Alternative ventilation strategies in U.S. offices: Saving energy while enhancing work performance, reducing absenteeism, and considering outdoor pollutant exposure tradeoffs

Abstract

Mechanical ventilation can improve occupant productivity, use or save energy, and increase outdoor-to-indoor pollutant transport. This work explores those impacts for eight ventilation strategies, relative to a baseline constant mechanical ventilation rate (VR) of 9.4 L/s/occ, in two representative offices. Strategies were unique combinations of airside economizing, demand-controlled ventilation, and supply air temperature reset, along with doubling the baseline VR. These were evaluated within a Monte Carlo analysis that varied climate and outdoor pollution, along with 19 building parameters. Energy modeling, empirical correlations, and indoor air quality (IAQ) modeling were used to quantify outcomes of: (i) energy use; (ii) profitable IAQ impacts, e.g. work performance; and (iii) negative IAQ health impacts due to indoor particle and ozone exposure. 'Win-win' strategies were defined as those that saved energy and increased work performance, and these always included an economizer. Relative to the baseline, the win-win strategies: increased annual geometric mean VRs by 5-10 L/s/occ; reduced mechanical system energy consumption by 12-27% (saving $1-1.75/m 2 /year); increased work performance by 0.5%; eliminated 5 hours of absenteeism per year; and increased indoor PM 2.5 by 0.5 μg/m 3 and ozone by 3 ppb. A sensitivity analysis identified infiltration and climate as the largest outcome drivers. Median annual benefits for small-to-medium-large offices in the U.S. (~75% of office floorspace) were $28 billion for implementing the win-win strategy with the greatest energy savings, and $55 billion for implementing the win-win strategy with the greatest work performance increase. Particle exposure tradeoffs were mitigated by use of efficient filters. IntroductionMechanical ventilation is the intentional supply of outdoor air (OA) inside buildings by heating, ventilation, and air conditioning (HVAC) systems. Minimum mechanical ventilation rates are prescribed throughout the developed world by standard-setting organizations like ASHRAE, as a crucial part of providing "acceptable indoor air quality (IAQ)" [1]. Ventilation dilutes indoor-emitted pollutants, reducing potentially unhealthy or irritating exposures and advancing occupant olfactory comfort and perceived IAQ satisfaction [2]. Low ventilation rates (VR) have been correlated with increased illness absence and sick building syndrome (SBS) symptoms, negative odor perceptions, and reduced task performance [3][4][5][6][7][8].Conversely, significant cognitive and task performance increases and sick leave reductions have been associated with VRs that well exceed ASHRAE Standard 62.1 recommendations [9][10][11][12]. From an energy © 2017. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ perspective, however, current ventilation practice is costly, accounting for ~1/4 of HVAC energy consumed by commercial buildings [13,14]. Increasing VRs could further increase energy use, but alternative ventilat...

Outcome‐based ventilation: A framework for assessing performance, health, and energy impacts to inform office building ventilation decisions

“…Many potential ventilation outcomes were considered for inclusion, and the rationale for the IAQ‐related components included has been previously discussed . In short, for an outcome to be included, it needed to have sound and practical methods to calculate its magnitude, assign it a value, and measure or estimate necessary physical quantities in a real building.…”

“…Together L e and L g are the energy consumption costs, both direct and social. (We neglected ventilation’s impact on sick building syndrome (SBS) symptoms, even though there is an existing relation that has been monetized, because work performance and sick leave absenteeism have associations with ventilation rate with values that are two orders of magnitude greater …”

“…The first outcome is lost work performance (LWP), which varies with VR based on the relation for relative work performance, or the proportional difference in worker productivity achieved at two VRs, developed by Seppänen et al for low‐to‐medium demanding cognitive tasks. As previously shown, this relation can be expressed as the sum of a deterministic function for the central estimate and another function indicating uncertainty. Seppänen et al gave the former directly, and we fit the latter to the 95% confidence limits under an assumption of normal distribution uncertainty.…”

“…which was provided in Fisk et al based on the relation in Seppänen et al and was developed in Ben‐David et al.…”

“…(With some modifications, the basic ideas could be extended to other commercial building types.) After formulating the loss function approach for OBV, we use the existing dataset representing much of the U.S. office sector, used in Rackes and Waring and Ben‐David et al, to examine its implications in the context of day‐averaged outcomes associated with day‐averaged optimal ventilation rates. Then, a case study is used illustrate how the loss function and loss‐minimal VRs might change over the year.…”