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Wood to Solar transition

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Nofossil, Apr 12, 2008.

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  1. Bob Rohr

    Bob Rohr Minister of Fire

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    Sounds like your mind is made up, Joe. Or you just like to argue :)

    I try to keep an open mind to options, which is one reason why I installed tubes on my own place to get a true comparison.

    I'd love to see that panel installation that need new glass every year, post a picture of the installation if you could. That need to be in the Guiness book of records as possibly the only solar panel in the world that need yearly glass replacement. Maybe that owner needs to reconsider his solar future.

    Being a professional in the field I would think that would surprise you and offer a challange as to why, and how to correct. It's glass over copper for crying out loud, not rocket science. Schuco and Solar Skies both have pictures of people standing on their glass collectors.

    My 30 years experience with glass covered flat panels on 4 of my own homes and shops and hundreds of other customer installations has yet to present a broken glass. My early Piper Hydro panels had a thin plastic covering and lasted for many years in the high mountains of Utah.

    I did see one out a four panel array break with baseball sized hail a few years back in my area. A fairly flat angle installation may have been part of it.

    It's not the case of the glass breaking on evac tubes, as you mentioned that shape is very strong. Their failure is typically loss of vacuum, although hail has been know to break even evac tube glass.

    Another weak link in my mind is the dependency on the thermal transfer grease connection between the header and tube connection. A lot of heat transfer "faith" is placed in that film.

    hr

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  2. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Not at all. That's why I asked you to drop me an email with your findings. I'm more than happy to learn something new...

    The installation is not exactly nearby, so it's unlikely that I will be able to take photos of it any time soon. The glass has broken under the snow and ice load every year.

    And how does the vacuum fail? Something has to break for that to happen.

    I guess that would depend upon the header design being used. The Thermomax headers make pretty good metal to metal contact, so I doubt that the grease is doing all that much. And the performance of heat transfer greases isn't exactly an article of faith; they've been used for many years in many different environments, for many different technologies. Simple stuff, really. And it's sealed inside the header, so there's not much to go wrong with it, once the tubes are installed. I suppose if you pull some of the tubes each summer, you might have an issue - I just size the tanks to handle the peak load, and use controllers that have cooling capability.

    Joe
  3. wdc1160

    wdc1160 New Member

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    Master, You bring up a good point. About year round use. I thought that I could create a use for some of this ultra hot water. Where I live it is extremely humid in the summer. I thought I may be able to use the hot water in conjuntion with a wood drying kiln. That is what I wanted to do with the extra heat. I also will have very large storage soon as well. And, during the summer months will only require 120 -140 degree water. Essentially I would be able to dry the wood even at night.

    As for winter usage (I am only going of anthony D's example) I figured that some days anthony D's setup would gain 40K but in winter. His overall system is speced for 100K btu. We don't know actual numbers as he doesn't log or track except on a per observation basis.

    Is 40K in the dead of winter doable?



    Further, some of the literature that you put up said one could run the evac tubes dry, if you don't want hot water from them. Do you agree with this?
  4. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    That's generally considered to be a "very bad idea."

    Some tubes have thermal cutoff valves built into them, but intentionally cycling those valves would be a bad plan.

    If you really wanted to shut down or reduce the heat output, you could always just build a shutter and clamp it over some or all of the tubes. That's what we do (albeit with cardboard and zip ties) when we are installing tubes during the day.

    Joe
  5. wdc1160

    wdc1160 New Member

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    I defer to your experience, but why would the literature say runnem dry if you like

    Any idea on what would fail if this approach was taken?? It sounded like a too good to be true situation.
  6. Bob Rohr

    Bob Rohr Minister of Fire

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    I have heard of some drainback designs using evac tubes. Apricus mentions that at their webste. Sounds like some incredible thermal shock potential?

    I measured over 400F on the evac tube that I had lying in the sun. That was some of my concern with the thermal transfer grease. That is much hotter than and aquastat well in a boiler or indirect tank sees. Some of the transfer grease manufacturers suggest removing, checking and re-greasing from time to time on high temperature applications. You need to use the proper type of grease for the application. I applied some typical off the shelf grease from Johnstone Supply and it turned to rock within minutes at those temperatures.

    hr
  7. Bob Rohr

    Bob Rohr Minister of Fire

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    And how does the vacuum fail? Something has to break for that to happen.

    There are different types of evac tubes, but they all have a seal somewhere to keep the vacuum. It my understanding when an evac tube fogs it has to do with a failed seal, not broken glass shells necessarily.

    Some info on various types from www.Apricus.com

    Type 1 (Glass-Glass) tubes consists of two glass tubes which are fused together at one end. The inner tube is coated with a selective surface that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss. These tubes perform very well in overcast conditions as well as low temperatures. Because the tube is 100% glass, the problem with loss of vacuum due to a broken seal is greatly minimized. Glass-glass solar tubes may be used in a number of different ways, including direct flow, heat pipe, or U pipe configuration. Apricus uses a high efficiency heat pipe and heat transfer fin design to conduct the heat from within the evacuated tube up to the header. For more information about heat pipes, click here.

    Type 2 (Glass-Metal) tubes consist of a single glass tube. Inside the tube is a flat or curved aluminium plate which is attached to a copper heat pipe or water flow pipe. The aluminium plate is generally coated with Tinox, or similar selective coating. These type of tubes are very efficient but can have problems relating to loss of vacuum. This is primarily due to the fact that their seal is glass to metal. The heat expansion rates of these two materials. Glass-glass tubes although not quite as efficient glass-metal tubes are generally more reliable and much cheaper.

    Type 3 (Glass-glass - water flow path) tubes incorporate a water flow path into the tube itself. The problem with these tubes is that if a tube is ever damaged water will pour from the collector onto the roof and the collector must be "shut-down" until the tube is replaced.
  8. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Yeah, you should use the right grease. Just like you should use the right insulation or the right piping, or the right anything else. These things (whether evac or flat-plate) work best when installed correctly.

    It depends on the tubes. A number of manufacturers include an oxygen-scavenging chemical (typically barium) within the evacuated chamber, which will fog up if exposed to large quantities of oxygen, thereby alerting you to the vacuum failure. Of course, the tube is still functional without a vacuum - it just loses some of its efficiency. Good idea to replace it when it's convenient.

    Joe
  9. Telco

    Telco New Member

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    Using solar heated water to dry wood is a great idea. Eventually I plan to do a solar shed with flat panels making up the southern wall to supply the bulk of my hot water, with a 1000 - 2000 gallon storage facility (I believe in overkill), and planned to use an overhang on the roof to control summer heating. If the overhang wasn't enough, was thinking about adding a thermostat controlled electric awning to deploy and add more shade when needed. Using the water to heat up a shed full of wood to dry it for the next winter would be a better use, since it means you can use the entire panel year round rather than having to shade half of it for half the year. This would also let you use summer heat in the winter, since the dried wood would work better in a wood fired stove. Excellent!
  10. brad068

    brad068 Feeling the Heat

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    Joe,
    I think I'm interested in the Caleffi iSolar 1 or 2. What is the price tag on these. We just had a grand opening for a Caleffi supplier and this item caught my eye. I acquired a solar system with 4- 4x8 tempered glass panels,trellis,couple finetube exchangers and the two piece fiberglass tank, insulation, all the lumber and 150' of copper tubing all for nothing as long as I removed it. I'm still reading through their literature and they sure have alot of products that I will need. Is this good stuff?
  11. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Excellent question...

    I've only used the Plus and the 3, so those are the only ones I have pricing stored for. And the 3 in the new catalog has a different part number than the 3 that i have pricing for, so I wouldn't trust that price.

    The plus would retail for about $450, at a guess (I don't really have retail numbers for it - just my wholesale pricing).

    Joe
  12. brad068

    brad068 Feeling the Heat

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    Joe, Is that electronic output relay for speed control the "cats meow"? Does it work with all circs within the amp rating?
  13. antknee2

    antknee2 New Member

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    Thanks for the link on Resol controller , I am very interested upgrading to a controller with more advanced features . Any links on a good reseller with a website ?
    Anthony
  14. Bob Rohr

    Bob Rohr Minister of Fire

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    The Caleffi I-Solar Plus with 2 variable speed outputs lists for $760.00,

    The I solar 3 with standard output relays (no speed control) has a list of $555.00. Discounts vary from wholesaler to wholesaler depending on their volume.

    The relay is rated at 1 amp. If you connect a valve or another relay to that output you need to lock it in the 100% mode, bypassing the V/S function.

    They show 3 sensors included, in the literature, I'd swear my last one had 4 sensors?

    All the Caleffi controllers include a pre wired power cord which is a nice feature.

    Many of the larger chain HVAC wholesalers have Caleffi inventory. You should be able to locate a dealer near you on the website. If no dealers or reps are in your area, you may be able to buy direct.

    hr
  15. antknee2

    antknee2 New Member

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    Thank you hr
    Definitely looking forward to a major upgrade on the solar controller and a system that can monitor all aspects of my heating system , which has taken on a life of it own out there in the boiler / pool room .

    https://event.on24.com/eventRegistr...5499F8B23B8D49727BA431A85&sourcepage=register
  16. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    I think it's a "nice idea" - not necessarily the be-all, end-all of solar control. I use the Plus because of how adaptable it is to a variety of situations, and to future expansion.

    For that matter, it can actually control charging of a storage tank using a wood boiler (not that a Garn would need that, but others might).

    Man, they make some money on those when they sell them retail, don't they?

    Yeah, mine did, as well. Two with 1.5m lead wires, and two with 2.5m lead wires.

    Rumor has it they will be adding their own pumping station to the mix, soon. The current pumping station (like the controller) is something they outsource.

    And a flat-panel collector, for those who like such things :)

    Joe
  17. Bob Rohr

    Bob Rohr Minister of Fire

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    Right out of the box the I-Solar controls will do some data logging. Operating hours for the various relays can be read. You can dial in the flow rate as observed from the flow meter and type and % of glycol and get some energy data in KW/hr. It will not be as accurate as a btu meter that measures the flow constantly, but it does give you some good ball park ideas of energy transfer.

    Some homeowner enjoy watching the hour meter to assure they are getting some solar energy return.

    I believe the Resol drainback control will be available soon, possibly a control for PV powered pumps.

    Remember today is the last day for the earlybird $49 sign up for Siggy's May 1 9o minute webinar on solar design. This should be an excellent show for those interested in solar design and installation. www.pmengineer.com

    hr
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