Distribution circuits
- Dennis De Beuckeleer
- Tim Rombouts (Unlicensed)
- Ruben Gielen
The distribution circuits library gathers circuits typically connected with the header/collector to control the net thermal power leaving the technical room or the power going towards a specific end unit. In general, distribution units are split into three categories:
Every category controls the power leaving the secondary gate differently. A dividing circuit divides the primary flow, a mixing circuit mixes part of the returning secondary flow with the primary flow, and a throttling circuit varies the primary flow rate.
The working principles of each category are explained in more detail on the next pages:
The main difference between the three categories in terms of system performance is their operational behaviour in partial load conditions. When the load is smaller than the designed peak load, distribution circuits will remain operating at high, constant flow rates, while the mixing & throttling circuits will operate at lower, variable flow rates. This already gives a first indication that dividing circuits will consume more pumping energy.
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Besides the flow rates, the return temperatures during partial load operation will also differ between the three categories. Dividing circuits will have high return temperatures, while mixing & throttle circuits have low return temperatures. In general, a throttle circuit will have slightly lower return temperatures than mixing circuits. The reason for this difference is the setup of the valves. A dividing circuit will take the higher flow and divide it into the cold return, which ends up heating up the return temperature.
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The lower left circle indicates a period of full (peak) load operation. The return temperatures of all three types of distribution circuits are nearly equal. The two upper circles indicate periods where the load is very low. The return temperature of the distribution circuit is nearly equal to the supply temperature, while the return temperatures of the mixing & throttle circuits drop to a low temperature.
More in general, the following trends are observed when comparing the three kinds of distribution systems:
In designed peak load conditions, the three distribution systems behave similarly, which results in the same return temperature, because all 3 of them will be sending the same flow at the same return temperature to the unit. However, whenever the heat flow drops from its peak load, they all three start behaving differently due to their different configurations.
In dividing circuits, the return temperature will increase linearly when the heat flow drops, as the part of the supply flow directed over the bypass will gradually increase and mix with the return flow. This is disadvantageous for the system, as a higher return temperature will decrease the production efficiency, while the constant flow rate will cause high pumping power consumption. The fact that the pump keeps on pumping has an advantage however, as the pipe will remain hot and ‘ready to go’ whenever demand picks up. In the case of fast working systems which are placed far away from production this might prove useful.
In mixing circuits, the return temperature will decrease quasi linear when the heat flow drops (based on the selected usage of the valve through BMS), as the part of the supply flow within the mix will gradually decrease, decreasing the secondary supply flow temperature, which in turn decreases the secondary return temperature. This is advantageous for the system, as a lower return temperature will increase the production efficiency. However, the constant flow rate at the secondary side will still cause high pumping power consumption.
In throttle circuits, the return temperature will initially decrease faster than linear when the heat flow drops, as the primary supply flow rate is throttled, decreasing the secondary supply flow rate. This is even more advantageous for the system. At the same time, the variable flow rate will decrease the pumping power consumption.
Distribution circuit components
Distribution circuits are built by combining balance valves, control valves & pumps. A more detailed elaboration on the working principles of those components can be found here:
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