If the goal is to keep it simple, do two things differently than you are contemplating:
1 - make your heat exchanger by putting multiple loops of coiled copper in a polypropylene tank - at most you will need soldering skill if you want to break up a 3/4 or 1" flow into multiple 1/2" coils (surface area = good). One logical loop for (may be many loops of a smaller pipe diameter) for the load (ie DHW or hydronic heat) and (2 below)
2 - use a "drain down" open system instead of glycol. This allows you to use water everywhere. A pump (not a circulator) pumps the water up to your rooftop collectors when the system senses available heat (standard, cheap solar differential controls) and gravity drains it down when the system is not in use [this method requires that the panels be above the storage tank and that the pipes exposed to freezing are graded towards the storage tank - usually very easy to do] Note that the PP tank in step one above is the drain down tank and storage tank for your hot water (they can be separated if desired, and a larger tank/multiple tanks will provide additional storage, which is the key to effective solar hydronic installations).
So you end up with one (open system) tank full of hot water from the sun, heating your coils of copper, containing the water from your (closed system) DHW. Similar technique (add a logical coil) for the hyrdonic side. Just make sure you don't always "preheat" your hydronic -sometimes the return water from your heating system will be hotter than your solar storage - you need a control to tell you whether there is heat available for the hyrdonic system (not an issue for preheating DHW - your solar storage temp will be almost always be above your groundwater temp).
Tom
From: Ken Dunn <[EMAIL PROTECTED]>
Subject: Re: [Biofuel] Double wall heat exchange - Solar Hot Water Heater
Date: Tue, 27 Sep 2005 09:53:41 -0400
To: Biofuel@sustainablelists.org
Kjell,
I will certainly give this a try for my own purposes, it seems simple
enough. But, I can operate a TIG and have access to one.
Unfortunately, a TIG welder and the associated experience are not
widely spread. I do want to keep this project as Appropriate as
possible. So, I'm trying to find materials that are as readily
available as possible. Also, I plan to use propolene glycol so, there
is the issue of double walls. I could certainly adapt this idea
accordingly. Its really too bad that brazing the plate together
wouldn't be sufficient - that would make it an easier DIY.
Thanks a bunch,
Take care,
Ken
On 9/27/05, Kjell Löfgren <[EMAIL PROTECTED]>wrote:
>
> Ken, to avoid the tube bending business you can use a plate heat exchanger -
> more compact but if DIY you have to do some welding. Cut two equally sized
> pieces of *thin* stainless steel plate. Make about two dimples about 2 mm
SNIP
Radiance Heating and Plumbing, Inc. (ROC 204149,204150)
Tom Scheel
928-380-6294
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