June 23, 2011
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Today I travelled to Bridgewater, NS to help an industry partner repair a Web Energy Logger (WEL) installation. The solar system uses 30 evacuated tube collectors to supply heat to an in-floor heating loop and dumps the heat in the summer time. Since I did not take part in the original monitoring system installation this presented challenges that were new to me. I had to look over the monitoring system to understand what it was doing before I started work. I needed to not just be able to understand how it was working, but also make sure that it was working. I located the sensors that were installed and tested their readings against readings on my temperature gun. I found one sensor that was not reading properly and replaced it with a new one. I also installed a current sensing switch on the glycol pump to detect when it is running. Since the in-floor heat loop has a constant flow rate we don’t need to install a flow meter to determine the heat provided by the system. I programmed the WEL with some thermodynamics calculations related to mass flow and it now calculates the energy output in kWh.
The repair job took just over an hour and I gained valuable experience in interpreting the work of others. Its easy to jump in and repair a system you set up yourself but when you are trying to follow the work of others it can be a challenge. Pictured below is the box containing the WEL and router (LEFT) and the building with evacuated tube solar collectors on the roof (RIGHT).
May 31, 2011
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Today I installed a web energy logger on a solar thermal system in Halifax. The system is in a large multi-floor residential building. The entire process took about 3 hours, which is a new record for me. The solar data logging system installed has 5 temperature sensors and a current switch to detect if the pump is on. With this setup we are able to calculate the amount of energy that the solar panels are able to extract from the sun and supply to the glycol. The data logger will provide real time data once each minute as well as log the data to a .csv file for analysis at a later time. It connects to the WEL Server (www.welserver.com) to transmit the data over the internet.
The limitation of this data logging system configuration is that it is unable to calculate how much of that energy is actually transferred to the water. Since the solar system was already installed prior to the decision to add a data logger, it does not have electronic pulse flow meters. Flow meters connected to the data logger would allow for accurate calculations of the energy supplied to residents and the savings on the buildings power bill associated with that energy. The decision to go back and install pulse flow meters will rest with the building owner.
May 10, 2011
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The WEL is a low cost but effective data logger that can be used to monitor energy use or generation. It contains a one wire bus that allows digital sensors to be strung along like christmas tree lights. It also contains 6 pulse inputs, 8 run inputs, and 2 4-20 mA analog inputs. Pulse sensors return an electronic pulse signal and applications may include paddlewheel flow meters for water flow. The digital pulses can be counted and converted into a volume flow rate. Run sensors tell you if the device connected is on or not. Current switches can be installed over power cables to current and return an on/off signal. 4-20 mA sensors send a mA current signal that can be scaled into engineering units.
Inside the WEL you are allowed 150 variables. These can be sensor inputs, constants, or simple expressions of other variables. The WEL has limited internal memory so it is limited to simple 2 variable expressions and is not capable of doing exponents or square roots. That being said most energy calculations can still be performed inside the WEL. It also has support built in to maintain running totals for the day, month, or year of any variable.
The WEL uses a rabbit board network chip to connect to the internet and transmit the data. It can be set to log data at any frequency, entered in minutes. By default it connects to the WELserver (http://www.welserver.com). This webpage contains a map of the world with all the other WEL’s shown on it. It is a great tool because it allows you to not only monitor your system, but see how others are doing as well. With some ingenuity you can connect the WEL to your own server to record and present the data there. The WEL posts data that can be received by a simple CGI or PHP script.
Typical WEL applications include monitoring of geothermal, solar thermal, solar photovoltaic, and energy use. The WEL is diverse enough to be used in other applications as well. A device called the WattNode (http://www.ccontrolsys.com/w/Advanced_Pulse_WattNode) must be added if you want to measure alternating current.