9.8.2. Radiant heating – unsatisfactory flow calculation results<br>

### 9.8.2. Radiant heating – unsatisfactory flow calculation results

! Messages on errors associated with excessive pressure drop, flow rate or pipe length contain suggestions on HZ division into parts that would solve the problem. This does not mean that division is essential – the message only implies that if no other changes are made, it will be necessary to divide the HZ into X parts. Often there is a better solution to the problem than HZ division, particularly when the suggested division leads to the creation of many new HZ’s.

¨ The following changes may be introduced in order to reduce flow rates and pressure drops:

- increase minimum temperature difference in the control circuit data or individually for selected HZ’s. Low differences of heating medium temperatures (less than 5 degrees) require high flow velocities. As flow increase induces a squared pressure drop, a slight change in temperature difference may substantially alter the pressure drop,

- increase slightly the supply temperature. After increasing it by, for instance, 1 degree, the same mean temperature of medium in the circuit is attained with the temperature difference higher by ca. 2 degrees, which induces a high decrease of flow velocity and even a higher decrease of pressure drop,

- increase insulation thickness under heating slab. Loss to the floor is compensated by increased flow. Better insulation results in lower loss to the floor and lower total flow,

- apply pipe laying pattern that ensures lower flow resistance. The spiral pattern, for instance, does not involve such sharp curves as the meander pattern, therefore the linear pressure drop is lower in the spiral pattern than in the meander pattern,

- use a pipe of larger diameter.

If these changes do not eliminate the errors in flows and pressure drops, it is necessary to divide the HZ into the appropriate number of parts. This operation should be carried out after applying other available methods, as the latter may have an effect on the division. Suggestions regarding the division are included in current messages displayed in the calculations error list. The message “... divide into 3, preferably 4” means that division into 3 parts provides results that are very close to limit values, and there is a risk that, for instance, pressure drop after implementing the division will be too high (introduction of more HZ’s implies more pipe feeds, which affects the effective area of the heating circuit and may induce a slight change in required operating parameters).

Often we have a contrary situation – the pressure drop in the floor heating circuit is too low in relation to available pressure at the manifold and correct adjustment of all circuits originating at the manifold is not possible. This situation occurs most often when very small and relatively large heating zones or HZ’s of diverse heat demand per square metre are connected to one manifold. In such situations the data may be modified in the opposite direction to the modifications done in the case of decreasing the flow (described above). In extreme cases it may be necessary to eliminate separate circuits in the smallest HZ’s and heat these HZ’s by means of pipe feeds. Manner of arranging pipe feeds in such situations is discussed in section 6.5.4.