fiber glass thermal store

[Chanireland]

So i have been given 2 900lt fiberglass tanks with lidis insulated they were built by kilarney plastics for portabale water headder tanks actualy came from a comercial site. new ish . would need to ad more insulation.
§just phoned them up and they recoment no higher than 30c but when i asked more they had tested up to 95c for 500hours at wich point they started to blister and not be water tight...
they are fiber glass  with gell coat. inside layer suposibaly 6mm fiber gell. polyutathane foam prob 25mm in sandwich.

http://www.killarneyplastics.com/onepiece.php

in proces or renovating a cottage all diy...

was going down the WBS smallsolar water panels and normal 170lt twin coil tank (plan in proces) then i looked at this tanks with ideas. any healp would be  great i gues as to how hot i could go with the fiber glass and how cheep is a heat exchanger have seen som lads on here make then but would like to try and keep things a littel simple

might be crazy
 thankz for your experiance

[dhaslam]

You could use a tank like that for secondary  hot water storage.   You could heat the smaller cylinder and transfer  heat to the other tank  when there is surplus heat.     This way you could limit the temperature.    If you have a coil in the other cylinder   you could use the bigger one  as a direct store but it would need a  connection on the bottom as well as the top but you could put a pipe down from the top inside if a bottom connection is not possible.      I have a similar situation with solar.  The 250 litre cylinder heats first, then heat is transferred to the 850 litre buffer tank at about 60C.    If the  buffer tank reaches 60C  I can just open the insulation and it drops  about 15C (approx 15kwh)  per day.     

[rt29781]

Hi, we have a regular polythene (low density) 500 lt rain water tank surrounded by concrete (tank positioned then concrete poured round it).   We regularly heat the tank to 60-65C but no hotter by our solar system.  In summer it is at 65C constantly.  Obviously at that temperature the plastic is very flexible but because it acts as a liner to the concrete so far it has been ok.  We float polystrene balls on the top of the tank to reduce evaporation and then cover the tank.  We have used the tank for 15months.  So you may need to support the fibreglass if you are going to get it quite hot.  Heat exchangers use either a copper coil or a plastic pipe coil (just use 100m of 16 mm pex tubing, cheap and bomb proof).  I agree with dhaslam use the fibregalss tanks as a secondary water store.  In our case the heat comes from solar and the floor gets the primary heat via a small plate heat exchanger with the plastic tank scavenging the remaining heat.  As you have a wood burner the flow temperature can get very hot so best put that into the regular tank then charge up your thermal store from the primary store when heat available.