[Greenbuilding] Solar & recirculation

[Drew A. Gillett, P.E.]

you hve the flow backwards.   under stable conditions, the flow is out the 
supply (insulated) to the end and back to the tank thru the small pipe 
which cooles and is heavier.

when there is a draw, most of the flow is thru the larger supply to the 
outlet. no need for check valve ( cost , maintenance, etc.    ) a simple 
ball valve set to create enough resistance so the average condition leaks 
just enough water back to the tank from the end of the line to keep the 
supply always warm is all that would be suggested.  usually the small pipe 
is suffiently restricted but large enough.
----- Original Message ----- 
From: "Clarke Olsen" <colsen at taconic.net>
To: "Drew A. Gillett, P.E." <deaneg at hotmail.com>
Cc: "Keith Winston" <keith at earthsunenergy.com>; 
<greenbuilding at listserv.repp.org>
Sent: Friday, June 22, 2007 11:44 PM
Subject: Re: [Greenbuilding] Solar & recirculation


> Is there an available valve for a thermosyphion return? Allowing water  to 
> return
> without letting drawn water flow to the use point through both pipes is 
> not on
> the program for check valves.
> On the subject of 3/8" pipe, at some point wouldn't the relationship of 
> volume to surface
> area might make it tough to maintain temp. to the end?
> Clarke Olsen
>
> On Jun 21, 2007, at 4:16 PM, Drew A. Gillett, P.E. wrote:
>>
>> the thermosyphion recirc tends to retain stratification since it is so 
>> slow
>> and continuous.  ( run a small (say 3/8 or 1/.4 inch line back from the
>> highest furthest outlet.  keep it in heated space, slope back to drain 
>> into
>> dhw tank at bottom.  it need not be well insulated ( infact some heat 
>> loss
>> is required).  do very well insulate the supply say 2 inches of 
>> urethane.
>> put a ball valve on  the small line so after installation you can tune 
>> the
>> flow rate.  recirc is only required if the runs are long  say greater 
>> than
>> 50 feet
>> ----- Original Message -----
>> From: "Keith Winston" <keith at earthsunenergy.com>
>> To: <greenbuilding at listserv.repp.org>
>> Sent: Thursday, June 21, 2007 8:36 AM
>> Subject: [Greenbuilding] Solar & recirculation
>>
>>
>>> You're wrong. You will, however, come to realize how much recirc costs
>>> you, energy-wise, if you have a timer system. And the on-demand recirc
>>> systems aren't in vogue.
>>>
>>> Ha ha, I see I'm giving the opposite response from Drew. Good, it'll
>>> keep you on your toes.
>>>
>>> My point: there's nothing stopping you from running an on-demand  recirc
>>> system (either cold-return or dedicated return) through the system
>>> described. Maybe on-demand recirc should be called something else,  like
>>> preheat or something. The energy it'll cost you would be required
>>> whenever you use a recirc system. You could oversize the solar
>>> (collectors and tank) to accommodate this. Of course, maybe you've got
>>> short runs and patience, and you don't really need recirc. That's 
>>> better
>>> yet. If you're going to be doing recirc anyway... However, as pointed
>>> out, recirc will mess with your tank stratification, which will
>>> seriously reduce the efficiency of your system. Especially if it's a
>>> timer system or otherwise gets common daytime use. Good luck!
>>>
>>> Keith
>>>
>>>
>>>
>>>>
>>>> Message: 2
>>>> Date: Wed, 20 Jun 2007 09:56:22 -0700
>>>> From: Eric Cadora <handygoy at bigla.com>
>>>> Subject: Re: [Greenbuilding] Baxi Luna question
>>>> To: Greenbuilder list <greenbuilding at listserv.repp.org>
>>>> Message-ID: <FFBA6C48-BAF0-48EE-BE48-3F783FB37C46 at bigla.com>
>>>> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>>>>
>>>> My understanding has been that if you have a solar hot water storage
>>>> tank that's backed up by a tankless water heater, than it's pretty
>>>> much impossible to add on a recirc pump.
>>>> Please tell me I'm wrong.
>>>>
>>>> Eric Cadora
>>>>
>>>>
>>>
>>>
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>>
>>
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>
>