19 Feb 2020
By Natalie Leonard
With the global climate crisis grabbing headlines around the world, and increased public awareness on the topic, Net-Zero and Passive House building strategies in residential and commercial construction are rapidly growing trends. According to the UN Global Status report: In 2017, buildings and construction and operations accounted for 36 percent of global final energy use, and nearly 40 percent of energy-related carbon dioxide (CO2) emissions.
Changing how we design and construct buildings can significantly reduce their carbon footprint. Net-Zero and Passive House are leading standards in the high-performance, energy efficient building.
The US-DOE defines a Net-Zero structure as, "An energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy".
"Passive House describes a set of design principles and defined boundary conditions that-if applied holistically-lead to a building that remains comfortable with only minimal active heating or cooling during extreme climate conditions." (Klingenblog, 2012-03-22)
A Net Zero house is not necessarily built using Passive House design, and a Passive House is not necessarily Net Zero. Net Zero is a calculation - energy supply and demand are in balance. Passive House design achieves ultra-low energydemand.
So, what is the perfect balance between implementing the Passive House building approach and the utilization of renewable technologies to generate site energy? The Passive House Institute of the US (PHIUS) has completed extensive work in partnership with the US Department of Energy to answer this question. The PHIUS+ 2018 Passive Buildings standard sets performance targets are based on regional factors like climate, solar potential, construction costs, and renewable energy system costs. The goal is to implement energy efficiency improvements to the point where they become more cost effective than traditional systems. Up to this balance point, energy efficiency is the cheapest fuel.
The Passive House approach will reduce building energy use by 60-70 percent, over a conventionally constructed equivalent. The building shell is designed to reduce transmission energy losses by up to 85 percent. Heating and cooling loads are also important metrics in determining occupant comfort. This strategy to design and construction can be applied to small single-family homes, as well as large commercial or residential buildings.
By drastically reducing the energy losses out of the building (as seen above), energy costs for heating and cooling drop nearly 85 percent.
The energy requirement of a Passive House building is so low that it doesn't require a conventional heating system. Typically, space heaters are enough to meet peak heat load required - an extremely easy and user-friendly solution for homeowners.
Principles of Passive House Design
- Compact Building Shape - A well-designed home can use a compact, energy efficient shape without compromising functionality or style.
- Super-Insulate - Floors, walls, windows and roofs all contain an extra layer of insulation.
- Make it Airtight - According to the U.S Department of Energy, air leakage through the conventional building shell accounts for 40-50 percent of all heat loss. Air leakage is 6 times lower in a typical Passive House, compared to a code-built home.
- High Efficiency Heating, Cooling, and Ventilation Systems - Central heating isn't necessary in a Passive House; a super-efficient "shell" allows compact, highly efficient heating, cooling, and ventilation systems to maintain comfort for the occupants.
- Design for Passive Solar - Good solar access further reduces the heating energy required by providing free winter heating from the sun.
Renewable Energy System
The energy demands in a Passive House are minimal. Selecting a technology to generate site energy that is cost effective, easy to operate, and low maintenance will provide the best solution to achieving Net-Zero. A variety of technologies are available, each with their pros and cons:
- Geothermal: Generally too expensive for the load sizes in a Passive House, but may be practical for very large buildings.
- Solar thermal: Appropriate for multifamily buildings, but difficult operationally for a single-family residence. Maintenance is required.
- Wind: Not cost-effective at a small scale, and presents issues with turbulence and roof mounting. May be practical in rural settings with space for ground mounting.
- Photovoltaic: Requires roof space but is very low maintenance, simple to operate, and continues to drop in cost.
Photovoltaic solar panels make the most practical choice for most Net-Zero projects. The panels produce electricity that is sold into the grid, and the building draws back the electricity it needs. Over the course of a year, this balances out to zero. Net metering is also available in most jurisdictions in North America.
Because heating, cooling, and hot water energy loads are drastically reduced in a Passive Home, up to 60 percent of energy use goes to lighting, appliances and plug loads. When sizing any renewable system, it's important to account for occupant behavior (which can vary up to 300 percent!). Homeowner education can help further reduce these loads.
Passive House has advantages in the path to Net-Zero that are unrelated to the energy reduction.
- For many projects, it's just not possible to fit the roof solar panels needed for a code-built home to achieve Net-Zero. Passive Home design reduces the number of panels needed by up to 75 percent and, therefore, only a quarter of the roof space is needed, compared to a code-built home.
- A 200-amp electrical service - the standard in single family homes - will only support a limited number of PV panels. Upgrading to a 400-amp service adds significant cost to the Net-Zero upgrade. The low energy demand of a Passive House keeps the number of panels needed below this limit.
- Improved comfort is a significant benefit of living in a Passive House. For most Passive House owners, consistent indoor temperatures, improved air quality, quiet spaces that block outside noise, and resiliency in storms and power outages outweigh the primary bonus of living with no energy bills.
From the perspective of total cost of ownership, Passive House is the most cost-efficient path to Net-Zero. Today's Passive Houses can be built for 5-10 percent more than code-built alternatives, a premium easily offset by the annual energy savings and efficiency grants and rebates. When combined with government incentives, the investment of the renewable energy system can be amortized within about seven years.
Natalie Leonard is a Certified Passive House Consultant and Certified Passive House Builder. As an engineer and the president of Passive Design Solutions, she has completed over 100 Passive House projects that are net-zero ready. Committed to reducing the housing industry's notable carbon footprint, the team has recently launched a line of ready-to-build Passive House design plans, available online to the general population.
Passive Design Solutions | www.passivedesign.info