Shop heating system, thinking out loud.....

[Larry Edgerton]

My new shop space is 36x48, 12' ceilings. I miss my 148'x50' shop, but not the heating bills. My new setup is all about low overhead. I have three ex-wives and so am never going to be able to actually retire, but my goal is to cut down on the number of hours I have to work till it becomes fun again.

So.....

I do not expect gas pricing to go down, and my old shop the bills were up to $1600 on a bad month. My new shop is on a wooded piece of property with an endless supply of deadfalls, but.... I don't really like to cut wood that much. The shop has a long wall facing directly south. On this wall I will have some kind of solar and the system I have in mind is a hybrid. I would discount hot air solar as it is of no use at night when I need it most.

Hot water solar on the south side, and on the north side there is a small cement block building about a foot away from the shop. This is where I am thinking of putting the wood boiler. It is in a seperate building, so no insurance problems, its block so no fire worries if I fireproof the ceiling.

Now here is my latest idea, and the one I am not as sure about. I would like to tie the two systems together with a common heat sink. I was originally thinking a 500-1000 gallon tank under the floor, this haveing the advantage of any heat escaping ending up in the shop anyway. But.... the problem with this system is that it would require two pumps, and the controls that go with it. Violates the KISS principle, the more you have the more it will break. Also in the case of a pump/control failure there is a chance of a system rupture from overheating.

So my latest thought is an elevated tank, common to both the solar and the wood boiler, the bottom being about the height of the top of the solar panels and of course above the boiler. Natural convection would be the pump system, as the water is heated in the boiler/solar heat sources it would rise and be dumped into the top of the tank, and cooler water at the bottom of the tank would be drawn to the heat source that needed it without any controls or pumps other than natural convection.

Now before you laugh, I have done on a smaller scale this same thing. I ran a loop around a woodstove in copper and to the top and bottom of a water heater. It was so effective that I had to choke it off as it would blow the pressure relief valve. So I am thinking this same idea on a much larger scale. Flow restrictions because of the distances involved are my concern. Will the flow restrictions overcome the power of the natural convection? Ideal size of the storage tank? Anyway, these are my thoughts and I would be happy to hear your thoughts, no matter what they are.

As far as the structure that is not a problem, just the flow characteristics, and the interaction of one system with the other.

And the missing link. Out of this tank the water will circulate to an infloor heat system in concrete, and this will of course require a pump. If this pump fails the water tank will be losing some heat, and there will be a gas fired backup heater as well in case I ever take a vacation.

Cost? cost would be too high if I had to buy this, but I have the capability to make all of this stuff myself. So piping would be my biggest expense and I have been hording stuff for some time.

Thoughts?

Larry

[Steve Meliza]

Would it make any sense to hire some young buck to cut, chop, and stack wood so you can just heat with a simple wood stove? It doesn't capture "free" solar energy, but it is about as KISS as it gets.

[Phil Thien]

My only thought is a question: When you have that large a heat sink, would it be tricky to maintain a temperature that isn't too warm (to make the shop uncomfortable) but also stores enough heat to derive a benefit during the night hours?

I don't know ANYTHING about this stuff (as I'm sure you can tell), but if I could have a separate building for the boiler, I'd also try to have a separate building where I could super-heat a lot of water. I'd want to absorb as much energy from the sun as possible. Then I'd draw that heat-off throughout the day and night as needed.

[Larry Edgerton]

No, that does not make sense. Try finding a kid that wants to work for starters. Now suppose that he gets hurt. He now owns my house. then I would have to feed the stove for the months that the solar would do the job alone.

No the system I have devised will heat the shop for about four months of the year with just the solar, and need a boost with the wood for about three. I am not afraid of work and actually enjoy these kind of projects. If I truely wanted to be practical I would have an auction and sell all of my tools and get a job as a greeter at Wallmart, but simple is never my way.

I'm building a replica of a one room schoolhouse on the same property for my home. If I used that line of thought I would have built a simple ranch and already be there. The shortest path is a straight line, but I have never taken that route......

Larry

[Jim Andrew]

If it's a new shop, did you put in a lot of south facing windows? That's about all passive solar is, orienting your building east and west so you have a long wall for windows. You might consider what I am doing, putting a wood furnace outside the shop in a small steel building, and ducting into your shop. They don't burn a lot of wood, and my plan is to burn my scrap along with some firewood. Guess if your block building is close enough, you could put the furnace in there.

[Randy Henry]

Larry,
I went through all of this a couple years ago, albeit not to your size. I considered an outdoor wood furnace that heats the water up and sends it in to a radiator, but when I talked to several friends that have them, they all said to stay away from them. Reasons: they will leak eventually, and if you are away for a few days and it gets cold, you have to drain the lines and tank, or suffer possible freezing/line breakage. I also considered putting a few more windows on the south wall, but doing that would make it that much more harder to cool in the summer. I know you don't want the wood option, but I went with a forced air wood furnace, made by Bryan. When I built my home 15 years ago, I went with GEO thermal. If I had been thinking, I would have got a bigger system and added a couple trunks to attach to at a later time when I built my detached shop. GEO is about the best system I have come across as you get heating/cooling/hot water all with the same setup.

[Dave Wagner]

Solar could work, but of course, not when the sun goes down, but could get the temps up so it stays warmer longer for free!

here is a good solar DIY site and some GOOD easy projects.
http://www.builditsolar.com/Projects...ce_Heating.htm

As an experiment, I build a small Solar collector to see if it would work for my garage, and it DOES! It doesn't raise the temps up that much. I used an old window, some downspout material, built a box, etc....It gets about 150-160 degrees coming out of it. I put a small blower on it to move the hot air. I just need to make it bigger now!!

[Marty Studer]

I like the idea. I would prefer the under ground tank. The residual heat into the shop and not having to get the tank to the high spot. Additionally it allows you to put most or all of the pipe underground and remove the chance of freezing. We use a similar solar set up for an indoor swimming pool. When we keep the pool warm it certainly heats the building. You will have use a glycol mixture in the solar to avoid freezing at night, but that's not a big deal with what you outlined. As for pressures, why can't you just build a relief valve into a pipe under the concrete and vent it outside the building envelope. I would think the two pumps would work together with the proper routing and some one way valves, put in a small photovoltaic panel and batteries to run a couple of dc pumps to move the water through the system. Sounds like a fun project, good luck.

[Carl Beckett]

Larry, a couple thoughts (yes I have some background in alt energy systems):

Natural convection will move the water - the 'friction' losses approach zero as the velocity of the fluid approaches zero. This means fluid has no pipe friction loss until it actually starts flowing. This doesnt sound like a problem.

Structural concerns on large water mass up high I wont comment on. (other than, there ARE some! - keep it safe!)

For most of these type of systems - ITS ALL ABOUT INSULATION!! The more you insulate your shop, the less heat will be needed. Thermal storage systems have to be insulated or the heat will be lost to the surroundings, instead of stored. This includes storage systems underground. So plan on a well insulated system.

Any closed fluidic system needs pressure relief safety valves, consideration for freezing, corrosion, and even structural design to consider weight.

A different approach I have been contemplating is a geo thermal WITHOUT the heat pump. Since I dont try to keep my shop that high in temp, and since going below the ground surface a few feet is relatively constant in temp - say mid 50's F - you might be able to keep your shop above freezing simply by recirculating to an in ground heat exchanger (geothermal typically uses a large trench with coils of plastic tubing). You have the cost of running the recirc pump in this case. But it depends on how warm you are trying to keep it.

[Carl Beckett]

here is a good solar DIY site and some GOOD easy projects.
http://www.builditsolar.com/Projects...ce_Heating.htm

Great site Dave, thanks for sharing!

[Ron Natalie]

If you want to be clever with sources, you can put in radiant heat (which is really nice I've got it in my shop). You can then heat it (it doesn't take very warm water, 120 degrees is plenty) from solar, geothermal heat pumps (what I have), propane, etc.... Here's a pretty good DIY source, my neighbor installed his own with materials from them: http://www.radiantcompany.com

[Larry Edgerton]

Larry, a couple thoughts (yes I have some background in alt energy systems):

Natural convection will move the water - the 'friction' losses approach zero as the velocity of the fluid approaches zero. This means fluid has no pipe friction loss until it actually starts flowing. This doesnt sound like a problem.

Structural concerns on large water mass up high I wont comment on. (other than, there ARE some! - keep it safe!)

For most of these type of systems - ITS ALL ABOUT INSULATION!! The more you insulate your shop, the less heat will be needed. Thermal storage systems have to be insulated or the heat will be lost to the surroundings, instead of stored. This includes storage systems underground. So plan on a well insulated system.

Any closed fluidic system needs pressure relief safety valves, consideration for freezing, corrosion, and even structural design to consider weight.

A different approach I have been contemplating is a geo thermal WITHOUT the heat pump. Since I dont try to keep my shop that high in temp, and since going below the ground surface a few feet is relatively constant in temp - say mid 50's F - you might be able to keep your shop above freezing simply by recirculating to an in ground heat exchanger (geothermal typically uses a large trench with coils of plastic tubing). You have the cost of running the recirc pump in this case. But it depends on how warm you are trying to keep it.

Jim Thanks for the input. On the friction losses, I have no idea how fast the water would flow with natural convection, but I would not think it would be extremely fast? I was thinking 1" feed and return, but maybe bigger would be better? I was going to use copper on the feed side because then I would not have to worry about temps getting to high and plastic on the return to cut costs.


Structurally I have a bunch of large I beams that I salvaged off of a job and was figuring on using these if I go overhead. I purchased a 500 gallon fuel oil tank yesterday that I may use. If not I'll use it for my tractor. Size of the tank is another question. How many gallons will it take to do what I want. If I go with too big of a tank I can always let some licquid out, but where to start. I need to find a way to calculate the heat that can be removed from one gallon?

The block building that the stove would be in is less than a foot from the barn so as this will be overhot as it is only 8x12 I figure on running the lines through a connecting duct that will circulate the excess hot air into the barn.

As far as pressure relief, I was figureing on the circulating loops from the heat sources being open to the tank, and some sort of vent on the tank above water level to allow for expansion and contraction. Would I need to pressurize the infloor heat section to make it work correctly? I have infloor in my current house and it runs at 20 psi, but I was thinking of more of a garden hose sort of affair pulling hot water from close to the top of the tank, pushing it through the Pex and returning it to the tank with no pressure. Maybe I should put a coil of pex in the tank and keep the floor loop a closed system?

I like Geo, but I am above the 45th parralel, so they are marginal up here. And I have to do this with the least amount of money. Ground loop would not be bad, give me an excuse to buy a backhoe [ugh, ugh, ugh] but not in the cards right now. Well systems now require a closed system with a return well here now, no more pump and dumps. But, I just can not afford it is my main issue with Geo.

Thanks, Larry

[Larry Edgerton]

Ron and Dave

Thanks for the links, I'll read up on them.....

Larry

[Larry Edgerton]

Larry,
I went through all of this a couple years ago, albeit not to your size. I considered an outdoor wood furnace that heats the water up and sends it in to a radiator, but when I talked to several friends that have them, they all said to stay away from them. Reasons: they will leak eventually, and if you are away for a few days and it gets cold, you have to drain the lines and tank, or suffer possible freezing/line breakage. I also considered putting a few more windows on the south wall, but doing that would make it that much more harder to cool in the summer. I know you don't want the wood option, but I went with a forced air wood furnace, made by Bryan. When I built my home 15 years ago, I went with GEO thermal. If I had been thinking, I would have got a bigger system and added a couple trunks to attach to at a later time when I built my detached shop. GEO is about the best system I have come across as you get heating/cooling/hot water all with the same setup.

Randy, I agree with you that outside boilers do just not make sense. The payback is just not there in the expected lifetime of the system, and you tave to cut almost twice as much wood due to losses, depending on setup. Lets see, cut 10 cord, or 18 cord?

In my new house that is on this same piece of property I did the research and put a wood furnace in the basement. All losses end up in the house and I built a totally concrete sealed wood room that can be fed from the outside. Fill it, throw in a bug bomb, and I am good for the winter. And I don't have to go outside on a cold Sunday morning! I have gas backup as well.

I would have liked to have a different heating system in the house but I am doing this project for cash, so some compromises had to be made. If I had my choice I would have infloor heat again.

Larry

[Charles Lent]

Do a Wikipedia search for BTU . A BTU is a unit of heat energy (British Thermal Unit) and heating equipment is rated for BTU/hr. Heat loss is calculated in BTU/hr. Once you read the Wikipedia response I think you will understand how much heat your 500 gallon tank of water can provide. Compare that to your calculated heat loss from the building and you will know the answer to your question.

Charley