A.O Smith Storage Tank

Peter_26

Hello,

I would like to know if anyone has any thoughts on A.O. Smith storage tanks? I was looking into Model# TJV-120M from SupplyHouse.com. I know it's a commercial unit, but the price is pretty reasonable for a 119 gal model. I included the picture of the layout for the tank connections and from what I can see there is only 1 1" tank port at the top front. Would there be any problems with using the 1" top port, plugging the front 2 2" ports closest to the center and the rear 2" port, bushing down the 2" bottom port to 1"? I would like to use it as a 2 pipe buffer tank for my oversized boiler while having the flexibility of converting it into a 3 pipe buffer tank in the future when the fin tube baseboard are replaced with panel radiators.

I am trying to keep the my 36 year old Vaillant GA92-100 for as long as I can while planing for a future condensing boiler replacement.

Any input or experience with that model storage tank is greatly appreciated.

Thanks!

hot_rod

That would be a great tank for buffer use.
You want the largest diameter ports that the tanks have.
I'd use the 2" on top and the lowest 2" on the front. That would use all the tank capacity and the 2" connections provide the hydraulic separation.

We wrote this issue before we discovered the Manning 3 pipe method. The top connection makes for a nice 3 pipe/direct to load option.

https://idronics.caleffi.com/magazine/17-thermal-storage-hydronic-systems


I'll look for a good schematic of 3 pipe.

hot_rod

Here is a 3 pipe schematic I did for some HP training, same principles apply to a heating application with a boiler.

It would be nice to have two connections on the bottom across from one another. A tee on a lower connection will work okay.

Peter_26

Thanks for the picture @hot_rod . Yes, Idronics 17, read that one and others too.

Would the 2 pipe be more fitting for a non-condensing boiler and the 3 pipe for a condensing boiler based on the fact that you want the coolest water returning for a condensing versus a non-condensing boiler?

I like the idea of running my cast iron boiler to maintain the temperature on the tank and letting the system initially draw from the tank and then when needed from both the boiler and tank. My system is not zoned yet, but when it's finally zoned it would have 3 zones and the smallest one would be approximately 12k btu, plus the panel radiators will be fitted with TRVs.

ScottSecor

These tanks are very popular here in NJ. For your use, I would think they would last a very long time.

STEVEusaPA

@hot_rod Would you still use that same 3 pipe set up/configuration if the load side circ was used injection mixing?

mattmia2

ScottSecor said:

These tanks are very popular here in NJ. For your use, I would think they would last a very long time.

A steel tank is fine cor a closed system. I would take a close look at insulation however, that could be worth a couple hundred extra to get more insulation.

JohnNY

We use a lot of these in NYC too since there are still a great many Burkay heaters floating around out there.

Peter_26

There are actually 2 119 gal models available at SupplyHouse.com. One is insulated ASME and the other just states it's insulated. The ASME is double the price of the other one. I've looked for the insulation specs on it , but can't find them.

mattmia2

I believe the ASME rating has to do with its certification as a pressure vessel and the insulation is the same on both.

Peter_26

If that's the case then the one that's not rated ASME should do just fine. I like the fact that it has a good number of connections for versatility and the ability to incorporate it in future updates. Some extra insulation around the jacket should help too.

mattmia2

You might want to do the math and see if you really need that big a tank as well. There is a formula involving the output of the boiler, the size of your smallest load and desired minimum cycle times.

Peter_26

Yes @mattmia2 , the formula is
V =t (Qhs-Qloadmin)/500(Delta T)

V = minimum buffer tank volume (gallons)
t = minimum heat source on time (minutes)
Qhs = rated heat output of heat source (Btu/hr)
Qloadmin = minimum concurrent heating load when heat
source is on (Btu/hr)
Delta T = change in average tank temperature during minimum
heat source on time (ºF)

I did not input a Qloadmin and used a 20 minute run time and a Delta T of 30 and came up with 113 gal, so decided on the 119 gal A.O Smith. I know I can get away with a smaller tank, but the 80 is actually $30 more. I want to have some flexibility for the future with other heating source possibilities.

Thanks

mattmia2

Without Qloadmin you are basically asking it to tell you what size tank can i heat in this time period. Unless your smallest load is or at some future point will be much smaller than the output of the boiler and it is likely to run by itself for long periods of time without other zones calling some of the tine that it is calling, that will give you a much bigger tank than you need. It won't hurt anything other than a bit more standby loss, but it also might cost a lot more than it needs to.

hot_rod

mattmia2 said:

I believe the ASME rating has to do with its certification as a pressure vessel and the insulation is the same on both.

Quite a bit involved with ASME ratings. The welder needs to be certified. All the components need to be documented right back to the steel plant that made the steel, any other components, heads, weld outlets, any mounting components, etc. That all gets factored into the price increase for ASME certified products.

hot_rod

Pros and cons to all three piping methods. With a non con you'll need return protection for the boiler if you start running low distribution temps.

A 3 way thermostatic, or a properly piped v/s temperature controlled circ, like this.
Thermostatic valves are parasitic, costing you some pumping power. An ECM, temperature controlled is the nicest solution.

The downside to 4 pipe is you always flow through the tank to get to and from loads. The tank needs to be up to temperature to start covering load. So some lag time and flowing across the tank does break up stratification a bit.

With two pipe, all boiler output goes directly to the loads. As the loads start dropping off, the tank gets charged.
I think you could use this piping, increase to 2"at the tank for a two pipe method.

Peter_26

I hear what you're saying @mattmia2 and yes the tank is most likely a little overkill, but I think it will be worth it in the long run. I could go with the 80 gal tank, but I would actually have to pay $30 more to go smaller. Also, yes, the smallest load would be around 2k btu. The plan is to use TRVs on all the radiators and for the one room that has the 2k btu heat loss use Caleffi TwisTop Thermo-electric actuators to control heat in those specific rooms (possibly use a couple more actuators, undecided about that). Even if I don't use actuators and one of the three zones or all call for heat the full load is still about 35k btu below the output of the boiler.

@hot_rod The idea is to reuse the ThermoMix on the non con boiler now and stick with a 130-140 SWT to the panel radiators to start with. The next step would be to lower the water temperature for the panel radiators as low as possible while covering the individual loss of each room. I actually bought the panel radiators to cover the heat loss of each room at 110 degrees SWT. Finally, incorporate ODR with a 3-way mixing valve for the additional savings. I open to other ideas if there is a better way of getting the most savings. I hope the investment in the panel radiators pays off, especially with the rising cost of fuel.

I like the idea of the ECM temp control to avoid condensation, but I would like to reuse the 3-way and avoid adding a circulator.

I really prefer the advantages of 2-pipe buffer for the non con and the 3-pipe for the possible conversion to mod-con in the future. I've looked at 4-pipe and it's a possibility for mod-con and better yet a heat pump if I wish to go with that in the future.

So, is there any specific length the 2" piping should be at the tank before any take offs. I am assuming it should be 2" Ts as close as possible to the tank to maintain the hydraulic separation and then go down from that?

hot_rod

Sure, you can use the 280 as the protection device.  

Yes on the 2” header being close to the tank, tees a few inches apart. It’s really more about the diameter of that header. We want flow velocity as low as possible in that pipe, so the various circuits do not flow into one another. It’s the logic of primary secondary piping. 

All things considered the 2 or 3 have the most advantages for mod cons and heat pumps

The only interface with the tank happens when the load is smaller, or off compared to the boiler. It’s mainly a parking space and a run time extender.

The 4 port piping just gets you a supersized hydraulic separator, there is always blending in the tank unless both sides have the exact same flow. So that can or will blend the return to the mod con or heat pump and effect it’s efficiency. Seps and closely spaced tees do the same.

We’d like to return directly to the source to optimize it performance 

Peter_26

@hot_rod I was actually referimg to the Ts on a 2-pipe buffer tank setup not the one on the picture you sent me with the v/s pump moitorimg the boiler return water tenp. 

The 2” Ts ona 2 pupe buffer tank setup should be as close as possible to the tank or is there some maximum length that can work? I’m guessing it’s like the p/s and the closer the better for hydaulic separation.