As climate change and green codes have challenged architects to make our built environment more and more sustainable, an ambitious new benchmark has appeared, an urban building that produces all the energy it needs in a year: net-zero.

So far this has been out of reach for existing office buildings in compact cities. Given the potential benefit from retrofitting existing office buildings to net zero, it is a timely goal.

Hickok Cole Architects has developed the following process to reach net-zero: reduce, re-use, and generate. The technologies we discuss here work to reduce the amount of energy a building uses, re-use the energy that conventional buildings waste, and generate new energy on site.

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Reduce the amount of energy a building uses.
1. Hydroponic phytoremediation: In insulated buildings, the air is conditioned to a comfortable temperature, but it gets stale and is replaced by outside air. The environmental designers NEDLAW developed “phytoremediation” systems to filter air by passing it in front of a wall of plants, removing toxins so that less outside air is needed. Energy is saved that would have been used to dehumidify, heat or cool the outside air.

2. Direct Current Grid: Electronics and LED lights use Direct Current (DC) electricity. Photovoltaic solar panels generate DC power. But the commercial power grid is Alternating Current (AC). To get solar energy to LEDs via a standard system, the energy is converted to AC and then back again, losing 10-20% of the energy in the process. With a DC grid, that waste goes away.

3. Electrochromic Glazing: Glaring sunlight heats up office spaces. This technology puts a film between the multiple layers of glass in an insulated window. By itself, the window is clear. Run an electric current through it and it darkens to block solar heat from passing through the window.

4. Radiant Ceilings: Radiant conditioning systems, seamlessly integrated into ceilings, absorb the heat dumped by bodies and machines into the air. That way, the air conditioning has to do less work to heat and cool a space.

Re-Use energy conventional buildings throw away.
5. Daylighting: Natural light is free, but it also can create glare. Through computer modeling, architects can design office spaces to distribute light evenly. With comfortable natural light, occupants are more productive and healthier and buildings need less energy for lighting.

6. Phase Change Materials: This is an innovative thermal storage technology. As heat fluctuates in a room, phase change materials—typically buried in the thickness of a wall—either melt or solidify, absorbing or releasing heat in the process. The result is a balanced room temperature resulting in improved thermal comfort, energy savings and potential HVAC downsizing.

7. Municipal Heat Exchange: Extracting heat from one source and transferring it to another is the principle behind the Municipal Heat Exchange. A closed pipe system loops from the city sewer pipes into the building. This loop is connected to a heat exchanger which transfers the heat to a working fluid, which can be used to either heat or cool the building.

Generate new energy on-site.
8. Photovoltaic Array: To get to net zero, a building needs to generate energy. Photovoltaic solar panels convert light directly into electricity. Support equipment like battery storage facilitate even distribution all day.

9. Rooftop Solar Concentrators: Solar Concentrators use mirrors to focus sunlight on a special fluid in a glass pipe. That fluid boils water to run a steam turbine generator. You can get more energy from fewer square feet, and the leftover water can be used to heat rooms and tap water, instead of burning more fossil fuels.