EKO 40 Supply two Heating Loads

[hartkem]

As always I need your guys help to understand how I need to hook up my boiler. I have my boiler installed in my boiler shack 130ft from my house. In the basement I have 500 gallons of pressurized storage. Im getting ready to purchase 1 1/4 thermopex for the run between the boiler and the house. I don't have my workshop built yet but I also want to be able to heat it when the time comes. My boiler shack has a concrete floor that was existing before I bought my house so I will need to use a concrete saw to cut a square in the floor to run my thermopex up through. While I have the trench dug under the boiler shack floor I also plan to install a 6" piece of pipe so I can later run thermopex from the boiler shack to my future workshop. So my question is how do I feed two heating loads with my EKO 40. Do I just Y off the outlet of the boiler and Y the returns back together? Im sure you guys know a recommended way. My workshop won't be heated all the time and when I do it will probably be only up to 60F. The workshop will use an air handler with heat exhanger. I included my original piping plans for the house and added a rudimentary sketch for the workshop so you guys get the idea of my current plans.

Thanks so much

 

[ewdudley]

I think you meant to draw the boiler pump on the boiler side of the mixing valve. The shop circuit needs to return to the other side of the mixing valve so the system can maintain return temperature protection.

So just put the pump where the shop return is, and the shop return where the pump is.

Also the shop supply should tee-in on the storage side of the boiler bypass, not the boiler side as drawn.

Since hot water floats so well on top of cooler water, you may prefer to eliminate the storage bypass circuitry.

And since your loads are high temperature loads, you might like a higher temperature boiler return mixing valve, for instance a 160 degF Danfoss. This would mean your supply temperatures would always be more like 180 or 185 degF and you wouldn't have to wait for all of storage to heat up before you had nice not water for your WAHX.

The right pump will be important with the remote storage, getting 10 or 12 gpm though that distance of 1.25" PEX efficiently will need just the right pump curve.

 

[jebatty]

With EW's suggested change on the shop plumbing, this is the way my system is plumbed and what I also would recommend. I agree that the bypass valves do not provide much advantage; even a horizontal tank stratifies very well with this setup. But, the higher temp boiler return mixing valve may not achieve the intended result of higher temp water to the wahx. The result also will depend on flow rates and bottom of storage temperature. If we assume the Eko has average output of 100,000 btuh, at deltaT of 20F, that is 10 gpm. The boiler return mixing valve will divert some of that output back to the boiler to maintain the set temp of the boiler return mixing valve, so actual flow to storage will be less than 10 gpm until all of storage is up to the set temp. The higher the set temp, the longer it will take to bring all of storage up to the set temp so that full 10 gpm flow goes to storage.

Next is the gpm flow through the wahx. If the flow is greater than the boiler circ flow to storage, maximum temp to the wahx will be a mix of boiler output/top of tank temp and lower tank temp based on the stratification within the tank, but it can't be the set temp of the boiler return mixing valve because more flow is required than boiler output to storage.

Another factor will be the return temperature from the wahx. Assuming a deltaT of 20F and 180F supply to the wahx, return to bottom of tank will be 160F, and there will be relatively rapid mixing of the tank to the wahx return temp. This mixing will affect boiler operation because now bottom of tank (assume possible 160F from wahx) water is now much warmer than from a bottom of a stratified tank with no mixing occurring. This is not necessarily bad, but it will make it important to make sure that the boiler circ is gpm-sized to handle boiler output based on expected storage return temperature.

Everything I have said does not change EW's affirmation of your plumbing plan, with which I agree. I'm not sure, however, that you will necessarily gain any system performance from a 180F vs. 160F boiler return mixing valve. The performance gain, if any, will depend on the flow rate of your wahx system, which likely will be increased when the shop loop is added.

Lastly, it would be very good if your wahx really doesn't need 180F water to meet your comfort requirement heat demand. As you likely are well aware, if that is the requirement, your storage will be of limited help in extending times between burns. Assuming the maximum temp your boiler will deliver is 190F, storage btu's from 10F in a 490 gallon tank is only about 40,000 btu's, which won't heat most houses for long in cold weather.

As said, EW's comments are solid. I really like the idea of plumbing storage as a hydraulic separator. It is simple, efficient, and can work very well.

 

[hartkem]

Thanks jebatty and EW! I will remove the bypass circuits and relocate the shop supply and return to the proper locations. Can I use ball valves to open / close the supply and return to the shop? I assume the shop circuit will need its own circuilator pump? I know I am going to need help sizing my circ pump for the house. I'm learning but very slowly.

 

[ewdudley]

Can I use ball valves to open / close the supply and return to the shop? I assume the shop circuit will need its own circuilator pump? I know I am going to need help sizing my circ pump for the house. I'm learning but very slowly.

You'll need some means of shutting off the shop circuit when it's not active, since the shop circuit is in parallel with the storage circuit, Perhaps a Taco Zone Sentry electronic ball valve and a small steep-curve pump like a 008 or a 15-58 would do the trick for the shop circuit.

Jim raises some issues you should look at concerning load flows.

I think a high temperature return mixing valve would be one way of insuring hot enough supply temperatures, another good way might be to play with the 'launch' temperature in the boiler controls. Or a boiler bypass loop with a separate return injection scheme. Any of these should insure that whenever hot water is available, it will be hot enough to do the job well. Again, I believe this is important for your system for two reasons: WAHX units generally require fairly high temperatures, and with remote storage you'll have relatively low flow rates going to storage so higher supply temperatures will help insure that the full output of the boiler can be sent to storage without idling.

But as Jim points out, what good is hot supply water if the load flow rates are too high and they're mixing storage on the other side?

A simple and effective solution would be to use a diverter valve on the return side of each of the load circuits. Have a look at the Tarm reference designs and you'll see where they use this technique to re-route hot return water back to the loads to keep it from mixing storage. Notwithstanding Siggy's recent warnings, a Taco 5000 series diverter valve--even with a Cv of 3.8--might well do the trick for heat loads below 75000 btu per hour, just need to sharpen your pencil to see what works. This way you can set a maximum return-to-storage temperature with the adjustable diverter valve.

 

[700renegade]

What about relocating the expansion tank to near the boiler? If valves were accidentally turned off between the boiler and your basement, you could have excitement with an over-pressure situation. Granted you have no fail-safe heat dump either, but that's in addition to the expansion tank issue.
Seems to me that the expansion tank should reside closest to the source of the BTU's ( and the most expensive equipment ).