SHW with dual-coil tanks [RE-wrenches]

[Doug Wells]

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Nik,

I am uncertain about the move to dual coil tanks in the NorthEast.
I doesn't make sense to me.  Besides the fact that much of the work is  
retro-fits.
Anyway, by keeping the 2 tank system you are keeping a much higher  
efficiency during the darker colder months.
By having a large body of cold water to dump heat into every time  
there is sun, you are keeping efficiencies way higher.
The solar can heat say 80 gallons of water to a temperature of 110 on  
a sunny winter day.  This can vary greatly, but stay with me.
Heating the incoming water from 50 to 110 degrees is a significant  
amount of heating.  The goal is to have as many of the Btu's coming from
the sun as possible.  Then the primary tank takes the water up to 120  
or 150 or whatever they have the tank set at.  Still a large reduction  
in the heating
of the primary tank.
Having a single tank does save money, but how much?  $1-2,000?  With  
the current cost of fuels it seems that 30 years of partial winter  
heating will
pay for itself.
The single tank system works in theory, but the stratification of the  
tank is not absolute.  It depends on demand, usage patterns and tank  
temperature.
As always, we need more concrete numbers on the temp. stat. in a  
single tank.  I am reluctant to give away an awful lot of partly  
cloudy days up here that
could heat a second tank, but might not be able to over come a single  
tank with boiler coil.
I might try a single tank system in a new application with an  
intelligent control system,
but I am sticking with 2 tanks for most work.
Thoughts?

Doug Wells
The Solar Specialists
Worcester, VT 05682
(p) 802-223-7014
(c) 802-498-5856
www.thesolarspecialists.com


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