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Adam Heisserer

Energy Monitoring at the Prow

Posted by on 12/17/15 at 03:00pm

Last month we installed an eMonitor on the Prow, a porch house in the Davis Mountains. This is our first time monitoring an off-the-grid project, and our most remote installation so far. eMonitors track the energy use of individual electric circuits, and transmit the data in real time to an online account where it can be observed and analyzed. Owners can use this feedback to make informed decisions about energy use and save significantly on their energy bills, and we can improve future design decisions based on real data.

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After a 7 hour drive through west Texas, we arrived in Fort Davis. We then took a dirt road 12 miles through the mountains near Davis Mountains State Park before reaching a more “advanced” road. At this point, we decided we couldn’t continue in our Subaru Outback, and loaded the equipment and ourselves into the back of Bill’s truck. 6 miles and one hour later, we arrived at the Prow, an off-the-grid porch house powered by solar panels.

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Above is the view from the Prow, which takes its name from this view from the porch. The site resembles the prow of a ship overlooking the valley below.

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First, we clip a current transformer (CT) around every circuit and install a transmitter inside each electrical panel. The transmitter communicates wirelessly to a nearby gateway, and data is transmitted over the internet to an online account. All wires and CTs fit neatly back into the panel, and we begin the software installation.

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The next morning, we enjoyed the six mile hike back through the mountains, complete with cattle, deer, and distant views of the McDonald Observatory. The following week, after each eMonitor started receiving a WiFi signal, we began to collect data.

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Indoor temperature and carbon dioxide monitors in the living room indicate when the room was occupied in the last two weeks. C02 levels spike to about 500 parts per million when the room is being used, then settle to about 400 ppm when no one is occupying the room.

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Above is a one week sample of energy data. When no one is home, the radiant heat system runs at a constant 86 watts to slightly warm the house and prevent pipes from freezing, while the refrigerator cycles on every couple of hours. The oven has a constant phantom load of about 4 watts, used to keep the clock running. So far, the unoccupied load of the house is about 2700 kBtu/year, far lower than the average unoccupied house. When the house is occupied, a variety of plugs and appliances are used, totaling a few hundred watts, with occasional, brief spikes over 1,000 watts.

Over the next several months, we will start to understand the energy use patterns of the Prow when it is occupied, and use that information to design even more energy efficient buildings in the future. This feedback loop is invaluable for the client, who can make adjustments and save significantly on their energy bills in the long run.

 

 

  • atomicsmith

    Great post. I’m interested in doing something similar can you give some more info about the monitoring equipment you used? It looks like the house has a limited AC system and presumably a larger DC system. Can the same monitors work on AC and DC?

    • Adam Heisserer

      We’re using a SiteSage Energy Monitor by Powerhouse Dynamics to monitor 21 individual circuits. The CT clips are installed directly inside the electrical panel and support either 120 or 240-volt circuits, then they communicate to the house’s Wi-Fi through a wireless gateway.

      It only works for AC, so we’re measuring solar PV after it’s inverted.

  • Adam Heisserer

    We’re using a SiteSage Energy Monitor by Powerhouse Dynamics to monitor 21 individual circuits. The CT clips are installed directly inside the electrical panel and support either 120 or 240-volt circuits, then they communicate to the house’s Wi-Fi through a wireless gateway.

    It only works for AC, so we’re measuring solar PV after it’s inverted.