i have read post after post and am unable to resolve my confusion. i hate to be redundant but have some questions. i am planning on and have room for 2-300 gallons of storage. i mainly do not understand the differance between pressurized and no pressurized storage. by the looks of the budget i am looking at using and insulating an oil tank or having a tank made out of 1/8th plate. is either system more efficient and what are the pro's and con's of each? again sorry if this is redundant but having trouble to sort this out.... thanks!
storage help
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pwschiller
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With pressurized storage, the water in your boiler(s), piping, baseboard heaters, radiant tubing AND storage tank(s) are all part of a closed system that prevents air from getting into the system. It would typically be at 12-25 psi. Ordinary oil tanks aren't designed for that, used LP tanks can handle that.
With non-pressurized storage, the water in your boiler(s), piping, baseboard heaters, radiant tubing and the heat exchanger (which sits in the non-pressurized storage tank) are all part of a closed system under say 12-25 psi. The water in your storage tank is insulated, but is open to the atmosphere enough to allow for expansion and contraction of the water. The boiler water and the water in the storage tank are separate. See: http://www.americansolartechnics.com/photos.html or http://www.builditsolar.com/Projects/SpaceHeating/Components.htm#Storage
Then there are open systems where nothing in the system is pressurized. I believe this is how outdoor wood boilers normally are set up. The problem is that the water in the system is open to the atmosphere, which allows oxygen into the system, which will rust out non-stainless steel or cast iron parts. To deal with this, you either have to regularly add an oxygen scavenger to the water, not use iron or steel parts, or replace parts when they inevitably rust out.
Search the forums for "pressurized vs unpressurized".
With non-pressurized storage, the water in your boiler(s), piping, baseboard heaters, radiant tubing and the heat exchanger (which sits in the non-pressurized storage tank) are all part of a closed system under say 12-25 psi. The water in your storage tank is insulated, but is open to the atmosphere enough to allow for expansion and contraction of the water. The boiler water and the water in the storage tank are separate. See: http://www.americansolartechnics.com/photos.html or http://www.builditsolar.com/Projects/SpaceHeating/Components.htm#Storage
Then there are open systems where nothing in the system is pressurized. I believe this is how outdoor wood boilers normally are set up. The problem is that the water in the system is open to the atmosphere, which allows oxygen into the system, which will rust out non-stainless steel or cast iron parts. To deal with this, you either have to regularly add an oxygen scavenger to the water, not use iron or steel parts, or replace parts when they inevitably rust out.
Search the forums for "pressurized vs unpressurized".
pwschiller
Member
The cheapest solution is pressurized storage, if you can find a used LP tank. In some states they can be hard to come by.
The downsides to non-pressurized storage are the cost of copper heat exchange coils and the fact that the EPDM liners used in most tanks can't handle water much above 180 F. That's probably fine if all of your heat is radiant, but may not be sufficient if you have baseboard heat. The new liners that Tom from American Solartechnics is putting in his tanks can handle temps up to 200 F: http://www.americansolartechnics.com/820.html
The downsides to non-pressurized storage are the cost of copper heat exchange coils and the fact that the EPDM liners used in most tanks can't handle water much above 180 F. That's probably fine if all of your heat is radiant, but may not be sufficient if you have baseboard heat. The new liners that Tom from American Solartechnics is putting in his tanks can handle temps up to 200 F: http://www.americansolartechnics.com/820.html
I am not sure I want to take this on before I had my first cup of coffee but since your from near where I live in northern Maine I'll do the basics.
Pressurized is more like your typically hydronic system, i.e. it is a "closed" loop an is pressurized somewhere above atmospheric pressure, normally in the 15psi range. The advantages include higher storage temps (more btu's stored per gallon of water), low oxygen in the water supply which means less hassle with corrosion control (you can use cheaper ferrous or steel components intsead of bronze/brass), probably less equipment, i.e. heat exchangers. and more. This is probably the way to go if you have high temperature baseboard installed since you can store at higher temps. One disadvantage is that you have to allow for a large amount of expansion when the water is heated which is costly. Tanks can be had on the cheap but typically they are costly.
Non-pressurized systems are considered "open" to the atmosphere and consequently operate at atmospheric pressure. Usually the materials used for the tanks don't allow for high temps so the storage temps will be somewhat lower than prsessurized. They typically have more dissolved oxygen in the system therefore it usually needs close attention to water treatment. Heat exchangers are also needed to separate the closed and open sides to the system. I think the biggest advantage to non-pressurized is that you may have more storage at a lower cost, especially if you don't have to deal with expansion of heated water. The one caveat to all this is that since the storage is at a lower temperature you can't run high temperature emitters as well (baseboard). To me non-pressurized is ideally suited to radiant floor heating since it operates at a lower temperature.
There is a lot of overlap here open to discussion. My first choice would be pressurized but I have seen non-pressurized work great. The key is the overall system design which needs balance between the heat source, heat load (or loss), and btu storage capacity. Both ways work with a properly designed system.
There's more to add here. Hopefully others can chime in. My gut tells me this is going to be a Ford/Chevy/Dodge fight.
Pressurized is more like your typically hydronic system, i.e. it is a "closed" loop an is pressurized somewhere above atmospheric pressure, normally in the 15psi range. The advantages include higher storage temps (more btu's stored per gallon of water), low oxygen in the water supply which means less hassle with corrosion control (you can use cheaper ferrous or steel components intsead of bronze/brass), probably less equipment, i.e. heat exchangers. and more. This is probably the way to go if you have high temperature baseboard installed since you can store at higher temps. One disadvantage is that you have to allow for a large amount of expansion when the water is heated which is costly. Tanks can be had on the cheap but typically they are costly.
Non-pressurized systems are considered "open" to the atmosphere and consequently operate at atmospheric pressure. Usually the materials used for the tanks don't allow for high temps so the storage temps will be somewhat lower than prsessurized. They typically have more dissolved oxygen in the system therefore it usually needs close attention to water treatment. Heat exchangers are also needed to separate the closed and open sides to the system. I think the biggest advantage to non-pressurized is that you may have more storage at a lower cost, especially if you don't have to deal with expansion of heated water. The one caveat to all this is that since the storage is at a lower temperature you can't run high temperature emitters as well (baseboard). To me non-pressurized is ideally suited to radiant floor heating since it operates at a lower temperature.
There is a lot of overlap here open to discussion. My first choice would be pressurized but I have seen non-pressurized work great. The key is the overall system design which needs balance between the heat source, heat load (or loss), and btu storage capacity. Both ways work with a properly designed system.
There's more to add here. Hopefully others can chime in. My gut tells me this is going to be a Ford/Chevy/Dodge fight.
makes more sense to me now, i have no interest in having to add heat exchangers to an open system or have to worry about corrosion. this is an add on to my heating system that i have decided to try where i have just done a large addition on my house. my plans are to use the boiler to take place of my oil boiler during the heating season. the addition has an 800 sq. ft radiant heated floor and the old portion is baseboard. in my uneducated mind at this point i think pressurized is my safest bet. what are we talking for expansion tank requirements in a closed system?
pwschiller
Member
Check this out and see if that answers your expansion tank question:91LMS said:
http://www.engineeringtoolbox.com/expansion-tanks-d_885.html
bout clear as mud to me on the formula's, will have to research the abbreviations and sort it out. looking at about 2-300 gallons of storage. however have some input from a coworker urging me to not use storage because of lag time he anticipates. my thoughts are storage would eliminate that but i suppose he has a valid arguement.
Properly plumbed there should be exactly ZERO lag time associated with thermal storage. Loads get heat first, tanks get heat second. Rinse, repeat.
Do you have some details on your boiler and heat loads? Personally, I don't think plumbing 300 gallons of storage is worth the expense. If you have "average" heat loads you'll find that 300 gallons of storage is not enough to drastically increase the flexibility of the system. If you're running 25k heat loss you're looking at maybe 4 hours of heat from those tanks depending on what kind of emitters you're using. Do you foresee 4 hours being beneficial?
Do you have some details on your boiler and heat loads? Personally, I don't think plumbing 300 gallons of storage is worth the expense. If you have "average" heat loads you'll find that 300 gallons of storage is not enough to drastically increase the flexibility of the system. If you're running 25k heat loss you're looking at maybe 4 hours of heat from those tanks depending on what kind of emitters you're using. Do you foresee 4 hours being beneficial?
well i guess 4 hours would not be that beneficial when i think of it that way. i was just thinking that possibly it could buffer the ammount of time the boiler was cold after a morning fire and the 10 hours elapsed till i got home from work to refire. i am thinking that possibly till i sort this out that i wont go with storage right off it its not right for my situation. confused also how my domestic will be wired in where the domestic coil is in my oil boiler and hot water from the wood boiler would need to circulated through the oil boiler to make dmh.
pwschiller
Member
If you are talking about diaphragm (bladder) style expansion tanks, if you assume a maximum storage temp of 200 F for an additional 600 gallons, you could probably get by with two of these: http://www.pexsupply.com/Amtrol-118-78-SX-40V-Extrol-Expansion-Tank-20-Gallon-Volume-7366000-p91LMS said:
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