[Greenbuilding] solar heat collection

[Eli Talking]

Clark
Good luck with your project.  Please keep us informed as it develops.

I have worked on this concept of annual cycle thermal storage. I have not 
found a client and a project to test the theories.  However, for total solar 
heat collection, according to my calculations 1000 gallons would be too 
small for significant storage.  Off season, depending on your collector 
size, you would store heat up to a high temp when there are no heating loads 
drawing off heat. As the heat rises, the standby heat losses increase. 
Having said that, I still see value in storing what you can off heating 
season such that you start the fall/winter with your maximum stored heat.

In my thermal models I worked with varying the solar collector size, tank 
size, and thermal loads (standby tank heat losses and building heat losses). 
With my local climate data for average solar and rated efficiencies of 
collectors, and conductive heat losses from tank, I found that in order that 
the minimum temperature does not drop below 90F, what I consider to be my 
lowest useful temp without boosting with another energy source, for single 
family homes, with good thermal envelope, this takes about a basement sized 
tank.  I was proposing converting basement or crawlspace into tank with foam 
and waterproofing.  The larger the tank if properly balanced, the more 
efficient the storage.  Heat losses are proportional to both the temperature 
difference to ambient (room temp for top of tank, outside air for above and 
near finish grade, and ground temp below ground) and ratio of surface area 
to volume.  Both of these increase with a smaller tank.

I too am considering am considering convert a 8'x8'x8 cellar room into a 
thermal tank at my house.  This would not be enough to store heat sufficient 
to provide all heat.  However, it could store enough heat to serve radiant 
wall heaters for 5 or 6 days of winter heat loads.  The off season stored 
heat would soon be consumed.  Therefore, I am wanting to boost temp with 
wood fired boiler with forced draft to assure a hot efficient burn.  In this 
way, I am heating with wood.  However, the dirt and ashes would be outside. 
Once a week I could charge my thermal tank, and draw off the heat with 
thermostat to get just the amount needed, unlike wood stove in the space. 
Taking the wood stove out of the house and the chimney reduces the air 
leakage for outdoor air feed and thermal bridges of chimney that would be 
removed, insulating and sealing those holes.

Eli
-----Original Message----- 
From: Clarke Olsen
Sent: Wednesday, July 04, 2012 3:36 PM
To: Green Building
Subject: Re: [Greenbuilding] solar heat collection

    Corwyn,
    Thank you for your considered advice.
     1. 1000 gal was the biggest (5'x10'x4' low boy concrete septic) tank 
that I could squeeze in the crawl,
          before the house went on.
     2. Bottom to top is obvious, though it seems that loops pulling heat 
out should be high in the water,
         and one putting heat in could stay on the bottom.
     3. I have no calculation.
     4. My collectors will mount on ground level frames against the south 
wall, making adjiustments easy,
         and inviting drain back. Tilting back to catch summer sun inceases 
the effective area by 50%.
     5. The house went through last winter with just the booster to heat the 
floor. Oh, yeah, and a wood stove.
Clarke Olsen
373 route 203
Spencertown, NY 12165
USA
518-392-4640
colsen at fairpoint.net


On Jul 4, 2012, at 2:35 PM, Corwyn wrote:

> On 7/4/2012 2:02 PM, Clarke Olsen wrote:
>>    I am putting together a system with tilt-adjustable panels and a 1000 
>> gal storage tank, in the hope of collecting
>> and storing heat year round. The 1400sqft house has radiant tubing in a 
>> 3" concrete floor sitting on 1/2" foam over
>> a crawl space. The boost from the tank temp to hot shower is handled by 
>> Eemax 6.5kw point-of-use instant water
>> heaters. The floor circuit also has an Eemax booster. My plan is to run 
>> both the domestic hot water and the floor
>> circuit through heat exchangers in the 1000 gal storage tank.
>>    My question is: should the storage water run through the collectors 
>> directly in a drain-back configuration, or is a
>> closed-loop, heat exchanger be preferable? This would make 3 sets of 
>> loops in the tank, with the collector circuit
>> on the bottom.
>
> Drain back is more reliable (fewer things to go wrong) but it requires a 
> larger pump to handle the head.  If your collectors aren't much higher 
> than your tank, I would consider a drain back system, otherwise a closed 
> loop.  Or, if you are prone to power outages, go closed loop on a solar 
> panel controlled pump.
>
> Other notes:
> 1. I think 1000 gallons is probably too large (or not large enough) 
> depending on your goals.
> 2. The heat exchanger loops should be side-by-side.  With the collector 
> loop flowing top to bottom, and the other two flowing bottom to top.
> 3. I recommend that you work out the math for the energy flow, if you 
> haven't (if you have, post it here to give us a better idea).
> 4. Adjusting tilt on water collectors is going to be a royal pain.  And 
> probably not needed.
> 5. I would forget the booster on the floor circuit, too high a current 
> needed, and the control circuit would need to be pretty sophisticated. If 
> you need supplemental heat just get a cheap heater (again, depending on a 
> number of details).
>
> Thank You Kindly,
>
> Corwyn
> -- 
> Topher Belknap
> Green Fret Consulting
> Kermit didn't know the half of it...
> http://www.greenfret.com/
> topher at greenfret.com
> (207) 882-7652
>
>
>
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