DIY Buffer Tank

hituw2x4

About a year ago I put in a TT solo 250 with an indirect water heater and have been running it like a cast iron boiler, high output temperature without use of outdoor reset. Recently I decided to try an maximize efficiency and utilize the outdoor reset and set the temperatures as low as possible. I have predominately Model 80 baseboard throughout with two kick heaters, a 12,000 and 4,200. In my efforts to find the lowest possible temperature curve I can use for my house I ran into the problem of short cycling which I have found a decent amount of people are having problems with. When I say short cycling I mean in the range of a run time of 30 seconds on 45-60 seconds off and then back on. I crunched some number and figured the output at 130-140 degrees on one zone to be about 22k-24k btu and with the realized minimum output of 65,000 btu for the TT 250. With that being the most extreme difference in output vs demand for the system I figured, using the buffer tank formula, about 28 gallons, which worked out perfect because during the Storm Sandy my basement flooded and my 30 gallon upright compressor was shot. I saved the tank figuring I would need it some time down the road and I did. Cut off all the mounting hardware for the compressor, motor, wheels, handles and welded on 1-1/2 thread-o-lets for the boiler input and output and the load input and output. I have a picture I will share of the tank in the process. Since the picture I have completed all the welding, primed and painted it I will get a picture of it. I don't think I will insulate it, since I wouldn't mind having it heat my basement since I spend a lot of time there. I will take a picture when it's installed too.

hituw2x4

The galvanized pipes were just used to assure squareness during welding.

Rich_49

Where will you put a sensor in that tank ? You are gonna want that tank to communicate with the boiler .

hituw2x4

No communication. Just adding mass

hituw2x4

That's a great PDF you attached. I just spun through it briefly and there is a great deal of information in it! Thanks

hituw2x4

The tank will serve to decouple and add mass. My intentions were to allow the interface of the boiler along with the monitory of the inlet and outlet temperatures to determine when to fire and not to fire. Just like if there was no tank involved.

hot_rod

There are a lot of ways a buffer tank can be added or controlled in a system. Often times they are piped to provide buffer volume and extend "burner off' times. The wood boiler installers tend to drive them pretty high and then pull off the tank to the lowest possible temperature, based on reset controls. tekmar has some ideal controls for that.

Ideally some ports into the tank at 3 levels helps get control, but sensors work well strapped tight against the tank with insulation over them, if wells are not available.

Insulation, at least partial will be needed of you have a oversized radiator added to the boiler load, running uncontrolled.

We will have a Thermal Storage Idronics out later this year with some really clever buffer piping and T circ integration, also a webinar in conjunction with the journal.

In the mean time there are some nice options for calculating and piping buffer in this issue.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

hituw2x4

I attached a couple of pictures after priming and paint with the can vent as a mock up. I am still trying to figure out why I would have to need a senor of any type in or on the tank. The primary loop circulating through the buffer tank should be more than adequate for regulated water temperature, correct? My understanding is this will act similarly to a set of closely spaced tees or a hydraulic separator only with buffering volume added.

Ironman

The reason for the tank sensor is because when different flow rates and loads occur between the primary and secondary loops, you want to use a "system sensor" so the boiler's control can know what the temp is there and adjust accordingly.

Nice job on the tank. Make sure you pressure test it - in a safe manner - like a tire cage.

icesailor

@hituw2x4:

You really know how to make sparks fly.

Nice job.

tim smith

nice tank.

hituw2x4

Thanks gents for all the positive comments and advice. I am going to add a sensor port in between the secondary piping ports (the one further spaced apart). I always get extra paint for times like these haha. I was thinking about putting a 1-1/2 x 1/2 x 1-1/2 tee on secondary supply outlet, but decided to do it right and add one that will allow full immersion in the tank. Any suggestions on insulation?

Thanks again

Mark Eatherton

If you wanted a sensor well IN the tank, any one of the flow thru fittings could easily be set up with a DIY sensor well using 1/2" copper pipe with cap on end, sent through reducing tee on any one of those fittings. All of this is IF you wanted a sensor well. As HR said, simply bonding a sensor to the tank exterior and insulating will work good 'Nuff. Nice job. I'd insulate the tank and figure out a better way to keep the mech. Room warm. Uncontrolled heat will come back to bite you eventually...

Also, as others have pointed out, do a good pressure test, preferably hydrostatic, prior to bringing on line and make certain that either a rated relief valve is installed on the tank, or there is no possible means of isolation from the boiler relief valve. If the vessel fails under a hydrostatic test, you get a little wet. If the tank fails during a compressed air test, people could die...

ME

RobG

One other thing to think about is adding a boiler drain on the bottom of the tank as that is where any system debris will be collected.

Harvey Ramer

And don't forget to add in an appropriately sized expansion tank for the increased water volume!!

Tank is looking great!

hot_rod

hituw2x4 said:

Thanks gents for all the positive comments and advice. I am going to add a sensor port in between the secondary piping ports (the one further spaced apart). I always get extra paint for times like these haha. I was thinking about putting a 1-1/2 x 1/2 x 1-1/2 tee on secondary supply outlet, but decided to do it right and add one that will allow full immersion in the tank. Any suggestions on insulation?

Thanks again

Fiberglass pipe insulation works and looks nice on tanks. What's the diameter?
Most commercial insulation shops stock up to 24". A small sheet of flat fiberglass board to cut the end circles out of.

hituw2x4

I don't think you can see in the pictures but on the bottom I have a 1/2" outlet for the sentiment blow off where I am going to put a 1/2" ball valve. I will hydro-test the tank with a garden hose, where I am at should give me a good 65 psi, although I am not too worried because the air compressor was asme stamped to 135 psi. Good point about the expansion tank, I didn't think of that either.
The diameter is roughly 16.25" and stands about 39" tall.

hot_rod

here is a compressor tank that I converted into a solar drainback tank. 12" insulation, fiberglass ends with bubble foil for a space age look

rick in Alaska

I guess my question would be as to how much baseboard you have? That is a big boiler. Maybe you just need to get a smaller one.
Rick

hituw2x4

@rick in Alaska I've Got right around 277 ft. of high intensity baseboard and the two kick heaters. House isn't huge but it's 120 years old with massive infiltration.
@hot rod That tank fit like a glove! Looks great. I wrapped mine with some duct work insulation I had around the shop. Probably around R8. I would have liked to have found some 16" fiberglass pipe insulation but I think that would have been a special order.