LCBS CONNECT SOLUTION
31-00118EFS—01
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MULTISPEED FAN
Multispeed Fan Theory and Operation. Almost 80% of the commercial heating and air conditioning systems in North
America feature a one speed, single speed fan. Rising energy costs, accompanied by increasing HVAC mechanical system
expertise and technology have given rise to the concept to alter the speed of a supply fan during occupied building hours.
A typical HVAC system is sized for regional, geographic "design conditions" at a certain rate of compliance. For example,
in Birmingham, Alabama, find metrological design facts of interest:
*Exceeds parameter, criteria N% of observed climatological condition.
As you know, commercial HVAC equipment is sized to operate at its full capacity limit at some percent level of design,
local climate condition. In Birmingham, an HVAC unit operates at full capacity when it's equal or above 95°F dry bulb and
75.1°F wet bulb outdoor temperature, further at the 99.0% design level. Specifically, this means that 99% of the time, the
HVAC unit operates at a LOWER load level. Bottom line, there is plenty of opportunity to mitigate, reduce air flow, thus
reduce operational supply fan speed. As you know, this is one of the basic tenets of "variable air flow" design and there is
no reason why we can't deploy load reduction principles to constant volume air handling units.
Multispeed Fan Operation
Honeywell LCBS Connect controller offers a variety of control strategies to control fan speed. Industry sources have
shown that varying supply fan speed can result in substantial energy and O&M savings by engaging the technique.
There are three basic ways that we can achieve this applying LCBS Connect control system. First, a traditional belt drive
single-speed motor controlled by a variable frequency drive (VFD) can be used, second, a two-speed motor with two sets
of preset motor windings, and lastly a direct-drive motor (PSC or ECM) controlled by relays or a digital control system.
Two speed motor
The two-winding, two-speed motor is the simplest of the three options that the LCBS Connect controller can control. The
motor will have two sets of windings; this motor is typically provided by an HVAC OEM or by a motor supplier directly. One
set is energized for one discrete speed and the other set energized for the second discrete speed. If you encounter a motor
like this, it is already wired to control the two discrete speeds with LCBS Connect controller. Again, note that the speeds
are probably unchangeable in the field.
VFD application
The LCBS Controller sends a control signal to a VFD that changes frequency and the speed of the supply fan motor. LCBS
Controller supports up to six discrete speeds. Each of the speeds can be assigned to a specific control "mode," like
"ventilation, stage 1 cooling, stage 2 - 3 cooling, stage 1 heating," and so on. Please note that if you are considering
retrofit of a motor, that motor bearings are able to support operation at less than the 60 Hz design speed. Cost of VFDs
have decreased over the years, they are efficient, and they can be preprogrammed to specific speeds. Because of their
electrical construction, VFDs can gradually increase supply fan speed, providing supply fan "soft start." This avoids
starting jolts that create excess noise and mechanical wear on the system.
Direct drive "ECM" motor
A direct-drive motor can received a control signal from the LCBS Controller that will change the supply fan motor speed.
You will find that these are typically low horsepower applications, usually found is system less than five (5) tons. You will
find that the direct-drive motor takes up no additional space in the base rooftop and can be field configured through the
LCBS Controller.
LCBS Connect can perform all currently accepted multispeed supply fan strategies. If you encounter an ECM type supply
fan motor or two speed, two winding fan, we can control it. For retrofit application, it is our recommendation that the
application of a VFD makes most sense. It provides ultimate ability to alter supply fan motor speed and provides soft start
operation for the fan motor. Make sure you are conscious of application of a VFD with the motor you are attempting to
control.
STATION
LAT
LON
ELEV
HEATING DB °F
COOLING DB/MCWB °F/°F
DB
WB
DB
WB
99.6%* 99.0%*
99.6%*
99.0%*
99.6%* 99.0%*
BIRMINGHAM
MUNICIPAL AIRPORT
33.56N
86.75W
630
19.6
24.0
95.0
75.1
92.6
74.9