Party Walls

The envelope of a Passive House building is designed to be significantly airtight. Mechanical ventilation systems introduce fresh, filtered air and exhaust stale, contaminated air 24 hours a day—which is extremely important in maintaining optimal indoor air quality and occupant comfort.

As the saying goes, build tight and ventilate right.

When ventilation systems are designed correctly, but installed, commissioned, or operated incorrectly, the system ends up being leaky and inefficient and uses more energy than expected.

Project teams for Passive House buildings must find solutions for these implementation and commissioning hurdles, or the potential energy penalty can adversely effect the building’s high-performance design intent.

What happens when a Passive House construction expert and a commissioning engineer collaborate to find a solution to common ventilation system issues that cause excess energy use? We, the authors of this blog post, did just that!

Keep reading to learn about common construction issues with Passive House ventilation systems and five lessons learned based on our experiences in the field. (more…)

The Clean Energy DC Omnibus Amendment Act of 2018 was signed into law in 2019, establishing minimum Building Energy Performance Standards (BEPS) for existing buildings. The law requires all private buildings over 50,000 SF to benchmark energy use and demonstrate energy performance above a median baseline beginning January 1, 2021. The law also lowers the threshold for buildings that need to benchmark; buildings between 25,000 and 49,999 SF will need to benchmark energy use beginning in 2021. Buildings between 10,000 and 24,999 square feet will need to benchmark energy use beginning in 2024.

If a building does not score above the median performance of Washington, DC buildings, it has five years to demonstrate improvement or face financial penalties. By definition, 50% of the buildings required to comply with BEPS will fall below the median—even those just a point or two under. (You can download a list of property types and their medians here.) Building owners can use this map from DOEE to check if their building meets the BEPS.

This month, DOEE released the final BEPS compliance rules. These rules cover the different compliance pathways and the documentation required for each pathway.

This blog post was originally published on September 11, 2019. It was updated on November 18, 2021 with new guidance in response to the DOEE’s final BEPS compliance rules. Click here to learn more.

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The District Department of Housing and Community Development (DHCD) recently updated their Qualified Allocation Plan (QAP), which is required by the IRS for issuance of Federal Low-Income Housing Tax Credits (LIHTC), and their Request for Proposals (RFP), a companion piece that governs all other funds, both federal and local.

While there has been a large public focus on the $400 million increase in Housing Production Trust Fund announced by Mayor Bowser, another major development has been the change in green building requirements. DHCD is now requiring that all applicants for any public funding for affordable housing achieve more stringent energy efficiency targets.

New Construction (larger than 50,000 SF)

For new construction projects 50,000 square feet or larger, buildings must meet Enterprise Green Communities (EGC) Plus certification. The Plus level requires deeper levels of energy efficiency by certifying with near zero or zero energy programs such as DOE’s Zero Energy Ready Homes (ZERH), Passive House International (PHI), or Passive House institute US (PHIUS) among other programs. Currently ZERH applies to projects five-stories or less, with an expanded multifamily version expected to be released for public comment in early 2022. EGC Plus certification also requires dehumidification strategies to address potential humidity concerns.

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This is part of a series; see the first post here.

This shouldn’t be news to anyone:  In most homes, insulation and air sealing are the most effective ways to improve comfort and reduce heating and cooling costs.

This holds true regardless of heating systems or fuels used. So why is it emphasized even more when talking about heat pumps and electrification? Four reasons.

1.  Heating System Capacity and Cost.

Say your home has a design heating load of 60,000 Btu/h.[1] If heating with fuel, you’ll need a furnace or boiler with a capacity of at least 60,000 Btu/h. These are easy to find. (In fact, you may have a hard time finding heating systems with capacities lower than this.) Air-source heat pumps, on the other hand, have smaller capacities. I don’t think you’ll find an ASHP with heating output of 60,000 Btu/h at cold winter temperatures. So to meet this load, you’ll need multiple ASHPs. And that gets pricey.

Even if you are not talking about multiple heat pumps, a 3-ton[2] heat pump is quite a bit less costly than a 5-ton heat pump. Costs of heat pumps scale more dramatically than costs of boilers and furnaces. So lower heating loads → fewer, smaller heat pumps → lower upfront costs.

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To meet the goals of the Paris Climate Agreement, we must make decisions that will result in the greatest near-term carbon savings. This means taking into account both embodied carbon—those upfront emissions associated with the extraction, manufacture, transportation, and assembly of building materials—as well as the carbon that’s emitted over the course of the building’s operational phase.

We can build a high-performance building with very low operational emissions, but if its embodied emissions are so high that even if it’s a net-zero energy building (meaning it has net-zero operational energy consumption) it would take decades for the building to reach net-zero carbon (meaning it has net zero whole-building lifetime carbon emissions), we’re not actually helping to solve the critical issue of near-term carbon.

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With LL97 fines around the corner, building owners and managers are looking to reduce greenhouse gas emissions. To do so, building systems will need to rely on an increasingly green electric grid rather than fossil fuels.

And as we look to electrify our buildings’ heating and cooling systems, Variable Refrigerant Flow (VRF) systems have emerged as one solution. With buildings increasingly turning to this technology, we are sharing our current best practices for designing, installing, and operating VRF systems to help everyone — from design engineers and developers to installers and building operators — learn more about the nuances of VRF.

These best practices are based on manufacturers’ literature, ASHRAE and IECC standards, conversations with field technicians, design engineers, building operators, and manufacturers’ representatives, as well as Steven Winter Associates’ extensive functional testing experience. While the focus is intended to be large VRF systems ( >5 tons), many of the best practices are also applicable to smaller mini-split or multi-split systems.

Common terms used throughout this post are defined for those new to the topic and can be found by scrolling to the bottom of the blog.

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The need for sustainably designed buildings and infrastructure is critical as extreme weather patterns and natural disasters resulting from climate change persist. One of the truest measures of sustainability in this case is resiliency. How the site, the building, and the systems respond to an extreme weather event or other consequences of climate change can determine its livability. For green building, resiliency can be passive or adaptive, meaning reactive to these types of events or proactive in surviving them.

The recent events in Texas highlight the need at a national level for building and infrastructure resiliency.  Sudden freezing temperatures forced the grid to shut down and left millions of residents without power. The failure of uninsulated water pipes and lack of winterization throughout the energy supply could (and should) have been remediated decades ago.  In fact, a commissioned report released after similar blackouts 22 years ago recommended the incorporation of resilient designs into the system by “installing heating elements around pipes and increasing the amount of reserve power available before storms”. Michael Webber, an energy professor at the University of Texas said: “We need better insulation and weatherization at facilities and in homes.. There’s weaknesses in the system we [still] haven’t dealt with.”[1] Now, politicians and leaders are calling for more of these passive solutions that may be too little too late on such a massive scale.

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Passive House design for large multi-family buildings aligns with and builds upon industry guidance for mitigating the spread of infectious diseases.

As the world continues to be turned on its head by the impacts of COVID-19, the building industry has been scrambling to respond, encouraging designers and building operators to learn about how their buildings are being ventilated. Industry experts have produced an array of documents and reports outlining guidelines for reopening buildings safely while minimizing the risk of transferring infectious disease. Much of the focus of this guidance has been on using mechanical ventilation and proper air distribution to dilute contaminant levels in spaces and minimize the spread of viruses. The American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) has produced a significant amount of guidance for designers. One of their main documents, produced in April, is the “ASHRAE Position Document on Infectious Aerosols,” which provides useful information for how buildings should be designed and operated in response to a pandemic. However, it has prompted questions from design teams about how this might conflict with the goals of very low energy buildings, such as Passive House (PH). This blogpost is written as a response to some of these questions and to highlight the benefits of Passive House design in light of recent recommendations by groups like ASHRAE.

Benefits of Passive House for Mitigating COVID Transmission

The following are some of the benefits of Passive House design for multi-family buildings compared to code requirements as well as some additional guidance for how to design to mitigate virus transmission.

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Most people who have lived or worked in a steam-heated building are familiar with the typical occurrences of uneven heat (underheating/overheating), banging pipes, and having to open windows all winter long. Not only are occupants uncomfortable, but the heating bills are high as well.

Balancing these systems is a huge opportunity for energy savings. It is important to point out that the root of the issue is in the distribution system, and it’s that distribution system that needs to be fixed. The steam traps are the weakest link, and when they fail, residents lose the ability to control the amount of heat delivered. This in turn makes the space uncomfortable and results in the necessity to open windows and waste fuel.

The steam traps are supposed to be replaced building-wide every three years to catch broken traps, but due to the expense and logistics of such a task, this is rarely done.

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A common strategy to provide ventilation in multifamily buildings is to design a central roof-top air handler that distributes outdoor air to each unit. The energy cost for this system, which commonly uses natural gas for heating for either a gas furnace unit or hot water from a central boiler is paid for by the building owner. However, there is another option – VRF[1]. With the unprecedented rise of VRF technology in the last decade combined with regulations such as New York City’s Local Law 97 of 2019[2] (carbon emission penalty), the industry is taking a giant leap towards building electrification. There are always questions and concerns raised against building electrification ranging from initial cost to operating cost to reliability of the VRF technology. From the owner’s perspective, the biggest question is usually surrounding the operating cost of an electric system compared to a natural gas system for heating, but the cost of ownership must consider multiple energy metrics. I was curious to understand the impact on various building energy profile metrics associated with a Dedicated Outdoor Air System (DOAS) using the conventional gas fuel source vs. the latest VRF heat pump technology using electricity in a multifamily building. The findings of this investigation challenge the deep-rooted notion that electricity, being more expensive than natural gas per BTU, will always cost more to operate.

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