Common return off 2 separate systems??

[bobbychocolate]

Hi guys. I am putting in 2 altherma heating system into a house. We need 5 pipes from the plantroom to the house however the plumber has only put in 4 pipes.
Would it be possible to have a common return off the upstairs and downstairs systems returning to 2 low loss headers in the plantroom. The pipes are already underground so what I'm ask8ng basically, can 2 separate 22mm returns tee into 1 22mm return and still flow back to the low loss headers at the same rate they are being pumped out at??many thanks rob.

 

[sammathias]

are the 4 pipes flow to zone vale, flow for upstairs, flow for downstairs and return?

 

[sammathias]

are the heat pumps both going to be working same time or one as a back up?

 

[Hibster]

5 pipes? Please explain your plan!
If it is meant for 2 zones then could you not move the valves into the house, if not then may need non return valves if combining the two returns.