Radiantec Solar Water Heater Owner's Manual - page 5
5
Solar Controller Operation –
There are two electrical temperature sensors (S1 and S2). S1 is placed where
it will read the temperature of the fluid coming out of the solar collectors and S2 is placed on the piping
returning from the storage tank where it will read the temperature going back to the solar panels. The
controller compares the two temperatures, and if S1 is greater than S2 by a selectable amount, the pump
comes on and fluid circulation begins between the solar collectors and the tank heat exchanger. When the
temperature difference is small, the variable speed pump runs slowly and when the temperature difference is
greater, the pump runs faster. The variable control feature has many benefits including improved low sun
performance, less control cycling and conservation of electrical energy at the pump.
The placement and insulation of the
temperature sensors is a very important.
Performance can suffer by 20% or more
if the sensors are not installed properly.
See the installation manual for more
details.
The heat dump -
The Radiantec Solar Heat Dump is a supplemental method for controlling undesirable
overheating of the solar energy system by automatically consuming some domestic hot water and sending it
down the drain. The occupant can select a lower setting for the activation of the heat dump if it desirable to
have lower overall temperatures in the solar system. Whenever the temperature at S1 (coming out of the
solar collectors) is greater than a selectable temperature (default is 250 degrees F), the heat dump is
activated.
The solar heat dump is a small solenoid type valve that sends a small 1/4” stream of water down the drain.
The effect is to slowly and gently cool down the entire solar energy system without consuming very much
water. The volume of a typical heat dump
is only about ten gallons
and it tends to occur twice per day if
the structure is not occupied and once per day or not at all if the building is occupied. Operation of the heat
dump will not compromise a septic system because of its low volume and high temperature, which
facilitates bacterial action.
Stagnation –
A solar heating system is said to be in stagnation when the solar collectors are exposed to
sunlight but the heat is not being taken away and put to use. This condition can occur for any of the
following reasons:
•
Pump failure
•
Controller failure
•
Electric power failure
•
An air bound system
•
Under stagnation conditions, the temperature in the solar collectors may go as high as 275 degrees F
and the system pressure could go to 50 psi.
As a condition of certification, solar collectors must be able to
withstand prolonged periods of stagnation. Nevertheless, these very high temperatures could eventually
cause appearance problems with the solar panels due to out-gassing of materials within the panel and
subsequent condensation in the inside of the glass cover sheet. Also, temperatures above 250 degrees F will
eventually degrade the glycol and cause it to require early replacement. Stagnation is an abnormal condition