Joint Circulation systems (JCS) are used for heat recovery in air conditioning systems. Additional water/water heat exchangers inside the circulation can substitute air heaters and air chillers. Due to their significantly lower temperature differences aggregates like heat pumps can be operated at good performance coefficients, similiarly as with thermoactive slabs. These JCS also provide the opportunity to extract waste heat from the return air which would otherwise escape with the exhaust air. This paper introduces design rules for these JCS under different operating modes.