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Figure 39: Mounting Elevations of M&M 150
pump controller and 63 Float Low Water Cut-offs.
N.
BOILER PIPING, DOMESTIC HOT WATER
(DHW) APPLICATION – The V11H 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 the 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 boilers solely to 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 three
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(s), 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 controls in place to prevent overheating
of the space heating zones. Figure 41 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 dish washing, washing machines and other
appliances.
46
Figure 40: Recommended Piping for Combination
Heating & Cooling (Refrigeration) Systems
Water Boilers
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 42a 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 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 42a.
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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