Airflow Balancing Using The Pitot Tube (All Models) - Healthy Climate HRV Series Installation Instructions And Home Owner's Manual

Read the application warning in the "Requirements" on
page 9 of this manual.
Balancing Preparation
1. All sealing of the duct system has been completed.
2. All of the HRV/ERV system components are in place
and functioning properly.
3. Balancing dampers are fully open.
4. Unit is on HIGH speed.
5. Airflow in branch lines to specific areas of the house
should be adjusted first prior to balancing the unit. A
smoke pencil used at the grilles is a good indicator of
each branch line's relative airflow.
6. Operate air handling unit to fan speed for normal
operation.
7. A field−supplied balancing damper for the stale air side
is required for system balancing.
Balancing the Unit
Balance the unit by measuring the unit's incoming fresh and
exhausting stale airflows and dampering down the higher
airflow to match the lower airflow.
Airflow Measuring Gauges
Airflow measurement is achieved by using a gauge with an
airflow measuring attachment connected to the high pres-
sure and the low-pressure side of the gauge. Use a Digi-
tal Manometer (reading down to 0 with resolution of 0.001"
w.g. (0.02 Pa) or a magnehelic gauge for airflow measure-
ment.
NOTE: A Magnehelic Gauge with a scale of 0 to 0.25" w.g.
(0 to 62 Pa) is necessary for using with a Pitot Tube
and Magnehelic Gauge with a scale of 0 to 1.00"
w.g. (0 to 249 Pa) is necessary for using on Door
Port Balancing).
Gauge Attachments
Common gauge attachments for measuring HRV/ERV air-
flows are:
• The pitot Tube - This will measure the airflow in the
ductwork for any HRV/ERV.
• Door Port Gauge Tube Set - This will measure the air-
flow using the door ports for models HRV3-150-TPD/
TPF, HRV5-150-200.
• Flow Stations - These are installed into the duck work.
Pitot Tube Balancing Procedure
1. Operate all mechanical systems that have influence on
the ventilation system at high speed. These systems
include the HRV/ERV unit itself and the air handler/
furnace (if applicable). This will provide the maximum
pressure that the system will need to overcome, and
allow for an accurate system balance.
2. Refer to next page for illustrations of Airflow Balancing
Using the Pitot Tube.
Determining the Actual Airflow
Actual airflow can be determined from the gauge reading.
The value read on the gauge is called the velocity pres-
sure. The Pitot tube comes with a chart that will give the
airflow velocity based on the velocity pressure indicated by
the gauge. This velocity will be either feet per minute or
liters per second. To determine the actual airflow, multiply
the velocity by the cross−sectional area of the duct being
measured. This is an example for determining the airflow in
a six inch (152 mm) duct with a Pitot tube reading of 0.025"
w.g. (6.2 Pa) water.
From the chart, this equates to 640 feet (16 meters) per
minute. The 6 inch (152 mm) duct cross−sectional area is
0.2 sq. ft. (0.019 m ) The airflow is 640 cfm x 0.2 sq. ft. =
2
128 cfm (302 L/s x 0.019 m
The cross sectional area of some common round duct is:
• 5" (127 mm) diameter duct has 0.14 sq. ft. (0.013 m
cross−section area
• 6" (152 mm) diameter duct has 0.20 sq. ft. (0.019 m
cross−section area
• 7" (178 mm) diameter duct has 0.27 sq. ft. (0.025 m
cross−section area
The accuracy of the airflow reading will be affected by how
close to any elbows or bends the readings are taken. In-
crease accuracy by taking an average of multiple readings
as outlined in the literature supplied with the Pitot tube.
Airflow Balancing Using the Pitot Tube (All
Models)
1. Drill a 3/16" (5 mm) in hole in the duct, ideally three
feet (914 mm) downstream and 12" (305 mm) upstream
of any elbows or bends in the fresh air and stale air
streams.
2. Insert the pitot tube with the tip facing towards the air
stream in the stale air from Building air stream. Move the
pitot tube around in the duct (facing toward the airflow)
and take an average reading. Record the reading.
Figure 38. Insert Pitot Tube
29
= 60 L/s)
2
Drill 3/16" (5 mm)
holes in stale and
Damper
fresh air ducts.
Figure 37. Drill
Pitot Tube facing
towards the air stream.
Minimum of 18" (457 mm)
from blower to elbows.
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