ERV + AHU?

Everyone pretty much gets that continuous (or very frequent) ventilation is necessary in high-performance homes. And – at least in theory – most people get why balanced, heat recovery ventilation is better (than unbalanced and/or without heat recovery). But the devil’s in the details.

A couple years ago we started an R&D project with funding from DOE’s Building America program, and one of the first steps was interviewing several developers about ventilation (single- and multi-family residential, mostly on the East Coast). For none of these developers were HRVs or ERVs standard.[i] They all had some experience with ERVs, however, and when asked about these experiences the word “nightmare” came up shockingly often.

The ERVs on the market now can certainly work well in the right application, but we see problems more often than not. One of the biggest challenges is trying to add ERVs on to central heating/cooling systems in homes. Most ERVs aren’t really designed for this, and here’s what we see:

  • Ducts connected to the wrong places! Outlet and inlet ducts get reversed, or the supply air from the AHU getting exhausted (sad how often this happens).
  • ERVs are attached to supply and/or return trunks of the AHU. Unless the AHU fan is running constantly (or whenever the ERV is turned on), outdoor air comes into the AHU and is sucked right back out the ERV exhaust.
  • If the AHU fan is turned on, the relatively small fans in the ERV can’t successfully compete with the big AHU fan. People don’t get the ventilation flow rates they want and/or the flows are very unbalanced.
  • AHU fans can use A LOT of electricity. Hundreds of Watts is common – I’ve measured over 1 kW (though this is changing – more below).

Even if installers follow manufacturer instructions for attaching ERVs to AHUs, they could still end up with low flows, unbalanced flows, or high electricity consumption. Through this DOE R&D effort, we’re trying to do better.
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Does Your Exhaust Fan Suck? Part 2

If you recall from Part 1 of this article written back in September, we discussed why exhaust fans often don’t operate as they are intended. Now, let’s discuss how to rectify these issues. First, we need to understand that all fans are not created equal. To do this, SWA participated in a “blind” study that analyzed a number of today’s common exhaust fans. The study emphasizes the importance of fan selection. With this understanding, we will then discuss solutions and best practices for installing bathroom exhaust ventilation.

The “Blind” Study

To get a comprehensive performance dataset for a number of exhaust fans, the Riverside Energy Efficiency Laboratory (REEL) was engaged for a “blind” study. REEL is the HVI/ESTAR neutral, third-party testing facility. In total, 7 multi-speed fans, 7 single speed fans, and 6 low-profile fans from six manufacturers were sent to REEL without manufacturer markings. In general, ten-point airflow tests were conducted on each fan. Testing adhered to standards used in the industry, namely, ANSI/AMCA Standard 210 and HVI Publications 916 and 920, where applicable. While the dataset is extensive, this paper focuses on the 50, 80, and 110 cfm ventilation rates, as these are the most common specified fan speeds for bathrooms. These fan curves show the relationship of airflow that will be delivered at various static pressures of the duct system.

Figure 1 shows fan curves for single speed fans that were tested. The units are rated for 80 cfm unless noted otherwise in the legend (two are rated for 70 cfm and one for 90 cfm). While all of these fans performed in a similar manner, would it surprise you that two of the fan curves in Figure 1 are for exhaust fans that use DC motors? People often assume that all fans using DC motors are the same and result in constant airflow for a range of static pressures (let’s say up to 0.4” w.g.).

Figure 1

Figure 1. Performance Data for Single Speed Exhaust Fans

It is clear in this data (Figure 1) that flow rates decrease rapidly when static pressure rises over 0.3” w.g., as it often does in real world installations. Oh, are you still wondering which two fans have DC motors? It is actually SS-05 and SS-06. A bit surprising, isn’t it?

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Here’s What DC’s New Energy Efficiency Requirements Mean for Existing Buildings

Mayor signing legislationDistrict of Columbia Mayor, Muriel Bowser, signed a landmark piece of legislation known as the Clean Energy DC Omnibus Amendment Act this past Friday. With the mayor’s signing, Washington, DC becomes one of the first jurisdictions in the country with a binding, comprehensive law aimed at reducing greenhouse gas emissions. “It allows us to make significant improvements to the energy efficiency of existing buildings in the District,” Mayor Bowser said at the signing ceremony located at the American Geophysical Union (AGU) Building, which is slated to become the first net zero commercial retrofit in DC when it reopens later this year.

The new law has several sections which will impact the buildings in which DC residents and businesses live and work. In this post, we’re going to focus on Title III of the Clean Energy Omnibus Amendment Act, which is designed to make the city’s existing buildings more efficient.

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Here’s to Our Buildings, Our Health! SWA’s Top 10 Tips for a Healthier Indoor Environment – Part 2

Quick pulse survey: in the last three months, since we published our Part I blog on tips for healthier indoor environments, how many of you have either incorporated some of our healthy recommendations into your home, or informed your clients on the most effective ways to address health risks in buildings (hint: if you need a refresher, please visit Part I)?

As previously discussed, there is overwhelming evidence for the business case for healthier buildings, from greater employee productivity and reduced sick days in the workplace to reduced asthma incidents and ER visits for children living in green housing. Leading organizations know that improved wellbeing helps employees to be healthier and lowers healthcare costs. It also helps employees to be more productive, creative and innovative, and less likely to leave for a competitor. The same concept can be applied to tenants in rental buildings and condos.

Before we dive into health tips #6-10, here are some fun (and not so fun) facts to keep in mind while we spend winter days INSIDE our workplaces, schools and homes:

  • USGBC graphic with health statsIn the winter, school-aged children ages 11-17 will spend 60 minutes a day outdoors, compared to 175 minutes in the summer. (Source: Schools for Health by the Harvard TH Chan School of Public Health.)
  • In a study of 73 elementary schools in Florida, students in schools cooling with the noisiest types of HVAC systems were found to underperform on achievement tests compared with students taking tests in schools with quieter systems.
  • According to a recent survey released by the U.S. Green Building Council (USGBC), employees who work in LEED certified green buildings are happier, healthier and more productive than employees in conventional and non-LEED buildings:
    • More than 90 percent of respondents in LEED certified green buildings say they are satisfied on the job and 79 percent say they would choose a job in a LEED certified building over a non-LEED building.
    • More than 80 percent of respondents say that being productive on the job and having access to clean, high-quality indoor air contributes to their overall workplace happiness.
    • 85 percent of employees in LEED certified buildings also say their access to quality outdoor views and natural sunlight boosts their overall productivity and happiness, and 80 percent say the enhanced air quality improves their physical health and comfort.

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The Top 10 Party Walls Posts of 2018!

2018 has been a year to remember for SWA’s Party Walls blog. Our consultants have shared their passion for high performance buildings by recounting stories from the field and providing information, new findings, and best practices to improve the built environment.

Whether discussing topics based in New York City or Southeast Asia, here are our fan favorites from 2018…

Collage of blog images

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