another solar thermal project question


Old 03-24-12, 05:14 PM
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another solar thermal project question MORE INFO ADDED

i'm back for more of your insight and advice. a quick history. In my house, i have a conventional hot water heat/gas boiler setup. I have a completely independent boiler that shares a boiler loop with a solar thermal array. the key on this system is the boiler and solar array never operate at the same time. both of these systems work fine. I am developing another solar thermal application that will run at a much higher temp using parabolic mirrors. Here's the question i have. I would like to have the ability to use this very hot glycol in either of the boiler loops. Kind of a figure 8, possibly with zone valve(s) controlling which loop the heated glycol would enter. I realize that the cold return would have to operate the same at the same time. I think this is possible but don't know the way to go about it. Would it be a manifold affair or something else? ALso, in earlier lessons from you, i totally understand the concept of thermal shock but that will not be an issue here. When this glycol enters either loop it will be coming in at least 180. thanks.

MORE INFO. I am thinking a solar controller will start a pump when the array reaches temperature, and would also activate a relay that has a leg connected to a thermostat in the house. if the house was calling for heat, the relay would open a zone valve connecting the solar array to the house heating loop on the cold return sideof the house loop. The boiler would not turn on until the return temp fell below 160. The other outlet on the manifold would go to the other loop. since there would always have to be a place for this glycol to go, it would go into the other loop unless the house was calling for heat. Can the end switch on one zone valve operate a second zone valve? can the end switch on a zone valve operate a 24 v relay? I am thinking that when either zone valve opened a matched zone valve on the return loop would have to open also. This would keep the array loop isolated when it was night or not operating on a cloudy day. Would this work?

Last edited by mtmtntop; 03-24-12 at 06:02 PM. Reason: added more details
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Old 03-24-12, 06:40 PM
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Hello mtmtntop,
Sorry, i need to see a drawing of the situation.
I'm not able to quite understand the description.

I'm not sure it would help and it is quite expensive, but you might want to take a look at the Tekmar 406 control. It has some good piping ideas in any case.
The way they inject heat from one souce to another is illuminating.

Old 03-25-12, 10:36 AM
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Glycol does not like to be superheated, which is what you want to do with concentration via parabolic mirrors. (In fact, solar concentration is really good for doing things like running a steam turbine....)

And like Peter, the written description mystifies me.
Old 03-25-12, 11:10 AM
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the general idea is this. i want to use heated glycol from a solar array in either of two existing boiler loops. I was thinking out loud in the first post trying to figure out how to go about it. Obviously i was not clear, especially in hvac terms. I was looking for some software online to draw this up but didn't find anything yet. After thinking about this with design pad and pencil for awhile, i now think 2 heat exchangers, one in each boiler loop with a 3 way valve would work. after some study on end switches, it seems to me that it is nothing more than a relay. i still have the question about where i can use the output from an end switch. it appears common to send the output to an aquastat, another form of relay , that then starts a circ pump. I am thinking to send the output to an ice cube relay to start a circ pump.
Regarding the superheated fluid, this will not be a large array, right now i only have 2 mirrors built, each 65" long and 2' wide. I think if the array is kept relatively small, the heat will be manageable. This is all a prototype. i hope this makes more sense.

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