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Old 02-01-2014, 12:16 AM   #1
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Hydronic Radiant Heating in a Bus

As a building Contractor, I've had the opportunity to install heating and cooling systems of all sorts. Most get the job done, but far less than perfect. Only one system covers all bases, is fully modular, and virtually limitless.

In the pages to follow, I will post pics, Tech, and ongoing research into how to install this all into a bus. Then in the spring I will install the system into the Haul All.

Some history.

The fist Hydronic Heating system I installed was in a small 416 square foot cabin. It's a realy small space, so I used a 40 gal propane hot water tank rated at 38 000 Btu output, but only 58% efficient. Two loops of 300 feet each run under the floor spaced every 6", laying in aluminum heat plates, under a layer of 3/8th OSB, fallowed by a layer of glue strip vinyl plank flooring. For redundancy, I used two Grundfos UPS15-58FRC 3-Speed Circulatory Pumps. System is a closed loop, run at 30PSI, filled with glycol.

Cabin has R60 in the floor and ceiling, R20 in the north and south walls, R12 in the east and west walls. All walls are wrapped with 1.5" rigid Styrofoam board decoupling the framing from the cold / heat of the outdoors.

Even with that realy low efficiency hot water tank, the Cabin uses less than $50 a month to heat. Potable hot water is done by a 12 gallon electric so the heating tank can be shut down in the summer.

Now it's the warmest / most efficient building on the farm. After that one install I was hooked. So was the guy who owns the land I live on. He has 2 more rentals, and his own house. All now to be converted to Hydronic Radiant Heating. At this time, a combination of propane and electric run the Hydronic Radiant Heating systems here. But in time they will all be converted to pulling heat from a massive, centrally located coal boiler. After that, this farm will finally start to make a sizable profit, rather than simply breaking even.

Nat
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Old 02-01-2014, 12:40 AM   #2
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Re: Hydronic Radiant Heating in a Bus

This Is my Revised system layout. My first layout used only one pump, but would have caused the tankless heater to short cycle under small loads. Also research indicates tankless heaters have internal restriction that must be overcome by a mid to large size circulation pump that use up to 2 amps at 120 volts. Trying to keep this system off grid, I added a smaller pump on the floor heating loop, and a custom buffer tank.

Click on the pic to view the whole picture.


This system uses a custom made stainless steel 60 gal Buffer tank that contains a 20 gal fresh potable water tank inside. Heated glycol from the tankless heater completely surrounds the fresh water tank. At the bottom of the outer tank are 6, 1" NPT pipe thread openings to accept common electric hot water heating elements, as well as low voltage water heating elements to utilize electricity from Solar and Wind. With this many heating element positions, I can use a 120 volt, 1500 watt, a 12 volt, a 48 volt, and three 240 volt heaters for when 50 amp shore power is available.

The configuration of the components allow for the tankless water heater to finish heating the loop if the alternative energy sources have failed to keep up to demand for heat. Main loop circulatory pump is activated by a temp switch located in the buffer tank's outer tank.

For high demand application, fresh water is directed through a flat plate heat exchanger before entering the buffer tanks inner tank. This way once the first 20 gal of heated fresh water is gone, the flat plate heat exchanger will have started heating as soon as the buffer tank lost heat. Hot fresh water flow should never run cold.

I also incorporated a flat plate heat exchanger and circulatory pump to heat engine coolant for preheating the engine. At the 199 000 BTU from the water heater, it shouldn't take longer than 20 min to bring the engine block up to near operating temperature. This would require manual activation of the Main, and the engine circulatory pumps.

I also added extra connections from the buffer tank for future heating loops. I could heat a fuel tank, or my tool trailer, or a fellow skoolie if they had a connection to their hydronic heating system.

Engine heat exchanger can also be used while driving to heat the main system. Both the main loop pump and the engine loop pump would need to be activated manually. Due to the engine coolant only reaching a set safe temp, there is no risk of overheating anything.

Extra heat loops can be connected to things like the wood stove using a different type of heat exchanger. However, this requires safety systems to avoid dangerous steam pressure build up. This I will cover separately in another post.

Nat
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Old 02-01-2014, 07:29 AM   #3
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Re: Hydronic Radiant Heating in a Bus

Nat,

Thanks much for posting this. I've been brainstorming a hydronic system myself.

In a previous post, you (at least I thought it was you) warned about taking care using care about possible leaks between glycol and potable water, as glycol is poisonous in even tiny quantities. I believe the recommendation you gave(WAS it someone else?) was to avoid cooking with the resultant hot water.

Playing devil's advocate, however, I'd expect that it's almost certainly going to happen someday. If not you, then a buddy who's a either few beers in and making ramen or a little foggy while making coffee one morning will likely say 'screw it' at some point. Murphy's law and all.

Wouldn't having the fresh hot water tank inside of the other greatly increase the danger of such a leak? Additionally, wouldn't you incur significant expense building the concentric tank?

Why not just use a single heat exchanger in a loop between a small hot water tank and a hot coolant tank, separate from each other? I'd think if your heat exchanger had enough exchange surface area, you could even get away without using a hot potable water tank at all. That would mean a single tank to hold all of your heat. This would only work if you planned on keeping your glycol tank significantly hotter than you you wanted your hot water. A 60 gallon glycol tank at 180* would store enough heat to raise 60 gallons of hot water from 40* to 110*, with a sufficiently large heat exchanger-- and if you had solar, engine coolant, propane, and/or a wood stove heating the glycol, too, it would be near limitless.

Just some food for thought. I'm pretty stoked to see your finalized system.

JDecker
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Old 02-01-2014, 07:40 AM   #4
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Re: Hydronic Radiant Heating in a Bus

Nat,

Here's one such heat exchanger I found with a cursory Google search:

http://www.pexsupply.com/Bell-Gosset...FYYF4godSRsAsQ

It's even rated for Domestic Water Heating:
Boiler Side: Water 180 Degree F Supply, 130 Degree F Return, Flow: 2.5 GPM, Pressure Drop: 1.6 PSI
Domestic Water Side: Water 50 Degree F Supply, 140 Degree F Return, Flow: 1.3 GPM, Pressure Drop: 0.3 PSI

What do you think?

JDecker
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Old 02-01-2014, 11:47 AM   #5
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Re: Hydronic Radiant Heating in a Bus

Thx JDecker

To avoid the possible contamination of toxic Glycol in the potable water, the system uses off set pressure differences between the fluids.

Most toxic is the Engine Coolant. This system is run at the lowest pressure of all. It is limited to the pressure held by the radiator cap, around 14 PSI.

Next is the Main Tankless heater loop filled with Glycol. This system is closed loop, and will be run around 25 psi.

Last is the potable fresh water Loop. It will be run at the highest pressure of all the systems, around 35PSI.

In the event of a leak in the custom buffer tank, or one of the flat plate heat exchangers, the lower pressure system will take the fluid transfer. With the potable water being the highest pressure, extra potable water would end up in the glycol loop. Upon inspection, it would be detected as a spike in the glycol loop pressure.

We can also use Double Wall Series flat plate heat exchangers. They have a air buffer between the systems, that is diverted to the outside of the unit so the leak can be visually detected.

Now we can also get non toxic Corn Glycol. At one time all I could get from our suppliers was the toxic industrial glycol. Now for $10 more a pail, I have the non toxic option.

Nat
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Old 02-01-2014, 11:50 AM   #6
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Re: Hydronic Radiant Heating in a Bus

Quote:
Originally Posted by JDecker
Nat,

Here's one such heat exchanger I found with a cursory Google search:

http://www.pexsupply.com/Bell-Gosset...FYYF4godSRsAsQ

It's even rated for Domestic Water Heating:
Boiler Side: Water 180 Degree F Supply, 130 Degree F Return, Flow: 2.5 GPM, Pressure Drop: 1.6 PSI
Domestic Water Side: Water 50 Degree F Supply, 140 Degree F Return, Flow: 1.3 GPM, Pressure Drop: 0.3 PSI

What do you think?

JDecker
Those are the heat exchangers I plan on using. If one is not enough, more can be added into the loop in series.

I like that site. Lots of good info, prices, ect.

Nat
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Old 02-01-2014, 11:55 AM   #7
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Re: Hydronic Radiant Heating in a Bus

Quote:
Originally Posted by JDecker
Nat,
Why not just use a single heat exchanger in a loop between a small hot water tank and a hot coolant tank, separate from each other? I'd think if your heat exchanger had enough exchange surface area, you could even get away without using a hot potable water tank at all. That would mean a single tank to hold all of your heat. This would only work if you planned on keeping your glycol tank significantly hotter than you you wanted your hot water. A 60 gallon glycol tank at 180* would store enough heat to raise 60 gallons of hot water from 40* to 110*, with a sufficiently large heat exchanger-- and if you had solar, engine coolant, propane, and/or a wood stove heating the glycol, too, it would be near limitless.
JDecker
The cost of the custom buffer tank will be around $1500 to have it fabricated. This is a special need in my system only for the use of Alternative energy. It also makes the system more efficient not having to use a pump to force the water across the heat source. This is realy important when all circulation pumps will be running off solar.

I will make drawings of more simple, less costly systems for others.

Here is one to start. This one is set up the way you mentioned. Hardest part to overcome, is the lack of ports on a electric water heater.
Using the store bought Electric water tank with only one element Limits you a bit. You have to decide if you want to be able to use it on 120, or 240 volt when running on shore power. Using it as a 1500 watt 120 volt, 5 000 BTU, water would take a long time to heat, but the propane could finish heating it. Using a 3000 watt, 240 volt, 10 000 BTU element, you could use the heat for space heating and potable water heating. Last using a 4500 watt, 240 volt, 15 200 BTU element, should be able to heat your bus, and potable water with no help from the propane tankless heater.

Click on the pic to view the whole picture.


Nat
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Old 02-01-2014, 12:00 PM   #8
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Re: Hydronic Radiant Heating in a Bus

Neat system. I'd also be looking at contamination issues with the dechilled cold water going back into the potable water tank. All the commercial hydronic systems I've seen have backflow preventers to keep system water from mixing with domestic cold water.

No idea whether this would work, but would RV antifreeze work in the heating loop? No poisoning issues with that.
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Old 02-01-2014, 12:17 PM   #9
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Re: Hydronic Radiant Heating in a Bus

Thx guys.

Quote:
Originally Posted by roach711
No idea whether this would work, but would RV antifreeze work in the heating loop? No poisoning issues with that.
Only approved glycol should be used with hydronic circulation pumps / systems. This is due to the mix of stabilizers, lubricants, and water tension additives that help the product do its job.

Other forms of antifreeze may contain dry alcohols (Methanol, Ethanol) that will destroy the system in a short time. Being RV antifreeze is food grade, I suspect the anti freezing agent to be a food safe Ethanol.

Quote:
Originally Posted by roach711
All the commercial hydronic systems I've seen have backflow preventers to keep system water from mixing with domestic cold water.
The commercial systems are preventing water that has been exposed to possible Bactria from water sitting at a neutral temperature. Food grade water (potable) needs to be treated like anything food grade. Storage needs to be hot, or cold to prevent the growth of harmful Bactria.

The loop I added to "Dechill" the water would only be used in cold environments, where having all that cold mass under my bed is a PITA. It would also work well to give the tankless water heater a good workout once in a while to burn the crud out of the system. Doing this prevents fouled burners that won't light due to constant low burn from small, on going loads.

Pasted from the site below.
"The FlatPlate DW Series Brazed Plate Heat Exchanger is a double-wall vented heat exchanger for isolating potable water in the safest possible manner. It is designed to meet local, state and provincial codes for double separation of potable water from boiler water, other non-potable fluids or refrigerants"

From this same site.


The down side is they cost twice as much.

Nat
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Old 02-02-2014, 09:07 AM   #10
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Re: Hydronic Radiant Heating in a Bus

sounds like a lot weight lots of pipes and things to go wrong just to heat a bus
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