Residental Hvac Design

Question 1

What should be taken into consideration when selecting a blower ?

Answer 1

Select a blower speed that will maintain proper tempature rise and correct cfm distribution on both cooling and heating cycles as well as the proper air circulation rate

Question 2

What should the heating output percent be ?

Answer 2

100-140%

Question 3

What should the cooling output percent be?

Answer 3

80-125%

Question 4

What is the recommended airflow per ton of cooling ?

Answer 4

400cfm

Question 5

What are some factors u should consider when designing a duct system ?

Answer 5

Ducts running through unconditioned spaces

Proper duct size

Zoneing systems

Combustion and dilution air

Question 6

What is the supply air ratio for an unfinished basement ?

Answer 6

1 supply air for every 430ft2

Question 7

What is the minimum undercut per cfm ?

30cfm
60cfm
90cfm
120cfm

Answer 7

30cfm = 1/2”

60cfm= 3/4”
90cfm=1”
120cfm=1 1/4”

Question 8

What does the Alberta building code state about return air ?

Answer 8

Must have one return air per floor and basment should only be 50% and any room that has atkeast one half of the floor area above an unconditioned space must have return air

Question 9

Where should return airs never be installed ?

Answer 9

Kitchens
Bathrooms
Laundry rooms
Utility rooms
Enclosed crawl spaces
Should also never be installed back to back in same stud space because light and sound transfer

Question 10

What are two things to consider with ventallation air ?

Answer 10

Fresh air size
Mixed air temp

Question 11

How far should the fresh air connection be from the blower ?

Answer 11

Minimum 10 feet

Question 12

What temp should air circulated through the blower never drop below ?

Answer 12

60 degrees F

Question 13

For a 2x4 opening what is the number of cfm that flows through it ?

Answer 13

120cfm

Question 14

For a 2x6 opening what is the number of cfm that will flow through it ?

Answer 14

180cfm

Question 15

What are four factors to consider when dragging a duct system ?

Answer 15

Proper duct size
Duct passing through unconditioned spaces

Zoneing for house
Combustion and dilution air

Question 16

What is an acceptable air velocity for the main trunk ?

Answer 16

700-900fpm

Question 17

When should a walk in closet have a supply ?

Answer 17

When the closet exceeds a heat loss of 1000btu

Question 18

What’s the result of installing a furnace to large?

Answer 18

Short cycling

Question 19

Before selecting a furnace what must be done first ?

Answer 19

Heat loss calc

Question 20

What must be done if duct is running through an unconditioned space ?

Answer 20

Seal and insulate the duct

Question 21

Where should the Vapor barrier be located when insulating ducts ?

Answer 21

On the warm side

Question 22

If a supply air measure more than 50ft in length what should be done to the cfm at the register ?

Answer 22

Should be sized to handle 10% more cfm than originally designed

Question 23

How far off the wall should supply outlets be located ?

Answer 23

8” or 20cm

Question 24

Why should we install supply register off the wall and not flush with wall ?

Answer 24

So it does not interfere with the drapes

Question 25

What must crawl space supply runs have installed ?

Answer 25

Lockable dampers or diffuser

Question 26

Why can a vertical return air not serve more than one floor ?

Answer 26

Prevent cold air from going floor to floor

Question 27

What is the design static pressure to be used for a house ?

Answer 27

1/2”of wc

Question 28

How do you determine cfm per return air opening ?

Answer 28

Floor return air flow rate divided by number of inlets

Question 29

What increments does return air go up in?

Answer 29

0 turbelence at the closest return air to a taper and then up 40’ from there

Question 30

What cfms should a transition be used at ?

Answer 30

Supply every 200-300cfm
Return every 300-400cfm

Question 31

What is the aspiration effect ?

Answer 31

The negative effect velocity has on the ability of rushing air to enter the branch duct on supply

Question 32

What 3 things are airflow rates based on?

Answer 32

Heating cfm
Cooling cfm
ACR

Question 33

What airflow rate do you use ?

Answer 33

The largest of the 3

Question 34

In areas where the dry bulb tempature exceeds 81 what must be done ?

Answer 34

The air volume for cooling shall be incorporated

Question 35

How many heat runs are required for a heated crawl space ?

Answer 35

One for every 80m squared

Question 36

What should the Tempature never exceed on supply air ?

Answer 36

158 degrees Fahrenheit
70 degrees Celsius

Question 37

What is the average pressure drop at a grille ?

Answer 37

.04

Question 38

How do we determine joists to trunk opening size ?

Answer 38

Return air branch size x 2

Question 39

1 kw =1.341 How many btu?

Answer 39

3412 btu