PB Heat Gas/Oil Boilers manual Constant Low Temperature, Variable Low Temperature

PIPE THE BOILER

b)Temporary low temperature operation is acceptable within limits. For occasional cold start- ups condensation will occur, but will have limited effects. If the system is frequently allowed to cool to room temperature, such as on night set-back systems or energy management systems, cold start-ups will occur often. These systems require a Variable Low Temperature piping and control arrangement, described below.

2.Constant Low Temperature

a)For systems with a relatively constant low operating temperature (such as heat pump systems), you can pipe a fixed flow by-pass arrangement as shown in Figure 3.3. This piping will not work for variable low temperature systems such as outdoor reset systems or primary/secondary systems with a large primary circuit temperature drop. See Figure 3.4 for multiple boilers.

3.Variable Low Temperature

a)When the return water temperature from the system will vary (outdoor reset, snow melt, etc.) a

fixed bypass will not work. Fixed bypass piping	Figure 3.3: Fixed By-Pass Piping, Single Boiler
works by setting a high temperature rise through
the boiler. As the system return temperature rises
(during primary heating months, for example)
the boiler will cycle on the limit control
frequently, causing poor performance and
excessive cycling. To protect the boiler and
provide proper operation, install a temperature

Figure 3.4: Fixed By-Pass Piping, Multiple Boilers

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