Cost Implications of Different Ventilation Strategies to Simultaneously Achieve Energy, IAQ, and Resiliency Goals

Published 02/29/2024
By Christian Weeks
K-12

For my last Ask the Experts blog post, I caught up with Dr. Bill Bahnfleth to discuss COVID, climate change, and carbon emissions and how ventilation and IAQ standards are evolving to keep up with market needs. One of the insights Bill shared is that the days of trading off energy and IAQ in how we design and operate ventilation systems are over. According to Bill, we need to embrace a new paradigm that simultaneously deals with energy, IAQ, and resiliency goals.  

Bill went on to discuss three recent updates from ASHRAE that enable these three goals: 

  1. Three addendums to Standard 62.1 between February 2022 and October 2023 that simplify and clarify the IAQ Procedure (IAQP) and better define requirements for air cleaning systems1; 
  2. The publication of the new Standard 241 Control of Infectious Aerosols that is based on the concept of equivalent clean air and the use of air cleaning; and  
  3. The new Guideline 44 that ASHRAE is finalizing to define strategies to make buildings resilient to wildfire smoke. 

Since my interview with Bill, ASHRAE published a paper by my colleagues Dr. Marwa Zaatari and Joe Maser that examines the cost implications of different ventilation strategies to simultaneously achieve energy/carbon reduction goals and new IAQ and resiliency benchmarks defined in Standard 241 and the proposed Guideline 44. The paper’s conclusion, which is based on extensive energy modeling, aligns nicely with another key point that Bill made: “The key to achieving this new paradigm is looking at alternatives to outdoor air, which is often expensive to condition and may be polluted.” 

The Analysis  

The peer-reviewed paper by Marwa and Joe, which is called “ASHRAE Standard 241: Energy Implications of Different Strategies to Meet Equivalent Clean Air Requirements for Commercial and Educational Spaces” and which can be purchased via the ASHRAE Technology Portal, analyzed the impact on cost, energy consumption, and carbon emissions of different ventilation strategies that comply with Standard 62.1 (normal operations), Standard 241 (“infection risk management mode” or IRMM), and the proposed Guideline 44 (“wildfire smoke mode” or WFSM).  

The design approaches considered included multiple “hybrid ventilation” strategies that combine filtration and air cleaning of recirculated indoor air with outside air using the Ventilation Rate Procedure (VRP) and the performance-based IAQ Procedure (IAQP), energy recovery ventilation (ERV), mechanical particulate filtration (MERV 7, 11, and 13), HEPA in-room air cleaners, and UVGI disinfection for 5 space types (office, K-12 classroom, lecture hall, retail, and warehouse) in 15 ASHRAE climate zones.  

The Results  

The analysis shows that it is possible to achieve IAQ benchmarks under all conditions (normal operations, IRMM, WFSM) in a cost effective, energy efficient way by providing the minimum prerequiste outside air using the IAQP with air cleaning and/or disinfection to reduce the concentrations of pathogens, particles, and gases rather than only depending on outdoor air for dilution using the VRP.  

The main conclusions of the paper for the five ventilation strategies considered (see Table 7 and Figure 1 below) are the following: 

  • Among all the ventilation strategies considered that comply with Standards 62.1 and 241, IAQP + ERV is the most energy efficient and the least costly to purchase, install, and operate. 
  • For offices, the only ventilation strategy that complies with both IRMM and WFSM is IAQP with MERV 11 filters. 
  • For K-12 classrooms and lecture halls, the ventilation strategies that comply with both IRMM and WFSM are IAQP with MERV 7 and HEPA filters or IAQP with MERV 13 filters and UVGI. 
  • For retail, the only ventilation strategies that comply with both IRMM and WFSM is IAQP with MERV 11 and HEPA filters or IAQP with MERV 13 filters and UVGI. 
  • For warehouses, one can comply with IRMM and WFSM using the VRP or IAQP coupled with at least MERV 11 filters. 

These results assume that the IAQP is enabled using a gas-phase air cleaning system with a minimum efficiency for formaldehyde of 70% to achieve a 75% reduction in outdoor air compared to the VRP baseline case. This is supported by a National Renewable Energy Laboratory report published in 2020.  

For office and K-12, the paper includes tables summarizing the cost to implement and operate each ventilation strategy that complies with Standards 62.1 and 241. Table 7 for K-12 shows that the least cost, most energy efficient ventilation strategy to comply with IRMM across climate zones is IAQP and ERV and that in-room HEPA with MERV 7 is more expensive to operate than UVGI and MERV 13 but has a lower first cost than UVGI and MERV 13.  

K-12 Classroom Cost Outputs Existing Buildings

For office, the least cost, most energy efficient ventilation strategy to comply with IRMM is IAQP and ERV. The results are similar for lecture halls, retail, and warehouses.  

Figure 1 in the paper shows energy consumption (kWh/sqft) for IRMM compliant scenarios in 4 climate zones for three existing buildings space types. The gray bubbles represent tons of carbon dioxide emitted per 100,000 sqft. A fire symbol is added when the scenarios comply with WFSM. The figure for the three space types in climate zone 1A is below and shows that strategies using the IAQP require the least energy, emit the least carbon, and are the only strategies that comply with both IRMM and WFSM 

Climate Zone 1A 

Energy Consumption (kWh/ft2

Office 

Compliant to Standard 241 

K-12 Classroom 

Compliant to Standard 241 

Retail 

Compliant to Standard 241 

 

Office

 

K-12

 

Retail

These findings correspond nicely with Bill’s call to embrace a new paradigm that simultaneously deals with energy, IAQ, and resiliency goals. Using the updated IAQP with high efficiency particle and gas-phase air cleaning, this new paradigm can be a reality now.  

Contact us to learn how to use Sorbent Ventilation Technology to cost effectively comply with the updated Standard 62.1 IAQ Procedure, Standard 241, and proposed Guideline 44.

1The three addendums are Addendum aa to 62.1-2019 published in February 2022, Addendum n to 62.1-2022 published in September 2022, and Addendum c to 62.1-2022 published in October 2023.  

Christian Weeks

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