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N°3 – Heating systems with a single return condensing boiler – Part 2 training (A to HND level)

Condensing Boiler Systems without DHW 2 and 3 connections N°3 – Heating systems with a single return condensing boiler – Part 2 training (A to HND level)

If the system has several differently orientated circuits, or on which it is useful to reduce heat at different times, each is fitted with a control valve which permits fine tuning of the outlet temperature subject to its own set-point line.

The boiler temperature is carried out subject to the greatest demand from the different circuits.

The system diagram below ensures the feed of 2 differently orientated circuits, which is why there are 2 exterior sensors.

Question  

Mark on the diagram above the numbers indicated in the description below.
System description:
– 2 radiator circuits n°1 (left) & n°2 (right).
– The controller ensures the regulating of circuit n°1 subject to exterior temperature measured on sensor n°3; it controls the circuit outlet temperature on the sensor n°4 by action on the 3WV (3 way valve) n°5.
– The controller ensures the regulating of circuit n°2 subject to exterior temperature measured on sensor n°6 (left); it controls the circuit outlet temperature on the sensor n°7 by action on the 3WV n°8.
– By action on the burner, the controller also regulates boiler production temperature on sensor n°9 subject to the requirements generated by the control of the 2 outlet temperatures.

For circuits with differing orientations or different heat reduction times, it can, in certain cases, be wise to fit a 3WV (3 way valve).

Question  

How, in the below system, is temperature variation effected on the circuit n°2 outlet?

Circuit n°2 temperature variation is carried out by action on the boiler burner, subject to exterior temperature measured by sensor n°6 and a weather dependant set-point line.




Question  

In the below system, the temperature of circuit n°2 is that regulated by the boiler. Is this temperature:
– Always inferior or equal to that of circuit n°1 ?
– Always equal to that of circuit n°1?
– Always superior or equal to that of circuit n°1?

The water outlet temperature of circuit n°2 is always superior or equal to that of circuit n°1 which can be reduced by its 3WV.



Question  

In the hypothesis whereby the 2 circuits of the below system are fitted with radiators of the same nominal operating regime, what difference(s) could explain that a 3WV has been fitted to circuit n°1 and not to circuit n°2 (which allows circuit n°1 to be fed at a lower temperature than n°2, from time to time).

Circuit n°2 always has an outlet temperature higher or equal to that of circuit n°1. We can, for example, suppose that circuit n°2 feeds a north-facing facade, whereas circuit n°1 is south facing.
Another hypothesis, is that the 2 circuits have the same orientation, but circuit n°2 feeds living accommodation 24/7, whereas circuit n°1 feeds commercial properties or offices where the temperature is reduced during inoccupation.
The idea that the 2 circuits are of the same orientation and even reduced, but of different temperature regimes (radiator, under-floor heating) is not optimal, because the fitting of a basic mixing bypass down-stream of the 3WV would suffice (see 1st §).

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