WARNING
A properly constructed Hartford Loop must be installed on all gravity return steam systems. Hartford Loop is not required on pumped return systems.
L.BOILER PIPING, DOMESTIC HOT WATER (DHW) APPLICATION – This section of the manual identifies the boiler piping details when domestic hot water is required. The two methods described for domestic hot water production are through the use of an indirect hot water heater or tankless coils. If a shell and tube or plate heat exchanger is desired, follow
the instructions for the indirect water heater. Always consult the heat exchanger manufacturer for specific instructions and limitations.
1.Hot Water Boiler/Indirect Water Heater – The use of indirect water heaters for domestic hot water generation is common. Consider prioritizing the generation of domestic hot water using an indirect water heater (See notice below).
a.Dedicated Boiler for DHW Production – If the boiler(s) is (are) dedicated to production of domestic hot water production, the diverting valve is not necessary. (see Appendix A.11 for details) However, the RTC should be used, along with a boiler circulation loop that includes a boiler circulator and return sensor. The boiler circulator and piping must be sized to circulate at a minimum, the flow rate required for a 40 ºF ∆T application. See Appendix B for circulator details. The circulator for the domestic hot water system is separate from the boiler circulator.
NOTICE
DO NOT use the boiler circulator as an indirect domestic hot water system circulator.
b.Shared Boiler for DHW Production – If the boiler(s) is(are) shared between the heating system and the production of domestic hot water, the diverting valve and all of the RTC components should be used. The piping arrangement is different between a system that utilizes the outdoor reset feature vs. one that doesn’t. See Appendix A for various applications. If the outdoor reset feature of the RTC is used, the domestic hot water piping is part of the boiler loop, independent of the diverting valve. Although this bypasses the protection devices of the RTC system, the volume and temperature conditions of a DHW system presents no deleterious impact on
the boiler. This prevents a reset system loop temperature from affecting DHW production.
Multiple boiler applications, utilizing an indirect water heater arrangement, require the use of
a sequencer and connection to the indirect water heater as a load on the secondary loop. An outdoor reset function for multiple boiler applications with DHW, require a DHW priority or reset override. Consult your sequencer manufacturer for recommendations.
2.Hot Water Boiler/Tankless Coil – Tankless coils, mounted into the side of boilers, have been used successfully for many years. Tankless coils may still be used in single and multiple boiler applications. (See Appendix A for typical applications.)
NOTICE
When possible, domestic hot water production should utilize a dedicated boiler(s). This will allow the other boiler(s) to be shut down and isolated during the summer months. If the boiler load is shared between heating and domestic hot water, then one needs to determine if a hot water priority is required. If a priority is not selected, erratic domestic hot water production may result during the beginning and end of every heating season. Conversely, a priority for domestic hot water production may cause a significant heating zone activation delay, in an improperly balanced system. Parallel piping conversions may require isolation from the heating system to prevent system flow influence on DHW performance. Consult a qualified system heating professional to design for the proper application.
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