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A Versatile Tool for Creating Energy Efficient Homes

Hunter Fanney, Senior Research Scientist, Engineering Laboratory

Just over five years ago, we were on the verge of starting construction on a unique addition to the ​NIST Gaithersburg, Md., campus, the Net-Zero Energy Residential Test Facility (NZERTF). My vision for the facility — a beautiful-looking house that’s really a high-tech laboratory — was that it would provide insight and lessons that would help us design more efficient and healthier next-generation single family homes.

Visitors to the NIST house are always impressed with how “normal” it appears. Many energy-efficient homes of the past had unique designs that made them stand out. But our facility demonstrates that you can have the style of house you want, while still being energy efficient.

Despite its looks, the NZERTF house is anything but normal. When a home is built, decisions have to be made about what type of heating and cooling system it will have and what types of ducts will carry air through it. In our house, though, we can run the heat through conventional venting one day and a small-duct high-velocity system the next. We can choose from three different types of geothermal systems that all use the stable temperature of the ground to efficiently heat and cool air.

Having multiple systems throughout the house gives us options that help us understand how different configurations affect things like energy efficiency and air quality. And as the facility enters its third year of operation, it is proving to be an invaluable platform for comprehensive, accurate measurements that let us explore various designs, technologies and control strategies so we can learn how to build houses that create as much energy as they use and achieve “net-zero” operation.

During two separate demonstration years, the house achieved net-zero operation while meeting the demands of a typical family of four — despite some extremely harsh winter weather. Based on what we learned in year one, for year two we improved controls to better anticipate conditions within the facility, introduced fresh air in strict accordance with an industry accepted standard, and used a different method to dehumidify the house.

These changes (and slightly milder weather conditions) resulted in a significant decrease in the energy consumed by the NZERTF in year two. We’ve since conducted in-depth analyses of each system in order to understand how they worked together and developed various computer models that can estimate how a system or other house will perform in different climates or under different usage scenarios.

We can even use computer models to look at how the NZERTF would have performed if we’d configured it differently. For example, we analyzed a range of water heating systems to determine which would result in the lowest energy consumption. And we’ve measured and modeled indoor air quality to examine the impact of energy efficient techniques.

It’s not just the multiple systems that make the house different from a home, it’s also outfitted with automation technology and sophisticated sensors that allow us to run our experiments. One of the rooms is currently decked out with a novel measurement system consisting of 27 temperature and humidity sensors, as well as air flow sensors that will help us compare the performance of the two heating and cooling systems.

Sensors on a heat pump water heater measure its impact on heating and cooling of the house itself. These types of water heaters extract heat from inside the house, which is great in summertime, but in cold weather, it’s essentially stealing heat you’ve spent energy to create. We’ll be able to get definitive information on how this type of system affects the overall efficiency of the house.

Another study will measure the amount of energy lost as hot water makes its way from the heater to fixtures throughout the house. We’ll try different usage patterns and report on the energy and water waste to encourage the implementation of efficient hot water distribution systems in homes.

To date, water use has not been studied to a great extent in sustainable homes. To begin to explore how the NZERTF could be used as a testbed for efficient water technologies, we’ll compare the water use within the facility to that of other homes. We then plan to start designing ways in which the house could be used to test technologies that could ensure water quality, reduce the amount of water used, or reuse water.

In year three, we’ll also be focusing on indoor air quality. Efficient homes are very air-tight so that you don’t waste energy on heating or cooling air that will slip out through gaps in the walls. But to keep the air in efficient homes healthy and fresh, ventilation is crucial. In order to create accurate models of ventilation rates and projected contaminant levels, we need to understand how air moves through the house — and between the house and the outdoors. We’re installing an automated tracer gas system to take regular measurements of certain gases in the air and that data will help to improve computer models of ventilation systems in energy efficient homes.

So while the NZERTF looks like a beautiful suburban home, it’s really more of a Swiss Army knife with lots of tools we can use to improve the modeling and design of future homes. It gives us endless possibilities for testing out today’s — and tomorrow’s — energy efficient, renewable, energy storage, and smart-grid technologies. Which is very normal for a place like NIST.

Originally published at on June 14, 2016.

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