maybe a pressure control valve. Maybe a gate valve that you could partially close. Or, something as simple as reducer fittings might be enough.
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Old 08-10-2011, 12:42 PM   #35
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I did think about trying to restrict the flow some while I was out camping. The one thing that I did try was to run the hot water pump at its highest setting which is 5 gpm with the water heater set to its lowest volume setting. I don't know what the lowest volume setting restricts the flow to but it should be less than the 2.7 gpm that the water heater supposedly handles as a max flow. Those settings did not improve the situation. I did not think about the fact that I do have two gate valves in the system that I could have tried shutting down some. The gate valves are intended to allow me to balance the two parallel heating zones. I am not sure how I feel about artificially restricting the flow in that sort of way though. The same hot water loops are used to furnish the faucets and shower with hot water too and that might reduce the flow more than desired. I should do the experiment though just to find out what happens.

In the meantime I did seek out and order another water heater that might in many respects be a better choice anyway. It is this model here:

Outdoor Tankless Water Heater by EZtankless.com

I was able to buy a so-called scratch and dent unit for $375 instead of the full $524.95 price tag. When I asked about the condition I was told that it was never installed. The customer that returned it wanted a different model and this one was never used so it should be the same as brand new. The documented low pressure start up point on this unit is only 2.9 psi. The person that I talked to said that they know for sure it works down to 8 psi but they do not have a good way to test it at lower psi settings. The unit also seems more suited for an outdoor installation. It has a stainless steel case that should look a lot better on the outside of an aluminum trailer. The total capacity of the unit is somewhat larger too with a max flow rating of 4.4 gpm and a BTU rating of 112,000. One other major difference is that it has fan forced combustion that needs 110 volt power. For that I think I will consider installing an inverter that can run off of my battery if I can not plug into shore power. I have intended to get an inverter anyway so this would prod me to do so. The power consumption is supposedly a max of about 45 watts at 110 so that does not seem too bad. The new unit has a remote controller that I can put inside my Airstream that seems like a really nice thing to do. It also does not have a timeout at 20 minutes like the other unit so that is one less thing I have to worry about.

The vendor did caution me about the potential danger of the unit freezing if the outside temperature is too cold. That was going to be an issue with the other unit too. My thinking is that since I am intending to use the unit for running radiant heating that it will naturally be cycling on enough in the process of heating the floor to keep itself warm enough. As I mentioned earlier I am also not particularly interested in camping in really cold places anyway. I also have had in mind putting a temperature sensor in the heater that could be used to trigger the water pump to start up the heater if the temperature gets too low at the heater end. I will have to wait and see about whether or not that seems to be needed.

The new water heater should arrive early next week. I will try the water restriction experiment on the current unit and report back but I think I will still go for the new unit.

Malcolm
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Old 08-21-2011, 10:20 AM   #36
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Malcom, I have installed a radiant system on my house, and it is my opinion that the manufacturer is wrong. I have never heard of a tankless heater that requires pressure to operate. Just think about it, the original intent is to heat hot water for normal user (shower etc). In this normal use, the faucet is open and the water pressure goes to almost nothing and the water exits the system. It's always flow that triggers a tankless unit. I think your unit may be defective. Just my opinion.
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Old 09-05-2011, 01:12 PM   #37
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Tis is the system I would like to install in my trailer- thank you for doing the experimental phase for me!!!
I VERY much want to use a tankess hearter for my aistream- there is so much difference between what the manufacturers tell you and how it actually works in real life.
Thank you! Can't wait to hear your further adventures.

Tess
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Old 09-05-2011, 04:51 PM   #38
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Pressure to operate - think popping or sizzling noises as hot spots from poor design or mineral scale build-up flash to steam... having a pressure minimum may be a function of the heat exchanger design, once there is a hot spot it would only get worse with time. I've seen several on-demand heater killed from mineral water, the higher pressure would delay possible damage or changes to the exchanger assembly...
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Old 09-06-2011, 01:49 PM   #39
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A progress update...

I am still working on the issues - now with the new water heater. My wife and I took the Airstream out this last weekend so I did not get a chance to do much on the water heater issue other than to finish attaching it so that it would not fall off during out trip. We were visiting our daughter and her family and were parked right next to their house while we were their. We did not need any hot water in our trailer during that time so I did not even turn it on.

I have done some further investigation relative to how this unit triggers with water movement. First of all I discovered from the vendor that it requires around 1 gallon per minute (gpm) to reliably trigger. My bathroom faucet is not passing enough water to reliably trigger the unit at the moment. Tech support suggested I try taking off the aerator and sure enough there is enough flow without it. I get a lot of splashing though. I clearly need some form of aerator but maybe I can find one with a little less restriction.

The unit still will not trigger with just the heating pump running. I did discover that I had mounted the pump in a position that was not recommended by the pump vendor. I changed that but still the water heater is not triggering. My next step is to find out what is really happening with the water flow from the pump. Yesterday I ordered a simple water flow meter so that I can monitor what is happening. Here is the unit that I ordered from Amazon.com:

Amazon.com: TOM Aquarium Flow Meter (measures 50gph to 250gph flow rate): Pet Supplies

I would have preferred something digital but was not finding anything at all reasonably priced. I just need the meter for a short while anyway. One positive thing about this meter is that since it is designed for monitoring flow in aquariums that implys that it should work fine with a pump.

Once I get the flow meter installed I will first check to see if the pump really is pumping at the rate that the dial setting on it indicates. The pump is supposedly adjustable from 1 to 5 gpm. At the moment I can not prove that it really is pumping at those rates. Once I determine for sure that the pump is working I will turn to measuring what his happening with the flow sensor in the water heater. This unit has a flow sensor that has a variable resistor in it. The unit starts at 21K ohms with no flow and the resistance reduces as the flow increases. The controller board in the heater monitors this resistance along with the temperature of the incoming and outgoing water. It then meters the correct amount LPG to heat the water sufficiently. What I am contemplating doing once I am convinced that the pump is actually working is to determine what the resistance value of the flow sensor is when it senses normal flow through it. I can then contemplate switching in some parallel resistance when my pump runs that will result in the sensor resistance appearing to be monitoring the correct flow. I guess that those of you that are not familiar enough with the electronics involved will have to sort of take my word for how this might work. The basic idea is that I will be tricking the controller into getting the reading it needs when my pump is pumping a specific amount of water. I think this should work but I have to go through the measurement process first to find out exactly what is happening with the pump, sensor and controller. Fortunately I have enough electronics background to feel like I know what I am doing. Time will tell...

Malcolm
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Old 09-08-2011, 09:18 PM   #40
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The flow meter arrived today...

I was delighted to receive a parcel from Amazon.com today that contained the flow meter that I ordered. This means that I should be able to start my flow experiments this Saturday. Hopefully all will go as planned and I will finally be able to get my water heater and radiant heating system working together correctly. I will report on progress when I have some more. I will also try to remember to post a photo of what the new water heater looks installed on the front of my Airstream.

Malcolm
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Old 09-13-2011, 08:27 PM   #41
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I think I have isolated the problem...

I was able to connect up the flow meter on the input side of the hot water heater. I took some photos of what it looks like but I used my wife's camera and she is way for a couple of days and took her camera before I downloaded the photo from it. I will have to try to remember to include it later.

Right away I was able to measure the flow for the kitchen and bathroom faucet to prove that the meter was working. I then turned on the radiant heating pump and found to my surprise that it did not seem to be moving any water! That of course would easily explain why the water heater would not come on when the pump was running. So the next obvious question was why there wasn't any water getting pumped. I did everything that I could to trouble shoot the pump and its connections. I looked closely to make sure that the one-way valve and the pump were installed pointing in the correction direction and etc. I even opened up the pump and ran the motor outside of the housing. Everything seemed to be completely in order. It was some time for some serious head scratching.

I still have to verify this conclusion but I believe what is happening is that water is indeed getting pumped but through a different path than what I had intended. Refer to my drawing which I believe I posted earlier in this thread and to the small part of it included below. I think water is getting pumped through the hot water pump to the right. It then continues to the right through the one-way valve. Instead of turning up to go through the radiant heating loops it turns down to the cold water line. It then turns left and up into the cold water input side of the mixing valve. It then flows out the hot water input side of the mixing valve and back to the input side of the hot water pump. What I think I need to do is to add a one-way valve on the hot water input side of the mixing valve that will only let water flow into the mixing valve but not out of it. I have confirmed with the supplier of the mixing valve that water could indeed flow backwards through the hot water input side.

I will certainly be both pleased and irritated at the same time if this does in fact fix the problem. Tracking this issue down has been difficult and it has cost me both time and money. As it turns out I may not have had to buy a different water heater. I do like the looks of the new one better though so all is not lost.

I will report on the results of this little bit of re-work when I get it done.

Malcolm
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Old 09-20-2011, 08:55 PM   #42
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Things are moving slowly....

I have yet to get the connections changed for the radiant heating lines so that I can prove my theory about why the water is not getting pumped around the heating loop. I am becoming increasingly convinced though that this will in fact prove to be the reason that the heating is not working. I have been thinking seriously about removing the mixing valve altogether rather than adding a one-way valve to the system to prevent back flow through the mixing valve. There are a couple of reasons I am thinking this. For one thing the flow through my faucets is marginal and it will reduce if any cold water gets added to the mix. Taking out the mixing valve will eliminate this as an issue. The other reason is that the new water heater does have a remote control with a temperature specific setting so that I should be able to set a safe water temperature for the whole system. The original water heater that I was using just had an adjustment knob with no settings in degrees. I will be limited to heating with 110 degree water so as to avoid danger of having scalding water coming out of the faucets or shower but I think that should be hot enough. We shall see.

I did get a chance to retrieve the photo of the new water heater on the front of my Airstream along with the water flow meter that is temporarily mounted there too.

Malcolm
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