return air duct design notes
The return air is to be sized as per local
building codes and good practices. It is good
design practice to line the first five feet of the
return air duct with a sound acoustic
insulation. This will reduce sound transfer
through the duct and operating sound levels.
It is recommended to install a grill which is
10-20% larger than the return duct area to
ensure adequate free area and no velocity
noise at the grill. Where allowed by local
codes, a single return air grill may be used.
When using flexible duct for return air, use
one size larger duct due to the higher friction
loss.
For areas that require fresh air make-up
(either direct or through an ERV or HRV), an
intake may be installed in the system. Size
and insulate the fresh air supply as per local
code. Remember, should you install a duct
that is too large, the excess fresh air will
increase the system operating cost and
effect overall equipment capabilities. It is
recommended to install a well fitted damper
into the return air plenum. The damper can
then be adjusted to supply the exact amount
of fresh air needed to meet local building
codes.
indoor air quality
The main factors of indoor air quality are air
filtration, humidity control, and fresh make-up
air. All of these factors can best be achieved
with a continuous run fan system. It is
important to have a good quality air filter for
your MaxAir™fan coil system. Maintaining a
clean air filter will increase the unit life span,
allow the unit to operate efficiently and
effectively, and will provide clean air for the
occupants.
Humidity control is also an important factor to
indoor air quality. It is acceptable to install a
humidifier following the manufacturers
installation requirements.
combination MaxAir™ and hydronic
heating
One of the benefits of using a hydronic
system is the versatility that you have when
designing the heating system. Radiant
underfloor heating is an excellent system, but
it does have limitations. You cannot have
cooling, air filtration, and humidification with a
radiant heating system.
It is in rooms such as this that a hybrid
system of both radiant heating and a
MaxAir™fan coil would be the optimum
system to provide comfort conditioning. This
will provide the homeowner with good indoor
air quality, and warm floor comfort.
One of the most common approaches to
heating with a hybrid system is using the
MaxAir™fan coil to provide the comfort
conditioning for the main floor (and second
floor if applicable) and radiant tubing in the
basement and tile areas. A few outlets
located in the basement is recommended in
order to provide good air circulation and
supplementary heating if required.
low water temperature systems (combo
systems with conventional hot water
tanks + geothermal sytems)
Operating MaxAir™fan coils in a low
temperature system, care must be taken
when designing and installing the system.
Due to the lower air temperatures, when
installing ductwork in an unconditioned
space, extra insulation is recommended in
order to maintain a consistent air
temperature at the outlets. The main supply
plenum must be insulated and wrapped with
a vapor barrier in order to meet local codes.
All duct work should then be covered with
another layer of insulation. Due to the fact
that with lower water temperatures you get a
lower supply air temperature, it is imperative
that the water temperature is known at the
design stage. If possible, a higher tank
setting should be used, and an anti-scald
valve be installed for the domestic use. The
