How to Build a Zero Energy Building

What is a Zero Energy Building?

A sustainable, zero energy building is one of the holy grails of development. And this article plots a roadmap to build one. But let’s start with defining what it is.

A zero energy building must balance the following equation:

Energy generated on site = Energy requirements at all times

Or put more simply, you make the energy you use. No more, no less. Although if you generate more, you can sell it back to the grid and get extra cash flow.

This means you have essentially no utility bill. That leads to better cash flows and higher resale value, protection from fluctuations in energy costs, and lower carbon emissions. In theory this sounds amazing, and you might wonder why every developer doesn’t pursue building a zero energy building.

Downsides of a Zero Energy Building

The technology required for a zero energy building is still developing. So there are often higher construction and soft costs associated with it. Assembling development teams and staying within budget can be difficult enough for normal buildings, so integrating new technology brings all new risks.

Case Studies

Discovery School

Despite the challenges, there are a number of successful zero energy building case studies, like the Discovery School in Arlington County VA. It has 1,710 Solar panels and saves $100,000 annually compared to traditional buildings. The building was also built under budget which is another huge step towards the future of construction.

Apple Park

On an even larger scale, Apple Park, the $5 billion dollar ring shaped headquarters completed in 2017, achieved a LEED platinum certification and is 100% powered by renewable energy. There’s a 17 MW solar installation as well as a 4 megawatt biogas fuel cell. And energy is stored in an onsite microgrid with battery storage.

My Own Development Project in NYC

I included a number of sustainable features in my first development project in Hell’s Kitchen. It’s the first building in the neighborhood to use a solar canopy, which generates 14.4 kWh of electricity from its 40 solar panels. I also installed a green roof to improve insulation on the top floor.

While I couldn’t achieve zero energy on this one, I’m definitely seeing positive cash flow from the sustainable investments. Check out the project video to see all the features.

Revisiting the balanced energy equation, there’s a lot of ways developers can achieve zero energy. On the usage side, landlords should study their building’s monthly, daily, and even hourly demand in kilowatt hours (kWh). That’s the building’s energy pie. Lowering the energy demands make it easier to hit the energy generation goal on the left side of the equation.

Reducing Energy Usage

Most people don’t live in buildings that have on-site renewable energy sources. But everyone can tweak their behaviors to reduce energy waste. The EPA estimates that approximately 30% of energy used in buildings is wasted.

Energy Culprit 1: HVAC and Insulation

Heating and Cooling accounts for nearly 50% of building energy usage. Heating and air conditioning are essentially heat transfer systems. They take air inside, pass it through a system that either adds or removes energy from the air, then pushes the air back into your rooms. But as you well know, the air doesn’t stay that way.

The second law of thermodynamics states that systems tend towards higher entropy, and likewise your house will tend to achieve thermal equilibrium between the interior and exterior. The air inside your house will want to rise or fall to match the air outside by escaping through poorly insulated areas.

R-Values

So it follows that one of the biggest energy savers in construction or renovation is good insulation. In construction, the effectiveness of insulation is called the R-value. It’s a measure of how well a layer of insulating material resists the flow of heat between two sides. R-values between 13-23 are acceptable for exterior walls, and the higher it gets, the better your insulation is. Roofs and attic spaces require around R-40 or more. For a zero energy building, you’ll want to double those numbers.

If you’re developing a ground up building, your architect and engineer will suggest materials to insulate windows, doors, and HVAC ducts, attics, and even your pipes. But if you’re not developing a ground up building, you can do little things like adding weather stripping on your doors and windows to prevent heat transfer.

Insulating Materials

Materials like the NASA-developed Aerogel can has R-values above 60, vs more commonly used Fiberglass which is in the teens or low 20’s. But that doesn’t matter so much if your building has huge windows. Glass has an R-value around 1. Heat practically passes right through it. You’ll need triple or quad paned glass to get R-values up to around 8.

So strategically placed windows and skylights can be used to capture sunlight and therefore heat in the winter, while closing your curtains in the summer can make a huge difference in keeping your building cool. Combining that with automated window blinds or electrochromic glass, which changes opacity on command, can help heat or cold air from escaping. Smart glass maker View Inc is one of the companies that makes these windows.

Exposed concrete floors are also fantastic at storing heat from the sun and releasing it at night, so having a skylight in a room with a concrete floor is a good way to keep a room warm during the winter.

Energy Culprit #2: Water Heaters

The 2nd biggest energy user in buildings is the water heater. This is another heat transfer system, but enclosed within the building. The challenge here is not to prevent heat from escaping outside, but rather to keep water hot after it’s been heated.

Here are three things you can do to make the system much more efficient:

1. Buy a tankless water heater. These can use electric or natural gas and heat water on demand instead of storing them in a water tank that needs to be constantly heated. They also save a ton of space, but they’re much more expensive than regular boilers and water tanks.
2. Insulate your pipes. That’s simple enough.
3. Install a water heat recycling system to recapture heat energy from used hot water from your dishwasher, washing machine, or tub. These systems are very rare.

Energy Culprit #3: Lighting and Appliances

The rest of the sources of energy usage in homes come from lighting and major appliances like the washer dryer, fridge, and electronics. In fact, Dryers are the most energy-hungry appliance that can be found in the average American home.  According to the Natural Resources Defense Council (NRDC), a typical dryer can consume as much energy per year as a new energy efficient refrigerator, washing machine, and dishwasher combined – and if you have an older model, that number could be even higher.

It’s really simple to reduce waste on these items. Make sure you get energy efficient appliances and light bulbs, and be cognizant of your behavior. Energy Star appliances meet EPA standards and usually come with a label. Even though they may cost a little more initially, they make up for it in energy savings. Use cold-water laundry cycles and sun-dry if you can. Keep your fridge door shut. Turn off lights.

Generating Energy On-Site

The left side of the energy equation is all about generating energy on site to match the demands of the pie. There’s plenty of natural energy in our environment that can be harnessed and repurposed for use in our buildings: Solar, Geothermal, Wind, and Hydroelectric.

Any developer or landlord considering these need to make sure these systems pass a basic financial test. The incremental cost of the renewable energy system above traditional systems must generate a return in-line with the IRR of the real estate project.

This is the single greatest hurdle to widespread adoption of renewables. Solar panels, for example, have a typical IRR of 7-10%. Real estate development deals usually require upwards of 12%. Tax rebates and government subsidies usually support newer technologies while adoption ramps up.

Solar Panels

Solar panels are the most popular renewable energy technology in buildings. Solar panels actually comprise many, smaller units called photovoltaic cells. (Photovoltaic simply means they convert sunlight into electricity.) Many cells linked together make up a solar panel.

A solar panel allows photons, or particles of light, to knock electrons free from atoms, generating a flow of electricity. Once installed, you don’t need much maintenance and it’ll generate free energy for about 30 years. If you have space for enough panels, you can actually generate all your energy requirements from solar alone.

However, if you’re in a region that doesn’t get a lot of sunny days, the costs aren’t justified without tax incentives and low interest loans. Other downsides are that finding installers can be difficult, and panels are still kind of expensive. Not every roof can hold solar panels. For the 2 installs I’ve done, I had to deal with all of these problems. And the industry is full of salespeople that push predatory leasing contracts where you don’t own the panels, so beware of those.

Batteries

Another downside of solar panels is that peak energy generation is usually mid day, which may not be peak usage time in homes. And at night, it’s not generating anything, so you have to use energy from the grid when the sun’s down. So you have to use it or lose it.

However, solar installers often sell home batteries with the panels. Home batteries allow the home to draw stored energy. So any completely off-grid building requires a battery in order to prevent outages.

The downside of batteries is cost. In the two installs I did, the financial returns didn’t justify batteries on the first one, and NYC’s fire department didn’t approve the use of batters in the city in the second one. So pricing has to come down and battery technology has to improve for this to become more viable.

Geothermal

The next best on-site renewable energy source is geothermal energy. About 6-8 feet below ground, the temperature remains constant between 40-60 degrees Fahrenheit (10-15 degrees Celsius).

A geothermal heat pump is an independent system that pumps water through pipes looping 6-8 feet underground, where it’s cooler than outside in the summer, and warmer than outside in the winter. When the water returns into your house, it’s at the same temperature as the ground. The temperature difference of that water can be used to supplement your existing HVAC system.

These systems are typically installed on new construction homes, but can save 50% on your heating and cooling bills. Dandelion Geothermal is a company born from Google’s X labs that produces single family home sized geothermal systems.

Wind and Hydroelectric Power

The last two sources of renewables are less popular because they’re geography specific- Wind turbines, and hydroelectric power. I’ve considered both for prospective deals that are next to rivers and along hills. They both use the same concept to generate electricity. Either air or water flows through the system to spin a turbine that generates electricity.

On a mass infrastructure scale, both these sources have been around for decades and generate an increasingly significant portion of the world’s energy supplies. But on the single building scale, the technology is very limited and almost impractical. You can install a small wind turbine on your property but you’re probably gonna kill some birds and piss off your neighbors. And it’s still gonna be huge.

Small Scale hydroelectric generators are definitely more feasible if you live next to flowing water.  A Belgian company called Turbulent has created this small scale generator in a river that supposedly powers up to 60 homes. Unlike a normal dam, which stores rainwater and controls the downward flow onto turbines, this system diverts a stream or river into a small whirlpool with a turbine in it, generating electricity as long as the river is flowing. The challenge here in the US is, if the costs pencil out, you need to find a way to get a system like this permitted and installed by people who know how to do it.

If net zero isn’t enough of a challenge for you, though, the next post covers how to build a negative carbon building.