The circuits should be spaced on the header at a minimum of 3" (7.6 cm) center to center. Install a balancing cock in each return line.
Manifold headers are recommended for split systems with or without zone valves and also those installations with zone circulators. If the system is to be split at remote points, good practice requires special attention be given to main pipe sizing to allow balancing of water flow.
COOLING PIPING
When the boiler is used in conjunction with a refrigeration system it must be installed so that the chilled medium is piped in parallel with the boiler. Appropriate valves, manual or motorized, must be provided to prevent the chilled medium from entering the boiler.
Water temperature in the heating system must be reduced to less than 100°F before cooling system is started, or damage to the chiller unit may occur.
If the boiler is connected to chilled water piping or heating coils exposed to refrigerated air, the boiler piping system must be equipped with flow control valves or other automatic means to prevent gravity circulation through the boiler during the cooling cycle. Primary/secondary pumping of both the chiller(s) and the boiler(s) is an excellent
SPACE HEATING APPLICATIONS
Controlling of these systems is decided mainly by the type of building system controlling that is desired. A single boiler
Figure 10. Single or Multiple Boiler Installation Diagram
installation might be controlled directly from space temperature thermostat(s). Multiple boiler installations are more effective when the boilers are sequenced in and out of operation by some form of main water temperature controller. With one or two boilers, individual control settings at progressive temperature may be used. For more than two boilers, electronic sequencing controlling is recommended.
Individual controls, or the separate stages of a step controller, should fire a boiler and also start the boiler loop circulator whenever that boiler is fired. Some large installations may require the firing of more than one boiler per stage.
The system or primary circulator may or may not be controlled by the boiler sequencer. When this pump is operated through the first switch of any type of step controller, care should be taken to determine if a motor starter is needed due to insufficient switch capacity.
If the primary pump is controlled by a manual switch or any other controllers, the electric current supply to the boiler group should be through the primary pump controller. The fast response of A.O. Smith boilers eliminates any need to maintain boiler temperature when the system is satisfied. Wiring should always prevent firing of boiler(s) when there is no water flow in the mains.
Installation diagrams show safety flow switches in the outlet piping from each boiler as good protection against any boiler being fired when the boiler loop circulator is not in operation. These safety flow switches will also provide some protection if there is a loss of water.
Multiple boiler installations are especially adapted to the use of outdoor reset for main water temperatures. This feature is not
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