What size line can I use for a drainback system?
Traditionally, Drainback installations have focused on using 3/4” line for both the supply and return lines on a system. During July 2007 at the ASES show in Cleveland I had lunch with Chuck Kutscher from the National Renewable Energy Laboratory and he had some information on “a better way.” Several years ago they did testing where they used 3/4” line on the supply of drainback systems and 1/2” line on the return. By using the smaller line on the return side they were able to generate suction from the falling water thereby reducing the effective head requirements on the pump. By reducing the head requirements on the supply pump they were able to get more flow with the same energy use. More flow through the collector and through the heat exchanger leads to higher overall system performance. In addition, a given thickness of insulation around the pipes has a better effective R-value the smaller the diameter of the pipe. In conclusion, be reducing the diameter on the return section of the pipe you improve the overall efficiency of the system at the same time you reduce your material costs. A win for both you and your customer.