Pressure - non pressure storage ?

[jjhpf]

Any one know a good link to review pros and cons of both?

jim

 

[sgschwend]

A link, you mean besides here?

There is also the no storage tank option.

You will find a thread about a month old covering the idea of why to have storage.

In my opinion if you are in the 2000 gallons or less tanks size pressure is better, but there are always other things to consider; such as the location for the storage tank. I believe it is commonly believed that the best storage is under the home that is being heated, tends to be the key consideration.

The good news is that both kinds of storage can easily be done, just takes some action.

 

[Gooserider]

Any one know a good link to review pros and cons of both?

jim

Do the search, you will find lots of debates on the topic, each has its pros and cons, and every situation puts it's own balance on them, so one has to make a tradeoff as to which will work better for a particular setup.

In short...

Pressure - Pro
1. Can be run to a higher temperature than Non.
2. Heats more efficiently - no HX losses (at least on boiler loop)

Pressure - Con
1. Comes in large, bulky, non-flexible tanks - can be difficult or impossible to get in and out of some locations, Tanks are heavy, can be difficult to move.
2. Requires very high volume (expensive) expansion tanks - much larger than Non.
3. Limited range of tank size choices
4. Hard to install in-tank HX's for things like DHW, or glycol loops
5. Pressure vessels, which can be problematic in some code jurisdictions (i.e. MA, among others)
6. Because of tank design, can be a challenge to plumb, modifying tank to add / change plumbing is possible, but difficult / expensive.


Non-Press - Pro
1. Flexible - can be built to fit into almost any space, and in any size
2. Because it can be made on-site access to get materials in is seldom a problem.
3. Easy to do almost infinite numbers of in tank HX coils
4. Adding / changing design easy

Non-press - Con
1. Requires careful design / build to get tank that will hold water safely
2. Can't be run to as high a temperature as P.
3. Somewhat less efficient because of physics of HX operation
4. Requires somewhat more attention to controlling water loss / evaporation.

Gooserider

 

[tom in maine]

As a manufacturer of non-pressurized tanks, allow me to add a couple thoughts.

Watching the Boiler Room, I think most people use pressurized systems because they are cheaper (Gas tanks).
In considering this option, labor is ignored, as is the convenience of moving it around and cost of insulating the tank.

As Goose mentioned, logistics are a major issue for pressure tanks.

I have never looked at heat exchangers as being a big drawback to non-pressure tanks.
If used within their design limits (which should match your needs) they should perform almost as if they are not there.
As an example, a heating loop might run a little longer with the hx in the loop, but I believe the compromise is minimal.

You need a dhw hx of some sort for either system, unless you are not using hot water from a wood system.
Here the non-pressurized system is much simpler to deal with.

I think, at least for Boiler Room readers, who are usually DIY'ers, it is a tradeoff between sweat equity and ease of installation in getting
a system operational in a short period of time.

Cleaning methyl mercaptan and welding piping and dealing with corrosion inhibitor is part of that sweat equity deal.

Someday soon I will post some pix of my non-ferrous unpressurized gasifier. The only hx is the DHW one.

 

[Chris Hoskin]

you asked for a link:

(broken link removed to http://www.woodboilers.com/heat-storage-systems.aspx)

 

[Birdman]

This is my second year using the Tarm 40 Solo. I bought it at Bioheat USA( Tarm USA.. when I bought it). Best purchase I have ever made. I will get to the point of this. I can definately see the need for storage. I am idling too much.. and yes i try to match the load of wood to the need of heat and hot water.. but it is very hard to do when temps go from 25 at night( last night) to 50 during the day. I will be getting set up to do storage hopefully this summer. I have my mind set up on doing the pressurized. I may buy the tanks at Tarm ( BIoheat ) Usa. I have been reading as much as i can about pressurized storage... great stuff on the Hearth site. HOwever... can someone explain the advantages, disadvantages to having 2 or 3 tanks set up for pressuized storage? I know there are alot of do it yourselfers on here that get tanks and do it themselves usually a 500 or 1000 gallon tank. How does the 2 or 3 tank thing work in comparison? And... could I buy and install 2 tanks.. and then later on install another tank or two easliy later?

 

[Gooserider]

My opinion is that from a purely heating standpoint, a single large tank is better than a bunch of small ones - less radiating surface area per volume, better ability to stratify and or distribute the heat evenly between the tanks, etc... The more tanks, the worse the issues of having multiple tanks get. However with a well designed system, this is not a huge issue. The downside of big tanks is the bigger the tank, the worse the logistics of moving and installing it get... I think the reason most folks here end up with the propane tanks in the double 500g size is as much a case of what is available as it is any inherent advantages to that size and shape.

Adding tanks is always an option, the question is how hard it will be - planning is key here... If I thought there was any chance I'd want to expand, I would suggest putting appropriate tees and stubs, valves, etc. so as to make it easy to tap into the existing system. Also choose a plumbing layout that is "friendly" to the idea of adding more tanks, and minimizes the amount of existing plumbing that you'd need to change when doing the add.

Gooserider

 

[tom in maine]

The other issue is the amount of foam on a storage system.
Spray foam being most desirable for pressure tanks is also pricey.
And 2" ain't enough.

 

[stee6043]

I personally found pressurized storage to be a fraction of the price of non-pressurized even when buying brand new tanks. According to my estimates by the time I included copper to build my own HX coils as well as the "ready to assemble" tank kits I was double the price compared to brand new propane tanks. No HX coils needed which meant a little less plumbing for me with pressurized. Overall it was a no brainer in my situation. Half the cost and better performance (higher temps). I was forunate enough to have a walk out basement that would easily accomodate the tanks going in. If you have the ability to clean used propane tanks the scales, in my opinion, tip even more in the direction of pressurized.

Insulation I would argue is a wash. Both types of tanks need to be heavily insulated. I used eleven (11) rolls of fiberglass R30 insulation on my 1000 gallons. I figure I have an average of R40-50 throughout the box I built. I loose roughly 10 degrees per day with no load on the system....

This is why I went with pressurized. Mostly because I'm Dutch...

 

[tom in maine]

As I had said earlier, there is a tradeoff between sweat equity and having someone do this for you. The choice is the consumer's.

Standby loss on foam insulated tanks is a lot lower, but if the heat loss is into living space, it is not a big deal. (Unless it is summertime!)

 

[jebatty]

I initially used 825 gal non-pressure storage with a plate hx, and then switched to 1000 gal pressure storage. The pressure storage is so much easier to heat, especially to high temp. Just let the boiler burn out today, brought the tank up to 185 top to bottom. I'll be gone for a few days, turned the heat down a bit, but everything will be warm until I'm back. Could never have accomplished that with the non-pressure storage. Might have been able to get it up to 165-175 with some real effort, including lots of boiler idling. Idling is nearly a thing of the past with the pressure storage.

 

[tom in maine]

I would have to say that there has not been an issue getting our tanks up to temperature with our coil hx.

Before we started working with Bioheat, we let them test our heat exchangers as they saw fit.
We have tanks that have been tested other boiler companies as well as solar companies with very positive results.

It is important to have properly engineered heat exchangers for use with unpressurized tanks.
Our design might not be perfect, but we have refined and have understood the basic concepts for a long time and IMHO,
have heat exchangers that do not throw any major bottleneck on a system's performance.

Again, you all know where I come from, being a manufacturer, but one big strength that unpressurized tanks offer is a simple rebuild and repair
path if and when any service is required. There is no corrosion, either.

Is the system perfect? No. But it has its place.

You can certainly do an unpressurized tank yourself and I encourage folks who want to do this.
We offer convenience and out of the box thermal performance.

And we will support the product. Having done this for 29 years (Yikes!) we have a little understanding of this system.

 

[flyingcow]

FWIW...the tank and hx Tom speaks of, I have. I can drive it to 180 fairly easy. Top/middle will go to 178/180 fairly easy, forget where the bottom ends up. Seems to work very good. In the heat of the summer, doesn't have much "heat" problems outside the tank. But i generally don't get much above 165, for summer DHW. That's about where I plan for it to be.
-
The HX is not just a coil of copper. It's a generation above it, or seems that way to me. My installer was impressed with it.
--
For some reason I thought of you plan on using your wood heat to make DHW in the summer time, unpressurized was the way to go.

 

[jebatty]

I'm not faulting non-pressure tanks, only relating my experience. Last winter when we were going to be gone for 10 days, I brought the 1000 gal pressure tank up to 192, top to bottom, and that's as high as my boiler will go.

 

[Gooserider]

I would have to say that there has not been an issue getting our tanks up to temperature with our coil hx.

Before we started working with Bioheat, we let them test our heat exchangers as they saw fit.
We have tanks that have been tested other boiler companies as well as solar companies with very positive results.

It is important to have properly engineered heat exchangers for use with unpressurized tanks.
Our design might not be perfect, but we have refined and have understood the basic concepts for a long time and IMHO,
have heat exchangers that do not throw any major bottleneck on a system's performance.

Again, you all know where I come from, being a manufacturer, but one big strength that unpressurized tanks offer is a simple rebuild and repair
path if and when any service is required. There is no corrosion, either.

Is the system perfect? No. But it has its place.

You can certainly do an unpressurized tank yourself and I encourage folks who want to do this.
We offer convenience and out of the box thermal performance.

And we will support the product. Having done this for 29 years (Yikes!) we have a little understanding of this system.

Just out of curiosity Tom, does your company offer any support services for people that are making the DIY tanks? - I like the square tanks you do, but they would be a poor fit in our space - but I could see a DIY tank construction to fit a space, and then getting liners / coils to fit from you, assuming you did such things...

Gooserider

 

[tom in maine]

We are presently only selling liners with our tanks.
The liner is the most critical component and we are making them in stock sizes.

If our size fits your tank, we would probably sell one separate from the tank.

We do sell coils for anyone's tank.

I will confess that I have only run my tank up to 170F at my home.
That is adequate for more than two days this time of year for heat and hot water.
Our dhw load is more than space heat any time of year.

And it is not our normal liner. Just one that I am testing but will probably not sell.

 

[flyingcow]

If I can get off my lazy butt and finish putting staple up in my livingroom, i wouldn't have to drive up the tank to 180. I've got staple up in my kitchen, and that helps a lot, but got to do the rest of the downstairs. Really only have to drive the tank that high after the deep cold sets in. The baseboard really uses the tank up quickly in the cold weather, and we are keeping the house warmer than we did with oil.

 

[Birdman]

I am sold on the idea of the pressurized storage. Can anyone direct me to a source where I can buy a 500 gallon tank? I have a walkout basement. I have plenty of room in the basement for any size tank. It may be easier for me to start out with a 500 gallon tank?... and then add another 500 gallon tank later? This may be a better solution than buying 2 tanks of 215 gallons... and then deciding I want more storage later and have to add another 2 tanks to get me up to 860gallons? Someone please chime in? I am luckily at the point where I really don't feel like getting and "" old " tank where I have to clean it out and so forth. I am perfectly happy to pay the extra and invest in a nice new clean tank. I have researched on this site and I think I did see a cool pic somewhere of someone stacking 2 500 gallon tanks on top of each other? Is that the best way? Or could I do side by side somehow and get the same results?

 

[stee6043]

I am sold on the idea of the pressurized storage. Can anyone direct me to a source where I can buy a 500 gallon tank? I have a walkout basement. I have plenty of room in the basement for any size tank. It may be easier for me to start out with a 500 gallon tank?... and then add another 500 gallon tank later? This may be a better solution than buying 2 tanks of 215 gallons... and then deciding I want more storage later and have to add another 2 tanks to get me up to 860gallons? Someone please chime in? I am luckily at the point where I really don't feel like getting and "" old " tank where I have to clean it out and so forth. I am perfectly happy to pay the extra and invest in a nice new clean tank. I have researched on this site and I think I did see a cool pic somewhere of someone stacking 2 500 gallon tanks on top of each other? Is that the best way? Or could I do side by side somehow and get the same results?

I have a few thoughts. 1.) If you're eventually going to end up with 1000 gallons I'd do it all at once. It'll be less work to do the plumbing one time, in my opinion. 2.) Stacking tanks is easy. I used high capacity pallet racking to stack my tanks (you may have seen my photos around). 3.) New tanks are not easy to get. I did, but I have a source that is a family friend. Most tank dealers will not sell new tanks direct to end-users. Many folks on this site have good strategies for cleaning used tanks, however...

 

[Birdman]

Can anyone direct to to a place where I can buy a 500 gallon tank(pressurized) that is all preset for storage? Clean and ready for a plumber to hook up? No welding etc.

 

[Mid Michigan]

It seems many people use propane tanks for storage. Hear in central Michigan we have a lot of Amish. They have there own store that anyone can shop at. It is full of propane equipment. Being they do not use electricity they use propane for everything. I bought a 500 gal. propane tank brand new for $900.00 from the Amish store. There are many sizes available: 100 gal., 200 gal., 330 gal., 500 gal., and 1000gal. If you have any Amish in your area it may be a avenue you can pursue.

I bought all the fittings and valves necessary to fill 20# and 30# tanks off of my 500 gal. tank. Much cheaper than exchanging tanks!

 

[Gooserider]

Can anyone direct to to a place where I can buy a 500 gallon tank(pressurized) that is all preset for storage? Clean and ready for a plumber to hook up? No welding etc.

(broken link removed) is a place that I have in my bookmark collection. They are out in CA, but they list all sorts of pressure vessels, including propane tanks. Downside is they say on the website that they only sell propane tanks to "licensed professionals"

Gooserider

 

[jebatty]

Not mentioned yet in this thread, but previously, is that many tank liners for open storage are not rated for use above about 170F, or at that range the liner is quickly approaching maximum. If the intent is to load a non-pressure tank with a liner above 170F, I think it is wise to be sure to check the ratings for the liner. Although the rating may be conservative, pushing the limits may shorten the life.

 

[tom in maine]

Not mentioned yet in this thread, but previously, is that many tank liners for open storage are not rated for use above about 170F, or at that range the liner is quickly approaching maximum. If the intent is to load a non-pressure tank with a liner above 170F, I think it is wise to be sure to check the ratings for the liner. Although the rating may be conservative, pushing the limits may shorten the life.

I am using my personal tank with a polymer liner that was spec'd at 160F. They said that 180F was okay. I never got a straight answer in writing that this company's material was usable to 180F, so I am beating on it at my house. At 180F + this liner might deteriorate it but that is my job to know.

Needless to say, this will probably never be a liner that we sell. The liner we use is rated 180F continuous and 200F intermittent.

When I evaluate a candidate liner material, the first test is to boil the hell out of it for several hours. If it can handle all that energy on the material and welds, it is worth
thinking about. Then we use and test it for several years.

The material we are currently using is something that we have used for almost 30 years. It has stood the test of time.

Unfortunately, EPDM, which is a great DIY choice, is not tolerant of temps over 170F and tends to deteriorate. Those deterioration byproducts will affect copper heat exchangers.

 

[Birdman]

I am finding info on accumulator tanks for woodboilers online... but... it looks to me like they are only sold in Europe? Frr example (broken link removed) looks like what I need? Is ther anything like this sold in the USA? Akvaterm tanks. It is quite amazing to me that everyone has to be a DIY person and find a way to get there own used propane tank if they want pressurized storage. I thought all these new boilers being sold required storage? Is the only option to buy the unpressurized system? .. or find your own propane tank? Has anyone tried to buy one of these Akvaterm tanks from a European distributor??