Talk me off the Ledge.... (Storage Question/Comment)

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Clarkbug

Minister of Fire
Dec 20, 2010
1,273
Upstate NY
I am just looking for a little friendly reassurance here all.

My installer called me the other day to discuss my system. (Varmebaronen Vedolux 37, 660 gallons of storage) He was concerned that my storage was too big for this system, and wanted to know if I had run the numbers on it. He was thinking that there would be a problem trying to heat up this much water, and that a big slug of cold water coming back from the zones would really hurt the performance of the system.

Now with all of the reading I have done here, Im positive this isnt the case. (Im wanting to use Tarm's PT-1 piping scheme, for those that want to know).

But it did make me wonder about the cold slug of water, since I hadnt thought of that before. When a zone first starts up, I could see getting back water thats around 65 degrees or so. If I understand this correctly, the idea is that this will go to the bottom of my storage tank, where my loading valve will allow it to get back to the boiler after its tempered.

He has installed a number of wood boilers, but was worried that since I was using more tanks than were called out for by Tarm, I was putting too much of a burden on the system.

Im just looking for a little reassurance that Im not crazy, and that I just need to do a little more explaining to him to make it all work...
 
You are not crazy.
It is important to calculate your heat load, consider the lowest temperature that your heat distribution system will allow and then calculate the amount of storage necessary.
I can tell you from my experience talking to a lot of people who use storage systems, they usually want a larger tank than they initially consider. Not always, but more often than not.
This is why heat load calculations are important and are also a valuable tool for analyzing problem areas in your home.

An energy audit is not a bad idea either.

In terms of cold water "shocking" the boiler, most boilers use a Termovar, Danfoss or some other mixing valve to make sure that a cold return temperature is tempered on its way back to the boiler.

My educated guess on storage is that 660g is not bad and is not too small for your area, but run the numbers. There are heat load calculators on www.builditsolar.com as well as Google.
 
Thanks Tom.

I have run the numbers, and most likely my design-day heat loss will be a little more than the max output of my boiler. This is due to my leaky single pane windows and my presumed lack of insulation. However, as I actually weatherstrip the windows and add storms (or air panels for this year) Im anticipating that I can meet my load on the design day with the output of my boiler.

My installer was actually worried I had too much storage, not too little. From reading here it seems like 500g is the minimum most people want to work with. My house is all baseboard fin tube, so I have to work with a relatively high temperature for the tank, which would lead me to think that the 660g is even going to be a little small for my needs.

The energy audit is on my list of things, but this home ownership thing has snuck up on me lately, and the to-do list has grown to the point that the audit will need to wait. (Plus I dont think the audit guys would have gone in my attic with the bats that took up residence)

I have a termovar loading valve that will prevent shocking the boiler, so Im set there. But in my piping scheme, cold water is coming back from the house, and it has to go somewhere. So my thought is that its going to fill up my storage (from the bottom up) and hot water will come from the top. Then my boiler (with the termovar) will allow the water to get heated back up as the boiler has capacity to do so.

Thanks again. I just started to freak out a little after talking with the guy who is piping it up for me, and the money for the boiler is already spent.
 
I have a Tarmsolo40. I use a 500 gallon propane tank for storage. I can burn a full load at full output. My boiler doesn't idle.
My storage is pressurized, and getting it up to 195* is normal.
I also have fintube, but I added some elements and can run my temps down to aprox. 155* of useful heat.
 
I have a vedolux 30 with 1700 +- gallons of open storage... 600 is definitely not to much for a 37.
As others have said storage should be based more on load then boiler size.

I could live with 1000 gallons closed storage but would not want any less for my load.
 
Clarkbug said:
... He has installed a number of wood boilers, but was worried that since I was using more tanks than were called out for by Tarm, I was putting too much of a burden on the system....
As others have already said, there have been comments here in the past that more storage perhaps would have been better, but I can't remember anyone posting that they should have used less. Tarm has been in the game for a long time, so it's really puzzling that they would be recommending less than 660 gallons. Did you see this in the Tarm manual? If not, how about asking him to show you the doc where Tarm makes that statement. If he can't find it in writing, then perhaps it was just his misunderstanding. You can relax - everything seems like a big deal at the moment, but it will work out fine. Enjoy the heat from your boiler - it sounds like a good one!
 
I think I'd be more concerned about your installers "professional opinion" regarding storage sizing. Has he installed thermal storage before? Does he understand how it works? Do you trust him?
 
Thanks all. I was pretty sure that I had the right idea, but its just that split second of panic when you think you have missed something glaringly obvious in front of you.

I dont have the option to fit more storage in my basement, so the 660 will have to do, and I lucked into that as it is. I figure I can make it work, or at least I hopefully can when all the dust settles.

Tarm actually makes that statement right on their piping schematic ( http://www.woodboilers.com/uploads/public/PressureTank(PT1).pdf ) on the right hand side.

And in his defense, he did say that he wasnt sure, and just wanted to know my intent for the system. My thought is the biggest concern is that Im using a Tarm schematic and a Varm boiler, and that means that you cant exactly follow that schematic, but its close. He is just wanting to make sure that he pipes up what I want, and not what he thinks I want. I appreciate that, and its always good to have someone ask you questions about your intentions, especially on something like this. Also, he was under the impression that this boiler had the on/off control (like the Tarm Solo Plus) so he didnt know the need for it. Ultimately, I need to make a new piping schematic and control diagram that shows the connections to the Varmebaronen and how it will tie into my house. So thats on my agenda for later this week. But I do trust the guy, since he did ask me what I wanted before he just went ahead and did something.

I appreciate everyones input, and Ill post my schematics here for review/comment before I go talk it over with him.
 
Our drawings are posted on the website for public consumption and, of course, we realize that people who purchase competitor's boilers will use the drawings. As wwfw said, we have been at this a long time and have figured out how to make things work; sharing that knowledge makes the whole industry better and that benefits all of us in the long run. I am concerned, however, that Clarkburg and his installer have a fundamental lack of understanding about what PT1 is trying to accomplish. First of all, the two tank suggestion is a MINIMUM recommendation, not a maximum - 660 gallons for the Vedolux 37 will work great. Second, the concern about cold return water means that, either there is no tempering valve being used or, again, there is little or no understanding of the drawing. What about the BLT? TV2? ZV1? If these components are not included in the installation, the system will not work as the schematic shows. What does your supplier recommend for an installation schematic?
 
I want to think I do have a good grip on PT1, but I just wanted to make sure that I was thinking along the right lines, hence my post here for a little reassurance. I also assumed that the two tanks was a minimum, since I know there are people running much more storage than I anticipate, and they have no problems with their systems.

I do have a loading valve, and the model I have is designed to prevent water less than 140 degrees from hitting the boiler. My guess (and its just that) is that while talking about my intent for the system, he assumed that I would have the tanks piped in series as opposed to being able to send water to the zones or to the tanks. We havent been able to have a good meeting of the minds since the day he was able to stop by to look at my basement, I was stuck out of state for work, and my wife was trying to run interference for me. Never the best of both worlds when you try to explain yourself running through the airport.

The BLT has already been purchased to simplify the oil backup control. The final temps will be up to me to tweak as far as when the aquastat will initiate the changeover, and that will be part of me fiddling around with it. The TV2 Im actually hoping to purchase from my local Tarm dealer, since he was very helpful when I was looking at different systems, and I would like to give him some of my business when I can afford to.

I too want to make sure my installer understands my intent, and actually the reason I selected him is that he was one of three suggested to me by the same Tarm representative I mentioned above. He has done a number of these installations, but Im assuming not many with storage, since thats still a new one to many people around my neck of the woods.
 
Im hoping so!

And I do want to thank Tarm for putting the diagrams up for general consumption. It has definitely come in handy for me to understand some of the finer points of how gasifiers can work, and they are a great visual reference tool.
 
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Our drawings are posted on the website for public consumption and, of course, we realize that people who purchase competitor's boilers will use the drawings. As wwfw said, we have been at this a long time and have figured out how to make things work; sharing that knowledge makes the whole industry better and that benefits all of us in the long run. I am concerned, however, that Clarkburg and his installer have a fundamental lack of understanding about what PT1 is trying to accomplish. First of all, the two tank suggestion is a MINIMUM recommendation, not a maximum - 660 gallons for the Vedolux 37 will work great. Second, the concern about cold return water means that, either there is no tempering valve being used or, again, there is little or no understanding of the drawing. What about the BLT? TV2? ZV1? If these components are not included in the installation, the system will not work as the schematic shows. What does your supplier recommend for an installation schematic?


Can you describe what is the purposes of ZV1 (zone valve)
Thank you
 
The simple math for sizing a buffer tank can be seen here, on page 35-36.
www.caleffi.com/sites/default/files/coll_attach.../idronics_10.pdf

The math is a bit more complicated if you want to charge the tank while there is a heat load, that math is in this article from 1999! The example considers a 40,000 heating load.
http://www.pmmag.com/articles/84944-mixing-wood-and-water

Keep in mind if the boiler is sized close to the heating load on a design day, you will not be adding much, if any to the buffer tank.

So another couple factor is to determine how often you are at, or below, design conditions. And how close your boiler actual output is to the actual calculated load. You will not charge a buffer tank to carry you through the night if all the boiler output goes to the load, 24/7.

Somewhere I have a link to data showing how many days various weather stations are at or below design conditions, maybe a NORA website or some ASHRAE data. Generally they have that data for the past 30 years.

But if in fact there is a change in weather conditions based on global warming, or cooling, those numbers are a guess also.

You can make yourself crazy with number crunching for two very un-predictable conditions, the building heatload, which varies from second to second, and the output of the boiler which is sensitive to many variables. The wood being burned is one of the biggest variables.

Or the rule of thumb tank sizing, gallons per boiler size, which seems to get most of the posters in a condition they are happy with..
 
I'm sure the Varms have some type of condensation protection built into the control.......or else they recommend using a boiler protection valve (AKA Termovar)....

As far as the storage volume is concerned, i recommend a minimum of 7 gallons per 1,000 btu boiler output. What's the rating on your Varm?
 
Greg, ZV1 stays closed until there is a call for heat from the zone control. That way if the wood boiler is running all the flow (heat) goes to storage. ZV1 stays closed if there is a call from a zone and you are running off the back-up boiler. The ZV1 is controlled by the BLT control.
 
I'm sure the Varms have some type of condensation protection built into the control.......or else they recommend using a boiler protection valve (AKA Termovar)....

As far as the storage volume is concerned, i recommend a minimum of 7 gallons per 1,000 btu boiler output. What's the rating on your Varm?

Loading unit mandatory.

Suggested storage volume per the manual is a bit different. 8-10l per sq.m. of heated surface area. That could maybe be taken as talking about walls too - but using my square footage of floors, I come up with around 550 imperial gallons for my house. Rating is 40kw max, which works out to 950 gallons (US?) +/- using your method. I think I've got close to 700 US, which works great and is pretty well on what the manual implies, but I would like a bit more if I could. But the desire for a bit more isn't related to boiler output, but rather heat load.
 
we recommend a minimum of 4 gallons per 1000 btu of boiler output and an ideal of 7 gallons per 1000 btu. We find a 30kW boiler does pretty well with two 220 gallon tanks but works better with two 300's. Available space, tank dimensions (doorway widths and ceiling height) and, of course, budget all play a role in choosing the "right" size thermal storage.
 
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