Every green building standard out there deals with energy, but what's the difference? I take a quick look at Net Zero Energy, PassiveHaus, and Living Building Challenge standards to find out.
The Net Zero Energy Building (ZEB)
Let's start with a ZEB. Now it would seem that a ZEB building would be fairly straight forward. It is a building that is net zero energy. For the net, we are presumably "netting" over the course of a one year cycle.
The assumption with ZEB buildings is that you have some sort of power production on site, most likely solar, that is over the course of a year, going to produce as much energy as the building and the occupants inside consume. The building will not produce enough electricity during the winter and night to equal the energy demand, but will produce more than necessary during days and summer months.
But again, we are needing to produce enough energy for building AND occupants…So when designing a ZEB, careful consideration must be placed on who the occupants are, what their energy loads will be, and how the planned building systems can reduce and compensate for those occupant loads. This is one of the hardest things to factor and plan for when designing a ZEB, because people's actions and consumption habits are difficult to accurately plan for.
Buildings like this are also called net-zero carbon or carbon neutral buildings due to the fact that the onsite production of electricity produced and put back on the grid with be equal or greater than the energy consumed from the grid. It is also an assumption that any energy produced on site would be a clean, renewable energy such as solar, wind, or mini-hydroelectric. Running your building on a diesel generator would not count because, though you are producing electricity on site, the energy embodied in the fuel is being extracted elsewhere.
If we were going to make a ZEB house an equation, it would look something like this:
Energy Consumed On Site x 1 year =Energy Produced on Site x 1 year.
Passive House (PassivHaus)
A Passive House (or it's more common brand name and official standard, German created PassivHaus) is a house that uses almost no energy to heat or cool the home. Heating and cooling are done through passive methods such as trombe walls, passive solar heating, low energy heat exchangers, and planned vegetation in conjunction with building being extremely airtight and super-insulated. The requirements for a PassivHaus are:
- The building must be designed to have an annual heating demand as calculated with the PassivHaus Planning Package of not more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and 15 kWh/m² per year cooling energy OR to be designed with a peak heat load of 10W/m²
- Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year (3.79 × 104 btu/ft² per year)
- The building must not leak more air than 0.6 times the house volume per hour (n50 ≤ 0.6 / hour) at 50 Pa (N/m²) as tested by a blower door,
If we were going to make a PassivHaus an energy equation, it would look something like this:
Total Energy Consumed on Site= 120kWh/m^2 per year
Living Building
A Living Building is a standard managed by the International Living Building Institute, and created originally by Cascadia Green Building Council. The Living Building, is at least to me, something that satisfies the right and left brained people of the world, while at the same time, is a standard that is extensive, and ultimately challenging.
The vision of the Living Building is modeled after a flower (See Jason Mclennan's speech as Bioneers). A flower can power itself completely from the sunlight it collects on site, and can sustain itself merely by the water that falls on it. It does not produce toxins, but habitat, and is ultimately beautiful.
This is roughly the vision of the Living Building, a building that can get all of its needs from the site it is placed on, is made of non toxic materials, provides habitat for other creatures, and is not ugly (a swipe at other building standards such as LEED and Net-Zero, which critics have long described as an eyesore.) The living building-flower metaphor continues with each requirement a "petal." Notice that these are absolute requirements, whereas most other green building systems have points you collect to make a grade (silver, gold, platinum for LEED).
The 20 petal requirements for a living building are:
Click To Enlarge. Image from The Living Building Institute
As we can see from the table, the living building challenge is something that is quite different and more holistic that our previous two mentioned standards, each progressively more complicated.
A Comparison of the Three
A ZEB home allows you to use as much power as you would like, as long as it can be offset onsite by a power source such as solar. Because of the cost of large solar installations are prohibitive, most ZEB houses try to be as efficient as possible to reduce the production offset they must install.
Thus, a Net-Zero energy house really has nothing to do with the requirements of being energy efficient. Energy efficiency is a byproduct of the desired cost savings when building the home, offset feasibility (can our roof/property support 100KW solar array?), and the building owners good intentions to actually reduce consumption. In reality, it is much easier to add a large solar array than it is to plan and build an energy efficient home. Which leads to the question, in the future as solar installation prices go down, will ZEB houses and buildings become less efficient? Can Zero energy homes stay relevant as a deep green building standard? (perhaps a question for a later post)
A PassivHaus on the other hand is an actual standard that's dynamic towards energy efficiency does not alter as external prices shift. There are energy load and air exchange requirements that need to be met, and the standard leaves it up to the builder on how to achieve those goals. An important thing to remember is that a PassivHaus can easily meet the standards of a ZEB with onsite production, but it may not always hold true that a ZEB can meet the standards of a PassiveHaus. Ultimately, a PassivHaus makes the best kind of ZEB currently because the electrical load is so low that on site electric generation would be minimal.
A Living Building, as shown by the chart above, is much more than either the ZEB or the PassivHaus. In reality, both of these only address one (maybe two because PassivHaus addresses air standards) or the 20 requirements of the Living Building.
In the end, the two rough formulas on how these three interact with each other are as follows:
PassivHaus = ZEB + Extremely Energy Efficient
Living Building = ZEB + 19 Other Requirements
Living Building ≠ PassivHaus (But Ideally it should)