Party Walls

Did you know that there are two pathways for earning Passive House certification? There’s Passive House International (PHI) and Passive House Institute US (PHIUS). Using an energy modeling software, both programs evaluate a building based on a variety of factors. Despite the misleading moniker, certification is not limited to just housing. In fact, building types from residential and commercial high-rises to industrial factories have earned Passive House certification around the globe. However, the two certification programs are run by separate institutions, using different energy modeling software and standards. However, both ultimately maintain the shared goal for high performance, low energy buildings.

Historically, around 2013, the PHIUS organization developed a new standard called PHIUS+ 2015 with a climate-specific approach and an alternate modeling software. Starting in March 2019, PHIUS projects will be held to updated requirements under the PHIUS+ 2018 program.

PHI also offers project and climate specific cooling demand thresholds, having previously begun offering alternate certification options in 2015. Additionally, PHI created a program called EnerPHit to provide more flexibility for retrofits. PHI recognizes buildings that exceed its standard certification by offering Plus and Premium certification, as well as a Low Energy Building certification pathway for projects that are near PH efficiency.

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The pattern along the water’s edge in Bridgeport, Connecticut presents a familiar scene to New Englanders: active harbors and historic homes interspersed with blighted buildings and weathered infrastructure. The city’s architecture suggests a prosperous past and a difficult present. But this city—prone to acute and chronic flooding, and facing the ills of climate change and sea level rise—will not leave its future to chance. The City of Bridgeport has a plan to survive and even thrive in the next decades of environmental change, and may position itself as a national leader in resiliency.

Map of the study area showing proposed flood barriers and low impact development

In this context, “resiliency” refers to adaptation to the wide range of regional and localized impacts that are expected with a warming planet. Last fall, David Kooris, former Connecticut Director of Housing, visited SWA’s Norwalk office and presented Bridgeport’s vision: Resilient Bridgeport. The project began in 2014 when the City assembled a multidisciplinary design team, led by New Orleans-based Waggonner and Ball, to prepare an integrated resilience framework for the U.S. Department of Housing and Urban Development’s (HUD) Rebuild by Design Competition. The following year, Connecticut was awarded a HUD grant of $10,000,000 to develop a plan for reducing flood risk, improving resilience for the South End and Black Rock Harbor areas, and building an ambitious pilot project in the South End that combines physical barriers and low impact development.

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Are you in? The US Green Building Council (USGBC) wants you to be. The “All-in” campaign has just officially expanded to include the new and highly anticipated LEED v4.1 for Building Operations and Maintenance (O+M).

Full disclosure: As a member of the Energy and Atmosphere (EA) Technical Advisory Group, I was involved in reviewing LEED v4.1 modifications. In the past, LEED had set significant barriers to entry for existing buildings. For example, LEED O+M EA Prerequisite Minimum Energy Performance set a baseline ENERGY STAR score of 75, which restricted certification to the top 25% of efficient buildings. This limitation often caused building owners to abandon LEED before even getting started, thus eliminating a key incentive for improving underperforming buildings’ environmental impact. LEED 4.1 has fixed this problem. The restrictive prerequisite for energy performance has been replaced with a voluntary credit, encouraging building owners to benchmark energy use and screen capital improvements against energy impacts.

The newest version of LEED O+M also incorporates Arc, USGBC’s performance tracking platform. In Version 4.1, the energy score is calculated based on two energy metrics:

1. The traditional ENERGY STAR metric of annual Source Energy Use Intensity (kBtu/sf);
2. The Arc metric of Annual Greenhouse Gas Emissions Intensity (GHG/person).

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*click here to read Part 1 of this blog

In climates with significant heating and/or cooling seasons, Passive House projects must have a balanced heat or energy recovery ventilation system. These systems use a heat exchanger to transfer heat and moisture between the outgoing return and incoming outdoor airstreams. The operation of recovery ventilators reduces the energy required to heat and cool decreasing the building’s carbon footprint. Project teams can select either:

• Heat Recovery Ventilators (HRV) that transfer heat from the return air stream to the outside air stream; or,
• Energy Recovery Ventilators (ERV) that transfer heat and moisture from the return air stream to the outside air stream.

Deciding between an HRV and an ERV gets more complex when the Passive House concept is scaled from a single-family home to a multifamily program. What the industry has learned from the development of airtight buildings and programs such as Passive House and R2000, is that indoor relative humidity must be controlled through continuous ventilation. The extremely air tight building envelope required of a Passive House, combined with high internal moisture gains from an occupant dense multifamily program (coming from occupants, kitchens and bathrooms), forces additional moisture management considerations during mechanical ventilation design. Maintaining acceptable interior relative humidity in both the heating and cooling season is paramount for building durability and occupant comfort. It’s appropriate that Passive House professionals claim this simple motto: “Build tight, ventilate right!”

In New York City where the multifamily Passive House market is rapidly growing, there is a significant heating season and a demanding cooling season with high humidity (Climate Zone 4A). With this seasonal variation, there are four primary operating scenarios for an HRV or ERV that need to be considered during design:

Summer Condition – HRV

An HRV operating in the summer (hot-humid exterior air and cool-dry interior air) introduces additional moisture to the building through ventilation. Heat is transferred from the incoming outside airstream to the return airstream leaving the building which cools supply air, but exterior moisture is not removed from the incoming air. The building’s dehumidification load increases as a consequence of additional moisture from the outdoor air.*CON*

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*click here to read Part 2 of this blog

Project teams pursuing Passive House frequently ask, “Where do we locate the HRV/ERV?” The answer is complex when the Passive House concept is scaled to a multifamily program.  While there are two primary arrangements for HRV/ERV systems, the trade-off is dynamic and needs to be carefully considered as multifamily Passive House projects begin to scale. A low volume HRV/ERV unit ventilating an individual apartment is a unitized HRV/ERV. High volume HRV/ERV units ventilating multiple apartments and often servicing several floors, is referred to as centralized HRV/ERV.

As Passive House consultants we can attempt to address the system arrangement question with building science; however, in New York City rentable floor space is very valuable, so considering the floor area trade-off is of particular interest to project teams. When a unitized HRV/ERV system cannot be located in a drop-ceiling due to low floor-to-floor height, it is placed in a dedicated mechanical closet. This closet is typically no smaller than 10 ft² and includes the necessary ductwork connections to the HRV/ERV unit. The alternative solution is to increase the floor-to-floor height to accommodate the HRV/ERV unit and horizontal duct runs in the ceiling. Centralized HRV/ERV systems, however, allow short horizontal duct runs but require floor space to accommodate vertical shafts. With supply and exhaust ducts coupled together the required floor area is about 8-12 ft². As a result, centralized HRV/ERV systems may actually require more floor area than a unitized system.

Example: In the case of Cornell Tech, vertical supply and exhaust duct work for the centralized HRV/ERV system required 222.5 ft² per floor, or 13 ft² per apartment (see image 1 below). Unitized HRV/ERV mechanical closets would have required an estimated 170 ft² per floor, or 10 ft² per unit (image 2 on right).

Image 1 & 2:  These images compare the amount of floor area required for centralized and unitized HRV/ERV systems. Image 1 on the left, shows the 12ft² floor area required for vertical shafts servicing the centralized ERV at Cornell Tech. Image 2 on the right is hypothetical, showing the typical location and 10ft² floor area required for a unitized HRV/ERV mechanical closet.

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Here’s a question that we’re often asked by our clients: “I’m building a new residential building, should I use LEED for New Construction (NC) or LEED for Multifamily Midrise (MFMR)?” The answer isn’t exactly simple, especially with the introduction of new credit requirements in LEED v4 and the fact that USGBC allows project teams to choose between the two rating systems. Ultimately, it will come down to a difficult decision based on the goals and final design of the project. So, in an effort to help clear up the confusion and possibly make the decision a little easier for you, we decided to break down a few scenarios that highlight key differences between the rating systems that may not be apparent upon first glance.

In our first installment, we took a look at a four story multifamily building and highlighted many of the key differences between the rating systems; you can find that post here. In this edition, we will explore the options for a different building type.

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Whether you’re a Clark Griswold or an Ebenezer Scrooge, it’s that time of year again: the holiday season is upon us.

A less-than-enthusiastic participant of a holiday photo shoot.

Even those of us who try to live a greener, more eco-conscious lifestyle have a tendency to abandon ship and surrender to the flow of unabashed consumerism and waste in the name of “just getting it done.” It’s hard to put added pressure on ourselves to be mindful of our environmental impact when there are gifts to be purchased, cards to be sent, stockings to be hung, and photos of dogs in Santa hats to be taken.

But you don’t need to do it all to have an impact.

Find one or two ways to improve your holiday traditions by making them greener. Perhaps pick the ones that justify you doing less work in the name of the environment (Reusable bags instead of gift wrap? Yes please). Think of it as a gift to Mother Earth or humanity, or as a way to further annoy that aunt who just can’t understand why on earth you would want use cloth diapers. Sigh.

Here are some ideas, tips, and tricks to help you be just a little more sustainable this holiday season:

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The International Energy Conservation Code (IECC) has a number of requirements involving energy recovery on ventilation systems. Requirements vary based on climate zone, building type and size, equipment capacity, and equipment operating hours. As a result, many new construction projects must now incorporate energy recovery considerations into their design.

An energy recovery unit (ERU) equipped with a heat wheel can be a great way to satisfy these energy recovery requirements. The ERU can be a roof-mounted air handling unit, or can be an air handling unit located inside a mechanical room with outdoor air and exhaust streams ducted in. The heat wheel is positioned so that half of the wheel sits in the exhaust air duct and the other half sits in the outdoor air intake duct. During cold weather, the wheel spins, transferring heat from the exhaust stream to the outdoor air intake stream. During hot weather, the wheel transfers heat from the outdoor air intake stream to the exhaust stream. In both cases the heat exchange enables the building to take advantage of the more comfortable conditions of the exhaust air, while still allowing fresh air to enter the building. During extreme weather conditions, heat wheels can save energy on space conditioning while still allowing for healthy indoor air quality.
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As the Passive House standard continues to make waves across New York City and the U.S., an entirely new design process has evolved to respond to the challenges of higher insulation levels, balanced mechanical ventilation, and perhaps the most difficult hurdle – an air tightness level that most would think is impossible. For the recently certified Cornell Tech building on Roosevelt Island, the tallest Passive House in the world, a several year-long coordinated effort was required to achieve such a feat. So what is the requirement, how is it measured, and what are the strategies and considerations required to achieve it?

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Many green building programs put a heavy emphasis on not only the sustainability of a building once it is built, but increasingly so on the sourcing and management of building materials in an environmentally responsible way. Sustainable Supply Chain (SSC), sometimes referred to as “cradle-to-cradle,” is the standard term to reference this process. But, what does it mean?

Circular Sustainable Supply Chain Image via https://www.cerasis.com

What is a Sustainable Supply Chain?

SSC embodies a cyclical approach to manufacturing that considers both the recovery and reuse of materials. This supply chain’s reverse logistics strives to continually sustain itself by returning materials to the land in either a safe molecular form or by continually reusing those materials for future products. Fully developed SSC’s consider sustainability for every contributor at every step – from design to manufacture, transportation, and storage to eventual end-of-life with a goal of re-use, recycling, or low impact disposal. This forward-thinking perspective serves to reduce waste, promote ethical and socially beneficial manufacturing practices, minimize or eliminate adverse health impacts, and enable compliance with increasingly stringent regulations. (more…)