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tank sizing - Page 2

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Posted by Solar Mike on March 22, 2008, 12:42 pm
 


If you are going to use all the heat stored the following night early
morning to keep your house warm then there is not much point in trying to
store it so a smaller tank can be used. If you keep the water temperatures
down by increasing the storage then you will have less losses and gain
efficiency.
The advantage of a DIY tank is it costs not much more to make it bigger than
you initially require for mid winter operation.
So as the days get warmer, but heating is still required, then just put some
more water in the tank, this will allow you to extend the output over > 1
day.

Cheers
Mike (NZ)



Posted by Jeff on March 22, 2008, 4:24 pm
 
Solar Mike wrote:

   Hi Mike,

  Nice to see that you are around. My collectors are largely based on
your notes.

   I remember, but can't find, that you had something to say about the
way you feed and withdraw water to keep the tank stratified. What was that?

   Jeff





Posted by Solar Mike on March 23, 2008, 3:26 am
 
Hi Jeff

Damm difficuilt to keep a single tank stratified when you are actively
circulating water out/in at a flow rate to the radiators sufficient to warm
up your house. The whole content will attempt to mix soon after the pump
starts.
With technology you can switch the returning cooler water to the correct
matching level using solenoids etc, but this is too complex, you want to
keep it as simple as possible, less hassle over the lifetime of the system.
The heat stored in the water will be the same regardless anyway, so I dont
think stratification is worth worrying about in this situation.

One idea that I would like to use, is to use multiple small tanks (44 gal
drums) connected in series to your solar panels for storage. Place the drums
inside a well insulated long box underneath the house floor boards, I was
going to purchase 2nd hand copper low pressure hot water cylinders for the
purpose, after removing their insulation. To warm your house circulate the
air with a fan through the box into the house. This is a bit like the solar
closet described by others and would seem to be of great merit provided you
have a central location to install it. Cheap plastic drums would work
provided you dont let them get too hot.

Cheers
Mike (NZ)



Posted by nicksanspam on March 23, 2008, 10:05 am
  

And moreso, while collecting heat over about 6 hours on an average winter day
at about 4 times the heat distribution rate on that day.


With good plug flow, ie stratification. How much better than 2 or N big
tanks in series, where each one is fully-mixed?

Stratification allows lower collection temps. If we can heat a house
with 100 F water that cools to 80 on an average day using a cool part
of the store and leave the 140 F cloudy-day store untouched, we lose
less heat to the outdoors via collector glazing, no?

Nick


Posted by Jeff on March 23, 2008, 4:02 pm
 Solar Mike wrote:

   Hi Mike,

   This is something I hadn't thought of but could tie in very well. The
rooms I wish to heat are directly over where I had planned to install
the tank and the old gravity feed coal ducts are nearby. I guess the
necessary calculation is how fast heat can be transferred from the drums
to the air. Some "fins" could help that.

   How would you connect the drums in series? Would that be a hose from
near the bottom of the source drum to the desired water level of the fed
  drum?


  This is a bit like the solar

   Yeah, I see that poly softens at what I think would be operating temps.

   I was thinking 55 gallon, or perhaps 40 gallon steel drums. Maybe
painted...

   Jeff


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