SHW with dual-coil tanks [RE-wrenches]

[Blair May]

Simple physics true, but what about the service life of the ExHEx when
in use w/ hard water, compared to internal HEx coils?

-----Original Message-----
From: Tom Lane [mailto:tom at ecs-solar.com] 
Sent: Tuesday, June 17, 2008 9:02 AM
To: RE-wrenches at topica.com
Subject: Re: SHW with dual-coil tanks [RE-wrenches]



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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