How to Make HRV/ERVs Work for Your Design ... and Your Client

All homes, rather all occupants, need fresh clean outside air. California building code requires a certain amount of outside air (OA) be introduced into our homes through a steady mechanical system. The OA system(s) are governed by California’s Energy and CALGreen Codes – referenced under the Indoor Air Quality (IAQ) Ventilation section.

As new construction builds become tighter, with less air-infiltration and exfiltration, we are starting to see more of our clients choose balanced ventilation systems in order to maintain the tight building envelope. Exhaust-only ventilation, such as a continuously running bathroom fan, meets the building code default minimum required ventilation, but also pulls makeup air through cracks in the building envelope, creating unwanted air infiltration.

Balanced ventilation systems can be as simple as one exhaust fan and one supply fan operating simultaneously. But for a more energy efficient system, and potentially a simpler installation, a ducted heat recovery or energy recovery ventilation (HRV /ERV) unit can be used. These units use a bypass system to recover heat (and in the case of ERVs, moisture) and exchange it between outgoing air and incoming fresh air.

Photo: Example of a multifamily installation with easily accessible Merv 13 filter and ERV Core.

Optimizing

While these products have been on the market for over a decade, we find that their performance and client benefit can be optimized by following a few tips.

First, noise levels are generally low for ERV/HRV units, but higher fan speeds can result in “humming” or vibrations. It’s always a good idea to consider options for isolating the unit from framing and/or using a duct silencer in the design.

Second, with any HRV/ERV system it is important to let the design/construction teams and the homeowner or maintenance personnel know that the code required MERV 13 filter needs to be changed regularly. Some HRV/ERV units can be ordered with HEPA filters, meeting and exceeding the MERV 13 requirement in California.  Additionally, the interior of the unit and core will need periodic cleaning, typically done with a vacuum.

Lastly, because HRV/ERVs run continuously, it is important to let the homeowner or occupant know that in cases of very poor outdoor air quality, such as in wildlands fire, that the unit can be turned off manually, then turned back on after the air quality improves. Installers should provide an easily accessible and labeled on/off switch. Providing information near the unit on how to purchase replacement filters does wonders for actually making it happen!

All-Electric Design & Construction Series (ZNCD)

In Balance Green Consulting is pleased to present a two-part education course entitled All-electric Design and Construction. The classes are in person in San Luis Obispo.

On the path to Zero Net Carbon Design, building electrification is the key to reducing operational carbon. In this in-person course, we’ll share the nuts and bolts of incorporating all-electric systems into residential and small commercial projects, including tips for implementation as well as client communication. We’ll provide straight-forward information on current systems and technologies, plus a look ahead at what’s emerging in the market. 

Day 1 - October 10, 2024 (8:30 AM - 11:00 AM)

• Overview: Carbon Reduction through Building Electrification 

• ZNCD for Heat Pumps for heating and cooling 

• ZNCD for Domestic Hot Water (Part 1)

Day 2 - November 7, 2024 (8:30 AM - 11:00 AM)

• ZNCD for Domestic Hot Water (Part 2)

• ZNCD for Ventilation and HRV 

• ZNCD for Appliances & Energy Storage 

This series has been developed to fulfill the California requirement for five hours of ZNCD education as part of architecture license renewal. Although created with architects in mind, the content is broadly applicable across the building industry.

Learning Objectives include:

• Learn the ‘why’ behind California’s shift to building electrification and the link to Zero Net Carbon Design

• Learn the pros and cons of various products to help in selecting appropriate systems that meet electrification and carbon-reduction goals

• Learn critical installation details such as dimensions and venting to call out in plans and/or identify early in construction

• Understand the local market for specific all-electric/ZNCD equipment, including cost, availability and lead times

Presenters:

• Jennifer Rennick, AIA, Certified Energy Analyst

• Andy Pease, AIA, LEED AP BD+C

• Grant Murphy, CEA, CBCP, PHT

This is an in-person course, provided in partnership with the AIA California Central Coast Chapter and through 3C-REN, funded by rate payer dollars.

Location: RRM Design Group, 3765 S. Higuera St., Suite #102, San Luis Obispo

Doors open at 8:00 AM for coffee, snacks and networking. Attendance is free.

5 AIA HSW & CA ZNCD Learning Units

For more information and registration: October 10 session, November 7 session

Indoor Air Quality in Times of Wildfire

When wildfire erupts, which happens more and more often, a primary concern for those out of immediate danger is air quality. Wildfire sends a variety of pollutants into our air that can include CO2, black carbon, acid gases, sulfur dioxide, nitrogen oxides, PM10 and PM2.5, aromatic hydrocarbons, and even lead. Yuck.

How do we keep what’s burning outside from getting inside our living spaces, and ultimately into our lungs? Fortunately, our buildings and attention to air quality details can make a big difference.

New Homes

California code for new residential construction (single family, multifamily and high rise) requires two mechanical ventilation functions.

·      Local exhaust in bathrooms and kitchens to remove occupant-generated moisture and odors where and when they are generated.

·      Whole dwelling ventilation systems to automatically ensure an adequate amount of indoor/outdoor air exchange year round, regardless of window operation.

Methods for ventilation fall into three categories:

·      Exhaust fan only (typical)

·      Supply fan only (uncommon)

·      Balanced ventilation (becoming more common, optimal if installed/designed correctly)

While code compliance can be achieved through any of these systems, typically it’s an exhaust-only design with continuous fan that is used. The code requires that a manual on/off switch be installed and signage posted so that users know to turn off the fan when the outside air is of poor quality, but it’s rare that we see the switch and signage implemented or enforced. What this means is that measures intended to provide fresh air might just be bringing in smokey air.

Older Homes

ASHRAE 62.2 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings went into effect January 2009. In prior code cycles it was allowable to show that operable windows were sized to meet ventilation standards. Research in the 1990s and early 2000s showed, however, that operable windows were not being used consistently by occupants and most exhaust fans were under performing or non-existent.

Because of this, occupants of homes constructed prior to code changes requiring ventilation and tightened building envelopes may have poorer automatic ventilation built in, i.e. no mechanical exhaust fans and only operable windows. Although an open window will do wonders, especially in our Central Coast climate zones, there are times when you need to close windows, and air changes would only occur through a leaky envelope, concentrating pollutants into your living space.

In all homes, understanding which pollutants are present, in what concentrations, and how to filter them out of your breathing air are key strategies to minimizing harm to your health.

Tip #1: Get familiar with air quality safety thresholds for key pollutants.

· CO2 – Yes, we usually talk about this molecule in the context of climate change, but it can also contribute to poor indoor air quality. Typical indoor air ranges from 400-1000 parts per million (ppm). Higher than 1000 ppm can lead to drowsiness; 2000-5000ppm can cause headaches, loss of focus, nausea.

· PM10 and PM2.5 – Both are abbreviations for “particulate matter” and the size (diameter) in microns. Particulate matter is not a single pollutant, rather a chemical mix of solids and aerosols from sources such as combustion, dust, pollen, and wildfires. PM10 is primarily associated with the smoke smell during a wildfire, while PM2.5 is smaller, generally odorless, and can enter more deeply into lung tissues.

· Ozone, NO2, VOCs, Formaldehyde – These pollutants all have their own health effects and safety thresholds. Notably, VOCs and formaldehyde are also generated in household cooking, so it can be helpful to have an air quality monitor in your kitchen that then serves double-duty in times of wildfire.

A note about safety thresholds and monitoring options: some standards are based on average annual exposure, while others specify a higher maximum exposure over a shorter time period (typically 24 hours).  And to confuse matters more, state, national and international bodies have set different thresholds for “safe” exposure.

For instance the California Air Resources Board and the National standards vary quite a bit from one another regarding PM2.5 and PM10…

… while the World Health Organization comes in with recommendations that are lower than both.

A commonly found aggregate measure AQI is often used with color coded messaging (green = good, yellow=caution, red=dangerous, etc.). While AQI is a convenient short-hand assessment, the built-in thresholds might be higher than you are comfortable with, so people with sensitivities might benefit from taking a closer look at the assumptions underlying the categories.

Tip #2: Know where your fresh air comes from.

When your home is supplied with fresh air through mechanical means, know whether it’s a continuous fan and where the shut off switch is located. If air changes come in the form of leakage through your building envelope (typically around doors and windows, through floors and wall penetrations), you may need to take into account an increased demand for filtration of the indoor air.

A tabletop air quality monitoring device can be a valuable tool for assessing your indoor air. In my home, we keep one plugged in near the kitchen so we notice spikes in certain pollutants (during cooking for instance) and can hear the gentle alarm chime when air quality goes from green to yellow or worse. As with the AQI however, take care to note the underlying threshold standard (found in the manual). Ours had a surprisingly high threshold of 75micrograms/m3 for PM2.5 before it signaled a problem, which is well beyond any of the standards listed above.

Tip #3: Make sure you have air filtration (with backup filters on hand).

Check your current filtration method. Is it a filter on your furnace or outside air intake? What’s the MERV rating? Has the filter been changed lately?

Although, ducted HVAC (heating, ventilation, and air-conditioning) are commonly closed systems with no outside air intakes, the filter can help clean up the inside air while the unit is running.  Depending on its age, the filter might be only a MERV 8 and 1” thick.  Changing out to a higher MERV filter may cause too much static pressure in your system, warranting a 4” thick filter that could require modifications to your HVAC system. Seek the help of an HVAC specialist if you want to use a higher MERV filter.  

You may also consider using a portable air filtration device. Many portable filters offer higher filtration options, including HEPA, which is equivalent to MERV 17 or higher. Check the square footage rating of the equipment to be sure it can clear the air quickly. Here’s a handy chart for MERV filtration, note the PM2.5 filtration capabilities.

The middle of a wildfire or bad air event isn’t the best time to try to buy replacement filters or a portable air filtration device. Waiting even a day or two for delivery is tough when you need it asap! Know your current filtration methods/options, then stock up for a smoky day. You’ll be glad you did.

All-Electric Multifamily Housing Project Pismo Terrace is Open!

In Balance is excited to share that the all-electric multifamily housing project, Pismo Terrace, is complete and open! The project in Pismo Beach is comprised of two three-story buildings with 50 affordable housing units and amenities such as a community room, commercial kitchen, laundry, playground, and bike racks.

In Balance Green Consulting worked with architect, Ravatt Albrecht & Associates, and contractor/developer, People’s Self-Help Housing (PSHH), on energy optimization, photovoltaic (PV) sizing, and other sustainability consulting.

The team decided early in the design process to go all-electric and implement features targeting energy efficiency to reduce overall energy consumption. The project incorporates electric heat pump space heating, heat pump water heating, and electric ranges, eliminating the need for gas infrastructure. This saved money as there was no need to place gas meters, nor run gas piping throughout the building.

Quality insulation installation (QII) and a high-performance roof with R-32 cavity fill insulation and continuous R-5 roof insulation reduce heat transfer that would cause higher energy use. The PV system was designed to generate 133,696 kWh of electricity per year, offsetting 65% of the predicted annual residential energy use.

In Balance is excited to see more of our multifamily housing projects going all-electric and prioritizing sustainable measures to contribute to healthier and more comfortable homes. As California’s energy grid becomes cleaner, going all-electric and eliminating fossil fuels from our buildings continues California’s progress to reducing greenhouse gas emissions. Congratulations to the team!

Have an all-electric project you are working on, contact us!