Manual D

Question 1

A rectangular duct measures 40 x 34 on the outside and has 2in of duct insulation lining the duct. What is the equivalent round duct size?

Answer 1

35.9

40 x 34 subtract 4 from the length and width due to insulation to get 36 x 30.

Pg. 104 Manual D

Question 2

A residential system design requires 1000cmf. The air handler you choose can deliver 1000cfm at an external static pressure of .3. The duct system has a total equivalent length of 475 feet so the design friction rate is?

Answer 2

.63 fr/100ft

Friction Rate(inwc/100ft) = Available Pressure ÷ TEL
TEL = Total Equivalent Length
FR = (.3 x 100) ÷ 475
FR = 30 ÷ 475
FR = .63inwc/100ft

Appendix 1 Manual D

Question 3

In a residential duct system, a 1R fitting has how many more feet of equivalent length than a 1Q fitting?

Answer 3

70ft

Pg. N-19 Manual D

Question 4

A wet residential unitary evaporator coil has approximately ______inwc of pressure drop when 1750cfm of air is moving through the coil.

Answer 4

.46

Pg. 27 Manual D

Question 5

What is the maximum allowable face velocity across a return air grill in North Carolina?

Answer 5

500fpm

Pg. 87 Manual D

Question 6

A residential HVAC system has a heating load of 34,500btu and a cooling load of 31,350btu. If the blower produces 1150cfm, the cooling factor is_____.

Answer 6

.037

Cooling Factor = Design Blower CFM ÷ Design
Sensible Cooling Load
CF = 1150cfm ÷ 31,350btu
CF = .037

Pg. 88 Manual D

Question 7

Per the manufacturers fan performance data, the air handling unit you are going to install can move the total design airflow at an external static pressure of .3inwc. After calculating the total equivalent length per ACCA Manual D procedures, you have determined the duct system will have a total equivalent length of 480ft. What is the design friction rate?

Answer 7

.0625

Friction Rate(inwc/100ft) = Available Pressure ÷ TEL
TEL = Total Equivalent Length
FR = .3 x 100 ÷ 480
FR = 30/480
Fr = .0625

Pg. 88 Manual D

Question 8

In a residential duct system with an ECM motor, _____cfm per nominal ton of capacity is appropriate for dwelling that have significant latent loads compared to sensible loads as defined by Manual J with a sensible heat ratio of .80.

Answer 8

400cfm/ton

Pg. 20 Manual D

Question 9

Flexible wire helix duct runs shall be straight, per ADC limit for droop and sag, with no more than _____% compression.

Answer 9

4%

Pg. N3 Manual D

Question 10

In a residential system, when dampers are installed in the return air system for balancing, where should they be located?

Answer 10

At the trunk entrance fitting.

Pg. 34 Manual D

Question 11

The pressure drop for return air grills in residential duct systems is?

Answer 11

.03

Pg. 27 Manual D

Question 12

The term system operating point refers to the?

Answer 12

Duct/Blower Performance

Pg. 11 Manual D

Question 13

A light commercial building has a sensible cooling load of 655,900btu/h. The supply air DB temperature in the duct is 55⁰ and the room DB temperature is 75⁰. What is the cooling cfm required for this load?

Answer 13

29,813cfm

Cooling CFM = Cooling Load ÷ 1.1 x ΔT
Cooling CFM = 655,900 ÷ 1.1 x (75 - 55)
Cooling CFM = 655,900 ÷ 1.1 x 20
Cooling CFM = 655,900 ÷ 22
Cooling CFM = 29,813

Pg. 87 Manual D

Question 14

A residential air handling unit will deliver the required design airflow of 1200cfm at a pressure drop of .4inwc. Assuming the duct system has 425ft of total equivalent length, what is the design friction rate?

Answer 14

.094

Friction Rate(inwc/100ft) = Available Pressure ÷ TEL
TEL = Total Equivalent Length
FR = .4 x 100 ÷ 425
FR = 40 ÷ 425
FR = .094

Pg. 88 Manual D

Question 15

An installation has a rectangular duct that measure 24in x 18in and it’s insulated on the outside. You are going to replace this with round duct. What is the appropriate equivalent round duct you will need to use?

Answer 15

22.7

Pg. 103 Manual D

Question 16

What is the approximate pressure drop across a wet 1200cfm residential evaporator coil?

Answer 16

.26iwc

Pg. 27 Manual D

Question 17

What is the Manual D default for excessive length of wire helix flexible duct?

Answer 17

0% to 4%

Pg. 26 Manual D

Question 18

The recommended grill size for a 200cfm residential transfer grill is _________.

Answer 18

14in x 10in

Pg. N43 Manual D

Question 19

What is the volumetric quantity of air moving in an 18in x 18in duct with R-6 (2in) liner when the velocity of the air is 1300fpm?

Answer 19

1759
18in x 18in
2in liner
14in x 14in
1.16ft x 1.16ft = 1.35ft²
CFM = 1300fpm x 1.35ft²
CFM = 1759
Pg. 88 Manual D

Question 20

A 20in round galvanized duct 100ft long, delivering 2000cfm air will be operating at a velocity of _______fpm.

Answer 20

766fpm

Pg. 89 Manual D

Question 21

What is the velocity in a 25in x 8in duct section when 1450 cfm flow down the duct if the duct is wrapped?

Answer 21

1277fpm
CFM = Velocity x Area(ft²)
A = 2.08ft x .67ft
A = 1.37ft²
1450 = V x 1.37ft²
1450 ÷ 1.37 = V
V = 1277fpm 
Pg. 89 Manual D

Question 22

What is the velocity of air traveling through a 24in x 24in filter grill when 75% of the grill is free area and the volume of air is 2000cfm?

Answer 22

666
CFM = Velocity x Area(ft²)
A = 24in(2ft) x 24in(2ft)
A = 4ft² x .75(percentage of free area)
A = 3ft²
2000 = V x 3ft²
2000 ÷ 3 = V
V = 666
Pg. 89 Manual D

Question 23

What is the equation to calculate the design friction rate for a residential duct system according to ACCA Manual D?

Answer 23

FR = Available Pressure(IWC) x 100 ÷ Total Equivalent Length

Pg. 88 Manual D

Question 24

A light commercial building has a sensible cooling load of 655,900btuh. The supply air temperature in the duct dry bulb is 55⁰ and the room dry bulb temperature is 75⁰. What is the cooling cfm required for this load?

Answer 24

29,813cfm
Cooling CFM = Sensible cooling load ÷ 1.1 x (RDB - SDB)
Cooling CFM = 655,900 ÷ 1.1 x (75 - 55)
Cooling CFM = 655,900 ÷ 1.1 x 20
Cooling CFM = 655,900 ÷ 22
Cooling CFM = 29,813
Pg. 87 Manual D