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Establishing Moisture Control in Multifamily Buildings

Most of us are familiar with the feeling of a humid apartment after taking a hot shower. Some of us kick on an exhaust fan, perhaps un-fog the bathroom mirror, or even open a window to get the moisture out. Domestic moisture generation—moisture from human activity—is a major factor driving the humidity levels in our residential buildings, especially in super air-tight, Passive House construction. Before diving into just how much of an impact domestic moisture has in our buildings, let’s first look at average daily moisture generation rates of a typical family of three[1]:

  • breathing and transpiration—6 to 9 pounds of water vapor/day;
  • 10-minute shower in the morning for each individual—3.6 pounds of water vapor;
  • cooking fried eggs and bacon for breakfast—0.5 pounds of water vapor;
  • cooking steamed vegetables with pasta for dinner—0.5 to 1.0 pounds of water vapor; and
  • one small dog and a few plants around the house—0.5 pounds of water vapor/day

This brings the daily total to 11.1 to 14.6 pounds of moisture generation per day, or about 1.5 gallons of liquid water.

Where does all of this moisture go? In a typical code-level apartment building with moderate to high-levels of air leakage, water vapor has two year-round exit pathways: exfiltration through the façade and dedicated kitchen or bathroom mechanical exhaust. Additionally, in the summer, moisture is removed via condensate from the cooling system.

Let’s now put this in the context of a highly energy-efficient apartment with very low levels of air leakage (about 5 to 10 times less than the code-compliant unit), and balanced ventilation with energy recovery. The first means of moisture removal, façade exfiltration, is virtually non-existent given the building’s superior air-tight design. Next is mechanical exhaust ventilation in the kitchens and bathrooms. Because the unit has balanced ventilation and energy recovery, the exhaust air stream in a Passive House project typically passes through the energy recovery core. Depending on the core selection, a large percentage of the interior moisture may be retained in the apartment air despite the constant mechanical air exchange.

There are two basic types of cores:

  • Heat recovery ventilator (HRV) in which a certain percentage of sensible heat is recovered (transferred from the exhaust air stream to the supply air stream) while no moisture is recovered.
  • Energy recovery ventilator (ERV) in which a certain percentage of sensible heat and a certain percentage of moisture in the air is recovered.

To fully understand this issue, Figure 1 breaks break down the moisture-related pros and cons of ERVs and HRVs in the context of a high-density, Passive House building.

  ERV HRV
Pros Summer – prevents high exterior air moisture load from being supplied to interior air; cooling loads are minimized Winter – flushes high internal moisture load out of building; humidity levels reduced
Cons Winter – if internal moisture generation is high, interior moisture load is not flushed out of apartment; humidity levels increase Summer – allows exterior air moisture load to be supplied to interior air: cooling loads increase

Figure 1. Moisture related pros and cons with ERVs and HRVs in high efficiency, airtight construction

 

Traditionally, the key factor in deciding between an ERV or HRV for a high-efficiency building has been the project’s climate. However, as internal moisture loads begin to exceed exterior moisture loads in high-density projects, the decision between ERV or HRV must be looked at more closely for each project regardless of climate.

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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 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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Does Your Exhaust Fan Suck? Part 1

You most likely don’t even think about it when using the bathroom. Flip the switch, hear the exhaust fan, and everything is working as it is intended…right? Far too often, the answer is NO, and it is no fault of the user. Sure, homeowners should take a minute each year to vacuum the inside of the exhaust fan housing, but otherwise, these fans should just work. So why don’t they? Hint…it all depends on how it was sized and installed.

Background

The purpose of exhaust ventilation is to remove contaminants (including moisture) that can compromise health, comfort, and durability. Exhaust fans are amongst the simplest mechanical systems in your home, but decades of experience working in homes has shown us that even the easiest things can get screwed up. Far too often, exhaust fans rated for 50 or 80 cubic feet per minute (cfm) of air removal are actually operating at less than 20 cfm. In theory, the exhaust fan should be installed in a suitable location and then ducted to the outside via the most direct path possible. However, the installation of an exhaust fan can involve up to three trades: an electrician typically installs and wires the unit; an HVAC contractor supplies the ductwork; and, the builder/sider/roofer may install the end cap termination. What could go wrong?

As energy efficiency standards and construction techniques have improved over time, new and retrofitted buildings have become more and more air-tight. If not properly addressed, this air-tightness can lead to moisture issues. Quickly removing moisture generated from showers is a key component of any moisture management strategy. While manufacturers have made significant advancements in the performance, durability, and controls of exhaust fans, these improvements can all be side-stepped by a poor installation.

So how do you correct this issue? Read more

The Second Leading Cause of Lung Cancer May Not be What You Expect

National Public Health Week is this week and Today’s theme is “Environmental Health”, which includes protecting and maintaining a healthy indoor environment.

While National Radon Action Month was in January, we wanted to share how this specific indoor air pollutant can affect your health and what compelled a group of us here at SWA to get our homes tested (and remediated).

What is radon and why does it matter?

Map of EPA Radon Zones

EPA Map of Radon Zones

Radon gas is a naturally occurring byproduct of the radioactive decay of uranium found in some rock and soil. You can’t see, smell or taste radon, but it may be found in drinking water and indoor air. This carcinogenic gas is currently the second leading cause of lung cancer after smoking, according to the National Cancer Institute.

Although radon in drinking water is a concern, radon in soil under homes is the biggest source of radon, and presents the greatest risk to occupants. This pressure-driven mechanism occurs when radon escaping the soil encounters a negative pressure in the home relative to the soil. This pressure differential is caused by exhaust fans in kitchens, bathrooms and appliances, as well as rising warm air created by furnaces, ovens and stoves.

Radon levels can vary dramatically within a region, county, or city. However, the EPA recommends that all homes be tested, regardless of geographic location. To see what the average levels are in your area, check the EPA Radon Zones map.

What radon levels are accepted? Ideal?

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