HVAC 6: Heat Gains and Heat Losses in Structures

Very little heat is lost through the roof.

a. False

Identify four ways that heat gains in the conditioned space can occur.

Through exposed (exterior) walls. Through doors. Through roofs, walls, floors and ceilings. Through windows. From people, appliances, lighting and other elements. Through cracks, openings and deficiencies in structure. Through duct runs through attics, ceiling cavities and other unconditioned spaces.

List two negative effects that oversized air conditioning equipment may have.

Costs more to manufacture, purchase, install and maintain Costs more to operate because of larger motors and other electrical loads Requires larger air distribution systems which cost more than smaller ones Will cool or heat the space quicker, resulting in more frequent system starts and stops

What should be taken into account when performing a heat gain or heat loss calculation?

How accurate do the results have to be? How critical does the temperature control need to be? How critical does the humidity control need to be? Is an equipment rebate being applied for?

If a wall of a structure is comprised of a number of different materials, how is the R-value determined?

If the wall of a structure is made up of a number of different materials, the total R-value will be the sum of all of the individual R-values that make up the wall.

____________________ walls are walls that separate a conditioned interior space from an unconditioned interior space.

Partition

The U-value and the ____________________ are inverses of each other.

R-value

Identify four ways that heat losses from the conditioned space can occur.

Through exposed (exterior) walls. Through windows and doors. Through roofs. Through ceilings to unconditioned attics or ceiling cavities. Through partition panels. Through below-grade (underground) walls. Through slab and basement floors. Through floors located above unconditioned spaces. Duct losses to attics, ceiling cavities and other unconditioned spaces. Through cracks, openings and deficiencies in structure.

The _____________________-value describes the thermal conductivity of a material.

U

If a material has an R-value of 30, then the corresponding U-value will be ____.

a. 0.033

Oversized air conditioning equipment will cool the space faster.

a. True

The heat gain on a structure can be summarized as the sum of the conduction loads, the internal loads, the solar loads and the infiltration loads.

a. True

The temperature on both sides of an exterior wall or panel is needed to help determine how much heat is entering or leaving the structure.

a. True

The total heat loss for a structure is simply the sum of the heat losses experienced by all of the construction elements that make up a particular structure.

a. True

The two important factors that affect the U-value for the below-grade portion of the wall are the materials used to construct the wall and how far below grade the floor is.

a. True

There are different methods to calculate the heat gain on a structure based on the type of house and the number of wall exposures it has.

a. True

Construction materials have a minor effect on the rate of heat transfer through the structural envelope.

b. False

The occupants of a house do not add to the heat gain of the structure.

b. False

When it comes to sizing air conditioning and heating equipment bigger is definitely better.

b. False

The term ____ is used to describe walls or portions of walls that are below ground level.

b. below grade

The cfm is found by: ____.

b. cfm (infiltration) = (ACH × HOUSE VOLUME) ÷ 60 min/h

Probably the easiest way to determine what size lumber was used to frame a house is to inspect the

blueprint

The net wall area can be expressed mathematically as: ____.

c. Net Wall Area = Gross Wall Area - Door Area - Window Area - Area of other components

One of the most commonly used characteristics of building construction materials is the ____-value.

c. R

The ____-value is typically used to rate the thermal resistance of insulation materials.

c. R

Which of the values given below corresponds to a wall with the highest resistance to the pass of heat?

c. U-value = 0.80.

The heat transfer rate through a window is found through: ____.

d. Q = U-value × TD × Area

The most basic heat gain and heat loss calculations are based solely on the ____ of the space being conditioned.

d. area

As the ____ increases, the rate of heat transfer from one side of the structure to the other will increase.

d. temperature differential

The walls of a structure make up a large portion of the ____________________ or shell of the structure.

envelope

The ____________________ is simply the sum of the individual heat losses of the structure.

envelope load

The term that is used to describe the area of a wall before any doors or windows are cut into it is ____________________.

gross wall area