GTC-58S-alu  type is specail designed for swiming pool, home hot water and room heating system,it can installed and connected in series or parrellel,our gtc solar company will make designation according to customers requestment.it is no need any heat exchanger and also any poor quality water can be used for this type,also with big water volume,you just tell us the information what we need to know then everything is drop to us,our egineer will make drawing and design acordingly.