Micro Zoning

Alan (California Radiant) Forbes

My Viessmann rep. just showed me this innovative piping design for micro zoning. Using the DHW indirect as a buffer tank.

mattmia2

Didn't I suggest using an indirect as a buffer tank like 6 months ago?

You would need something that control it, a mixing valve on the indirect, and an indirect that wouldn't have its warranty voided if you run it over 140.

Gordy

Well that’s not a revolutionary idea. Look no farther than HTP at the versa hydro, that’s set up for handling micro zoning.

Size rad/towel warmer for 140, or less.

Tom_133

Yikes, you guys are a bit tough today. I like that schematic, and I can see the benefit from it. The check valves in the piping mean you dont fire or flow through the boiler unless the tank cools down and it needs to be reheated. If I have that correct, I like it, now can I remember it when I need it.

hot_rod

It is a bit tougher to pull heat out of a tank like that via the coils. The temperature around the coil drops and without moving the water in the tank, two moving flows, heat transfer is not great

We tested our solar tank upper coils for heat removal, a bit disappointing, and they were in the stratified portion of the tank

Some buffering no doubt, and a good dual use option, using the tank water content would be better.

mikeg2015

Not a good idea to store water over 140 as there is potential for increased mineral deposits. Most tanks give a recommended upper limit for this.

hot_rod

I'd like to know more about that drawing. What is the flow directions? How do red pipes turn blue, or vice versa all of a sudden

Alan (California Radiant) Forbes

It's easier to understand if the colors are removed from the horizontal pipes and instead, labeled supply and return from the boiler. Or better yet: arrows. Circulation is clockwise for both systems, heating of tank and heating of towel warmer.

When the boiler is off and the tank is fully charged with hot water and there's a call from the towel warmer to turn on the pump, hot water is drawn from the return line to heat the circuit.

TAG

Is that a check valve or some type of clean out in the line between the boiler and the indirect.

This would be perfect for my new build ... Guess it depends on the indirect size and if it would remove too much BTU's

mattmia2

they are strainers.

Think carefully about what @hot_rod said about transfer ability of the coils in the indirect. They are typically designed for a boiler supply of around 180 degrees so they don't have a whole lot of surface area. Unless your system is designed for a low supply temp you won't be able to get much heat out of the tank (which might be ok if the goal is to keep the boiler from running a short cycle to satisfy a 5000 btu radiator or 2 each on their own zone)

hot_rod

Certainly do some math first.

What is the SWT required at the radiator
What tank temperature would be required to supply that temperature
The load of the micro zone

Indirect tanks tend to stratify when they heat, as much as 20° from top to bottom, so the aqua stat may need to be low enough to sense when the tank needs to fire to maintain adequate swt.

If the load is low enough it could have some value. A dual coil tank with the heat takeoff from the upper, warmer portion of the tank would be another option.

Indirect tanks heat up quickly due to a huge delta, like 60° incoming and 180° or so coil swt. Taking heat out you may not have much delta to leverage.

If the tank had a DWH recirc that would help heat transfer in that lower coil.

Alan (California Radiant) Forbes

There is the added dimension of circulating directly in the path of the boiler loop. When the boiler is firing and heating up the indirect, there is plenty of useful media (high temperature water) to satisfy the micro zone, that is, if it's calling for heat at the same time.
Also, depending on the size of the secondary circuit, it will starve the indirect (possibly only to a small degree). The return water will be cooler and the run time to satisfy the indirect will be longer, allowing the micro zone a greater availability of time to drink from the well.
I have no empirical data and it might be wishful thinking. My imagination sometimes runs wild.

mattmia2

I was thinking it myself until @hot_rod pointed out stagnation and the relatively small area of the coil in most indirects.

Might work better with a 2 coil tank and both coils piped in series or parallel, maybe with some valving to use them both for more surface area and to cover more of the tank. Might be able to do it by just controlling the indirect with a zone valve and opening that zone with a single small zone call or for a DHW call and letting the tank heat the system water or take heat from it while the small zone is calling.

Gman66

Would this not be a perfect application for a reverse indirect?

Alan (California Radiant) Forbes

"If the load is low enough it could have some value. A dual coil tank with the heat takeoff from the upper, warmer portion of the tank would be another option."