American Aldes HRV 1500 SFD - Manual (Page 14)

14
Pilot Tube Air Flow Balancing - Commercial
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 building
• The unit may not defrost properly
• Failure to balance HRV properly may void warranty
Excessive positive pressure may drive moist indoor air into the ex-
ternal walls of the building where it may condense (in cold weather)
and degrade structural components. May also cause key holes to
freeze up.
Excessive negative pressure may have several undesirable effects.
In some geographic locations, soil gases such as methane and ra-
don gas may be drawn into the building through basement/ground
contact areas. Excessive negative pressure may also cause the
backdrafting of vented combustion equipment.
Read the Application Warning on the front of this manual!
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. Air flows 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 air
flow.
6. 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.
7. 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 stations are not installed
in the ductwork. Procedure should be performed with the HRV on
high speed.
The first step is to operate all
mechanical systems on high
speed, which have an influence
on the ventilation system, i.e. the
HRV itself and the forced air fur-
nace or air handler if applicable.
This will provide the maximum
pressure that the HRV will need
to overcome, and allow for a
more accurate balance of the
unit.
Drill a small hole in the duct
(about 3/16"), three feet down-
stream of any elbows or bends,
and one foot upstream of any el-
bows or bends. These are rec-
ommended 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 resolution. 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 pres-
sure or reference side of the gauge.
I nsert the Pitot tube into the
duct; pointing the tip into the airflow.
For general balancing it is sufficient to move the pitot tube around in
the duct and take an average or typical reading. Repeat this proce-
dure in the other (supply or return) duct. Determine which duct has
the highest airflow (highest reading on the gauge). Then damper that
airflow back to match the lower reading from the other duct. The
flows should now be balanced. Actual airflow can be determined
from the gauge reading. The value read on the gauge is called the
velocity pressure. The Pitot tube comes with a chart that will give the
air flow velocity based on the velocity pressure indicated by the gauge.
This velocity will be in either feet per minute or meters per second.
To determine the actual airflow, the velocity is multiplied by the cross
sectional area of the duct being measured.
The accuracy of the air flow reading will be affected by how close to
any elbows or bends the readings are taken. Accuracy can be in-
creased by taking an average of multiple readings as outlined in the
literature supplied with the Pitot tube.