August 2013 • 23
Circulator motors are notoriously small
(
1
/
25
HP is typical), so electrical savings are
minimal. On the other hand, blower motors
will be anywhere from
1
/
3
HP to
3
/
4
HP, so
the electrical savings are significant when
switching to an ECM.
In the case of a circulator, the true
benefit of an ECM motor is the ability to
affordably control the water flow and thus
control the BTU supply to the air handler,
but only if that circulator has the ability to
track temperature modulation versus pres-
sure drop. In other words – Delta-T versus
Delta P.
With a conventional hydro-air system,
we have a fixed BTU output from the
boiler and a single-speed circulator. The air
delivery is most often controlled by either
an aquastat that brings on the blower when
hot water is sensed in the coil or a timer
delay function.
This arrangement becomes even more
complex if outdoor reset is factored
into the equation; with modulating
supply temperatures and fixed blower
speeds, the temperature of delivered air
at the registers can vary significantly.
The efficiency of the condensing boiler
may also be impacted as the boiler control
is often programmed to maintain a
minimum of 130°F.
SOPHISTICATED SOLUTIONS
Now, imagine if we could program a
fixed air delivery temperature at the regis-
ters … say 120°F? But this can be done, you
say, by controlling the blower with pulse
width modulation. How about a less costly
but more efficient method?
By locating a sensor in the output air-
stream of the air handler and programming
the pump to maintain a desired delivery
temperature, the pump will speed up or
slow down as it sees fit. If the sensor detects
an increase in output air temp, the pump
will slow down and deliver less flow and
fewer BTUs to the coil. When the sensor
detects a decrease in temperature due to
lower return air temperature, the pump will
speed up and deliver more flow and more
BTUs to the coil.
The result will be a more even tempera-
ture at the registers. In effect, the pump is
responding to real time conditions, which
can be affected by events such as doors
opening and the introduction of heat from
secondary sources such as stoves, etc.
STEADY TEMPERATURES
One pump that has this capability is
the Bumblebee or HEC2 from Taco. This
ECM circulator can be programmed to
maintain either
T or a fixed set point.
This pump, which has its own sensor
inputs, is factory programmed to main-
tain a 20°F delta between the supply and
the return. It takes just a few seconds
to reprogram the circulator for a fixed
supply temperature, and by placing
the supply sensor in the air stream, the
pump will speed up or slow down based
on conditions. No more fluctuating air
temperatures at the registers.
Air handlers come in all shapes and
sizes. But the heart of the appliance is
the motor. While it is still available, the
traditional PSC motor is fast giving way
to the ECM. This electrically commutated
motor offers significant advantages over the
split-phase motor in terms of efficiency and
performance.
The same logic applies to the wet side
of the equation, and when properly applied,
both the cost of operation and overall com-
fort can be greatly enhanced.
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