My manifolds are always piped supply opposite to the return or "reverse return". Flow is partially defined by pump speed which means that the dT can be designed, to some extent. While turbulence does help in heat transfer, 50% or more will still occur with laminar flow. When the heat loss of a particular building gets close to passivHaus standards, it is very difficult to pump fast enough to have a high reynolds number and meet the design criteria for the system.
If we are using the heat pump as a heat source and you want to have a 10C dT over the loop (typical with a boiler), some the capacity of the buffer tank will be quickly overcome. The HP may have some trouble keeping up. The dT over the loop will probably have to be lowered which means shorter loop lengths.
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