Monitoring and Controlling Solar Heating Systems
Date Published: July 9, 2012
dataTaker DT80 Intelligent Data Logger Can Handle it All
A solar hot water system installer had a need for automated monitoring to track the temperature, water flow rate, and several other parameters at various points in the system. The goal was to setup control for the system’s various circulating pumps, to store the data for performance tracking, and to monitor energy production for billing. To save on cost, the company wanted a single solution with flexibility to connect with many different sensor types including thermistors, pyranometer voltage, 4-20mA current loops, and pulse signals from the flow meters and energy meter. This device would also need to capture near real-time data snapshots for periodic monitoring during the day and also save historical data to an offsite location.
A dataTaker DT80 Intelligent Universal Input Data Logger was installed in the solar hot water system as the main controller. The dataTaker provided a standalone data logging solution featuring analog, digital, pulse, and serial data recording capabilities. 9 thermistor sensors were connected to the datalogger to record highly accurate temperature measurements at different points in the system including the solar collectors’ inlet and outlet, the heat exchanger inlet and outlet, and the hot water storage tank. Flow meters with 4-20 mA outputs provided data on the various flow rates within the system including the solar loop, the heat exchanger loop, and the storage tank outlet. The pyranometer provided data recording the level of incident sunlight.
The DT80’s digital outputs were connected to relays controlling the contactors for the different circulating pumps such as the solar loop pump, the heat exchanger pump, and the rejection pump, which dumped excess energy to a radiator if the incoming solar energy exceeded what the system could use or store. Finally, a counter input was used to capture data from a certified meter that determined how much energy the system produced.
A major part of the project involved designing the logic and control routines for the system. The dataTaker data logger monitored the temperature differential across the solar panel to determine if there was an adequate net temperature gain, and if so, it then directed the system to send hot water to the storage tank and then into the rest of the system. If the temperature in the storage tank became too high, the logger would switch on the rejection pump to dump the excess energy back into the atmosphere.
To facilitate data accessibility to remote locations, the FTP capabilities of the datalogger were used to periodically send the data to a server located in the installer’s office. The data was uploaded in 2 formats, a full data set for archiving and detailed analysis, and a decimated data set consisting of every 10th data point uploaded at more frequent intervals providing near real-time monitoring. Furthermore, this data was sent in formats which allowed quick parsing out of the various values and presentation through a monitoring website.
The DT80 stored up to 10 million data points in user-defined memory so that users could log as much or as little as needed using independent control of schedule size and mode, and also overwriting or stopping logging once memory was full. Additionally, dataTaker’s user-friendly dEX software was included free with the datalogger. This software came pre-installed and used a Windows Explorer-style graphical interface so users could quickly setup and configure the datalogger directly from a web browser enabling access either locally or remotely over the Internet. Operators could use any of the logger's built-in communications ports to view dEX, including Ethernet, USB and RS-232.
The installer’s monitoring and control needs were all met by installing the intelligent dataTaker solution. This cost-effective device had the versatility to capture many different physical values including thermistors, 4-20mA current loops, voltage from pyranometers, and pulse signals from the flow meters and energy meter. This entirely replaced the need for several different monitoring devices with different software and specifications. The dataTaker also gave users a hassle-free means to control the pumps, save large amounts of recordings, and remotely send all the data. Management were also provided with options for future expansion including boosting the number of inputs with dataTaker CEM20 modules to handle larger systems; the built-in web server to provide real-time updates directly from the logger; and a serial interface to allow direct connection to the energy meter to capture additional data or to an HMI for a local operator or service technician.
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