Please take a look at my hydronic design

[emesine]

Please take a look at my diagram. A few notes:

The boiler will be fired about twice weekly. I will fire up the boiler, turn on the boiler pump, open the solenoid, and turn on the pump in the storage tank to pull cool water off the bottom and deposit hot water on the surface. At the end of the firing, I will shut down these pumps, shut down the boiler, and close the solenoid. a 12 by 5 by 40 HX should be enough to transfer the 175K btu this boiler is capable of putting out.

Thermostat calls will activate the pump that pulls water off of the top of the tank and deposits it at the bottom, as well as the appropriate circulator.

The tricky part here comes down to the mixing valves. When the boiler is off, there shouldn't be any problem with the setup. However, when the boiler is firing there will be about 20 gpm of water flowing across the HX. This is enough to put about 5 feet of water pressure at the hot port of the mixing valve.

Using a standard mixing valve, will hot water leak across the hot port to the mix port and give me unwanted flow through my radiant loops?

Hot water will certainly leak across my hot water heater. I considered installing a zone valve here, but I think the easiest solution is to use a popit valve- a one way valve with an adjustable spring that will allow flow, but only above a certain pressure. The water flow in the system will make about 5 feet of head pressure; as long as this valve takes more than 5 feet to open, there will be no unwanted flow through that loop.

Any thoughts? I am about to spend quite a few dollars on this setup, so I would like for it to work!! I am most concerned with how to do the mixing valves.

Thanks!

 

[stee6043]

That's a whole lotta storage! I have a few thoughts:

You'll need a bypass loop at your boiler for return water temp protection. Is that in the works?

I'd avoid a "solenoid" in your only supply line going away from the boiler. This could be hazardous in a power out situation if the solenoid is normally closed.

I'm not sure the setup you have with bi-directional flow through your HX is the easiest way to do what you want to do here. It seems like you have a lot of pumps and will require a lot of control. Any thoughts on installing traditional "coils" in your tanks instead of using the flat plate HX?

Last thought - I'm sure you've done some math on the amount of storage you have. Based on my quick math you have just under 2,000,000btu's of usable heat in these tanks if you can operate between 120 and 180 degrees. Keep in mind how long it'll take to recharge. I'd bet a good 15-18 hours of full-bore burning with your E200 will be required to get the tank back up to temp on an average day with average wood. Have you considered a bigger boiler to cut this time down?

 

[Nofossil]

I don't have time to think deeply on this one, but that's never stopped me from posting ;-)

I'll echo the comments on the solenoid valve and inlet protection. It might make the system more bulletproof if you put a zone valve ahead of the mixing valve and replaced the solenoid valve with a flow check.

I personally wouldn't worry about the size of the boiler relative to the size of storage, as long as you can maintain stratification. For that reason I think that P3 should probably be a smaller pump, preferably one that can be slowed down to the minimum speed that will satisfy your house heat load.

 

[emesine]

3500 gallons is a bit more than I originally planned..... I simply left the area under the porch as a storage tank.

The main loop is 1.5 inches, so a 3 way mixing valve would be problematic (I don't know of one that large). I am planning on a 1" injection type valve that will form a bypass across the boiler loop. It will open if the boiler return drops below 140F, allowing hot water from the boiler supply back into the boiler return.

I had considered the problem of stratification, but I don't know enough about pumps. How does a variable speed pump work? How do I make sure it is running at high speed when many zones are operating, and at low speed when only one or two are operating?

Controls are actually fairly simple. The circulators and the storage pump are wired to a SR406 TACO controller. If a thermostat calls, then the appropriate circulator and the storage heat pump turn on. When I go to fire the boiler, I turn the storage pumps from heat to store, turn on the boiler pump (the solenoid is wired such that it is open as long as the boiler pump turns on) and load wood.

Any thoughts on the mixing valve? Will there be any leakage with pressure on the hot side, no pressure on the cold side, and no pressure on the mix side?

Thanks for your help!

 

[emesine]

As to coils vs. plate type heat exchanger....

That would save me a lot of trouble. I could eliminate all pumps and controlls within the heat storage tank. In order to get the heat out of the boiler, it would have to be 1.5 inch (!!) copper pipe. I have no idea how to calculate the heat transfer. I suspect it would take a long coil of pipe. The nice thing about the current set up is that it is all counter-flow. The cold water and hot water at the HX are traveling in opposite directions, which makes for highly efficient heat transfer. I'll have to give that one some thought.

Andrew

 

[julien]

«coils vs. plate» ?

No risk of cavitation with plate on side storage ?


For coil we have no chart to calculate heat transfer...

American Solartechnics offer this 150,000 btu/hr. I estimate is 6 x 50' - 5/8" OD tubes in parallel on ~16" spiral.

(broken link removed to http://www.americansolartechnics.com/space.html)