Is there a difference between a buffer tank and a storage tank?
August 12, 2015

Is there a difference between a buffer tank and a storage tank?

Are they the same thing? What's different?

Really a tank is a tank. Anytime we use a tank for storage of hot or cold water it could be a buffer, storage or both. We usually think of a buffer tank as one that stores thermal mass (sort of like a "flywheel") so a heating or cooling source doesn't cycle too much when smaller loads are turning on and off.  We would use the term "storage tank" for a project that is generating chilled water during the nighttime when electricity is cheap, then drawing off the cold storage during the day to provide HVAC cooling.

Of course the tank you choose must be built and listed for the application temperature and pressure and must have the correct safety relief valves. Choose a well-insulated tank. Also, large pipe connections are important to minimize pressure drop, especially for two-pipe connection applications. A four-pipe tank also provides the added benefit of hydraulic separation for systems that have primary/secondary pumps.

Caleffi ThermoCon and SolarCon tanks are built exactly for these and many other storage/buffer applications. They are well-insulated and have plenty of large, easy-to-use ports. Check out our NAS200 Series, and contact us with any questions!

Bob "Hot Rod" Rohr

Blog post comments
HR
August 12, 2015

Also an electric immersion element could be added to the tank to give you an additional energy source, perhaps to take advantage of off-peak rates. Many manufacturers offer UL listed elements and control options.

Mark Olson
August 13, 2015

I've always liked this photo sent in on Caleffi Excellence showing a Caleffi buffer tank in a Combi GEO Heat Pump/Boiler system.

Bob Deering

In reply to by Mark Olson

November 11, 2016

Mark, is the supply from the heat pump piped into the upper port of the buffer tank, and the supply to the zones leaving the other upper port? That's my assumption but I can't tell for sure from the photo.

tech_support

In reply to by Bob Deering

November 15, 2016

You are correct, yes. The thermal stratification is maintained for best performance. Check out page 7 of our idronics issue #17 "Thermal Storage in Hydronic Systems".

Kelly Burnham
October 26, 2018

I'd like to add a 500 gallon tank to the open side of a OWB system connected to a greenhouse and was wondering you had any suggested piping arrangements.

Thanks,
Kelly

Cody Mack

In reply to by Kelly Burnham

November 01, 2018

Kelly,

I would highly suggest looking through our Idronics journals for some inspiration.

https://www.caleffi.com/usa/en-us/technical-magazine

Specifically issue #10 (HYDRONICS FOR WOOD-FIRED HEAT SOURCES) and issue #17 (THERMAL STORAGE IN HYDRONIC SYSTEMS).

Best Regards,
Cody Mack
Applications Engineer
Caleffi North America

Kelly Burnham

In reply to by Cody Mack

November 01, 2018

Hey Cody,
Iv;e been reading thru the Stratification section of issue #17. I'll be re-thinking my tank pipe connection strategy. It's opposite to what you'd think.

Thanks,
Kelly

Bob Rohr

In reply to by Kelly Burnham

November 01, 2018

Sure, you can add a buffer, if you pipe it in series, it just becomes an addition to the OWB capacity. keep in mind it will see O2 and rust away if it is a plain steel vessel. Add O2 scavenger chemicals from time to time available from the OWF dealers. Is the distribution a pressurized loop? If so you need a heat exchanger in the mix, shown on page 20, for example.
https://www.caleffi.com/sites/default/files/file/idronics_10.pdf

Bob Rohr
November 01, 2018

If you pipe it in series, it just becomes an extension of the OWB tank. keep in mind any steel vessel will be subject to corrosion on an open system. Add O2 scavenger chemicals form OWF dealers.
If the distribution side is pressurized, you will need a heat exchanger in the piping, page 20 here
https://www.caleffi.com/sites/default/files/file/idronics_10.pdf

Kelly Burnham

In reply to by Bob Rohr

November 01, 2018

Hey Bob,
Thanks for your comments. We are using 500 gal horizontal propane tank and Yes, there are (2) Brazed plate heat exchangers between the OWB and the load loops (3). It would appear that the recommended orientation of the tank is Vertical, where this is not possible/practial in this installation. The tank will be horizontal so the inlet will be at one end at low level and the outlet at the opposite end at high level. Given that propane tanks are pressure rated for 200+ psi and the closed loop is operating at 10 to 12 psi it should be acceptable to pipe the tank into the (closed) load loop, where corrosion would be mitigated - which is a good idea.

Question: Given that the intended use of the tank is to provide thermal storage for the greenhouse, would it make sense then to pipe the tank in series with the loop that serves the greenhouse? All the loops are connected via common header so the thermal storage would serve all loads indirectly, e.g. house, garage, shop, etc.

Thanks,
Kelly