Storage Piping

[NCPABill]

I've read until I think I know what to do, to the point of thoroughly confused. I'm not a hvac or plumber, but seem to muddle my way through ok. I'm going to try to attach a Google Sketch-up image of what I want to do, along the lines of the Simplest Storage Design. I will have one circulator each for the gas boiler, wood boiler, and house heating loops, (three total with one circulator and three zone valves (existing). I understand the near boiler piping well, and will do all of that as well. The gas boiler is existing, quite old, but works ok, and hopefully will be used very little. The wood boiler is a Biomass 40. Storage is 500 gallons, the most I could fit in the space. The gas boiler is in another basement 40' away from the wood boiler. The storage is next to the wood boiler. I am planning 2" black iron welded into the tank, reduced to 1-1/4" piping to the wood boiler.

I sure would appreciate any advice before I get fully underway. Again, I'm not totally incompetent, but build construction and farming are more my thing. (Feel free to pick my brain on those!)

Thanks in advance for your time,

Bill

 

[DaveBP]

Do those cold lines continue to near the bottom of the tank internally?

 

[jebatty]

If you are welding couplings to the tank, or could do that, my choice for a horizontal tank would be to put all couplings on the ends of the tank. Example, hot from boiler horizontal input on end near top of tank, hot to house horizontal output on opposite end near top of the tank. Cold return to boiler on opposite end of hot from boiler, horizontal output near bottom of tank; cold from house on opposite end of tank, horizontal input near bottom of tank.

A 500 gallon tank horizontal tank likely will have a fair amount of mixing, but I think this plumbing arrangement will reduce that somewhat and as much as possible keep hot at the top of the tank and cold at the bottom of the tank.

 

[NCPABill]

Do those cold lines continue to near the bottom of the tank internally?

Yes, they will. I plan on putting 2" iron pipe to about 6" off the bottom. Sound right?

Thanks for the reply.

Bill

 

[NCPABill]

If you are welding couplings to the tank, or could do that, my choice for a horizontal tank would be to put all couplings on the ends of the tank. Example, hot from boiler horizontal input on end near top of tank, hot to house horizontal output on opposite end near top of the tank. Cold return to boiler on opposite end of hot from boiler, horizontal output near bottom of tank; cold from house on opposite end of tank, horizontal input near bottom of tank.

A 500 gallon tank horizontal tank likely will have a fair amount of mixing, but I think this plumbing arrangement will reduce that somewhat and as much as possible keep hot at the top of the tank and cold at the bottom of the tank.

Thanks for the info. My tank ends are rounded, and I'm not sure how I'd keep it horizontal until I welded it in, but I'll give it some thought.

Again, thanks,

Bill

 

[jebatty]

My 1000 gal tank has rounded ends also. A friend who does welding at the nearby nuke and coal fired power plants cut the holes and welded in 2" couplings for me, two couplings on one end only: boiler hot water horizontal input at top of tank and cold water horizontal return at bottom of tank. With no system draw on the tank, this achieves a very high level of stratification based on sensors installed at top of tank, down 1/3, down 2/3 and bottom of tank.

My system (radiant in-floor) is supplied from a fitting on the top of the tank about 1/3 from one end, with return via a dip-tube located about a foot away. The system draw results in a high level of tank mixing. This is not an issue for me as I mix down system supply to 100F and I don't need the hottest water from top of tank. I believe that if I had plumbed the tank as I suggested, stratification would have been accomplished and maintained both on tank charging and on tank draw down.

 

[in hot water]

Buy some 2" weld-O-Lets they are heavy iron adapters built to weld onto round tanks. Weld them onto the top of the tank.

Then you can but double tapped bushings. This allows you to reduce the opening and screw a pipe or adapter from either side. Now you can add a dip tube to get into the tank at any level. Solder a cap on a dip tube and drill holes around the side to better spread the water in the tank without mixing the temperature levels.

They also have duplex bushings that allow multiple connections into one opening, like gauge or sensor wells, etc.

www.oil-equip-mfg.com/docs/productsduplexbushings.html

 

[in hot water]

Thread o Let

 

[NCPABill]

Thanks for all of the advice. I'm getting closer every day. Trying to get rid of the mercaptan smell right now! Welding on tank soon.

Thanks again,

Bill

 

[woodsmaster]

Thanks for all of the advice. I'm getting closer every day. Trying to get rid of the mercaptan smell right now! Welding on tank soon.

Thanks again,

Bill

I had a small propane tank that had a little liquid in the bottom. I dumped it in the driveway and could smell it over half a year later when it was hot and sunny out, so be carefull where you dump.

 

[NCPABill]

Thanks for the advise!

 

[NCPABill]

I have one 1-1/2" and one 1" threaded hole now, with two 2" dip tubes planned. Can I put hot water from the boiler in at 1-1/2" and draw out of the tank to go to the boiler at 2"?

Thanks again,

Bill

 

[in hot water]

The hole size doesn't matter so much but the pipe size does. If the pipe is sized too large for the flow rate it sees, velocity decreases. When the velocity drops below 2 feet per second the air will not be pushed along and out of the system. If the pipe is undersized you will have excessive velocity, noise, erosion corrosion and the in-ability to move enough energy.

Some basic rules of thumb based on a 20 degree ∆T

1" copper 8 gpm or @ 80,000 BTU/hr
1-1/4 copper 14 gpm @ 140,000 BTU/hr.
1-1/2" copper 22 gpm @ 220,000 BTU/hr
2" copper 45 gpm @ 450,000 BTU/hr

Size the pipe to the actual output of the boiler not the input rating. if you have a 40KW/hr boiler that is about 136,000 BTU/hr. At 75% efficiency you have about 102,000 BTU/hr to move. 1-1/4" copper or iron pipe would be best for that size boiler.

60 KW/hr. = 204,000 BTU/hr. at 75% efficiency figure 153,000BTU/hr to move. 1-1/4 is a bit to tight I'd go with 1-1/2" for that size load.

2" connections are nice as you can bush down, or use duplex bushings for multiple connection points at one opening, like sensor wells, gauges, air vents, etc.

hr

 

[NCPABill]

Again, thanks for the info. I'm slowly but surely gaining ground on this project!

Bill

 

[jebatty]

Another thing you might consider is the probable temperature of the return water to storage. If you have a high temperature heating system, such as most baseboard and water to air heat exchangers, then the return water temperature maybe in the 140F+ range. It may make sense to have your return to storage port mid-tank rather than bottom of tank. This particularly may be useful if your system also has low temperature elements which will return water at a much lower temperature. That return might best be at bottom of tank. This arrangement will reduce tank mixing, better meet the high temperature demand, and provide the coolest return water from bottom of tank to boiler.

Also, if along with high temperature elements you also have low temperature elements, such as radiant in-floor, etc., and you use a mixing valve to mix down high temperature water to 100-120F or so for the low temperature elements, then you may want the return from the mixing valve also to mid-tank, as that return water temperature may be relatively high, and returning to bottom of tank may result in undesirable mixing, etc.

Some who have both high temperature and low temperature elements use the return from the high temperature elements as the supply to the low temperature elements. This seems to be a very useful and efficient scheme to consider where it applies.

Take these suggestions with common sense and don't over-complicate your system. Almost whatever you do with storage will result in improved performance from your system. Just think it through as best you can.