Replacing Solar Hot Water Tank

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bohintze

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I have a typical solar hot water system with roof mounted panels and an external heat exchanger module plumbed to an 80 gallon glass lined storage tank that preheats water to a hybrid heat pump hot water tank
I will need to replace the storage/preheat tank that has begun to leak after 7 yrs. Should have checked anode...
The current tank has 4 ports, two standard domestic in/out and two ports that recirculate hot water from the external heat exchanger of the panels.
I am looking at a few options for the replacement storage;
1."stone" lined or stainless steel indirect hot water heaters,
2. stainless steel hot water storage tank or
3. seamless blow molded polybutene inner tank with a structural fiberglass shell.
My objective is to store as much preheated water produced by the panels. Best production days in August are in the 150 - 160 degree range. I'm thinking that the replacement storage should be in the 80 - 100+ gal range.
My questions are:
Your opinions on the molded polybutene tanks with a structural fiberglass shell?
Some of the options being considered do not have a "thermistor" that my current design uses to sense differential temps between internal tank water and solar panel fluid temps. Can the thermostat units for the internal electric heating elements be used as a substitute to thermistor?
Thanks for your replies.
 

hj

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None of the tanks "have" a thermistor. They have a stud that the thermistor mounts on. As for the last question, the thermostat and thermistor have completely different functions and are NOT interchangeable. Solar tanks use the spot where a conventional tank has a lower element to mount the thermistor. I doubt that "checking the anode" would have had much effect on the tank's life.
 

bohintze

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None of the tanks "have" a thermistor. They have a stud that the thermistor mounts on. As for the last question, the thermostat and thermistor have completely different functions and are NOT interchangeable. Solar tanks use the spot where a conventional tank has a lower element to mount the thermistor. I doubt that "checking the anode" would have had much effect on the tank's life.
hj,

Thanks for the information. I did not think that the thermostat would substitute. I'm leaning toward the molded polybutene/fiberglass tank, as they have long life warranty and weigh much less in installation. The storage tank I'm considering has no heating elements, it's strictly a storage tank, consequently no port to insert a thermistor. I hoping that using the drain valve's stub as a mounting spot, well insulated, will give me a good reading of water temp at bottom of tank.

Suggestions or alternatives would be appreciated from the forum.
 
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