Aprilaire 8100 manual Balancing the System, Balancing Airflow, Airflow Approximations, Gauge, Cfm

BALANCING THE SYSTEM (continued)

Balancing Airflow

1.Drill a 7/8” hole in the return and supply ducts..

2.Install the two airflow measuring devices in the duct using the drilled holes and seal with tape.. Verify the airflow arrows are pointed in the direction of airflow.. The measuring devices should be a minimum of 2-1/2’ from the damper in a 5’ section of straight duct.. (See Figure 19..)

3.Set up the pressure gauges so that they are vertical and level and adjust to zero..

4.Connect the tubing from the airflow measuring devices in the ducts to the pressure gauges (see Figure 19).. The high pressure tap on the airflow measuring device must be connected to the high pressure tap on the pressure gauge.. Similarly, connect the low pressure tap on the measuring device to the low pressure tap on the pressure gauge..

Figure 19 – Set-up for Balancing Airflow
5 FT. MIN.	DAMPER	DAMPER	5 FT. MIN.
2-1/2 FT			2-1/2 FT
FRESH AIR			STALE AIR
TO HOUSE			FROM HOUSE
STALE AIR			FRESH AIR
TO OUTSIDE			FROM OUTSIDE
AIR FLOW MEASURING			AIR FLOW MEASURING
DEVICE #5158			DEVICE #5158
	PRESSURE GAUGES		90-1746

5.Verify the dampers are in the fully open position..

6.Turn off the HVAC system blower and any other exhaust fans..

7.Plug in and turn on the unit..

8.Read the pressure gauges.. If the gauge readings are the same, the system is balanced and does not require further adjustment.. Proceed to Step 10..

9.If the readings are different, slowly close the damper on the duct with the higher gauge reading until the two readings are identical.. When the readings are the same, the system is balanced..

10See Table 1 for approximated airflow based on pressure gauge readings..

11.Secure the damper positions to prevent them from changing during operation..

12.Disconnect the tubing and pressure gauges and remove the airflow measuring devices.. Seal the duct openings where the measuring devices were located..

Table 1 – Airflow Approximations

Airflow in a 6” Duct as Measured using

Airflow Measuring Device #5158

Gauge		Gauge
Readings	Airflow	Readings	Airflow
(in. w.c.)	(cfm)	(in. w.c.)	(cfm)
0..005	30	0..065	119
0..010	44	0..070	124
0..015	55	0..075	128
0..020	64	0..080	132
0..025	72	0..085	137
0..030	80	0..090	141
0..035	86	0..095	145
0..040	93	0..1	149
0..045	98	0..105	152
0..050	104	0..110	156
0..055	109	0..115	160
0..060	114	0..120	163

NOTE: If airlow is restricted by more than 20% (see bold values in Table 1), check ductwork and connections to increase flow..

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