Checking Airflow

When checking Air Flow:

• Make sure that all duct dampers and registers are open and un-blocked

• Ensure that a CLEAN filter is in place

• Make sure that all interior doors are open

• Is The Blower Wheel Clean?

• Is The Evaporator Coil Clean?

• Make Sure You Have approximately 400 CFM Of Air Flow Per Ton

When checking Air Flow (cont.):

Temperature Rise

Temperature Rise

1. Place the indoor fan blower motor speed to it’s original setting for

heat mode operation

2. Subtract your measured return air temperature from your supply

air temperature. This is the Delta-T value.

3. Multiply the Delta-T value by 1.08. Record this value.

4. Divide your BTUH Output by the value you obtained in Step 3.

5. The answer is your actual system airflow.

Airflow Calculations for Furnaces (Heating Mode)

Airflow Calculations For Furnaces

BTUH 100,000

Supply Air Temp: 120 F

Return Air Temp. 70 F

120 F – 70F = 50F (Delta T)

100,000

1.08 X 50

100,000 = 1851 CFM

54

_________________________________ BTUH OUTPUT

1.08 X Temperature Rise ( Delta T) CFM =

____________________________________________________

Example

BTUH = 70,000 x 90% (AFUE) = 63000 BTUH

Return Temperature = 70°F

Supply Temperature = 125°F

∆T = 55°F

63000 BTUH

59.4

1060 =

Sensible Heat Method

CFM = 1060

1. Place the unit in the HEATING mode of operation

2. Move the blower speed tap for cooling to the heating terminal

3. Be sure to disconnect the Heating speed lead and secure it safely

4. Subtract your measured return air temperature from your supply air

temperature. This is the Delta-T value.

5. Multiply the Delta-T value by 1.08. Record this value.

6. Divide your BTUH Output by the value you obtained in Step 5.

7. The answer is your actual system airflow.

Airflow Calculations for Furnaces (Cooling Mode)

Formulas:

Heating Output = KW x 3413 x Corr. Factor

Actual CFM = CFM (from table) x Corr. Factor

BTUH = KW x 3413

BTUH = CFM x 1.08 x Temperature Rise (T)

CFM = KW x 3413

1.08 x T

T = BTUH

CFM x 1.08

3 5 6 8 10 15 20 21

600 17 27 34 39

800 13 20 25 30 40

1000 10 16 20 24 32 48

1200 8 13 17 20 27 40 53 59

1400 7 11 14 17 23 34 46 51

1600 6 10 13 15 20 30 40 44

1800 6 9 11 13 18 27 36 39

2000 5 8 10 12 16 24 32 35

CFMHEAT KIT NOMINAL kW

Formulas

• Static pressure is the resistance to airflow from objects in the air stream

• Filters, coils, heat exchangers, registers, grills, balancing dampers and, of course, the duct itself, are just a few

• After the resistance of these objects is subtracted, the balance is what is available for the duct system

Static Pressure

Air Handler Static Pressure

Furnace Static Pressure

Most Residential Systems Including

Goodman/Amana Are designed To Operate

At 0.5” Water Column maximum Total System Static Pressure

Fan Performance

Static Pressure

Magnehelic or Inclined Manometer

Total System Static Pressure Is A Combination Of Two Readings The First Taken Just Before The Blower And The Other Just After The Blower. The Pressure Drop Between The Two Readings Is The Static Pressure Imposed On The Blower.

+0.3”WC -0.2”WC

Total External Static Pressure =

0.5”WC

Static Pressure In A System Is Typically Determined With The Help Of A Magnehelic, an inclined manometer or a digital manometer

Measuring Devices

Dirty Coil

Blower on Wrong

Speed

Wrong Size Duct

Dirty Filter

Conditions That Affect Duct Static

Understanding Superheat

Superheat Adding HEAT to Steam at 212°F causes the steam to increase in temperature (sensible heat). Heat added to a vapor above the vaporization temperature for that pressure is called Superheat.

212°F Steam

242°F Steam 1325 BTU

15 BTUs Added

242°F Steam

- 212°F Steam = 30°F Superheat

Regardless of what the heat source is;

Sensible & Latent Refer to the process

Or How the heat is being utilized

REMEMBER:

Sensible Heat = change in temperature

(no change in state)

Latent Heat = change of state (no change in temperature)

THE TEMPERATURE AT WHICH AT A GIVEN PRESSURE, THE REFRIGERANT IS NEITHER 100% LIQUID NOR 100% VAPOR

IT IS THE POINT WHERE THE REFRIGERANT IS CHANGING STATE FROM LIQUID TO VAPOR OR VAPOR TO LIQUID

Saturation Point

Saturated Suction Temperature

Pressure

Sat. Evap. Temp.

Evaporator Side

Saturated Liquid Pressure

Sat. Cond. Temp.

Pressure

Condenser Side

WEIGHING METHOD

SUPERHEAT METHOD

SUBCOOLING METHOD

Methods Of Charging Systems

The proper method of charging a heat pump in the heat mode is by weight with the additional

charge adjustments for line size, line length, and other system components.

Weighing The Charge

THIS METHOD CAN BE USED ON ALL TYPES OF REFRIGERATION SYSTEMS

1. DETERMINE THE PROPER WEIGHT OF THE CHARGE FROM THE DATA PLATE ON THE CONDENSING UNIT. THIS WILL USUALLY INCLUDE ENOUGH REFRIGERANT FOR THE STANDARD EVAPORATOR AND 15 FEET OF LINE SET.

2. MEASURE THE AMOUNT OF LINE SET INCLUDED IN THE SYSTEM. USING THE CHARTS IN THE INSTALLATION INSTRUCTIONS, ADD OR SUBTRACT THE PROPER AMOUNT OF REFRIGERANT TO DETERMINE THE FINAL CHARGE.

3. USING A CALIBRATED SCALE, ADD OR REMOVE REFRIGERANT BASED ON YOUR CALCULATIONS

Weighing In Method

R-410A condensers are factory charged for 15 feet of line set. To calculate the amount of extra refrigerant (in ounces) needed for a line set over 15 feet, multiply the additional length of line set by 0.6 ounces. Note for the formula below, the linear feet of line set is the actual length of liquid line (or suction line, since both should be equal) used, not the equivalent length calculated for the suction line. Use subcooling as the primary method for final system charging of long line set system application.

Extra refrigerant needed = (Linear feet of line set – 15 ft) x X oz/ft. Where X = 0.67 for 3/8” liquid tubing.

Weighing Method

Extra refrigerant needed per lineal foot =. Where X = 0.67 for 3/8” liquid tubing and 7/8”.

EXAMPLE: Measured Line Set 25 feet 25 feet Line Set – 15 feet =

10 feet x 0.67 = 6.7 oz.

Weighing Method