In order to avoid tensions in the heat exchanger and for calcification protection, a primary pump can be installed. This reduces the primary supply temperature "PriSupTemp" below the district heating supply temperature "SysSupTemp". For this configuration the heating valve must be a three way valve.
Fig. 9. Primary Pump Control
For the primary pump the same conditions apply as for the secondary pump, except the maximum temperature thermostat condition (see Secondary Pump Command section).
Start-up hint
Take care that the primary pump always starts earlier than the secondary pump. The primary pump start-up delay must be shorter than the secondary pump start-up delay. The secondary pump must stop later than the primary pump.
Table 10. Parameter List
Description |
Value Range |
Default Value |
Unit |
PRP-01: primary pump start-up delay |
0...600 |
0 |
sec |
PRP-02: primary pump switch off delay |
0...1200 |
5 |
sec |