Burnham V9A - Manual (Page 39)

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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 DT.
NOTICE
DO NOT use the boiler circulator as an indirect
domestic hot water system circulator.
4. Steam Boiler/Indirect Water Heater – 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.