SHW with dual-coil tanks [RE-wrenches]

[Ray Walters]

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Also don't forget you're trading electrical efficiency (to run the  
extra pumps) for thermal efficiency. We've had cases where customers  
added both solar thermal and PV systems at the same time, and the  
thermal system ate most of the PV production.

Ray Walters


On Jun 18, 2008, at 8:23 AM, Blair May wrote:

>
> 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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R. Walters
Solarray.com
NABCEP # 04170442	




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