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Passive Survivability and Back-up Power During Disruptions

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Pilot-Credits IPpc100: Passive Survivability and Functionality During Emergencies 1 point

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© Copyright U.S. Green Building Council, Inc. All rights reserved.

Intent

Option 1: To ensure that buildings will maintain safe thermal conditions in the event of an extended power outage or loss of heating fuel, or provide backup power to satisfy critical loads.

Option 2: The electricity needed by a building to maintain a reasonable level of functionality during an extended power outage will vary greatly, depending on building function.

Context:

For many reasons, buildings are likely to become more vulnerable to extended power outages in the years and decades ahead. Climate change is projected to cause a wide range of impacts, including more intense storms, sea level rise, drought, wildfire, and heat waves. Any of these disturbances can result in extended power outages. Other, non-climate-related disturbances, including earthquakes, Tsunamis, and human actions, such as terrorism and cyber-terrorism, can also result in power outages and interruptions in heating fuel.

For these reasons, there is growing interest in ensuring that our buildings will keep occupants safe and provide a reasonable level of functionality during extended power outages or loss of heating fuel. This credit addresses these needs by focusing on passive design strategies for buildings that will ensure that reasonably safe thermal conditions will be maintained passively in the event of lost power or heating fuel.

For certain building types, such as hospitals and nursing homes, code requirements for habitability may require backup power systems; providing for passive survivability will not be adequate to maintain legally required conditions.

Requirements

Option 1: Provide for Passive Survivability (thermal safety) (1 point)

Demonstrate through thermal modeling or Passive House certification that a building will passively maintain thermally safe conditions during a power outage that lasts four days during peak summertime and wintertime conditions of a typical meteorological year. This performance will be achieved through a combination of design measures that could include careful building orientation, a highly insulated building envelope, natural ventilation, cooling-load-avoidance measures, passive solar heating, and integration of thermal mass. The precise systems and designs employed to achieve passive survivability are not specified; the required performance is demonstrated through thermal modeling. Any of three compliance paths may be used to demonstrate compliance with these requirements.

Note that some buildings are required by code to provide thermal conditions that may not be achievable through passive means. Most nursing homes, for example, must not fall below 71°F (22°C) in the wintertime, or exceed 81°F (27°C) during the summer. Backup power may be required to maintain these conditions. Such buildings could still be designed to achieve passive survivability as defined herein, but such buildings would also need to rely on backup power to achieve those code-mandated comfort conditions.

Three thermal safety compliance paths exist:

  • Path 1: Psychrometry

    Using the Center for the Built Environment (CBE) Comfort Tool’s psychrometric chart, demonstrate that indoor conditions (dry-bulb air temperature and humidity) never breach the specified overheating and under-heating thresholds, which include Heat Index and / or WBGT (wet-bulb globe temperature) during the peak summer and winter analysis periods (see Documentation for Heat Index and WBGT threshold values and requirements).

      Use either:
    • Heat Index (U.S. NOAA and OSHA Heat Advisory Levels)

      During hot-season periods of utility-grid power outages or heating fuel interruptions, provide operable windows and/or non-powered natural ventilation and passive cooling to maintain indoor temperatures at or below Heat Index calibrated temperatures identified in the Thermal Modeling Table 1.0. In cold seasons provide passive heating and/or heat retention strategies to maintain interior building temperatures as identified in Thermal Modeling Table 2.0. located in the Appendix Requirements.

    • OR

    • Wet Blub Globe Temperature

      Using the Center for the Built Environment (CBE) Comfort Tool’s psychrometric chart or USGBC approved local equivalent, demonstrate that indoor conditions never breach the specified overheating and under-heating WBGT (wet-bulb globe temperature) thresholds identified in the Thermal Modeling Table 2.0 located in the Appendix Requirements.

  • OR

  • Path 2: Standard Effective Temperature (SET)

    Limit deviations from the defined livable Standard Effective Temperature (SET) thresholds (see Definitions) to the specified number of degree-days (degree-hours) during the peak summer and winter analysis periods (see Documentation for threshold values and degree day requirements, or meet requirements of local code, whichever is more stringent).

  • OR

  • Path 3: Passive House certification

    Using either Passive House Institute U.S. (PHIUS) or Passive House Institute standards and methodologies, confirm the project has earned the relevant Passive House certification AND includes operable windows or other means of natural ventilation to meet the requirements in Table 3. The very high standards for energy performance with Passive House is an adequate indicator that the building will maintain passive survivability as described in this credit.

Standards applicable to all three compliance paths:

Thermal Safety Zones:
The design team may designate which zones are considered thermal safety zones during the power outage. The total population in all thermally safe zones must be equal to or greater than the normal building occupancy.

Occupant Density:
Thermal Safety zones shall be modeled with the occupant density necessary to accommodate the total building population in the thermally safe zones. The zone occupant density shall be no greater than one person per 20 ft² (1.9 m).

Ventilation:
All habitable zones must have access to natural ventilation. Windows, doors, panels, and louvers are all acceptable.
Refer to Analysis Table 3.0 Passive Ventilation for more information on Passive Ventilation

AND / OR

Option 2: Provide Backup Power for critical loads (1 point)

Demonstrate that adequate emergency power will be available to provide for critical loads that have been identified by the design team as being necessary for the building.

These critical loads will differ by project. Satisfy at least one of the following compliance paths:

  • Compliance Path One:

    Meet the Thermal Safety criteria of Option 1. above using back-up power or a combination of back-up power and passive strategies

  • AND/OR

  • Compliance Path Two:

    Provide electricity for at least three (3) or more of the following power demands:

    • Operation of electrical components of fuel-fired heating systems.
    • Operation of a fan sufficient to provide emergency cooling if mechanical air conditioning equipment cannot operate (could be ceiling fans, plug-in window fans, or fans integral with central air distribution).
    • Operation of water pumps if needed to make potable water available to occupants (if pumps are required for distribution of water within the building).
    • Lighting level a minimum of three (3) foot candles (32 lux) in all building spaces to define a path of egress to all required exits and to a distance of 10 feet (3 m) on the building exterior.
    • One location for every 500 square feet (46 m) that provides a minimum of 30 foot candles (320 lux) measured 30” (76 cm) above the floor.
    • At least one functioning electrical receptacle per 250 square feet (23 m2) of occupied space.
    • Operation of cable modem and wireless router or other means of providing online access within the building.
    • Operation of one elevator in building in hospitals (or in other buildings as per local code).

>Duration over which backup power must be provided:
Backup power time durations for thermal safety and / or critical functions are identified in the Table 1. Meet the below requirements or meet requirements of local code, whichever is more stringent.

Back-Up Power Time Duration Table 1.

Facility Type Time Duration for Back-up Power
Baseline Facilities
Residential Buildings, lodging, hospitals, nursing homes,
emergency shelters and emergency facilities: fire stations,
911 call centers, police stations and similar.
Four (4) Consecutive days, 24 hours per day.
Fundamental Community Service Organizations
Pharmacies, convenience stores, grocery stores and
facilities with significant stocks of refrigerated or
frozen food and ATMs* (Automated Teller Machines) at these
facilities
Four (4) Consecutive days, eight (8) hours each day during
daylight hours for general operations. Refrigeration and
freezers, four (4) consecutive days, 24 hours per day.
Gas Stations Four(4) Consecutive days, 12-hour each day (or until fuel
stocks are exhausted), primarily during daylight hours.
Backup power or built-in hand pumps for fuel distribution.
*ATM’s at banks, credit unions and other similar facilities
such as malls
Powered during regular business hours.
Solar and Wind Electric Back-up Power Systems with
Energy Storage
For all facilities identified above, except hospitals,
nursing homes and emergency facilities.
One-half (1/2) of the duration of backup power as
identified as described above (excluding elevators) for
solar or wind electric systems and battery storage. Gas
stations must have built-in hand pumps for fuel
distribution.

Cleaner burning fuels include natural gas (if allowed by local code)

See Requirements Appendix on Resources Tab for more information.

Documentation

General
Register for the pilot credit

Participate in the LEEDuser pilot credit forum http://www.leeduser.com/pilot
Complete the feedback survey:

Pilot Credit Survey

Credit Speciic
Documentation Passive Survivability/Thermal Safety
  • Path 1: Psychrometry and Heat Index

    Provide graphic comparison of all indoor hourly conditions during cooling analysis period in relation to either the appropriate WBGT or the Heat Index threshold. Whole building energy modeling hourly output data for indoor dry-bulb temperature (DBT) and Relative Humidity (RH) shall be inputted into the provided Comma Separated Value File (CSV) which contains DBT and RH values for the WBGT and Heat Index thresholds; model output data shall be inputted below the existing DBT and RH values listed in the CSV file. The resulting composite CSV file shall be uploaded to the CBE Comfort Tool (http://comfort.cbe.berkeley.edu/upload) in order to graphically illustrate compliance via the CBE comfort tool Psychrometric Chart function for either I-P or SI values; capture the resulting CBE comfort tool image and include it with the credit documentation.
    Alternatively, teams may calculate the peak indoor WBGT or Heat Index values for the simulation period, and minimum DBT, and compare them to the corresponding threshold values.

  • Path 2: SET
    • Building plans demarcating Thermal Safety Zones
      Calculation of maximum available natural ventilation rate, minimum required ventilation rate and emergency occupancy for each thermal safety zone.
      Summary of calculated °F SET-hours for heating and cooling for each representative thermal safety zone.
    • Emergency Operation Plan. Explain how the building should be operated in the case of emergency in order to provide livable thermal conditions. Explain the rationale behind vent operation that was modeled given likely outside temperature and humidity.
    • Thermal Habitability - Definitions and Methodology: Thermal Habitability: 100% of the normal building occupancy can occupy thermal safety zones that maintain “livable temperatures” during a power outage for durations as presented.
    • SET: Livable temperatures are defined using standard effective temperature (SET) as the metric. SET factors in relative humidity and mean radiant temperature and is a more relevant metric than dry-bulb temperature for defining livable conditions in buildings that lose power or fuel for space-conditioning systems. The influence of air temperature (dry-bulb temperature) and relative humidity on the SET can be seen in the CBE Thermal Comfort Tool from the Center for the Built Environment at UC Berkeley.
    • SET: defined in ASHRAE 55 as:
      The temperature of an imaginary environment at 50% rh, <0.1 m/s (20 fpm) average air speed (v_a), and t_mrt = t_a, in which the total heat loss from the skin of an imaginary occupant with an activity level of 1.0 met and a clothing level of 0.6 clo is the same as that from a person in the actual environment, with actual clothing and activity level.
Documentation Passive Back-up Power

As part of the credit submission, a list of critical loads being served by the backup power system must be provided. This list will vary by the building type and specific circumstances, and for most building projects, provide calculations for KWH electricity demand based on the critical loads being served based on duration. Provide calculations for fuel or battery storage and estimated run-time durations based on the calculated loads. Provide drawings showing back-up power equipment along with product data sheets that clearly indicate power production capacity.

See all forum discussions about this credit »

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Our tab contains overall cost guidance, notes on what “soft costs” to expect, and a strategy-by-strategy breakdown of what to consider and what it might cost, in percentage premiums, actual costs, or both.

This information is also available in a full PDF download in The Cost of LEED v4 report.

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Documentation toolkit

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USGBC logo

© Copyright U.S. Green Building Council, Inc. All rights reserved.

Intent

Option 1: To ensure that buildings will maintain safe thermal conditions in the event of an extended power outage or loss of heating fuel, or provide backup power to satisfy critical loads.

Option 2: The electricity needed by a building to maintain a reasonable level of functionality during an extended power outage will vary greatly, depending on building function.

Context:

For many reasons, buildings are likely to become more vulnerable to extended power outages in the years and decades ahead. Climate change is projected to cause a wide range of impacts, including more intense storms, sea level rise, drought, wildfire, and heat waves. Any of these disturbances can result in extended power outages. Other, non-climate-related disturbances, including earthquakes, Tsunamis, and human actions, such as terrorism and cyber-terrorism, can also result in power outages and interruptions in heating fuel.

For these reasons, there is growing interest in ensuring that our buildings will keep occupants safe and provide a reasonable level of functionality during extended power outages or loss of heating fuel. This credit addresses these needs by focusing on passive design strategies for buildings that will ensure that reasonably safe thermal conditions will be maintained passively in the event of lost power or heating fuel.

For certain building types, such as hospitals and nursing homes, code requirements for habitability may require backup power systems; providing for passive survivability will not be adequate to maintain legally required conditions.

Requirements

Option 1: Provide for Passive Survivability (thermal safety) (1 point)

Demonstrate through thermal modeling or Passive House certification that a building will passively maintain thermally safe conditions during a power outage that lasts four days during peak summertime and wintertime conditions of a typical meteorological year. This performance will be achieved through a combination of design measures that could include careful building orientation, a highly insulated building envelope, natural ventilation, cooling-load-avoidance measures, passive solar heating, and integration of thermal mass. The precise systems and designs employed to achieve passive survivability are not specified; the required performance is demonstrated through thermal modeling. Any of three compliance paths may be used to demonstrate compliance with these requirements.

Note that some buildings are required by code to provide thermal conditions that may not be achievable through passive means. Most nursing homes, for example, must not fall below 71°F (22°C) in the wintertime, or exceed 81°F (27°C) during the summer. Backup power may be required to maintain these conditions. Such buildings could still be designed to achieve passive survivability as defined herein, but such buildings would also need to rely on backup power to achieve those code-mandated comfort conditions.

Three thermal safety compliance paths exist:

  • Path 1: Psychrometry

    Using the Center for the Built Environment (CBE) Comfort Tool’s psychrometric chart, demonstrate that indoor conditions (dry-bulb air temperature and humidity) never breach the specified overheating and under-heating thresholds, which include Heat Index and / or WBGT (wet-bulb globe temperature) during the peak summer and winter analysis periods (see Documentation for Heat Index and WBGT threshold values and requirements).

      Use either:
    • Heat Index (U.S. NOAA and OSHA Heat Advisory Levels)

      During hot-season periods of utility-grid power outages or heating fuel interruptions, provide operable windows and/or non-powered natural ventilation and passive cooling to maintain indoor temperatures at or below Heat Index calibrated temperatures identified in the Thermal Modeling Table 1.0. In cold seasons provide passive heating and/or heat retention strategies to maintain interior building temperatures as identified in Thermal Modeling Table 2.0. located in the Appendix Requirements.

    • OR

    • Wet Blub Globe Temperature

      Using the Center for the Built Environment (CBE) Comfort Tool’s psychrometric chart or USGBC approved local equivalent, demonstrate that indoor conditions never breach the specified overheating and under-heating WBGT (wet-bulb globe temperature) thresholds identified in the Thermal Modeling Table 2.0 located in the Appendix Requirements.

  • OR

  • Path 2: Standard Effective Temperature (SET)

    Limit deviations from the defined livable Standard Effective Temperature (SET) thresholds (see Definitions) to the specified number of degree-days (degree-hours) during the peak summer and winter analysis periods (see Documentation for threshold values and degree day requirements, or meet requirements of local code, whichever is more stringent).

  • OR

  • Path 3: Passive House certification

    Using either Passive House Institute U.S. (PHIUS) or Passive House Institute standards and methodologies, confirm the project has earned the relevant Passive House certification AND includes operable windows or other means of natural ventilation to meet the requirements in Table 3. The very high standards for energy performance with Passive House is an adequate indicator that the building will maintain passive survivability as described in this credit.

Standards applicable to all three compliance paths:

Thermal Safety Zones:
The design team may designate which zones are considered thermal safety zones during the power outage. The total population in all thermally safe zones must be equal to or greater than the normal building occupancy.

Occupant Density:
Thermal Safety zones shall be modeled with the occupant density necessary to accommodate the total building population in the thermally safe zones. The zone occupant density shall be no greater than one person per 20 ft² (1.9 m).

Ventilation:
All habitable zones must have access to natural ventilation. Windows, doors, panels, and louvers are all acceptable.
Refer to Analysis Table 3.0 Passive Ventilation for more information on Passive Ventilation

AND / OR

Option 2: Provide Backup Power for critical loads (1 point)

Demonstrate that adequate emergency power will be available to provide for critical loads that have been identified by the design team as being necessary for the building.

These critical loads will differ by project. Satisfy at least one of the following compliance paths:

  • Compliance Path One:

    Meet the Thermal Safety criteria of Option 1. above using back-up power or a combination of back-up power and passive strategies

  • AND/OR

  • Compliance Path Two:

    Provide electricity for at least three (3) or more of the following power demands:

    • Operation of electrical components of fuel-fired heating systems.
    • Operation of a fan sufficient to provide emergency cooling if mechanical air conditioning equipment cannot operate (could be ceiling fans, plug-in window fans, or fans integral with central air distribution).
    • Operation of water pumps if needed to make potable water available to occupants (if pumps are required for distribution of water within the building).
    • Lighting level a minimum of three (3) foot candles (32 lux) in all building spaces to define a path of egress to all required exits and to a distance of 10 feet (3 m) on the building exterior.
    • One location for every 500 square feet (46 m) that provides a minimum of 30 foot candles (320 lux) measured 30” (76 cm) above the floor.
    • At least one functioning electrical receptacle per 250 square feet (23 m2) of occupied space.
    • Operation of cable modem and wireless router or other means of providing online access within the building.
    • Operation of one elevator in building in hospitals (or in other buildings as per local code).

>Duration over which backup power must be provided:
Backup power time durations for thermal safety and / or critical functions are identified in the Table 1. Meet the below requirements or meet requirements of local code, whichever is more stringent.

Back-Up Power Time Duration Table 1.

Facility Type Time Duration for Back-up Power
Baseline Facilities
Residential Buildings, lodging, hospitals, nursing homes,
emergency shelters and emergency facilities: fire stations,
911 call centers, police stations and similar.
Four (4) Consecutive days, 24 hours per day.
Fundamental Community Service Organizations
Pharmacies, convenience stores, grocery stores and
facilities with significant stocks of refrigerated or
frozen food and ATMs* (Automated Teller Machines) at these
facilities
Four (4) Consecutive days, eight (8) hours each day during
daylight hours for general operations. Refrigeration and
freezers, four (4) consecutive days, 24 hours per day.
Gas Stations Four(4) Consecutive days, 12-hour each day (or until fuel
stocks are exhausted), primarily during daylight hours.
Backup power or built-in hand pumps for fuel distribution.
*ATM’s at banks, credit unions and other similar facilities
such as malls
Powered during regular business hours.
Solar and Wind Electric Back-up Power Systems with
Energy Storage
For all facilities identified above, except hospitals,
nursing homes and emergency facilities.
One-half (1/2) of the duration of backup power as
identified as described above (excluding elevators) for
solar or wind electric systems and battery storage. Gas
stations must have built-in hand pumps for fuel
distribution.

Cleaner burning fuels include natural gas (if allowed by local code)

See Requirements Appendix on Resources Tab for more information.

Documentation

General
Register for the pilot credit

Participate in the LEEDuser pilot credit forum http://www.leeduser.com/pilot
Complete the feedback survey:

Pilot Credit Survey

Credit Speciic
Documentation Passive Survivability/Thermal Safety
  • Path 1: Psychrometry and Heat Index

    Provide graphic comparison of all indoor hourly conditions during cooling analysis period in relation to either the appropriate WBGT or the Heat Index threshold. Whole building energy modeling hourly output data for indoor dry-bulb temperature (DBT) and Relative Humidity (RH) shall be inputted into the provided Comma Separated Value File (CSV) which contains DBT and RH values for the WBGT and Heat Index thresholds; model output data shall be inputted below the existing DBT and RH values listed in the CSV file. The resulting composite CSV file shall be uploaded to the CBE Comfort Tool (http://comfort.cbe.berkeley.edu/upload) in order to graphically illustrate compliance via the CBE comfort tool Psychrometric Chart function for either I-P or SI values; capture the resulting CBE comfort tool image and include it with the credit documentation.
    Alternatively, teams may calculate the peak indoor WBGT or Heat Index values for the simulation period, and minimum DBT, and compare them to the corresponding threshold values.

  • Path 2: SET
    • Building plans demarcating Thermal Safety Zones
      Calculation of maximum available natural ventilation rate, minimum required ventilation rate and emergency occupancy for each thermal safety zone.
      Summary of calculated °F SET-hours for heating and cooling for each representative thermal safety zone.
    • Emergency Operation Plan. Explain how the building should be operated in the case of emergency in order to provide livable thermal conditions. Explain the rationale behind vent operation that was modeled given likely outside temperature and humidity.
    • Thermal Habitability - Definitions and Methodology: Thermal Habitability: 100% of the normal building occupancy can occupy thermal safety zones that maintain “livable temperatures” during a power outage for durations as presented.
    • SET: Livable temperatures are defined using standard effective temperature (SET) as the metric. SET factors in relative humidity and mean radiant temperature and is a more relevant metric than dry-bulb temperature for defining livable conditions in buildings that lose power or fuel for space-conditioning systems. The influence of air temperature (dry-bulb temperature) and relative humidity on the SET can be seen in the CBE Thermal Comfort Tool from the Center for the Built Environment at UC Berkeley.
    • SET: defined in ASHRAE 55 as:
      The temperature of an imaginary environment at 50% rh, <0.1 m/s (20 fpm) average air speed (v_a), and t_mrt = t_a, in which the total heat loss from the skin of an imaginary occupant with an activity level of 1.0 met and a clothing level of 0.6 clo is the same as that from a person in the actual environment, with actual clothing and activity level.
Documentation Passive Back-up Power

As part of the credit submission, a list of critical loads being served by the backup power system must be provided. This list will vary by the building type and specific circumstances, and for most building projects, provide calculations for KWH electricity demand based on the critical loads being served based on duration. Provide calculations for fuel or battery storage and estimated run-time durations based on the calculated loads. Provide drawings showing back-up power equipment along with product data sheets that clearly indicate power production capacity.

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