Field Monitoring of Solar Domestic Hot Water Systems Based on Simple Tank Temperature Measurement

By dynamically measuring solar storage tank temperature(s), the solar storage tank effectively becomes a dynamic calorimeter to measure the energy flows in a solar system. The energy flows include solar loop gain, tank losses, and potentially draw extraction. With one-channel temperature loggers storing data over several days to several weeks, this approach provides low-cost, modest-accuracyperformance assessment, useful for determination of savings persistence and diagnostics. Analysis is based upon the tank energy balance, identifying solar gain during the day and tank losses at night. These gains and losses can be compared to expectations based upon prior knowledge, and estimated weather conditions. Diagnostics include controller and pump operation, and excessive nighttimelosses. With one point temperature logger, solar gain accuracy is expected to be 20 to 50%, depending on draw frequency and volume. Two examples are shown, a properly operating system and a system with excessive nighttime losses.