Just wondering but is it possable to use your storage tanks as both storage and expansion? I'm looking into two 500 gal LP tanks and was thinking if I only filled them up to say about 900gal could the rest be used for expansion? Just wondering thanks.
Storage and Expansion Tank
- Thread starter chrishh
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil. -
Super Cedar firestarters 30% discount Use code Hearth2024 Click here
- Status
I dont think you can do that.
My system is connect like this.I think it`s really simple
http://www.termoventiler.se/intra/uploaded/illustrationer/LM21_L.gif
You can se the Expansion in the topp of the pic
The Expansion got to be 5% of the tank size
My system is connect like this.I think it`s really simple
http://www.termoventiler.se/intra/uploaded/illustrationer/LM21_L.gif
You can se the Expansion in the topp of the pic
The Expansion got to be 5% of the tank size
problem is that eventually that air is absorbed into the water and your expansion capacity goes away. A dedicated expansion tank typically has a bladder (barrier) between the air and water so the air does not get absorbed. Another possible problem is that you would normally be pulling hot water out of the tank at or near the top and could suck air if the tank level were too low. Good thought though!
In North America we would tend to use 10% of system volume for expansion tank size, but if you go to the Amtrol or Watts web site you can find their expansion tank sizing calculators.
Chris
In North America we would tend to use 10% of system volume for expansion tank size, but if you go to the Amtrol or Watts web site you can find their expansion tank sizing calculators.
Chris
One perpetual source of confusion regarding expansion tank size is how they are rated.
There's the total volume of the tank that is often the first number that you see. But an expansion tank will NOT accept that much water as the system expands. The air cushion cannot compress to zero. In a bladder tank the bladder can't stretch that far. About half is more like it. And the more it compresses the air cushion the higher the pressure goes. There's no black/white limit here and that is how it is possible to get different recommendations. It depends on how much you like to see your pressure rise and how much room for unusual temp spikes you are comfortable leaving in your design. My intuition says that wood boilers might be better designed with more fiddle factor than oil or gas burners that can shut off instantly.
As Hansson says, 5% of total system volume is a good figure to use; lots of room for unusual high temperatures on occasion. But realize that systems over there are open onto the roof (that's where the overflow goes). They don't build up pressure as the temp rises like closed pressurized systems normal over here.
Amtrol expansion tanks (non-ASME models) have a maximum acceptance volume of a little more than 50% of their tank size. That's what the bladder is designed to take. And that is for fossil fuel boilers.
After my research (and I'm no pro heating guy) I think it safe to say that you want a tank at least double the size of your actual system water expansion from room temp to the highest water temp you want to see. I don't think you can hurt anything but your budget by having more than that.
There may be more factors involved, too. Hope some pros could step in if there are.
There's the total volume of the tank that is often the first number that you see. But an expansion tank will NOT accept that much water as the system expands. The air cushion cannot compress to zero. In a bladder tank the bladder can't stretch that far. About half is more like it. And the more it compresses the air cushion the higher the pressure goes. There's no black/white limit here and that is how it is possible to get different recommendations. It depends on how much you like to see your pressure rise and how much room for unusual temp spikes you are comfortable leaving in your design. My intuition says that wood boilers might be better designed with more fiddle factor than oil or gas burners that can shut off instantly.
As Hansson says, 5% of total system volume is a good figure to use; lots of room for unusual high temperatures on occasion. But realize that systems over there are open onto the roof (that's where the overflow goes). They don't build up pressure as the temp rises like closed pressurized systems normal over here.
Amtrol expansion tanks (non-ASME models) have a maximum acceptance volume of a little more than 50% of their tank size. That's what the bladder is designed to take. And that is for fossil fuel boilers.
After my research (and I'm no pro heating guy) I think it safe to say that you want a tank at least double the size of your actual system water expansion from room temp to the highest water temp you want to see. I don't think you can hurt anything but your budget by having more than that.
There may be more factors involved, too. Hope some pros could step in if there are.
Reread my post above and think I left the same ambiguity that I was trying to clear up. Let me try again...
A given volume of water will expand almost 4% going from 40F to 210F.
But not all the water in a system will be at boiler max temp. Some of it will be circulating around through the various emitters and piping at lower temps.Once in service the water will probably never get down to 40F and most folks will not likely get over 200F typically. But if you have a wood boiler with a pressurized storage system most of your water could get to near boiling (tanks often get filled with water over 200F in Europe) when Murphy comes to call. Some members of this forum have seen higher temps than that. You have to ask yourself what kind of margin of safety you will feel comfortable with. And how much you like water all over the floor near your pressure relief valve.
Expansion tank volume is not cheap and somewhere a line needs to be drawn. Whether you feel 4% is adequate (that's about what Amtrol's calculator comes out at) or more margin is needed (ASME rated tanks require a greater margin of safety, more like 5%) that number is the actual volume of water the expansion tank has to absorb. Your expansion tank volume needs to be double that amount of actual expansion. If you live in a state that requires ASME tanks (Mass. I think does) then the tank needs to be 2 1/2 times that actual expansion volume.
Chris's rule o'thumb of 10% for an actual tank volume is probably a pretty good one for those prone to waking at funny sounds in the night. Nice round number that could even cover Massachusetts boilers. You still might need that ASME tag and that's really going to cost some money.
I'm not saying anything new here just trying to clear up this confusion between expansion tank volume and actual water expansion volume.
A given volume of water will expand almost 4% going from 40F to 210F.
But not all the water in a system will be at boiler max temp. Some of it will be circulating around through the various emitters and piping at lower temps.Once in service the water will probably never get down to 40F and most folks will not likely get over 200F typically. But if you have a wood boiler with a pressurized storage system most of your water could get to near boiling (tanks often get filled with water over 200F in Europe) when Murphy comes to call. Some members of this forum have seen higher temps than that. You have to ask yourself what kind of margin of safety you will feel comfortable with. And how much you like water all over the floor near your pressure relief valve.
Expansion tank volume is not cheap and somewhere a line needs to be drawn. Whether you feel 4% is adequate (that's about what Amtrol's calculator comes out at) or more margin is needed (ASME rated tanks require a greater margin of safety, more like 5%) that number is the actual volume of water the expansion tank has to absorb. Your expansion tank volume needs to be double that amount of actual expansion. If you live in a state that requires ASME tanks (Mass. I think does) then the tank needs to be 2 1/2 times that actual expansion volume.
Chris's rule o'thumb of 10% for an actual tank volume is probably a pretty good one for those prone to waking at funny sounds in the night. Nice round number that could even cover Massachusetts boilers. You still might need that ASME tag and that's really going to cost some money.
I'm not saying anything new here just trying to clear up this confusion between expansion tank volume and actual water expansion volume.
chrishh said:
I think the answer is "yes" with an LP tank (because it can take pressure). As comment above mentions, you need a way to monitor free air space in the tank to make sure you have adequate expansion, and a way to add air as needed from time to time. There is a thread on this forum somewhere that describes how to do what you may desire.
Hansson has an easier way to go, by having a vented/overflow expansion vessel at the high point in the system. That gives you the pressure you need in the system and allows minimal air entry through the venting. I think that there will be some evaporation, so need to monitor water volume, and also monitor pH as water is added from time to time. I believe pH in the 8-9 range is usually the recommendation. You also could add an O2 scavenger, like that use in OWB's, but probably not necessary.
This would be easy to do by watching your psi gauge. Water height will give you psi (roughly 12 psi for a two story house), and if pressure starts to drop, means that water needs to be added. Seems to make sense to me.
It take alot of volume fo expansion, I have 80 gallons now and it is not enough to handle my system. I think I will add another 30 gallon air tank to mine. hopefully that will be enough.
Just as a note... Before I installed my storage I used an extrol 60 for my ewb 200 and the approximately 60 gallons of water or so that is in the system. With a cold system pressure of about 12 psi, the system would rise to about 20 psi when it reached operating temps. I kind of liked this as it gave me a little headroom regarding temps that could produce steam in the event of an overheat... not that I needed it... but it was there.
When I added the 1000 gallons of thermal storage, I left the extrol 60 tank on the boiler, and added an extrol 160. Preloading the system at 12 psi, I test fired the storage the other day (no insulation on the tanks yet) and never moved a single psi from 50* water all the way up to 165*. We'll see... maybe when I get to 180 or 190* in the tanks the pressure will come up a few psi. No sense in firing the storage any more until I get the tanks insulated though.
Anyone have any ideas how many Btu's a 500 gallon propane tank can radiate at 165*? They have about 97 sq feet of surface area. The kitchen floor was quite warm above the tanks for sure.
cheers
When I added the 1000 gallons of thermal storage, I left the extrol 60 tank on the boiler, and added an extrol 160. Preloading the system at 12 psi, I test fired the storage the other day (no insulation on the tanks yet) and never moved a single psi from 50* water all the way up to 165*. We'll see... maybe when I get to 180 or 190* in the tanks the pressure will come up a few psi. No sense in firing the storage any more until I get the tanks insulated though.
Anyone have any ideas how many Btu's a 500 gallon propane tank can radiate at 165*? They have about 97 sq feet of surface area. The kitchen floor was quite warm above the tanks for sure.
cheers
Everyone I wanted to thank you for the comments. From what I have gathered it looks like if I where going to use the storage tanks as expansion tanks as well as storage I would need to have maybe a site glass to monitor water volume or use the psi method jebatty mentioned. I also would want to make sure I was always drawing the hot water from the top tank low enough in the tank to make sure I wasn't going to get any air. Please correct me if I'm wrong on this next comment. If the air will slowly be dissolved into the water over about a 2 year period the water volume in the tank should go up on the site glass??. If this is correct I would have to make sure that I placed the outlet for the hot water low enough on the tank only for initial filling. As for charging the system with air for the first time I would need to have some kind of valve on top of the top tank. I was thinking of some kind of ball valve with maybe an air hose nipple that I could connect a compressor to?? I should be able to use the pressure gange on the system to tell when I have it charged to 12psi? And for checking the Ph of the system what is the best way to do this? Thanks everyone for the comments.
Chris
Chris
I'm not sure we're talking about the same things. If you consider the psi method, then you have an expansion tank like Hansson, located above the highest point in the system. This would have an overflow spigot open to the atmosphere. The tank would need a minimum capacity of about 4% of your total system + tank water volume (5% would be better). A 1000 gal system + storage = 50 gal elevated expansion tank. That's 418 pounds + the weight of the tank. Again, the expansion tank needs to be open to the atmosphere. My thought would be that when you need to add water due to evaporation or air dissolved into the system, you add it to the expansion tank. When it overflows, you know it is full. You need to be very sure that this tank can expel pressure safely, that is, have 0 pressure, else it will rupture or explode as the water expands. With this elevated expansion tank, your expansion tank always will be mostly full of water, and then your system including your storage tank always will be full of water. You can add/draw hot water from the top of a lower elevation storage tank; return from the bottom. Remember that each foot of elevation results in 0.43 psi; so 30 ft of elevation will show 12.9 psi at the low point in the system. If you measure pressure at any other point, you will have to adjust the reading that you are looking for.
I don't believe the psi method will work with an integral storage/expansion tank located below the high point in the system. A site glass would work in this case to know that you have expansion room. I have no experience with this type of pressure system, so there is very little I can tell you as to how to do it, maintain it, or use it safely. I don't know how fast the air will dissolve into the system, etc, etc. I suggest you research this much more carefully before going this route. Personally, I would opt for a bladder expansion tank setup or the Hansson method rather than this type of expansion setup.
As to pH, you can get litmus paper from a health goods, swimming pool supply, or chemical supply business. The litmus paper will tell you the pH.
I don't believe the psi method will work with an integral storage/expansion tank located below the high point in the system. A site glass would work in this case to know that you have expansion room. I have no experience with this type of pressure system, so there is very little I can tell you as to how to do it, maintain it, or use it safely. I don't know how fast the air will dissolve into the system, etc, etc. I suggest you research this much more carefully before going this route. Personally, I would opt for a bladder expansion tank setup or the Hansson method rather than this type of expansion setup.
As to pH, you can get litmus paper from a health goods, swimming pool supply, or chemical supply business. The litmus paper will tell you the pH.
If you go the Hansson route, you could install a toilet float valve in the tank to automatically keep it full to the desired level.
One of the things that I've gathered from reading here and on other sites with hydronic "how-to" info, is that it is a very mixed bag to have any sort of automatic refill mechanism that is always connected and on... The argument is that a properly functioning system shouldn't loose water, as there is no place for it to go, or at least the water losses should be extremely trivial.
Thus adding water shouldn't be needed more often than as part of a routine maintainance procedure which can be manually supervised - i.e. a fill valve regulator that is shut off with a ball valve except when manually turned on to top off the system.
If you get a leak, and it's in a non-obvious location, or even if it is obvious, an always on auto-fill will effectively give you an infinite sized flood, and may keep you from noticing a small leak until it's done major damage. A low water shut down, and a manually controlled fill valve would limit the flood to the amount of water in the system (and minimize other damages) - still a lot, especially for those w/ pressurized storage, but at least there would be SOME limit. Leaks would also get noticed faster because you'd be needing to add water, and answering the question as to WHY...
In the case of a non-pressured or open system, putting a layer of some sort of non-volatile oil or wax on top of the water is claimed to greatly reduce or eliminate water loss from evaporation.
Gooserider
Thus adding water shouldn't be needed more often than as part of a routine maintainance procedure which can be manually supervised - i.e. a fill valve regulator that is shut off with a ball valve except when manually turned on to top off the system.
If you get a leak, and it's in a non-obvious location, or even if it is obvious, an always on auto-fill will effectively give you an infinite sized flood, and may keep you from noticing a small leak until it's done major damage. A low water shut down, and a manually controlled fill valve would limit the flood to the amount of water in the system (and minimize other damages) - still a lot, especially for those w/ pressurized storage, but at least there would be SOME limit. Leaks would also get noticed faster because you'd be needing to add water, and answering the question as to WHY...
In the case of a non-pressured or open system, putting a layer of some sort of non-volatile oil or wax on top of the water is claimed to greatly reduce or eliminate water loss from evaporation.
Gooserider
If you are subject to any kind of code enforcement and inspection I would have a careful diplomatic discussion with your code inforcement officer before doing anything.
Something about hot water and pressure together makes those folks very unwilling to put their initials on any kind of variance from established norms. Not all that I have met are unreasonable. In fact, I've been pretty lucky myself but I have watched friends go through stonewalls to get simple details cleared. We had one notorious CEO next town over that tried to carry a sidearm on the job to display his authority. He didn't last long.
I love the simplicity of the Swedish open systems but I don't trust authorities not to come down on me and say I can't have one in my house and get testy about it.
When I built the cabin we've been living in for the last 30 years I didn't even need a building permit. Now they want all circuit breakers in a panel to be AFCIs or GFCIs and you can't put up drywall before they inspect what is in the wall.
I gotta finish this new house before they slap any more rules on me.
Something about hot water and pressure together makes those folks very unwilling to put their initials on any kind of variance from established norms. Not all that I have met are unreasonable. In fact, I've been pretty lucky myself but I have watched friends go through stonewalls to get simple details cleared. We had one notorious CEO next town over that tried to carry a sidearm on the job to display his authority. He didn't last long.
I love the simplicity of the Swedish open systems but I don't trust authorities not to come down on me and say I can't have one in my house and get testy about it.
When I built the cabin we've been living in for the last 30 years I didn't even need a building permit. Now they want all circuit breakers in a panel to be AFCIs or GFCIs and you can't put up drywall before they inspect what is in the wall.
I gotta finish this new house before they slap any more rules on me.
DaveBP,
Good point I just fired off an e-mail to my local code enforcer to see if there will be any problems with using the LP tanks.
Thanks,
Chris
Good point I just fired off an e-mail to my local code enforcer to see if there will be any problems with using the LP tanks.
Thanks,
Chris
- Status
Similar threads
