Manual D Flashcards
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?
35.9
40 x 34 subtract 4 from the length and width due to insulation to get 36 x 30.
Pg. 104 Manual D
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?
.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
In a residential duct system, a 1R fitting has how many more feet of equivalent length than a 1Q fitting?
70ft
Pg. N-19 Manual D
A wet residential unitary evaporator coil has approximately ______inwc of pressure drop when 1750cfm of air is moving through the coil.
.46
Pg. 27 Manual D
What is the maximum allowable face velocity across a return air grill in North Carolina?
500fpm
Pg. 87 Manual D
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_____.
.037
Cooling Factor = Design Blower CFM ÷ Design
Sensible Cooling Load
CF = 1150cfm ÷ 31,350btu
CF = .037
Pg. 88 Manual D
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?
.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
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.
400cfm/ton
Pg. 20 Manual D
Flexible wire helix duct runs shall be straight, per ADC limit for droop and sag, with no more than _____% compression.
4%
Pg. N3 Manual D
In a residential system, when dampers are installed in the return air system for balancing, where should they be located?
At the trunk entrance fitting.
Pg. 34 Manual D
The pressure drop for return air grills in residential duct systems is?
.03
Pg. 27 Manual D
The term system operating point refers to the?
Duct/Blower Performance
Pg. 11 Manual D
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?
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
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?
.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
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?
22.7
Pg. 103 Manual D
What is the approximate pressure drop across a wet 1200cfm residential evaporator coil?
.26iwc
Pg. 27 Manual D
What is the Manual D default for excessive length of wire helix flexible duct?
0% to 4%
Pg. 26 Manual D
The recommended grill size for a 200cfm residential transfer grill is _________.
14in x 10in
Pg. N43 Manual D
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?
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
A 20in round galvanized duct 100ft long, delivering 2000cfm air will be operating at a velocity of _______fpm.
766fpm
Pg. 89 Manual D
What is the velocity in a 25in x 8in duct section when 1450 cfm flow down the duct if the duct is wrapped?
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
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?
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
What is the equation to calculate the design friction rate for a residential duct system according to ACCA Manual D?
FR = Available Pressure(IWC) x 100 ÷ Total Equivalent Length
Pg. 88 Manual D
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?
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
