What is the difference between a hot water heating system with the same or different processes?

Hot water heating systems are widely used in residential and public buildings, as well as industrial plant buildings. They have the advantages of high thermal energy utilization rate, minimal ineffective heat loss, long service life, fast operation, and are suitable for long-distance transportation. Recently, I have seen many netizens confused about the same and different hot water heating systems. Here, I would like to summarize and hope it can be helpful to everyone.

The so-called same flow and different flow refer to the direction of water flow in the supply and return main pipes. When the two directions are the same, it is called same flow, and vice versa, it is called different flow. In practical engineering, different flow is more common. In a hot water heating system, regardless of the classification method you use, it can be arranged as a same or different flow system according to the direction of water supply and return (see attached figure for details). We set the first loop as the heat medium passing from point A through riser A to point B; The second loop is from point A to point B via riser B; The third route is from point A to point B via riser C; From point A to riser point d is the fourth loop; The fifth loop is from point A to point B via riser e; The 6th loop is from point A to point B via riser f. Based on the layout of the main pipes shown in the attached diagram, we can draw the following conclusion:

1. From the same process system in the above figure, it can be seen that the flow direction of the heat medium in the supply and return main pipes is consistent. The distance traveled by the supply and return water main pipes of the starting and ending pipes A and F is basically equal, that is, the consumed resistance along the way is basically the same. Therefore, the resistance of each loop is basically balanced. The thermal effect of the radiator carried by the starting and ending pipes of the system is relatively close, and there will be no overheating or non heating phenomenon, which is an ideal layout. However, this arrangement of the same process system increases the length of the return water main pipe compared to the opposite process. During construction, it is not possible to lay the return water main pipes together (due to the different slope directions of the supply and return water pipes), which is more labor-intensive and material intensive, and will increase some initial investment costs.

2. In the differential system shown in the figure below, the flow of heat medium in the supply and return main pipes is consistent. The distance from point A to point B through pipe A is much greater than the distance from point A to point B through pipe F. This will result in an imbalance of resistance in each loop. Designers usually take measures such as selecting pipe diameter and installing regulating valves to reduce this imbalance. If these measures are not taken, it will inevitably lead to a gradual decrease in heat dissipation from pipe A to pipe F. Although theoretically speaking, the opposite way system is not as reasonable as the same way system, due to the short return water main pipe of the opposite way system, it saves initial investment to a certain extent, and can be laid on a common frame during construction (because the slope direction of the supply and return water main pipes is consistent), which is easy to construct, so it is widely used in practice.