California’s new indoor air quality regulations for multifamily dwellings require smart engineering

In a recent post, we showed why California’s latest energy code for new buildings and retrofits will require targeted MEP design in order for projects to be both code-compliant and cost-effective. The 2019 Code addresses all classes of buildings, from residential to commercial, low to high-rise, as well as design specifics such as on-site renewable energy production and water prudence. One area that deserves special focus is updated guidance on building and mechanical features that impact indoor air quality. When taken individually, the stricter requirements for ventilation systems, exhaust ducts, airflow, and air filtration may seem minor, but when approached as a whole they present a host of new challenges that building owners are only beginning to comprehend. Each of the new standards will require design methods that, if approached hastily or without a full understanding of the implications for the entire system, will result in costly and time-consuming corrections.

Indoor air quality has health and comfort implications

Before getting into these new design considerations, it’s important to understand the motive behind these code changes. Ultimately, by focusing on the mechanical components that regulate indoor climate, the state hopes to improve the health, comfort, and overall well being of indoor occupants. Commercial buildings are already subject to similar regulations, and business units such as offices and factories invest considerable time and money in modulating indoor air properties. In doing so, they have achieved benefits such as higher worker comfort, which leads to improved job satisfaction, productivity boosts, and increased output. Up until now, however, multifamily dwellings such as apartment buildings and single-family homes have not been subject to tight regulations.

“Natural ventilation” is imperfect and ineffective

Typically, “natural ventilation” which is achieved via windows, fans, and open doors has been deemed adequate for residential units. However, these methods make it difficult to control airflow and can negatively impact the building’s envelope. For example, when new apartment buildings are constructed a host of airborne contaminants and chemicals are emitted from fresh construction materials and manufactured installations. Mold leakage and fumes from household cleaners can also seep into rooms over time. For inhabitants with existing health problems, weakened immune systems, or infants and the elderly, these airborne contaminants have the potential to cause illness and respiratory problems. Further, unfiltered outdoor air presents its own set of risks, such as urban air pollution, dust, and seasonal attributes such as pollen. In both cases, opening a window or installing a fan cannot provide a comprehensive solution. An efficient and reliable ventilation system works to remove polluted air while continuously introducing fresh, clean air.

Balance is key with airflow

Besides the purity of the air, how it flows through an indoor space deserves equal attention. Air currents impact the well being of building occupants. A room with the windows closed and without ventilation and exhaust systems will feel stale and suffocating. At the other extreme, too much draft creates chill and discomfort. To achieve a pleasant medium, airflow should be enough to continuously replace stale air with fresh air, but light enough so as not to create a discernible draft. The relationship between the rate at which air is supplied to a room and the rate at which it is released is referred to as a ventilation system’s “balance”.

Updated regulations are individually small, but as a whole make an impact

Changes made to the 2016 Title 24, Part 6 Building Energy Efficiency Standards and incorporated in the 2019 Energy Code that apply to air quality and airflow in low-rise residential buildings are mainly detailed in section 150(m) and 150(o) and include the following:

• Any new or complete replacement HVAC system must now install MERV 13 air filters. The “13” rating is a measure of efficiency and indicates a nominally 2” thick filter. Previously, only MERV 6 (or nominally 1” thick) filters were required. Because of the increased thickness of the new filters, system design airflow will be impacted and should be taken into account during the design process.

• HERS-verified AHU fan efficacy for gas furnace systems manufactured after July 3, 2019, has decreased from 0.58 to 0.45 W/CFM or less, meaning fans must consume less energy per cubic feet per minute of air they discharge.

• In the case of small duct high velocity forced air systems, both airflow and fan efficacy must be HERS-verified, and system airflow must be 250 CFM/ton, compared to 350 CFM/ton previously.

• 2016 ASHRAE 62.2 ventilation and IAQ requirements now apply to multifamily dwelling units. This in effect increases the total ventilation rates for these structures. For single-family residences, town-homes, and multifamily dwelling units, the following equation establishes the Total Required Ventilation Rate:

Q_tot = 0.03(A_floor) + 7.5(N_br + 1)

where:

Q_tot = Total Required Ventilation Rate, CFM

A_floor = Dwelling Unit Floor Area, ft²

N_br = Number of Bedrooms (must be ≥ 1)

• Multifamily buildings have two options to provide the required outside air to each unit. Option one is a balanced ventilation system consisting of supply and exhaust fans operating simultaneously via a shared control system that keeps the mechanically supplied outside air and exhaust air within 20% of each other. Option two is an unbalanced system consisting of supply fans or exhaust fans only, with the dwelling unit envelope meeting air leakage requirements. This latter point implies leakage being less than or equal to 2 ACH50, where ACH50 is the air change per hour at a 50 Pascal pressure differential.

What do these changes mean for your new multifamily dwelling unit build?

“These new rules for multifamily dwelling units present several challenges for building owners, architects, and project managers,” says Amir Amiri, CEO of 120 Degreez Engineering.

One of the biggest changes that impact the engineering design is the requirement that the ventilation intake and the point of exhaust must be located ten feet apart.

“Imagine you have an apartment building where each unit is between ten to twenty feet wide and side-by-side maybe ten to twenty of such units,” explains Amiri. “That’s an enormous challenge from an engineering standpoint because you simply don’t have enough space when applying the traditional design methods to meet the new code.”

Putting energy-saving design principles into play

When the new energy codes were released, Amiri and his team realized they had to devise new design methods. As the construction of multifamily dwelling units got underway in 2020 California, developers would be blindsided by the new spacing requirements. If they realized the problem only once the design process was in progress, they would be forced to assemble untested last-minute solutions, or go back to drawing board and start from scratch.

“We came up with some unique, cost-saving solutions,” says Hady Makhmalbaf, a senior mechanical engineer at 120 Degreez. “What we can now offer is engineered solutions that meet the stringent new energy code, including the updated rules on airflow and indoor air quality.”

120 Degreez’s engineering team has developed energy-saving measures that incorporate an energy recovery unit (ERU), which is a heat exchange system that continuously draws exhaust air from a space and provides fresh air to it. For these systems, effectiveness is defined by how much of latent/sensible load is recovered versus the maximum theoretically recoverable amount. This number for a modern ERU is expected to be between 60-75% for both latent and sensible loads.

“Compared to 20 or 30 years ago, these systems have become cheaper and more efficient and much more popular to the point that we even see them in houses in many projects,” concludes Amiri. “With the tighter air quality standards in California, they’ll be an invaluable asset and one that we are championing.”

Resources:

2019 Building Energy Efficiency Standards (California)

https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/2019-building-energy-efficiency

http://epubs.iapmo.org/2019/CMC/mobile/index.html