From this month's Oil & Energy magazine
Hydro-air systems have been around for a long time…even hydro steam. I remember the
first time I saw a radiator mounted inside of a plenum and I thought “what the heck is
this?” Back in the day when fresh air was deemed a necessity (unlike today in our tight
energy efficient homes - ha!), duct work would draw air from the outside and heat it with
these duct mounted radiators before delivering it to the living space. Not very efficient
but fuel was a lot less costly back then and the owners of these homes weren’t shy of a
few pennies. Times have changed however. Today when we say hydro-air we think of air
handlers with internal coils for heating and/or cooling.
For the most part, hydro-air is a product of the electric conversion market when
electricity prices started to rise. Replacing that old electric furnace and installing a
boiler with an air handler allowed versatility when it came to zoning and potable hot
water. Indeed, the ability to run additional emitters off the boiler often led to systems
with multiple heat delivery schemes such as warm air, convection and radiant. Entire
sections of the home could be heated by a different medium e.g. warm air upstairs;
radiant downstairs; baseboard in the basement. And all of this with air conditioning and
endless hot water as well. The more recent decades have seen an increased demand for air
conditioning and, for homes heated with water, hydro-air is a very convenient solution.
One of the major differences between air handlers and direct fired furnaces is the quality
of the air delivered to the home. The heat exchangers in fuel fired furnaces are subjected
to extremely high surface temperatures which tend to dry out the delivered air. Whereas,
with an air handler, the heat exchanger never sees temperatures above 180°F resulting in
a much more comfortable living environment.
The implementation of ECM technology in HVAC motors has had a significant impact
on the efficiency of the equipment. We first began to see ECM motors in air handlers
and condensing furnaces which resulted not just in increased motor efficiency but also
enhanced the performance of the blower by compensating somewhat for inadequate duct
design. ECM motors make a lot of sense for air handling equipment because of the larger
size motors needed to move large volumes of air.
And more recently we have seen the introduction of ECM motors into the wet side of the
equation. All of the leading pump manufacturers boast ECM circulators - which begs the
question of how best to use this technology in a hydro air application.
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 1/3HP to ¾ 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 pressure 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
which 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.
Now, imagine if we could program a fixed air delivery temperature at the registers…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 airstream 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 BTU’s 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 BTU’s to
the coil. The result will be a more even temperature 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.
One pump that has this capability is the Bumblebee or HEC2 from Taco. This ECM
circulator can be programmed to maintain either ΔT or a fixed set point. This pump,
which has its own sensor inputs, is factory programmed to maintain 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 still available, the 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 comfort can be greatly
enhanced.
Learn more about hydro air
here.
The Taco Zone Sentry leads the industry in energy efficiency, flow capacity, shutoff pressure rating, diagnostic capability and the number of valves (12) that can be used on a standard 40VA transformer. Learn more here.
Emerson Swan Training's: Held at 300 Pond St. Randolph, MA 02368
