2.7.10 Gauges. Measurements of two properties are usually necessary;
temperature and pressure. Other things can be measured or monitored, but these
two are the most critical.
Temperatures in solar systems are measured in one of three ways:
PT plugs or thermometer wells (with movable thermometers)
Electronic sensors (usually thermistors)
Price and accessibility are the usual criteria for deciding which approach to use at a
particular system point. All are sufficiently accurate for normal purposes.
Measuring collector feed and return line temperatures allows service personnel to
confirm solar loop flow, and to get a rough idea of system performance. More
information on this subject is found in Section 4.3.5 in the troubleshooting chapter.
Figures 2-51 and 2-52 are examples of two methods of measuring these
In systems with a pumped storage loop between a heat exchanger and the storage
tank, two more temperature measurement points may be appropriate. At a
minimum, the storage tank outlet should be equipped with a way to measure
temperature. This allows service personnel to confirm that energy has been
transferred into storage, and is being used.
2.7 COMPONENT OPERATION