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Active and passive solar strategy for so cal.

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  • Active and passive solar strategy for so cal.

    I will be building a home in socal and want to take the time to get a good idea of what I can do solar thermal and any other systems in advance of seeing the architect.

    Heating is not as intensive of a job out here than where I grew up (MN). I know I will incorporate passive solar and active solar thermal. I could supplement it (if needed) with natural gas or with a heat pump.

    Cooling is where a good system can really pay off out here.

    Absorption chiller or Absorption heat pump.

    I have not seen it done on the household level but there are solar thermal cooling systems that use higher end evacuated tube thermal collectors or even solar thermal concentrators because the output temperature needs to be at least 190f. The absorption heat pumps are just now being scaled down to household size. So that is probably a no on this setup. I only looked into it since it was the only way to use solar thermal energy to cool.

    ASHP or GSHP will be left as my two prefered options for primary cooling and backup heat. I know it will be responsible for all of the cooling. I am unsure of how much heating it will have to do. I guess I will have to find some homes with solar thermal/radiant floor systems in so cal and see how often they have to use their heat pump, electric or gas backup. I also have an interesting question about solar thermal out here, In the winter what is the temperature after it exits the in floor and heads back to the collectors?

  • #2
    I suggest you study using the in floor radiant tubing for cooling. I had that offered to me and even some contractors saying it was the only way to go.

    Fan coils are not that expensive and much more flexible. I much prefer them and it keeps you away from any condensation problems. The one drawback to in floor is that it is slow to respond whereas fan coils are quick.

    To use solar thermal for in floor radiant you need a storage tank. That is something I am studying in depth. This fellow has a concentrator pool heating system that could be used -

    He didn't use it for home heating as at his location there is too little sun in the winter (far north with too many clouds) but it easily could be used where you are and the same for here. He sells the plans for a quite reasonable price.



    • #3
      Ive been installing radiant floor, absorbtion chillers and solar for 10 years. The storage capacity for an absorbtion chiller is extremely high and the amount of solar thermal panels is many when required to keep up with the chiller. Evacuated tube would be the way to go. For example. We have (14) 25 tube panels and it barely keeps up. We are not that large of an office. And they can have problems with crystalization.
      For the cooling in the the floor. I also recommend a forced air coil for the cooling of the house. This can be done by having a storage tank circulating through a normal chiller during off-peak hours. Cooling of the tank to 32 (glycol would be needed). And running the low wattage pump ans fans during the hot day.
      The heating for the floor would best be done with a instantaneous gas heater. (Quietside) Under a closed loop. This way the heater will cycle on/off as the temp of the floor rises. Theres not many therms to be produced during winter from solar thermal. Especially not enough to keep you warm.
      Happy New Year


      • #4
        It is typically sunny here even in the winter and not all that cold. What region are you installing systems in. Here in So-cal there seems to be quite a few therms available even in the winter.


        • #5
          Sacramento and have done many projects in San Diego. Let me restate. With solar thermal only. You wouldn't get enough therms to comfortably heat your home. You would need a backup. Or a Heat Exchange off a descent solar combi tank.(solar/spaceheating/ dhw.) Absoebtion chillers generally require a certain flow. It would be difficult to get that flow through a radiant manifold.
          I should mention we have a 400 gallon storage tank for our chiller. Office size is about 3000 ft2.


          • #6
            See what the flow should be to an in floor radiant system - it will be high. My heat pump recirculates 2.57 m3/hour. Many panels are required and a large amount of storage.

            One m3 = about 240 gallons. If I were to go to such a system I would build a large in ground concrete tank of between 10 and 30 m3 depending on the water temperature from the collectors.

            This is where the concentrator like George's would be nice - reduces the storage volume needed. Easier to store heat with 150
            Last edited by russ; 12-31-2010, 03:38 AM. Reason: correction - 120° not a20°


            • #7
              I like the idea of the concentrator type collectors and the higher temperature storage tank. Being able to make hay while the sun shines and store it away for when it is not shining is a big deal. You already bought the most expensive parts and the cost of more "thermal battery" is not as much compared to the rest.

              I was wondering if a 725 gallon spa at 100-105*F of any use for storage. Then I considered it is not as efficient as even the the dedicated 120*f storage tank.

              For the main pool if I used the middle range of the pool sizes I am considering I would have around 20,000 gallons at 82-85* F. Heating the pool and spa with solar and using it as storage would only make sense if you used it with a GSHP instead of a ground loop when heating.

              Assuming the ground temperature is around 65* F here and a 20,000 gallon pool at 85*F there would be 3,332,000 BTU's available for the heat pump before the pool temperature is lowered to 65*F.

              Now I need to compare it to a smaller high temp storage tank going directly to the radiant floor. I am not sure what the minimum water temp would be where it would still actually heat. In order to have some number to work with I will go with 85*F. If you had 3m^3 or 720 gallons in a storage tank at 240*F you would have just 929,628 BTU's to use before the tank temperature went down to 85*F. If you had 10m^3 2400 gallons it would be 3,098,760 BTU's.

              The pool is a far less dense energy storage than a dedicated storage tank. The two big pros for using the pool is the large volume and that I was going to buy one and an insulating cover already. You can store up a lot of thermal energy but you can not get it back as efficiently because you would need to use a heat pump. A follow on project could be a wind turbine and battery setup to power the heat pump. Actually if there is consistent wind on the lot I might just go with the wind turbine, GSHP and a solar thermal DHW system.

              I work on some rather sophisticated aircraft, Fly-by wire 4000psi hydraulic flight controls... etc.. So when it comes to actually installing hydronic heating and solar thermal systems I am not too worried about my craftsmanship. Learning exactly what to build as far as sizing and matching everything up has me really hitting the books and will be the most work for me.

              So Solar.

              What are your thoughts on evacuated tube panels vs a parabolic trough concentrator with an evacuated tube?


              • #8
                Manufacturing a parabolic dish for the tubes would definitely help with heat production during winter. I would use caution during the summer though. Evacuated tubes can get extremely hot. If too much steam is produced it can cause havok in any system. And if glycol was utilized it could cause breakdown of glycol, causing acidity and damaging of equipment and pipe. Use caution if considering a pool as a storage source. Although, a strange idea, with indeterminant variable; some codes don't allow pool water with in a living space. Chlorine gases.
                Also, in my experience, a good flow for radiant floor is about 4GPM.


                • #9
                  If I design it so that the parabolic trough can pivot far enough in the summer they can be intentionally rotated at less efficient angles or even rotated around far enough to act as a shutter. I don't think that preventing over temp is too hard of a design requirement.


                  • #10
                    If you wanna devise something like that. Then sure. While your at it. Design it to tilt for latitude.


                    • #11
                      Originally posted by So solar View Post
                      If you wanna devise something like that. Then sure. While your at it. Design it to tilt for latitude.

                      He has some pretty good ideas. Rotating the reflectors is not too hard. Tilting on the other axis will have to be done on the whole frame. Perhaps a linear actuator or two.


                      • #12
                        His ideas are good. But I question whether or not a system like that would be cost effective. Why not just add another panel. When it comes to hot water. The less active. The better. Besides. A system like that has too many unknown variables. For example: at what point can the glass melt on the tube. I've seen evacuated tubes heat solder to its melting point. And what if the accuuators fail. Then you have a serious condition in so many ways its tool lengthy to type. I've seen fireplaces with hydrocoils ran through them. It failed. And caused a home fire. Sometimes less is better. Its simple. Size the system according to needs. Without the hoopla and over-controling and it's fine. There's alot of products out there that are safety tested and work for everyones needs. Without unauthorized manipulation and unknown variables.


                        • #13
                          Flat plate collectors will not provide adequate heat for an in floor radiant heating system - summer time they provide more but in the winter no.

                          My three Shuco panels provide enough hot water at 50


                          • #14
                            Well I have some ideas that will would make things stronger, more precise, lighter and easier to reproduce. The parabolic trough would be composite and reproduced on a mold. The plans also do not incorporate an evacuated tube.

                            I am still looking for parabolic trough evacuated tube concentrators so that I can compare the price of an off the shelf section vs rolling your own.


                            • #15
                              Parabolic troughs do not typically use vacuum tubes to collect the heat - the focal point of the concentrator will probably be a copper tube.

                              Vacuum tube panels do not collect more heat than a flat plate panel - they can provide a higher temperature but generally not more total heat.

                              The solder melting on a vacuum tube sounds strange - shouldn't see temps so high I thought.