M.BOILER PIPING, DOMESTIC HOT WATER (DHW) APPLICATION – The V9A boiler can be used in many different piping applications to produce Domestic Hot Water (DHW). In some applications, depending on the control strategy (outdoor reset, setpoint operation, etc.) and size of boiler, it is recommended to isolate the space heating load from the DHW load. For example, if the domestic load is more than the space heating load, it is beneficial to dedicate one or more boilers solely to DHW production and one or more other boilers to solely space heating, since during mild weather conditions, the boiler(s) will have more capacity than is required. Piped in the recommended manner, the space heating boiler(s) can be shut down during the summer months to conserve energy and to avoid short cycling. This section
will address four methods of piping and controlling domestic hot water generation.
1.Hot Water Boiler/Tankless Coil(s) - Tankless coils, mounted into the side of the boiler, have been used successfully for many years and may be used in single and multiple boiler applications. When a boiler is arranged with tankless coils, it is not recommended that outdoor reset be used, unless there are control systems in place to prevent overheating of the space heating zones.
Figure 37a depicts the addition of an automatic mixing valve to the tankless heater piping to obtain a dual temperature domestic system. The mixing valve provides tempered water to the fixtures, while the branch prior to the valve provides high temperature water for dishwashing, washing machines and other appliances.
2.Hot Water Boiler/Tankless Coils/Storage Tank - This application involves the use of several tankless coils piped in parallel, emptying into a large storage tank, and is typically used in larger DHW production
applications, such as hotel showers and laundries. See Figure 37b for recommended piping and wiring details for this type of application. The tempering valve and recirculation loop are advantageous in these applications, because they provide both high temperature and tempered domestic hot water to the system, eliminating the need to purge and waste water until it reaches the desired temperature. In the case where the boiler is used for domestic production only, and there is no space heating involved, a destratification pump is utilized to provide flow within the boiler. This flow acts as a means of preventing the hot water from stratifying at the top of the boiler. Destratification pump flow rates are given in the table in Figure 37b.
3.Hot Water Boiler/Indirect Water Heater - The use of indirect water heaters for domestic hot water generation is common and somewhat advantageous over tankless coils alone, since they also provide DHW storage. A tempering valve and recirculating pump are again recommended for a dual temperature system, to provide a constant temperature to the fixtures without waiting for cooler water to warm up. Figure 37c shows a typical indirect heater piping application with no space heating. Indirect pump flow rates are calculated based on a 20°F ΔT.
NOTICE
DO NOT use the boiler circulator as an indirect domestic hot water system circulator.
4.Steam Boiler/Indirect Water Heater – Consult I=B=R Installation and Piping Guide No. 200. Use the Indirect Water Supply tapping, “R” (Special Order Only – see Figure 24) when connecting an Indirect Water Heater directly to the boiler.
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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