Buffer tank - need advice

hot_rod

As long as flow moves across or through the media inside it will grab air bubbles. Although I never flow tested that prototype.
Its actually a Discal/ Dirt body, I brazed the thread of a 1/2 coupling into. 2" steel fits into the bottom of it.

What size tube are you using. I have a 3/4" threaded body that you could experiment. There is enough brass to machine out for 1" copper, maybe even 1-1/4", or use a fitting reducing coupling 1-1/4- 1" to get to 1-1/4.

If you have a lathe you could spin it and machine the tube ports. I've used a holesaw also to enlarge threads. Braze the nipple in if it gets too sloppy

Not exactly approved mods, but if you want one, let me know.

SweatHog

I don't mean to hijack this thread, but I am intrigued by HotRod's 2- or 3-pipe piping recommendations. How can I improve this 4-pipe setup which was done per manufacturer's diagram?

hot_rod

Is that a combi system where DHW and heating water are all combined?
If so, get a combi boiler, keep the DHW separate. Then a 3 pipe buffer.

SweatHog

No, not a combi. Using an indirect heated by the boiler. A third pump, not shown, pulls the water directly throught the DHW loop dumps the return back into the buffer tank.

hot_rod

3 pipe buffer, indirect parallel to boiler

SweatHog

So eliminate the 4th pipe existing the top of the tank and put a T to the zone supply header in front of the buffter tank where supply pipe enters the tank and move the expansion tank to the hot supply side. Got it. What's the square at the top of the boiler supply pipe? Is that significant?

Dave Carpentier

Do you use an aquastat or thermal sensor in the indirect tank to control a separate temperature for DHW at the boiler ?

hot_rod

SweatHog said:

So eliminate the 4th pipe existing the top of the tank and put a T to the zone supply header in front of the buffter tank where supply pipe enters the tank and move the expansion tank to the hot supply side. Got it. What's the square at the top of the boiler supply pipe? Is that significant?

The square at top is an air separator, like a Caleffi Discal

If you have an 1-1/4" top opening, here is an even cleaner piping option. The expansion tank and fill could be at any of the 3 connection points into the tank, wherever it fits best. It turns the buffer tank into a PONPC.

So the concept with 2 or 3 pipe is all the boiler flow goes directly to the three zones when they are open. If the boiler pump moves more GPM then the zones use, a portion of the flow goes through the tank. As the zone valves close off a portion of the boiler output starts warming the buffer. When all zones close the tank warms to whatever temperature you set it to.

On the next heat call flow comes out of the tank only, the boiler circ is off, UNTIL the tank temperature drops, then the boiler and its circulator start again to go direct to load, or to load and a % into the tank. So the tank hydraulically engages and disengages based on flow rates and available temperature or energy stored in tank.

An ecm delta P circ on the distribution is another nice addition to regulate flow rates based on which zone valve are open. And save some electricity costs.

SweatHog

Thanks very much for the explanation.

152NP

@hot_rod I too thank you for the explanation you offered @SweatHog about the system's logic of operation. It took a lot of meditation for me to figure it out, and your explanation verifies my understanding is correct.

The attached piping design you gave @SweatHog shows the expansion tank and feed where I intended to hook them up on my 3-pipe buffer. I am curious why you chose to put the air separator where you did. I was going to put mine at the top of the buffer tank, or directly after it. Where you show it seems to be a higher pressure point coming out of the boiler.

I asked you about the modified Discal with the 2" pipe out the bottom because it was also mentioned that the buffer tank would be the best place to capture air because of the lack of flow velocity in the tank.

Thank you for the generous offer of the Discal body to experiment on. The 3/4 tappings won't work for me. I am running 2" coming out of the top of the tank and 2" coming from the boiler for hydraulic separation, and will transition at some point to 1 1/4 going out to the system. I thought a 2" T configuration at the top of the tank with an air vent at the top would be elegant. It seems like something I would have to build. Finding the correct mesh to put in it is the challenge. I can buy a spirotherm replacement cartridge, but they don't give specs on their diameter, so I don't know if it would work well. I may just settle for off the shelf components. I already have a 1 1/4 spirotherm from my old system that can use. Like I said, I thought it would be good to put it directly after the top outlet of the 3-pip buffer tank.

hot_rod

You could put a 2" cross on top of the tank, air vent on top with a bushing. Use a 1/2 or 3/4 vent.
The spiro element will fit inside a 2" nipple, need to find a way to lock it in.

The Caleffi is a composite, glass reinforced nylon product, you could trim it with a tin snips. Our welded vessels have a stainless steel expanded mesh inside.
Anything with a lot of sharp edged really, mesh, rings, fitting brush, etc. I'd stay away from a ferrous metal anything.

The air sep anywhere in the hot supply from the boiler or tank top if you care to home-build one.