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Accumulator tanks

Started by farlet, March 29, 2015, 04:08:42 AM

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farlet

Hello, We live in Sweden in the North, so heating is very important !

We have a large wood furnace in the basement which heats water for the radiators. It is an old system with big bore pipes and it works without any pump, just gravity. I have been given 2 x 300 litre accumulator tanks which are insulated and I would like to try and incorporate them into the system to keep the house warm for longer after the furnace goes out. Everyone else I know with accumulator tanks uses a pumped system with two circuits, one for the furnace and accumulator tanks and one for the radiators.

Does anyone know how well it would function if I just plumbed them into my existing circuit ? I was thinking that they could be plumbed straight into the furnace so that the hot water comes out of the furnace and into the tanks first. Am I going to get any benefit ? Is there a better system which would keep it simple with no pumps ?

Thanks for any help

mapleveneer

I think that you will find it quite challenging to make such an arrangement work.  First, the big bore pipes that you currently have, do they all pitch slightly upward from the boiler to the radiators?  I suspect so, as this will enhance the gravity circulation of the water.  The heated water likes to rise, not go downhill in any section of piping.  If that is the case, then you would need to install your supplemental heat storage tanks with the inlet at the bottom and the outlet at the top.  The inlet will need to be above the level of the outlet at the top of your boiler and the outlet from the tank will need to be below the level of your lowest radiator.  For two tanks to work they would need to be in series with the inlet of the second above the outlet of the first only further compounding your problem.

farlet

Hello, thanks for the reply.

So if I could find somewhere to put the tanks higher than the outlet of the furnace, it would work ? I can do this, but it would be quite a bit of work, am I going to get a big benefit from just having them inline in the standard system like this ?

I dont want to create a whole load of work without much benefit

Thanks again

r.man

Farlet my advice would be to pipe the new tanks into the old, as close as you can get them, without interfering with the existing rad pipes. This should increase your reservoir size and your heating capacity after the fire is out. Thermo-siphoning should be adequate for what you want but keep the pipe size as large as is convenient. Do it the easy way first and if that doesn't work try harder options.
Life is too short or my list is too long, not sure which. Dec 2014

Gary_C

Quote from: farlet on March 29, 2015, 04:08:42 AM
Hello, We live in Sweden in the North, so heating is very important !

Is there a better system which would keep it simple with no pumps ?


Hello from Minnesota, the Sweden of the west.  ;D

The effective pump in your system is the temperature difference between the lower and upper levels of your home. Unless you increase that temperature difference, an increase in volume in the system may have little effect. Plus without a mechanical pump in the system you will have a lot of trouble getting the temperature of the water up in all of your tanks with out boiling the water in the furnace.

Without seeing your actual system layout, I would suspect you will be doing a lot of work for little benefit. Plus a trial and error installation to see what works is not a good idea either.

So my best answer to your question would be to put in the pump.
Never take life seriously. Nobody gets out alive anyway.

farlet

Thanks again for your replies.

The water temp in the radiators gets to about 60 degrees celcius, so I was assuming that the water in the tanks would get to this also if they were plumbed into the radiator circuit. Most of the year the system works great as it is and keeps the house very warm. Its just in January and December, we can get down to -45 celcius outside and in the mornings it is a little cold in the house until you light the furnace. I was hoping that the tanks would give us a few extra hours and it wouldnt be so bad in the morning. We get a few times a year when the storms take out the electric and because we are so remote, it is sometimes a week before we are back on, this is why I want to try and avoid the pump as typically you get a cold spell after the storm.

On a side note, we installed triple glazed windows this year, and the difference was phenomenal, such a difference.

I will draw a rough schematic and try and figure out how to post it and see if there is a simple solution worth pursuing.

Thanks

Holmes

  I agree with maple and r.man. .  Is about 135000 btu's of extra storage really any help?  maybe 2 hrs?   I think if the inlet are low and separate  and the outlets tie into a manifold , then go into the storage tank you may get the gravity feed you want.  Sounds interesting.   Gravity systems have been around forever they do work with out pumps as you well know.
Think like a farmer.

farlet

I think if I got an extra 2 hours, it would make the world of difference. We fill up the furnace before bed, and I guess it burns until about 2am, so if this stretched to 4am, then there are only a few hours without a fire.

Any chance you can explain the bit about the inlets and outlets. Do I definitely need the tanks higher than the outlet on the furnace ? As I understand it, The hot is going to come from the furnace into the tanks at the bottom, out of the top of the tanks and into the radiator circuit, then the rest of the system remains unchanged. Is this right ?

Thanks

Tim

Holmes

  That sounds like the simplest way to do it.  Make certain  the tanks do not have built in thermal traps.  If the tappings are 3/4" ish I would increase the piping maybe to  1.25" ish.  Why?  I believe gravity systems function better with larger piping. All the gravity systems I worked on had large pipes.  Isolating the tanks from the original tank with ball valves will make redo's easier.
Think like a farmer.

Gary_C

How do you control the fire in the furnace?

If you look at your system from an overall view, if you want to heat the house more hours, that will take more wood in the furnace. If the furnace is relatively balanced for your house, more heat will either require more hourly capacity or more hours.

More storage capacity for water will introduce more lag time in the system both on start up and after fire out. So more storage capacity may only move the cold hours from the fire out time to the morning on fire start time unless you increase flow in the system.

As far as I can see, more flow can only be accomplished with a pump, not more storage.
Never take life seriously. Nobody gets out alive anyway.

Holmes

 I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.
Think like a farmer.

Gary_C

Quote from: Holmes on March 29, 2015, 02:18:55 PM
I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.

He is actually looking for more heat, not more storage. Storage does not equal heat.  ::)
Never take life seriously. Nobody gets out alive anyway.

farlet

I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

I can see what you mean about it taking a little longer to heat up in the morning, but I think it would be worth it for those extra hours in the night. We have a small stove in the living room which we can use to boost first thing in the morning.

In any case, we have unlimited supplies of free wood and we are setup for processing it, so its no problem if we burn a little more - maybe burn the furnace hotter prior to going to bed.

Another thing we are doing is improving the insulation each year, and this of course helps, but we are more or less at the practical limit of this now.

I think that I have to figure out the best way to get the tanks higher than the furnace and then the pipe it up and try. Thanks for all your help

Holmes

Quote from: Gary_C on March 29, 2015, 02:40:04 PM
Quote from: Holmes on March 29, 2015, 02:18:55 PM
I believe farlet is not looking for more flow. He wants to add more storage and then make certain the added storage enters the heating system.

He is actually looking for more heat, not more storage. Storage does not equal heat.  ::)
The heat is stored in the tanks Gary. :P
Think like a farmer.

beenthere

Quote from: farlet on March 29, 2015, 04:30:39 PM
I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

.....................

IMO, you need to fix this problem first... and get some control of the distribution of the heat so the house doesn't get too hot and you don't have to open windows in the winter.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

farlet

I dont mean that we open the windows every day, its just now and then when you let the furnace burn too hot. What I meant was that once you have done this, it takes a long while for it to come back down to a sensible temp hence the open windows

Gary_C

Quote from: farlet on March 29, 2015, 04:30:39 PM
I am pretty sure that during the day, there is spare capacity in the system as the house gets pretty hot. Actually, this is one of the downsides of the gravity setup in that it isnt very controllable, and you can get to where you have to open the windows in the middle of winter.

I can see what you mean about it taking a little longer to heat up in the morning, but I think it would be worth it for those extra hours in the night. We have a small stove in the living room which we can use to boost first thing in the morning.

In any case, we have unlimited supplies of free wood and we are setup for processing it, so its no problem if we burn a little more - maybe burn the furnace hotter prior to going to bed.


I still don't understand how you control your wood stove.

Are you manually adjusting a damper on the air flow or is there an automatic water temperature control that sets the damper?

Or perhaps you don't have a control other than the amount of wood you put in the stove?

Do you have any control of water temperature?
Never take life seriously. Nobody gets out alive anyway.

farlet

Oh sorry, we control the temperature manually with the air dampener. It is quite basic and you have to get used to it. It heats the hot water for the taps as well and you cant take the water in the radiator system over 60 degrees C as it will boil the hot water for the taps.

beenthere

Quote from: farlet on March 29, 2015, 10:22:39 AM
................. We get a few times a year when the storms take out the electric and because we are so remote, it is sometimes a week before we are back on, this is why I want to try and avoid the pump as typically you get a cold spell after the storm. ................

Thanks

Either put in pumps or zone valves that will let hot water flow through when you have electricity, and then switch to your gravity system when the electricity is off.
I have three zones that the pumps are turned on/off with thermostats. If the electricity goes off, I can open the back-flow preventing valves and let the system heat the house with gravity feed. Works pretty good. And I have only a 9 gal storage tank around my hot water wood boiler.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Hilltop366

Wondering if it would work to put a bypass around the extra storage to get heat faster in the morning then switch back to the tanks later to store your extra heat.

I have a samson draft control, it is non electric and works well. It requires a place to install in the boiler.

Also wondering what the triple glazed windows replaced.


Gearbox

I think you might plumb it into the boiler first top to top lower to lower and fire it up cold and get it up to temp and see what happens . All your out is a lot of water and some wood + pipe fittings . Go the easy way first . The other way cold water moves better than hot so put it into the return .Gearbox
A bunch of chainsaws a BT6870 processer , TC 5 International track skidder and not near enough time

Gary_C

OK, now I understand your system.

It's going to take more total BTU's to heat your house for more hours per day and since you are running your heat system at maximum capacity for the hours you are feeding the stove wood, you cannot get more hours of heat from your existing system. You could either add wood more hours per day or put in a larger firebox to hold more wood at a time.

If you add more storage, you will only shift the cold hours from night to morning. If that is acceptable as you can add other heat during the morning hours then the additional storage will work but it's going to be a lot of work to get the storage installed right.

If you do add the storage capacity, it's not necessary to have ever increasing heights on the tanks, but it's critically important to eliminate air at every high point in each tank as well as having large sized pipes to reduce flow restrictions. Plus of course having a closed system and the tanks in series, not parallel.
Never take life seriously. Nobody gets out alive anyway.

John Mc

This may be getting more complicated than you want, but I'm wondering if you want to put a bypass around your storage tanks. If you bypass thm in the morning, when you want a quicker response, you can heat just the water in your boiler and start circulating it around the house. Once the house is up to temperature, then you open the loop to include your storage tanks and start heating them up. (This might also help with the overheating during the day - if it gets too warm, dump some heat into the storage tanks.)

Another thing to consider: If you are limited to 60˚C so the water in your taps does not get too hot, have you considered adding a mixing valve to the line that feeds the hot water to your taps? (or to the output side of your hot water tank, if you have a separate tank that feeds your hot water taps.) Mixing valves take no power to operate. They take the incoming hot water, and mix it with enough cold water to get a preset output temperature for your hot water taps. All automatic. That would let you run your boiler at higher temperatures, without worrying about someone getting scalded from your tap water. Including a mixing valve is a requirement for new construction in my area.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

John Mc

Quote from: Gary_C on March 29, 2015, 06:56:50 PM
... It's going to take more total BTU's to heat your house for more hours per day and since you are running your heat system at maximum capacity for the hours you are feeding the stove wood, you cannot get more hours of heat from your existing system. You could either add wood more hours per day or put in a larger firebox to hold more wood at a time.

I don't think he is running it at its maximum capacity while he is feeding the stove wood. If this is the case, more storage will help him, if he can just figure out how to get the heat into and out of the storage when needed. That problem is rather simple, if you use pumps and electronic controls. It takes a bit more thought on how to accomplish this if you just want to use gravity/thermosiphon.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Gary_C

John, as I understand the system, his firing rate in the stove is limited by boiling in the hot water system. Unless he can change the ratio of the heat going into the two systems, he is stuck with the same firing rate. So the only way to get more heat in the house is to fill the stove more hours in the day.

It sounds like farlet has a very simple elegant system that cannot be altered without making it much more complex. The simple easy solution is to get up in the night and fill the stove. Easier said than done on a nightly basis.
Never take life seriously. Nobody gets out alive anyway.

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