Posts

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.

Read more

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

Read more

Multifamily Green Building Certification Program Comparison

If you’re designing and constructing multifamily buildings, chances are you’ve run into one of the many green building certification programs. Whether mandated by code, tax credits, your loan, or because you want to improve building performance, the differences between programs can be difficult to understand. One of the most frequent questions we help design teams answer is “which multifamily green building program should we choose?”

To help shed some light on the major green building standards, we’ve outlined some of the most important requirements for multifamily building performance that tend to differentiate the programs the most.

ENERGY STAR

Administered by the U.S. Environmental Protection Agency, ENERGY STAR is a free program that includes envelope, mechanical, and moisture management requirements. There are two pathways to certification – ENERGY STAR Certified Homes and ENERGY STAR Multifamily High-rise – based on the height of the building. In the near future these programs will merge into one Multifamily New Construction standard.

Although it isn’t considered a full green building program (it doesn’t address materials, site or water), ENERGY STAR is included in this comparison because several programs and standards reference it as a base requirement.

Energy Star comparison chart Read more

Just Your Typical Blower Door Test… in Sri Lanka – Star Garment Innovation Center

As the number of projects pursuing Passive House certification increases, so does the demand for whole building blower door tests. And so, performance of recent blower door tests took us to uncharted territory, not only for SWA, but for the Passive House Standard.

Rendering of Star Garment Facility

 

Working remotely with a project team across the globe, the Passive House team at SWA was tasked with retrofitting an outdated factory in Katunayake, Sri Lanka, into a Passive House certified garment manufacturing facility. Jordan Parnass Digital Architecture (JPDA) recruited SWA to provide technical assistance to the project team. Responsibilities for this project included Passive House design analysis and recommendations, mechanical design review, energy and thermal bridging modeling, and the testing and verification necessary to achieve certification from the Passive House Institute (PHI).

Read more

The Results Are in from the NYC Ice Box Challenge!

On April 21, 2018, two blocks of ice weighing exactly one ton each were placed into what appeared to be identical sheds in Times Square. The purpose? To measure how much each block would melt over a 30-day period, ultimately demonstrating the efficacy of Passive House construction methods.

The first shed, or Ice Box, was built to meet current NYC Building Code standards, which lack stringent requirements for building envelope performance. The second was constructed using building principles adopted from the Passive House Standard, including the utilization of high performance building materials, a superior airtight building envelope with advanced insulation, and triple-pane windows.

Graphic of Iceboxes

After 30 days of exposure, the Ice Boxes were publicly unveiled, and the results were exactly what building professionals had anticipated. The block of ice contained in the Ice Box constructed to NYC Building Code resulted in a final weight of 126 pounds, while the block of ice within the Passive House Ice Box weighed an astonishing 756 pounds, retaining 42% of its mass!

So, What Did We Learn… Read more