Published 10/17/2023
The summer of 2023 turned out to be one of the hottest on record for North America. The European Union Climate Monitor said July 2023 was earth’s warmest month on record, and 2023 will end up displacing 2016 as the hottest year since records began in 1850. According to the latest data from NOAA, the average surface temperature across the contiguous 48 states has risen at an average rate of 0.17° F per decade since 1901, and more than twice as fast since 1981.
These rising temperatures, coupled with increasing electricity rates, have material impacts for building owners and operators in terms of the cost to maintain comfortable indoor environments. Based on my analysis, the combined effect of rising temperatures and increasing electricity costs have resulted in a 29-72% increase in ventilation cooling costs from 2013 to 2022 for six major cities on the east coast of U.S. And these numbers will only increase as temperatures and electricity costs continue to rise.
The good news is that there are energy efficient ways to maintain comfort and indoor air quality (IAQ) in buildings that can offset much of this cost increase. One such way is to clean and recycle a portion of the already-conditioned air in a building so that the same or better IAQ can be achieved with less conditioning of hot and sometimes polluted outside air. I estimate that up to 80% of total ventilation cooling costs can be offset using this approach.
The cost of cooling ventilation air increased 29-72% from 2013 to 2022
In 2022, cooling accounted for ~12% of the electricity used in commercial buildings in the U.S., and this percentage is likely to grow as climate change intensifies. Cooling Degree Day (CDD) is a measurement designed to quantify the demand for energy needed to cool buildings. It is the number of degrees that a day’s average temperature is above a base temperature (50° F per ASHRAE 90.1). I compared the cooling degree days of six major cities on the east coast between two five-year periods — from 2009 to 2013 and 2018 to 2022 — and observed 3-8% increase in CDDs in just over a decade across the six cities. This leads to an increase in cooling energy consumption in buildings and adds load on the electric grids.
Along with temperature, the electric utility rates for commercial and residential sectors have also been steadily increasing. According to the U.S. Energy Information Administration (EIA), commercial electricity rates have increased nationally by around 27% in the last 10 years. Residential and industrial electricity rates have also increased by similar percentages. For the six U.S. cities considered for this analysis, the percentage of increase in electric utility rate (blended across all sectors) was between 19% to 48%. As a result, electricity bills have become a larger share of building operating expenses and annual budgets.
Both the increase in cooling degree days and electric utility rates have a compounding effect on the cost of cooling ventilation air required to maintain IAQ. This is shown in Figure 1, which compares the cost of cooling ventilation in 2013 and 2022 per ft2 across the six cities.
As Figure 1 shows, the cost of cooling ventilation air increased 29-72% from 2013 to 2022 across the six cities modeled. Note that for this analysis, I used a cooling system co-efficient of performance (COP) of 3.0.
A hybrid ventilation approach can offset up to 80% of total ventilation cooling costs
Instead of continuously conditioning large volumes of outside air to maintain IAQ, a more energy efficient approach to maintaining comfort and IAQ in buildings is to clean and recycle a large portion of the conditioned air already in the building. This “hybrid ventilation” approach, which combines cleaned indoor air with some volume of outside air, can be implemented using a ventilation design method in ASHRAE Standard 62.1 and the International Mechanical Code called the Indoor Air Quality Procedure (IAQP). This ventilation design method can be used with sorbent media-based air cleaning technology such as Sorbent Ventilation Technology® (SVT®) to filter harmful gaseous contaminants including carbon dioxide (CO2), volatile organic compounds (VOCs), and ozone directly from indoor air so that code mandated IAQ targets can be maintained with less outside air ventilation. Lower outside air requirements, in turn, mean less energy is spent conditioning outside air for comfort. In 2022, ASHRAE made significant updates to the IAQP procedure to make it both easier for engineers to apply and more robust. At the same time, several manufacturers including enVerid, Daikin, and Trane have developed HVAC products with SVT to support the adoption of the IAQP.
In each commercial building, hybrid ventilation design with sorbent-based air cleaners can reduce the outside air ventilation requirement by up to 80%, which can result in significant energy savings and carbon emission reductions. Figure 2 shows the dollar savings per ft2 from reducing 75% of outside air requirement for ventilation in the same six cities looked at above.
There are substantial savings across all six cities from using hybrid ventilation as compared to the traditional approach that relies only on outside air “dilution ventilation” to maintain IAQ. Reducing outside air requirements also means smaller HVAC systems can be used, which are less costly and take up less space. An additional benefit is that less reliance on outside air ventilation for IAQ makes buildings more resilient when the outside air is polluted.
According to U.S. Global Change Research Program (USGCRP), by 2100 the average temperature in the U.S. is projected to increase by another 3-12oF, depending on emissions scenarios and climate models. In the face of these projected increases, hybrid ventilation approaches utilizing the IAQP and sorbent media-based air cleaning technology for indoor generated gaseous contaminants is an important resource to help commercial building owners beat the heat, save money, reduce emissions, and improve resiliency. If you haven’t yet used the IAQP or sorbent-based air cleaning technology, I encourage you to give them a try. My colleagues and I would be happy to assist.
Check out case studies of buildings where SVT has been successfully deployed.
Karthik Radhakrishnan
Application Engineer, enVerid Systems