The Passive House Institute US (PHIUS) is an organization that promotes passive building standards and best practices. They also offer certification programs for buildings and products, as well as professional certifications for architects and engineers. This article will provide an overview of some their main guidelines for passive house construction. It is important to note that, although the word “house” is used, these concepts apply for high-rise multifamily buildings and commercial facilities as well.
The PHIUS summarizes its building philosophy as “maximize your gains, minimize your losses”, focusing on achieving synergy between energy efficiency and comfort. The five main principles to consider for passive building are the following:
- High-performance insulation
- Airtight building envelope
- High-performance windows
- Using heat and moisture recovery to minimize HVAC expenses
- Managing solar heat gain, promoting it during the winter and reducing it during the summer
According to PHIUS, a passive building is around 5% to 10% more expensive than a conventional one, but this is compensated many times during the building lifetime through energy savings. In addition, passive buildings are more comfortable, since they eliminate two main issues affecting conventional buildings: air drafts and temperature fluctuation. In commercial settings, comfort can also lead to increase profits, by stimulating employees to be more productive.
1) High-Performance Insulation
The main benefit of high-performance insulation is that space heating and cooling loads are reduced. As a result, HVAC systems can be sized smaller, compared with a building that uses the minimum insulation required by construction codes. A smaller HVAC system can be installed with less capital and also has alower operating cost.
The PHIUS emphasizes the importance of avoiding thermal bridges, which are concentrated spots in the building envelope where insulation is deficient compared with the surroundings. Heat transfer tends to concentrate in thermal bridges, causing unwanted heat gain in the summer and heat loss in the winter.
Current building codes are limited when addressing thermal bridges, since their specifications are based on U-values for insulation and one-dimensional modeling of thermal envelopes. Thermal bridges are a complex three-dimensional phenomenon that can be addressed more effectively with building modeling software.
Air leaks can be just as detrimental as poor insulation when it comes to building envelope performance. Any air exchange between conditioned and unconditioned spaces causes heating and cooling equipment to work harder. Air leakage tends to be more common around windows, doors, plumbing fixtures and electrical fixtures.
In existing constructions, air leakage can be addressed effectively with caulking and weatherstripping. Both have the same purpose, which is blocking spaces where air leakage occurs. The main difference is that caulking is designed for fixed elements like plumbing and electrical fixtures, while weatherstripping is designed to tolerate friction in moving elements like doors and windows. However, caulking should be used for the external edges of door and window frames, which are not subject to relative motion. In new constructions, airtightness can be built into the envelope during the project construction phase.
3) High-Performance Windows
Significant heat transfer occurs through windows, even when the surrounding walls are well insulated. High-performance windows are one of those energy efficiency upgrades that can be deployed in existing constructions, but which is much more cost-effective in new buildings.
- In an existing building, the upgrade cost is the full price of the window plus the associated labor cost.
- In new constructions, there is a baseline window and labor cost that is unavoidable, and only the price premium of a high-performance window is considered for financial analysis.
The most energy-efficient windows in the market currently use a triple pane, inert gas to fill the two resulting spaces, a fiberglass frame and low-emissivity coating for the glass. Double pane windows apply the same concept, giving up on part of the energy efficiency to achieve a lower price. However both triple-pane and double-pane windows are much more efficient than conventional models with single uncoated sheets of glass and metallic frames. A double-pane window is around 50% more efficient than a conventional one, while a triple-pane window provides an efficiency boost of 20-30% compared with a double-pane one.
4) Heat and Moisture Recovery
Since HVAC systems have the goal of controlling temperature and humidity, a higher efficiency can be achieved if the exhaust air is used to precondition the intake air. Heat-recovery ventilation (HRV) only exchanges heat between the supply and exhaust airstreams, while energy-recovery ventilation (ERV) exchanges heat and moisture. The operating principle is reversed for summer and winter conditions:
- Outdoor air tends to be warmer and more humid during the summer. Therefore, the exhaust air can be used to remove some of its heat and moisture. This reduces the HVAC load and improves energy efficiency.
- Outdoor air is cool and dry during the winter, so the exhaust air can be used to preheat and humidify it before reaching the HVAC system. This also achieves a load reduction.
5) Solar Heat Gain Optimization
Managing solar heat gain can be tricky. It is beneficial during the winter, since it reduces the load on space heating systems; however, during the summer it increases cooling load and must therefore be minimized. Also, solar glare should be avoided regardless of the time of the year - it causes discomfort and distraction, while having the potential to damage human vision.
Window shades are a simple and effective measure to control solar heat gain. The sun is higher in the sky during the summer, and shades block a larger portion of its radiation. The sun’s altitude drops as winter approaches, and more radiation enters the building, reducing space heating loads. In NYC and other locations in the northern hemisphere, is important to note that south-facing windows get the most sunshine throughout the year, and north-facing windows get the least. East-facing windows receive plenty of sunshine during the morning, and west-facing windows during the afternoon. Windows should be arranged so that the sun itself is not in direct line-of-sight for occupants. Greater control is possible with optimal building orientation, window shades and well-placed vegetation.
Developers interested in passive building can achieve the best results by working with certified design professionals. For example, the Passive House Institute US has the Certified Passive House Consultant (CPHC) program. There are more than 1,300 CPHCs in the USA, and they have been extensively trained in energy modeling software and passive building, while considering the variety of climate zones in the USA. The US Green Building Council also offers the LEED certification for professionals, where many topics covered deal with energy-efficient construction.
In the case of New York City, another advantage of passive building is that it helps meet the requirements of the NYC Energy Conservation Code. Many code requirements can be met and exceeded by following the passive house construction guidelines established by the PHIUS.