Here are some screenshots from Google Powermeter that show the net electricity consumption (consumption – generation) for the duplex and the solar generation as well. Unfortunately, the TED5000 that is installed in the circuit panel is not terribly accurate and seems to be bothered by some of the fluorescent lights in the duplex. The device overestimates the solar generation by a significant amount and depending on when a fluorescent light is turned on, it may over or underestimate the house electricity consumption. In other words, these graphs can give us a general idea of how the house is performing, but the data should not be considered robust. The monthly data from the EnPhase units are also displayed as a comparison for the solar generation numbers.
May 2010 Net Consumption: -32 kwh
May 2010 Solar Generation: 520 kwh
Enphase May 2010: 487.98 kwh (difference of ~32 kwh)
June 2010 Net Consumption: 330 kwh
June 2010 Solar Generation: 510 kwh
Enphase June 2010: 420.48 kwh (difference of ~90 kwh)
Obviously May was a milder month than June, resulting in much lower energy usage, but it is still kind of crazy to see such a huge jump. I think that Brian and I were able to keep the AC off for most of May, and then we succumbed to the luxury of mechanically cooled air in June. May was a little better solar month as well–lots of rain in June. I will post July numbers soon, but July looks to be much better than June, which can be explained by the fact that the lower unit has largely been unoccupied during July. I’ll also put these numbers into perspective a bit.
We held a flip-the-switch ceremony to dedicate the solar array installation on Thursday, November 19th. A tremendous thanks to Green Mountain Energy for their generous contribution. Additionally, Alternative Power Solutions donated two additional solar panels that we plan to use on our science building to generate power for one of our laptop carts–so, big thanks to them as well. Here are some pictures of the event:
APS just installed the Envoy/Enlighten system that accompanies the Enphase micro-inverters that are on each solar panel. This system transmits information about each inverter to Enphase and they have a nifty piece of online software that allows you to monitor the solar array. Check out what our array is producing! I recommend checking out the time-lapse feature–very cool. There were a few issues with the inverters taking a while to come all online, but tomorrow should give us a good look at what our panels are capable of producing on a late-fall sunny day. From what we can tell, we might be able to get another 0.5-1 kwh per day more out of the array if we trimmed a tree that is shading the bottom left of the array. We hope to also soon have an online chart system to show how much energy the house is consuming, not just what the panels are producing.
A 3.5 KW (before conversion) PV array has been installed and is now up and running. The PV installation was generously donated by Green Mountain Energy Company and its Big Texas Sun Club and installed by Alternative Power Solutions. The array consists of twenty 175W Suntech solar panels equipped with Enphase micro-inverters. We are currently working on getting the monitoring up and running and should soon have a link to live energy production/consumption data.
As I work on other projects this semester, I’ve passed the energy meter over to Brian and the Environmental Science class (which I will take over next semester). His class has produced an impressive website detailing their various projects around campus, including the energy monitoring project. I hope to do some deeper analysis on their findings in the near future, but for now, please enjoy their website (requires Chinquapin Google Apps account).
We have been running our energy monitor (Brultech 1220.H) for roughly a month now. Here is a typical summer day/night cycle. It is difficult to separate out the upstairs and downstairs units, but in general the upstairs AC unit uses slightly more energy. The tallest peaks represent when both compressors are running (~4 KW). The pattern shows a recognizable difference between day/night usage, but the fact that the difference isn’t all that dramatic seems to be consistent with the fact that the house is well insulated. I also wonder how much heat from the day is stored in the walls and radiates in during the night.
Unfortunately I reset the logger while experimenting with it, so I only have 4 days of data and no longer have the cumulative KWh count. The projected monthly total is 720 KWh, which would mean a cost of ~$100 for the month ($50 per unit), assuming $0.14/KWh. I’d say that’s pretty good considering I remember paying $150/month during the summer months at my house in Austin that was roughly the same size as one of the duplex units (~1100 sf). I will update this post with actual monthly totals in a few weeks to see how accurate the energy monitor’s prediction is.
*Post update: The actual total energy usage from July 25- August 25 was 704 KWh, so the projection of 720 KWh was fairly accurate (and it is good to know that we beat the projection by 15 KWh). For the hottest time of the year, I think that the house performed rather well, though we will need to compare this data to other duplexes on campus. More to come…
Rainwater collection seems like an obvious addition to a house at first, but of course nothing is simple. There are many purposes behind collecting rainwater depending on your location/needs. We live in a fairly wet part of Texas that has cheap water and rare droughts (though we had one of the worst this summer). In general, people install rainwater tanks to supplement their main water supply in an effort to save water, save money, and prevent excess storm-water runoff. Excess runoff is caused by impermeable surfaces (such as houses and driveways) that prevent soil from otherwise absorbing rainwater and divert it to ever widening flood control ditches along with oil, pesticides, and whatever other nasty chemicals the water picks up along the way.
The school’s water supply comes from a well located on the east side of campus. We pay for the electricity to run the well, the chlorine, and the inspections. Saving water might save a small amount of electricity, but little in terms of cost to the school. Thus, we decided to include rainwater collection mainly for the environmental/educational opportunities available. Our system is unfiltered and is used solely for irrigation at this point. We have two 300 gallon rain barrels that collect water from the north half of the roof. These barrels are connected by a system of hoses underneath the house and lead to a pump that supplies a spigot near the stairs. The pump is controlled by both a manual on/off switch in the storage closet and by an internal pressure switch that shuts the pump off at 40 PSI (thus you can leave the pump on and it will turn itself off when you close the spigot).
Most of the landscaping around the duplex consists of native plants that do not really need to be watered much, but the house is also surrounded by St. Augustine grass which can handle little water if it is shaded, but gets scorched in the sun, requiring supplemental water during dry periods. It is amazing how quickly 600 gallons of water goes (a few hours) when you are trying to water your lawn. It certainly makes you appreciate the incredible volume of water that is consumed by any lawn irrigation system (think about all those golf-courses!).
Sometime this year, I hope to connect the rainwater system to a sediment filter and then the toilets in the duplex. Because the toilets are conveniently located along the ventilation shaft, it would be a trivial addition to connect them to the pump underneath the house. The plumbing contractor did not want to connect the toilets to the rainwater system during construction because he was worried about being responsible for issues in the future (non-standard design). We would design the toilet connection with a two-way valve (with a backflow preventer) that would allow the toilets to use the regular water supply when the rainwater tanks are empty.
Rainwater collection design makes for a wonderful geometry or algebra project, putting the concepts of surface area, volume, and rates together in a practical application. I plan on including such a project in both my algebra and geometry classes this year.
In the Spring of 2009, my architecture elective class put together a packet summarizing the sustainable features of the duplex. The students then presented the details of each feature at the ribbon cutting ceremony to an audience of donors, board members, architects, and faculty. I have included some of the pages here, but I also encourage you to download the full packet.
The general contractor for the project was GEMS Custom Homes. As with any custom project, there were plenty of construction hurdles and hiccups, but we ended up with a high quality building in the end. During construction I lived in a trailer next door to the construction site, giving me a great view of the process in action. While I have seen plenty of buildings constructed on campus and have been a part of various construction projects myself, I had never been part of the process from start to finish as in this project. Keeping a close eye on the construction process led me to appreciate both the simplicity and complexity of your standard wood-frame, drywall interior home. Home construction is a remarkably straight-forward process conducted by a team of sub-contractors that are often experts at what they do–and remarkably fast. However, the shear number of different people working on site, the speed at which they work, language barriers, and the changing details of how particular architects like a building constructed vs. the habits of the contractors all lead to the potential for a lot of mistakes. As in any construction project, plenty of mistakes were made and some were caught and others weren’t. The more eyes you have on a particular project, the better, and luckily we had quite a few eyes on this one. It was very helpful to have detailed reviews at each stage of construction by the architects, structural engineer, and LEED rater. A recent article in the New York Times makes a strong case for stricter energy building codes in tandem with inspections to ensure compliance. For all of the complaints about the LEED system, the required energy-related audits are one of its strongest points. Our ducting had to be tested/fixed three times before it passed inspection. Without proper installation, the use of energy efficient materials and appliances is a waste.
The students’ designs were given to the architecure firm Glassman Shoemake Maldonado, who then put together a design that included both educational and green elements. LEED documentation is currently being prepared and we expect the building to easily attain the certification level. Specific sustainable features of the house will be discussed in the next post, but I have included the building plans below. The plans are property of Glassman Shoemake Maldonado Architects.
Click on the caption link to get a larger image.
Each unit is roughly 1000 sf and is designed to house a single faculty member or couple. The duplex has a simple, comfortable, and practical layout that is centered around a ventilation shaft that is used to exhaust hot air from the house. The house is oriented to take advantage of the dominant southeast winds as well as the solar gain in the winter and shading in the summer. The large porch areas make wonderful faculty gathering spots and provide a pleasant, breezy view of the surrounding landscape (which unfortunately is mostly invasive Chinese Tallowtrees).
The house is built ~5 feet above ground to comply with flood codes. Unfortunately due to the bureuacratic mess that governs flood control in Harris County (or this country for that matter), every few years (or whenever Chinquapin decides to build something) they change the flood maps and require us to build higher. Apparently we are now in the 10 year flood plain, which not even the experts (builder, surveyor, or architect) knew about because it wasn’t published on Harris County’s website. Nevertheless, we were stuck changing our plans to account for the fact that within the 10 year flood plain, all structural elements in the flood level must be either steel or concrete. We just happened to be on the wrong side of Wallisville Rd. and in a particularly low-lying area because none of the hundreds of new cheap cookie-cutter homes down the street had to build off of ground level (or perhaps they had the right connections). As far as the 10-year theory goes, in my 27 years at or associated with Chinquapin, there has only been one serious flood that led to water damage in a ground-level building, and that flood happened prior to significant drainage improvements to the main drainage ditches that border our property. Just in case anyone is curious, I’ve posted the new Harris County flood control map for our block.
Flood Control Map