8.1.4. Flow calculations and system adjustment<br>

### 8.1.4. Flow calculations and system adjustment

After sizing diameters of pipes and determining pressure drops on all pipe couplings and fittings and all terminal units, the required available pressure at sources is determined along with, when necessary, pumps on pipe-runs. At this stage radiant heating units and single-pipe systems are treated as internally adjusted and equivalent to terminal units of known pressure drop. Regulating fittings have initial pressure drop assigned equal to the higher of the two values: minimum internal pressure drop (DPmin) taken from data or pressure drop at maximum Kv.

The required available pressures are sized and calculated along with differential pressure valves. These components may often have the minimum stabilised pressure drop higher than that required by the stabilised circuit. This imposes higher requirements on the available pressure drop upstream of them. This does not apply to pressure relief valves, which are not strictly true regulating components.

If there is a bypass bottle in the system, it is treated as a no-pressure drop component (pressure difference between supply and return ports is equal to zero).

When pressure drop is determined (or specified) for the sources and pumps, system adjustment is performed: pressure drops in individual circuits are balanced in relation to each other and in accordance with the available pressure difference. If there are several control valves at different points between terminal unit and source, and the remaining excess pressure exceeds the required minimum pressure drops of these valves, their “weight” (participation in throttling of excess pressure) may be adjusted by means of a slider displayed on the flow calculation options screen.