New Econo burn 200k... Storage Questions

[boilERIK]

Hello All,
I have been enjoying reading all the great post on this site. I am the new owner of an Econoburn 200k btu boiler. I am currently not using any storage and with just a few days under my belt I am seeing the great advantage I could gain from storage. I am considering two options for unpressurized storage tanks. The first and simplest would be to build a plywood tank with epdm liner build two heat exchanger coils one coming off the boiuler and the second to supply the house. I figure I could probably build a storage tank of about 900 gallons using this method. this wood tank would sit in the shed where I have the boiler. There is room for a tank but it would cramp things. The second option I am considering is an outside in-ground poured concrete tank. I would =make this out of ICFs or cast inplace concrete with insulation outside of the concrete. This tank could be considerably larger. I am a little hesitant about this approach because it seems to be very permanent. If I were to change things up I don't know how much flexibility I would have with a cast in-place concrete swimming pool. where as a 4x4x8 plywood tank could be used for a variety of things. I am just beginning to understand how the plumbing of the current system works and it seems that it would be most easily adapted to non-pressurized storage.

I am a carpenter and feel up to the task of building either type of tank but am curious to hear peoples thoughts on one versus the other and also curious to know how i should size the home made heat ex changer coils I would use. It seems that this would be a critical issue for both safety and efficiency The coil from the boiler needs to release as much heat as possible to the water bath so that there isn't a risk of over heating. on the supply side if the HX is not sized right I would have troubles heating the house properly. I look forward to your input.
Thanks
Erik

 

[boilERIK]

Has anyone used a septic tank for a no pressurized storage tank?

 

[leon]

The plastic liner will melt.
I was going to do the same thing BUUUUT an aquaintances
knowledge of the subject helped me by preventing a big mistake,
HE sells lined tanks for a living.


The circular tanks offered by HS TARM are the best option for you as
they have coils in them to transfer heat in and out of the water that is used as thermal mass.


There are septic tanks used for thermall storage but the excavation and
plumbing is the issue and it runs into a lot of money unless you have an
excavator handy and a money to buy the tank and $13 thermo pex and time.


For the money an HS Tarm Tank will be a better value and you can always
install more of them to create even more thermal mass.


Installing a cast in place tanks is also going ot require a great deal of steel rabar and form works to make a clean pour and your going to to need a concrete vibrator as well as a patient cement truck driver.

the other issue is the top cover and that is going to be just nasty to do.

I had to replace an existing cast in place tank with a new precast tank for a new sand filter and the 1,000 gallon tank was $2,500 from what I remember of it.

You could invest in a ten by twenty hoop shed and put one tank in to start and then add a another tank or a third and have the best of both worlds.

 

[Clarkbug]

Hello All,
I have been enjoying reading all the great post on this site. I am the new owner of an Econoburn 200k btu boiler. I am currently not using any storage and with just a few days under my belt I am seeing the great advantage I could gain from storage. I am considering two options for unpressurized storage tanks. The first and simplest would be to build a plywood tank with epdm liner build two heat exchanger coils one coming off the boiuler and the second to supply the house. I figure I could probably build a storage tank of about 900 gallons using this method. this wood tank would sit in the shed where I have the boiler. There is room for a tank but it would cramp things. The second option I am considering is an outside in-ground poured concrete tank. I would =make this out of ICFs or cast inplace concrete with insulation outside of the concrete. This tank could be considerably larger. I am a little hesitant about this approach because it seems to be very permanent. If I were to change things up I don't know how much flexibility I would have with a cast in-place concrete swimming pool. where as a 4x4x8 plywood tank could be used for a variety of things. I am just beginning to understand how the plumbing of the current system works and it seems that it would be most easily adapted to non-pressurized storage.

I am a carpenter and feel up to the task of building either type of tank but am curious to hear peoples thoughts on one versus the other and also curious to know how i should size the home made heat ex changer coils I would use. It seems that this would be a critical issue for both safety and efficiency The coil from the boiler needs to release as much heat as possible to the water bath so that there isn't a risk of over heating. on the supply side if the HX is not sized right I would have troubles heating the house properly. I look forward to your input.
Thanks
Erik

Erik,

I suggest you do some searching here for threads on this topic, but also look for the member "Tom in Maine". He is the resident expert (my opinion) on unpressurized storage tanks, and his company sells liners, heat exchangers, and the sides. I would avoid using plywood, but instead would use insulation, lots of it. But do some googling for "American Solartechnics" to see what you find for some good reading.

Another member here was going to go the septic tank route, but I think there was general concern that there would be lots of heat loss and potential issues with groundwater intrusion.

Any way to get a used propane tank into your shed? Or to build an overhang on it that could just be an insulated box to hold a propane tank? Then you get pressurized storage, you could put it outside the shed to free up room, and maybe some money over dealing with trying to excavate a pit for a tank.....

 

[boilERIK]

Erik,

I suggest you do some searching here for threads on this topic, but also look for the member "Tom in Maine". He is the resident expert (my opinion) on unpressurized storage tanks, and his company sells liners, heat exchangers, and the sides. I would avoid using plywood, but instead would use insulation, lots of it. But do some googling for "American Solartechnics" to see what you find for some good reading.

I am not sure what others have done but It would seem necessary to use plywood in a wood framed tank. Structural integrity would be hard to maintain with foam board as the only sheet material for side wall construction....?



Another member here was going to go the septic tank route, but I think there was general concern that there would be lots of heat loss and potential issues with groundwater intrusion.

Any way to get a used propane tank into your shed? Or to build an overhang on it that could just be an insulated box to hold a propane tank? Then you get pressurized storage, you could put it outside the shed to free up room, and maybe some money over dealing with trying to excavate a pit for a tank.....

I can rent a mini excavator for $400/day dig the tank hole in an hour and pull up stumps for the rest of the day. Ground water intrusion seems like it would be able to be dealt with via water proofing the exterior and the use of foam board insulation on the exterio would go a long way towards keeping water from contacting the concrete sides. The construction of an in ground concrete tank doesn't dissuade me. Is there that much greater heat loss from an in ground insulated tank than from an above ground insulated tank?

 

[Fred61]

Unless you're in the Mojave desert you will have more loss than a tank surrounded by air. All materials surrounding your tank will conduct better than air. Add the condensation that will occur and that will make a perfect conduit to draw heat away from your tank. I'm a crushed stone addict since I live in a state that is mostly covered by heavy "wicking" soil so I use tons of the stuff to keep moisture away from my buildings and I can still dig into it and it will not be dry. You live more or less in the same neighborhood as I do so I don't expect you would see anything different.

 

[maple1]

I think in the ground is the last place I would put storage - mostly for what Fred mentions, but also create a very hard to service situation. IMO. I would want any & all heat loss to be 'lost' to where I could get some good out of it - and there will be heat loss.

 

[TimfromPittsburgh]

I just built and brought online a 200 gallon heat storage tank built of plywood, polyiso... insulation boards and a tank liner purchased from American Solartechnics and am very pleased with the end result. In my case the boiler and tank are in the basement so I was constrained to what would fit through the basement door. I briefly considered casting in place a concrete tank in the basement, but concerns about making it waterproof and the permanency of it made me abandon that approach. I plan to build a second 200 gallon tank next week to increase my heat storage capacity to 400 gallons.

If you search this forum for "heat exchangers" you will find lots of useful information on sizing heat exchangers. In my case, I am using two 60' coils of 3/4" copper tubing. Heat exchangers are not my area of expertise, so I won't comment further on that. I would also recommend you visit Nofossil's website (Nofossil is a frequent contributer to this forum) where he describes a very clever method for using a single heat exchanger to both put heat into and take heat out of a storage tank.

 

[Rory]

I have a 4x4x8 plywood box insulated with two thicknesses of 2" foil faced foam inside and lined with EPDM. I think the capacity ends up around 670 gallons. My heat exchangers are two parallel loops of 120' each for the charging/discharging loop and a single 180' coil for DHW. I'm on my 5th or 6th season, and it works very well.

 

[boilERIK]

What are people using for their heat exchangers? are they home made? does everyone use soft copper tube or does anyone solder hard copper to make an exchanger? I have a bunch of thin wall hard copper tube left over from a deck railing project that I was considering using for my hx. Thanks for the advice about the in ground tank I will be building a plywood tank most likely. I did see a 1000 gallon fiberglass fuel tank for sale on craigslist for $250 not sure about how fiberglass would strand up to the continuous heat.