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  5. 3.1.1 Standard 90.1 Section G3.2 HVAC System Map

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).

G3.2 New Construction/Major Alterations

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 the combined gross conditioned and semi-heated floor area for each of the following building area types in the proposed design:

  1. Residential and residential associated zones
  2. Public Assembly
  3. Heated-Only Storage
  4. Retail
  5. Hospital
  6. Other Non-Residential

Step 2: Determine Predominant Nonresidential Building Area Type

Classify the nonresidential building area type with the largest combined area determined in step 1 as the predominant nonresidential building area type. Add the combined area of any remaining nonresidential building area types with less than 20,000 ft2 to the combined area of the predominant nonresidential building area type.

Step 3: Select Baseline HVAC System Types

Select a baseline HVAC system type from Table 3, HVAC System Map, for each of the following building area types included in the proposed:

  1. Residential + residential associated
  2. Predominant nonresidential
  3. Each additional nonresidential building area type with more than 20,000 ft2 of combined area based on 90.1 G3.2.1.1.

For the purposes of selecting baseline HVAC system types from Table 3, HVAC System Map, the total number of stories (i.e., floors) in a building, includes above-grade and below-grade stories but does not include stories solely devoted to parking. A floor (above grade or below grade) with any conditioned area should be counted as a floor.

Step 4: Adjust Baseline HVAC System Types based on other Rules in 90.1 G3.2.1.2

As described in Section 3.1.1.1 above, the adjustments will be determined following order in 90.1 G3.2.1.2 shown below:

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

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

Example scenarios:

  • If a building qualifies for two baseline HVAC systems in accordance with Section G3.2.1 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 three system types. System 4 (PSZ-HP) will serve the residential associated zones on the residential floors, system 2 (PTHP) will serve the dwelling units on the residential floors, and System 8 (VAV with PFP boxes) will serve the retail floors since the number of stories in the building is greater than 5 stories.
  • A 6 story dormitory building in climate zone 4a, includes 40,000 ft2 of dorm rooms with 27,000 ft2 of common spaces (corridors, lounge, library, common kitchen and dining, study rooms, etc.). The common space HVAC zones comprise more than 32 percent of the gross conditioned floor area on each floor of the building. 6,000 ft2 of the common spaces are storage and mechanical spaces that are heated-only. The dorm rooms, which are classed as residential building area type, would be modeled with System 1 (PTAC). The common areas constitute over 32% of the gross conditioned floor area on each level, which means that that the dormitory room floor area (i.e., the residential gross conditioned floor area) does not exceed 75% of the total gross conditioned floor area on each floor. As a result, these common area HVAC zones fall under the category of nonresidential building area, as opposed to being classed as residential-associated HVAC zones and would be modeled with system 7 (VAV with reheat) because the building is greater than 5 stories. The heated only zones will be modeled with baseline system 9 (90.1 G3.2.1.2 (c)).
  • A 6 story dormitory building in Climate Zone 4a, includes 140,000 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 common space HVAC zones comprise less than 20 percent of the gross conditioned floor area on each floor of the building. The dorm rooms, which are classed as residential building area type, would be modeled with System 1 (PTAC). The common areas constitute less than 20% of the gross conditioned floor area on each level, which means that that the dormitory room floor area (i.e., the residential gross conditioned floor area) exceeds 75% of the total gross conditioned floor area on each floor. As a result, these common area HVAC zones fall under the category of residential-associated HVAC zones, as opposed to being classed nonresidential building area, and would be modeled with system 3 (PSZ AC) per 90.1 G3.2.1.2 (f). The heated only zones will be modeled with baseline system 9 (90.1 G3.2.1.2 (c)).
  • Project is a mixed use 9 story hotel and retail in climate zone 5a (each floor includes 55,000 ft2 of gross conditioned floor area). The hotel portion includes 264,000 ft2 of guest rooms, 99,000 ft2 of common spaces (corridors, reception, restaurant, etc.), and 22,000 ft2 of event spaces (convention center). On floors 5-9 the hotel rooms comprise 80% of the gross conditioned floor area. On floor 4 hotels rooms comprise 50% of the gross conditioned floor area with common space occupying the remainder. On floor 3 hotels rooms and common areas each comprise 30% of the gross conditioned floor area with the convention center occupying the remaining gross conditioned floor area. The two lower floors (110,000 ft2 ) are occupied by various retail tenants.

The first step is to determine the combined gross conditioned floor area and semiheated floor area for residential, other nonresidential, retail, public assembly, and heated-only storage building area types in the proposed design (hospital is not relevant for this building).

  1. Residential = 264,000 ft2 + residential associated HVAC zones (55,000 ft2/floor * 20% * 5 stories) = 319,000 ft2
  2. Public assembly = 22,000 ft2
  3. Retail = 0 ft2 (this is because the building is more than two stories and so the retail building area is required to be classed as other nonresidential instead of retail)
  4. Heat-only storage = 0 ft2 (none was mentioned in the building description)
  5. Other nonresidential = 110,000 ft2 (retail floors) + (55,000 ft2/floor * 50% * 1 story) + (55,000 ft2/floor * 30% * 1 story) = 154,000 ft2

Next identify the predominant nonresidential building area type which is “Other nonresidential”. The public assembly combined area is 20,000 ft2 or greater so its building area does not get absorbed into “Other nonresidential” building area type.

Next select the baseline HVAC system types. The following are the baseline HVAC system type selections.

  1. Residential – System 1 (PTAC)
  2. Public assembly – System 3 (PSZ-AC)
  3. Other nonresidential - system 7 (VAV with reheat)

Lastly, apply any adjustments to the baseline HVAC system types. Based on the internal loads for the restaurant space type, it might qualify for baseline system 3 (Standard 90.1-2022, Section G3.2.1.2a).