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7) Manual Reset High Limit (Required by some codes) - This control is required by ASME CSD-1 and some other codes. Install the high limit in the boiler supply piping just beyond the boiler with no intervening valves. Set the manual reset high limit as far above the operating limit setting as possible, but not over 240°F. Wire the control to break the 120 VAC electrical supply to the boiler. 8) Flow Control Valve (Required under some conditions) - The flow control valve prevents flow through the system unless the circulator is operating. A flow control valve may be necessary on converted gravity systems to prevent gravity circulation. Flow control valves are also used to prevent “ghost flows” in circulator zone systems through zones that are not calling for heat. 9) Isolation Valves (Optional) - Isolation valves are useful if the boiler must be drained, as they will eliminate having to drain and refill the entire system. 10) Drain Valve - The drain valve is shipped in the boiler parts bag. Install it in the tee under the circulator as shown in Figure 1. Piping for Special Situations Certain types of heating systems have additional requirements. Some of the more common variations follow: 1) Indirect Water Heaters - Figure 12 shows typical indirect water heater piping. Boiler piping is the same as for any two- zone system. Figure 12 shows circulator zoning, which is usually preferred for indirect water heaters. Size the circulator and indirect water heater piping to obtain the boiler water flow through the indirect water heater called for by the indirect water heater manufacturer. 13 2) Large Water Volume Systems - The piping shown in Figure 13 will minimize the amount of time that the boiler operates with return temperatures below 120°F on these systems. A bypass is installed as shown to divert some supply water directly into the return water. The bypass pipe should be the same size as the supply. The two throttling valves shown are adjusted so that the return temperature rises above 120°F during the first few minutes of operation. A three-way valve can be substituted for the two throttling valves shown. If the circulator is mounted on the supply, the bypass must be on the discharge side of the circulator. 3) Low Temperature Systems - Some systems, such as radiant tubing systems, require the system water temperature to be limited to a value below the temperature of the water leaving the AWI or TWI. These systems also typically have return temperatures well below the 120°F minimum. Figure 14 illustrates the use of a heat exchanger to connect the AWI or TWI boiler to this type of system. The heat exchanger will permit the transfer of heat from the boiler water to the low temperature system while holding the system supply and boiler return temperatures within their limits. For this system to work properly the heat exchanger must be properly sized and the correct flow rates are required on either side of the heat exchanger. Consult the heat exchanger manufacturer for sizing information. The water in the boiler is completely isolated from the water in the system. This means that separate fill and expansion tanks are required for the heating system loop. There are several other ways to connect low temperature systems to the non-condensing boilers like the AWI or TWI such as four way mixing valve and variable speed injection pumping systems. 4) Systems containing oxygen - Many hydronic systems contain enough dissolved oxygen to cause severe corrosion damage to a cast iron boiler such as the AWI or TWI. Some examples include: • Radiant systems that employ tubing without an oxygen barrier. • Systems with routine additions of fresh water. • Systems which are open to the atmosphere. If the boiler is to be used in such a system, it must be separated from the oxygenated water being heated with a heat exchanger as shown in Figure 14. Consult the heat exchanger manufacturer for proper heat exchanger sizing as well as flow and temperature requirements. All components on the oxygenated side of the heat exchanger, such as the pump and expansion tank, must be designed for use in oxygenated water. FIGURE 12: INDIRECT WATER HEATER BOILER SIDE PIPING 14 5) Piping with a Chiller - If the boiler is used in conjunction with a chiller, pipe the boiler and chiller in parallel as shown in Figure 15. Use isolation valves to prevent chilled water from entering the boiler. 6) Air Handlers - Where the boiler is connected to air handlers through which refrigerated air passes, use flow control valves in the boiler piping or other automatic means to prevent gravity circulation during the cooling cycle. FIGURE 13: BOILER BYPASS PIPING FIGURE 14: ISOLATION OF BOILER FROM SYSTEM WITH A HEAT EXCHANGER 15 FIGURE 15: BOILER PIPING WITH CHILLER FIGURE 15: BOILER PIPING WITH CHILLER WARNING All wiring and grounding must be done in accordance with the authority having jurisdiction or, in the absence of such requirements, with the National Electrical Co...

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