[Code of Federal Regulations]
[Title 10, Volume 3]
[Revised as of January 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 10CFR435.111]
[Page 586-611]
TITLE 10--ENERGY
CHAPTER II--DEPARTMENT OF ENERGY
PART 435--ENERGY CONSERVATION VOLUNTARY PERFORMANCE STANDARDS FOR NEW BUILDINGS; MANDATORY FOR FEDERAL BUILDINGS--Table of Contents
Subpart A--Voluntary Performance Standards for New Commercial and Multi-
Family High Rise Residential Buildings; Mandatory for Federal Buildings
Sec. 435.111 Building energy cost compliance alternative.
11.1 General
11.1.1 This section provides an alternative compliance path that
allows greater flexibility in the design of energy efficient buildings
using an annual energy cost method. Energy cost is used as the common
denominator in determining compliance. Using unit costs rather than
units of energy or power such as Btu, kWh or kW allows the energy use
contribution of different fuel sources at different times to be added
and compared. This path allows for innovation in designs, materials, and
equipment, such as daylighting, passive solar heating, heat recovery,
better zonal temperature control, thermal storage, and other
applications of off-peak electrical energy, that cannot be adequately
evaluated by the prescriptive or system performance alternatives found
in sections 3.4, 3.5, 5.4, 5.5, and 7.4. This compliance path is
intended for design comparisons only and is not intended to be used to
either predict, document, or verify annual energy consumption or annual
energy costs.
11.1.2 The Building Energy Cost Compliance Alternative is to be
used in lieu of the prescriptive or system performance methods and in
conjunction with the minimum requirements found in sections 3.3, 4.3,
5.3, 6.3, 7.3, 8.3, 9.3 and 10.3.
[[Page 587]]
11.1.3 Compliance. Compliance under this method requires detailed
energy analyses of the entire Proposed Design, referred to as the Design
Energy Consumption; an estimate of annual energy cost for the proposed
design, referred to as the Design Energy Cost; and comparison against an
Energy Cost Budget. Compliance is achieved when the estimated Design
Energy Cost is less than or equal to the Energy Cost Budget (see Figure
11-1). This section provides instructions for determining the Energy
Cost Budget and for calculating the Design Energy Consumption and Design
Energy Cost. The Energy Cost Budget shall be determined through the
calculation of monthly energy consumption and energy cost of a Prototype
or Reference Building design configured to meet the requirements of
sections 3.0 through 10.0.
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[GRAPHIC] [TIFF OMITTED] TC04OC91.222
11.1.4 Designers are encouraged to employ the Building Energy Cost
Budget compliance method set forth in this section for evaluating
proposed design alternatives in preference to using the prescriptive/
system methods. The Building Energy Cost Budget establishes the relative
effectiveness of each design alternative in energy cost savings,
providing an energy cost basis upon which the building owner and
designer may select one design over another. This Energy Cost Budget is
the highest allowable calculated Energy Cost Budget for a specific
building design. Other alternative designs are likely to have lower
annual energy costs and life cycle costs than those that minimally meet
the Energy Cost Budget.
[[Page 589]]
11.1.5 The Energy Cost Budget is a numerical target for annual
energy cost. It is intended to assure neutrality with respect to choices
of HVAC system type, architectural design, fuel choice, etc., by
providing a fixed, repeatable budget target that is independent of any
of these choices wherever possible (i.e., for the prototype buildings).
The Energy Cost Budget for a given building size and type will vary only
with climate, the number of stories, and the choice of simulation tool.
The specifications of the prototypes are necessary to assure
repeatability, but have no other significance. They are not recommended
energy conserving practice, or even physically reasonable practice for
some climates or buildings, but represent a reasonable worst case of
energy cost resulting from compliance with the spirit and the letter of
sections 3.0 through 10.0.
11.2 Determination of the Annual Energy Cost Budget
11.2.1 The annual Energy Cost Budgets shall be determined in
accordance with the Prototype Building Method in section 11.2.5, or the
Reference Building Method in section 11.2.5. Both methods calculate an
annual Energy Cost by summing the 12 monthly Energy Cost Budgets. Each
monthly Energy Cost Budget is the product of the monthly Building Energy
Consumption of each type of energy used multiplied by the monthly Energy
Cost per unit of energy for each type of energy used.
11.2.2 The Energy Cost Budget shall be determined in accordance
with Equation 11-1 as follows:
ECB=ECBjan+ . . . ECBm+ . . . +ECBdec
Equation 11-1
Based on:
ECBm=BECONm1 x ECOSm1+ . . .
+BECONmi x ECOSmi
Equation 11-2
Where:
ECB=The annual Energy Cost Budget
ECBm=The monthly Energy Cost Budget
BECONmi=The monthly Budget Energy Consumption of the
ith type of energy
ECOSmi=The monthly Energy Cost, per unit of the
ith type of energy
11.2.3 The monthly Energy Cost Budget shall be determined using
current rate schedules or contract prices available at the building site
for all non-depletable types of energy purchased. These costs shall
include demand charges, rate blocks, time of use rates, interruptable
service rates, delivery charges, taxes, and all other applicable rates
for the type, location, operation, and size of the proposed design. The
monthly Budget Energy Consumption shall be calculated from the first day
through the last day of each month, inclusive.
11.2.4 The Energy Cost Budget, Design Energy Consumption and Design
Energy Cost calculations are applicable only for determining compliance
with these standards. They are not predictions of actual energy
consumption or costs of the proposed building after construction. Actual
experience will differ from these calculations due to variations such as
occupancy, building operation and maintenance, weather, energy use not
covered by these standards, changes in energy rates between design of
the building and occupancy, and precision of the calculation tool.
11.2.5 Prototype Building Procedure
11.2.5.1 The Prototype Building procedure shall be used for all
building types listed below. For mixed-use buildings the Energy Cost
Budget is derived by allocating the floor space of each building type
within the floor space of the prototype building. For buildings not
listed below, the Reference Building procedure of section 11.2.5 shall
be used.
11.2.5.1.1 Prototype buildings include:
(a) Assembly;
(b) Office (Business);
(c) Retail (Mercantile);
(d) Warehouse (Storage);
(e) School (Educational);
(f) Hotel/Motel;
(g) Restaurant;
(h) Health/Institutional; and
(i) Multi-Family.
11.2.5.2 Use of the Prototype Building to Determine the Energy Cost
Budget
11.2.5.2.1 Determine the building type of the Proposed Design using
the categories in section 11.2.5.1. Using the appropriate Prototype
Building characteristics from Tables 11-1 through 11-8,
[[Page 590]]
the building shall be simulated using the same gross floor area and
number of floors for the Prototype Building as in the Proposed Design.
11.2.5.2.3 The form, orientation, occupancy and use profiles for
the Prototype Building shall be fixed as described in section 11.5.3.
Envelope, lighting, other internal loads and HVAC systems and equipment
shall meet the prescriptive or system requirements of section 3.0
through 10.0 and are standardized inputs.
11.2.6 Reference Building Method
11.2.6.1 The Reference Building procedure shall be used only when
the Proposed Design cannot be represented by one or a combination of the
Prototype Building listed in section 11.2.5.1 or the assumptions for the
Prototype Building in section 11.5, such as occupancy and use-profiles,
do not reasonably represent the Proposed Design.
11.2.6.2 Use of the Reference Building to Determine the Energy Cost
Budget
11.2.6.2.1 Each floor shall be oriented in the same manner for the
Reference Building as in the Proposed Design. The form, gross and
conditioned floor areas of each floor and the number of floors shall be
the same as in the Proposed Design. All other characteristics, such as
lighting, envelope and HVAC systems and equipment, shall meet the
prescriptive/system requirements of section 3.0 through 10.0.
11.2.7 Calculation Procedure and Simulation Tool
11.2.7.1 The Prototype or Reference Buildings shall be modeled
using the criteria of section 11.5 and section 11.6. The modeling shall
use a climate data set appropriate for both the site and the complexity
of the energy conserving features of the design. ASHRAE Weather Year for
Energy Calculations (WYEC) data or bin weather data shall be a default
choice.
11.3 Determination of the Design Energy Consumption and Design Energy
Cost
11.3.1 The Design Energy Consumption shall be calculated by
modeling the Proposed Design using the same methods, assumptions,
climate data, and simulation tool as were used to establish the Energy
Cost Budget, except as explicitly stated in 11.5. The Design Energy Cost
shall be calculated per Equation 11-3. If the Proposed Design includes
cogeneration or non-depletable energy sources designed for the sale of
energy off-site, then energy cost and income resulting from outside
sales shall not be used to reduce the Design Energy Costs. Such systems
shall be modeled as operating to supply energy needs of the Proposed
Design only.
DECOS=DECOSjan+ . . . DECOSm . . . .
+DECOSdec
Equation 11-3
Based on:
DECOSm=DECONm1 x ECOSm1+ . . .
+DECONmi x ECOSmi
Equation 11-4
Where:
DECOS=The annual Design Energy Cost
DECOSm=The monthly Design Energy Cost
ICONmi=The monthly Design Energy Consumption of the
ith type of energy
ECOSmi=The monthly Energy Cost per unit of the ith
type of energy
The DECONmi shall be calculated from the first day
through the last day of the month, inclusive.
11.4 Compliance
11.4.1 If the Design Energy Cost is less than or equal to the
Energy Cost Budget, and all of the minimum requirements of sections 3.0
through 10.0 are met, the Proposed Design complies with the standards.
11.5 Standard Calculation Procedure
11.5.1 The Standard Calculation Procedure consists of methods and
assumptions for calculating the Energy Cost Budget for the Prototype or
Reference Building and the Design Energy Consumption and Design Energy
Cost of the Proposed Design. In order to maintain consistency between
the Energy Cost Budget and the Design Energy Cost, the input assumptions
to be used are stated below. These inputs shall be used to determine the
Energy Cost Budget and the Design Energy Consumption.
[[Page 591]]
11.5.2 Prescribed assumptions shall be used without variation.
Default assumptions shall be used unless the designer can demonstrate
that a different assumption better characterizes the building's energy
use over its expected life. No modified default assumptions shall be
used in modeling both the Prototype or Reference Building and the
Proposed Design unless the designer demonstrates clear cause to do
otherwise. Special procedures for speculative buildings are discussed in
section 11.5.9. Shell buildings may not use section 11.0.
11.5.3 Orientation and Shape
11.5.3.1 The Prototype Building shall consist of the same number
of stories, and gross and conditioned floor area as the Proposed Design,
with equal area per story. The building shape shall be rectangular, with
a 2.5:1 aspect ratio. The long dimensions of the building shall face
East and West. This is intended to provide an energy budget that can be
met even if there are unfavorable site constraints. The fenestration
shall be uniformly distributed in proportion to exterior wall area.
11.5.3.2 Floor-to-floor height for the Prototype Building shall be
13 ft except for dwelling units in hotels/motels and multi-family high
rise residential buildings where floor-to-floor height shall be 9.5 ft.
11.5.3.3 The Reference Building shall consist of the same number of
stories, and gross floor area for each story as the Proposed Design.
Each floor shall be oriented in the same manner as the Proposed Design.
The geometric form shall be the same as the Proposed Design.
11.5.4 Internal Loads
11.5.4.1 The systems and types of energy specified in this section
are intended only as constraints in calculating the Energy Cost Budget.
They are not intended as either requirements or recommendations for
either systems or the type of energy to be used in the Proposed Design
or for calculation of Design Energy Cost.
11.5.4.2 Internal loads for multi-family high rise residential
buildings are presented in Table 11-1. These assumptions shall be
prescribed assumptions. Internal loads for other building types shall be
modeled as noted in this subsection.
11.5.4.2.1 Occupancy
(a) Occupancy schedules shall be Default Assumptions. The same
assumptions shall be made in computing Design Energy Consumption as were
used in calculating the Energy Cost Budget.
(b) Table 11-2, Occupancy Density, establishes the density, in
ft\2\/person of conditioned floor area, to be used for each building
type. Table 11-3, Building Schedule Percentage Multipliers, establishes
the percentage of total occupants in the building by hour of the day for
each building type.
11.5.4.2.2 Lighting
(a) Interior Lighting Power Allowance (ILPA), for calculating the
Energy Cost Budget shall be determined from section 3.0. The lighting
power used to calculate the Design Energy Consumption shall be the
actual adjusted power for lighting in the Proposed Design. If the
lighting controls in the Proposed Design are more effective at saving
energy than those required by section 3.3, the actual installed lighting
power shall be used along with the schedules reflecting the action of
the controls to calculate the Design Energy Consumption. This actual
installed lighting power shall not be adjusted by the Power Adjustment
Factors listed in Table 3.5-2.
(b) Lighting energy profiles are shown in Table 11-3 that establish
the percentage of the lighting load switched-on in each Prototype or
Reference Building by hour of the day. These profiles are default
assumptions and can be changed when calculating the Energy Cost Budget
to provide, for example, a 12 hour rather than an 8 hour work day.
11.5.4.2.3 Receptacles
(a) Receptacle loads and profiles are default assumptions. The same
assumptions shall be made in calculating Design Energy Consumption as
were used in calculating the Energy Cost Budget.
(b) Receptacle loads include all general service loads that are
typical in a
[[Page 592]]
building. These loads exclude any process electrical usage and HVAC
primary or auxiliary electrical usage. Table 11-4, Receptacle Power
Densities, establishes the density, in W/ft\2\, to be used for each
building type. The receptacle energy profiles shall be the same as the
lighting energy profiles in Table 11-3. This profile establishes the
percentage of the receptacle load that is switched on by hour of the day
and by building type.
11.5.5 Building Exterior Envelope
11.5.5.1 Insulation and Glazing
11.5.5.1.1 The insulation and glazing characteristics of the
Prototype and Reference Building envelope shall be determined by using
the first column under ``Base Case'', with no assumed overhangs for the
appropriate Alternate Component Tables (ACP) in section 5.0, as defined
by climate range. The insulation and glazing characteristics from this
ACP are Prescribed Assumptions for Prototype and Reference Buildings for
calculating the Energy Cost Budget. In calculating the Design Energy
Consumption of the Proposed Design, the envelope characteristics of the
Proposed Design shall be used.
11.5.5.2 Infiltration
11.5.5.2.1 For Prototype and Reference Buildings, infiltration
assumptions shall be prescribed assumptions for calculating the Energy
Cost Budget and default assumptions for the Design Energy Consumption.
Infiltration shall impact perimeter zones only.
11.5.5.2.2 When the HVAC system is switched ``on'', no infiltration
shall be assumed. When the HVAC system is switched ``off'', the
infiltration rate for buildings with or without operable windows shall
be assumed to be 0.038 cfm/ft\2\ of gross exterior wall. Hotels/motels
and multi-family high rise residential buildings shall have infiltration
rates of 0.038 cfm/ft\2\ of gross exterior wall area at all times.
11.5.5.3 Envelope and Ground Absorptivities
11.5.5.3.1 For Prototype and Reference Buildings, absorptivity
assumptions shall be prescribed assumptions for computing the Energy
Cost Budget and default assumptions for computing the Design Energy
Consumption. The solar absorptivity of opaque elements of the building
envelope is assumed to be 70%. The solar absorptivity of ground surfaces
is assumed to be 80% (20% reflectivity).
11.5.5.4 Window Management
11.5.5.4.1 For the Prototype and Reference Building, window
management drapery assumptions shall be prescribed assumptions for
setting the Energy Cost Budget. No draperies shall be the default
assumption for computing the Design Energy Consumption. Glazing is
assumed to be internally shaded by medium-weight draperies, closed one-
half time. The draperies shall be modeled by assuming that one-half the
area in each zone is draped and one-half is not. If manually-operated
draperies, shades, or blinds are to be used in the Proposed Design, the
Design Energy Consumption shall be calculated by assuming they are
effective over one-half the glazing area in each zone.
11.5.5.5 Shading
11.5.5.5.1 For Prototype and Reference buildings and the Proposed
Design, shading by permanent structures, terrain, and vegetation shall
be taken into account for computing energy consumption, whether or not
these features are located on the building site. A permanent fixture is
one that is likely to remain for the life of the Proposed Design.
11.5.6 HVAC Systems and Equipment
11.5.6.1 The specifications and requirements for the HVAC systems
of the Prototype and Reference Buildings shall be those in Table 11-5,
HVAC Systems for Prototype and Reference Buildings. For the calculation
of the Design Energy Consumption, the HVAC systems and equipment of the
Proposed Design shall be used.
11.5.6.2 The systems and types of energy presented in Table 11-5
are intended only as constraints in calculating the Energy Cost Budget.
They are not intended as either requirements or recommendations for
either systems or the type of energy to be
[[Page 593]]
used in the Proposed Building or for the calculation of the Design
Energy Cost.
11.5.6.3 HVAC Zones
11.5.6.3.1 HVAC zones for calculating the Energy Cost Budget of the
Prototype or Reference Building shall consist of at least four perimeter
and one interior zones per floor. Prototype Buildings shall have one
perimeter zone facing each cardinal direction. The perimeter zones of
Prototype and Reference Buildings shall be 15 ft in width, or one-third
the narrow dimension of the building, when this dimension is between 30
ft and 45 ft inclusive, or one-half the narrow dimension of the building
when this dimension is less than 30 ft. Zoning requirements shall be a
default assumption for calculating the Energy Cost Budget. For multi-
family high rise residential buildings, the prototype building shall
have one zone per dwelling unit. The proposed design shall have one zone
per unit unless zonal thermostatic controls are provided within units;
in this case, two zones per unit shall be modeled. Building types such
as assembly or warehouse may be modeled as a single zone if there is
only one space.
11.5.6.3.2 For calculating the Design Energy Consumption, no fewer
zones shall be used than were in the Prototype and Reference Buildings.
The zones in the simulation shall correspond to the zones provided by
the controls in the Proposed Design. Thermally similar zones, such as
those facing one orientation on different floors, may be grouped
together for the purposes of either the Design Energy Consumption or
Energy Cost Budget simulation.
11.5.6.4 Equipment Sizing and Redundant Equipment
11.5.6.4.1 For calculating the Energy Cost Budget of Prototype or
Reference Buildings, HVAC equipment shall be sized to meet the
requirements of section 7.3.2, without using any of the exceptions. The
size of equipment shall be that required for the building without
process loads considered. The designer shall determine the final
equipment sizing including the process loads by separate calculations.
Redundant and/or emergency equipment need not be simulated if it is
controlled so that it will not be operated during normal operations of
the building. The designer shall document the installation of process
equipment and the size of process loads.
11.5.6.4.2 For calculating the Design Energy Consumption, actual
air flow rates and installed equipment size shall be used in the
simulation, except that excess capacity provided to meet process loads
need not be modeled if the process load was not modeled in setting
Energy Cost Budget. Equipment sizing in the simulation of the Proposed
Design shall correspond to the equipment actually selected for the
design and the designer shall not use equipment sized automatically by
the simulation tool.
11.5.6.4.3 Redundant and/or emergency equipment need not be
simulated if it is controlled to not be operated during normal
operations of the building.
11.5.7 Service Water Heating
11.5.7.1 The service water loads for Prototype and Reference
Buildings are defined in terms of Btu/h per person in Table 11-6. The
service water heating loads from Table 11-6 are prescribed assumptions
for multi-family high rise residential buildings and default assumptions
for all other buildings. The same service water heating load assumptions
shall be made in calculating Design Energy Consumption as were used in
calculating the Energy Cost Budget.
11.5.7.2 The service water heating system, including piping losses
for the Prototype Building, shall be modeled using the methods of the
ASHRAE Handbook, 1987 HVAC Systems and Applications Volume using a
system that meets all requirements of section 9.0. The service water
heating equipment for the Prototype or Reference Building shall be
either natural gas or 2 fuel oil, if natural gas is not available at
the site, or an electric heat pump.
11.5.7.3 Exception to section 11.5.7:
11.5.7.3.1 If electric resistance service water heating is
preferable to an electric heat pump when analyzed according to the
criteria of section 9.3.7.1
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or when service water temperatures exceeding 145 deg.F are required for
a particular application, electric resistance water heating may be used.
11.5.8 Controls
11.5.8.1 All occupied conditioned spaces in the Prototype,
Reference and Proposed Design Buildings in all climates shall be
simulated as being both heated and cooled. The assumptions in this
subsection are prescribed assumptions. If the Proposed Design does not
include equipment for cooling or heating, the Design Energy Consumption
shall be determined by the specifications for calculating the Energy
Cost Budget as described in Table 11-7.
11.5.8.2 Exceptions to section 11.5.8:
11.5.8.2.1 If a building is to be provided with only heating or
cooling, both the Prototype or Reference Building and the Proposed
Design shall be simulated, using the same assumptions. If such an
assumption is made, the analysis shall show that the building interior
temperature meets the comfort criteria of ANSI/ASHRAE 55-1981 ``Thermal
Environmental Conditions for Human Occupancy,'' at least 98% of the
occupied hours during the year.
11.5.8.2.2 If warehouses are not intended to be mechanically
cooled, both the Energy Cost Budget and Design Energy Consumption shall
be modeled assuming no mechanical cooling; and
11.5.8.2.3 In climates where winter design temperature (97.5%
occurrence) is greater than 59 deg.F, space heating need not be
modeled.
11.5.8.3 Space temperature controls for the Prototype or Reference
Building, except multi-family high rise residential buildings shall be
set at 70 deg.F for space heating and 75 deg.F for space cooling with
a deadband per section 7.3.4.5. The system shut off during off-hours
shall be according to the schedule in Table 11-3, except that the
heating system shall cycle on if any space should drop below the night
setback setting of 55 deg.F. There shall be no similar setpoint during
the cooling season. Lesser deadband ranges may be used in calculating
the Design Energy Consumption.
11.5.8.3.1 Exceptions to section 11.5.8.3:
(a) Setback shall not be modeled in determining either the Energy
Cost Budget or Design Energy Cost if setback is not realistic for the
Proposed Design, such as 24 hour/day operations. Health facilities need
not have night setback during the heating season;
(b) Hotel/motels and multi-family high rise residential buildings
shall have a night setback temperature of 60 deg.F from 11:00 p.m. to
6:00 a.m. during the heating season; and
(c) If deadband controls are not to be installed, the Design Energy
Cost shall be calculated with both heating and cooling thermostat
setpoints set to the same value between 70 deg.F and 75 deg.F
inclusive, assumed to be constant for the year.
11.5.8.3.2 For multi-family buildings, the thermostat schedule for
the dwelling units shall be as in Table 11-8.
(a) The Prototype Building shall use the single zone schedule. The
Proposed Design shall use the two-zone schedule only if zonal
thermostatic controls are provided. For Proposed Designs that use heat
pumps employing supplementary heat, the controls used to switch on the
auxiliary heat source during morning warm-up periods shall be simulated
accurately. The thermostat assumptions for multi-family high-rise
buildings are prescribed assumptions.
11.5.8.4 When providing for outdoor air ventilation in calculating
the Energy Cost Budget, controls shall be assumed to close the outside
air intake to reduce the flow of outside air to 0 cfm during setback and
unoccupied periods. Ventilation using inside air may still be required
to maintain scheduled setback temperature. Outside air ventilation,
during occupied periods, shall be as required by ASHRAE Standard 62-
1981, ``Ventilation for Acceptable Indoor Air,'' or the Proposed Design,
whichever is greater.
11.5.8.5 If humidification is to be used in the Proposed Design,
the same level of humidification and system type shall be used in the
Prototype or Reference Building. If dehumidification requires subcooling
of supply air, then reheat for the Prototype or Reference Building shall
be from recovered waste heat such as condenser waste heat.
[[Page 595]]
11.5.9 Speculative Buildings
11.5.9.1 Lighting
11.5.9.1.1 The interior lighting power allowance (ILPA) for
calculating the Energy Cost Budget shall be determined from Table 3.4-1.
The Design Energy Consumption may be based on an assumed adjusted
lighting power for future lighting improvements.
(a) The assumption about future lighting power used to calculate the
Design Energy Consumption must be documented so that the future
installed lighting systems may be in compliance with these standards.
Documentation must be provided to enable future lighting systems to use
either the Prescriptive method of section 3.4 or the Systems Performance
method of section 3.5.
(b) Documentation for future lighting systems that use the
Prescriptive method of section 3.4 shall be stated as a maximum adjusted
lighting power for the tenant spaces. The adjusted lighting power
allowance for tenant spaces shall account for the lighting power
provided for the common areas of the building.
(c) Documentation for future lighting systems that use the System
Performance method of section 3.5 shall be stated as a required lighting
adjustment. The required lighting adjustment is the whole building
lighting power assumed in order to calculate the Design Energy
Consumption minus the ILPA value from Table 3.4-1 that was used to
calculate the Energy Cost Budget. When the required lighting adjustment
is less than zero, a complete lighting design must be developed for one
or more representative tenant spaces, demonstrating acceptable lighting
within the limits of the assumed lighting power allowance.
11.5.9.2 HVAC Systems and Equipment
11.5.9.2.1 If the HVAC system is not completely specified in the
plans, the Design Energy Consumption shall be based on reasonable
assumptions about the construction of future HVAC systems and equipment.
These assumptions shall be documented so that future HVAC systems and
equipment may be in compliance with these standards.
11.6 The Simulation Tool
11.6.1 Annual energy consumption shall be simulated with a multi-
zone, 8760 hours per year building energy model. The model shall account
for:
11.6.1.1 The dynamic heat transfer of the building envelope such as
solar and internal gains;
11.6.1.2 Equipment efficiencies as a function of load and climate;
11.6.1.3 Lighting and HVAC system controls and distribution systems
by simulating the whole building;
11.6.1.4 The operating schedule of the building including night
setback during various times of the year; and
11.6.1.5 Energy consumption information at a level necessary to
determine the Energy Cost Budget and Design Energy Cost through the
appropriate utility rate schedules.
11.6.2 While the simulation tool should simulate an entire year on
an hour by hour basis (8760 hours), programs that approximate this
dynamic analysis procedure and provide equivalent results are
acceptable.
11.6.3 Simulation tools shall be selected for their ability to
simulate accurately the relevant features of the building in question,
as shown in the tool's documentation. For example, a single zone model
shall not be used to simulate a large, multi-zone building, and a
steady-state model such as the degree-day method shall not be used to
simulate buildings when equipment efficiency or performance is
significantly affected by the dynamic patterns of weather, solar
radiation, and occupancy. Relevant energy-related features shall be
addressed by a model such as daylighting, atriums or sunspaces, night
ventilation or thermal storage, chilled water storage or heat recovery,
active or passive solar systems, zoning and controls of heating and
cooling systems, and ground-coupled buildings. In addition, models shall
be capable of translating the Design Energy Consumption into energy cost
using actual utility rate schedules with the coincidental electrical
demand of a building. Examples of public domain models capable of
handling such complex building systems and energy cost translations
available in the United States are DOE-2.1C and
[[Page 596]]
BLAST 3.0 and in Canada, Energy Systems Analysis Series.
11.6.4 All simulation tools shall use scientifically justifiable
documented techniques and procedures for modeling building loads,
systems, and equipment. The algorithms used in the program shall have
been verified by comparison with experimental measurements, loads,
systems, and equipment.
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