Energy Performance Modeling w PHPP
Passive house is an energy efficient building standard. The primary goal is to build in a way that lasts longer and uses significantly less energy than standard construction to heat and cool. Secondary benefits include a quieter home where street noise is virtually eliminated, and a more comfortable home with more precise control of heating, cooling, and humidity. Through proprietary energy modeling software, and certain performance tests completed during construction, Passive House ensures the built form will achieve the efficiency requirements. This standard has been in place in Europe since the 1990's and has recently made inroads into the American market.
There are currently 2 organizations that regulate PH standards in the US. iPHA and PHIUS. iPHA is the international standard and PHIUS is the US version. Both provide certification within the US, but only iPHA is accepted abroad. Both standards are similar with some differences on regionally specific design, and how to use occupancy when determining energy efficiency. PHI and PHNY provide training and support locally.
PASSIVE HOUSE AFFILIATED ORGANIZATIONS
NY PASSIVE HOUSE, PASSIVE HOUSE INSTITUTE, INTERNATIONAL PASSIVE HOUSE ASSOCIATION, PASSIVE HOUSE INSTITUTE US
ACTIVE USER CONTROL OF VENTILATION. WITH AN OPEN STAIRWELL AND OPERABLE SKYLIGHT, OUTSIDE EVENING AIR CAN REPLACE ALL OVERHEATED INTERIOR AIR IN A MATTER OF MINUTES. DOORS AND PANELS CLOSE THE STAIRWELL TO AVOID UNNECESSARY AIR CONDITIONING OF THE LIVING AND DINING SPACES LATE AT NIGHT.
ADDING INSULATION AND PREVENTING THERMAL BRIDGING IS THE CHEAPEST EASIEST WAY TO CREATE ENERGY SAVINGS. THE DEPTH OF THE WALL CAN THEN BE USED RATHER THAN SEEN AS A LIMIT. THESE THRESHOLDS CAN BECOME PLANTERS, WINDOW SEATS, AND SURPRISINGLY WAYS TO CONNECT TO THE OUTSIDE.
TOWARD A SINGLE METRIC FOR ENERGY-EFFICIENT NEW CONSTRUCTION
In the auto industry, the standard of miles per gallon, allows us to compare different cars using one simple metric. Consumers understand that a car like a Mercedes-Benz G550 (13 MPG) is a gas guzzler, and a Nissan Rogue (30 MPG) is much more efficient. We need a similar metric for buildings. Although buildings consume more of this country’s energy than cars, we still don’t have a simple, clear way to assess them. It’s time.
In construction, the direct equivalent of MPG is total annual energy supplied to the building from the electrical grid, gas or oil company. To be valuable to construction, this metric must account for the number of occupants, and the amount of energy the building took to construct (embodied energy). Although MPG doesn’t account for these factors, they each vary much more significantly in buildings than in automobiles. While cars typically hold between one and eight people, a building can house a single person or thousands. Embodied energy is both more variable in buildings and a larger portion of the total energy budget than in cars. To understand building energy efficiency we must include embodied energy.
In order to understand energy efficiency and to represent this in a single number, we need to add the embodied energy to the energy used during occupancy. To see both data sets in the same units, embodied energy must be understood in terms of its efficiency, per occupant, per year. This figure is determined by dividing the total building embodied energy by the building life expectancy, and by its number of occupants. The life expectancy of the building represents the one component of the calculation not based on measured data but instead on industry standards.
Total energy consumed (BTU) per occupant per year = (annual occupancy BTU/ number of occupants) + (embodied BTU/ number of occupants X building life expectancy)
Unlike cars, every building is unique, and needs its own evaluation in real world conditions. This means that we need to collect data post occupancy. Embodied energy can be evaluated through construction material area schedules. The energy use per occupant per year can be documented using utility bills, showing energy use, and tax records to identify the number of occupants using it as their primary residence. Making this information public, will be a point of contention, but there are ways to incentivize its release.
It is critical to avoid the mistake of looking at energy use per square foot. A well insulated 6000 sqft mansion will likely require more energy than a poorly built small apartment. Similarly embodied energy is a critical and overlooked component. A super narrow skyscraper may be sprinkled with energy saving features, but they are unlikely to balance the significant embodied energy required to build with huge amounts of steel to counter wind loads. If this skyscraper has been divided into enormous apartments, half of which are vacant because they aren’t primary residences, then we can assume a very poor building energy efficiency.
A more sophisticated understanding can be achieved by dividing energy into its root sources to determine the total global warming potential of each building material. Currently keeping the metric to energy use in BTU’s, will make it simple and understandable for the general public, but this data should be collected as well.
Without a metric to understand and compare energy use in buildings, consumers will never be able to evaluate choices in construction and make informed decisions to live more energy efficient lifestyles. Any metric will be an imperfect simplification of real life, but it doesn’t need to be perfect to be useful. Without it, although I am an architect, with a singular focus on energy efficiency, I’m unable to compare energy efficiency between buildings.
Look for my next article about how to incentivize information release.