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  • #16
    Many in the two best solar heating groups I know of use under floor radiant tubing at temps down to near room temperature, but that's when it's circulating from a solar heated storage tank. Join- solarheat and simplysolar Yahoo groups

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    • #17
      Hydronic heat temp

      İ am using an air source heat pump (air to water) to supply the hydronic 'in floor' heating system. İt is a 5 ton unit and produces 3.5 m3/hour of water at set point - right now it is set at 30 deg C min & 35 deg C max.

      To supply that quantity of hot water would take more solar panels than İ have roof and this is a big house! İ have 3 Schuco collectors - Flat plate panels (good ones) may make roughly 200 liters per day - summer time very hot and winter time İ have electric backup come on at 50 deg C.

      İ didn't find a solar thermal connection to the hydronic 'in floor' heat system of interest.
      [SIGPIC][/SIGPIC]

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      • #18
        Mtmtntop is using the same idea I am working towards. Solar water during the day, boiler in the evening. I am trying to convert an old wood/coal buring unit into a boiler to supply hot water at night (still at it).
        Besides trying to lower my winter heating expense as much as possible, I am also trying to correct a cold floor on the lower level on my house. It's a bi-level design & the floor of the main level is 'cold'. It is over a crawl space (4' tall) but the floor temp is about 55 degrees (regardless of room temp).

        It's cold enough you can not be bare-foot during the winter. I have tried everything I know to eliminate the cold floor. The floor is insulated with 6" of insulation. I have done extensive sealing/insulating in the crawl space.

        I have considered installing an air-duct from my furnace in the crawl space to heat the space (700 sq ft) to eliminate the cold floor. However, that doesn't lower my overall heating bills....thus my concentration on Solar thermal.

        I may have to concede the solar idea & open a furnace ductwork, until I can get the wood-burner/boiler to work.

        Thanks for the input.
        Jeff
        [url="http://solarpaneltalk.com/album.php?u=2072"]First panel 40 volts, 140+ watts[/url]

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        • #19
          Originally posted by netttech View Post
          Mtmtntop is using the same idea I am working towards. Solar water during the day, boiler in the evening. I am trying to convert an old wood/coal buring unit into a boiler to supply hot water at night (still at it).
          Besides trying to lower my winter heating expense as much as possible, I am also trying to correct a cold floor on the lower level on my house. It's a bi-level design & the floor of the main level is 'cold'. It is over a crawl space (4' tall) but the floor temp is about 55 degrees (regardless of room temp).

          It's cold enough you can not be bare-foot during the winter. I have tried everything I know to eliminate the cold floor. The floor is insulated with 6" of insulation. I have done extensive sealing/insulating in the crawl space.

          I have considered installing an air-duct from my furnace in the crawl space to heat the space (700 sq ft) to eliminate the cold floor. However, that doesn't lower my overall heating bills....thus my concentration on Solar thermal.

          I may have to concede the solar idea & open a furnace ductwork, until I can get the wood-burner/boiler to work.

          Thanks for the input.
          Jeff
          Pull the insulation down, and tack up PEX with aluminum heat spreaders, reinstall insulation, pump solar heated water thru. This will put heat up into the room thru the floor, and not heat the crawl space.

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          • #20
            Sundug, that was my original plan. Install Pex tubing under the floor, pump solar heated water thru it. My panel design (flat) just couldn't heat water hot/fast enough.

            It could heat water to 150 degrees (in about 10-15 minutes), but could only muster 90-100 sustained pumping 1 gpm thru it. A loss in heat will occur between the panel to the pex tubing. That's why I was hoping to get 130 water leaving the panel. My house to panel location is about 15' apart so it will lose heat. If the panel can only muster 90-100 hot water @ the panel, the water temp would surely be 80 (or less) by the time it enter the pex.

            I doubt if any benefit would occur with water only in the 80's range.

            I haven't 'totally' given up on solar water. I just don't expect to get it working for this winter. I can easily open a duct-vent to my crawl space to eliminate the cold floor, then close it 'IF' I can get a solar water panel to perform.

            I have been avoiding heating the crawl space because it's also where I store my wine collection. The wine needs the natural 50-65 temp range (winter/summer) to ensure it doesn't go bad. It's a 'catch-22' isn't it.

            It's one of the reasons I joined this forum, to get ideas.
            Thanks
            [url="http://solarpaneltalk.com/album.php?u=2072"]First panel 40 volts, 140+ watts[/url]

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            • #21
              Originally posted by netttech View Post
              It's cold enough you can not be bare-foot during the winter. I have tried everything I know to eliminate the cold floor.
              http://www.mec.ca/Products/product_d...=1261700478477

              made in an ethical sweat-shop

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              • #22
                Perfect Solution Mountain!

                Your temperature loss problem can be solved by insulation.

                The quantity of water you need to recirculate you are not going to get from solar panels unless you have a lot of them.

                Vacuum tube only has the capability to produce hotter water - not more total heat. Your location - winter time you are never going to get 200 liters per panel per day from solar panels.
                [SIGPIC][/SIGPIC]

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                • #23
                  Flat solar heating panels - Have had them for 10 years

                  Hi All
                  I put 3 flat solar hot air panels on the south side of my home at least 10 years ago. I live in the northern lower part of Michigan.
                  They have worked well and work good with snow on the ground.
                  There is a fan to blow the hot air in too my basement.
                  In the beginning I figured that the 3 panels would carry 30 % of my heating load. That is when the sun was out. I just foget they are there and only when the fan comes on do I think of them. Some what care free.
                  I hope to get my solar electric panels some what care free too.
                  Ernie

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                  • #24
                    Don't forget about the maintenance and overheating

                    Before purchasing either the Evacuated Tubes or Flat Panels, you should consider the costs for system maintenance and any overheating concerns especially with closed loop glycol systems. Flat panels are a better value for the money but they are also a lot easier on the glycol during stagnation and the flat panel system can last up to 10 times longer on the glycol.

                    System maintenance and repair can distroy any chance of payback if you do not have the right system.

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                    • #25
                      Flat Plates vs. Evacuated Tubes

                      There's a lot of good information contained in this thread. I work for a manufacture where we distribute both flat plates and evacuated tubes.

                      It all comes down to value - which system produces the most in your area for what you spend. However, there are a few general pros and cons for each technology to consider.

                      Evacuated tubes produce more on cloudy / overcast days than flat plates. They also produce higher internal temperatures (our manifolds generally stay around 160-170F during the day), and are easier to maintain.

                      The internal temperatures will not burn anyone or cause a hazard - the heat is inside the glass tubes, and the vacuum insulation makes the outside the same temperature as it is outside.

                      If damage occurs - such as in a storm - a tube can be replaced easily and with minimal expense, and without draining the system or messing with any piping or components. Most manufactures will pack in a few extra spare tubes with each collector - however, replacement tubes cost around $25/each.

                      Evacuated tubes are also modular - they come in separate pieces that are assembled on the roof. Therefore, it's generally easier to install from a labor standpoint.

                      The cons, are that evacuated tubes are generally about 20% more expensive than their flat plate counterparts. They also can get very hot - and generate too much heat, so a form of heat dissipation is needed, especially in the summer months. This adds about 10% extra cost in components.

                      In a closed loop system (or a drain back), this is the only real difference in cost versus a flat plate. Flat plates have the same general components - controls, tanks, pumps, glycol, etc - other than dissipation and the valve that controls them.

                      The real point to consider is it it worth the extra $300 to $500 in system costs for an evacuated tube versus a flat plate for what you receive in return?

                      The answer to the question is that it depends on really where you live. In warmer climates where the outside air temperature stays fairly warm (70F+), and the weather is fairly consistently sunny, the flat plates can be a better value overall, as they will perform as well as the evacuated tubes. So in areas like Florida, Texas, Arizona, etc, most contractors and homeowners tend to opt for flat plates.

                      In cooler and/or cloudy climates, the evacuated tubes out perform the flat plates. So if your temperature in the winter and shoulder months stays 50F or lower, or you have rainy/cloudy seasons, most contractors and homeowners tend to opt for evacuated tubes.

                      The other thing to keep in mind and consider is that some flat plates can be very inexpensive and cheaply made - and some evacuated tubes can be very expensively priced. I have seen a flat plate sell for $450 or so, and an evacuated tube collector sell for $3500. Therefore, at times, when people compare costs, they run across prices like these and get an idea that tubes are vastly more expensive.

                      My recommendation would be to shop around and ensure you get the best value for your money. Look at the SRCC certificates and see what kind of production you get for the price you pay, and make sure you get nothing less than a 10 year warranty on either technology.

                      Our flat plates generally sell to a contractor for around $950 or so and the evacuated tubes that we manufacture in the states generally sell for around $1250 or so - and other manufactures will generally be around the same price or so.

                      Hope this information helps!
                      Please read the Forum Rules before you post. If you want to advertise, send a message to Jason.

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                      • #26
                        Thanks Joe,

                        Excellent post from someone who is in a good position to know.

                        Take a look at a pdf from Home Power - issue 132 date August September 2009 with the title Flat-Plate & Evacuated-Tube Solar Thermal Collectors.

                        It is a free download - would be interesting to hear your take on the article.



                        Russ
                        [SIGPIC][/SIGPIC]

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                        • #27
                          Here's a link for what Russ is referring too:

                          http://www.solarpanelsplus.com/solar...Flat-Plate.pdf

                          It's actually hosted on Jbergess's website...not sure if he just put it on there, or if it's a coincidence.

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                          • #28
                            Article

                            Originally posted by Jason View Post
                            Here's a link for what Russ is referring too:

                            http://www.solarpanelsplus.com/solar...Flat-Plate.pdf

                            It's actually hosted on Jbergess's website...not sure if he just put it on there, or if it's a coincidence.
                            Just a coincidence - we've had the article on our site for a while now since it came out. We try to bridge the gap between flat plates and evacuated tubes, showing the advantages and disadvantages of both vs. pushing just a single technology.

                            It's a very well written article, and goes into some technical details regarding design, tilt, and differences in efficiency based on what Delta-T you're working with. Definitely a good read.
                            Please read the Forum Rules before you post. If you want to advertise, send a message to Jason.

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                            • #29
                              Generally speaking,

                              1) Tubes enjoy a significantly longer and more productive solar day. Evacuated tubes begin BTU production earlier in the day, and continue to produce BTU later in the day than flat plate collectors. The round shape of a tube allows solar gain no matter what the angle of the sun. In contrast, a flat plate collector has a low solar angle in the morning and afternoon, with direct angle occurring only at the middle of the day.

                              2) Tubes operate at higher temperatures than flat plate collectors. The old rule of thumb for flat plate collectors is hot water at approximately 50 degrees above ambient temperature. This rule of thumb appears accurate. Evacuated tubes greatly exceed this threshold.

                              3) For a high temperature tank or for winter radiant demand, evacuated tubes perform better.

                              Check out: http://simpledrainback.com/ for more information on this subject.

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                              • #30
                                Those are the common claims made by manufacturers but - observations I have made from my system and my thoughts have trouble with their statement. I collect power readings from four meters every morning and hot water system data about every hour. Solar insolation is collected from my Davis weather station both Global solar radiation and UV are recorded.

                                1) I consider that my system is functional for about 85% of available light. The very early morning and late evening light no system will pickup. If the insolation for a day is 2000 watts/m2 then you really have 1700 watts to work with. Even if the vacuum tube collectors extend the day you might say 50% of nothin is still nothin.

                                2) My hot water system electrical backup is set for 50 degrees. I don't need or want water hotter - now for a radiator heating system OK hotter is needed. For in floor radiant heating I have the temperature set at 35
                                [SIGPIC][/SIGPIC]

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