Norbert;
Just got a reply from Alex and in reading it I noticed the "buried" text in this message on the boiler. My apologies for missing this.OK -- thanks for the offer. I'd be interested in your comments on the bell boiler at John McDougall's shop. My question is, is it reasonable to eliminate the storage tank?. Basically, you don't care about close regulation of the slab temperature, you just want to be able to dump the heat from a given batch burn of wood into the floor and use the slab for storage. Is it feasible to switch to a parallel loop layout, where you have large headers and a bunch of parallel runs, to reduce pipe friction and allow increased flow for a given amount of pressure from the pump? I know with an air core floor, for example, that this is the only way to do it.
You are on track with the parallel loops allowing for the highest volume of water and the lowest resistance to flow so that the maximum amount of heat is transferred to the slab. By using a concrete slab you do not generally need a buffer tank as the average slab can suck up millions of BTU going from 70 to 80F. Ideal comfort temp for a radiant slab in a home is 85F but in a shop comfort can be obtained by an active, dressed for work person at a lower temperature. Perhaps as low as 70F. Useful rule of thumb for heat transfer in a straight water system is 1gpm flow at 10F rise = 10,000 BTU. Most 1/2" pex loops of 250 to 300' are good for about 1 gpm without going to expensive high head pumps. The other side of this is that the typical delta T is around 30F so you can dump about 30,000BTU of heat per loop.
My thoughts on a mass heater was to more fully "bury" the "boiler" part of the heater in the mass of the heater so as to lower the speed at which you need to remove the heat making it more controllable and perhaps safer as the water is less likely to flash to steam.
Let me know if I can help more. I enjoy this kind of stuff.....
John-------------------------------------------------------------------------------------------------------------------------------
Hi John:
Thanks very much for your thoughts on PEX loops in concrete. I'll cc this reply to some of the other participant's in John McDougall's experimental boiler workshop.
Seems like using the slab as storage for a high output boiler is a viable idea.
Your concept of removing the heat exchanger from the heat is one that I have crossed path with a number of times. Including one-off systems designed by engineers that
in my view didn't work at all. There are lots of ideas out there, but nobody measures or collects data afterwards.
The very fist hot water coil I tried was a 4 loop run in the exit channel of a contraflow heater (directly in the flue gases), more than 35 years ago. It was a big flop.
The system I use in our own heaters right now is a very short DHW coil, right in the hottest part of the firebox. Small surface area, high delta T. It works pretty well for its intended purpose, is cheap, easy and simple. If the DHW or tempering tank is right behind the heater, it will thermosyphon with hardly any height difference. Nowhere near enough output for hydronic heating, however.
I also learned the hard way that if you try to put a big heat exchanger directly in the firebox, that is amazingly bad for combustion. Outdoor boilers are living proof of this.
Since I am trying to build the largest heater that I can that is also durable, having a bit of cooling at the hottest spot in the firebox can actually be a good thing.
The main issue with large masonry heaters is thermal shocking and thermal cycling of the refractories near the firebox.
Alex's Kuznetsov boiler to me is a great proof of concept of how a clean burning masonry boiler should work -- you want to remove the heat exchange from the combustion, and you still want to max out the heat transfer from the fire into the coil. Certainly, other schemes such as you propose would be very interesting to build, and measure. However, for sure you would be building a larger heater with more mass and a bigger coil (costing more money). It might make sense if you need closer regulation of the output, as you describe for a domestic situation. In essence, you are replacing the water storage tank with masonry.
You'd also need considerably more flue path to accomplish the heat transfer from the combustion. You then have to ask, "why not just heat with the heater, and forget the hot water?".
It is an interesting trade-off between investing in a larger and more expensive heating plant, and investing in reducing the heat load of the house. As you drop the house heat load, issues such as stratification and heat distribution tend to disappear. The big bonus is, you have to deal with way less wood.
Alex, for example, just sent in an article on a stacked high output set of heaters that he has recently built that will do 60,000 BTU/hr. That is about 300 lbs of wood, per day.
An upgraded R-2000 house in our 9,000 degree day climate here will get by on about 100 lbs/day, for a 3,000 sq. ft. house during the coldest part of the year.
Best .......... Norbert
--------------------------previous email---------------------------------------------------------------------------------
From: Norbert Senf <mheat@heatkit.com>
To: john wood <johnwood@oddpost.com>
Cc: Alex Chernov <alex_stovemaster@yahoo.ca>; jmc@ripnet.com; Joel Dick <jdontario@yahoo.com>; Ksenia Chumakova <aksinia@gmail.com>
Sent: Friday, June 5, 2009 4:51:59 AM
Subject: Re: Russian "bell" heater fan...
At 10:53 PM 6/4/2009 -0700, you wrote:
> Norbert;
>
> I have been desirous of building a "Russian" or mass heater for many years having been exposed to several built by a mason in Kalispll MT. I have also been reading all I can on the subject and have a reasonable understanding of Kuznetsov's bell system. Makes perfect sense! I am residing in Carson City NV and would like to build a bell style heater. Would you be interested in helping design one for me that I could work with a local mason on?
>
> My background is in construction, specifically plaster and stucco as a journeyman and contractor for years and then as a radiant floor heating contractor. (don't ask how it happened, just did and it was a good move..) I would like to do a nice sand finish stucco, somewhat like a southwestern kiva look. Have done some open fireplaces this way that look nice.
>
> If you are not able or available for this could you perhaps refer me to someone who is well versed in the bell type heaters and also in the top down firing? I believe that burning a top fire is cleaner and more efficient if the fuel is not going up as unburned carbon.
Hi John: I'd be happy to help you on the design. However, you should also check out Alex Chernov
http://www.stovemaster.com/html_en/home.html
Alex specializes in the double bell design, communicates directly with Igor Kusnetsov in Russian, and also does custom design for clients such as yourself. I'll cc him on this reply.
> Also; If you or your fellow masons would like some help with the radiant floor plumbing design, I would like to offer my assistance. (Just read the article on the bell boiler.)
OK -- thanks for the offer. I'd be interested in your comments on the bell boiler at John McDougall's shop. My question is, is it reasonable to eliminate the storage tank?. Basically, you don't care about close regulation of the slab temperature, you just want to be able to dump the heat from a given batch burn of wood into the floor and use the slab for storage. Is it feasible to switch to a parallel loop layout, where you have large headers and a bunch of parallel runs, to reduce pipe friction and allow increased flow for a given amount of pressure from the pump? I know with an air core floor, for example, that this is the only way to do it.
> Thanks for publishing the data you do on the MHA website.
Glad you find it of use ........ Best ......... Norbert
> Hope to hear from you soon.
>
> John Wood
-------------------------------------------
Norbert Senf---------- mheat(at)heatkit.com
Masonry Stove Builders
25 Brouse Rd.
RR 5, Shawville------- www.heatkit.com
Québec J0X 2Y0-------- fax:-----819.647.6082
---------------------- voice:---819.647.5092