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 Confirm also that the sensor resistance changes as the sensor temperature
changes. This may require warming a cool sensor in your hand, or moving a sensor
off a warm collector or tank into the cooler air.
CAUTION
Do not immerse sensors in warm or cold water. Most sensors are not
waterproof and can be damaged with water. Resistance readings of
an immersed sensor will not be correct. If water must be used to
provide temperature extremes for testing, place sensor in a watertight
plastic bag.
Remember, sensor resistance goes up as temperature goes down. A temperature
increase results in a resistance decrease. If the ohmmeter shows a direct short
(zero ohms), or an open circuit (infinite ohms), check the sensor wiring as well as
the sensor itself.
Make sure sensor wiring is located at least 1 foot away from 120V, and 2 feet away
from 240V wiring and motors. It is very easy for a tiny electrical current to be
induced in the low voltage sensor wires. This current will make normal control
operation impossible.
6.1.7 Storage Tanks,
Drain Valves
Check that the drain valve on the storage tank opens and closes properly without
leaking. On DHW or process heating systems, rapidly drain one gallon for every ten
gallons in the tank. For example, drain eight gallons from an 80 gallon tank.
Insulation
Tank insulation must be complete, dry and properly jacketed. If foam insulation has
been applied to the exterior, make sure it is still in good condition.
If the tank is buried, take tank-top temperature readings one hour after the end of a
solar collection day and again the next morning. During that night, bypass the tank,
so any temperature loss is through the tank wall and insulation, not to a load. The
overnight loss of heat on a properly insulated tank will typically result in a
temperature loss of less than ten degrees Fahrenheit.
MAINTENANCE
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6.1 MAINTENANCE PROCEDURES
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