DHW generation is through brazed plate water heaters with boiler water bypass. System-wide efficiency is further increased utilizing indirect water heaters with this design.įigure 1 illustrates the combination boiler plant with dual return boilers for SH and DHW generation. This bypass line diverts excess boiler water back to the system or the boiler’s upper inlet to ensure condensing temperatures are always returned to the lower inlet. Using this approach, efficiency increases by as much as 6%, depending on the upper to lower inlet flow rate ratios and return water temperatures.įor more operational savings in this combination plant design, indirect water heaters with boiler supply bypass can be paired with the dual return boilers. Because the space heating and domestic loops are separated, the dual returns boilers split high- and low-temperature return water to increase the heat exchanger’s condensing zone. Additionally, initial plant cost is lowered, since less equipment and fewer controls are required.Īnother benefit to this design is it lends itself well in the utilization of boilers with dual returns. This switching capability offers a major benefit in reducing the number of boilers required to meet plant peak load, thereby shrinking the system footprint. As per ASHRAE, it is assumed that both SH and DHW peak loads may not happen concurrently. For example, when the DHW boiler(s) cannot meet their load, the controller directs the swing valves to divert the swing boiler(s) from SH to DHW. Load prioritization is managed by a smart controller, as well. Swing boiler(s) that can alternate between SH and DHW are also assigned and separated using swing valves.

Smart controllers handle the different temperature requirements by designating boilers to be assigned to SH while others are allocated for DHW.

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