Still confused a bit

[James Ascherl]

I am a bit confused about the flow of my system when both circulators are running. I question whether I will get flow into my storage tanks when I don't want it to go there. My system seems to be similar to NoFossil's "Simplest Pressurized Storage" but it looks like his would have the same issues. Will the amount of flow into the tanks be minimal because the load pump will be running? I have installed a valve (not shown) between the expansion tank and the storage tanks but am scratching my head as to whether this is neccessary or even how to control this valve. I would need it to open when the tank is charging (the load circ is off) as well as when heating from storage (the load circ is on and eko circ is off).

Also, My electric boiler has only one thermostat for all four zones. I have always had trouble keeping the zone that was furthest from the boiler warm. I plan on installing four thermostats for the eko in the four zones of the house to allow the furthest one to run longer. My electric boiler will run independent of the eko with its own thermostat. It will be set much lower than the eko and will kick on only when my storage is cold and the eko is not running. I know this is not the normal setup but does anyone see any issues with this?

Thanks for all the input.

 

[ewdudley]

It should work OK.

If storage is hot and WB circulator is not running, then all load flow pulls from top of storage and returns to bottom of storage. Mixing valve should close the C-to-M port down tight, so there will be no parallel flow through the WB.

If WB circulator is running and load circulator is not running, then all WB flow will pull from bottom of storage and supply hot water to top of storage. No flow will go through loads because all zone valves will be closed.

If storage is hot and both the WB circulator and the load circulator are running, then there are three cases: WB and load circulator flows are the same; WB flow greater than load flow; load flow greater than WB flow.

If WB flow equals load flow, all WB flow goes to load and no WB flow goes to storage. If WB flow greater than load flow then all load flow will come through the WB and some excess WB flow will go to storage. If WB flow less than load flow then all WB flow will go to load and the deficit will come from storage.

Only problem is that if load circulator is oversized whatsoever then load flow will tend to mix storage, but that's the way the 'Simplest' works, and it's not called 'Simplest' for nothing. One way to address this problem would be to use an adjustable constant head ECM pump like a Grundfos Alpha or a Wilo Stratos. That way the load circulator could be adjusted down to where hopefully excess load flow will be below an acceptable minimum in most cases.

No problem when storage is not hot and EB is running, assuming all zone valves are disabled and therefore closed.

--ewd

 

[jebatty]

If WB flow less than load flow then all WB flow will go to load and the deficit will come from storage.... Only problem is that if load circulator is oversized whatsoever then load flow will tend to mix storage ....

This situation brings up a couple of other issues. If storage temperature is low, then output to load will mix cool storage with hot WB output, resulting in lower temperature to load, which may cause insufficient btu's to load. And vice versa, if storage is hotter than WB output, mix temperature will be higher than WB. Higher temperature normally does not cause a problem.

A second issue. If load flow and WB flow are equal, or if load flow is greater than WB flow, and also if the WB is "over-sized," that is, btu output is greater than load, then full WB output will be going to load, and since what goes out must come back, the WB return may be hot, small delta-T, depending on the load, which may cause the WB temperature to rise to idling, even if storage temperature is low, making excess WB output unusable.

IMO a very satisfactory way to deal with these issues, and probably others, is to plumb storage as a hydraulic separator. This lets the WB do its work unaffected by the load conditions, and lets the load demand be met without causing any WB problems.

 

[ewdudley]

IMO a very satisfactory way to deal with these issues, and probably others, is to plumb storage as a hydraulic separator. This lets the WB do its work unaffected by the load conditions, and lets the load demand be met without causing any WB problems.

Plumbing storage as 'hydraulic separator' doesn't really buy you anything.

Whether the top of storage acts as a flow tee or it the tee is in the piping elsewhere it makes little difference. If there is not enough hot water in the top of storage to make up for what the WB cannot supply and any point in time then there is no rearrangement of plumbing that can change that.

 

[jebatty]

If there is not enough hot water in the top of storage to make up for what the WB cannot supply and any point in time then there is no rearrangement of plumbing that can change that.

We have no disagreement at all on this point. Depending on the load requirements it may be better, however, to not draw from storage when storage < WB output temperature or < another setpoint. Priority zoning might help address a need for hot WB output, without being cooled by storage, and also reduce likelihood of starved zones.

The hydraulic separator does address the over-sized WB issue which arises when load flow is >= to WB flow, so long as there is capacity in storage. And all I mean by "over-sized" is that WB output is greater than load. It can be quite convenient to over-size the WB to allow for quick storage charging, as well as charge to storage where there is a load. An idling result would not be desirable.

 

[ewdudley]

The hydraulic separator does address the over-sized WB issue which arises when load flow is >= to WB flow, so long as there is capacity in storage. And all I mean by "over-sized" is that WB output is greater than load.

I thinks it's simpler than that. When the flow from the WB hits the tee at the top of the schematic the amount of flow going to load will be determined by what the load circuit is doing at that moment. Any excess will take a left and head off to storage, making two WB flow circuits, partially to load and partially to storage. The two flows meet at the bottom of the schematic and return to the boiler according to the net flow of the mixing valve. And yes, excess WB capacity with storage is what it's all about, to charge storage and supply load heat at the same time.

--ewd

 

[jebatty]

ew, you're right in theory. The problem that I have is a system plumbed this way but it's not working like the theory, which probably means the source of the problem is something else in the system that is not permitting this result. I think I know what that is but I have not yet come to a conclusion. If the result impacts this thread, I'll put in a new post. Glad this came up because it helped to focus the analysis.

 

[ewdudley]

in theory...

I never knew before I googled it that this was a Yogiïsm:

"In theory, theory and practice are the same. In practice, they are not." --Yogi Berra