www.PDHcenter.com PDH Course M196 www.PDHonline.

org

3) Altitude
4) Weather data (coincident dry bulb and wet bulb temperatures, daily range)
5) Wind direction and speed
6) Precipitation

Check the following….

a) What is daily temperature range, minimum/maximum?
b) Are there significant variations from ASHRAE weather data?

C. Select Indoor Design Conditions

The information noted below is to be determined.
1) Temperature and relative humidity for each space/room
2) Permissible variation or control limits of the temperature and relative humidity
3) Room Pressurization requirements
4) Ventilation rate: Determine if there is special equipment such as kitchen or lab hoods that require a minimum
exhaust rate and eventually shall affect the ventilation rate.
5) Room function, number of occupants and the period of occupancy in each room

Check the following….

a) Estimate temperatures in un-conditioned spaces
b) Infiltration or ventilation load in accordance with ASHRAE Standard 62

D. Operating Schedule
Obtain the schedule of occupants, lighting, equipment, appliances, and processes that contribute to the internal loads
and determine whether air conditioning equipment will be operated continuously or intermittently (such as, shut down
during off periods, night set-back, and weekend shutdown). Gather the following information:
1) Lighting requirements, types of lighting fixtures
2) Appliances requirements such as computers, printers, fax machines, water coolers, refrigerators, microwave,
miscellaneous electrical panels, cables etc
3) Heat released by the HVAC equipment.
4) Number of occupants, time of building occupancy and type of building occupancy
5) Determine area of walls, windows, floors, doors, partitions, etc.
6) Compute conduction heat gains for all walls, windows, floors, doors, partitions, skylights, etc.
7) Compute solar heat gains for all walls, windows, floors, doors, partitions, skylights, etc.
8) Infiltration heat gains are generally ignored unless space temperature and humidity tolerance are critical.
9) Compute ventilation heat gain required.
10) Compute internal heat gains from lights, people, and equipment.
11) Compute sum of all heat gains indicated in items above
12) Consider equipment and materials, which will be brought into building above inside design temperature.
13) Cooling load calculations should be conducted using industry accepted methods to determine actual cooling load
requirements.

Typical Assumptions
Design cooling load is intended to summarize all the cooling loads experienced by a building under a specific set of
assumed conditions. The typical assumptions behind design cooling load are as follows:
1) Weather conditions are selected from a long-term statistical database. The conditions will not necessary represent
any actual year, but are representative of the location of the building. ASHRAE has tabulated such data. The
designer may select a severity of weather that seems appropriate for the building type in question--although energy
codes often specify what data shall be used (to minimize over-sized systems).
2) The solar loads on the building are assumed to be those that would occur on a clear day in the month chosen for
the calculations.
3) The building occupancy is assumed to be at full design capacity.
4) The ventilation rates are either assumed on air changes or based on maximum occupancy expected.
5) All building equipment and appliances are considered to be operating at a reasonably representative capacity.
6) Lights and appliances are assumed to be operating as expected for a typical day of design occupancy.
7) Latent as well as sensible loads are considered.
8) Heat flow is analyzed assuming dynamic conditions, which means that heat storage in building envelope and
interior materials is considered.

Page 65 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Appendix - B

THERMAL TRANSMISSION THROUGH BUILDINGS

All the materials that are used in the construction absorb and transfer heat. By knowing the resistance of heat flow
through a building component (R-value), you can calculate the total amount of heat entering the building. The basic
equation to determine the heat loss or gain through an opaque surface such as walls, roof, etc. is given by relationship:
Q = U x A x ΔT
Where:
Q = the heat flow through the walls, etc., in BTU per hour
U = the U-value in BTU per (hour) (square feet) (°F)
A = the area in square feet
ΔT = Difference in outside and inside temperatures in °F.
Q is the rate of heat flows through a medium. For example, the heat transfer in 24 hours through 2 sq-ft. of material, 3"
thick, having a thermal conductivity factor of 0.25, with an average temperature difference across the material of 70°F
would be calculated as follows:
Q = 0.25(k) x 2 sq. ft x 24 hours x 70° ΔT = 280 BTU
Before we go further, let’s refresh few basic fundamentals and definitions.
Heat is transferred from a high temperature zone towards a low temperature zone by three mechanisms;
1. Conduction
2. Convection
3. Radiation
For HVAC load calculation purposes, conduction and radiation are primarily considered. Conduction is the transfer of
heat through an object and radiation is the transfer of heat through electromagnetic waves, in this case sunlight. Heat
travels from hot to cold and construction materials resist the flow of heat through them differently. For example, heat
passes through glass much easier than wood siding.
With buildings, we refer to heat flow in a number of different ways. The most common reference is "R-value,” resistance
to heat flow or “U-value”, which is a measure of flow of heat through a material. The higher the R-value of a material,
the better it is at resisting heat loss (or heat gain).
R-value and U-factor are the inverse of one another: U = 1/R. Materials that are very good at resisting the flow
of heat (high R-value, low U-factor) can serve as insulation materials.

"R" values, “k” values, “C” values, “U” values, what it all means?
Basically all these letter symbols are used to denote heat transfer factors. All of these terms describe the same
phenomenon; however, some are described as determined by material dimensions and boundaries.
Building envelope is typically composed of various elements. A wall may be constructed of hardboard (facing outdoors),
plywood (facing indoors) and sandwich insulation in between.
When a building structure is composed of various layers of construction elements having resistances R1, R2, R3…. Rn,
the overall resistance value is sum of all individual resistances for whole wall, internal air spaces, insulation materials
and air films adjacent to solid materials. Individual R-values are used in calculating overall heat transfer coefficients.

k = Thermal Conductivity
“k Value” is the material property, which measures conductivity and is the quantity of heat (BTU's/hr) that passes
through one inch of a homogeneous material. A material is considered homogeneous when the value of its thermal
conductivity does not depend on its dimension. It is the same number regardless of the thickness of insulation. Thermal
2
Resistivity, or “R” is the reciprocal of thermal conductivity i.e. R = 1/k. Thermal conductivity is expressed in (Btu-in/hr ft
°F). Materials with lower k-values are better insulators.

Page 66 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Insulation materials usually have K-factors less than one and are reported at what is called mean temperature. To
determine the mean temperature, measure the surface temperatures on both sides of the insulation, add them together
and divide by two. “As mean temperatures rises, so does the K-factor”

R = Thermal Resistance
The R-factor is the thermal resistance factor and is a measure of the ability to retard heat flow in a given thickness of
material. R is the numerical reciprocal of C (R = 1/C). The higher the R-value, the higher (better) the insulating value. R
Values change as the thickness of the insulating material changes. Primarily building insulation products and plans are
measured and specified by the material's R factor. R-value for material only deals with conductive heat transfer. Since
the total heat transferred by conduction varies directly with time, area, and temperature difference, and varies inversely
with the thickness of the material, it is readily apparent that in order to reduce heat transfer, the ‘k’ factor should be as
small as possible, and the material as thick as possible. For example, a wall with a U-value of 0.25 would have a
resistance value of R = I/U = 1/0.25=4.0. The value of R is also used to represent Thermal Resistivity, the reciprocal of
0 2
the thermal conductivity. Thermal Resistivity is expressed in (hr F ft )/(Btu in)

C = Thermal Conductance.
The C-factor (thermal conductance factor) is the number of B t u’s that will pass through a square foot of material with a
one-degree Fahrenheit temperature difference for a specified thickness. C factor is similar to ‘k’, except it is the rate of
heat flow through an actual thickness of material, where ‘k’ is a factor per inch. The C-factor is the K-factor divided by
the thickness of the insulation. The formula is the reciprocal of the R-factor formula. The lower the C value, the better
the insulator.
Note that the conductance of an air space is dependent on height, depth, position, character and temperature of the
boundary surfaces. Therefore, the air space must be fully described if the values are to be meaningful. For a description
of other than vertical air spaces, see the 1981 ASHRAE Handbook of Fundamentals, Chapter 23. Thermal
0 2
Conductance is expressed in Btu/ (hr F ft )

h = Film or Surface Conductance.

The rate of heat exchange between a unit or surface area and the air it is in contact with. Subscripts i and o are used to
0 2
denote inside and outside conductances, respectively. Film or surface conductance is expressed in Btu/(hr F ft ).

U = Overall Coefficient of Heat Transmission.

The U-value is the rate of heat flow passing through a square foot of the material in an hour for every degree Fahrenheit
2
difference in temperature across the material (Btu/ft hr°F). This is the property that should be determined when figuring
the heat loss or gain through walls, floors, ceilings, etc. The U-value or conductance flows through a material and the R-
value denotes the resistance, or how slowly heat flows. The two terms are reciprocal. (R=1/U, U=1/R). The Overall
0 2
Coefficient of Heat Transmission is expressed in Btu/(hr F ft ).
Windows are commonly described by their U-values. Descriptions of building walls, floors, or ceilings, often
use R-values instead of U-values.
U factor has to be computed for each part of the structure. Most good insulating materials have a thermal conductivity
(k) factor of approximately 0.25 or less, and rigid foam insulations have been developed with thermal conductivity (k)
factors as low as 0.12 to 0.15.

Combined Modes of Heat Transfer

1) Heat transfer by convection Qch and radiation QRH from the hot air and surrounding surfaces to
the wall surface,
2) Heat transfer by conduction through the wall Qk
3) Heat transfer by convection Qcc and radiation Qrc from the wall surface to the cold air and
surrounding surfaces.

Page 67 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Hot air Wall Cool air

T ambient T
s

Ts
Tindoor
Qch Q cc

Q Qk Q rc
rh

Heat Exchange Configuration

When one side of the wall is warmer than the other side, heat will conduct from the warm side into the material
and gradually move through it to the colder side. A temperature gradient is established across the thickness of
the wall. The temperature gradient is linear between the two surfaces for a homogenous wall and the slope of
temperature gradient is proportional to the resistances of individual layers for a composite structure.
If both sides are at constant temperatures--say the inside surface at 77°F (25°C) and the outside surface at
95°F (35°C)--conductivity will carry heat inside the building at an easily predicted rate.
Under steady state conditions, the total rate of heat transfer (Q) between the two fluids is:

Q = Q ch + Q rh = Qk = Qcc + Q rc

In real-life situations, however, the inside and outside temperatures are not constant. In fact the driving force for
conductive heat flow can reverse during the course of a day. As night falls, the outside air temperature may drop to
50°F (10°C). As the temperature difference across the wall is reversed, the heat flow is also reversed--drawing heat
back towards the outside of the building.
Another scenario is when the outside temperature fluctuates but never crosses the indoor set point temperature. In this
case, the direction of heat flow never changes, but the thermal lag or time delay in heat flow can still be beneficial by
delaying the peak heating or cooling load.

Calculation Methods
Conductance and resistances of homogeneous material of any thickness can be obtained from the following formula:
Cx=k/ x, and Rx=x /k
Where:
x=thickness of material in inches.
Materials in which heat flow is identical in all directions are considered thermally homogeneous.
This calculation for a homogeneous material is shown in Fig. below. The calculation only considers the brick component
of the wall assembly. Whenever an opaque wall is to be analyzed, the wall assembly should include both the outside
and inside air surfaces. The inclusion of these air surfaces makes all opaque wall assemblies layered construction.

Page 68 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Thermal Transmittance through Materials

In computing the heat transmission coefficients of layered construction, the paths of heat flow should first be
determined. If these are in series, the resistances are additive, but if the paths of heat flow are in parallel, then the
thermal transmittances are averaged. The word "series" implies that in cross-section, each layer of building material is
one continuous material. However, that is not always the case. For instance, in a longitudinal wall section, one layer
could be composed of more than one material, such as wood studs and insulation, hence having parallel paths of heat
flow within that layer. In this case, a weighted average of the thermal transmittances should be taken.

Series heat flow

For layered construction, with paths of heat flow in series, the total thermal resistance of the wall is obtained by:
R Total =R1+R2+...
Or R Total = 1/C + x1/k1 + x2 /k2…
Where
C is the conductance
x1 is the thickness of material one
x2 is the thickness of material two
k1 is the thermal conductivity of material one
k2 is the thermal conductivity of material two
And the overall coefficient of heat transmission is:
U = 1/R Total
or

Page 69 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Where:
Ri = the resistivity of a "boundary layer" of air on the inside surface.
R1, R2 …= the resistivity of each component of the walls for the actual thickness of the component used. If the
resistance per inch thickness is used, the value should be multiplied by the thickness of that component.
Ro = the resistivity of the "air boundary layer" on the outside surface of the wall.
The formula for calculating the U factor is complicated by the fact that the total resistance to heat flow through a
substance of several layers is the sum of the resistance of the various layers. The resistance to heat flow is the
reciprocal of the conductivity. Therefore, in order to calculate the overall heat transfer factor, it is necessary to first find
the overall resistance to heat flow, and then find the reciprocal of the overall resistance to calculate the U factor.
NOTE:
Note that in computing U-values, the component heat transmissions are not additive, but the overall U-value is actually
less (i.e., better) than any of its component layers. The U-value is calculated by determining the resistance of each
component and then taking the reciprocal of the total resistance. Thermal resistances (R-values) must first be added
and the total resistance (R-Total) divided into 1 to yield the correct U-factor.

The total R-value should be calculated to two decimal places, and the total U-factor to three decimal places.

Parallel Heat Flow

Average transmittances for parallel paths of heat flow may be obtained from the formula:
U avg [AA (UA) + AB (UB) +...] / A t
Or
U avg = [1/ (RA /AA) + 1/(RB/AB)...]/AT
Where:
2
AA, AB, etc. = area of heat flow path, in Ft ,
UA, UB, etc.= transmission coefficients of the respective paths,
RA, RB, etc.=thermal resistance of the respective paths.
2
A t= total area being considered (AA+AB+...), in Ft

Such an analysis is important for wall construction with parallel paths of heat flow when one path has a high heat
transfer and the other a low heat transfer, or the paths involve large percentages of the total wall with small variations in
the transfer coefficients for the paths.

Example #1
Determine the U-value for a layered wall construction assembly composed of three materials:
1) Plywood, 3/4-inch thick (R1 = 3/4 X 1.25 = 0.94)

Page 70 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

2) Expanded polystyrene, 2-inches thick (R2 = 2" X 4.00 = 8.00)

3) Hardboard, 1/4-inch thick (R3 = 0.18)
4) Ri = 0.68 ("still" air)
5) Ro = 0.17 (15 MPH wind, winter conditions)

Ti k
k k
1 2 3

T
1
T
2
T
o
T
x x x
1 2 3
3

Q
Q

R R R
1 2 3

Thermal Resistance of Composite Wall

The U-values is:

To calculate heat loss for say for 100 square feet of wall with a 70° F temperature difference would be:

In the calculations above the TD is taken as 70°F, which is temperature difference between indoor and outside air. If the
sun shines on a wall or roof of a building and heats the surface much hotter than the air (as typical in the summer), the
heat flow through the wall or roof would be greatly influenced by the hot surface temperature; hence, use a surface
temperature rather than air to obtain a more realistic heat flow rate. Similarly, when calculating the heat flow through a
floor slab resting on the ground, there will not be an air boundary-layer resistance underneath (Ro = 0) and the
temperature (to) will be the ground temperature (not the outside air temperature).

Example #2
Calculate the U factor of a wall composed of 2" of material having a ‘k’ factor of 0.80, and 2" of insulation having a
conductance of 0.16.
U value is found as follows:
R total = 1/C + X1/k1 or
R total = 1/0.16 + 2/0.80
R total = 8.75
2
U = 1/R or 1/8.75 = 0.114 Btu/hr ft °F

Page 71 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Once the U factor is known, the heat gain by transmission through a given wall can be calculated by the basic heat
transfer equation. Assuming an area of 100 square feet wall with an inside temperature of 85°F and an outside
temperature of 115°F, the heat transmission would be:
Q = U x A x TD
Q = 0.114 x 100 x 30
Q = 342 Btu/hr

HEAT TRANSMISSION COEFFICIENTS OF COMMON BUILDING MATERIALS

Material Description Density Conduction Resistance (R)
3
Lb/ft (k) (C) Per inch For
Btu-in/hr Btu/hr ft2 thickness L/k thickness
0
ft2 °F F listed L/C
Masonary Units
Face Brick
130 9.00 0.11
Common Brick 120 5.00 0.20
Hollow Brick
4” (62.9% solid) 81 1.36 0.74
6” (67.3% solid) 86 1.07 0.93
8” (61.2% solid) 78 0.94 1.06
10” 60.9% solid) 78 0.83 1.20
Hollow Brick vermiculite fill
4” (62.9% solid) 83 0.91
1.10
6” (67.3% solid) 88 0.66
1.52
8” (61.2% solid) 80 0.52
1.92
10” 60.9% solid) 80 0.42
2.38
Lightweight concrete block-100 Lb
density concrete
4” 78
0.71 1.40
6” 66
0.65 1.53
8” 60
0.57 1.75
10” 58
0.51 1.97
12” 55
0.47 2.14
Lightweight concrete block vermiculite fill
- 100 Lb density concrete
4” 79 0.43 2.33
6” 68 0.27 3.72
8” 62 0.21 4.85
10” 61 0.17 5.92
12” 58 0.15 6.80

Building Board
3/8” -Drywall Gypsum
50 3.10 0.32
1/2” -Drywall Gypsum
50 2.25 0.45
Plywood
34 0.80 1.25
½” Fiberboard sheathing
18 0.76 1.32
Siding
7/16” harDBoard 1.49 0.67
40
½” by 8” Wood bevel 1.23 0.81
32
Aluminum or steel over sheathing 1.61 0.61
Insulating Material
Batt or Blanket
• 2 to 2 ¾”
• 3 to 3 ½” 1.20
• 5 ½” to 6 ½” 1.20 7.0
Boards 11.0
• Expanded Polystrene 1.80 0.25 4.00 19.0
• Expanded Polyurethane 1.50 0.16 6.25
• Poly isocyanurate 2.0 0.14 7.14
Loose Fill
• Vermiculite 4-6 0.44 2.27

Page 72 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Material Description Density Conduction Resistance (R)

3
Lb/ft (k) (C) Per inch For
2
Btu-in/hr Btu/hr ft thickness L/k thickness
0
ft2 °F F listed L/C
• Perlite 5-8 0.37 2.70

Woods
Hard woods 45.0 1.1 0.91
Soft woods 32.0 0.80 1.25
Metals
Steel - 312 0.003
Aluminum - 1416 0.0007
Copper - 2640 0.0004
Air Space
¾” to 4”- winter 1.03 0.97
¾” to 4” - summer 1.16 0.86
Air Surfaces
Inside – Still air 1.47 0.68
Outside – 15 mph wind-winter 6.00 0.17
Outside – 7.5 mph wind -summer 4.00 0.25

Page 73 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Appendix - D
RULE OF THUMB FIGURES
Only for rough estimating purposes
The following table can be referred for quick but rough estimate of cooling requirements for commercial applications.
Application Average Load
Residence 400-600 sq. ft. floor area per ton
Apartment (1 or 2 room) 400 sq. ft. of floor area per ton
Church 20 people per ton
Office Building
Large Interior 340 sq. ft. of floor area per ton
Large Exterior 250 sq. ft. of floor area per ton
Small Suite 280 sq. ft. of floor area per ton
Restaurant 200 sq. ft. of floor area per ton
Bar or Tavern 9 people per ton
Cocktail Lounge 175 sq. ft. of floor area per ton
Computer Room 50 – 150 sq. ft. of floor area per ton
Bank (main area) 225 sq. ft. of floor area per ton
Barber Shop 250 sq. ft. of floor area per ton
Beauty Shop 180 sq. ft. of floor area per ton
School Classroom 250 sq. ft. of floor area per ton
Bowling Alley 1.5 – 2.5 tons per alley
Department Store
Basement 350 sq. ft. of floor area per ton
Main Floor 300 sq. ft. of floor area per ton
Upper Floor 400 sq. ft. of floor area per ton
Small Shop 225sq. ft. of floor area per ton
Dress Shop 280 sq. ft. of floor area per ton
Drug Store 150 sq. ft. of floor area per ton
Factory (precision manufacturing) 275 sq. ft. of floor area per ton
Groceries – Supermarket 350 sq. ft. of floor area per ton
Hospital Room 280 sq. ft. of floor area per ton
Hotel Public Spaces 220sq. ft. of floor area per ton
Motel 400 sq. ft. of floor area per ton
Auditorium or Theater 20 people per ton
Shoe Store 220 sq. ft. of floor area per ton
Specialty & Variety Store 200 sq. ft. of floor area per ton

Caution… these figures are for estimating purposes only! Many conditions such as orientation, sun loads, number of
occupants and light wattage can greatly affect the total tonnage requirements. A detailed load calculation must be made
to ensure accuracy. These figures are only for sanity check.

Page 74 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Appendix - E
DESIGN Software’s
Computerized simulations are now commonly used to estimate design-cooling load in practice. The good software’s
available today contain all database information on the weather data, CLTD, CLF, SC and SCL tables, descriptions of
walls and roof types, heat gains of lighting, appliances, and people, duct losses, ventilation air requirements, and
building materials thermal properties with calculators to determine overall R and U values. Learning load calculation
software is not difficult, but taking a class can help. Many software manufacturers offer technical support, as well.
It is hard to make a case for manual calculations in current IT environment but still basic understanding of design
principles won’t hurt before software can be profitably used. Basic knowledge about the subject is required to judiciously
evaluate the inputs and perform the sanity check on the output results of computer analysis. The most common manual
load computation method is cooling load temperature difference CLTD method and with advent of computer programs,
CLTD manual method is suppressed, but not invalidated. Manual J method is used as a baseline because it is the most
widely accepted load calculation methodology and is generally recognized as providing a safe estimate of cooling load.

HVAC Load Calculations and Psychrometric Analysis

1) Trace 700 by Trane

2) E-20II by Carrier
3) Hevacomp by Hevacomp Ltd.
4) Htools & RHVAC by Elite software
5) Loadsoft by Carmel software
6) HVAC-calc by HVAC computer systems Ltd

HVAC Load/Energy/Economic analysis

1) DOE EnergyPlus
2) Trace 700 by Trane

Page 75 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

Appendix - F
DEFINITIONS OF USEFUL TERMS
1) Ambient Air - The air surrounding a building; outside air
2) Air Change - The term air change is a rate at which outside air replaces indoor air in a space. It can be expressed
in one of two ways: the number of changes of outside air per unit of time air changes per hour (ACH); or the rate at
which a volume of outside air enters per unit of time - cubic feet per minute (CFM).
3) Building Envelope - The term building envelope indicates the surfaces that separate the inside from the outdoors.
This includes the parts of the building: all external building materials, windows, walls, floor and the roof. Essentially
the building envelope is a barrier between the conditioned indoor environment and the outdoors.
4) Building Location Data- Building location data refers to specific outdoor design conditions used in calculating
heating and cooling loads.
5) British thermal unit (BTU): Theoretically, it is approximate heat required to raise 1 lb. of water 1 deg Fahrenheit,
0 0
from 59 F to 60 F. Its unit of heat and all cooling and heating load calculations are performed in Btu per hour in US.
6) Cooling load: The rate at which heat is removed from a space to maintain the constant temperature and humidity at
the design values
7) Cooling Load Temperature Difference (CLTD) – A value used in cooling load calculations for the effective
temperature difference (delta T) across a wall or ceiling, which accounts for the effect of radiant heat as well as the
temperature difference. CLTD value calculates the instantaneous external cooling load across a wall or roof. CLTD
value is used to convert the space sensible heat gain to space sensible cooling load.
8) Cooling Coil Load – The rate at which heat is removed at the cooling coil that serves one or more conditioned
spaces and is equal to the sum of all the instantaneous space cooling loads.
9) Cubic feet per minute (CFM) - The amount of air, in cubic feet, that flows through a given space in one minute. 1
CFM equals approximately 2 liters per second (l/s). A typical system produces 400 CFM per ton of air conditioning.
10) Comfort Zone- The range of temperatures, humidity’s and air velocities at which the greatest percentages of people
feel comfortable.
11) Design Conditions- Cooling loads vary with inside and outside conditions. A set of conditions specific to the local
climate is necessary to calculate the expected cooling load for a building. Inside conditions of 75°F and 50%
relative humidity are usually recommended as a guideline. Outside conditions are selected for the 2.5% climate
occurrence.
12) Exfiltration- Uncontrolled air leakage out of a building through window and door openings
13) Exhaust - The airflow leaving the treated space from toilets, kitchens, laboratories or any hazardous area where
negative pressure is desired.
14) Enthalpy - Heat content or total heat, including both sensible and latent heat.
15) Fenestration – is an architectural term that refers to the arrangement, proportion and design of window, skylight
and door systems within a building. Fenestration consists of glazing, framing and in some cases shading devices
and screens.
16) Heating load: The heating load is a rate at which heat is added to the space to maintain the indoor conditions.
17) Infiltration- Leakage of air inward into a space through walls, crack openings around doors and windows or through
the building materials used in the structure.
18) Latent Cooling Load- The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and
any other moisture source. The amount of moisture in the air can be calculated from a combination of dry-bulb and
wet-bulb temperature measurements. The latent loads will affect absolute (and relative) humidity.
19) Latent Heat Gain – is the energy added to the space when moisture is added to the space by means of vapor
emitted by the occupants, generated by a process or through air infiltration from outside or adjacent areas.
20) Radiant Heat Gain – is the rate at which heat absorbed by the surfaces enclosing the space and the objects within
the space is transferred by convection when the surface or objects temperature becomes warmer than the space
temperature.

Page 76 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

21) Sensible Cooling Load- The heat gain of the building due to conduction, solar radiation, infiltration, appliances,
people, and pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load raises
the dry-bulb temperature.
22) Space Heat gain: The rate at which heat enters to and/or is generated within a space during a time interval.
23) Space Heat loss: The rate at which energy is lost from the space during a time interval.
24) Sensible Heat Gain or Loss – is the heat directly added to or taken away the conditioned space by conduction,
convection and/or radiation. The sensible loads will affect dry bulb air temperature.
25) Space Cooling Load – the rate at which energy must be removed from a space to maintain a constant space air
temperature. Note that “space heat gain ≠ space-cooling load.”
26) Space Heat Extraction Rate: The rate at which energy is removed from the space by the cooling and
dehumidification equipment. Space heat extraction rate is usually the same as the space-cooling load if the space
temperature remains constant.
27) Shading- The effectiveness of a fenestration product plus shade assembly in stopping heat gain from solar
radiation is expressed as the Solar Heat Gain Coefficient (SHGC). SHGC values range from 0 to almost 1. The
more effective at stopping heat gain, the lower the SHGC value.
28) Solar Heat Gain Coefficient (SHGC) - Solar heat gain coefficient (SHGC) is the ratio of the solar heat gain entering
the space through the fenestration area to the incident solar radiation. Solar heat gain includes directly transmitted
solar heat and absorbed solar radiation, which is then reradiated, conducted, or convected into the space. Solar
Heat Gain Coefficient (SHGC) replaces the Shading Coefficient (SC) used in earlier versions of the standards as a
measure of the solar heat gain due to windows and shading devices.
29) Temperature, Dry Bulb – is the temperature of a gas or mixture of gases indicated by an accurate thermometer
after correction for radiation.
30) Temperature, Wet Bulb – is the temperature at which liquid or solid water, by evaporating into air, can bring the air
to saturation adiabatically at the same temperature.
31) Temperature, Dewpoint – is the temperature at which the condensation of water vapor is a space begins for a
given state of humidity and pressure as the temperature of the air is reduced.
32) Thermal conductivity – is the time rate of heat flow through a unit area and unit thickness of a homogenous
material under steady conditions when a unit temperature gradient is maintained in the direction perpendicular to
the area.
33) Thermal Transmittance or Coefficient of Heat Transfer (U-factor) – is the time rate of heat flow per unit area under
steady conditions from the fluid on the warm side of a barrier to the fluid on the cold side, per unit temperature
difference between the two fluids.
34) Thermal Conduction – is the process of heat transfer through a material medium in which kinetic energy is
transmitted by particles of the material from particle to particle without gross displacement of the particles.
35) Thermal Convection – is the transfer of heat by movement of fluid. Forced convection is the transfer of heat from
forced circulation of fluid as by a fan, jet or pump. Natural convection is the transfer of heat by circulation of gas or
liquid due to differences in density resulting from temperature changes.
36) Thermally Light Buildings- A building whose heating and cooling requirements are proportional to the weather is
considered a thermally light building. That is, when the outdoor temperature drops below the desired room
temperature, heating is required and when the outdoor temperature goes above the desired room temperature,
cooling is needed. In a thermally light building, the thermal performance of the envelope becomes a dominant
factor in energy use and can usually be seen as seasonal fluctuations in utility consumption.
37) Thermally Heavy Buildings- When factors other than weather determine the heating and cooling requirements, the
building can be considered thermally heavy. The difference between thermally light and thermally heavy buildings
is the amount of heat generated by people, lighting, and equipment within the building. Thermally heavy buildings
typically have high internal heat gains and, to a certain extent, are considered to be self-heating and more cooling
dominated. This need to reject heat makes them less dependent on the thermal performance of the building
envelope.

Page 77 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

38) Thermal Weight- A simple "rule of thumb" for determining the thermal weight of a building is to look at heating and
cooling needs at an outdoor temperature of 60°Ft. If the building requires heat at this temperature, it can be
considered thermally light and if cooling is needed, it is thermally heavy.
39) Ton - A unit of measure for cooling capacity; One ton = 12,000 BTUs per hour
40) U-Factor- The U-factor is the “overall coefficient of thermal transmittance of a construction assembly, in Btu/(hr ft2
ºF), including air film resistances at both surfaces."
41) Zone- Occupied space or spaces within a building which has its heating or cooling controlled by a single thermostat
or zone is a is a space or group of spaces within a building with heating and/or cooling requirements sufficiently
similar so that comfort conditions can be maintained throughout by a single controlling device.
42) Zoning - A system in which living areas or groups of rooms are divided into separate spaces and each space's
heating/air conditioning is controlled independently.

Window Glossary
43) Air leakage rating - Air leakage rating is a measure of the rate of infiltration around a window or skylight. It is
2
expressed in units of cfm/ft of window area or CFM/ft of window perimeter length. The lower a window's air
leakage rating, the greater is its air tightness.
44) Conduction- the flow of heat from one particle to another in a material, such as glass or wood, and from one
material to another in an assembly, such as a window, through direct contact.
45) Convection - the flow of heat through a circulating gas or liquid, such as the air in a room or the air or gas between
windowpanes.
46) Cooling Load Factor (CLF) - CLF is the ratio of actual total cooling compared with total steady-state cooling during
the same period at constant ambient conditions.
47) Gas fill - a gas other than air placed between windowpanes to reduce the U-factor by suppressing conduction.
48) Glazing - the glass or plastic panes in a window or skylight.
49) Infiltration - the inadvertent flow of air into a building through breaks in the exterior surfaces of the building. It can
occur through joints and cracks around window and skylight frames, sash, and glazing.
50) Low-emittance (low-e) coating - a microscopically thin, virtually invisible, metal or metallic oxide layer deposited on
a window or skylight glazing surface to reduce the U-factor or solar heat gain coefficient by suppressing radiative
heat flow through the window or skylight.
51) Radiation - the transfer of heat in the form of electromagnetic waves from one separate surface to another. Energy
from the sun reaches the earth by radiation, and a person's body can lose heat to a cold window or skylight surface
in a similar way.
52) R-value - a measure of the resistance of a material or assembly to heat flow. It is the inverse of the U-factor (R =
2
1/U) and is expressed in units of hr-ft °F/Btu. The higher a window's R-value, the greater are its resistance to heat
flow and its insulating value.
53) Shading coefficient - a measure of the ability of a window or skylight to transmit solar heat, relative to that ability for
1
/8-in clear, double-strength, single glass. It is equal to the solar heat gain coefficient multiplied by 1.15 and is
expressed as a number without units between 0 and 1. The lower a window's shading coefficient, the less solar
heat it transmits, and the greater is its shading ability.
54) Solar heat gain coefficient - the fraction of solar radiation admitted through a window or skylight, both directly
transmitted and absorbed and subsequently released inward. The solar heat gain coefficient has replaced the
shading coefficient as the standard indicator of a window's shading ability. It is expressed as a number without
units between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits, and the
greater is its shading ability.
55) Spectrally selective glazing - a specially engineered low-e coated or tinted glazing that blocks out much of the sun's
heat while transmitting substantial daylight.
56) U-factor (U-value) - a measure of the rate of heat flow through a material or assembly. It is expressed in units of
2
Btu/hr-ft -°F. Window manufacturers and engineers commonly use the U-factor to describe the rate of non-solar

Page 78 of 79
www.PDHcenter.com PDH Course M196 www.PDHonline.org

heat loss or gain through a window or skylight. The lower a window's U-factor, the greater are its resistance to heat
flow and its insulating value.
57) Visible transmittance - the percentage or fraction of visible light transmitted by a window or skylight.

Page 79 of 79