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APPLICATION CONSIDERATIONS • MQL
5
Application Considerations
Model MQL blower coil units offer
a wide range of application flex-
ibility, while maintaining a simple,
easy to install unit design. These
units are intended to provide
comfort cooling and heating
within a small footprint. They
may be applied in many types of
building structures including
schools, office buildings, hospi-
tals, condominiums, assisted liv-
ing facilities, apartments or stores.
Applications can be constant or
variable volume.
There are many applications in
which the MQL product can be
utilized. Some examples include:
Constant volume applications
• Two-pipe hydronic system for
cooling and/or heating
• Two-pipe hydronic cooling
system with electric heat
• Four-pipe system with dedi-
cated heating and cooling
coils
• Direct Expansion (DX) split
systems with hydronic heat
• Direct Expansion (DX) split
systems with electric heat
Variable volume applications
• Two-pipe hydronic system for
cooling and/or heating.
• Two-pipe hydronic cooling
system with electric heat.
• Four-pipe system with dedi-
cated heating and cooling
coils.
Acoustics
Control of noise within both occu-
pied and unoccupied spaces has
become increasingly important
to designers and building own-
ers/occupants. Proper considera-
tion must be given to placement
of indoor air conditioning units,
particularly in the occupied space.
Inherent flexibility of the fan and
coil combination in the vertical
configuration allows application
in sound-sensitive areas. In such
instances, a fan running at low
speed with a high capacity coil
normally yields satisfactory
results. It also may be desirable to
select a larger nominal capacity
unit and operate it at a less than
nominal airflow for further
acoustic benefit.
Three phase motors are recom-
mended for sound-sensitive appli-
cations to avoid potential single
phase motor hum. Unit operation
in the stall region of the fan curve
is not recommended since it may
cause unsatisfactory noise levels
and excessive unit vibration.
Installation
These floor mounted or ceiling
hung units can be installed on a
base rail or hanger rods at the cor-
ner points. All units have internally
isolated fan decks; therefore, flex
connections are not required,
which will reduce installation
costs. One of the most important
and basic IAQ issues is condensate
management. The first step to
ensure trouble-free operation is
proper installation. It is very
important that the unit be
mounted high enough so that the
condensate drain from the unit
may be properly trapped. Please
refer to the MQL IOM Manual at
www.enviro-tec.com for specifics
on this issue. As with all HVAC sys-
tems, these units should be
installed according to all applica-
ble ASHRAE standards, SMACNA
and local code requirements.
Operating Limitations
Units must not be operated above
maximum fan speed or unit air-
flow as listed in the Fan
Performance section of this cata-
log. Unit operation at greater
than maximum fan speed could
drastically reduce bearing life and
may result in a catastrophic fail-
ure. Operating at greater than the
maximum allowable airflow in
the cooling mode may result in
unsatisfactory operation due to
moisture carry over from the coil.
In addition, it is often not eco-
nomical to operate a unit at its
maximum fan speed due to the
greater motor power require-
ments.
Units with electric heat should not
be operated with leaving air tem-
perature greater than 104°F, to
prevent excessive leaving air tem-
peratures and electric heat limit
trips. A hydronic (or steam) coil
and electric heat should not be
operated simultaneously to pre-
vent excessive leaving air tem-
peratures and limit trips. Electric
heat units are equipped with a
lockout switch that disables the
electric heater if the temperature
of the hydronic (or steam) coil is
greater than 104°F (40°C).
Water coils must not be operated
above a fluid velocity of 8 ft./sec.
to reduce the possibility of veloc-
ity induced erosion and flow
noise. Water coils must not be
operated below a fluid velocity of
1 ft./sec. to prevent degraded coil
performance caused by laminar
flow. These high or low fluid flow
rates may not be included in the
ARI coil certification.
ENVIRO-TEC