Unique radiant application

zeke

There are hotwater heaters out there that have built-in heat exchangers for that purpose so tha you don't need to use an external heat exchanger.

I have a problem with the radiant source proposed, (the heart of the system proposed) obtained by "wrapping" coil around a drum. You have a significant heat transfer problem there that would have to be analyzed and designed very carefully. You are dealing with contact thermal resistance which is not only difficult to determine, but will surely deteriorate with time.

I would stay away from that part of the concept and leave it up to some serious engineering input and point out to the customer that you personally could not guarantee its performance.

L'town radiant

What do you think?

I was recently asked by customer to come up with a heating system design with some interesting variables. Here's what the job consists of:

-650 sqft area to heat, compacted earthen floor, heatloss of 16,869 BTU, 25BTU/sqft.

-Customer wants system to handle both space heating and domestic water heating. Want radiant heat in floor and domestic side to be very high efficiancy, all one heat source for both applications...well kinda. Here's where it gets a little different...The customer wants to use what is called a "Rocket Mass heater" that he is building. It is basically a high efficiency wood stove that is constructed with a 55gal drum. ( www.rocketstoves.com ) The stove is already its own kind of radiant heat source, but he also wants to tie it in to the radiant floor by wrapping the drum with a copper coil to transfer the heat. On top of all this he wants to have a back up heat source that will kick in when the Rocket stove can't handle the load and at the same time will be the primary source of domestic hot water.

-On the domestic side there is a small kitchen an one bathroom (entire living space is contained in the 650 sqft)

-Since the heat load is so small most equipment I would normally use is pretty much out of the picture. I was thinking of maybe using a residential water heater and recirculating through a braze plate exchanger and back into the drain valve of the heater. Or, as the customer wanted to do, use a tankless heater (Noritz) and basically do the same thing....I'm just a little leary of using a tankless heater in hydronic applications.

- I have attached a drawing of what I was thinkig of so far, this drawing show a tankless heater being used.

-Sorry for the long post....let me know what you guys think about this!

Kevin O. Pulver

I didn't even look

at the link, but RUN for your life.
A wood stove wrapped with copper tubing is not a boiler. Will it work? Maybe. Sounds like the stove would heat the space without the radiant in the floor.
Bid him insulation under his dirt slab, a heat loss analysis, and tubing layout and manifolds. Then write in the bid that you can hook up whatever rocketship he wants for T&M (If you deem it safe) but you don't guarantee it. Write in the bid that you spec. a Knight (Or your favorite here) and will guarantee that to do what he wants. I've been there and done that and got the T-shirt. I'm all about alternative stuff, but how many BTUs will his contraption transfer? You don't know, and he doesn't know either. Be careful. Kevin

hot_rod

a Bradford White CombiCor 2

would be perfect for that job.

Homemade boilers can be risky. Combustion air, return water sweating and cooling the flue leading to creasote issues. Temperature control, flashing to steam, on and on.

How do they qualify that as a high efficiency heat source? Any data to back up those claims? I'd guess 20- 30% wood to water efficiency, personally.

Check with your liability carrier if you touch that homemade solid fueled device

hot rod

L'town radiant

Yep, you would normally be right on the money with that....but in all honesty, this is a freind of mine who happens to be very in touch with his hippy self....so no worries about being responsible for the systems "complete success". Of course safety is important....he's completely aware of the "Maybe factor" for this job!

hot_rod

In my younger days

I built a very similar device. I used a 30 gallon barrel on it's side with a copper loop around it. We lived in a 12X 12 cabin in Montana, no running water, an outhouse, garden, etc.

The coil connected to a galv tank in the loft for DHW. Open system, thermo siphon.

Closed loop pressurized brings a lot more concern.

An old stem guru told me that a gallon of water is like a stick of dynamite when it flashes to steam, in a closed, unprotected systems!

Plenty of low, low pressure relief capacity if you do walk that road. B&G has some 20, maybe even 10lb pressure relief valves available.

hot rod

L'town radiant

Excellant point on the steam issue, thanks!

Unknown

If he's a friend, you need to help him figure out a "dump zone", preferably an unpowered one, using one of those valves that is "normally open" when not powered. Otherwise, the wood stove is a bomb waiting to happen.

I'd stick with the tank heater here. small loads are not friends of tankless heaters. Unless you want to use the rocket stove as an emitter/buffer tank maybe....

Weezbo

i took a look at it...

the first question that came to mind is..."Is he 'Responding to the medication ,', yet?"

that lash up might help him achiece his wish to not have to Wait for a hot shower though.

i think he would be dollars and time ahead to use it as a solar collector on the roof that way when it exploded he could wash down the entire building while he was at it.