scope:

Foreword

Thermal energy systems resilience is especially important in extreme climates. While metrics and requirements for availability, reliability, and quality of power systems have been established (DoD 2020), similar metrics and requirements for thermal energy systems are not well understood despite a clear need in earth's cold regions.

Thermal energy systems addressed by this Guide consist of both the demand and supply side. The demand side is comprised of active and passive systems including thermal demand by the process; heating, ventilating, and air-conditioning (HVAC) systems maintaining required environmental conditions for the building's operations and comfort for people; and a shelter/building that houses them. The supply side includes energy conversion, distribution, and storage system components. Requirements to maintain thermal/environmental conditions in the building (or in a part of the building) needed for housing critical mission-related processes and for occupants include criteria to maintain thermal comfort and health, to support process needs, and to prevent mold, mildew, and other conditions that can damage building materials or furnishings.

In one of the first-of-its-kind attempts to address a deficiency in our ability to monitor and model thermal decay in cold environments, a thermal decay test (TDT) was envisioned, developed, and conducted by a team of Engineer Research and Development Center (ERDC) researchers with collaborators from the University of Alaska, Fort Wainwright, Fort Greely, and Alaska Thermal Imaging, LLC to better understand the level of reliability required for energy supply systems that can support environmental conditions required for the facility's mission, comfort of people, and sustainment of a building in arctic environments under predominant threat scenarios. The TDT included testing the reliability of the thermal systems in real time under actual extreme conditions (in extreme temperatures, down to -40 °F (-40 °C) and high winds up to 62 mph (100 kmph), summer and winter air leakage tests, and the build out of a model to better forecast future cases and vulnerable failure mechanisms. Based on field studies, a reliable building model has been developed to identify the maximum allowable time available to correct any problems with energy supply to mission critical facilities for different facility archetypes (building mass and insulation characteristics) and air leakage rates before the indoor air temperature reaches habitability or sustainability thresholds.

During an emergency (black sky) situation, requirements of thermal parameters for different categories of buildings or even parts of the building may change. When normal heating, cooling, and humidity control systems operation is limited or not available, mission critical areas can be conditioned to the level of thermal parameters required for supporting agility of personnel performing mission critical operation, but not to the level of their optimal comfort conditions. Beyond these threshold (habitable) levels, effective execution of a critical mission is not possible and mission operators have to be moved into a different location. The Guide establishes these threshold limits of thermal parameters that may be in a broader range compared to that required for thermal comfort, but not to exceed levels of cold stress thresholds: in a heating mode, air temperature in spaces with mission critical operations should be maintained above 60.8 °F (16 °C) (ACGIH 2018).

Prescriptive guidelines for thermal insulation in the design of buildings in cold climates have traditionally been derived by a holistic consideration of climatic factors, energy policy, environmental policy, and economics. The differences in thermal barrier requirements in buildings across the Arctic and Subarctic regions of the world are as influenced by the differing priorities of the governing bodies that set these requirements as they are on actual physical demands and conditions. Usually, national requirements for building envelope characteristics, e.g., thermal insulation values of its components, building envelope air tightness, vapor permeability, building mass, detailing, etc., are based on economic and environmental considerations. Thermal energy system resilience consideration brings another dimension to the optimization process of these parameters. This Guide summarizes best practice requirements to the building envelope characteristics for buildings located in cold and arctic climates of the United States, Canada, and Scandinavian countries and compares the effect of different levels of building envelope efficiency and mass on indoor air temperature decay when heat supply is interrupted.

Arctic climates provide unique challenges for designers of HVAC, plumbing, and thermal energy systems. The importance of considering the operation outside air temperatures, system reliability, and building resiliency cannot be understated. This Guide describes best practice examples of robust and reliable systems with the emphasis on their redundancy, durability, and functionality. It also discusses the most common heating system and ventilation system approaches used in arctic climate and emphasizes the importance of a maintenance program that allows building operators to successfully troubleshoot and maintain buildings in the arctic. Concepts are illustrated by several best practice examples, e.g., U.S. military bases in Alaska and Søndre Strømfjord and the international airport of Greenland that previously was used as a U.S. military base.

This Guide is designed for energy systems designers, architects, energy managers and building operators and is a valuable resource for those who are involved in building planning and operation in cold and arctic climates. This Guide, with its focus on resilience of thermal energy systems, is meant to complement the ASHRAE Cold-Climate Buildings Design Guide, Second Edition (ASHRAE 2021).