Propane tank stacking thought

jdboy9,

I too am wanting to better understand heat storage in water and it's stratification to best design my heat storage. In seeing an old thread by sdrobertson https://www.hearth.com/econtent/index.php/forums/viewthread/18299, I wonder the very thing your talking about -- wouldn't stacking be better? The purpose of the heat storage I'm sure defines the best configuration. I'm wanting storage for a wood boiler plus solar collectors to heat my home in the winter months plus heat my dhw year round. For my purposes, I believe proper management of stratification can have big payback over time. If someone could expound or point us to old threads on this subject, I'd be most appreciative.

My tanks are stacked 2 X 500 gallon. First find a supplier for your tanks. In some areas they are getting harder to come by. One important thing to remember is the tanks were originally designed to carry their own weight + liquefied gas partially full. Our designs are to fill full of water. On mine I reinforced the bottom legs and welded a frame around both tanks. Also you need to pay attention to the floor loading.

I have personally been involved in several gasification systems with storage and hear are my thoughts:

1.) The taller the storage tank the better as the top of the tank will be given the greatest opportunity to keep its hot temperature. The middle and bottom of the tank will continually feed the top of the tank and thus the taller the tank the more it will be kept hot at top (this process is called temperature stratification).

2.) When loading/charging the buffer tank with hot water from the boiler it is critical to do this from the top of the tank to the bottom, thus forcing the hot water towards the bottom of the tank where it will later be used to keep the top of the tank hot.

3.) When pulling hot water for the heat loads (ie baseboard, water to air HX, radiant floor heat etc) it is critical to pull the supply for the heat loads from the top of the tank and return this water to the bottom of the tank, thus ensuring that the heat loads are supplied with the hottest water possible.

I personally have (2) 500 gallon tanks stacked on top of each other and am able to get good stratification. When I make a fire in my effecta boiler I am able to get the top of the top tank to 190 F + and the bottom of the bottom tank to 180 F +. The temperature probe on the bottom of the tank is only attached to the outside of the tank and thus I think the actual water temperature is higher than my gage is saying. This summer I will put a hole in the bottom tank and insert the temp. probe into the tank using a well.

Having traveled to Effecta AB in Kungsbacka Sweden and attended the World Energy Fair in Sweden last summer I learned that all the tanks Effecta manufactures are vertical. They make these tanks in several sizes and join these multiple vertical tanks together at the top, middle and bottom. They pull water for the radiant heaters from the top of the tank but for DHW and radiant floor heat they pull the water off the middle of the tank where it is not as hot as the top, but because DHW and radiant floor heat require water that is 120-150 F pulling water from the middle of the tank works just fine. By doing so they are using the water in the tank more efficiently then taking hot water off the top of the tank and mixing it with cold water for the radiant and DHW.

I've atatched a photo of the typical European buffer tank and one of two 500 gallon tanks stacked on top of each other.

NWM

I forgot to attach the effecta boiler/tank photo to my last post so let's try this again.

This system is a typical Effecta gasification boiler/buffer tank setup that is put inside their house/basement. However, if more storage is required additional tanks can be added easily.

NWM

Effecta Boiler Agent (US) said:

I forgot to attach the effecta boiler/tank photo to my last post so let's try this again.

This system is a typical Effecta gasification boiler/buffer tank setup that is put inside their house/basement. However, if more storage is required additional tanks can be added easily.

NWM

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It appears to me that with this storage set-up you couldn't use all of your storage. If your drawing from the middle you could never let the middle drop below 130 to make dhw. Am I missing somthing here?

jdboy9 said:

First off I am not an engineer I also haven't the slightest comprehension on thermodynamics.

I went searching but couldn't find any info on this particular idea. Would it be a viable option if one need 2000 gallons of storage to use four 500 gallon propane tanks with two stacks. First stack of two on floor level, second stack starting with bottom tank halfway up first stacks bottom tank. Some sort of platform would be needed to get the second stack that high but that isn't a big deal.

Or just stacking two 1000 gallon tanks?? Has anyone attempted this? It seems like a lot of weight would be on the bottom tank.

I am curious which setup would work better for heat addition and removal.

Click to expand...

Sounds like you may have enough room to stand them verticle ?

Just wanted to clear up the 2nd to last post.

In Europe, most homes are connected to the tank in two places for optimum efficiency. The DHW loop and radiant floor heat (lower water temps) are connected to the middle of the tank and the baseboard heating circuit (higher water temps) is connected to the top of the tank. If only the middle area of the tank is used than the hot water on top will move downward to heat up the cooler water in the middle of the tank (physic's tell's us that heat always moves toward cold).

In addition, effecta even installs electric water heating elements towards the top of the storage tanks to heat the water if it gets to cold due to a wood fire not being made. You can see these heaters on the photo of the tank I posted in my previous post.

In my Northern Michigan area forced air furnaces are very common and thus the water to air heat exchanger would be connected to the top of the tank for hottest temperature.

Thanks,

NWM

Effecta Boiler Agent (US) said:

Just wanted to clear up the 2nd to last post.

In Europe, most homes are connected to the tank in two places for optimum efficiency. The DHW loop and radiant floor heat (lower water temps) are connected to the middle of the tank and the baseboard heating circuit (higher water temps) is connected to the top of the tank. If only the middle area of the tank is used than the hot water on top will move downward to heat up the cooler water in the middle of the tank (physic's tell's us that heat always moves toward cold).

...

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It may be that European metric hot water will move toward cold, but any water that I've ever seen that was heated with BTUs goes to the top and stays there.

--ewd

On my verticle tanks the hoter water stays on top even if I'm not drawing off it or "mixing"

Your set up looks exactly like what I have in mind....You haven't insulated your tanks?

After doing the work to stack 2X 500G tanks I would suggest a couple of things. 1) Usable temps and stratification. I have a hot water coil, for forced air heating. I need 140+ water this time of year. I feel stratification is less of an issue the higher water temps are needed. I have to charge my tanks once every 24hrs regardless. 2) Keep your system simple. If I wanted 2000G I would stand tanks on end or stack. The advantage of on end would be access to all the available BTU's for low temp water setups like radiant or a DHW coil. DHW especially in the summer. I would try to do a set up with two tanks rather than four. Less fittings and all. One thing with pressurized systems is, when pumping in and out of tanks, try not to stir the water up in the tanks. One way is to increase the pipe diameter the last few feet before entering the tank.
Here's a link with some pictures.
https://www.hearth.com/econtent/index.php/forums/viewthread/44600/

I am posting to apologize for my last post regarding water moving from hot to cold even when the hot is at the top of the tank.

In further discussions with effecta engineering they "set me straight" so here we go:

The hot water stays at the top of the tank for DHW and for high temperature radiators. However, if the house has lower temp. radiant floor heat or lower temp. radiators they pull hot water from the top of the tank, warmer (not hot) water from the middle of the tank and even less warm water from the bottom of the tank and use a "shunt valve" (we call them mixing valves in the US) to mix the water from all three locations before it goes to the heating device. Sometimes they only use water from the top and middle of the tank.

By doing this they are able to preserve the hot water in the top of the tank if it is not needed.

You can see this "shunt valve" on the boiler/tank diagram I recently posted a few days ago.

Once again, I appolagize for any confusion I created in making an incorrect statement.

NWM

That sounds like a good idea.

The simple answer is "hot water weights less" My question is say on a 200 gallon tank, fully charged how many gallons of water can be drawn off before some mixing starts - I understand there are a lot of variables- I am struggling to see how 3 different layers offer much flexibility unless the GPM draw is very very low. If a cycle time was 7 minutes for a floor zone at 4 GPM that's got to be most of the usable hot water. Assume floor only.

bigburner said:

The simple answer is "hot water weights less" My question is say on a 200 gallon tank, fully charged how many gallons of water can be drawn off before some mixing starts - I understand there are a lot of variables- I am struggling to see how 3 different layers offer much flexibility unless the GPM draw is very very low. If a cycle time was 7 minutes for a floor zone at 4 GPM that's got to be most of the usable hot water. Assume floor only.

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I think it may involve a few things.

First the northern Europeans do strive for the lowest flow rates and highest temperature deltas in their emitters.

Another is they like to segregate the return water by using cascading diverting valves. If the return water is hot enough it is diverted to a higher zone of the tank system, else if hot enough for the next level it is diverted to that level, and so forth down the tank.

Likewise for integration with solar water heating, the heated water is routed through the diverting array and is sorted into the highest zone achievable.

Then on the demand side the loads can pull from the appropriate diversion level, but in the opposite direction using diverting array as a mixing array, where each category of heated water is supplied using the lowest temperature water available that will mix to the required temperature for that draw-off zone.

--ewd