Title 24
Energy Codes - Commonly Used Terms
Additions
An addition is an extension or increase in the conditioned floor area and
volume of a building. This includes converting an existing unconditioned space
to a conditioned space, such as remodeling a basement, garage or attic. The
standards require energy compliance analysis and documentation for all
additions that increase the conditioned space and volume of the building.
AFUE (Annual
Fuel Utilization Efficiency)
The ratio of annual output energy to annual input energy, which includes
any non-heating pilot input loss and, for gas- or oil-fired furnaces or
boilers, does not include electric energy.
Airflow Across the
Evaporator
The efficiency of air conditioners and heat pumps is affected by the
airflow across the evaporator (or condenser in the case of a heat pump).
Measuring the temperature split or temperature drop across the evaporator and
comparing this measurement to reference tables can verify proper airflow. See
also Thermostatic Expansion Valves (TXV).
Alteration
An alteration is any change to a building's water heating system,
space conditioning system lighting system, or envelope that is not an
addition.
Alternative
Calculation Method (ACM)
An alternative calculation method is one of "the Commission's Public
Domain Computer Programs or any other calculation method approved by the
Commission."
Alternative
Component Packages
An alternative component package is one of the sets of prescriptive
requirements contained in the
standards. Each package is a set of measures that achieve a level
of performance, which meets the standards. These are often referred to as the
prescriptive packages or packages. Buildings that comply with the
prescriptive standards shall be designed, constructed and equipped to meet all
of the requirements of one of the alternative packages of components for the appropriate climate
zone.
Btu/hr (Btu/h)
British thermal unit per hour, also abbreviated Btu/h. One Btu equals the
amount of heat needed to raise the temperature of one pound of water one
degree Fahrenheit. Used for measuring heating and cooling equipment output.
Building Envelope
The Building Envelope is made up of the elements of a building that
enclose conditioned spaces and through which thermal energy may be transferred
to or from the exterior.
Climate Zone
The Energy Commission established 16 climate zones that represent a
geographic area for which an energy budget is established. These energy
budgets are the basis for the energy standards.
Coefficient of
Performance, Cooling (COP)
The coefficient of performance for cooling is the ratio of the
rate of net heat removal to the rate of total energy input, calculated under
designated operating conditions and expressed in consistent units.
Coefficient of
Performance, Heating (COP)
The coefficient of performance for heating is the ratio of the
rate of net heat output to the rate of total energy input, calculated under
designated operating conditions and expressed in consistent units.
Combined
Hydronic Space/Water Heating
A combined hydronic space conditioning and water heating system is one in
which both domestic hot water and space heating is supplied from the same
water heating equipment. Combined hydronic space heating includes both radiant
floor systems and convective or fan coil systems.
Conditioned Floor
Area (CFA)
Conditioned floor area (CFA) is the [total] floor area (in square feet) of
enclosed conditioned space on all floors of a building, as measured at the
floor level of the exterior surfaces of exterior walls enclosing the
conditioned space.
Conditioned
Footprint Area
The conditioned footprint is the total area of the building footprint, in
square feet, not including unconditioned space. The conditioned footprint area
may be equal to the first floor area, or it may be greater. The footprint area
is the total area of floor over unconditioned space (not over conditioned
space), ambient air and slab-on-grade. One way to think of the conditioned
footprint area is as the area of the largest conditioned floor in the building
plus the conditioned floor area of any projections from other stories that
extend beyond the outline of that largest floor.
Conditioned Space
In residential compliance, conditioned space is space in a building that
is either directly conditioned or indirectly conditioned.
Controlled
Ventilation Crawl Space (CVC)
The Energy Commission has approved an exceptional method for analyzing the
energy impact of buildings with raised floors which use foundation wall
insulation and have automatically controlled crawl space vents. The method is
available as an option using an approved computer method with unique modeling
criteria.
Cooling Load
The rate at which heat must be extracted from a space to maintain a
desired room condition.
Cool Roof
A cool roof is a roof surface with a high reflectivity and high emittance.
A cool roof rejects solar heat
before it enters the building by reflecting it back to the atmosphere.
Crawl Space
A crawl space is a space immediately under the first floor of a building
adjacent to grade that meets the under-floor clearance requirements of the UBC
[§101]. The thermal characteristics of a crawl space (or any similar vented
unheated space below a raised floor) tend to reduce heat loss and heat gain
into the building compared with an open, unprotected space below the floor.
Compliance credit for the crawl space is assumed to be equivalent to an
additional R-6 insulation value. R-6 insulation is not modeled when a
raised floor is over an open area or over a garage.
Decorative Gas Appliance
A decorative gas appliance is a "gas appliance that is designed or
installed for visual effect only, cannot burn solid wood, and simulates a fire
in a fireplace." A decorative gas appliance installed in a new
residential building or addition cannot contain a continuously burning pilot
light, and cannot use indoor air for cooling a firebox jacket if the indoor
air is vented to the outside of the building.
Design Heat Gain
The design heat gain is "...the total calculated heat gain through
the building envelope under design conditions."
Design Heat Loss
The design heat loss is "...the total calculated heat loss through the
building envelope under design conditions."
Directly
Conditioned Space
"Directly conditioned space is an enclosed space that is provided
with wood heating, is provided with mechanical heating that has a capacity
exceeding 10 Btu/(hr×ft²), or . . . mechanical cooling that has a capacity
exceeding 5 Btu/(hr×ft²), unless the space conditioning system is designed
and thermostatically controlled to maintain a process environment temperature
less than 55°F or to maintain a process environment temperature greater than
90°F for the whole space that the system serves, or unless the space
conditioning system is designed and controlled to be incapable of operating at
temperatures above 55°F or incapable of operating at temperatures below 90°F
at design conditions."
Dominant
Occupancy
In mixed occupancy buildings, the dominant occupancy is the occupancy type
with the greatest percentage of total conditioned floor area.
Dual-Glazed
Greenhouse Windows
"Dual-Glazed Greenhouse Windows are a type of dual-glazed
fenestration product which adds conditioned volume but no conditioned floor
area to a building."
EER (Energy Efficiency
Ratio)
The energy efficiency ratio (EER) is "the ratio of net cooling
capacity (in Btu/hr) to total rate of electrical energy (in watts), of a
cooling system under designated operating conditions, as determined using the
applicable test method in the Appliance Efficiency Regulation or § 112."
Electric
Resistance Heating
As mentioned in the explanation of Energy Budget in this Glossary,
electricity is inherently less efficient than gas as a heating energy source
because it must account for losses associated with generation from depletable
fossil fuels and transmission to the building site. A source energy multiplier
of 3.0 (representing a net efficiency of 33 percent) is assigned to
electricity by the standards.
Enclosed Space
"Enclosed space is space that is substantially surrounded by solid
surfaces."
Energy Budget
"Energy budget is the maximum amount of source energy that a proposed
building, or portion of a building, can be designed to consume, calculated
with the approved procedures specified in Title 24, Part 6."
The low-rise residential
standards are based upon the concept of an annual energy budget. This is the
measure of source energy used per year in a building. The energy budget for
low-rise residential buildings includes space heating, space cooling and
domestic water heating. To comply with the standards, the energy use of the
proposed building design must be less than the annual energy budget.
Energy Efficiency Standards
The California state energy standards as set forth in the California Code
of Regulations, Title 24, Part 6.
Energy Factor
(EF)
Used to measure the efficiency of water heaters, the Energy Factor (EF) is
"the ratio of energy output to energy consumption of a water heater,
expressed in equivalent units, under designated operating conditions over a
24-hour use cycle, as determined using the applicable test method in the
Appliance Efficiency Regulations."
Energy Obtained
From Depletable Sources
"Energy obtained from depletable sources is electricity purchased
from a public utility, or energy obtained from burning coal, oil, natural gas,
or liquefied petroleum gases."
Energy Obtained
From Nondepletable Sources
Also referred to as renewable energy, including solar and wind power,
energy from nondepletable sources is defined as energy that is not obtained
from depletable sources.
Enforcing Agency
The enforcing agency is "the city, county, or state agency
responsible for issuing a building permit."
Evaporative
Cooler
Evaporative coolers may be installed as an alternative to air
conditioning, particularly in climate zones with dry air. These systems use
water evaporation and air circulation to provide cooling. Evaporative coolers
use less energy for cooling than minimum efficiency air conditioners, so the
Energy Commission has established higher SEERs to use when modeling them for
compliance.
Exterior Door
An exterior door is any openable opaque surface that separates
conditioned and unconditioned space. A door with one half or less of the
surface area as glazing is an exterior door. A door with more than 50 percent
of its surface area made up of glazing is a fenestration product.
Fenestration Area
(Glazing Area)
Fenestration area is defined as the area of all fenestration products
(i.e., windows, skylights and glass doors) in exterior openings, including the
sash or frame area. The nominal area (from nominal dimensions such as 4o4o) or
rough opening is also acceptable. For details on calculating fenestration area
for glass doors, see Exterior Door. Where the term "glazing
area" is used in the standards it means the entire fenestration area, not
just the area of glazing, unless stated otherwise
Fenestration
Product
A fenestration product is: "any transparent or translucent
material plus any sash, frame, mullions, and dividers, in the envelope of a
building, including, but not limited to: windows, sliding glass doors, French
doors, skylights, curtain walls, garden windows, and other doors with a glazed
area of more than one-half of the door area."
Fireplace
A fireplace is a "hearth and fire chamber or similar prepared
place in which a solid fuel fire may be burned, as defined in UBC Section 3102
; these include but are not limited to factory-built fireplaces, masonry
fireplaces, and masonry heaters."
Gas Log
A gas log is "a self-contained, free-standing, open-flame,
gas-burning appliance consisting of a metal frame or base supporting simulated
logs and designed for installation only in a vented fireplace."
Geothermal Heat
Pump
A heat pump that uses the earth as a source of energy for heating and
a sink for energy when cooling. Some systems pump water from an aquifer in the
ground and return the water to the ground after transferring heat from or to
the water. A few systems use refrigerant directly in a loop of piping buried
in the ground. Those heat pumps that use either a water loop or pump water
from an aquifer have efficiency test methods that are accepted by the Energy
Commission. These efficiency values are certified to the Energy Commission by
the manufacturer and are expressed in terms of heating Coefficient of
Performance (COP) and cooling Energy Efficiency Ratio (EER).
Glazing
Glazing is defined as the translucent portion of any fenestration
product, typically glass.
Ground Floor Area
For compliance, the ground floor area is defined as the slab-on-grade area
of a slab-ongrade building and the conditioned footprint area of a raised
floor building.
Habitable Story
A habitable story in a building is a story that "contains space in
which people may work or live in reasonable comfort. A habitable story is
defined as having at least 50 percent of its volume above grade." The
standards use this definition to determine whether a building is high-rise or
low-rise.
Heat Capacity
(HC)
The heat capacity of an assembly is "the amount of heat necessary to
raise the temperature of all the components of a unit area in the assembly one
degree F. It is calculated as the sum of the average thickness times the
density times the specific heat for each component, and is expressed in Btu
per square foot per degree F."
Heat Pump
A heat pump is an air conditioner capable of heating by refrigeration. It
may or may not include a capability for cooling. Outside air or water is used
as a heat source or heat sink, depending upon whether the system is heating or
cooling.
Heating,
Ventilating and Air Conditioning (HVAC)
The mechanical heating, ventilating and air conditioning system of the
building is also known as the HVAC system. The standards use various measures
of equipment efficiency defined according to the type of equipment installed.
Gas (fossil fuel) heating equipment is rated according to its Annual Fuel
Utilization Efficiency (AFUE). The heating efficiency of electric heat pumps
with less than 65,000 Btu/h cooling capacity is rated according to Heating
Seasonal Performance Factor (HSPF). The heating efficiency of heat pumps with
cooling capacity of 65,000 Btu/h or more is rated according to Coefficient of
Performance (COP). Electric resistance heating is rated according to its HSPF.
All electric cooling with less than 65,000 Btu/h output capacity is rated
according to the Seasonal Energy Efficiency Ratio (SEER). Electric cooling
with an output capacity of 65,000 Btu/h or more is rated according to its
Energy Efficiency Ratio (EER). (Heat pump cooling is rated according to its
SEER or EER, and heat pump heating by the HSPF or COP). Since few residential
buildings use air conditioners or heat pumps with an output capacity greater
than 65,000 Btu/h, the Low-Rise Residential Standards only use SEER and HSPF
ratings, not EER or COP.
High-Rise
Residential
A high-rise residential building is "a building, other than a
hotel/motel, of occupancy group R-1 with four or more habitable stories."
[§101] All hotels and motels, regardless of the number of stories, and
multi-family residential buildings with four or more habitable stories must
comply with § 120 through 149 of the standards (Nonresidential and High-Rise
Residential Standards), rather than §150 through 152 (Low-Rise Residential
Standards).
HSPF (Heating
Seasonal Performance Factor)
The Heating Seasonal Performance Factor (HSPF ) is "the total heating
output of a heat pump (in British thermal units) during its normal usage
period for heating divided by the total electrical energy input (in
watt-hours) during the same period, as determined using the applicable test
method in the Appliance Efficiency Regulations."
HVAC
See Heating, Ventilating and Air
Conditioning.
Hydronic Space
Heating
A hydronic space heating system uses water-heating equipment, such as a
storage tank water heater or a boiler, to provide space heating. Hydronic
space heating includes both radiant floor systems and convective or fan coil
systems.
Indirectly
Conditioned Space
"Indirectly conditioned space is enclosed space including, but not
limited to, unconditioned volume in atria, that (1) is not directly
conditioned space; and (2) either (a) has an areaweighted heat transfer
coefficient to directly conditioned space exceeding that to the outdoors or to
unconditioned space, or (b) is a space through which air from directly
conditioned spaces is transferred at a rate exceeding 3 air changes per
hour." [§101] Indirectly conditioned space must be included when
calculating total conditioned floor area. Examples of areas that may be
indirectly conditioned space include enclosed porches, enclosed sunrooms,
laundry rooms and furnace closets.
Infiltration
"Infiltration is uncontrolled inward air leakage from outside a
building, or unconditioned space, including leakage through cracks and
interstices, around windows and doors, and through any other exterior or
demising partition or pipe or duct penetration."
Insulation
Insulating material of the types and forms listed in 118(a) of the
standards (Chapter 2) "may be installed only if the manufacturer has
certified that the insulation complies with the California Quality Standards
for Insulating Material, Title 20, Chapter 4, Article 3." [§118(a)]
Insulation must be placed within or contiguous with a wall, ceiling or floor,
or over the surface of any appliance or its intake or outtake mechanism for
the purpose of reducing heat transfer or reducing adverse temperature
fluctuations of the building, room or appliance. Insulation may be installed
in wall, ceiling/roof and raised floor assemblies and at the edge of a
slab-on-grade. Movable insulation is designed to cover windows and other
glazed openings part of the time to reduce heat loss and heat gain.
Insulation R-Value
The R-value of insulation or any material or building component is the
measure of its thermal resistance expressed in ft2-hr-°F/Btu (see R-Value).
This value may be obtained from Appendix B or from manufacturer's literature.
The rated R-value of mineral fiber (batt) insulation is based upon its fully
expanded thickness. When the insulation is compressed, the R-value is reduced.
For example, an R-19 batt of insulation expands to a thickness of 6 inches. If
it is compressed into 2x6 framing with an actual depth of 5.5 inches, the
insulation R-Value is lowered to R-17.8.
Interior Partition
An interior wall or floor/ceiling that separates one area of conditioned space
from another within the building envelope.
Knee Wall
A knee wall is a sidewall separating conditioned space from attic space under
a pitched roof. Knee walls should be insulated as an exterior wall as
specified by the chosen method of compliance.
Lighting
The low-rise residential standards have mandatory measures for kitchen and
bathroom lighting, and for incandescent lighting fixtures recessed into
insulated ceilings. Both kitchens and rooms containing a bathtub or shower are
required to have at least one luminaire with lamps that have an efficacy of at
least 40 lumens per watt.
Low-Rise Residential
Any building of occupancy group R, excluding all hotels, all motels and
apartment buildings with four or more habitable stories.
Lumens/Watt
A lumen is a measure of the amount of light available from a given light
source. A watt is a measure of the power requirement for that light source.
The efficacy of a light source is measured by dividing the lumens by the
wattage. The more usable light that a light source provides per watt, the
greater its energy efficiency.
Mixed Occupancy
A building designed and constructed for more than one type of occupancy,
such as a three story building with ground floor retail and second and third
floor residential apartments.
Multi-Family
A dwelling unit of occupancy type R, as defined by the UBC, sharing a
common wall and/or ceiling/floor with at least one other dwelling unit.
North-Facing
"North-facing is oriented to within 45 degrees of true north, including
45°0'0" east of north (NE), but excluding 45°0'0" west of north
(NW)." This definition applies only to the prescriptive packages and
master plans analyzed according to the multiple orientation alternative as
explained in Chapter 8. In the computer methods the actual building
orientation must be used, except in the case of master plans as stated above.
Outside Air
"Outdoor air (Outside air) is air taken from outdoors and not previously
circulated in the building."
Radiant Barriers
Radiant barriers are shiny metallic surfaces that are applied to the roof of
the attic and its end walls. In attics, the radiant barrier is typically
installed on the underside of the attic roof. Often the radiant barrier is
pre-applied to the structural deck of the attic roof.
Raised Floor
A "raised floor is a floor (partition) over a crawl space, or an
unconditioned space, or ambient air."
Refrigerant Charge
The term “refrigerant charge” refers to the amount of refrigerant that is
installed or “charged” into an air conditioner or heat pump. The
refrigerant is the working fluid in an air conditioner or heat pump. It is
compressed and becomes a liquid as it enters the condenser. The hot liquid is
cooled in the condenser and flows to the evaporator where it released through
the expansion valve. When the pressure is released, the refrigerant
expands into a gas and cools. Air is passed over the evaporator to provide the
space cooling. When an air conditioner or heat pump has too much refrigerant
(overcharged) the compressor may be damaged. When an air conditioner has too
little refrigerant (undercharged), the efficiency of the unit is reduced. A
thermostatic expansion valve (TXV) can mitigate the impact of improper
refrigerant charge.
R-Value (Thermal
Resistance)
The R-value of a material is “the [thermal] resistance of a material or
building component to the passage of heat in (hr-ft2-ºF)/Btu." The
R-value indicates how well a material prevents heat from flowing through it.
R-19 insulation, for example, is only half as effective at slowing heat
transfer as R-38 insulation. When more than one material is put in series with
another in a construction assembly (such as exterior siding, insulation and
interior gypsum board), the thermal resistance of the assembly is equal to the
sum of the individual resistances.
SEER (Seasonal Energy
Efficiency Ratio)
The total cooling of a central air conditioner or heat pump in Btu during 12
months divided by the total electric energy input in watt-hours during the
same period
Single Family
Attached
A multi-family building whose dwelling units share common walls but do not
share any common floors/ceilings is considered Single Family Attached.
Single Family
Building
A single dwelling unit of occupancy type R, as defined in the UBC,
which stands separate and unattached from other dwelling units, but may have
an attached garage. A dwelling unit that is separated only by a property line
and double wall construction (with a space between the walls) from another
dwelling unit and that shares no common floor/ceiling is also treated as
single family.
Solar Heat Gain
Coefficient (SHGC)
The solar heat gain coefficient is a measure of the effectiveness of a
fenestration product or window covering to stop solar gains through the
window. 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.”
Skylight
A skylight is "glazing having a slope less than 60 degrees from the
horizontal with conditioned space below."
Standards
The California Energy Efficiency Standards as set forth in the California Code
of Regulations, Title 24, Part 6.
Standby Loss
Standby loss is the ratio of heat lost per hour to the heat content of the
stored water above room temperature. It is one of the measures of efficiency
of water heaters required for water heating energy calculations for some types
of water heaters. Standby loss is expressed as a percentage.
Thermal Mass
"Thermal mass is solid or liquid material used to store heat for later
heating use or for reducing cooling requirements." Commonly used thermal
mass materials include concrete, masonry, brick, tile, rock and water. These
materials are readily available and have excellent thermal properties. The
more mass a building has, the slower its interior temperatures will change.
Thermal mass can conserve energy in a residential building in two basic ways:
• In the winter, solar radiation entering a building
through glass is absorbed directly or indirectly into areas of thermal mass
exposed to indoor air. The mass material tends to store its heat during the
day and release it into the room air during the evening and night when more
heating is required.
• In the summer months, the mass material can be cooled
down at night by natural ventilation. During the daytime, the mass absorbs
excess heat and helps keep down indoor air temperatures. If glazing is well
shaded to keep out direct sunlight, the mass can substantially reduce or
eliminate completely the need for mechanical cooling.
Thermostatic expansion
valves (TXV)
A thermostatic expansion valves (TXV) is a metering device for refrigerant
flow into the evaporator of an air conditioner or heat pump. Refrigerant flow
is metered in response to the temperature of the refrigerant leaving the
evaporator. A TXV improves efficiency and mitigates the effect a system with
improper refrigerant charge. The valve is placed upstream from the evaporator
inlet and is connected to a temperature sensing bulb and pressure tap that are
located at the evaporator outlet. As the gaseous refrigerant leaves the
evaporator the TXV senses its temperature and pressure (superheat) and adjusts
the flow rate to maintain the super heat at a constant value. Eligible systems
must provide a removable door or other method of access for verifying the
valve is installed and must include verification by a HERS rater. Package D
requires either a TXV or testing of refrigerant charge and airflow in climate
zones 2 and 8 through 15.
U-factor
The U-factor is the "overall coefficient of thermal transmittance
of a construction assembly, in Btu/(hr x ft2 x ºF), including air film
resistances at both surfaces."
Unconditioned Space
"Unconditioned space is enclosed space within a building that is not
conditioned space..."
A space is unconditioned if:
• It is not provided with space conditioning;
• It can be isolated from conditioned space by closeable
doors; and
• It is not indirectly conditioned.
Common unconditioned spaces include garages, attics, crawl spaces, mechanical
closets and sunspaces. Refer to Chapter 5 for further information concerning
modeling unconditioned spaces using approved computer methods.
Vapor Barrier
A vapor barrier is "a material with a permeance of one perm or
less which provides resistance to the transmission of water vapor." Vapor
barriers are only mandatory in Climate Zones 14 and 16.
Zonal Control
Zonal control refers to the practice of dividing a residence into
separately controlled HVAC zones. This may be done by installing multiple HVAC
systems that condition a specific part of the building, or by installing one
HVAC system with a specially designed distribution system that permits zonal
control.
