3.1 Overview

The HVAC system in the baseline building depends on the primary building activity, the size of the building and the energy source used for heating in the proposed design. [bookref id="hvac-mapping"] shows the HVAC system types that apply in each case. Details about these systems are provided in subsequent sections.

Many of the building descriptors have a one-to-one relationship between the proposed design and the baseline building, for example, every wall in the proposed design has a corresponding wall in the baseline building. For HVAC systems, this one-to-one relationship generally does not hold. The HVAC system serving the proposed design and the baseline building may be completely different, each with different components, etc.

[figure title="HVAC Mapping" id="hvac-mapping"][/figure]

For systems 1 through 4, each thermal block shall be served by a separate system. For systems 5 through 8, a single system serves the whole building with a separate air handler for each floor. Systems 5 and 6 are packaged equipment with DX cooling and fans combined in the same box. For these systems, each floor will have its own system.

There are several important exceptions to the HVAC mapping rules that apply to spaces with unusual internal heat gains, different schedules, special pressurization requirements, or unique outside air needs. These exceptions will typically apply to laboratories, data centers, and many spaces in healthcare facilities. See Chapter 7 for the special requirements for these building types. The exceptions are described below:

• Separate occupancies in mixed use buildings are served by separate baseline building systems. Examples include residential spaces located over retail and other similar conditions. (See the PRM, G3.1.1, Exception a.)
• A separate baseline building system shall serve laboratories or group of laboratories with an exhaust system designed for 5,000 cfm or more of air movement. The baseline building system serving the laboratory spaces shall be either system 5 (PVAV with hot water reheat) or system 6  (PVAV with parallel fan-powered boxes and electric reheat), depending on the heating source in the building. The PVAV system must be capable of reducing the exhaust and makeup air volume to 50% of design values during unoccupied periods. This exception essentially requires VAV for both the supply fan and the exhaust system. (See the PRM, G3.1.1, Exception c.)
• Spaces that do not trigger the laboratory exception above may still have a separate baseline building system. Either system 3 (PSZ-AC) or system 4 (PSZ-HP) shall serve spaces in the baseline building (depending on the heating source for the building) when one of the following conditions apply:
  • Spaces on a floor have significantly different schedules or internal heat loads. Heat gain differences of more than 10 Btu/h or operation schedule differences of more than 40 hours/week trigger this exception. (See the PRM, G3.1.1, Exception b.)
  • Spaces on a floor have "special pressurization relationships, cross-contamination requirements, or code-required minimum circulation rates". Many laboratory spaces with fume hoods would likely trigger this exception. (See the PRM, G3.1.1, Exception c.)

These special systems serve just the spaces that trigger the exceptions. The rest of the building/floor is served by the baseline building HVAC system and air handlers shown in [bookref id="hvac-mapping"].

3.1    Overview

This chapter specifies the rules that apply to the proposed design and to the baseline building for each building descriptor. 

3.1.1    HVAC System Map

The HVAC system in the baseline building depends on the primary building activity, the number of floors, conditioned floor area and climate zone. Details about these systems are provided in subsequent sections.

For many of the building descriptors there is a one-to-one relationship between the proposed design and the baseline building; for example, every wall in the proposed design has a corresponding wall in the baseline building. However, for HVAC systems, this one-to-one relationship generally does not hold. There may be the different number of HVAC systems serving the proposed design compared to the baseline building, and equipment such as cooling towers, circulation pumps, etc. may be present in the baseline but not proposed design.

The HVAC system in the baseline building shall be selected from Table 3, HVAC System Map, and be based on building type, number of floors, conditioned floor area, and climate zone. The selected system shall conform to the descriptions in Table 4, HVAC System Descriptions. For systems 1, 2, 3, 4, 9, 10, 11, 12, and 13, each thermal zone shall be modeled with its own HVAC system. For systems 5, 6, 7, and 8, each floor shall be modeled with a separate HVAC system. Floors with identical thermal zones can be grouped for modeling purposes. 

Table 3. HVAC System Map

Building Type	Size	Baseline Building System Type
		Cool Climates (3b, 3c, and 4-8)	Warm Climates (0 to 3A)
Residential	Any size	System 1 PTAC	System 2 PTHP
Public Assembly	< 120,000 ft²	System 3 PSZ-AC	System 4 PSZ-HP
	≥ 120,000 ft²	System 12 SZ-CV-HW	System 13 SZ-CV-ER
Retail	Low rise ≤ 2 floors	System 3 PSZ-AC	System 4 PSZ-HP
	Other than low rise	Use “Other Nonresidential”
Hospital	Not more than 5 floors and not >150,000 ft2	System 5 PVAV with Reheat	System 5 PVAV with Reheat
	more than 5 floors or >150,000 ft2	System 7 VAV with Reheat	System 7 VAV with Reheat
Heated-only Storage		System 9- Heating and Ventilation	System 10- Heating and Ventilation
Other Nonresidential	Small, 3 floors or less and <25,000 ft2	System 3 PSZ-AC	System 4 PSZ-HP
	Medium, 4 or 5 floors and <25,000 ft2 or 5 floors or less and 25,000 ft2 to 150,000 ft2	System 5 PVAV with Reheat	System 6 PVAV with PFP boxes
	Large, more than 5 floors or >150,000 ft2	7 VAV with Reheat	8 VAV with PFP boxes

Building Type Descriptions for Baseline System Definition:

•    Residential
Residential buildings They include, but are not limited to, dwelling units, hotel/motel guest rooms, dormitories, nursing homes, patient rooms in hospitals, lodging houses, fraternity/ sorority houses, hostels, prisons, and fire stations.

•    Public Assembly
Public assembly buildings include houses of worship, auditoriums, movie theaters, performance theaters, concert halls, arenas, enclosed stadiums, ice rinks, gymnasiums, convention centers, exhibition centers, museums, exercise centers and natatoriums

•    Heated Only
This category applies to an entire building with heating only systems in the proposed design, such as warehouses 

•    Retail
Retail buildings that are two floors or less must use single-zone packaged equipment. In the baseline building, cooling will always be DX but heating will be dependent upon the climate zone. Retail buildings that are 3 or more stories are included in the Nonresidential category below. Restaurants are also included in the nonresidential category described below.

•    Hospital
This excludes outpatient medical buildings and offices.

•    Other Non-Residential
This category would cover all buildings that are not included any other category 
Where attributes make a building eligible for more than one baseline system type, the predominant condition should be used to determine the system type for the entire building, except as notes in Section G3.1.1. of Standard 90.1-2019 and also documented in Section 3.1.1.1 of this manual.

Table 4. HVAC System Descriptions

System No.	System Type	Fan Control	Cooling Type	Heating Type (note 3)
1 – PTAC	Package terminal air conditioner	Constant volume	Direct expansion	Hot water fossil fuel boiler
2 – PTHP	Packaged terminal heat pump	Constant volume	Direct expansion	Electric heat pump
3 – PSZ AC	Packaged roof top air conditioner	Constant volume	Direct expansion	Fossil fuel furnace
4 – PSZ HP	Packaged roof top heat pump	Constant volume	Direct expansion	Electric heat pump
5 – PVAV Reheat	Packaged rooftop VAV with reheat	Variable volume	Direct expansion	Hot water fossil fuel boiler
6 – Packaged VAV with PFP Boxes	Packaged rooftop VAV with PFP boxes and reheat	Variable volume	Direct expansion	Electric resistance
7 – VAV with Reheat	Rooftop VAV with reheat	Variable volume	Chilled water	Hot water fossil fuel boiler
8 – VAV with PFP Boxes	VAV with parallel fan-powered boxes and reheat	Variable volume	Chilled water	Electric resistance
9 – Heating and Ventilation	Warm air furnace, gas fired	Constant volume	None	Fossil fuel furnace
10 – Heating and Ventilation	Warm air furnace, electric	Constant volume	None	Electric resistance
11 – SZ-VAV	Single zone VAV	Variable air volume	Chilled Water	See Note 2
12 – SZ-CV-HW	Single zone with hot water heat	Constant volume	Chilled Water	Hot water fossil fuel boiler
13 – SZ-CV-ER	Single zone with electric resistance heat	Constant volume	Chilled Water	Electric resistance
Notes:​​​​​​​​​​​​​​ For purchased chilled water and purchased heat, see G3.1.1.3. System 11 is only used for the exceptions stated below. For climate zones 0-3A, the heating type shall be electric resistance. For all other climate zones the heating type shall be hot-water fossil-fuel boiler. The fossil fuel type shall be natural gas if it is available at the site, otherwise propane.

3.1.1.1    Exceptions to HVAC System Requirements

There are several important exceptions to the HVAC mapping rules that apply to zones with unusual internal heat gains, different schedules, or unique outside air needs. Where attributes make a building eligible for more than one baseline system type, use the predominant condition to determine the system type for the entire building except as noted in exceptions below. These exceptions should be applied in the order defined below, to avoid inconsistencies in baseline system definition-
1.    Exception (a) for mixed residential and non-residential buildings
2.    Exception (d) for heated only zones
3.    Exception (e) for baseline system 9 and 10
4.    Exception (f) for computer rooms
5.    Exception (c) for laboratory spaces
6.    Exception (b) for internal loads

a.    Mixed Residential and Non-Residential Buildings:
The baseline HVAC system must be determined separately for buildings with both residential and non-residential zones. Additional system type(s) are required to be used if the non-predominant conditions (use type) apply to more than 20,000 ft2 of conditioned floor area. Residential building types include dormitory, hotel, motel, and multifamily. Residential space types include guest rooms, living quarters, private living space, and sleeping quarters. Other building and space types including common areas associated with residential buildings are considered nonresidential. 

b.    Internal Loads:
This exception is triggered for HVAC zones with total non-coincident peak internal gains (excluding ventilation or envelope loads) that differ by more than 10 Btu/h-ft2 (31.5 W/m2) from the average of the other HVAC zones served by the system or when the weekly operating hours of the HVAC system are different by more than 40 equivalent full load hours (EFLH) per week from the other HVAC zones served by the system. A full load hour is an hour during which the zone is occupied and supply and return fans operate continuously. The baseline system for such spaces would be system type 3 or 4, depending on the heating source for the main building. This exception does not apply to computer rooms, see (f) below for the exception related to computer rooms.

When multiple proposed systems with schedules varying for less than 40 hours are combined into a single baseline system as a whole floor variable air volume (VAV), the baseline system fan schedule is defined to include the earliest start hour and latest end hour, so that all HVAC zones are designated to have HVAC system availability. Section 3.7.2.1 has more details regarding HVAC availability.

This exception doesn’t apply to computer rooms (see f. below).

The process for calculating internal loads for spaces is defined below-

1.    Step 1: Eliminate zones that meet both exceptions (internal loads and EFLH)
a.    Find all zones whose  peak coincident internal loads are more than 10 Btu/ft2 from the area-weighted average of all other zones and whose EFLH are more than 40 hrs from the average of all other zones. Remove all of those zones and assign them to baseline system 3 or 4 depending on the climate zone. 
b.    Repeat until no zones meet this criteria. 
2.    Step 2: Eliminate zones that meet the EFLH exception
a.    Find any zones whose EFLH is more than 40 hrs from the average of all other zones.  Remove the zone with the highest EFLH greater than 40, and assign to baseline system 3 or 4 depending on climate zone. 
b.    Repeat until no zones meet this criteria
3.    Step 3: Eliminate zones that meet the internal loads exception
a.    Find any zones whose peak coincident internal loads are more than 10 Btu/ft2 from the area-weighted average of all other zones.  Remove the zone with the highest peak internal load greater than 10 Btu/ft2, and assign system 3 or 4 depending on the climate zone. 
b.    Repeat until no zones meet this criteria
4.    Step 4: Assign remaining zones to the appropriate multizone system. 

Example 1: For a floor with zones with peak internal gains specified as 9 Btu/h-ft2, 14 Btu/h-ft2, 16 Btu/h-ft2, and 34 Btu/h-ft2. The difference between the zone’s peak internal loads and the average for all other zones is shown in Table 5 . Zone D would be subject to the exception since its coincident peak internal gains differ by more than 10 Btu/h-ft2 from the average for all other zones and the baseline system for this space would be system type 3 or 4 (depending on building heating source). Zone D would then be removed from the list and the the difference between remaining zone’s peak internal loads and average for all other zones would be calculated again. The difference is now under . 10 Btu/h-ft2 and would hence stay on the same baseline system.

Table 5. Example 1 Calculations

Zone	Internal Loads (Btu/hr)	Avg. of All Others Zones (Btu/hr)	Difference from the Average
A	9	21	12
B	14	20	6
C	16	19	3
D	34	13	-21

Example 2: An office building with baseline system 5 has the following thermal blocks on one floor:

•    Thermal Block A: Zones with predominantly office occupancy, to be occupied 50 hours per week; 
•    Thermal Block B: Zones to be occupied 55 hrs per week; 
•    Thermal Block C: Zones for help desk, to be occupied 65 hours per week.
•    Thermal Block D: Zones to be occupied 100 hours per week

Following the methodology outlined above, the difference between the zone’s EFLHs and the average for all other zones is shown in Table 6. Since the difference from the average is greater than 40, Thermal Block D would be modeled with baseline system 3 and the  difference between remaining zone’s EFLH and average for all other zones would be calculated again. The difference is now under . 40 hours and hence the remaining zones would hence stay on the same baseline system.

Table 6. Example 2 Calculations

Zone	EFLH	Avg. of All Others Zones (EFLH)	Difference from the Average
A	50	73	23
B	55	72	17
C	65	68	3
D	100	57	-43

 
Example 3: An office building with baseline system 5 has the following thermal zones on one floor:

•    Zone A: Occupied 25 hours per week; 
•    Zone B: Occupied 30 hours per week; 
•    Zone C: Occupied 35 hours per week; 
•    Zone D: Occupied 45 hours per week; 
•    Zone E: Occupied 80 hours per week; 
•    Zone F: Occupied 90 hours per week;
•    The coincident peak internal loads for these zones are 6 Btu/h-ft2, 8 Btu/h-ft2, 10 Btu/h-ft2, 20 Btu/h-ft2, 16 Btu/h-ft2, and 28 Btu/h-ft2 respectively.

Following the methodology outlined above, following would be the steps for elimination

1.    Step 1: Eliminate zones that meet both exceptions (internal loads and EFLH)
a.    Based on this, zone F is eliminated and assigned baseline system 3 or 4 depending on the climate zone.
2.    Step 2: Eliminate zones that meet the EFLH expection
3.    Step 3: Eliminate zones that meet the internal loads exception

Table 7. Example 3 Calculations

Step 1
		Schedule												Internal load
Zone		EFLH			Avg. of All Others Zones (EFLH)				Difference from the Average					Internal loads (Btu/hr)			Avg. of All Others Zones (Btu/hr)			Difference from the Average
A		25			56.0				31					6			16			10
B		30			55.0				25					8			16			8
C		35			54.0				19					10			16			6
D		45			52.0				7					20			14			-6
E		80			45.0				-35					16			14			-2
F		90			43.0				-47					28			12			-16
Step 2
	Schedule										Internal load
Zone	EFLH			Avg. of All Others Zones (EFLH)				Difference from the Average			Internal loads (Btu/hr)							Avg. of All Others Zones (Btu/hr)		Difference from the Average
A	25			47.5				22.5			6							14		8
B	30			46.3				16.3			8							13		5
C	35			45.0				10.0			10							13		3
D	45			42.5				-2.5			20							10		-10
E	80			33.8				-46.3			16							11		-5
(Zone F is eliminated and assigned baseline system 3 or 4)
Step 3
	Schedule											Internal load
Zone	EFLH		Avg. of All Others Zones (EFLH)				Difference from the Average					Internal loads (Btu/hr)			Avg. of All Others Zones (Btu/hr)				Difference from the Average
A	25		36.7				11.7					6			13				7
B	30		35.0				5.0					8			12				4
C	35		33.3				-1.7					10			11				1
D	45		30.0				-15.0					20			8				-12
(Zone E is eliminated and assigned baseline system 3 or 4)
Step 4
	Schedule												Internal load
Zone	EFLH					Avg of Others				Diff			Btu/ h-sf			Avg of Others				Diff
A	25					17.7				-7.3			6			6				0
B	26					17.3				-8.7			8			5				-3
C	27					17.0				-10.0			10			5				-5
(Zone D is eliminated and assigned baseline system 3 or 4)

c.    Laboratory Spaces:

All zones with laboratory spaces in a building having a total laboratory exhaust rate greater than 15,000 cfm, use a single system of type 5 or 7 serving only those spaces. .The baseline system serving laboratory spaces shall be system 5 (PVAV with hot water reheat) or 7 (VAV with hot water reheat) depending on the size of the building. If the building is more than 5 floors or >150,000 ft2 use system 7. Otherwise, use system 5. The lab exhaust fan shall be modeled as constant horsepower reflecting constant volume stack discharge with outdoor air bypass. 

d.    Heated Only Zones

Thermal zones designed with heating only systems in the proposed design, serving storage rooms, stairwells, vestibules, electrical/mechanical rooms, and restrooms not exhausting or transferring air from mechanically cooled thermal zones in the proposed design shall use system type 9 or 10 in the baseline building design. If a space type doesn’t fall in the list of “storage, stairwells, vestibules, electrical/mechanical rooms or restrooms,” then, despite being heated only, it would be modeled as heated and cooled. This rule applies even if the total area of such zones is below 20,000 ft2.

e.    Baseline System 9, 10:

If the baseline HVAC system type is 9 or 10, all zones that are mechanically cooled in the proposed building design shall be assigned to a separate baseline system determined according to Table 3 by using the climate zone and floor area of the mechanically cooled zones. This rule applies even if the total area of such zones is below 20,000 ft2.

f.    Computer Rooms:

Standard 90.1-2019 defines computer rooms as a room whose primary function is to house equipment for the processing and storage of electronic data and that has a design electronic data equipment power density exceeding 20 W/ft2 of conditioned floor area. This exception would also apply to server closets or telecom equipment closets if these requirements are met. 

All zones with computer rooms would be modeled with systems 3 or 4 with the exception of-

i.    Computer rooms in buildings with a total computer room peak cooling load for the proposed building>3,000,000 Btu/h
ii.    Computer rooms in buildings with a total computer room peak cooling load for the proposed building >600,000 Btu/h where the baseline HVAC system type is 7 or 8.

Computer rooms meeting either of these two exceptions will use system 11 with the heating source determined by climate zone as described in footnote 2 to Table 4.

These special systems serve just the HVAC zones containing spaces that trigger the exceptions. The rest of the building/floor is served by the baseline building HVAC system as indicated in Table 3.

3.1.1.2    Process for Determining the Baseline System

This section provides guidance for determining the baseline HVAC system for a proposed design to address all requirements and exceptions specified in Section 3.1.1. 

Step 1: Determine Predominant Building Type

The building type for use in Table 3 is determined by the “predominant occupancy” type. The predominant occupancy is defined as the occupancy with the greatest conditioned floor area (CFA) and other occupancy types are defined as the “non-predominant occupancy”. The building types include:

a.    Residential
b.    Public Assembly
c.    Retail
d.    Hospital
e.    Heated-Only Storage
f.    Other Non-Residential

Once the building type is determined based on the predominant occupancy as described above, the appropriate baseline system is chosen from Table 3 based on:

a.    Number of floors (including floors above grade and below grade but not including floors solely devoted to parking).
b.    Gross conditioned floor area (CFA).
c.    Climate zone 

Step 2: Determine Non-Predominant Building Type(s)

If the CFA of a non-predominant occupancy exceeds 20,000 ft2, a separate baseline system is to be chosen from Table 3 for the non-predominant occupancy. The appropriate system for the non-predominant condition is based on the same three criteria as used for the predominant condition as they apply to the non-predominant occupancy. There could be more than one non-predominant occupancy if each exceeds 20,000 ft2. For example:

•    A building with 100,000 ft2 residential, 35,000 ft2 retail and 35,000 ft2 public assembly, would have the predominant occupancy as residential and non-predominant occupancies as retail and public assemble. The baseline systems for all 3 occupancies would be determined based on the number of floors, gross conditioned floor area and climate zone.

Step 3: Determine Other Exception Area

As described in the section above, the ‘other exception area’ will be determined in the following order:

1.    Exception (d) for heated only zones
2.    Exception (e) for baseline system 9 and 10
3.    Exception (f) for computer rooms
4.    Exception (c) for laboratory spaces
5.    Exception (b) for internal loads

Spaces qualify for additional systems if they have unusual internal loads (Section 3.1.1.1 Exception (b)), are certain laboratory spaces (Section 3.1.1.1 Exception (c)), are certain heated only spaces (Section 3.1.1.1 Exception (d)) or are cooled spaces within a heated only building using systems 9 or 10 (Section 3.1.1.1 Exception (e)). The HVAC systems used for these exception areas is determined as described in Section 3.1.1.1. 

Step 4: Calculation of number of floors for a building:

•    Calculation of number of floors based on occupancy type:

–    If a mixed occupancy building does not have enough area of each (greater than 20,000 ft2) to qualify for additional system type, all floors should be counted as the predominant type. 
–    If a mixed occupancy building has enough area of each (where area of each occupancy type is greater than 20,000 ft2) to qualify for more than one system type, then a mixed use floor should be counted in both. So, a five-story building with two floors of residential occupancy, two floors of non-residential occupancy, and one floor of both residential and non-residential occupancy would be defined as three floors of residential occupancy and three floors non-residential occupancy.

•    Calculation of number of floors for above-grade and below-grade floors:

–    Both above and below grade floors will be counted for the calculation of number of floors. 

•    Calculation of number of floors for partially conditioned floors:

–    A floor (above grade or below grade) with any conditioned area should be counted as a floor. However, floors devoted solely to parking (above grade or below grade) would not be included. For example, an unconditioned below- or above-grade parking garage where only the elevator, lobbies, or stairwells are conditioned at each floor

Other example scenarios:

•    If a building qualifies for two baseline HVAC systems in accordance with Section G3.1.1 (b) and both systems use hot-water boilers for heating; the same boiler(s) will serve both systems.

•    If a building in climate zone 2A has two floors of retail at 30,000 ft2 and 15 floors of high rise residential at 225,000 ft2 it will have two system types. System 4 (PSZ-HP) will serve the retail floors and system 2 (PTHP) will serve the residential floors. 

•    A 6 story dormitory building in climate zone 4a, includes 40,000 ft2 dorm rooms, 27,000 ft2 common spaces (corridors, lounge, library, common kitchen and dining, study rooms, etc.). 6,000 ft2 of the common spaces are storage and mechanical spaces that are heated-only. The predominant occupancy would be residential and the dorm rooms would be modeled with System 1 (PTAC). The common spaces would qualify as non-predominant non-residential (Standard 90.1-2019, Section G3.1.1b) and would be modeled with system 7 (VAV with reheat). The heated only zones will be modeled with baseline system 9.

•    A 6 story dormitory building in Climate Zone 4a, includes 19,000 ft2 dorm rooms, 23,000 ft2 common spaces (corridors, lounge, library, common kitchen and dining, study rooms, etc.). 6,000 ft2 of the common spaces are storage and mechanical spaces that are heated-only, hence the effective area for common spaces is 17,000 ft2 The predominant occupancy would be residential since the floor area of dorm rooms is more than that of the common spaces or the heated-only spaces and those would be modeled with System 1.The common spaces (excluding the heated-only areas), are less than 20,000 ft2, hence do not qualify for the occupancy exception and are modeled with system 1. The heated only zones will be modeled with baseline system 9.

•    Project is a mixed use 9 story hotel and retail in climate zone 5a. Hotel portion includes 250,000 ft2 of guest rooms, 170,000 ft2 of common spaces (corridors, reception, restaurant, etc.), and 70,000 ft2 event spaces (convention center). The two lower floors (110,000 ft2 ) are occupied by various retail tenants.

The predominant occupancy is residential and the guestrooms would be modeled with baseline system 1. The other areas (convention center, retail, and common areas) are all non-predominant conditions, each over 20,000 ft2 and thus need to be considered independently according to Standard 90.1-2019 Section G3.1.1b. The 70,000 ft2 convention center qualifies as public assembly < 120,000 ft2  and would modeled with system 3. The retail area is greater than 20,000 ft2 and would be modeled with system 4.  The remaining common spaces would qualify as non-residential more than five floors and will be modeled with baseline system 7. Based on the internal loads for the restaurant space type, it might qualify for baseline system 3 (Standard 90.1-2019, Section G3.1.1c).

3.1.1.3    Purchased Heat and Purchased Chilled Water

Purchased Heat 

For systems using purchased hot water or steam, the heating source shall be modeled as purchased hot water or steam in both the proposed and baseline building designs. Hot water or steam costs shall be based on actual utility rates, and on-site boilers, electric heat, and furnaces shall not be modeled in the baseline building design.

Purchased Chilled Water 

For systems using purchased chilled water, the cooling source shall be modeled as purchased chilled water in both the proposed and baseline building designs. Purchased chilled water costs shall be based on actual utility rates, and on-site chillers and DX equipment shall not be modeled in the baseline building design.

Baseline system requirements for proposed designs using purchased heat or chilled water for heating or cooling are mentioned in Table 8. Modeling requirements for on-site distribution pumps are documented in Section 3.8.5.

Table 8. Baseline Requirements for Purchased Heat and Purchased Chilled Water Systems

Proposed		Baseline System
Heating	Cooling
Purchased heat	Chiller or DX	The baseline heating and cooling source shall be based on the applicable cooling system as determined by Table 3 and Table 4.
Boiler/electric resistance or gas furnace	Purchased chilled water	Table 3 and Table 4 shall be used to select the baseline HVAC system type, with the following modifications: Purchased chilled water shall be substituted for the cooling source in Table 4. Systems 1 and 2 shall be constant volume fan coil units with fossil fuel boiler(s). Systems 3 and 4 shall be constant volume single zone air handlers with fossil fuel furnace(s). Refer to Section 3.7.6 of this document for details. System 7 shall be used in place of System 5. Refer to Section 3.8.1 of this document for details. System 8 shall be used in place of System 6. Refer to Section 3.8.2 of this document for details.
Purchased heat	Purchased chilled water	Table 3 and Table 4 shall be used to determine the baseline HVAC system type, with the following modifications: Purchased heat and purchased chilled water shall be substituted for the heating types and cooling types in Table 4. System 1 will be constant volume fan coil units. Refer to Section 3.7.5.5 of this document for details on this system type. System 3 will be a constant volume single zone air handler. Refer to Section 3.7.5.2 of this document for details. System 7 will be used in place of System 5. Refer to Section 3.8.2 of this document for details.

3.1.2    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 its geometry, thermal performance, etc. Each building descriptor contains the following information.