SHW with dual-coil tanks [RE-wrenches]

[Tom Lane]

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All dual pumped EXTERNAL HEAT EXCHANGE SYSTEMS WHERE THE approach 
temperature IS PROPERLY SIZED   will outperform all  HEAT EXCHANGE TANKS 
THAT RELY  on convection by 20% with the same collector area --simple 
physics.  gatortom
----- Original Message ----- 
From: "Doug Wells" <dwells at thesolarspecialists.com>
To: <RE-wrenches at topica.com>
Sent: Monday, June 16, 2008 1:02 PM
Subject: Re: SHW with dual-coil tanks [RE-wrenches]


>
> 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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