Hot Water Radiant Heat - My Installation

[tvoneicken]

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.

[tvoneicken]

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!

[malconium]

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

[tvoneicken]

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.

[malconium]

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

[tvoneicken]

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.

[malconium]

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

[tvoneicken]

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.

[malconium]

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

[malconium]

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

[doorgunner]

I lived on a sailboat for a few years, most of the marine industry stuff works well in trailers.
I've enjoyed reading this thread, keep on experimenting, testing..

[malconium]

Originally Posted by doorgunner

I lived on a sailboat for a few years, most of the marine industry stuff works well in trailers.
I've enjoyed reading this thread, keep on experimenting, testing..

There does indeed seem to be a lot of marine industry stuff that works for our Airstreams. When I go looking for a solution that is very definitely one of the places I look. I do appreciate your letting me know that you are following the thread too. I sometimes wonder just how much of my experimenting to share with the forum since it does not all go as planned. In general though I think that learning from mistakes can be of value so I try not to hold back too much.

Thanks,

Malcolm

[tvoneicken]

The flow sensors are pretty awesome, thanks for posting the links! I'm already hooked :-)

WRT the heater, I'm leaning towards a residential unit. Probably the Turbonics Toester T6/8 Turbonics Inc., Specialists in Hydronic Heating Solutions.. The one you link to is nice and small, but must be loud given the fan type and the 150CFM. That seems great for a short term boost, which is probably exactly what you're looking for. I need something that can be on permanently and thus must be quieter.

[malconium]

Turbonics makes some pretty interesting looking products. Thanks for the pointer. I have not heard of them before. It never ceases to amaze me how I can search for things on the Internet and completely miss a major supplier of the type of thing that I am looking for. Do these folks sell through any Internet based supplier?

You are right that I especially want a quick heat up boost for when I first turn on my heating system. I will very likely put in a switch that will let me turn off the fan and let the rest of the system run if I want to reduce noise or to save power.

Thanks,

Malcolm

[crazeevw]

Malcolm,
I'm finding that between eBay and Amazon, I've been able to locate just about anything that I'm unable to purchase locally. As well, I thought I wasn't going to be able to find non-silicone caulking, but an Internet search led me to a local supplier. May have been a $1.00 more than online, but I saved over $9.00 in shipping costs.
Which reminds me, I need to get to Amazon after paycheck hits tomorrow and purchase new charger/converter for my Airstream.
Thanks, Derek

[malconium]

Hi Derek,

I buy a lot of things from Amazon.com too. A really good place to check for chargers is the following link:

BestConverter - Converters, Inverters, Electrical Supplies, Electronics

I believe that the owner is a forum member and I know that they can answer compatibility questions about their products versus your specific needs. I bought my charger with an integrated power panel from them a few years back and I am very happy with it.

Malcolm

[animatt]

I did not see it mentioned anywhere. For anyone in the future the aluminium plates for the pex radiant install would have helped out a bit in this situation.

It pulls much more heat from the pex. Which would have heated space quicker, and left the water going to how water heater much cooler.

With out the plates the flooring directly over the tube heats up. This then slow the movement of heat for tube to the floor. Air does heat up much slowee and does transfer heat but not nearly as much as heat transfer plates.

It would only been another $140 for the plates for such a small area. Maybe even less.
Try pexuniverse.com. they have 200 linear feet of pex for about ~$130-140.

If anyone else is going to try this highly recommend they do not skip the plates. Also go with a small efficient gas, tank style water heater would allow for a very small pump to be the circulator which would help alot. 15watt pump verse more than 100 watt pump.
Tankless heaters are very trickey and have lots of controls and requirements. Tank heaters for the most part are very simple. KISS

Also if you go the tankless route you will already need a bigger circulator may opt to go for one long pex loop rather than 2 shorter loops. This will also help the water loss more what by time it gets back to the sensitive tankless.

Sorry for any typos, typing on 7 inch screen 4:30 in morning.

One last thought comes to mind. Can you recap on what the floor insulation consists of. Entire floor. Vertically speaking. You maybe lossing a lot of heat downwards.

Matthew Wright

[malconium]

Hi Matthew,

It is too bad that you did not see this thread sooner. I would have been able to be more open to suggestions earlier in the process than I can be now.

To answer your question about my floor insulation what I have starting from the bottom and working up is the following - no insulation below the floor line:

3/4" of Polyboard subfloor - a plastic plywood substitute

Layer of reflective aluminum foil insulation

PEX tubing sitting on top of the foil insulation and surrounded by air

The air cavity is 3/4" tall and is divided up with 1x1 wood strips at 6" on center.

The finish floor is 3/8" thick tongue and groove engineered wood flooring.

I suspect that the aluminum foil insulation will in some ways help spread out the heat. It will not be as effective as aluminum plates at spreading it out but it is aluminum and it is in contact with the tubing. I am also hoping that the major heat loss down through the floor would be of type radiant which should be stopped in large part by the reflective foil. I also have places above the holding tanks where I intentionally left out the reflective foil so as to let some heat leak down to to the tanks. I added reflective foil under my new black and grey water holding tanks instead of putting it above the floor. Of course some heat will be consumed in warming up the holding tanks.

Relative to the size of the pump I did make a rather startling discovery recently when I was replacing the water in my system with RV antifreeze. I discovered that there was a screen water filter at the input of the hot water heater that I did not know about. I would guess that about 60 to 80 percent of its surface area was clogged up with debris of one kind or another. This could have been playing a very large part in just how much flow resistance I have been getting in my system. I have been collecting parts to add to the system and I am just about to make some changes and see where I stand now. I expect to see a difference in the rate of flow. How much I don't yet know. The water heater itself is capable of heating water at up to something like 3 plus gallons per minute. If the clean filter now allows for a greater rate of flow then the dynamics of the whole system will be changing. I will be adding the flow meter I purchased - mentioned above - and the fan assisted radiator. I will be very interested to see what happens. I may just add the flow meter first and test the flow rate before I add the fan assisted radiator.

Relative to tank type water heaters it was my thought that typical RV units simply do not have enough BTU capacity to heat water enough. Perhaps I am wrong about that. If I recall most of the units that I looked at were rated somewhere in the range of 30k BTU's which did not seem like enough.

Malcolm

[BigAl]

I believe that Best Converter give forum members a discount if you tell them.
Al

[animatt]

[QUOTE/]Relative to tank type water heaters it was my thought that typical RV units simply do not have enough BTU capacity to heat water enough. Perhaps I am wrong about that. If I recall most of the units that I looked at were rated somewhere in the range of 30k BTU's which did not seem like enough.
u
Malcolm[/QUOTE]

You would really have to see what heat losses are to Calulate that. One thing is, these heaters do not do so bad in radiant as water goes around as losses some heat but the heater is reheating water that maybe 100 degrees versus water source that may end up being 50f. The tank can recover much quicker. Not a huge deal in your case but for people doing this in a home install is. It is important to check efficiency for tank heater versus tankless.

I am currently doing an open system radiant install in a house using their existing tankless. It will make the radiant side more interesting as more restrictive in operation, but design should overcome that. I tried to push them to do system of a tank heat. Very simple radiant, just pump off the tank and back to the tank. If for some reason your loops do not loss tons of heat to the floor it is alright as the tank heater will not care. System will work and can be fine tuned. I think just more forgiving than tankless. They already had tankless installed and did not to spend extra for another heaterer, very understandable, just radiant is more sensitive.

Anyway your idea to raise water temps in the loops to 140f seems like a winning idea for your issues. Should definately heat much quicker. If you have an IR GUN to measure temps, or maybe with just temp probes you may want to check the outside temp under the floor. Measure from a cold start a see where it goes to. It does sound like there could be enough heat going through the floors. Probably not to much at 55f but as the floor reaches 70f heat loss will double when the out door temps are 40f.

The strainer maybe an issue. Once removed you may have to much flow. Now the water will pass through floor quicker but each unit/ molecule of water will not loss as much heat and will return hotter to the heater. Overall more pump speed means more heat into the space collectively, but individually will mean higher water temps returning to heater. If you are lucky you maybe able to put your smaller DC pump back in. Anyway i am curious to see how it turns out.

Keep posting. I try to learn everything by reading full installs and expirences. It fine and good to read theories, but to see them put in place and to see if they hold water is much more helpful.
The failires are just as important as sucess as they help you better understand design issues.


Oh your idea of keeping the addiontal heater out of the equation sounds very reasonable. Get the radiant working well and see if it is needed. Or definately have a toggle switch which allows you to turn off. Maybe only needed on very cool night into the 30s but radiant may work from 40f and higher.