Sizing the Expansion Tank In closed loop systems, expansion
tanks must be appropriately sized for the system to operate
properly. For expansion tanks the acceptance volume must be
sufficient to accommodate expansion of the heat transfer fluid
when the solar loop goes into stagnation. Provided below are the
basic sizing rules for selecting and sizing expansion tanks in
closed loop solar systems. Expansion tanks used for potable
water are not the same as those used for glycol based non-
potable fluids. Potable water expansion tanks are designed to
resist corrosion that may occur due to oxygen in the water. Non-
potable expansion tanks have bladders designed to resist
chemicals typically found in closed loop applications. For
closed loop solar systems, the expansion tank must be acceptable
for use with propylene glycol or other heat transfer fluid used
in the collector loop. In addition, the temperatures and
pressures in closed loop solar systems can be significantly
higher than found in typical hydronic systems.