14 June 2002
pull boxes should not be located in concealed areas.
Monitoring Equipment. Monitoring devices are provided at various points in
the system to enable inspection and maintenance personnel to visually check system
Pressure Indicators. Pressure gauges should be installed on the supply
and discharge sides of both pumps, on all inlets and outlets of the heat exchanger, and
on the storage tank. Duplex gauges can be used or single pressure gauges can be
connected to supply and discharge pipe with small plug valves installed in the gage
lines. This arrangement allows the pressure to be monitored on either side of the pump
by closing the opposite valve. A decrease in the pressure rise across the pump
indicates a potential problem with the pump, whereas an increase may mean flow
restrictions are developing in the loop. Monitoring the pressure drop across the heat
exchanger can also alert system operators to heat exchanger fouling. Pressure gauges
should be rated for 125 psi (862 kPa) and 210 degrees F (99 degrees C) operation.
Temperature Indicators. Thermometers should be provided at the heat
exchanger inlets and outlets (hot and cold sides) and at the top and bottom of the solar
storage tank. These can be used to monitor both heat exchanger performance and the
fluid temperature being supplied by the collector array. Although some differential
temperature control units are capable of monitoring all of these temperatures remotely,
it is recommended that local fluid-in-glass or bi-metal thermometers be retained in the
system as a backup.
Flow Indicators. Show and specify a flow indicator in the collector loop,
and in the storage loop, after the pump(s) to verify that flow exists. Venturi-type flow
meters are recommended when quantified flow measurement is deemed necessary,
whereas rotary or impeller-type flow indicators suffice to visually confirm flow in the
collector loop. Since the flow indicator is wetted by the propylene glycol solution,
components within it should be brass, bronze, or other compatible non-ferrous material.
Flow devices should be installed at least five pipe diameters downstream of any other
Elapsed Time Monitor. An elapsed time monitor is required to record the
operating time of each circulation pump. This time recorder is used to alert
maintenance personnel to problems with pump operation.
Btu Meter. An optional Btu meter may be specified for cases when the solar
energy system performance is monitored. Btu meters are not required for control of the
system. Therefore, if it is not essential to monitor performance, the cost of a Btu meter
is not justified. When used, this device is installed in the storage loop to measure the
total thermal energy that is delivered to the storage tank. It consists of a flow meter,
temperature sensors for the heat exchanger inlet and outlet, and electronics to
calculate the amount of energy (in Btu) delivered from the measured temperature
change and flow. These units are available commercially and should be installed
according to the manufacturer's recommendation.