HOT|COOL NO. 4/2017 "Technical Innovation and Optimization"


For section 1-2, we run the system by 90°C until the two first branches. Where the arrows are pointing, we install two mixing loops in pits, enabling us to reduce the flow temperature from 90°C to 70°C. The positive effect is that the pressure loss in this part of the network is reduced from 287.5 to 80 kPa. This is the main reason why the total cost for operating the pumps is reduced to 508,358 kWh/year. This is still an increase, but what’s more important is that the associated heat losses are reduced from 1,252,700 kWh/year to 549,300 kWh/year. This is a stunning 703,400 kWh/saving every year. On top, total CO2 will be reduced further, as the boilers will not have to produce this heat.

We have a traditional tree-structured network, where calculations have shown that flow temperatures can be reduced to 70°C. This is just an example, as each network has its own unique conditions for what is possible. First let’s see what the current heat losses as well as pump operating cost are.

To sum up the comparison, please see below:

With a delta T at 50°C, the flow rates are relatively modest, which is also reflected in the pump operating cost of 113,690 kWh/year. But with the high flow temperature the heat losses are considerable, in this case 1,252,700 kWh/year.

If we, just for the experiment, lower the overall flow temperature to 70°C, the scenario will look like below:

CONCLUSION By introducing the concepts of dynamic DH we can add speed controlled pumps when we need to boost pressure. As these pumps typically will be connected to an overall monitoring system, like SCADA, we can get information like temperature, flow and delivered heat energy (This information is readily available in at least some new pumps). The increased knowledge can lead to increased system efficiency. Where system design requires an “in network” approach, we can adjust network temperature to the lowest possible levels. This dynamic approach is possible due to use of pits with prefab mixing loops, including pumps and all needed components.

Now the heat losses will be reduced dramatically, but on the other hand the pump operating cost increases to 818,180 kWh/ year for the original 113,690 kWh/year, quite dramatically.

The alternative to this could be to change flow temperatures where this is possible, as in below example:

For further information please contact:

Grundfos Att.: Anders Nielsen Grundfos Poul Due Jensens Vej 7 8850 Bjerringbro

Direct: +4587504601

J O U R N A L N 0 . 4 / 2 0 1 7

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