How to Electrify Buildings Using Sorbent Air Cleaning & Energy Recovery

Electrifying buildings to achieve net zero energy goals is a key policy goal in a growing number of cities and states around the country. New York City, which is implementing one of the most ambitious plans for reducing building emissions in the nation under Local Law 97, is leading the way, but many other cities and states are quickly following suit.

A key challenge with electrifying buildings currently heated with fossil fuels is the additional strain on building electrical infrastructure. This strain comes from peak heating capacity associated with ventilation requirements. Additionally, conditioning lots of outside air in colder climates often requires resistive electric heating of incoming air, which further strains the electrical infrastructure. These challenges can be mitigated by electrifying buildings using sorbent air cleaning and energy recovery to reduce peak heating capacity requirements.

In our May Ask the Experts blog post with RMI’s Brett Bridgeland we discussed New York State’s Empire Building Challenge and the Resource Efficient Electrification framework that NYSERDA developed with the help of RMI and others to get New York City’s biggest buildings to zero carbon.

This blog post builds on our May post by showing how cleaning indoor air with sorbent filters and installing high efficiency energy recovery systems can enable Resource Efficient Electrification by reducing ventilation heating capacity requirements by up to 85%. This reduction in heating capacity requirement enables Resource Efficient Electrification by:

1. Reducing the capacity requirements for new heat-pump systems
2. Avoiding expensive electrical upgrades for heat-pump retrofit projects
3. Downsizing or eliminate dedicated outside air systems (DOAS) using fossil fuels for pre-heat
4. Reducing the mechanical footprint, and the size and cost of ventilation distribution ductwork

When designing new HVAC systems or upgrading existing systems, specifying engineers and building engineers have two procedures they can follow to calculate mechanical ventilation rates under ASHRAE Standard 62.1:

• Ventilation Rate Procedure (VRP) – a prescriptive method to determine minimum outside air requirements based on space size and occupancy rules of thumb without considering the benefits of source control and removal measures such as air cleaning and filtration.
• Indoor Air Quality Procedure (IAQP) – a performance-based method to determine minimum outside air requirements based on specific IAQ targets and a combination of outside air ventilation with source control and removal measures such as air cleaning and filtration.

The key difference between the two approaches is that the VRP relies only on outside air ventilation to achieve code required IAQ thresholds whereas the IAQP allows for all design strategies to be considered and compared to achieve the same IAQ thresholds. This distinction is critical for Resource Efficient Electrification because replacing outside air with cleaned indoor air has a significant impact on heating capacity requirements.

That said, the use of the IAQP and even the best air cleaning systems will not eliminate the need for outside air ventilation entirely due to building pressurization requirements. Therefore, the most efficient ventilation designs also incorporate energy recovery to precondition the remaining required outside air. When space and maintenance is a concern, high efficiency counterflow energy recovery cores, which can be as efficient and lower maintenance than larger energy recovery wheels, are an ideal solution.

The benefits of combining IAQP-compliant sorbent filters and high efficiency counter-flow energy recovery cores with optimized ventilation rates using the IAQP are shown in the following chart. The numbers displayed represent the percent load reduction relative to a baseline code minimum VRP design scenario with no energy recovery or sorbent filters for a typical commercial office or educational space. These calculations are based on the efficiencies of Oxygen8’s Ventum high-efficiency counterflow core  and enVerid’s HLR 200M sorbent air cleaning system.

The chart shows that adding high efficiency energy recovery to a VRP-based design can reduce the peak ventilation cooling load by 34-65% and annual ventilation energy load by 40-64%, depending on the climate zone. The chart also shows that adding sorbent air cleaning to an IAQP-based design can reduce peak ventilation cooling load by 60-72% and annual ventilation energy load by 57-61%, respectively, depending on the climate zone.

As shown in the chart, the best result is achieved by combining high efficiency energy recovery and sorbent air cleaning with an IAQP-based design. This can reduce peak ventilation cooling load and annual ventilation energy load by 73-86%, depending on the climate zone.

Importantly, all scenarios shown comply with acceptable IAQ thresholds defined by ASHRAE Standard 62.1-2019. Enhanced IAQ thresholds can also be achieved using the IAQP by applying more stringent design targets and more outside air or more sorbent air cleaning.

As more building codes adopt net zero energy as the target for new construction and existing building operations, energy efficient technologies and strategies that do not undermine IAQ goals are critical. Combining an IAQP-based design with sorbent air cleaning and high-efficiency energy recovery is a key enabler to achieve net zero energy goals through Resource Efficient Electrification.

To learn more about how to layer different technologies to achieve better indoor air quality more energy efficiently, read our white paper How to Achieve Sustainable Indoor Air Quality or take our free online course for CE/PDH credit.