I built a wood-fired boiler to heat the house some thirty years ago. It is basically an airtight stove with a manifold constructed of 1-inch schedule 40 steel pipe (A53). All the pipes of the manifold pitch uphill at about 1 inch per foot. The cold water in is on the left side lower corner and the hot water out is on the top left corner, but it runs the length of the fire box and the entire manifold consisting of about 100 feet of pipe is free to expand and contract while the cold water in is in a fixed position.
The water circulates through the manifold and up through a 15 gallon stainless beer keg that sits atop of the firebox. A reverse acting aquastat kicks in at about 180 degrees F and circulates the hot water through the baseboard in my home. When the temperature drops to 150 degrees, the aquastat shuts off the circulator and the water is heated in the tank by convection once again. The system heats the entire home with a temperature differential of only about 3 degrees room to room. The circulator only activates when the water is sufficiently heated so that it does not have to run continuously. The secret is to pitch all the pipe upward to allow for convection and to include a loop so the water can circulate through the manifold and the holding tank (beer keg).
The pressure needs only to support the hydrostatic head, which in my two story home is only 10 feet (about 5 psi) since the boiler is located in my living room. A wall covers all the interesting stuff so my wife does not have to look at it. She put up with all the pipes and beer keg exposed one winter, but insisted it be covered by the second winter. Women have no sense of style.
There are two blow off valves in the system. One at the beer keg plumbed in with with pipe to vent into the basement where it can collect at a sump. Then there is a second blow-off on the original boiler system, which is plumbed into the wood-fired boiler as a backup should the primary fail to activate. The system was hydrotested to 50 psi when I built it, so there is plenty of safety factor built in. Should the electricity go out, which it does once or twice a year, I have an inverter in the van that will power the circulator, refrigerator, television, etc. You know, the essentials.
The operating pressure is well below 15 psig, so it is legal in my state.
I almost forgot to mention, the front of the boiler opens (about 15 X 20 inches) so I can use it as a fireplace when I want to watch the flames flicker. While most fireplaces act as a huge vacuum sucking all the hot air out of the house, this one recovers the heat and sends it through the baseboard radiators.
I am trying to get around to modifying a pellet stove because I am too busy to split wood and I am too lazy to carry the wood it into the house. It is just a matter of finding the time to do what I want to do. I have got the stove; now all I have to do is rip out the fireplace and connect the new improved design. For the most part, it will be similar to the existing system.
Best regards - Al
Pipe size should be fine either way but thicker will last longer. I would however offset the tube and coil about 3 lengths to provide more heat surface area in the fire chamber.
The 1 inch schedule 40 pipe has lasted thirty years without a problem. The corrosion rate seems to be rather slow. Once the system was in use for a while it appears the corrosion rate may stabilize because the water is recirculated rather than being replace with fresh water. To be honest, I didn't think the pipe in the manifold would last as long as it has.
The piping in the system is mixed, i.e., copper and steel. Maybe the heavy coating of pipe dope between the steel and copper fittings has helped insulate the two electrically from each other. Then again, it might be ready to pop a hole somewhere in the system this afternoon!
Best regards - Al
interesting AL, I've been meaning to build an evacuated solar hot water system, connected to the cold water feed of a standard hot water heater. On sunny days it should be capable of taking care of 100% of my hot water needs. First I need to own a house though.
In looking at your diagram everything makes sense but I see you have a return line out of your holding tank to your cold water feed with a check valve. Excuse my ignorance, but what is the purpose of this line and how does it return water to the "boiler"
You should also consider Geo-thermal if you end up purchasing a home where it is available to tap into... California has a bunch of locations where Geo-thermal (24/7availability) can be readily accessible, and installed rather inexpensively. ;) Something else to consider.
Respectfully,
Henry
yah I've been reading up on the "passive house" standard in Germany and Sweden. With some upfront engineering and design consideration, a house can be built to need no supplemental heating or cooling. economies of scale in germany mean they can be built only slightly more expensive than a traditional built home but with no heating or cooling bills.
One can also generate electricity with this system as well, because the steam is readily available to have a small turbine generator hooked up to the system and Voila! Utility Bills??? What's that??? ;) ;) ;) We have a system installed in our family's "Finca" down in the Dominican Republic that my dear Grandfather designed, and installed because we needed both heat, and cooling as the "Finca" is situated right by the base of Monte Christi which is the tallest mountain in the Dominican Republic.
There they even have snow at the top in the tropics of all places!!! :) :) :) We have more than enough electricity available, so we give the excess to the neighbors, and when none of us are there, they keep a close watch of our land as part of living in harmony with one another! ;) when I know there is no longer any hope for me to keep on fighting this disease... That is where I'll want be so that I can pass in peace, and in paradise to hopefully a greater paradise than what I know of there. ;) In the meantime, I might just go down there after the Holidays to spend some R & R once the treatment is done and I get permission from my Doctor, or not!!! :) :) :)
Respectfully,
Henry
I wasn't aware of Geo thermal systems being used economically in home scale systems. I thought the pipe/ water recovery had to be driven relatively deep.
The systems I'm more aware of are thermal mass, heat pumps, and
http://en.wikipedia.org/wiki/Annualized_geothermal_solar annualized geothermal solar systems.
As well as theories like
http://en.wikipedia.org/wiki/Passive_house the passive house and super insulation.
My dream has been to build a net-positive house, that produces more electricity than I use. Not so much for all the "green" reasons but because I want to stick it to the man and have the electrical company pay me. Also i'm an engineer and I like to tinker with such things. I was thinking of building a solar thermal system system that cogenerates both heat and electricity by using a steam system for electricity and having the condenser feed the hot water heater. I was going to start small and build a solar thermal hot water heater first.
Joel,
We know that you're an engineer already, so there's no need to constantly remind me of this for whatever reason you choose to do so... Now to focus on your previous "presumption" that one had to drill deep, and afterwards install enough piping to tap into Geo-thermal is not the case as it is really dependent on where your house, place of business is to be located... In other words, some locations offer Geo-thermal energy potential more so than others, and if you find a location where it is readily available without having to drill so deep into the earth in order to tap into it... For instance, if you can find a location where there's a hot spring nearby, one can tap into that without the need for such extensive drilling or layinog out so much piping which is what my Grandfather discovered in the early fifties!!! Remember Joel, Geo-thermal has been around for a long time, and has been adapted for many uses since including recently - relatively speaking of course, to generate electricity.. So it really depends on the location of the energy source, and what is required in order to tap into it. Btw, my Grandfather was an engineer also, only he didn't have degree! ;) Had you have known him, you would not have thought that for a minute! ;)
Respectfully,
Henry
Our first solar water heater was a home built, made of 3/4" copper vertical tubes on a 1" header with copper flashing soldered to the back of the pipes. It was in an insulated box and had a discarded thermopane patio door for a cover glass, This worked well, but it was a fresh water system and had to be drained in winter. It was built largely of salvaged materials, except the pipe fittings, which were numerous.
About '80 We went to a manufactured system that used glycol and a heat exchanger. This system is still in operation today, but I did have to change the tank several years ago.
My buddy in California is instaling a PV solar/electric system. After all the rebates & tax incentives, it will cost about $40K out of pocket [bank]. This is for an 8 KW system. The plan is to keep the avaraged monthly bills in the lowest cost use range [5,000 KWH/month or less]. Suposedly the anual cost for grid power should be about $500. Their house, pool & irrigation uses a lot of juice. California law is favorable to on grid solar, go for it.
The so called geothermal, really a ground couppled heat pump is a good system any place You can drill a well & get water. This increases the efficiency of both heating and cooling, as the 52 degre water temperature works well both ways. My cousin has a home in southeastern Pa. using this system. water comes from and is returned to the same well.
The solar/steam/electricity project is a bit more ambitious. Another cousin of Mine built a model as a school project in the '70s. He did manage to light a flash light bulb from a generator powered by a model reciprocating steam engine. He used a concentrating reflector.
Remaining on grid with solar makes the most sense. It gives You backup and surge capacity at very little cost to You, and eliminates the need for storage. California's buy back & averaging laws ar extremely favorable to the homeowner. Just by participating in the program You are "sticking it to the man".
The "ball type" check valve allows the water to circulate through the manifold and holding tank by convection. It prevents the cold water feed (from the circulator pump) from pushing cold water directly into the hot water holding tank, but instead forces the cold water through the manifold before going into the holding tank.
Best regards - Al
I just had an " OH!" moment.
I got the function of the check valve but I was failing to understand why there was a return line directly off the storage tank. Is it used when water temperature in the storage tanks drops too low so it is sent back to the boiler for reheating? Otherwise I would of thought a a single loop system would be much less complex.
In the summer any plans on using the radiant heat system for AC?
Now you have it. When the water temperature in the tank hits 180, the circulator dumps the heat by pumping it through the baseboard radiators. When the temperature drops below 150, the circulator pump stops and the water is circulated through the manifold (in the firebox) and up to the holding tank by convection. When the temperature of the water in the holding tanks hits 180, the circulator pump kicks in again.
Without the check valve, the circulator pump would simply circulate the cold water through the holding tank because water, like electricity is going to follow the path of least resistance. The manifold with its 100 feet of pipe with a multitude of bends would represent higher resistance, so the water would bypass it and go through the holding tank. The check valve forces the cold water through the manifold before going into the holding tank.
Believe it or not, the system was fabricated because the airtight fireplace was too hot for the living room and I had to have a means of getting rid of the excess heat. The manifold was the mechanism to accomplish the task and it heated the entire house in the process.
I used it for about twenty-five years. Then I got tired of splitting wood and carrying into the house. I purchased a pellet stove, but I have to convert it before I install it in the living room. Before that can happen I have to pull out the existing fireplace, which was originally a zero clearance fireplace the previous homeowner started, but never finished.
Best regards - Al
That makes sense now. Simple enough design.
As this isn't under floor radiant heat, it sounds like it wouldn't be practical to have a single loop where the water made one pass through a boiler, out to a small tank for expansion reasons then to the radiators and finally back to the boiler in one line. I've seen systems like that, and they don't use a return line like that. That's what confused me.
I'm not saying it is the optimum design, but it is straight forward without too many bells and whistles. The important thing is that it worked and did its job for many years.
Best regards - Al
that's all you can ask for. Perfect only exists in calculations. It takes a lot of hubris in an engineer to think they can build the most efficient or optimal system, and have it work in the real world.
That is an interesting approach, batch heating the water.
The system I mentioned at Our house had another, larger colector made from finned tube on the sides & back of the firebox. These fed to the base rays & radiators in the house and would circulate by convection. Due to the way it was plumbed, the water flow was opposite from what the circulator provided.
The stove was in the basment, a lot of heat went to the house by convection, right up the steps. This carried dust & ash with it, because My Dad did not keep the area around the stove clean. Mom put her foot down and there was no more wood stove, but for about 20 years it heated the house and provided heat to the solar setup regardless of sunshine.
Water in a closed system like a boiler becomes less active, rust is not generally a problem on the inside of the pipes. The boiler I took out of the house in 2001 had been in place since '52, There was practically no rust on the inside. This system had a steel boiler, cast iron radiators and copper pipe.
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