Residential HVAC Design

Question 1

Why is the proper selection of a furnace so important?

Answer 1

It affects the overall comfort of a building.

Question 2

What is the result of installing a furnace that is too large for the home?

Answer 2

It will short cycle and deliver an overwhelming amount of heat in a short period of time.

Question 3

What is the result of installing a furnace that is too small for the home?

Answer 3

It will not be able to provide the heat energy that is required.

Question 4

Before selecting a furnace or air-conditioning unit for a residence, what must be done first?

Answer 4

A load calculation

Question 5

The output of a heating appliance must be no less than ___% and no more than ___% of the heat loss calculation.

Answer 5

100% and 140%

Question 6

Cooling equipment must range from ___% to ____% of the heat gain calculation.

Answer 6

80% and 125%

Question 7

One ton of cooling equals how many Btuh?

Answer 7

12000 Btuh

Question 8

When calculating air flow rates for cooling, what are the manufacturers recommended air flow rates?

Answer 8

400 cfm per ton

Question 9

Why do manufacturers recommend this air flow rate (400cfm) for cooling?

Answer 9

To prevent the evaporator coil from freezing

Question 10

When selecting a proper blower speed, what three things must the blower maintain?

Answer 10

temperature rise

cfm distribution

air circulation rate

Question 11

What must be considered when trying to achieve a proper air circulation rate (ACR)?

Answer 11

Heating output, temperature rise range, ESP, heating airflow rate, cooling input, cooling airflow rate.

Question 12

What three factors is airflow rates based on?

Answer 12

Heating cfm
Cooling cfm
ACR

Question 13

What is the formula for calculating Temperature Rise?

Answer 13

Output ÷ (cfm x 1.08)

Question 14

When designing an HVAC system, what must it be designed to meet?

Answer 14

The heat load calculation

Question 15

List four factors that must be considered when designing a residential HVAC system.

Answer 15

Proper duct size

Duct running through unconditioned spaces

Zoning

Combustion and dilution air

Question 16

When sizing ductwork, why is it important that the volumes stay within a certain range?

Answer 16

It must provide comfortable circulation, within the appropriate temperature rise for the equipment.

Question 17

Where should the vapour barrier be placed when insulating a duct, and why?

Answer 17

On the warm side of the insulation to prevent condensation.

Question 18

What must be factored in if you notice that a duct is running through an unconditioned space?

Answer 18

You must factor in heat loss or heat gain for these ducts.

Question 19

What should be done when designing a residential HVAC system in a home that has large differences in the heat loss or heat gain in different areas?

Answer 19

You should use a zoned system.

Question 20

Where can you find the combustion and dilution air requirements?

Answer 20

In the gas codes.

Question 21

What is the recommended maximum cfm per register (Supply air)?

Answer 21

100 cfm

Question 22

Which types of rooms would not have a perimeter outlet?

Answer 22

Kitchens, bathrooms and utility rooms.

Question 23

When would a walk-in closet be required to have a supply air outlet?

Answer 23

When the closet has a heat loss of over 1000 Btuh.

Question 24

If a walk in closet is not required to have a supply air, where would we add the heat loss that is needed to actually heat this room?

Answer 24

In the adjacent room

Question 25

What must be installed in a crawl space supply air?

Answer 25

Either a diffuser or lockable dampers.

Question 26

Where should return air inlets be located to avoid short circuiting of the warm air in a residential home?

Answer 26

Centrally or on the interior walls

Question 27

Why would we want to install a high low return air inlet?

Answer 27

If our system was being used for heating and cooling

Question 28

What are three ways to return air from a room in a house?

Answer 28

Wall grill, floor grill, undercut door

Question 29

How much return air should be moved on each floor of a house?

Answer 29

The total volume of air supplied to that level

Question 30

Why is it good trade practice to only return 50% of the supply air back to the duct system in a basement?

Answer 30

To ensure the basement does not develop a negative pressure

Question 31

Why can a vertical return air duct not serve more than one floor in a residential application?

Answer 31

To prevent cold air from traveling from floor to floor

Question 32

What two things must be considered when introducing fresh air into a residential HVAC system?

Answer 32

Inlet size and mixed air temperature

Question 33

At what mixed air temperature could you possibly void the warranty on a heating appliance?

Answer 33

16ºC or lower

Question 34

Where can we find the pressure drop or losses needed to design a heating/cooling system?

Answer 34

From manufactures specifications

Question 35

What must be included when calculating the available design pressure?

Answer 35

Available design pressure= External static pressure- pressure drop total

Question 36

What is the maximum amount of cfm that a 2” x 4” wall can draw through the floor to joist opening?

Answer 36

120 cfm

Question 37

What is the maximum amount of cfm that a 2” x 6” wall can draw through the floor to joist opening?

Answer 37

180 cfm

Question 38

What causes turbulence in a return air duct?

Answer 38

All fittings and connections found between the equipment and the grill

Question 39

When should trunk ducts be transitioned for Return Air?

Answer 39

If one transition is used, place it after 50% of the air volume has been collected If two are used, after 33% of the air volume is collected