Alternative Power sources - water furnace question....

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water furnace question....

hdivr@earthlink.net

2005-07-26, 10:21 pm

I'm going to build my own outdoor water fired boiler. I was thinking
of a hahsa design - where the firebox is surrounded by concrete blocks
and sand poured in to help conserve heat. I was thinking of a couple
of designs and wanted some input from people who have done something
similar.

First, I'm thinking of two possible ways for heating the water. In one
way, the firebox is actually a 55 gallon drum with 1/2 inch copper
tubing spiraled from the front to the back (say 100' or so). Not as
much water as a water jacket, but less chance of rust, leaks, etc.

Or, having the metal tank from a stripped out water water located on
top or a few inches above firebox. More water capacity, but I've been
reading when the fire burns low, the coals on the bottom of the drum
wouldn't really heat the tank above but in the first design, the copper
spirals would be right next to the coals.

Or I could just take the plunge and weld up a 1200 lb monster firebox.
Though I am leaning towards the 55 gallon drum idea. Especially if I
can design it where I don't have to have a "water jacket" around the
drum. If I keep it nice and dry and oil the interior after winter use,
could I expect many years from the barrel?

Everything else would be exactly like commercial units - damper
controls/thermostats/pumps/heat exhangers in ductwork and on water
heater, etc.

Anyone have any comments or would like to share their experiences???

Cosmopolite

2005-07-26, 11:21 pm

hdivr@earthlink.net wrote:
> I'm going to build my own outdoor water fired boiler. I was thinking
> of a hahsa design - where the firebox is surrounded by concrete blocks
> and sand poured in to help conserve heat. I was thinking of a couple
> of designs and wanted some input from people who have done something
> similar.
>
> First, I'm thinking of two possible ways for heating the water. In one
> way, the firebox is actually a 55 gallon drum with 1/2 inch copper
> tubing spiraled from the front to the back (say 100' or so). Not as
> much water as a water jacket, but less chance of rust, leaks, etc.
>
> Or, having the metal tank from a stripped out water water located on
> top or a few inches above firebox. More water capacity, but I've been
> reading when the fire burns low, the coals on the bottom of the drum
> wouldn't really heat the tank above but in the first design, the copper
> spirals would be right next to the coals.
>
> Or I could just take the plunge and weld up a 1200 lb monster firebox.
> Though I am leaning towards the 55 gallon drum idea. Especially if I
> can design it where I don't have to have a "water jacket" around the
> drum. If I keep it nice and dry and oil the interior after winter use,
> could I expect many years from the barrel?
>
> Everything else would be exactly like commercial units - damper
> controls/thermostats/pumps/heat exhangers in ductwork and on water
> heater, etc.
>
>
> Anyone have any comments or would like to share their experiences???
>

The type of fuel you will use - combustion temp. - may influence design.

Harry Chickpea

2005-07-27, 12:21 am

hdivr@earthlink.net wrote:

>I'm going to build my own outdoor water fired boiler. I was thinking
>of a hahsa design - where the firebox is surrounded by concrete blocks
>and sand poured in to help conserve heat. I was thinking of a couple
>of designs and wanted some input from people who have done something
>similar.
>
>First, I'm thinking of two possible ways for heating the water. In one
>way, the firebox is actually a 55 gallon drum with 1/2 inch copper
>tubing spiraled from the front to the back (say 100' or so). Not as
>much water as a water jacket, but less chance of rust, leaks, etc.
>
>Or, having the metal tank from a stripped out water water located on
>top or a few inches above firebox. More water capacity, but I've been
>reading when the fire burns low, the coals on the bottom of the drum
>wouldn't really heat the tank above but in the first design, the copper
>spirals would be right next to the coals.
>
>Or I could just take the plunge and weld up a 1200 lb monster firebox.
>Though I am leaning towards the 55 gallon drum idea. Especially if I
>can design it where I don't have to have a "water jacket" around the
>drum. If I keep it nice and dry and oil the interior after winter use,
>could I expect many years from the barrel?
>
>Everything else would be exactly like commercial units - damper
>controls/thermostats/pumps/heat exhangers in ductwork and on water
>heater, etc.
>
>
>Anyone have any comments or would like to share their experiences???

Unless you want a smokey inefficient monster, keep coils and water
jackets away from the burn chamber. If you insulate the burn chamber
to insure complete combustion, and then extract the heat after the
burn you avoid most of the creosote, soot, and smoke. Creosote on
cold copper pipes makes an insulator. 1/2 inch pipe doesn't allow much
flow. All this stuff has been done many times before.

hdivr@earthlink.net

2005-07-27, 12:21 am

I would burn hardwoods. The commercial units have their damper
controls shut down the fire after water reaches 180 deg and then open
the damper when the water reaches 160 deg. The water tank idea would
take longer to heat up but having a tank may lessen the furnace just
starting and stopping as often. Or, is the water storage needed as the
sand would hold the heat and then transfer it to the copper coils???
As you see, many questions.............

hdivr@earthlink.net

2005-07-27, 1:21 am

Creosote on copper??? I was thinking of wrapping the copper tubing
around the outside the barrel. Maybe tack welding it into place. One
long piece of copper tubing w/ no joints that could possibly fail.

You're right.....I was thinking 1" copper pipes (not 1/2 inch) that
would mount directly to the circulation pump. Sorry about the
confusion.

Carla Fong

2005-07-27, 11:21 am

hdivr@earthlink.net wrote:
> I'm going to build my own outdoor water fired boiler.
<snip>
>
> Anyone have any comments or would like to share their experiences???
>

I would ignore all other issues and rush to the Patent Office if you
have actually succeeded in firing a boiler with water.

<grin>

Carla

Harry Chickpea

2005-07-27, 12:21 pm

hdivr@earthlink.net wrote:

>Creosote on copper??? I was thinking of wrapping the copper tubing
>around the outside the barrel. Maybe tack welding it into place. One
>long piece of copper tubing w/ no joints that could possibly fail.

Creosote will deposit on anything that is cool enough and within the
combustion area. You also have to plan for what happens in worst case
scenarios. If you wrap tubing around the barrel and the circulator
pump fails, the tubing at the top will get hot enough to generate
pockets of steam, which will allow the copper to heat even higher,
which could reduce the strength of the copper, which could fail in the
presence of pressurized steam, etc. That is probably less
catastrophic than a pressurized tank failing, but a costly problem
non-the-less. In an outdoor furnace, you also have to account for the
possibility of the water freezing in the pipes, if the unit is left
unfired, due to a vacation or illness.

barry@sme-online.com

2005-07-27, 12:21 pm

Maybe you miss Harry's main point- physically separate combustion and
heat-transfer as much as possible, to boost combustion efficiency and
reduce emissions. You want the firebox to run just as hot as possible,
with careful admission of primary & secondary air. I'd do some
research also on how best to preheat secondary air. Ideally gas temps
in firebox should be well above 1000 deg F.

Then focus on transferring the heat. You may want just enough cooling
of the firebox to prevent it burning through. Internal insulation
around fire would help on both counts.

Many modern woodstoves incorporate much insulation around the fire- see
Morso, Rais, etc., etc.

HTH,
J

Loren Amelang

2005-07-27, 4:21 pm

On 26 Jul 2005 17:38:33 -0700, hdivr@earthlink.net wrote:

>I'm going to build my own outdoor water fired boiler. I was thinking
>of a hahsa design - where the firebox is surrounded by concrete blocks
>and sand poured in to help conserve heat. I was thinking of a couple
>of designs and wanted some input from people who have done something
>similar.

I use an 18" (H) x 18" (W) x 36" (front door to back end) welded steel
box, with fourteen three-foot lengths of 3/4 copper zigzagging across
the inside top of the box. I built a sheet-metal enclosure around the
outside of the box, and ducted it to the adjacent bathhouse, thinking
I would make use of the otherwise wasted heat. Amazingly enough, with
over 50KBTU/hr going into the water, the heat escaping through the
bottom, sides, and top of the stove barely gets the 8' x 12' bathhouse
to 80F - I had expected I would have a sauna! The heat isn't escaping
from my enclosure, I can hold my hand on the outside sheet metal
during a fire.

I'd say building a massive stove outdoors is counter-productive. You
have to heat the mass initially, and you can't efficiently extract the
heat later. Not like building a massive stove inside your heated
space, where the heat trickling back out is useful.

>First, I'm thinking of two possible ways for heating the water. In one
>way, the firebox is actually a 55 gallon drum with 1/2 inch copper
>tubing spiraled from the front to the back (say 100' or so). Not as
>much water as a water jacket, but less chance of rust, leaks, etc.

100' and a 1" circulator seems way more than necessary. My ~40' was
plenty (in a previous incarnation) with thermosyphon flow, and is way
overkill with my tiny DC circulator pushing it. If you have to use
100', divide the flow among several parallel paths. That probably lets
you use a smaller, less power-hungry circulator.

>Or, having the metal tank from a stripped out water water located on
>top or a few inches above firebox. More water capacity, but I've been
>reading when the fire burns low, the coals on the bottom of the drum
>wouldn't really heat the tank above but in the first design, the copper
>spirals would be right next to the coals.

You mean "next to" as in "under"? My stove has firebrick in the
bottom, so there is very little heat transfer in that direction. I'd
hate to think of going to all this work and not using firebrick to
prolong the life of the burn chamber.

The hot part of the coals is on top where the air is, and radiant
transfer works amazingly well from there to tubing inside the top of
the box.

>Or I could just take the plunge and weld up a 1200 lb monster firebox.
>Though I am leaning towards the 55 gallon drum idea. Especially if I
>can design it where I don't have to have a "water jacket" around the
>drum. If I keep it nice and dry and oil the interior after winter use,
>could I expect many years from the barrel?

If you line the bottom half with firebrick...

Some people mentioned creosote. Yes, it collects on my tubing. I made
a special long-handled scraper that can be run along each straight
section to strip most of it off. Surprisingly, using it doesn't make
much difference. Creosote may be an insulator, but it is also
amazingly black and non-reflective, and there is plenty of absorption
area available to catch the radiant heat.

The comment about your spiral wrap of tubing was very important. My
zigzag also zigzags up and down about 2" between two levels. Big pain
to deal with. Arrange your tubing so the liquid will cooperate if you
need to drain it! I've ended up with a closed loop antifreeze system,
mainly to protect the solar collectors that share the coolant, so I no
longer have to blow out the stove tubing with compressed air in
freezing weather.

There were several mentions of separating burn time from heat capture.
How do you think you are going to store enough heat in the stove to
make that work? Water is one of the most compact stores of heat, and a
good hot burn of my stove will heat 60 gallons of water over 60F.
Enough concrete and sand to store that many BTUs is going to be huge
and heavy, and the heat will go in and come out slowly. As the stove
store heats up, there will be less differential between fire and heat
sink; the last half of your fire won't accomplish much. In my system,
the control computer senses in and out water temperature, and can stop
the flow to capture the heat from the last handful of coals.

I realize there are higher-tech boiler designs. The main inefficiency
in mine is not capturing more heat from the flue gas, and as someone
mentioned, not pre-heating the combustion air. I'm not sure chasing
those is cost-effective, especially since I want to avoid the power
draw of combustion fans.

Hope some of this helps!

Loren

JoeSixPack

2005-07-27, 4:21 pm

<hdivr@earthlink.net> wrote in message
news:1122424712.911782.92190@f14g2000cwb.googlegroups.com...
> I'm going to build my own outdoor water fired boiler. I was thinking
> of a hahsa design - where the firebox is surrounded by concrete blocks
> and sand poured in to help conserve heat. I was thinking of a couple
> of designs and wanted some input from people who have done something
> similar.
>

First of all, fire is very erosive on metal. You could try burying your heat
exchanger in sand or behind fire brick. Metal drums tend to be fairly
thin-walled these days and are likely to burn out very quickly.

Shooting for maximum efficiency tends to bring on a load of problems like
condensation, added complexity and added expense. My suggestion would be to
go for reasonable efficiency and take the benefits from there.

If you're planning to heat water on demand, it could be very difficult to
do. My suggestion is to build in some sort of heat storage reservoir,
perhaps in the ground, well insulated against heat loss.

I know a farmer who heats his whole farm by burning anything he has at hand,
straw bales, logs, leaves or cardboard boxes. The firebox has a hinged,
counterbalanced lid, which can be opened manually, and is made to open
automatically when the tractor and front-end loader drives up to it. The
water continually circulates thru underground lines, and supplements a gas
boiler which originally heated everything.

nicksanspam@ece.villanova.edu

2005-07-27, 6:21 pm

JoeSixPack <olegp@telus.net> wrote:

>Shooting for maximum efficiency tends to bring on a load of problems like
>condensation...

....which can adds about 15% to the efficiency.

Nick

JoeSixPack

2005-07-28, 2:21 am

<hdivr@earthlink.net> wrote in message
news:1122433848.730016.237170@g49g2000cwa.googlegroups.com...
>I would burn hardwoods. The commercial units have their damper
> controls shut down the fire after water reaches 180 deg and then open
> the damper when the water reaches 160 deg. The water tank idea would
> take longer to heat up but having a tank may lessen the furnace just
> starting and stopping as often. Or, is the water storage needed as the
> sand would hold the heat and then transfer it to the copper coils???
> As you see, many questions.............
>

You would burn hardwoods why? Because they burn hotter? What if softwoods
cost half as much and produce 75% as much heat? I don't get your rationale.
I don't think it matters which kind you use if you have wood to burn.

nicksanspam@ece.villanova.edu

2005-07-29, 9:21 am

Harry Chickpea <hchickpeaREMOVEME@hotmail.com> wrote:

>Unless you want a smokey inefficient monster, keep coils and water
>jackets away from the burn chamber. If you insulate the burn chamber
>to insure complete combustion, and then extract the heat after the
>burn you avoid most of the creosote, soot, and smoke...

I second that, but why move heat with water?

Woodmaster's 1,340 pound model 3300 smokey monster has a water jacket
with R38 insulation around it. Its $3,600 price does not include a
circulating pump nor the 1" PEX pipe ($1.19/ft) nor the pipe insulation
nor the corrugated pipe surrounding the insulation nor the 100 gallons
of antifreeze nor the 2' trench to the house nor any house radiators...

Alternatively, we might put a horizontal 55 gallon drumstove in an box
near a house window and circulate air between the house and the box
through 2 10" round ducts in the lower part of the window with Grainger's
61 W 550 cfm 4C847 $72 10" round fan and 2E158 $14 room temp thermostat.
If the fan pushes 500 cfm of 70 F room air into the box and 170 F air
comes out, it moves about (170-70)500 = 50K Btu/h.

The drum box might be 2'x2'x4' long, made from a $30 4'x8'x2" sheet of
Atlas Energy Shield "R13.6" double-foil polyiso board (which merely
crinkles at 400 F) with a 10'x8" chimney pipe inside a 1'x2'x10' tall
chimney box on top of the drum box, like this, viewed in a fixed font:

barry@sme-online.com

2005-07-29, 2:21 pm

Anyone interested in balancing efficiency and clean-burning might want
to research the system UMO Mech Eng prof Hill put together some years
ago for the Audubon Center in (IIRC) York ME. Forced-draft,
very-high-temp insulated combustion, then heat transfer via smokepipe
~3" into large mass of crushed stone. Exhaust temp ~ambient.

Complete combustion made for essentially zero "crud" condensing in
exhaust. Water, ok. Dr. Hill designed various similar systems in the
late '70s- early '80s; some used hogged fuel at a couple $/ton. All
high-efficiency & aerobe-friendly. Like "DuMont boiler."

Bottom line(s):
If combustion is complete (high-temp, good air/fuel) low pipe exit temp
is okay.
But, if that temp is low draft is lousy and combustion efficiency
suffers.
Forced-draft breaks that linkage.

HTH,
J

daestrom

2005-07-29, 4:21 pm

"JoeSixPack" <olegp@telus.net> wrote in message
news:K7ZFe.107003$wr.101010@clgrps12...
>
> <hdivr@earthlink.net> wrote in message
> news:1122433848.730016.237170@g49g2000cwa.googlegroups.com...
>
> You would burn hardwoods why? Because they burn hotter? What if softwoods
> cost half as much and produce 75% as much heat? I don't get your
> rationale. I don't think it matters which kind you use if you have wood to
> burn.
>

Don't some of the softwoods require more frequent chimney cleaning? Don't
know for sure, but thought I heard that softwoods like pine and poplar build
up soot/tar much faster in the flue than hardwoods like maple or oak.

Not that one can't just clean the flue more often, but it might be something
to check on...

daestrom

hdivr@earthlink.net

2005-07-29, 8:21 pm

My father has a Hardy Wood fired boiler and loves it. As for creosote,
it never has bothered him. He said "So what if it gets creosote and
burst into flame??? Once the water gets hot enough, it shuts down the
air flow". So I figure creosote doesn't matter on an outside wood
boiler furnace. He burns everything in it - Trash, hardwoods,
softwood,etc. He did say that one time he saw a flame coming out of
the chimney that was probably a creosote fire, but it can't go
anywhere. I was looking for an alternative to spending the 4 or 5
grand for a good outside water furnace. I've seen the outside wood
stoves that blow air into your house, but I don't like the idea of
cutting a huge hole in the side of my house and then have uneven
heating. I like the idea of running two simple insulated water lines
to an exchanger above my existing electric furnace blower. I've read
some of the following ideas -
1) Split a 55 gallon barrel and adding a 12" strip, rewelding and
effectively making a 75 gallon barrel and then putting a 55 gallon
barrel inside it. Instant water chamber.

2) Wrapping a spiral of 1" copper tubing on the OUTSIDE diameter of the
fire barrel and circulating water continuously through it.

3) Similar to above, just making a 12 " coil that is situated about 8"
above the firebox (buried in the sand) that runs the whole length of
the firebox. No direct contact with firebox, but the heated sand
should warm the water in the pipes to where I need it.

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