Nordic AH4P Series, Service Manual

Page: 11 / 30

5-Jul-2022 Page 11 002596MAN-01
Ductwork
Zoning
The air handler is most commonly configured as one of
several zones on the hydronic system.
Zoning of the air handler’s air duct system can also be
performed; that is, it can have several zones of its own. Unlike
with a heat pump, there is no consideration of having too small a
zone, since there is no compressor. However, the control sys-
tem should be set up so that airflow from the AHW / AH4P
matches the open air ducting. This is done with using 5 discreet
air flow levels called for by 24VAC signals, or for –VSP models
using a 0-10VDC signal to call for any airflow from 0 to 2500
cfm.
Refer to airflow tables in the Model Specific Information
chapter for airflows with the various input signals.
Commercial/Industrial Installations
If a large area, for example a warehouse or greenhouse, is
to be dehumidified or heated/cooled, the units may be ceiling-
hung and it is possible that minimal or no ductwork is specified.
Check the jobsite plans.
Duct Systems - General
Ductwork layout for a hydronic air handler will differ from
traditional hot air furnace design in the number of leads and size
of main trunks required. Air temperature leaving the air handler
varies widely with water temperature, water flow, and air flow
according to the performance tables later in this manual. But it
may be 95º-105ºF (35-40ºC) , much cooler than that of a
conventional fossil fuel furnace. To compensate for this, larger
volumes of lower temperature air must be moved and
consequently duct sizing must be able to accommodate the
greater airflow without creating a high static pressure or high
velocity at the outlet diffusers.
A duct system capable of supplying the required airflow is
of utmost importance. Maritime Geothermal Ltd. recommends
that the external static pressure from the duct system be kept
below 0.2 inches of water total. In some instances the number
of diffusers will actually double when compared to the number
that would be used for a hot air furnace.
1. Generally allow 100 cfm for each floor grill.
2. All leads to the grills should be 6'' in diameter (28 sq.in. ea).
3. The main hot air trunks should be at least 75% of the cross
sectional area of leads being fed at any given point.
4. Return air grills should have a minimum of the same total
cross sectional area as the total of the supply grills.
5. The the cross sectional area of the return trunks should
equal the cross sectional area of the grills being handled at
any given point along the trunk.
It is
VERY IMPORTANT
that all turns in both the supply
trunks and the return trunks be made with
TURNING RADII
. Air
act like a fluid and, just like water, pressure drop is increased
when air is forced to change direction rapidly around a sharp or
irregular corner.
It is recommended that flexible collars be used to connect
the main trunks to the air handler. This helps prevent any vibra-
tions from travelling down the ductwork.
Duct Systems - Grill Layout
Most forced air heating systems in homes have the floor
grills placed around the perimeter of the room. Heating supply
grills should be placed under a window when possible to help
prevent condensation on the window. As mentioned in the pre-
vious sub-section, supply grill leads should be 6'' in diameter (28
square inches each) to allow 100 cfm of airflow.
In a typical new construction, there should be one supply
grill for every 100 square feet of area in the room. When rooms
require more than one grill, they should be placed in a manner
that promotes even distribution, such as one at each end of the
room. It is always a good idea to place a damper in each grill
supply or place adjustable grills so that any imbalances in the
heat distribution can be corrected.
The total number of supply grills available is based on the
design airflow. The table shows the number of grills recom-
mended vs. airflow.
Return grills should be mounted on the floor. At minimum
they should be the same size as the supply grill, it is highly
recommended that they be 25% to 50% larger than the total
supply. They should be placed opposite the supply grills when
possible to ensure distribution across the room. For rooms re-
quiring more than one supply grill, it may be possible to use one
larger return grill if it can be centrally positioned opposite of the
supply grills, however it is preferred to have one return for each
supply to optimize heat distribution across the room.
Thermostat Location
Most air handlers are installed as a single ducted air zone
with one thermostat. The thermostat should be centrally located
within the conditioned space. It should be placed away from
any supply grills, and should not be positioned directly above a
return grill. Most installations have the thermostat located in a
hallway, or on the inner wall of the living room. It should be not-
ed that most buildings do not have any supply ducts in the hall-
way. This can lead to a temperature lag at the thermostat if
there is very little air movement in the hallway, causing the
space to be warmer than indicated by the thermostat.
Plenum Heater
The plenum heater will be usually installed inside the air
handler, as described in the Installation Basics section. If a
plenum heater is installed in the discharge ductwork outside the
air handler, it should be at least 12” away from any flexible duct
collars.
TABLE 6 - Airflow vs. Hot Air Grills
Airflow # of Grills (@100 cfm)
900 cfm 9
1200 cfm 12
1500 cfm 15
1900 cfm 19
2300 cfm 23