DHW Project- I think I have a bit of a problem

I have been slowly working on connecting the hot water coil on my KA-2 to my DHW tank. Many of you have given me advicealong the way.Thanks agin.
But as you can see from my drawing I think I have a problem with my propose aquastat location. After a few responses and PM's I think it is going to cause the circulator to come on quite frequently.

So now I am wondering how to proceed. Here are a few options ,some have been provided by smarter gys than I!

1) Gizmo's idea is to use the upper thermostat on the electric hot water heater. I like this idea but it would require that I not have the electric as a back-up without going through and rewiring. ( I was wondering if there would be a "switch that I could use to toggle between the two,i.e. DPDT?)
2)Remove the upper element and make this the well for the aquastat. But I have the same concern as above.
3) Run the pump constantly, using valves to restrict the flow, and thus simulate "thermoshiponing" to a degree. The pump is a Taco 1/40 hp.

So here i sit wondering how to proceed.
looking forward to your help!
Thanks,
Tom

KISS-
Pipe the cold water to the keystoker and back again to the cold water inlet of the water tank. Put a valve between the two tees and in each branch line. Summer mode - no coal fire open the bypass valve and close the branch lines. Winter mode - coal fire - close the bypass valve and open the branch lines.

No pump or controls needed.

Only issue is for prolonged hot water draws, the hot water tank contents gets very hot. A thermostatic tempering valve on the discharge of the hot water tank is recommended.

I have been running my wood boiler like this for years with no problems. Only a slight pressure drop in domestic water pressure in Winter mode.

steamup wrote:KISS-
Pipe the cold water to the keystoker and back again to the cold water inlet of the water tank. Put a valve between the two tees and in each branch line.

but but but -- opps there goes that pesky motor boat again

What if the tank sits all day when folks are away - there is no chance for thermal siphon on the tank or replenishment of lost energy in the standing vessel ? Why is there even any hot water in the morning after this design standing stagnant all night - unless the DHW tank heat train is still active and this arrangement is only to augment energy used during peak use and washing?

But then -- whats the use ?

Just asking I value your advice steamup

Kind Regards
Sting

could you put a pump between the boiler and the tank with a timer to switch on 10 min. every hour,to keep the tank hot all day/night without therosyphon. Do you really need to circulate the boiler water 24/7 ?, except for high demands.

All good valid points being brought up here.

All I'll add is, in combination with any of the above ideas, to augment the hot water tank's factory insulation to a greater level for less stand-by heat losses.

Dennis,
I thought about the timer idea something like what is on the KA-2. But there are about $150.
I thought about the need for running the pump 24/7. Maybe I will shop around for some other timers.
Thanks

how much demand do you need for hot water. My boiler has a 5 gpm. coil, my first time i filled the hot tub with water i had turned the hot spicket on full for 20 mins. The water in the tub was 125 degrees, i had to turn the cold water on for 10 mins.
That much hot water does take the boiler down to 140 degrees. Dennis

I guess I am not sure what our demand would be. It is just my wife and I.
I think what I may do is try to find a used timer. I see a few on ebay .
But to start I think I will try running the pump 24/7 with the valves closed down. Since it is such a small pump I think it would be less costly than turning it on multiple times a day.

Sting wrote:

steamup wrote:KISS-
Pipe the cold water to the keystoker and back again to the cold water inlet of the water tank. Put a valve between the two tees and in each branch line.

but but but -- opps there goes that pesky motor boat again

What if the tank sits all day when folks are away - there is no chance for thermal siphon on the tank or replenishment of lost energy in the standing vessel ? Why is there even any hot water in the morning after this design standing stagnant all night - unless the DHW tank heat train is still active and this arrangement is only to augment energy used during peak use and washing?

But then -- whats the use ?

Just asking I value your advice steamup

Kind Regards
Sting

You are correct in noting that there is repleshment of loss from the tank in non-use hours such as daytime work and nighttime sleep. Standby losses can be significant is some cases. However, I have found that my tank hardly ever, if ever, ran - mainly due to the much hotter water being dumped into the tank from the tankless coil. It takes a long time to cool down to the point the water heater kicks on.

My tank is over 15 years old and is PVC vented power draft type. No stack losses in the off mode. Good quality unit with fair tank insluation.
Newer, better quality electric tanks are insulated with non-cfc foam and really hold their heat.

I figure the use of a little standby energy was much cheaper than pumps, wiring, controls.

With all that said, my new coal arrangement does'nt permit me the luxury of a simple setup. I am going with a heat exchanger off of the boiler return water, bronze pump and a preheat tank. Much too complicated but I got a good deal on stuff off of Flea-Bay at the right time. A indirect water heater would be my best option but they are too pricey for my wallet at this time. Could'nt resist another science experiment.

Now another idea I had come up with but did not experiment with is to pump from the cold side of the hot water tank, through the heat exchanger (tankless coil) and back to the hot water outlet pipe (on the water heater). A strap on or immersion aquastat on the cold water inlet pipe of the water heater would start the pump any time the water fell below setpoint. In a non-use time, the water would be reverse flowed through the tank until the hot water came back out the tank cold water inlet and the aquastat shut the pump off. The pump may kick on occasionaly due to pipe losses, but pipe insulation would minimize this.

Of course, when there was no hot water in the boiler it would have to be valved off to prevent cold water bypassing the water heater through the tankless coil setup.

It gets messy trying to use a water heater as a storage tank and backup heater.

steamup wrote:Newer, better quality electric tanks are insulated with non-cfc foam and really hold their heat.

Agreed. The 80 gallon electric water heater in my last house could be shut off for 2-3 days and still provide warm water. As long as sending all the hot water through the 1/2" coil doesn't cause flow problems, your suggestion of hooking the coil in series with the tank should work fine.

on NG even today it only costs 5 to 8 bucks a month to stand a 40gal DHW tank at code temp

a point I attempted to make in the past but

I agree with steamup...KISS. Pipe your cold water to the coal boilers coil then to the water heater. Valve in a bypass for summer. No pumps or timers. Your water heater never sees cold water. It may come on a little bit to keep up to temperature but so what? It's the heating of cold water to temp that is the big energy user. You are saving so much on your heat and DHW that the little energy your water heater will use is not worth worrying about. And timers and pumps cost $$$ to buy, install and operate. Add the extra tank insulation and forget about standby loss.