heating water

Others allow the coil to be removed
by unbolting a sealed end plate at one
end of the shell.
Shell & coil heat exchangers have
been used for heat transfer between
two liquids as well as between a liquid
and a refrigerant. In the latter case, the
refrigerant typically passes through a
welded steel shell, while the liquid
passes through a copper coil. In some
systems, the volume of the shell also
serves as a liquid accumulator within a
refrigeration circuit.
Shell & coil heat exchangers are not
commonly used for liquid-to-liquid
heat transfer in hydronic systems.
One limitation is the amount of coil
surface area versus the overall size
of the heat exchanger. Another is
Figure 2-18
hot
domestic
water
air vent
w/ check
the higher fluid volume in the shell,
which increases thermal mass and
decreases the heat exchanger’s
response time to temperature
changes relative to that of other heat
exchanger designs.
One application where the increased
thermal mass of a shell & coil design is
desirable is when the heat exchanger
also serves as a thermal storage
device. A “reverse” indirect water
heater, as shown in Figure 2-18, is a
good example.
One can think of this reverse indirect
water heater as a high surface area
shell & coil heat exchanger with
added thermal mass and insulation.
Domestic water is fully heated on a
single upward pass through multiple
T&PRV
copper coils that are manifolded
together at the top and bottom of the
tank. Hot water from a boiler or other
heat source passes through the steel
shell of the tank, transferring heat to
the copper coils.
FLAT PLATE HEAT EXCHANGERS
One of the most contemporary devices
for fluid-to-fluid heat exchange is
called a flat plate heat exchanger. This
type of heat exchanger is now used
in many types of hydronic heating and
cooling systems, as well as for the
evaporator and condenser in some
refrigeration systems.
Fundamentally, a flat plate heat
exchanger is created by stacking
several pre-formed metal plates and
sealing the perimeter of those plates
together. The plates are shaped to
create narrow flow channels between
them. One fluid passes from one end
of the heat exchanger to the other
through the odd-numbered channels
(1, 3, 5, 6, etc.). The other fluid passes
from one end of the heat exchanger to
the other through the even-numbered
channels (2, 4, 6, 8, etc.). This concept
is illustrated in Figure 2-19.
hot water from
heat source
domestic water
passes up
through multiple
copper coils
Figure 2-20 shows examples of the
preformed stainless steel plates and
a partially disassembled flat plate
heat exchanger.
Figure 2-19
water back to
heat source
cold
domestic
water
16