Filter
Top Products
8
Pitot Tube Air Flow Balancing
It is necessary to have balanced air flows in an HRV. The
volume of air brought in from the outside must equal the
volume of air exhausted by the unit. If the air flows are not
properly balanced then:
* The HRV may not operate at its maximum efficiency
* A negative or positive air pressure may occur in the house
* The unit may not defrost properly
* Failure to balance the HRV may void warranty
Prior to balancing, ensure that:
1. All sealing of the ductwork system has been completed.
2. All of the HRV's components are in place and functioning
properly.
3. Balancing dampers are fully open.
4. Unit is on high speed.
5. After taking readings of both the stale air to the HRV duct
and fresh air to the house duct, the duct with the lower
CFM ([L/s] velocity) reading should be left alone, while the
duct with the higher reading should be dampered back to
match the lower reading.
6. Return unit to appropriate fan speed for normal operation.
Balancing Procedure
The following is a method of field balancing an HRV using
a Pitot tube, advantageous in situations when flow sta-
tions are not installed in the ductwork. Procedure should
be performed with the HRV on high speed.
Choose the straightest section of duct between the HRV
and the weatherhoods. This will be used for both the sup-
ply and return ducts.
Drill a small hole in the duct (about 3/16"), three feet
downstream of any elbows or bends, and one foot
upstream of any elbows or bends. These are recommend-
ed distances but the actual installation may limit the
amount of straight duct.
The Pitot tube should be connected to a magnehelic
gauge or other manometer capable of reading from 0 to
0.25 in. (0 - 62 Pa) of water, preferably to 3 digits of reso-
lution. The tube coming out of the top of the Pitot is
connected to the high pressure side of the gauge. The
tube coming out of the side of the Pitot is connected to the
low pressure or reference side of the gauge.
Insert the Pitot tube into the duct, pointing the tip into the
airflow.
Installation