5.1 Overview

This chapter specifies, for each building descriptor, the rules that apply to the proposed design and to the standard design for nonresidential buildings and multifamily buildings as referenced in Chapter 6: Multifamily Building Descriptors Reference.

5.1.1 Definition of Building Descriptors

Building descriptors provide information about the proposed design and the standard design. In this chapter, the building descriptors are discussed in the generic terms of engineering drawings and specifications. By using generic building descriptors, this manual avoids bias toward one energy simulation engine. The building descriptors in this chapter are compatible with commonly used simulation software.

Each energy simulation program has a unique way of accepting building information. EnergyPlus uses a comma delimited data file called an input data file (IDF). DOE-2 uses BDL (building design language) to accept information. It is the responsibility of the compliance software to translate the generic terms used in this chapter into the “native language” of the simulation program. Figure 7: Information Flow illustrates the flow of information.

5.1.2 Organization of Information

Building descriptors are grouped under objects or building components. A wall or exterior surface (an object) would have multiple building descriptors dealing with the geometry, thermal performance, and so forth. Each building descriptor contains the following pieces of information:

Applicability: Information on when the building descriptor applies to the proposed design.

Units: The units that are used to prescribe the building descriptor; A “list” indicates that a fixed set of choices applies, and the user shall be allowed to enter only one of the values in the list.

Input Restrictions: Any restrictions on information that may be entered for the proposed design.

Standard Design: This defines the value for the “standard design” or baseline building applied for this building descriptor. A value of “same as proposed” indicates that the building descriptor is neutral, that is, the value is set to match the proposed design value. In many cases, the value may be fixed or may be determined from a table lookup. In some cases, the input may not be applicable.

Standard Design: Existing Building: Standard design for existing buildings if different than new buildings.

5.1.3 HVAC System Map

The Nonresidential HVAC system in the standard design depends on the primary building activity, the size of the building, and the number of floors. Details about these systems are provided in subsequent chapters.

Many of the building descriptors have a one-to-one relationship between the proposed design and the standard design; for example, every wall in the proposed design has a corresponding wall in the standard design. For HVAC systems, however, this one-to-one relationship generally does not hold. The number and type of HVAC systems serving the proposed design and the standard design may be completely different in type and components.

The HVAC systems in the standard design are determined by Table 2: HVAC System Map, which is based on space type, system cooling capacity, number of above-grade floors, climate zone, conditioned floor area, and, for some spaces, process load, and laboratory exhaust rate. Table 3: System Descriptions, provides additional detail for each standard design system. . Unless otherwise noted, all non-residential systems are set to meet the efficiency requirements for 3-phase equipment.

For Systems 1, 3, 7, 9, 10, and 11, each thermal zone shall be modeled with a respective HVAC system. For Systems 5, and 6, each floor shall be modeled with a separate HVAC system. Floors with identical thermal zones and occupancies can be grouped for modeling.

Space Type	Above-Grade Floors	Climate Zone	System Cooling Capacity	Standard Design
Multifamily				(See NRMFACM Chapter 6)
Hotel/motel guestrooms	No limit	All	No limit	System 1 – RAC
Retail or grocery¹	Buildings ≤ 2 floors	2-15	< 65 kBtu/h	System 3b – SZHP
Retail or grocery¹	Buildings ≤ 2 floors	2-15	≥ 65 kBtu/h	System 7b – SZVAVHP
Retail or grocery¹	Buildings ≤ 2 floors	1, 16	< 65 kBtu/h	System 3a – SZAC
Retail or grocery¹	Buildings ≤ 2 floors	1, 16	≥ 65 kBtu/h	System 7c – SZVAVDFHP
Retail or grocery¹ total building area < 25,000 ft²	Buildings = 3 floors	2-15	< 65 kBtu/h	System 3b – SZHP
Retail or grocery¹ total building area < 25,000 ft²	Buildings = 3 floors	2-15	≥ 65 kBtu/h	System 7b – SZVAVHP
Retail or grocery¹ total building area < 25,000 ft²	Buildings = 3 floors	1, 16	< 65 kBtu/h	System 3a – SZAC
Retail or grocery¹ total building area < 25,000 ft²	Buildings = 3 floors	1, 16	≥ 65 kBtu/h	System 7c – SZVAVDFHP
School²	Buildings ≤ 3 floors	2-15	< 65 kBtu/h	System 3b – SZHP
School²	Buildings ≤ 3 floors	2-15	≥ 65 kBtu/h	System 7b – SZVAVHP
School²	Buildings ≤ 3 floors	1, 16	< 65 kBtu/h	System 3c – SZDFHP
School²	Buildings ≤ 3 floors	1, 16	≥ 65 kBtu/h	System 7c – SZVAVDFHP
Warehouse and light manufacturing that do not include mechanical cooling in the proposed design³	No limit	All	No limit	System 9 – HEATVENT
Office in buildings with warehouse and light manufacturing space³	Buildings ≤ 3 floors	All	< 65 kBtu/h	System 3b – SZHP
Office in buildings with warehouse and light manufacturing space³	Buildings ≤ 3 floors	All	≥ 65 kBtu/h	System 7b – SZVAVHP
Office, financial institution, and library and total building area < 25,000 ft²	Buildings ≤ 3 floors	1-15	< 65 kBtu/h	System 3b – SZHP
Office, financial institution, and library and total building area < 25,000 ft²	Buildings ≤ 3 floors	1-15	≥ 65 kBtu/h	System 7b – SZVAVHP
Office, financial institution, and library and total building area < 25,000 ft²	Buildings ≤ 3 floors	16	< 65 kBtu/h	System 3a – SZAC
Office, financial institution, and library and total building area < 25,000 ft²	Buildings ≤ 3 floors	16	≥ 65 kBtu/h	System 7c – SZVAVDFHP
Covered process computer room with total process load ≤ 800kW	No limit	All	No limit	System 11 – CRAC Unit
Covered process computer room with total process load > 800kW	No limit	All	No limit	System 10 – CRAH Unit
Covered process laboratory with total building laboratory design maximum exhaust < 15,000 cfm and total building area < 25,000 ft²	Buildings ≤ 3 floors	All	No limit	System 7a – SZVAVAC
Covered process laboratory with total building laboratory design maximum exhaust > 15,000 cfm and total building conditioned floor area < 150,000 ft²	No limit	All	No limit	System 5 – PVAV
Covered process laboratory with total building laboratory design maximum exhaust > 15,000 cfm and total building conditioned floor area ≥ 150,000 ft²	No limit	All	No limit	System 6 – VAV
Covered process commercial kitchen for buildings that use System 6 – VAV	No limit	All	No limit	System 13a – BKITCHMAU
Covered process commercial kitchen for buildings that don’t use System 6 – VAV	No limit	All	No limit	System 13b – PKITCHMAU
Healthcare facilities	No limit	All	No limit	Same as the Proposed Design
All other spaces in buildings < 25,000 ft²	Buildings ≤ 3 floors	All	< 65 kBtu/h	System 3a – SZAC
All other spaces in buildings < 25,000 ft²	Buildings ≤ 3 floors	All	≥ 65 kBtu/h	System 7a – SZVAVAC
All other spaces in buildings < 25,000 ft²	4 - 5 floors	All	No limit	System 5 – PVAV
All other spaces in buildings < 25,000 ft²	> 5 floors	All	No limit	System 6 – VAV
All other spaces in buildings 25,000 – 150,000 ft²	≤ 5 floors	All	No limit	System 5 – PVAV
All other spaces in buildings 25,000 – 150,000 ft²	> 5 floors	All	No limit	System 6 – VAV
All other spaces in buildings > 150,000 ft²	No limit	All	No limit	System 6 – VAV

“Retail or grocery” building space types include “Pharmacy Area,” “Retail Sales Area (Fitting Room),” “Retail Sales Area (Grocery Sales),” “Retail Sales Area (Retail Merchandise Sales),” “Concourse and Atria Area,” “Exercise/Fitness Center and Gymnasium Areas” and “Beauty Salon Area.” To qualify for this system, the building story that includes these spaces must predominantly have a “Retail” function schedule group (FuncSchGrp), per Appendix 5.4A, and be part of a building with only three above-grade stories. If these are not met, the standard design system is determined using the “All other spaces” categories.

“School” building space types include “Classroom, Lecture, Training, Vocational Areas.” To qualify for this standard design system, the building story that includes these spaces must predominantly have a “School” function schedule group (FuncSchGrp), per Appendix 5.4A, and be part of a building with only three above-grade stories. If these are not met, the standard design system is determined using the “All other spaces” categories.

Warehouse and light manufacturing spaces are those identified as having a “Warehouse” or “Manufacturing” function schedule group (FuncSchGrp), per Appendix 5.4A.

§ Office, financial institution, and library spaces include “Copy Room,” “Financial Transaction Area,” “Library, Reading Areas,” “Library, Stacks,” “Office (Greater than 250 square feet in floor area)," “Office (250 square feet in floor area or less),” “Videoconferencing Studio,” and “Waiting Area.” To qualify for this system, the building story that includes these spaces must predominantly have an “Office” function schedule group (FuncSchGrp), per Appendix 5.4A, and be part of a building with only three above-grade stories. If these are not met, the standard design system is determined using the “All other spaces” categories.

System Type	Description	Detail
System 1a – RAC	Residential air conditioner	Single-phase single-zone system with constant volume fan, no economizer, direct expansion cooling, and gas furnace heating.
System 2 – RESERVED
System 3a – SZAC	Packaged single-zone air conditioner	Single-phase single-zone system with constant volume fan, direct expansion cooling, and gas furnace heating.
System 3b – SZHP	Packaged single-zone heat pump	Single-phase single-zone system with constant volume fan, direct expansion heat pump cooling and heating, and electric resistance supplemental heating.
System 3c – SZDFHP	Packaged single-zone dual fuel heat pump	Single-zone system with constant volume fan, direct expansion heat pump cooling and heating, and gas supplemental heating.
System 4--Reserved
System 5 – PVAV	Packaged VAV	Multizone packaged system with variable volume fan, direct expansion cooling, gas furnace heating, and hot water reheat terminal units served by a central gas boiler.
System 6 – VAV	Built-up VAV	Multizone built-up system with variable volume fan, chilled water cooling provided by a central water cooled chiller and cooling tower, and hot water heating provided by central gas boiler.
System 7a – SZVAVAC	Packaged single-zone variable air volume air conditioner	Single-zone system with variable air volume fan, direct expansion variable-speed drive cooling, and gas furnace heating. Minimum fan speed ratio of 0.2 for laboratory spaces and 0.5 for all other spaces. Integrated economizer for standard design cooling capacities ≥ 33 kBtu/h.
System 7b – SZVAVHP	Packaged single-zone variable air volume heat pump	Single-zone system with variable air volume fan, direct expansion heat pump cooling and heating, and electric resistance supplemental heating.
System 7c – SZVAVDFHP	Packaged single-zone variable air volume dual fuel heat pump	Single-zone system with variable air volume fan, direct expansion heat pump cooling and heating, and gas supplemental heating.
System 8 – RESERVED
System 9 – HEATVENT	Heating and ventilation only	Single-zone system with a constant volume fan and gas furnace heating.
System 10 – CRAH	Computer room air handler	Single-zone built-up system with variable volume fan, chilled water cooling provided by a central water cooled chiller and cooling tower, and no heating.
System 11 – CRAC	Computer room air conditioner	Single-zone packaged system with variable volume fan, direct expansion cooling, and no heating
System 12--Reserved
System 13a – BKITCHMAU	Built-up kitchen makeup air unit	Built-up single-zone makeup air unit with dedicated exhaust fan, chilled water cooling, and hot water heating.
System 13b – PKITCHMAU	Packaged kitchen makeup air unit	Packaged single-zone makeup air unit with dedicated exhaust fan, direct expansion cooling, and gas furnace heating.

The standard design systems serving mixed-use buildings are different from the standard design systems serving nonresidential space types. Also, spaces containing covered processes are served by dedicated standard design systems separate from systems serving other nonresidential space types. Examples include hotel/motel guestroom and related spaces located over retail and other similar conditions. For example, a 100,000 ft² building that has retail and restaurant on Floor 1, offices on Floors 2, 3, and 4, a 600 kW process load computer room on each office floor, and guestrooms on Floors 5, 6, and 7 would have the following systems in the standard design:

• Retail spaces follow the system map, since the building has more than three stories

• Separate System 1 – RAC systems serving each guestroom space, with a System 6 – VAV system serving corridors and other non-guestroom spaces on each floor

The standard design building shall have only one central chilled or hot water plant, so if there are multiple systems that incorporate a plant (for example, CRAH and VAVS), then a single plant shall serve all plant loads.

For nonresidential additions and alterations projects, the standard design building shall follow the same rules as the HVAC system map above, except for the following changes:

1. The building that will follow the logic of the system map rules may be the modeled building (the addition or alteration alone, or the addition or alteration and a portion of the existing building),) or the entire building (the entire existing building, plus an addition, if present).

2. Section 140.4(a)2, Single zone space-conditioning system type is not applicable to additions and alterations. Any system designated as a heat pump in the system map is replaced with an air conditioner of equivalent type.

The following rules apply to any building that has both heating and cooling systems.

• Plant: If the change in plant cooling capacity exceeds 50 percent of the existing total cooling capacity of all cooling systems, the system map is based on the entire building characteristics. (See Chapter 5.2.2 Existing Building Classification.)

• Airside System: If the change in cooling capacity of the air side system (for example, air handling units, DX packaged units) of all cooling sources other than chilled water exceeds 50 percent of the existing rated cooling capacity for the building, then the HVAC system map is based on the entire building characteristics. Also, if the combined net cooling capacity of all altered airside systems exceeds 90 percent of the building cooling capacity, then the HVAC system map is based on the entire building characteristics.

• Zone Level: If the change in the cooling capacity of the zonal systems (SZAC units for example) exceeds 50 percent of the rated total cooling capacity of all zonal systems in the existing building, then the HVAC system map is based on the entire existing building characteristics. Also, if the combined net cooling capacity of all altered zonal systems exceeds 90 percent of the building cooling capacity, then the HVAC system map is based on the entire building characteristics.

• If none of these three conditions apply, then the HVAC system map is based on the building characteristics of the modeled building for additions and alterations compliance, which may be just a portion of the entire building.

Since some additions and alterations projects will trigger the HVAC system map for the standard design, the user must enter a minimum set of building characteristics for the entire building (existing plus any addition); existing building floor area and number of stories must be entered.

• Plant: If the change in plant heating capacity exceeds 50 percent of the existing total space heating capacity of all heating systems, the system map is based on the entire building characteristics.

• Airside System: If the change in heating capacity of the airside system (unitary DX equipment, heat pumps, for example) of all heating sources other than heating hot water exceeds 50 percent of the existing rated cooling capacity for the building, then the HVAC system map is based on the entire building characteristics. Also, if the combined net heating capacity of all altered airside systems exceeds 90 percent of the building heating capacity, then the HVAC system map is based on the entire building characteristics.

• Zone Level: If the change in the heating capacity of the zonal systems (SZAC units, for example), exceeds 50 percent of the rated total heating capacity of all zonal systems in the existing building, then the HVAC system map is based on the entire existing building characteristics. Also, if the combined net cooling capacity of all altered zonal systems exceeds 90 percent of the building cooling capacity, then the HVAC system map is based on the entire building characteristics.

• If none of these three conditions above apply, then the HVAC system map is based on the building characteristics of the modeled building for additions and alterations compliance, which may be just a portion of the entire building.

§ Since some additions and alterations projects will trigger the HVAC system map for the standard design, the user must enter a minimum set of building characteristics for the entire building (existing plus any addition): existing building floor area and number of stories must be entered.

5.1.4 Special Requirements for Additions and Alterations Projects

Compliance projects containing additions or alterations or both require that the user designate each building component (envelope construction assemblies and fenestration, lighting, HVAC, and water heating) as either new, altered, or existing. Many of the building descriptors in Chapter 5: Nonresidential Building Descriptors Reference of this manual do not have explicit definitions for the standard design when the project is an addition or alterations project or both. For these terms, the standard design rules for existing, altered components follow the same rule as the standard design rule for newly constructed buildings.

For example, the receptacle loads are prescribed for both the proposed design building and standard design building for a newly constructed buildings compliance project. For additions or alterations to an existing building, since the rules are not explicitly defined in the building descriptor in Chapter 5.3.3: Receptacle Loads, the same rules apply to the proposed design and standard design for the additions or alterations compliance project.

Building descriptors that are prescribed for the proposed and standard design models for newly constructed buildings projects are also prescribed for the proposed and standard design models for additions and alterations projects.

For additions and alterations projects, there are three modeling approaches that can be taken when modeling the existing building:

• Model the addition or altered portion alone. For this option, the addition or alteration is modeled as a stand-alone building, and the boundary or interface between the addition or alteration or both and the preexisting building is modeled as an adiabatic partition (an adiabatic wall, ceiling, roof, or floor).

• Model the entire existing building and any additions and alterations. For this option, the existing, unaltered components of the building would be modeled “as designed” (as specified by the user), with the standard design components modeled the same as the proposed design.

• Model part of the existing building and any additions and alterations. For this option, all components of the existing, unaltered building (HVAC, lighting, envelope, spaces) would have to be distinguished from the components that are added and altered. The existing building components would be modeled “as designed” (as specified by the user), with the standard design components modeled the same as the proposed design. Added or altered building components would follow the rules for additions and alterations.