Froling S3 Turbo Install with 850 Gallons of Storage - OffGridICF

[hyfire]

Thanks for the feedback. I'm a little concerned at this point but not ready to order another tank yet. My wallet is still scorched from the recent flurry of orders ;-)

The Watts calculator run for 12psi - 28psi, 40F - 190F and 850 gal said the required acceptance was 26.6 gal. The two tanks on order will provide 42.6 gal which seems like about 60% more than required but this turns out to not be relevant (more below). The overall required tank volume of 105.4 gal is the limiting factor and the tanks will provide 106 gal which is very close at 28psi max.

The actual system volume will be closer to 825 gal and it will probably only be run to 185F so there's a little extra safety margin there. Also, only the storage and boiler loop will be at the max temperature. All the radiant loops will only be around 105F max and the radiators 140F max. There is very little volume in the water heater preheat loop. This will reduce the effective system volume to around 810 gal.

The initial fill pressure could also be reduced a little since the maximum height in the system is only 12'. The minimum pressure for 12' should be (elevation in feet / 2.31 feet per psi) + 4psi = 9.2psi, or rounded up to 10psi. The max pressure can then be reduced to 25psi as you suggested.

Re-running the calculator for those conditions, 10psi - 25psi, 40F - 185F and 810 gal, drops the required acceptance from 26.6 gal to 23.8 gal and the required tank volume from 105.4 gal to 91.1 gal which is a much more comfortable margin.

This whole expansion tank business was still a bit confusing to me. Digging deeper and using the Watts tool to generate a plot of max pressure vs. acceptance volume for a fixed expansion tank total volume of 106 gal, 40F - 190F, 12psi min was helpful. It turns out that the tanks on order will only accept 42.6 gal once the pressure reaches about 40psi, far above the 30psi PRV limit. I also ran the numbers for a 106 gal expansion tank, 40F - 185F, 10psi min for comparison. Both with 825 gal water total.
View attachment 330431

With the ability to make these changes if needed, it seems like the tanks on order should work OK. If necessary, another smaller tank can be added later. I'll add another tee and cap it off just in case.

You did a good job on figuring this out, rather safe than having the prv start to leak. The total expansion volume is what will change most once it hits 185f as you see on your calcs.

 

[OffGridICF]

What is the spacing between the 2 black pipe tee's and what diameter is the black piping?

Those two tees are about 8" apart. This might be a little much for optimum hydraulic separation but simplified the piping to the circulators. That section of black iron pipe is 2" all the way to the storage tank. It's basically a two-port storage tank system with 2" connections at all the tank ports and up to the tees for heat emitter supply and return circuits. The boiler piping is all 1 1/4".

 

[hyfire]

What GPM do you plan to run in the boiler loop and the other loops? The spacing should work like you said. Looking at this again what is the purpose of the differential pressure valve?

 

[OffGridICF]

The radiant floor loop will run about 85F - 95F at <2gpm total and the radiators about 140F at 1.5gpm - 2gpm. The radiators may get fan assist to extract more heat at lower water temps so when storage drops below 140F they will still provide good heat output.

The loop to the heat exchanger that will preheat water entering the water heater will run a higher flow but only intermittently. Its flow can also be adjusted as needed by changing the target temp.

The loop from boiler to storage will vary based on the delta-T. At a 20F delta-T it will require about 8gpm to transfer 80kBTU/hr. Here's a chart of flow vs. delta-T:

The Resideo circulator will move 17gpm at 3' of head (just guessing at 3') so it should be able to maintain a delta-T down to 10F. Near the end of the burn the boiler output will probably drop off so this seems OK. I did see one system where there were two circulators in parallel on the boiler main loop to storage. This puzzled me initially then I realized the second circ could be turned on to get higher flow at low delta-T. Pretty clever.

From Figure 2 in the article "Pellet boiler meets modern hydronics" here:
https://www.pmmag.com/articles/106106-pellet-boiler-meets-modern-hydronics

A differential pressure valve, set for an opening pressure of 1 to 1.5 psi is installed between the pellet boiler and thermal storage tank. It serves two purposes: First, preventing flow returning from the load from passing through the pellet boiler when it and the loading unit circulator are off. And secondly, preventing reverse thermosiphoning from the thermal storage tank through the cooler piping connected to it. A normally open zone valve provides a bypass around this valve in the event of a power failure, and thus enables forward thermosiphon flow between the boiler and thermal storage tank.

 

[hyfire]

I am not sure if your going to run into any issues with the bigger piping, like unable to get the air out of the piping since the velocity maybe too low. Check the min, and max velocity ratings for your air separator , and dirt mag. 1" sch 40 will be perfect for up to 9 gpm copper similar. Your hot water plate exchange will probably not work to well if there is not very much DHW flow in the system. I have similar size plate exchanger and it does not work well at all, I am going to have to remove it from the tank feed and use it direct off the boiler with a 3 way solenoid and use electric backup in the tank. You need to plumb that in reverse order as well so the hottest water meets the coldest water.

 

[OffGridICF]

Thanks for taking the time and effort to comment on my work. I really appreciate it!

Hopefully all the pipes slope a little toward an air vent. The worst place is probably right at the boiler circ output since the circ has an internal check valve. That location will see the highest static pressure and highest flow rate which should help flush any air. Otherwise, there are vents at the top of all the storage tanks and at each radiant manifold. I've tried to avoid high spots without vents where air might be trapped.

The plate HX is being used in a slightly unconventional way. It will heat the incoming cold water before it enters the propane water heater. this does not rely on thermosiphoning and does not require another circ so it saves power. There will be a mixing valve at the water heater output. This approach is covered in the following two videos:

Part 1: Designing for Low Temperature Systems with John Siegenthaler

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Part 2:

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From the first video:

In both of these, John shows the HX plumbed for counter flow so I did it that same way. What is the benefit of reversing it so the flow is in parallel?

 

[all night moe]

The method I thought was correct is to use the boiler out on the cold in. Then boiler in heats cold out.
The boiler out would give a quick "preheat" of the curb side water supply.

Hope this makes sense.

 

[all night moe]

Yea I just described your diagram....LOL