Transcript airflow/fsr97

SERVICE PROCEDURE
 Airflow
measurement
 System
charging
 Performance
measurement
Airflow measurement
An accurate airflow measurement
must be performed before the
system can be properly charged with
refrigerant or before any attempt is
made to measure performance.
Airflow measurement
BTUH (OUTPUT)
CFM =
TEMP DIFFERENCE X 1.08
Measurement Methods

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

power measurement - watt-hour meter
– electric resistance heat and heat pumps
power measurement - volt-ampere
– electric resistance heat
clocking a gas meter
– natural gas furnaces
calculating input by orifice capicity
– propane gas furnaces
total static pressure
WATT-HOUR METER

Power input measurements, by the watthour meter require power interruption to
all appliances in the structure except the
indoor fan motor and electric heaters.

Do not turn off power to:
– Life support devises
– Appliances subject to damage from
power interruption
WATT-HOUR METER

Set the thermostat to heat or emergency
heat and adjust the setpoint to 90 degrees.

Locate the watt-hour meter serving the
structure.

Clock the black mark on the meter disc for
20 revolutions using a stop watch or the
second hand on your wrist watch.
Power Input Formula
Revolutions x KH factor x 3.6
KW (KILOWATT) INPUT =
Seconds
20 revolutions
kh = 7.2
65 seconds
Power Input Formula
20 rev x 7.2 kh x 3.6
KW =
518.4
= 7.97 kw
=
65
65
1 KW = 3413 BTU PER
HOUR
7.97 kw x 3413 = 27,202 btuh (input)
electric resistance heat is 100% effecient
input = output
Take Return Air Temperature Measurement as Close
to Equipment as Possible
Do NOT Take Temperature Measurement in the Line of
Sight of Heat Source.
Take an Average of ALL Supply Duct Temperatures
Use a Calibrated Thermometer to Measure Temperature.
Use the Same Thermometer for ALL Temperature
Measurements
Airflow measurement
BTUH (OUTPUT)
CFM =
TEMP DIFFERENCE X 1.08
EXAMPLE:
27,202 BTUH (output)
27 degrees delta “T”
Airflow measurement
27,202 BTUH
CFM =
27,202 BTUH
=
27 X 1.08
= 933 CFM
29.16
Measurement Methods

power measurement - volt-ampere
– electric resistance heat
POWER MEASUREMENT
VOLT-AMPERE

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
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set the thermostat to the heat or emergency
heat mode, in the case of a heat pump, so
that only the resistance heaters and the fan
motor are activiated.
measure the applied voltage to the resistance
heaters while they are operating.
measure the current draw for each circuit if
more than one and add them together.
measure the temperature difference entering
and leaving the air handler.
POWER MEASUREMENT
VOLT-AMPERE

multiply the applied volts times the total
current draw (amperes)
VOLTS X AMPERES = WATTS
BTUH (OUTPUT) = WATTS X 3.413
Measurement Methods

Clocking a gas meter
– Natural gas furnaces
2 cubic feet
per revolution
GAS FURNACE INPUT
make sure no other appliances are
on during the test.
 set the thermostat to heat mode and
90 degrees.
 record the seconds required for one
revolution of the 2 cubic foot dial on
the gas meter.
 determine the gas flow rate in cubic
feet per hour from the following
equation or use a gas flow table.

GAS FURNACE INPUT
2 cu. feet per revolution x 3600
cu. ft per hour =
GAS FURNACE INPUT
2 cu. feet per revolution x 3600
cu. ft per hour =
time (in seconds) per revolution
GAS FURNACE INPUT
2 cu. feet per revolution x 3600
cu. ft per hour =
time (in seconds) per revolution
example: 1 rev. (2cu.ft. dial) = 60 seconds
GAS FURNACE INPUT
2 cu. ft. per revolution x 3600
cu. feet per hour =
60
2 x 3600
cu. feet per hour =
7200
=
60
= 120 CFH
60
60 SECONDS
120 CFH
GAS FURNACE INPUT
BTUH = HEAT CONTENT X CUBIC FOOT/HOUR
BTUH = 1000 BTU X 120 CFH = 120,000 BTUH (INPUT)
BTUH (OUTPUT) = BTUH (INPUT) X EFFECIENCY
USE A MIN. OF 80% EFFICIENCY FOR NAT. GAS
USE FURNACE AFUE EFFECIENCY IF HIGHER THAN
80%
GAS FURNACE INPUT
120,000 BTUH X 92%
CFM =
55 X 1.08
110,400 BTUH (OUTPUT)
CFM =
= 1858 CFM
59.4
Measurement Methods
calculating input by orifice capacity
– propane gas furnaces
CALCULATING CFM AND INPUT BY
ORIFICE CAPACITY
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determine the burners orifice size.
count the number of orifices in the
furnace.
set the gas valves outlet manifold
pressure to 11 inches of water column.
set the thermostat to heat mode and 90
degrees.
measure the temperature difference
entering and leaving the furnace.
CALCULATING CFM AND INPUT BY
ORIFICE CAPACITY



determine the btu per hour input for the
selected orifice size using table f-2 in
apendix f of the national fuel gas code.
multiply the btu per hour input times
the number of orifices counted in the
furnace.
multiply the btu per hour input times
the furnace effeciency (minimum 80%).
table F-2
Measurement Methods
 total
external static pressure
STATIC PRESSURE
Definition:
The pressure measured above or
below atmospheric pressure created
by the blower independant of air
velocity. It is exerted in all direction
to the inside walls of the ductwork
and is measured at a 90 degree
angle to the airflow.
Measure
return
static
pressure
close
to
air
messure return static pressure as close to
handler
or furnace
cabinet.
air handler
or furnace
cabinet as possible
Measure supply static pressure downstream
of all pressure drops. Average readings where
turbulant airrflow is present
PRODUCT DATA
TWEO48C140B - BAY96X1415
PUB # 22-1298-03 PAGE # 8
 EXAMPLE:
Measured external static pressure = .5
In. W.C.
Blower set on high speed tap
Product Data
TWE048C140B - BAY96X1415
 EXAMPLE:
Measured external static pressure = .5 In.
W.C.
Pressure drop accross heater = .13 In. W.C.
Final static pressure = .63
Airflow = approx. 1550 CFM
TUD100C948H - TXC049C4HPB
 EXAMPLE:
Measured external static pressure = .30
In. W.C.
Blower set on black - high speed tap
Product Data
TUD100C948H - TXC049C4HPB
 EXAMPLE:
Measured external static pressure = .30 In.
W.C.
Pressure drop accross coil = .30 In. W.C.
Final total external static pressure = .60 In.
W.C.
Blower set on black - high speed tap
Airflow = 1595 CFM
Product Data
TUD100C948H

EXAMPLE:
Temperature rise = 47 degrees
Airflow = 1550 CFM