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Cold Climate Passive Collector

Kevin_in_Denver_2 Member Posts: 588
SunRain makes this unit:

<a href="http://freefuelforever.com/Scripts/pressure_solar_system.php">http://freefuelforever.com/Scripts/pressure_solar_system.php</a>

To me, it's got almost everything. Thermosyphoning collector, electric backup, etc.

No pumps, controls, sensors, antifreeze, or heat exchangers.

Apparently in Toronto, they have hundreds installed. The supply and return piping is freeze protected with heat trace:

<a href="http://www.globesolarenergy.com/sales_kit/Questions_answers/a_about_working_principle/a2.html">http://www.globesolarenergy.com/sales_kit/Questions_answers/a_about_working_principle/a2.html</a>

They must get away with this because the piping is PEX, so they don't get any catastrophic failures if the pipes freeze.

Anybody have any better ideas than heat trace to freeze protect the supply and return?

The bread and butter solar DHW systems currently being installed in the US cost two to three times as much as this system, so it's worth investigating.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Early bread box heaters...

    I installed a couple of these, and removed a couple. We put 3" fiber glass insulation on the supply and return piping, but still lost copper tubing during freezing considerations.

    With the advances in piping technology (PEX, not PEX-AL-PEX) and advances in heat tape technology (self limiting, change their resistance based on temperature) the parasitic energy consumption for freeze protection can possibly be justified based on KW's delivered on an annual basis.

    The biggest problem with all of these passive heaters is going to be the installation. That is the weak point. Also, heat tapes do fail, and would be a royal pain to replace after the fact. I suppose that an alternative would be to have a pump to move fluid, along with strategically placed freeze sensors, and an emergency electric element in the tank to maintain a minimum temperature of 40 degrees F, but if the system is hit with a total blackout power failure, all bets are off.

    Not a new technology by any means, and has had good and bad reviews, depending upon the location and installation methodology. Patents dating back to the 1800's.

    One other thing that has to be taken into consideration is the dead weight addition to the structure. Might (most probably) require some beefing up.

    But I DO like the KISS principle at work here. Just not sure of the appropriateness of the application in certain climatological considerations :-)


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  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    edited February 2011
    The Sun Cache is apparently Dead

    A lot of money was invested in the Sun Cache collector.

    It was an evolution of the classic bread box using plastic to keep it light and cheap.

    There were three problems with it:

    1. Freeze protecting the supply and return lines.

    2. It's large and heavy when full.

    3. It loses all its heat overnight. Not that many people shower in the evening.

    In my opinion, only #3 is a fatal flaw, #2 is hard to solve, but is OK in many applications.

    So a fail-safe solution to #1 is worth finding. Does anyone have any experience freeze protecting things with a thermosiphoning loop? The idea is that as long as the house is warm, it can send heat upwards through the pipes.

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This discussion has been closed.