key: cord-0934896-o3fqxc8w authors: Cortiços, Nuno D.; Duarte, Carlos C. title: COVID-19: the impact in US high-rise office buildings energy efficiency date: 2021-06-15 journal: Energy Build DOI: 10.1016/j.enbuild.2021.111180 sha: 074db8c26034254d0da90687743bafe68144db3d doc_id: 934896 cord_uid: o3fqxc8w The COVID-19 pandemic, through governmental stay-at-home orders, forced rapid changes to social human behavior and interrelations, targeting the work environments to protect workers and users. Rapidly, global organizations, US associations, and professionals stepped in to mitigate the virus's spread in buildings' living and work environments. The institutions proposed new air system HVAC settings without efficiency concerns, such as improved flow rates and filtering for irradiation, humidity, and temperature. Current literature consensually predicted an increase in energy consumption due to new measures to control the SARS-CoV-2 spread. The research team assumed the effort of validating the prior published outcomes, applied to US standardized high-rise office buildings, as defined and set by the key entities in the field, by resorting to a methodology based on software energy analysis. The study compares a standard high-rise office building energy consumption, and CO2 emissions and operations costs in nine US climate zones — from 0 to 8, south to north latitudes, respectively —, assessed in specifically the most populated cities, between the previous and post COVID-19 scenarios. The outcomes clarify the gathered knowledge, explaining that climate zones above mixed-humid type (4) tend to increase relative energy use intensity by 21.72%, but below that threshold the zones decrease relative energy use intensity by 11.92%. It remains unclear the impact in buildings energy consumptions and CO 2 emissions induced by the COVID-19 pandemic mitigation guidelines, despite some authors empirical assumptions (ASHRAE, 2020-1; ASHRAE, 2020-2; Taylor Engineering, 2020; Nadel, 2020, REHVA, 2020; Cutler & Summers, 2020). Unable to telework and did not telework Unable to telework and did telework Able to telework and did not telework Able to telework and did telework The SARS-CoV-2 virus acts similarly to regular flu. When individuals with the COVID-19 disease touch surfaces, cough, or exhale, they release droplets of infected fluid and spread the virus. The risk is alarming by only touching contaminated surfaces and then the face, nose, eyes, mouth, or merely breathing the surrounding air in a two-meter range or higher, depending on the exhalation pressure. Situations are particularly distressing in indoor climatecontrolled environments, especially when malfunctioning or inadequately preset ventilation systems favor the virus's survival for extended periods in surfaces (Santarpia et al., 2020) . The severity of the infection tends to be mild in individuals under 40 years of age; above that or weakened immune systems can lead to a severe illness or even death (WHO 2020-1). Since the beginning of the pandemic, several institutions start developing a set of guidelines to mitigate the virus spread and transmissibility to build readiness for the economy reopening. The research address the Worldwide and US entities in charge of this recommendations with focus on work environments and office buildings: The following table sums up the measures recommended by the previous mentioned institutions on COVID-19 pandemic mitigation; see Table 1 . Measures and recommendations References -Decrease building occupancy on working hours; -Request social distance; (WHO, 2020-3, 2021) (CDC, 2020-1) (OSHA, 2020-1, 2020-2) (AIHA, 2020) (ASHRAE; 2020-1, 2020-5) (CDC, 2020-1) (OSHA, 2020-1) (AIHA, 2020) -Limit meetings to 10 people; (AIHA, 2020) -Increase the percentual rate of outdoor air; -Increase the airflow rate in indoor occupied spaces; -Higher ventilation rates; (WHO, 2020-2, 2020-4, 2021) (CDC, 2020-1, 2020-2) (OSHA, 2020-1) (AIHA, 2020) (ASHRAE; 2020-1, 2020-2, 2020-3, 2020-4, 2020-5) -Set a two-hours outdoor air flush at maximum rate pre-and-post occupancy schedule (3 air changes of space volume); (WHO, 2020-2, 2021) (CDC, 2020-2) (ASHRAE; 2020-1, 2020-2) -Increase of ventilation, at maximization outdoor air rate, from 20% to 90% under BACS allowance, or even 100%, if under higher risk of SARS-CoV-2 dissemination; (ASHRAE; 2020-1, 2020-2) -Set the outdoor air rate per person to 10 l/s; (WHO, 2021) -Open doors and windows to promote natural ventilation; (WHO, 2020-3, 2021) (CDC, 2020-2) (ASHRAE; 2020-3, 2020-4) -Decrease indoor air recirculation to bare minimum; (WHO, 2020-4, 2021) (CDC, 2020-1) (ASHRAE; 2020-1) -Control cross air movements to avoid airflows between workers and visitors; (WHO, 2020-2) (AIHA, 2020) (ASHRAE; 2020-3) -Adjust airflow and space pressure to avoid aerosols transport; (CDC, 2020-2) -Preset the air flush in restroom facilities at full capacity during occupancy periods; (WHO, 2020-2) -Keep a working temperature set between 23.8 ºC and 26.9 ºC for cooling during the warmer weather; (a) -Keep the indoor relative humidity value set between 50% and 60%; (GHHIN, 2020) -Keep the indoor relative humidity value set between 40% and 60%; -In buildings without BACS, keep heating at 65ºF under a relative humidity at 40%, and cooling at 80 ºF with a relative humidity at 60%; (ASHRAE; 2020-1, 2020-2, 2020-3) -Relax temperature and humidity set points to reduce energy consumption and cost during vacancy periods; -In non-working hours keep the BACS system running under the minimum adjustments to improve the energy efficiency, lower heating (<5ºF) and increase cooling (>5ºF), maintaining the relative humidity in the first and slightly rise it in the second (>5%); (ASHRAE; 2020-1) -Building Automation and Control System (BACS) upgrade and optimization; (AIHA, 2020) (ASHRAE; 2020-1, 2020-2) -Set BACS to operate through remote and security control, hiring diagrams, services contracts and maintenance logs, BACS trend reports, alerts, and notifications; (ASHRAE; 2020-1, 2020-2) -Disable demand-controlled ventilation (DCV) based on temperature; (CDC, 2020-1) (WHO, 2020-2) (ASHRAE; 2020-4, 2020-5) HVAC and SHW systems -Push for 24/7 air changes to for assure the best indoor air quality (if possible); (CDC, 2020-1) (ASHRAE; 2020-1, 2020-5) -Push for the ventilation system readiness and reconfiguration: consult HVAC professionals to perform analysis, testing, design, construction, control programming, balancing, commissioning, maintenance and cleaning, and operation services to comply with the published ASHRAE's recommendations; (GHHIN, 2020) (WHO, 2021) (AIHA, 2020) (ASHRAE; 2020-1, 2020-2, 2020-4) -Reevaluate the position of supply and exhaust air diffusers and/or dampers; -Use restroom fans at maximum capacity in full-time during buildings occupation; (CDC, 2020-2) -Shutdown or redirect of desk, pedestal, or hard-mounted fans capable of blowing air droplets; (AIHA, 2020) -Avoid air re-entrainment of contaminants exhaust of indoors; -Evaluate the HVAC and Plumbing Water systems to reduce the potential bioburden of infectious particles; (ASHRAE; 2020-1, 2020-2) -Signal the energy recovery ventilation systems, installed in-ducts and equipment casings, due to its danger of mixing indoor and outside airstreams; -Consider HVAC designs approved to work up to 5% or 10% of Exhaust Air Transfer Rate (EATR), although indicating the possiblility to reduce to 1% or 0% by resorting to purge section under lower pressure 0.5 in. H2O; (ASHRAE; 2020-1) -Keep proper maintenance on Plumbing Water systems and the water temperature above 140 ºF to avoid microbial manifestation; (ASHRAE; 2020-2) Air cleaning -Improve filtration, air cleaning and proper maintenance; (WHO, 2020-2, 2021) (GHHIN, 2020) (CDC, 2020-1) (OSHA, 2020-2) (AIHA, 2020) (ASHRAE; 2020-1, 2020-2, 2020-3, 2020-4) -Use highly efficient filters in buildings with central ventilation and/or climate control systems, as MERV13 to 16; (GHHIN, 2020) (CDC, 2020-1) (ASHRAE; 2020-1, 2020-2, 2020-5) -Intall highly efficient particle air filtration (HEPA) or higher allowed MERV filters to clean the recirculated air in closed ventilation circuits; (GHHIN, 2020) (CDC, 2020-2) -Install portable HEPA filters in lobbies and entrances; (ASHRAE; 2020-1, 2020-5) -Control other standard Indoor Environmental Quality (IEQ) issues, i.e., odorcontrol; (AIHA, 2020) -Install UVGI devices to inactivate airborne virus on the upper-room air of common occupied spaces following industry guidelines; (CDC, 2020-2) (ASHRAE; 2020-1, 2020-2, 2020-3, 2020-4, 2020-5) Other measures -Eliminate reception seating areas and promote workplace layout reconfiguration; (AIHA, 2020) (ASHRAE; 2020-1) -Request negative pressure ventilation in risk places, i.e., isolation rooms; (OSHA, 2020-1) (AIHA, 2020) -Promote individual hygiene and the use of personal protection equipment (PPE); (OSHA, 2020-1, 2020-2) (ASHRAE; 2020-3) -Train workers about SARS-CoV-2 symptoms and risks; (OSHA, 2020-1) -Clean and desinfect surfaces and objects; (WHO, 2020-3) (ASHRAE; 2020-5) (a) According with the CDC (2015) document "Indoor Environmental Quality". Note: The research team highlight that some measures are cross referenced between institutions which indicates a positive articulation in dealing with the pandemic issue. The research team highlights the WHO and ASHRAE guidelines as the most pertinent, considering the research scope and measure precision level. In this way, the The ASHRAE "Epidemic Task Force Available Resources" (2020-2) stands out, by providing provides an interactive infographic webpage 5 with a set of where some guidelines related to the energy efficiency of HVAC systems efficiency, containing information about Energy Recovery Ventilation (ERV) systems, either stand-alone or integrated with Air-Handling Units (AHUs) 6 . Plus similar information published on June 9, 2020, the "Practical Guidance for Epidemic Operation of Energy Recovery Ventilation Systems, authored by ASHRAE TC 5.5. focusing the Outside Air (OA) and Exhausted Air (EA) mixture by Re-entrainment and Exhaust Air Transfer (EAT) rates (EATR) in Energy Recovery Ventilation (ERV) systems; The following table show the variations in several parameters in HVAC operation between the ASHRAE 62.1 standard and the ASHRAE COVID-19 mitigation guidelines summary; see Table 2 Table 1 . Air mechanical prior distributed across rooms change exclusively room use, fresh air intake and directly exhausted. The mitigation measures also consider the resort to windows to promote higher ventilation rates under favorable climate. Filters upgrade from MERV8 to 13, preferable to 14, complying with ISO ePM1 70-80%. Additional free HEPA filters and UVGI (UVc) devices were introduced for air hyalinization in systems cleaning boxes, conducts, and furniture and space surfaces. The ASHRAE kept the previous temperature set; nevertheless, the relative humidity needed an adjustment to a shorter range, reducing 10% on both margins. The "ventilation" field Ventilation, aside from extended surface cleaning, represents the best known non-medical measure to prevent the spread of COVID-19 in buildings. Specifically, the WHO incites clean air in workplaces, schools, and tourist accommodations. It also recommends an increased airflow rate, preferably without recirculation.; and if If not possible, it advises regular filter cleaning, especially for workers under medium or high risk of exposure to COVID-19 (WHO, 2020-2). This measures can be reflected in the operations systems as: -Active: including demanding the maximization of airflow rates (impacting affecting energy consumption of ventilation and acclimatization), including hospital-grade filters and the introduction of ultraviolet germicidal irradiation (UVGI) ultraviolet light; and, -Passive: enforcing opening windows policies and ultimately limiting buildings' maximum occupancy. The pandemic mitigation set of measures (Table 1) guidance document" (REHVA, 2020), mentions the impact of the mitigation measures on energy overconsumption during hot and colder seasons. Taylor Engineering (2020) notes that some ventilation devices increase the airflow rate with a "(…) significant negative impact on both energy costs and thermal comfort" (pp. 23, 24) . It also alerts to the energy costs of UV-C installation devices (pp. 33). Nadel (2020), expresses concern about how energy consumption impacts 24/7 schedules linked to higher outdoor airflow, resulting in ventilation systems and upgraded filtration devices. Office buildings, by definition, operate under high-occupancy with centralized and enclosed climate control and ventilation systems, 9 where breathing, talking, singing, coughing, sneezing -from the lowest to the higher -lead to airborne aerosols spread by the airflow with risks to others, plus surface deposition, aside from direct contact and via insects. In addition, water devices and plumbing add droplets and compromise the indoor air humidity levels compromised humidity of the indoor air, in toilet flushing, use of hot water, or sink splashing (Bahnfleth et al., 2020) . Air room distribution under previous sets can function as a flow spreader, traveling across the room carrying droplets and aerosols and entering others' breathing zone. When under an increased higher air velocity, it can worsen prior effects if not reset to divert from other areas. In other words, systems must perceive a personalized ventilation flux, air insufflation, and extraction with further circulation (Bahnfleth et al., 2020) . Recent studies underline the reduced number of days that the SARS-COV-2 virus remains viable in indoor environments if climate control settings to "cold" temperatures (below 70 ºF/21 ºC) (Chin et al., 2020) and "dry" relative humidity (below 40%) are avoided, as these are optimal conditions for the virus to survive ( A well-operated and maintained ventilation system mitigates SARS-CoV-2 transmission risk while ensuring comfort, safety, and health against other threats. Prevention, inspection, maintenance, and regular cleaning play a critical role in air conditioning and industrial ventilation systems from single homes to high occupancy buildings (offices, schools, hotels, and hospitals) (WHO, 2020-1). On the contrary, poorly maintained air conditioning and ventilation systems under unstable conditions (temperature and humidity) provide conditions for the virus to survive. A compromised and recirculated air between rooms reproduces the perfect situation for an uncontrolled high-risk, according to the WHO and other worldwide authorities (WHO, 2020-1). Ventilation and pressurization dilute indoor air contaminants, thereby increasing exposure time to contract infectious and airborne diseases. On the one hand, this leads to an increased rate of air change and, consequently, airflow speed on higher energy consumption, even thwarted by energy recovery systems; on the other hand, energy consumption does not translate into higher overall efficiency compared with the costs of illness absenteeism. The new ventilation system set ensures the balance between exhaust and pressurization to mitigate the spread (Sun et al., 2011). Engineering controls on the HVAC system can play a decisive role in spread SARS-CoV-2, managing the small droplets (Ø ~ 60μm -initial dimension) and aerosols (Ø ~ 10μm) on airflow, recently identified as the second higher risk to humans only supplanted by floor surfaces, in in-hospital environments . The HVAC and BACS BAS systems' goal is to ensure the ideal quantity and quality of air under thermal and humidly preset conditions to support human indoor activities. The air temperature and relative humidity that better Air temperature and humidity impact the contamination risk of infection, particularly the relative humidity between 40% -60%, from SARS-CoV-2, although studies outline the virus' resilience. On the one hand, the scientific community agrees on low relative humidity advantages enabling faster droplet evaporation, reducing, at the same time, mucosa production, surface deposition, and microorganism conditions to live and spread (Arundel et al., 1984) . On the other hand, higher indoor air humidification and temperature favor different pathogens' reaction, moisture enables mold, compromises the UVGI effectiveness, and unbalances occupants' comfort. Nevertheless, the effectiveness on the SARS-CoV-2 stays unmeasured, in terms of impact on infectious aerosols. The two main HVAC associations guidelines, ASHRAE and REHVA, follow different approaches. The first demands humidity adjustments on building systems. The second states that humidification has no practical contribution, based on regional climate and literature review (Bahnfleth et al., 2020) . This research intends to measure the impact of COVID-19 pandemic guidelines 10 Table 3 . The Our research resorts to a Building Energy Simulation (BES) to perform an energy analysis (Shiel et see Table 3 Table 2 and Annex B-a. The standardized building rises to 399.9 ft high, or 24 stories, from basement/parking below grade to penthouse, located in the central business district (CBD), along the south-north axis, facing east and west; see Table 3 and Figure 1 . The construction relies on standard, widespread solutions applied between the 1960s and 1990s, with the opaque envelope being a concrete finishing "mass" type with a 0.85 (ε) emissivity coefficient (ToolBox, 2003 Table 4 , Table 5 , Annex B-a and Annex C. The simulation intends to emulate the building operations pre-and post-COVID-19 pandemic, "pre-C19" and "post-C19," respectively, throughout mitigation measures; see Table 1 The remote work policies impact the occupation rate by recommending a 50% cut during the pandemic period. As result, this, In addition, the measure doubles the amount of available space to 398 ft²/person and 2 500.68 ft²/person, working and unoccupied hours, accordingly (TRANE, 2020). The guidelines focus mainly on HVAC's ventilation strategies, which increases the outdoor airflow rate and reduces the recirculated air to the bare minimum (ASHRAE, 2019-1; TRANE, 2020; CDC, 2020-2; WHO, 2020-2; EPA, 2020). The latter enforces natural plus mechanical ventilation under a reduced air recirculation, from 0 to 20% (ASHRAE, 2020-2; ASHRAE, 2020-3; WHO, 2020-2). The Demand Controlled Ventilation (DCV) becomes fundamental to ensure the maximum indoor air dilution during non-occupancy periods, which requires the highest outdoor air rate possible (TRANE, 2020). The outdoor air rate per person increased to 21.19 CFM (Li, 2020), and "per area" while "per area" it increased to 0.12 CFM/ft² (ASHRAE and ANSI, 2019), 15 doubling the pre-C19 standard value. In addition; additionally, setting a "fan schedule" for a two-hour indoor air flush at maximum power pre-and post-occupancy on workdays and Saturdays is setted, according to CDC and WHO guidelines (CDC, 2020-2; WHO, 2021). This is followed by a filtration system upgrade, from MERV 8 to 13, which increases the airflow resistance from 0.31 in. w.g. (MERV8) to 0.41 in. w.g. (MERV13) (NCDA, 2017), considering a similar filter size and specification,. This procedure generates higher energy consumption values in "fans" systems energy coinsumption values leading to a higher fan energy consumption (ASHRAE, 2020-2); see Table 6 Table 5 The indoor relative humidity should drop to 40%-60% due to a proven decrease in reducing decreasing the infection risk (TRANE, 2020; ASHRAE, 2020-4). The post-C19 guidelines recommend installing ultraviolet germicidal irradiation (UVGI) devices (TRANE, 2020) to complement higher air supply strategies (CDC, 2020-3; ASHRAE, 2019-1)., An based on the "upper-room" (air) UVGI strategy, is suitable to disinfect the air near the ceiling area of occupied spaces, along with an "in-duct" strategy to eradicate microbiological agents inside the ventilation systems (ASHRAE, 2020-6; Taylor Engineering, 2020). Nevertheless nevertheless, to reduce the water vapor/humidity of tap hot water, and the suspense molecules of the sanitary discharges or suspense molecules , tap hot water, and the sanitary discharges, respectively, the ventilation should operate continuously, with or without building occupation of the building. The BES method relies on the assessment of thermal zones and the ASHRAE's guidelines following the Building Although the Cove.tool software does not perform dynamic analysis, its outcomes do not surpass 5% compared with EnergyPlus (NREL, 2019) 19 . Also, In addition, the Cove.tool presents a simplified interface resorting to key data on ASHRAE Standards and specifications, focused primarily on the North American market, being highly recognized and applied worldwide. The method's simplicity builds its reliability: the researchers resort to inserting data on BEM's, as presented by the ASHRAE 62.1, pre-C19 scenario, against the scenario given by key institutions on COVID-19 mitigation. Nonetheless, the new settings for office buildings derive from hospital nursing room current guidelines, which are not new for the industry and its supportive software, and substantiate the research method, especially in terms of energy efficiency assessment. The model follows the preliminary studies presented by Li (2020) on SARS-CoV-2 transmission through ventilation and other cited sources on COVID-19 mitigation. The research team expects to reveal, by resorting to BES, the impact of COVID-19 mitigation guidelines on the US' Standard High-rise Office Buildings' energy consumption (kBtu/ft 2 .yr), and environmental impact (tonne/CO2/yr) and annual energy costs ($kWh/yr). The scientific community already pursues the path of energy consumption due to the COVID-19 guidelines, as shown by the literature. It builds the consensus around the post-pandemic scenarios toward healthier and safer living and working environment under energy efficiency principles.; However however, it does not focus on quantitative but rather on qualitative data and estimations (ASHRAE 2020-1; ASHRAE 2019-2; Taylor Engineering, 2020; Nadel, 2020). With these in mind, this This research's primary goal is to quantify energy-related (pre-and-post) scenarios based on the COVID-19 guidelines on US high-rise office buildings across the US territory. It does so by following the presented method to assess the adjustment's impact on HVAC, lighting and SWH systems. acclimatization and ventilation systems in the assessed sample on heating, cooling, ventilation, and SWH. All the following values of this section represent their relative values between pre-C19 and post-C19 scenarios. Table 7 Table 1 , and Annex E-a, b:  In "warm-dry" to "very hot-humid" climates (zone 0 to 3), the post-C19 scenario induces a reduction in EUI from 9.66% (zone 3) to 14.34% (zone 0) when compared to the preexisting conditions, whereas the EUI tends to decrease at lower latitudes; see Chart 4, orange and blue color "Linear" lines. , as an example between zone 2 and 4;  In "mixed-humid" to "subarctic" climates (zone 4 to 8), the post-C19 measures increase the EUI on average 21.72%, from 15.37% (zone 4), up to 28.33% (zone 8), whereas the EUI tends to increase when the latitude is higher; see Table 7 and Chart 4, orange and blue color "Linear" lines. (Table 6) ;  The EUI increases significantly from zone 7 to 8 (Chart 4), which diverge from the tendency, with differences between pre-C19 and post-C19 scenarios being roughly the double (22.41 to 45.02 kBtu/ft².yr) in zones 7 and 8, respectively;  There is a steady increase in energy consumption in post-C19 as we move towards northern latitudes which confirms an overconsumption trend; see Chart 4, orange and blue color "Linear" lines. The gap between both pre-and post-C19 trend "Lines" gets wider as we move into colder climate zones (zone 7, 8).  From zone 3 to 4, the energy consumption balance changes from decrease to increase; and,  A standard high-office building located in Honolulu (zone 0) decreases its energy consumption up to 5.23 kBtu/ft².yr. By ; in comparison, the same building design under different construction codes in Fairbanks (zone 8) increases it by 45.02 kBtu/ft².yr; see Table 7 . Table 14 (Table 7) . Fairbanks shows the highest impact on absolute values, consuming an extra 44.91 kBtu/ft²yr for heating;  Zones 0 and 1 do not present heating EUI needs;  Overall, the cooling's EUI represents 4.51% of the heating needs; the post-C19 scenario decreases the cooling EUI its energy consumption by, on average, by 42.59% in all climate zones, ranging from 19.61% (zone 1) to 80.77% (zone 7); see Table 14 (Table 7) . whereas Honolulu displays the highest impact on absolute values, consuming less 1.61 kBtu/ft²yr of energy for cooling; and,  Zone 8, when compared to 7, shows nearly twice the heating's EUI in the post-C19 than the pre-C19 scenario. The EUI for lighting decreases consistently in every climate zone at an average rate of 35.03% (-2.63 kBtu/ft²yr) with post-C19 mitigation measures; see Table 14 . The EUI for fans in the post-C19 scenario behaves similarly to cooling and heating; see Chart 6. In addition, Also, there is a trend in fans EUI for overconsumption as we move towards colder climates; see Chart 6, orange and blue color "Linear" lines. However, the trend behavior inverts from zone 2 into lower latitudes, leading to energy savings; lower latitudes tend to reduce energy consumption while higher latitudes tend to increase it; as shown in Annex E-b:  In "very hot-humid" and "hot-humid" climates (zone 0 to 2), the fans' EUI decreases on average 13.63%, with a minimum of 4.29% (zone 2) and a maximum of 19.33% (zone 0);  In contrast, in "mixed-humid" to "subarctic" climates (zone 4 to 8), the consumption growth, on average, points to 29.19%, with a minimum of 18.90% (zone 4) and a maximum of 39.14% (zone 7);  Zone 3 displays a slight increase in energy consumption (+4.46%), paired with zone 2, which is the least impacted by post-C19 mitigation guidelines; and,  After post-C19 scenario simulations, Honolulu (zone 0) displays the highest reduction in fans' EUI, with a decrease of 0.93 kBtu/ft²yr, while Fairbanks (zone 8) exhibits the most significant increase, 3.07 kBtu/ft²yr; see Table 14 . These systems do not present any variation in consumption. The researchers verified a similar behavior between the "total energy consumption" (Chart 4) and the "CO 2 emissions" (Chart 7) on post-C19, as follows: Tonne/CO2e/yr  In "very hot-humid" to "warm-dry" climates (zone 0 to 3), CO 2 emissions tend to decrease with COVID-19 mitigation guidelines by, on average, by 13.84%, with a minimum of 11.41% (zone 3), and a maximum of 15.86% (zone 0); see Table 8 (Table 7) ;  In contrast, in "mixed-humid" to "subarctic" Climates (zone 4 to 8), CO 2 emissions tend to rise, on average, 13.82%, with a minimum of 7.41% (zone 6) and a maximum of 22.11% (zone 8); see Table 8 (Table 7) ;  There is a steady increasing trend in CO 2 emissions after the mitigation measures are in place as we move into northern latitudes; see Chart 7, orange and blue color "Linear" lines. Nonetheless, in warmer climates (zone 3 to 0) the trend lines suggest a consistent emission decrease behavior towards lower latitudes.  A The standard high-rise office building located in Honolulu (zone 0) decreases its CO 2 emissions by 698.6 tonne/CO 2 /yr, while the same building in Fairbanks increases it by 1 450.9 tonne/CO 2 /yr; and,  Once more, Zone 3, again, establishes the turning point between an increase and a decrease in CO 2 emissions; see Chart 7. The US States diverges on average energy retail prices, considering natural gas and electricity. Natural gas prices are, on average, 77.81% lower than electricity in all the studied States; see Annex E-c: Although the ASHRAE, WHO, REHVA, CDC, OSHA, AIHA, and EPA produced guidelines and scientific literature on the COVID-19 mitigation, the impact in energy efficiency was relatively unexplored; spreading the simple concept that health and safety prevail above all social costs (Cutler & Summers, 2020) . However, this research opens a new dimension towards a healthier, safer, and more productive consensus, as demonstrated by applying the guidelines to ensure life quality in general, and indoor comfort, and air quality in particular. Simultaneously, it responds to other global issues where energy consumption and CO 2 emissions are crucial, like to climate change mitigation and national energy transition, the "newest" challenges in the post pandemic era. The produced knowledge aims to clarify the issue for regulators, for the market, and for related professional associations., It emphasizes emphasizing the relationship between the US high-rise office buildings under HVAC/AHU unities and energy efficiency, while ensuring a healthier, safer, and more productive work environment. The COVID-19 mitigation guidelines impact on buildings' impact on energy consumption (ASHRAE, 2020-1; ASHRAE, 2020-2; Taylor Engineering, 2020; Nadel, 2020, REHVA, 2020; Cutler & Summers, 2020) (ASHRAE, 2019-2; ASHRAE, 2020-1; ASHRAE, 2020-2; Taylor Engineering, 2020; Nadel, 2020) confirms the research results, although limited to standard high-rise office buildings. Table 7 Table 6 ). The post-C19 measures guidelines focused on the ventilation field, and, primarily, the introduction, such as natural ventilation rates and outdoor airflow per person/area increment, pre-and-post occupancy two-hour air flush, of natural ventilation rates and outdoor airflow per person/area increment, two-hour air flush (pre-and post-occupancy), air recirculation reduction (20%), and DCV disabling, contribute to increase increasing the fans' EUI and energy losses via ventilation., The result is the rise of with the consequence of rising the heating energy demands, with higher expression in colder climates; see Chart 5. However, in cities located in "warm-dry" to "very hot-humid" climates (zone 0 to 3), energy consumption and CO 2 emissions tend to decrease by, on average, by 11.92% and 13.84%, respectively; see Chart 4 and Table 7 Table 6 ). This is mainly due to changes in natural ventilation and outdoor airflow per person/area, (which enables free cooling), air recirculation reduction up to 20%, and DCV disabling, forcing continuous outdoor air supply (TRANE, 2020). This measures leads to lower colloing needs despite the and leading to lower cooling needs to be caused by fan energy overconsumption; see Chart 5. The ASHRAE Handbook 2019, Chapter 62 on "Ultraviolet Air and Surface Treatment" (ASHRAE, 2019-1), Nadel (2020), and TRANE (2020) relate energy overconsumption with filtration upgrades (MERV8 to 13) due to additional fan power needs. However, it proved irrelevant for the final usable energy output in the assessed sample. By comparison, measures applied to natural ventilation and outdoor airflow rates exhibit higher impact in all assessed locations. In the post-C19 scenario, high-rise office buildings located in warmer climates benefit from remote work policies and social distancing, cutting 50% of the occupation, which leads to less internal gains and less energy consumption for cooling. In contrast, the The opposite impact occurs in colder climates due to lower internal heat gains, increasing the energy demand for heating. Researchers tend to outline the energy overconsumption of lighting due to UVGI devices' installment on broader schedules, upper-rooms, and in-duct solutions (ASHRAE, 2019-1; Taylor Engineering, 2020), signaling the variation that may occur under different climates (ASHRAE, 2019-1). Despite the surplus caused by these systems, measures like the BACS upgrade to class B (ASHRAE, 2020-1), following the daylight and occupancy sensors and remote work policies, led to a lighting's EUI optimization, lowering the energy consumption in the evaluated climate zones/cities. From an environmental perspective, post-C19 measures present a harmful scenario for latitudes higher than Los Angeles, CA (latitude >34) (Chart 7 and Table 7 ) due to the CO 2 emissions aggravation effect, which tends to follow the total usable energy consumption behavior; see Chart 7 and Table 8 . The costs related to energy overconsumption align with literature that advocates a general cost increase (ASHRAE, 2019-2). The present study highlights the effective cost-savings in the hottest climates due to the energy consumption decrease in lighting, fans, and cooling, against the above-proclaimed trend; see Chart 8. Electrically powered systems tend to present higher costs than natural gas, explaining the substantial impact on cost savings in the given year. However, in northern latitudes or colder climates (zone 5 to 8), heating and fan EUI usable energy consumption increase, leading to higher energy costs, despite the lower natural gas prices for the same amount of energy delivered; see Chart 5 and Chart 6. The methodology resorts to assumptions and simplifications, which, at the same time, help to frame the assessment strength, as follows:  A standard architectural layout with a 60-40% wall-to-window ratio, although following local construction requirements;  The reduced number of cities representing climate zones;  The number of model key-points assessed by the Cove.tool, which forces it to resort to additional calculations, such as fan airflow pressure and UV light consumption;  The conjecture of the office standard design, although based on guidelines;  The assumption of airflow equivalent to that set for the "Outpatient Health Care Facility -General Examination Room;" as the ASHRAE guidelines established the maximum allowed by the system;  The study does not account for any costs associated with the proposed guidelines (BACS upgrades, UVGI devices, sensors, and filters); and,  The study considers 21.19 CFMs of outdoor air rate per person as published by Li (2020) regarding post-C19 scenarios. The BEM method presented above gathers the potential to assess the extensive use of building types in different regions under local regulations and standards. The next steps will involve:  Applying the accumulated knowledge in China's vast territories following the same principles;  Making adjustments; and,  Disclosing new outcomes and confronting the presented results. Under its common regulations, the European Union represents another territory of interest. Although, the method presented resorts to reliable Cove.tool simulations, we intend to test software to understand other potential solutions outside the COVID-19 range, e.g., air-pollution, such as Rhino 20 plus Grasshopper's 21 Ladybug plugin 22 . Also, Above all, we also aim to understand how these measures can affect the path to achieve achieving the Paris Accord's short-term goals -recently rejoined by the US under the President Biden administration. The research assesses the COVID-19 pandemic mitigation guidelines published by WHO, CDC, OSHA, AIHA, and ASHRAE, WHO, REHVA, CDC, OSHA, and AIHA, and EPA applied to US high-rise office buildings. The goal is to measure is to focus on measuring the guidelines impact on usable energy consumption, and CO 2 emissions and annual energy costs on a standard US high-rise office building prototype in 9 key locations under ASHRAE-IECC climate zones. between pre-C19 and post-C19 scenarios. by considering 9 key cities in each climate zone, under the ASHRAE-IECC Equivalent Energy Code standards, as core values for the "Large Office" building prototype. The study resorts to Building Energy Simulation (BES) assessment to perform an energy analysis in a Building Energy Model (BEM), using the Cove.tool plus SketchUp plugin simulation software. based on the Cove.tool/Building Energy Model (BEM) software via its SketchUp plugin, comparing the total usable energy consumption and CO 2 emissions performance outcomes between both scenarios pre-C19 and post-C19 scenarios. The simulation outcomes enable the BEM performance comparison between both scenarios. The institutional most highlighted set of measures focus on personal hygiene recommendations, remote work policies (building occupancy decrease), and promotion of natural ventilation (outdoor air flow rates increase) with a HVAC systems filter upgrade. These measures are the main factor for The results for the post-C19 scenario point to energy overconsumption in high-rise office buildings, located in "mixed-humid" to "subarctic" climates (climate zones 4 to 8), on average, adding, on average, 21.72% to existing pre-conditions to maintain the post-C19 work environment. The updated ventilation strategies and telework policies (with a 50% cut in occupation), mainly increasing outdoor airflow rates, plus the remote work policies (with a 50% cut in occupation), led to higher energy losses and lowered internal gains, respectively,. As consequence, the which increase usable energy consumption increase, with higher expression in the colder climates heating EUI especially heating in colder cold climates. These The outcomes follow the current literature forecasts results on COVID-19 mitigation measures, underlining the growing trend towards energy overconsumption. However, the outcomes show that in "warm-dry" to "very hot-humid" climates (climate zones 0 to 3), the tendency inverts, decreasing the usable energy consumption by, on average, by 11.92%. In warmer locations temperatures, the same measures reveal the opposite outcome -favoring a lower energy demand for cooling. Heating and cooling EUI have the highest impact weight on usable energy consumption, which increases or decreases depending on the building's location. Higher latitudes exceed the relative heating energy consumption while lowering the cooling energy. Geographically, the fans' EUI and CO 2 emissions follow the same pattern. The lighting's EUI, contrary to what the current literature advocates, drops by, on average, by 35.03%, due to BACS's upgrade new configuration and daylight and occupancy sensor settings, despite the UVGI devices' consumption surplus. Overall, the post pandemic guidelines are environmentally harmful, aggravating the carbon dioxide emissions, except in buildings located in cities with "warm" to "very-hot" climates, like Los Angeles or Honolulu. The annual energy operation costs follow the same tendency, increasing, on average, by 7.27% in colder locations (climate zone 5 to 8), and decreasing in warmer latitudes (climate zone 0 to 4), on average, by 11.41%. Finally, the financial analysis confirms that the energy costs following the usable energy overconsumption or its tendency to relatively rise by, on average,7.27% in colder latitudes (Climate zone 5 to 8), and decreases in warmer latitudes (Climate zone 0 to 4) by, on average,11.41%, under post-C19 mitigation measures. The research team intends to call the cited guidelines' attention to the need for adjustments concerning the particularities of climate zones' diversity. Rethinking the future (after COVID-19) becomes mandatory in the path towards a healthier and safer work environment considering eventual threats, as simple as air over-pollution. In Particularly in cold climates, where every measure comes with a higher cost, regulators must conciliate the principles written in guidelines related to minimal energy expenditure and CO 2 emissions., This matter is particularly relevant considering the on vast building stock represented by the US high-rise offices. Rethinking the future (after COVID-19 pandemic) becomes mandatory in the path towards a healthier and safer work environment. For this, two key features will play a mandadory role in shaping the future offices work spaces: indoor air quality and remote work policies. The indoor air quality is a rising concern among the scientific community. It reflects society's interests, where the sick building syndrome (identical to COVID-19 HVAC adjustments) gathers exponential interest, following Scopus publications record: from 120 a year in 1988 to 558 a year in 2020 23 . As e.g., today, 136 countries have adopted at least on measure to ban smoking in indoor spaces (WHO, 2019). Security and health are pillars among the most educated societies following active and aware lifestyles, from food growth to exercise, to name a few. As for telework, the research team foresee that is here to stay. Statista (2021) measure a steady hold tendency increase between September 2020 and March 2021. Before the pandemic's, US public and private sectors telework accounted for 5% and 7%, respectively, the latter still holds a third of the workforce at home. In conclusion, not all workers are getting back to offices. 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Average Price of Electricity to Ultimate Customers by End-Use Sector «Average Commercial Price -Natural Gas Price The authors envision the future in three steps, based on big-tech companies' plans, e.g., Apple (Evans, 2021) , Google (Hartmans, 2020) , and Facebook (Westfall, 2021) . First, we will experience the hybrid workplace, with 50% working in situ and 50% in telework. Second, a two-way situation. The non-creative office-building professions will fully embrace teleworking before being replaced by technology. The most creative will gather in high-quality spaces, similar to housing comfort and full amenities. Third, the workplace will be fully-virtual without physical spaces profiting from full-cover and hi-speed global communications. The author would like to acknowledge the Foundation for Science and Technology (FCT -Portugal) for the financial support of the research project UID/EAT/04008/2013, through the Research Centre for Architecture, Urbanism and Design of the Lisbon School of Architecture, University of Lisbon (CIAUD -Portugal). Also, we would like to acknowledge the Cove.tool team for providing an educational version of the software, and their readiness to provide additional help to pursue the research goals.