heating water

One fundamental distinction between
fan coils and air handlers is that the
latter is typically designed to connect
to a ducted air delivery system. This
allows the air stream created by the
blower to be simultaneously delivered
to several locations in a building.
Another distinction is that most air
handlers are intended to be installed
in non-occupied locations such as
mechanical rooms, interior soffits,
basements or attics. They are not
designed with aesthetic details to
make them acceptable in finished
occupied spaces.
Figure 2-34 shows a small,
horizontally oriented, 2-pipe air
handler connected to a ducted
forced-air delivery system.
This unit is mounted in an accessible
area within a conditioned attic. A
removable panel will eventually be
installed to conceal the unit. The coil in
this air handler is supplied by insulated
piping carrying chilled water for
cooling. Because it is installed above
a finished space, this air handler is
mounted over a secondary drain pan
that would capture any condensate
that might leak from the unit’s primary
condensate drip pan. The condensate
formed on the coil during cooling
mode is carried to a drain through the
small PVC pipe seen at the lower right
of the unit.
Small air handlers that are commonly
used in homes or small commercial
buildings may have heating and
cooling capacities ranging from about
12,000 Btu/hr (1 ton) to about 60,000
Btu/hr (5 tons). However, many air
handlers are available with heating
and cooling capacities much higher
than those of fan-coils.
Large air handlers can have heating
and cooling capacities of several
million Btu/hr. These large units are
typically custom-built for specific
applications. They typically have
separate water-to-air coils for heating
and cooling, separate blowers for the
supply and return air streams, energy
recovery devices, and more elaborate
air-filtering systems compared to small
air handlers. Figure 2-35 illustrates
some of these internal details.
The thermal performance of fan-coils
and air handlers will be discussed in
Section 4.
GREYWATER HEAT RECOVERY
HEAT EXCHANGERS
Heat exchangers are also used in
plumbing applications. One example
is recovering heat from domestic
hot water that has passed through a
fixture such as a lavatory or shower.
This water is commonly referred to as
“greywater.”
Much of the heat in domestic hot water
remains in that water as it goes down
the drain. In most buildings, this heat is
simply carried into the sewer. However,
it is possible to recover up to 40% of
this otherwise wasted heat using a
greywater heat exchanger, an example
of which is shown in Figure 2-36.
Figure 2-35
DOAS air handler
rotating desiccant wheel
(exchanges enthalpy
b/w air streams)
exhaust air
heat &
moisture
flow
filter
return air from
building
outdoor air
delivered air
(very low humidity)
filter
pre-conditioned air
heating coil
chilled water coil
supply duct
to building
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