Let's Get Some Fresh Air in Here: Operable Window Automation for IAQ

In November, I shared information about our visit to Living Places Copenhagen, a demonstration home in Denmark addressing energy efficiency, environmental impacts and indoor air quality. Using the project as a ‘living laboratory’, the Living Places team collected data throughout the project and has now published the results. Through my weeklong stay at the house and subsequent review of the data, I found the approach to, and results of, the indoor air quality (IAQ) design particularly informative and inspiring.

Typically, we rely on one of two approaches to IAQ in residential projects: an open window or mechanical ventilation.  Opening a window is great but relies on humans to be present and aware of indoor conditions. Mechanical ventilation is also crucial, especially balanced ventilation with heat recovery, but unless you’re actively heating or cooling the building, mechanical ventilation expends unnecessary energy. A third option is the one used in Living Places – operable fenestration (windows or skylights) linked to CO2 sensors to open and close automatically. In that project, the automation is also linked to temperature and humidity sensors for thermal comfort.

CO2 Data Collection and Analysis

The two occupiable homes in Living Places were designed with discreet differences so they could analyze components in isolation. For IAQ, they set up one house to only use the automated skylights, while the other house used a hybrid, adding mechanical fans as well. CO2 levels were measured with calibrated environmental sensors placed in habitable rooms of occupancy. After two months, they found that both homes meet the European Standard (EN 16798-1:2019) for indoor air quality! The European standard is generally equivalent to 750 ppm or below.

Two caveats: First, the homes are designed for effective air movement throughout all spaces, incorporating the stack effect to connect all three floors. Other homes may not have enough connectivity to achieve adequate air movement.

Second, the study was conducted over the summer in Denmark. Air conditioning was not installed or needed, based on the climate and the passive thermal strategies. The home is extremely well insulated and designed for passive heating in the winter, but the homes were not tested for IAQ with thermal comfort demands during winter conditions.

Note that, in California, operable windows and skylights do not replace the code requirement for mechanical ventilation.

Comfortable Personal Experience

For those of us staying in the house, we all felt comfortable and appreciated the indoor conditions. Throughout the day, we would see individual skylights and roof windows open and close. We had remote controllers to override the automation at any time if desired, and the units include weather sensors to automatically close skylights if there is rain. The sensors throughout the house were tied to an app that we could check at any time. Use of the app, along with directly observing the automation, helped build awareness as we ‘tuned in’ to our activity levels, the number of people in the room and changes in temperature, and the collective impact on our comfort.

Using automation for operable skylights and windows can support comfortable temperature and indoor air quality under many conditons. Our experience in the home was for Velux brand of products, but other automatic operation systems are available. One more tool in shared toolbox!

For more information on the project analysis, see “Learnings” on the Velux website.

Questions about optimizing IAQ for your project? Reach out.

All-Electric Remodel Construction Site Tour - February 11

Do you love visiting construction sites? We do too! So we’ve partnered with 3C-REN to offer tours of high performance, all-electric projects on the Central Coast.  The first will be in San Luis Obispo on February 11 at 3:30pm, visiting a major residential remodel. The builder, Mike Horgan of Cairn Collaborative, will lead us through the energy efficiency and electrification upgrades, providing first-hand information on implementation, lessons learned and best practices.

Topics covered include:

• Installation requirements and options for heat pump mechanical systems.

• Observe an installed heat pump hot water system and learn the space and location requirements and potential pitfalls to avoid.

• Discuss ventilation and indoor air quality and different options appropriate for retrofits versus new construction.

• Review wall, floor and roof assemblies for both insulation and air sealing best practices.

Project location will be provided to registered participants. To register for this free program, go to the 3C-REN calendar page HERE.

Stay tuned for tours in Santa Barbara and Ventura Counties. Have a project you would like to include on a tour? Let us know!

Living Spaces - A View from Cophenhagen

In our industry, we are always looking for innovative ways to create the buildings we need while reducing environmental impacts. Throughout California, we need housing that is more affordable so families who work here can afford to live here. We also need to reduce our carbon footprint, protect our open spaces and conserve energy. So, when I learned about a low-carbon, energy-efficient prototype housing in Copenhagen Denmark, I was very interested. And when lead partner Velux invited me and some others to go live in one of the houses for a week over the summer, I jumped at the chance.

Called Living Places, the project was developed in 2023 as an exhibition at the UIA World Congress of Architects. Located in an older industrial area of the city, the project consists of seven structures – five open pavilions and two completed homes – connected by an elevated system of walkways, patios and gardens.

The core principles of the project include building homes that are healthy for people and planet, shared spaces to strengthen community, simple so the cost is lower, adaptive to accommodate more ways of living, and scalable for builders to adopt the approach quickly and broadly.

I was impressed with so many aspects of the project and plan to write up some blogs over the next few months. In the meantime, check out this 4-minute video highlighting some of the project features. More information is also available on the Velux website. Or reach out to me, andy@inbalancegreen.com so we can chat about innovation and how to implement great ideas here at home.

Disclaimer: Velux sponsored my travel and stay at Living Places; all opinions are my own.

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!