Hydronic Radiant Heating in a Bus

[opus]

Originally Posted by nat_ster

I will have one for back up and versatility. However many of us need more than it offers at a much lower operating cost than it has to offer.

Nat

Mine costs me .35gph so roughly $1. 45,000btu. Wonder how that will compare to propane.

[taskswap]

Originally Posted by nat_ster

With a $400 propane hot water tank, you want to heat the water to the lowest heat that can still effectively heat the space. The hotter you have it set, the lower the efficiency.

All true. I should have clarified that solar is a big part of my design. Bigger storage heated hotter is better. (I think poetry isn't my schtick.)

Curious to know more about this boiler you were thinking of making. Was that a real plan or just a dream? I've built wood boilers but trying to make an efficient DIY diesel burner was just way beyond what I was prepared to do. I pretty much figure I'll be getting one on eBay at this point.

[nat_ster]

Originally Posted by taskswap

Curious to know more about this boiler you were thinking of making. Was that a real plan or just a dream?

To keep my system simple, I have no choice but to build my boiler.

100 gallon
It will be full 3/16th stainless.
Two internal one inch heat exchangers.
Six one inch NPT thread ports for the electric elements.
Four sets of one inch hot and cold ports for direct connection to zone pumps.
Propane burner unit that needs no electricity to operate. 76% efficient at 140 degrees.

The size is chosen for the ability to store the heat from my coal stove loop, the electricity of the day, the engine running if driving somewhere, Shore power, ect. It also stops my propane burner from short cycling.

When it comes to a diesel fired unit, there are burner assemblies available for the same set up. However they need 120 AC to work.
For my diesel backup I will just use a wabasto

Nat

[taskswap]

Wow... I thought I was going all out, but as usual you put others to shame. I don't even want to know HTH you're going to fit a 100-gallon tank just for heat storage in addition to everything else. Your bus is going to be something to see for sure!

I wanted to drop a comment on valves just for newbies who might read the thread. Personally I agree with Nat's opposition to zone valves - they're extra load and inefficiency in a system that's going to need a circulator anyway. They're done in houses mostly because you can throw a huge Taco 007 on there and it's cheaper to just have the one. But energy savings is all the rage these days, and they're quickly being replaced with delta-T setups like the Bumble Bee. Those are especially great for radiant.

But that doesn't mean you shouldn't have _isolation_ valves - ball valves (two per zone, one at each end) that are manual and always open unless you have a leak or need to service something. If you get any kind of leaks or need to replace a pump, it's super nice to be able to just close off the leaking zone/loop until you can deal with it.

For my part I think I'm just going to have two zones: front and rear. The front of our bus will be the living area, and the rear will have the master bed and bunks. This way we can draw a curtain across the front at night and let it be cooler to save energy (or vice-versa during the day).

Pro tip: take lots of camera pictures as you lay down your subfloor on top of your loops, and Sharpie in where the loops are. Nice to be able to "see" this if you have to drill a hole somewhere for a tube or wire you forgot to add originally...

[family wagon]

I'm curious to know whether any of you has done a heat loss calculation for your bus, or whether the heat figures are more-or-less educated guesses.

The closest I've come was a little experiment I ran last winter: two electric baseboard heaters each about 7 feet long and with maybe 5 feet between them, roughly centered in the bus. I left one temperature sensor inside the bus and another outside; both logged through the night.

The two heaters were rated 2250 W each (I didn't verify it). I left them continuously powered all night (no thermostat). The minimum outdoor temperature was 14 F at 5:47 and 7:42 am local time; the temperature in the bus was 57 F. So nominal 4.5 kW was able to hold a 43 F temperature difference.

I figure that:

• I probably won't be RVing in temperatures that cold very often
• even if I do, nobody is going to suffer at 57 F and it'll warm very quickly when the morning sun rises
• things can only get better when I delete half the windows and add more insulation

So for me 5 kW/hr or 17000 Btu/hr of space heat is probably adequate. My bus came with an Espar D12W, but its burner wick is unobtainium, so I've had my eye on those 5 kW Webasto or Espar heaters pulled off a European car from eBay instead. Unfortunately, my estimates for water heating indicate that a respectable shower is going to demand more heat.. maybe two of the "parking heaters" will do!

[taskswap]

I'm not sure if you're talking to nat_ster or me. For myself, I haven't done a heat-loss calculation, mostly because I have no way to do it accurately - there are SO many variables involved in a custom build like this that you'd have to actually measure it to really know for sure. It really ends up being a judgment of work quality, doesn't it?

What I do know is that I heat my house now with a 130kBTU/hr oil boiler and a 100kBTU/hr wood boiler. (The wood is the primary, and the oil is the backup if we're away to keep the pipes from freezing). This is a 2000 sq. ft. poorly-insulated house with terrible windows in the back woods of CT - for reference, the weather channel says it's supposed to be 19F outside right now, but because of our valley location and tree cover, it's actually 12F at our house.

Given all this I don't think it's at all unreasonable to expect to be able to heat a well-insulated (I plan to do spray foam and all that) small (~300 sq. ft.) space with a 17kW/hr unit.

For shower water, we plan to boondock only part-time, mostly for pleasure - the reality is that I still have to work and we're traveling with 3 kids. When we aren't "vacationing" we need the electricity. Off-grid solar might be great for some and I do plan to install a few panels, but I don't expect it to make up 100% of our demand. We're just realistically not the kind of healthy, well-balanced people that can make off-grid living a reality.

That means full hookups and generators. THAT makes a standard electric hot water heater a good component in this kind of system. Primary will be solar (hot water, not electric) - when available. Secondary will be diesel, making up the difference when solar isn't cutting it. Tertiary will be electric, directly in the tank. I could add more options but I honestly don't expect to need it.

[Missourileo]

I just read all five pages of this................Amazing ideas here. I am building my bus on paper, before I even buy one. When it comes to potable hot water, I'm leaning towards sweating together a nice copper array, powdercoating it black, encasing the whole works in a home built solar box and mounting it on top of the bus. Run said piping to the shower and sinks, then to a return tank(electric/gas water heater), small GF pump to push it back up to the collector for reheat. This would create a loop system for potable water with an electric/gas backup for cloudy days. Complete with iso/drain valves for cold days, to drain the solar section and rely on shore power or gas.
Still on the fence about heating for the bus. I will be in a 30 Pax more than likely, much less space to heat/cool, and I will insulate very well. I like the idea of radiant heat and think it has great potential for use in the bus. Open to ideas. I wonder if it would be efficient to run a larger storage tank and run copper pipe in the subfloor, tie it in to the potable system. As a pipefitter, I'm a fan of copper.

[zoomy]

SO not in floor heat but i'm trying to figure out my water system specifically the hot water because I want to have alternative heating methods. in the diagram below the very simple drawing on top is a tried and true water heater that I grew up with. hot water tank elevated above heating coils, 4 outlets to the tank hot and cold intake and out put then tank water to and from heating coil. the heating coils was 3/8" copper tubing coiled around the 6" chimney pipe. 6" pipe x pie 18+" time 10 coils a little better than 15' of coil creating thermal up lift and cycling the water WITH OUT any pumps or moving parts. only 2 cons to this. 1 too hot a fire and the water would boil in the coil... not bad just make funny sounds and then the pressure valve would vent. 2. we had hard water so every few years the coil would lime up and we would have to replace it. my dads advice was to use coolant/ oil in the coil.

this is where i need you guys the bottom part of the diagram is my skoolie blue is cold water, red is hot water, green is coolant. i'm going to have a disconnect panel going to the solar for movement and possibly for cold months, wood for winter, and LP heater if I end up some where with no room for panels and to hot for wood. now the question is where do i place the heat exchanger and the oil reservoir where i can still capitalize on the thermal moment and reduce the need for 3 pumps for the system.


the feed in to the bus is looped so when i take it to cold climates there will be more circulation to keep the pipes and tanks from freezing. i also wanted to have the heat exchanger in the under storage with the tanks but i'm not sure if that will be conducive to thermal flow.

also i thought i had an exchanger lined up that would be conducive to thermal flow but this is all i can find now.
50 Plate Wood Boiler Heat Exchanger 1" Ports Outdoor Wood Boiler Radiant Heat | eBay

let me know your thoughts

[Eden]

if this has already been covered, I'm sorry I missed it, but is it possible to run radiant floor heating with water using the same L5 eccotenp tankless heater as runs my bath or sink water? or at all?

[john61ct]

Yes, anything is possible with knowledge skills and tools.

Finding a pro willing to think outside the box can be difficult.

Maybe best to start your own thread.

[o1marc]

I don't see why you couldn't "T" off of the hot water out line to supply the floor. Check the limits of how long the heater can run.