SHW with dual-coil tanks [RE-wrenches]

[Tom Lane]

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internal heat exchangers scale up much faster than doubled pumped  external 
heat exchangers  -- ten times faster scaling on immersed heat exchangers 
GATOR TOM
----- Original Message ----- 
From: "Blair May" <tump at hughes.net>
To: <RE-wrenches at topica.com>
Sent: Wednesday, June 18, 2008 10:23 AM
Subject: RE: SHW with dual-coil tanks [RE-wrenches]


>
> 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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>
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