Updates to ASHRAE Standard 90.1 Make Unlocking Energy Savings using the IAQP Even Easier

Our last blog post summarized recent updates to ASHRAE Standard 62.1 that make it easier to design HVAC systems with less outside air ventilation using the Indoor Air Quality Procedure (IAQP) in order to reduce the cost and climate impact of HVAC systems.  

In this blog post, we examine a recent update to ASHRAE Standard 90.1-2022, the Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings, that enables design teams using the IAQP with gas-phase air cleaning to claim energy savings with respect to a design that uses the VRP and no gas-phase air cleaning. This update was approved by the ASHRAE Standards Committee on March 27, 2024 and subsequently published here as Addendum n to Standard 90.1-2022.  

Addendum n to Standard 90.1-2022 

As the foreword to Addendum n states, Standard 62.1 offers two procedures for determining minimum outdoor air intake flow: the Ventilation Rate Procedure (VRP) and the Indoor Air Quality Procedure (IAQP). The foreword also points out that, “The IAQP can lead to a more energy efficient design (lower outdoor air requirement) by incorporating gas-phase air cleaning to offset a portion of the outdoor air requirement under the VRP.” According to Section 6.1 of Standard 62.1-2022, “although the intake airflow determined using each of these approaches [the VRP and the IAQP] may differ significantly because of assumptions about the design, any of these approaches is a valid basis for design.” 

Despite these two procedures for determining minimum outdoor air intake flow for acceptable indoor air quality, Standard 90.1 Normative Appendix G used to require baseline and proposed case ventilation rates be the same. As such, Appendix G did not enable design teams using the IAQP with gas-phase air cleaning to claim energy savings with respect to a design that uses the VRP and no gas-phase air cleaning.  

Addendum n fixes this by doing the following: 

• Introducing a new Exception 5 to Section G3.2.2.4 

• Adding a new section, “Air Cleaning” to Table G3.1 to explicitly specify that the baseline-case energy model should not include gas-phase air-cleaning system energy 

The new Exception 5 to Section G3.2.2.4 reads as follows: 

Where designing systems in accordance with Standard 62.1, Section 6.3, “Indoor Air Quality Procedure,” baseline ventilation airflow rates in those zones are permitted to be greater than the proposed design and shall be calculated in accordance with Standard 62.1, Section 6.2, “Ventilation Rate Procedure” and the following: 

• For single-zone Systems 1, 2, 3, 4, 9, 10, 11, 12, 13, as specified in Table G3.1.1-4, the zone air distribution effectiveness shall be (Ez) = 1.0 as defined by Standard 62.1, Table 6-4. 

• For multizone Systems 5, 6, 7, 8, as specified in Table G3.1.1-4, the system ventilation efficiency shall be (Ez) = 0.75, as defined by Standard 62.1, Section 6.4.2.3.

Energy Savings Potential of the IAQP 

A recent study by Performance Systems Development (PSD) and enVerid compares energy modeling results for IAQP designs with gas-phase air cleaning and VRP designs with no air cleaning. According the study, up to 23% of building energy can be reduced when applying the IAQP with gas-phase air cleaning. The findings of this study are supported by measurement and verification (M&V) of energy savings from projects that used the IAQP. The M&V results from an example university project are summarized below.  

University Project – Building 1 – M&V Summary 

Building 1 is a 45,000 square foot university building primarily serving offices and classrooms. There are two mixed air AHUs in the basement mechanical room, each serving half of the building. As shown in Figure 1 below, the baseline (VRP) outdoor airflow for AC-1 and AC-2 was 3,500 CFM and 3,000 CFM, respectively. By installing 1 enVerid HLR air cleaning module on each AC unit, the IAQP outdoor airflow for AC-1 and AC-2 was reduced to 1,100 CFM and 1,000 CFM, respectively. This represents a 68% reduction (4,400 CFM) in outdoor airflow compared to a VRP design baseline.  

Figure 1 – VRP and IAQP Outdoor Airflow

The reduction in outdoor airflow resulted in a savings of 215,000 kBtu/year, saving about $9,000/year in annual energy costs. The energy cost savings are broken out by utility in Table 1 below.  

Table 1 – Energy Cost Savings 

 In addition to the PSD study and M&V results, ASHRAE has also discussed the advantanges of IAQP designs over VRP designs. According to the ASHRAE Standard 62.1-2019 User’s Manual: 

• “The IAQP may allow for a more cost-effective solution to providing good IAQ, as all design strategies may be considered.” (pg 100)  

• “The use of air cleaning with recirculation could allow for a reduction in the amount of outdoor air required with a concurrent reduction in associated energy costs.” (pg. 20) 

Given the significant energy benefits achieved with the IAQP, we expect this important update to Standard 90.1 will lead to more design teams using the IAQP in their HVAC designs and energy models.  

Need assistance with an HVAC design or energy modeling? Our team of Application Engineers is standing by to provide design and modeling assistance. Contact us here.