The Tank › Can you convert gas direct hwh to a buffer tank?
- March 22, 2008 at 10:48 pm #8479
I guess you need four connections all together. Is it possible?
DavidMarch 22, 2008 at 11:02 pm #8481
Hello: Whenever I fool myself into thinking I can read minds, wham, reality sits on me 😛 It would be nice to have more of a description of what you’re trying to do.
Yours, LarryMarch 23, 2008 at 11:50 am #8483
Thanks Larry. Well earlier this year I had to replace my direct HWH before I had intended. (hoped to get an indirect with a new boiler, but too many other projects going on to get a boiler, so…)
I figure I’ll get a new boiler in a few years–and indirect–and was hoping I could make use of the direct unit in some way at that time so as not to waste the investment. Buffer tank came to mind since that might help elongate firing cycles and save $$. I know electric HWH’s are more adaptable that way, but…..
Thanks and I hope that’s clearer.
DavidMarch 23, 2008 at 2:57 pm #8485
Hello: Thanks for the clarification. The main negative in using any fuel fired heater is flue losses. If you’re going to use it as an unfired tank, you could insulate and cap off the flue. Also, the gas control and burner could be removed. This would give you another 3/4″ port near the bottom to connect to. It beats tying into the drain as sediment would likely not ever become an issue with the higher port. I’m not sure you need four connections; three might work. It’s OK for two connections to be tied together with a “T” as long as the other two connections are separate. In your case, tie the hots together and have separate colds using the cold connection on top and the “new” cold connection where the gas control was. This hydraulic separation should prevent flow in one loop from inducing flow it the other.
A true indirect tank will perform better than anything you can do with a gas fired tank, but the difference can be minimized by starting with a well insulated tank. One last thing is this could create warranty issues, because manufacturers really don’t like folks modifying their tanks. As you would be removing the combustion component, I don’t see any increased safety risk. Is that the info you’re looking for?
Yours, LarryMarch 23, 2008 at 5:45 pm #8487
Yes, that helps. Though I never realized the gas port could be used as a water input–that doesn’t go into the water tank does it? just heats the water from below?….
Note that I’m not planning on using the direct hw tank as an indirect, just a buffer. I’ll buy a new indirect when the time comes. I’ve seen a diagram for an ‘upflow’ buffer tank where the boiler output goes right into the bottom of the buffer and exits the top, then divides into the zones. so for that you’d only need 2 ports.
Come to think of it, the cold water inlet of a direct goes pretty deep down into the tank doesn’t it? (have to check your book which i have). If so, you could have the boiler supply go in the CW inlet, down the tank a bit, then up the hw outlet.
DavidMarch 23, 2008 at 7:24 pm #8488
Hello: Just to keep from plumbing water into a gas line :), the port I’m talking about is the one that the current gas control screws into in the lower side of the tank. It does go directly into water. As you have a copy of our book, have a look at the diagram at the start of chapter one. It shows the relative positions of gas control, drain valve, etc.
By “buffer” do you mean putting the tank in series with your heating loads and plumbing it in such a way so it’s downstream of the load, just before water goes back into the boiler? Or, if you’re doing primary/secondary, the tank would be in the primary loop? Also, this tank would not see potable water once you add the indirect? Now, if it’s in the primary loop, what sort of gpm flow are you going to have and will you be able to get that through the buffer without serious head loss? Is this why you were looking for two inlets and two outlets?
I’m trying to steer things so you don’t wind up aground 😉 Assumptions are bad, clarity is good.
ps, be sure to read the quotes in our book. Those are the best part!March 23, 2008 at 7:35 pm #8489
Thanks for your replies Larry. My comments on two/two inlets/outlets were from recollecting a diagram for a buffer tank in a primary/secondary system which I don’t anticipate having. Yes, this would not be for potable water but in series with heating zones. Some installers do buffers upstream, some on return. I appreciate your diligence–please know that while I’m always learning about HVAC, I’m not a DIY’er, and licensed and experienced techs would be the ones to do any work. This is all a few years in the future.
DavidMarch 23, 2008 at 9:26 pm #8490
Hello: All good. One thing: I’d want to put the buffer tank downstream of the heating zones, so that it would operate at a lower temperature, reducing heat loss. There may be reasons to put it upstream, but I don’t know them. One more thing: The concept of hydraulic separation is a fairly new one in the US. John Siggenthaler has written about it and Caleffi makes equipment to do it. You may be able to use your buffer tank to accomplish the same thing. Here’s a link that might clarify ;~)
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