Which design of indirect tanks are best?

Uni R_2

T-T's parent ACV can and does make upside down tank-in-tank indirects that are fully drainable. The Prestige Excellence (not sold over here) has a small internal indirect inverted tank-in-tank (as opposed to the Solo which is similar doesn't have an integrated tank).

Anyway, if the need to drain was strong enough and people wanted to pipe domestic connections at floor level, it could be done.

dan_47

indirect tank design

good day to all,

am installing a new indirect boiler mate tank and am wondering if the tank within a tank design (Triangle Tube, W/M Ultra) or the coil (Superstore) design is better with respect to recovery rate, cost, and maintenance.

thank you very much for any info.

cheers,

dan

Brad White

I am always learning...

What I recently learned was that the TT/W-M style of tank in a tank is probably superior overall for the following reasons:

Lower boiler-side pressure drops

Proportional increase in exchanger area to tank volume.


Potential for minimizing mineral build-up.

Pressure Drop:
The coil style has a measurable pressure drop which may or may not be an issue. If it is, it shows up as needing a booster circulator. The Viessmann Vitocell has a low pressure drop and the internal circulator on a Vitodens is matched to it when in DHW mode, as one example. Other brands (SuperStor in my case) needs a circulator and relay. No big deal in the end, but a consideration.

Exchanger Surface Area:
Coil types tend to have a fixed heat exchanger size or limited sizes within their tanks. These also have mechanical connections to them. In other words, with only so many sizes of heat exchanger matched to several tanks, you can go up a tank size or two and have the same heat exchanger.

As the tank-in-tank size increases, both tanks grow together retaining some proportionality. Now, this latter point really can be confirmed by knowing the actual coil-tank exchanger surface area versus the tank-in-tank surface area. I have not done so myself.

Mineral Build-Up:
I can see finned tubular heat exchangers with the potential to have those nooks and crannies fill up with minerals over time whereas smooth tube or tank styles which allow expansion and with relatively smooth surfaces, would promote drop-off of scale. Surmising, no direct experience in this regard.

Overall, I think both are excellent products and will give years of service but my next tank recommendation would be a tank-in-tank type for the reasons noted.

I am sure there are other reasons and opinions which I am anxious to hear.

Glenn Sossin_2

Recovery Rate

is a function of surface area and BTU's. The more btu's of heat you have, the higher the potential recovery rate. The higher the surface area, the higher the potential heat transfer rate and more heat you can absorb - larger surface area means you can take advantage of a large boiler output.

The WM and Triangle Tube Smart Tank are identical items - WM plays with the model numbers but made in exactly the same factory - different jacket.

Couple of points:

The head loss of the Superstor SS-80 (7.3') is approximately double that of the Prestige Smart 80 (3.5'). Essential this will mean less water flowing through the unit with the same size pump.

The Supertor SS60 has 60 gal and 15 sqft of exchanger surface.

The SM-60 (Triangle Tube) has 56 gallons and 29 sqft of exchange surface.

I would use the Triangle Tube Tank. One main disadvantage of this tank - no drain valve.

I attached some detaile recover info on the Triangle Tube tanks.


What size boiler and what size indirect were you thinking of?

bruce_21

Brad's said it well. Last year I replaced a customer's coil-in-tank indirect with a Phase III. It wasn"t heating because it was full of sediment that had covered up most of the inner coil. Fortunately it was a walkout basement or that sucker might still be there it was so heavy.

ALH_4

Coil vs Tank-in-Tank

A drawback to the tank-in-tank design is that there is no drain the bottom of the inner tank. Another is that the outer tank holds the boiler fluid, which is warmer than the potable water. Therefore the temperature differential across the tank insulation and tank heat loss is increased.

I prefer the coil type, because the entire boiler fluid is encased in potable water. Smooth coils make most sense than finned coils as they are less susceptible to mineral buildup and the entire coil area, both inside and out, is "wetted surface". The potable water side is cooler than the boiler side, so this minimizes heat loss off the tank compared to the tank-in tank design. The main drawbacks, as Brad pointed out already, are the pressure drop across the coil and less surface heat exchanger surface area. In general, the pressure drop is not an issue as long as the DHW pump is sized correctly.

Coil-type indirects vary significantly in material and performance from manufacturer to manufacturer. Tank-in-tank type indirects are all made by Triangle Tube (ACV), and therefore the performance does not vary by "manufacturer".

Both designs work well.

Aidan (UK)

Agree

Your choosing between two well made products. The key is choosing the right one within their line. What size boiler do you have compared to radiation load? What size indirect were you thinking of? How/why did you arrive at that size?

This last question is likely to draw lots of varied opinions.

dan_47

indirect tank design

to all,

thank you for all the input, all appreciated very much.

glen, the unit i have is a W/M Gold CGa-8, it puts out around 200,000 and it is presently matched to an Amtrol WH-10DW in 80 gallon. i have it installed in a 4-plex in Anchorage and was thinking of switching to a 60 gallon size because of how I am utilizing the building.

once again, thanks to everyone for all the info.

dan

Rich Kontny_5

I Agree

I like the TT and I overcame the draining problem with a home made 1/2 syphon tube. I would like to see a bottom drain however!

I like to use the heater as the design temperature buffer tank with it as the primary zone. Then I take lower temp. infloor zones off as secondary zones.

I am currently being educated about the injection pump concept to see if I can apply this to my preferred piping arrangement.

Rich K.


Make Peace our Passion while Supporting our Troops!

Leo

Piping Diagram

"I like the TT and I overcame the draining problem with a home made 1/2 syphon tube. I would like to see a bottom drain however"

Alot of guys do not follow the piping diagram which calls for syphon tube.

Leo

ALH_4

Coils

In my opinion, the Amtrol coil is very pooly designed compared to nearly any other indirect tank. The coil is very tight, which discourages convection within the tank. Double wall coils should only be used where code dictates, because it further inhibits heat transfer.

You probably will not see significant energy savings by replacing the tank with a smaller version. You can always turn down the tank temperature to save energy.