1. Introduction
Buildings account for 41% of US energy consumption, with nearly half of that energy usage coming from the commercial sector [
1]. In office buildings, over half of the end-use energy expenditures are attributable to heating, ventilating, and cooling [
2]. The environmental impact of these energy expenditures has been well documented; greenhouse gases emitted during power production are associated with climate change impacts including rising sea level, extreme temperatures, and more frequent weather events [
3,
4]. Emissions of sulfur dioxide (SO
2) contribute to acid rain, which can damage sensitive ecosystems [
5]. More important, however, are the downstream human health effects related to these environmental impacts. Elevated temperatures and droughts will increase the likelihood of heat-related illness and mortality [
6]. Extreme weather effects also pose health and economic risks, especially in developing regions [
7]. Emissions from power plants also have several direct health effects: (1) exposure to particulate matter, in particular SO
2, increases the risk of respiratory and cardiovascular disease and (2) nitrogen oxides (NO
x) cause airway inflammation and respiratory symptoms, especially in asthmatics [
8,
9].
At the building level, buildings managers are incentivized to reduce costs, which often is achieved by reducing ventilation rates. Similar incentives are not set for optimizing the health performance of buildings as occupant health is more difficult to characterize. Further, building managers tend to overestimate the energy costs related to ventilation. When asked the cost per occupant to double the ventilation rate from 20 cfm/person to 40 cfm/person and improve filtration from a minimum efficiency reporting value (MERV) 6 to a MERV 11 filter, building managers reported a perceived cost per occupant of $100 while the modeled estimates were consistently below $32 per occupant for all climate zones [
10]. Consultants, tenants and owners also overestimated the costs of improved ventilation per occupant at $60, $115, and $80, respectively. Owners and building managers believe that tenants do not consider indoor air quality (IAQ) when leasing a space: 58% of respondents reported that 20% or less of their tenants take IAQ into consideration [
10]. As a result, the cost of energy is often prioritized over IAQ and minimum required ventilation rates are met.
The guidelines that buildings operate under are by definition minimally acceptable. ASHRAE defined its original ventilation Standard 62 as “the minimum and recommended air quantities for the preservation of the occupants’ health, safety and well-being” [
11]. In the initial standard, the minimum ventilation requirement was 10 cfm/person. Sick building syndrome (SBS) was first reported around the time of early standard adoption and coincided with improved sealing of building envelopes; occupants of poor performing buildings started reporting a wide range of symptoms including respiratory irritation, allergies, and headaches, which were later linked to the buildup of biological and chemical pollutants in the indoor environment [
12].
In response, ASHRAE has since increased minimum acceptable ventilation rates under Standard 62.1 to approximately 20 cfm/person depending on the size and occupancy of the rooms within the building [
13]. SBS symptoms and productivity losses have still been observed at this ventilation rate compared to higher ventilation rates. The prevalence of many SBS symptoms, such as throat/mouth dryness, feeling generally bad or good, and difficultly thinking, are reduced at ventilation rates above 20 cfm/person [
14]. Recent research by our team also show cognitive improvements at 40 cfm/person compared to 20 cfm/person [
15]. Absenteeism, productivity losses, and healthcare costs due to ventilation are estimated to have annual economic impacts in the hundreds of billions of dollars in the U.S. [
16]. According to this analysis, a 5% change in productivity is equivalent to $125 billion in economic value based on the annual GNP of U.S. office workers, which is equivalent to $186 billion in 2015 dollars.
Sustainable or “green” design has sought improve occupant wellbeing in buildings while also reducing their environmental footprint. In 1990, Building Research Establishment Environmental Assessment Methodology (BREEAM) was founded as an international certification agency for green buildings. Three years later the Leadership in Energy and Environmental Design (LEED) rating system was established with a similar concept, focusing on U.S. buildings. Both agencies utilize design credits, which are subdivided into various sections, such as energy, water, and waste. Within each section there are required credits, which typically conform to local standards and guideline, and optional credits. To achieve a certain ranking, designers and architects can choose which optional credits to pursue. For example, LEED offers optional credits for both energy efficiency and increasing ventilation by 30%. In practice, the energy efficiency credits are preferentially chosen: only 40% of the new construction and 23% of the existing buildings rated under LEED v2009 obtained the enhanced ventilation credit. With advances in HVAC equipment such as energy recovery ventilators (ERVs), which significantly reduce energy use, it is possible to obtain credits for both energy efficiency and enhanced ventilation.
There is currently a lack of consensus about whether the energy costs and environmental impacts of increased ventilation outweigh the resulting health and productivity benefits. The burden of all four of these factors is estimated in a standard office building at 20 cfm/person (9.4 l/s/p), 27.6 cfm/person (13.0 l/s/p) (the ventilation rate to obtain the enhanced ventilation credit with LEED), and 40 cfm/person (18.8 l/s/p). We also test the effect of adding ERV to the higher ventilation scenarios. We then compare these scenarios to place the energy, environmental, health, and productivity factors into context.
4. Discussion
Our motivation for this analysis stemmed from the observation that the public health benefits of enhanced ventilation have been researched and described for several decades, and our own recent research observed significant improvements in decision-making performance for office workers with enhanced ventilation, yet when we reviewed the prevalence of the selection of the enhanced ventilation credit in the leading green building rating system (LEED), we found that enhanced ventilation credit was pursued in only 40% of new buildings and 23% of existing buildings [
15]. We hypothesized that one of the key barriers to more widespread adoption was the corresponding energy costs associated with increasing ventilation rates.
We found that the additional costs per occupant for enhancing ventilation rates were quite low; too low, in fact, to be a barrier for more widespread adoption. These costs are trivial (less than $40/year in the worst case scenario) when compared to the large improvements in cognitive function (greater than $6000/year) from increased ventilation. In our analysis, we examined the impact of including an ERV to offset energy usage and costs. As expected, energy usage costs dropped significantly with the use of these ERV systems in all U.S. cities. Most importantly, enhancing ventilation to 30% above the minimum, when paired with an ERV, led to cost savings in three of the seven cities in our model for VAV and seven of seven for FCU.
These findings are in agreement with Hamilton
et al. that estimated annual costs from enhanced ventilation to be < $32 per person per year. In addition, they found cost perception may be a barrier to enhancing ventilation, despite the analysis that shows the actual costs to be low [
10]. While the costs are low compared to productivity benefits, they do comprise a significant portion of building management budgets. The split incentive system, whereby building managers are responsible for energy costs while tenants are responsible for the cost of their employees, is a barrier to adoption as tenants cannot simply implement ventilation changes themselves. In addition, the health benefits of enhanced ventilation are not well-understood by most tenants as of yet.
The environmental costs represent another potential barrier to adoption of higher ventilation rates. While these costs are real, especially when magnified by all buildings in the U.S., the per building environmental impact on greenhouse gas emissions is not as impactful as the estimated benefits. These environmental impacts can be offset at three levels: individual, building, and system level. Pursuing other design features that promote alternative transportation options for individuals can reduce the environmental impacts from the building overall (incentivizing biking, preferred parking for electric cars, public transportation access). On a building-level, similar to the energy cost analysis, when ERVs are used the overall effect can be a net reduction in greenhouse gas emissions for the building. The environmental impacts can be reduced further through the use of more energy efficient HVAC systems, and, in new buildings, incorporation of advanced air distribution systems that deliver ventilation when and where it is needed to raise the effective ventilation per person, as opposed to the current approach of whole-building ventilation [
23]. Last, on a systems-level, in cities with a greater percentage of use of non-combustion energy sources there is a lower environmental cost associated with enhancing ventilation.
The energy and environmental impacts are offset by the dramatic positive impacts that enhanced ventilation has on human health and productivity. In our recent study of office workers, when we mapped raw test scores onto normative data we found an eight percentile increase in decision-making performance when ventilation was increased from 20 cfm/person to 40 cfm/person, corresponding to a $6500 change in a typical office worker’s productivity. This is a conservative estimate of productivity gains and economic costs. First, the analysis in this paper only investigates cognitive impacts while in the office. The impacts of ventilation on other domains of health are well documented in the literature and lead to significant economic costs [
24]. The risk of sick leave, illness, influenza and pneumonia are all elevated at lower ventilation rates and have additional productivity impacts (
Table 5). With respect to sick leave, the cost per occupant is estimated to be an extra $400 each year at reduced ventilation rates [
25]. The same study found this impact alone to dwarf energy costs by a factor of six among corporate workers. Second, as outdoor CO
2 levels and temperatures rise as a result of climate change, the energy usage and IEQ of poor and high performing buildings will become increasingly disparate [
26]. Third, our analysis only accounts for the direct costs associated with salaries; the employer cost for employee compensation is approximately 30% higher when considering benefits [
22]. As higher paid positions have more expensive benefits, the reduction in costs to the company will be higher than estimated in this analysis. Fourth, the testing occurred in a LEED platinum building with low chemical concentrations. Even larger cognitive deficits were observed when chemicals were added to the space [
15]. Enhanced ventilation in buildings with poor IAQ will lead to larger productivity gains than what was seen in this green environment. Lastly, the cognitive domains that have the highest correlations with other measures of productivity such as education level, salary at age, and number of employees supervised were the ones that had the largest improvements at higher ventilation rates [
27]. The participants shifted from the 46.5th percentile to the 57th percentile on the information usage, strategy, and crisis response domains.
Table 5.
Health impacts of ventilation rate in medium office prototype building (adapted from Fisk
et al. [
24]).
Table 5.
Health impacts of ventilation rate in medium office prototype building (adapted from Fisk et al. [24]).
| Reference | Outcome | Ventilation Rate (cfm/Person) | Relative Risk |
|---|
| Low | High |
|---|
| [25] | Short term sick leave | 12.9 | 25.8 | 1.5 |
| [28] | Illness all years | 4.5 | 30 | 1.5 |
| [28] | Illness 1983 data | 4.5 | 30 | 1.9 |
| [29] | Illness | 48 | 120 | 2.2 |
| [29] | Influenza | 48 | 120 | 4.7 |
| [30] | Influenza | 15 | 45 | 3.1 |
| [30] | Rhinovirus | 15 | 45 | 2.1 |
| [30] | TB | 15 | 45 | 3.3 |
| [31] | Pneumonia | 20.4 | 30 | 2.0 |
| [32] | SBS symptoms | 8.5 | 42.4 | 5.0 |
These findings indicate that standard HVAC design and operation are not optimal for occupant health and decision making. New building construction should include ERVs and systems that can provide modifiable ventilation rates depending on outdoor air conditions. They should also invest in other ventilation strategies such as advanced air distribution systems and improved filtration, which reduces contaminants that may cause cognitive impacts. Green building architects and designers, which have the goal of improving occupant wellbeing while simultaneously reducing their environmental impact, should be particularly cognizant of ventilation strategies that can optimize these two factors. Credit-based rating systems should revisit their design requirements and properly incentivize these approaches.
Many existing buildings, on the other hand, have HVAC systems that are designed for a specific ventilation rate and may not be easily modified to increase ventilation rates. This limits the ability of building managers to make changes to the ventilation rate, even in light of the evidence presented in this paper. This limitation is similar for ERVs, which may not be easily installed into some existing systems.
Our analysis focused on one office type—the Department of Energy “Medium Office Type” template—and may not be applicable to other building types. In addition, this research and our previous research on cognitive function did not explicitly investigate thermal conditions, which may have independent productivity impacts. However, the modeling is straightforward and building owners for all buildings types could replicate our analysis for their specific building to estimate indoor conditions, energy costs, and environmental impacts. Last, energy costs fluctuate, but in our analysis model inputs are based on local costs and energy fuel mix as of the date that this manuscript was submitted. Any changes to the fuel mix or costs will change our estimated costs. Regardless, variation in the overall energy costs per occupant will be minor relative to their employment costs.
Several assumptions were made to derive the economic benefits of improved ventilation. First, we assume that the population of knowledge workers that took the cognitive testing was representative of the U.S. office workforce. 20% of that group held management positions compared to 12% in the BLS data, and 60% had professional occupations compared to 50% in the BLS data. Second, we assume a one percentile change in cognitive function corresponds to a one percentile change in value as an employee (e.g., someone who scores in the 62
nd percentile is salaried at the 62nd percentile). Previous work with the SMS tool has shown high correlations (>0.6) between cognitive scores and salary [
27]. Third, this analysis demonstrates the competitive advantage to be gained by improving ventilation in comparison to workforce at large. As improvements to ventilation are adopted by a larger percentage of buildings, there will be an equilibration of wages to account for a generally more productive workforce.
