Heat Rejection Loop in a VM Tube

To avoid system stagnation in a solar heating system, a heat rejection loop removes the excessive heat. The heat rejection loop can be a radiator or fan coil.


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Unlike flat plate collectors, vacuum collectors can reach very high temperatures if there is an imbalance between the collected energy and the load. A good design foresees the over-performing of vacuum tubes during high insolation* seasons (Spring, Summer, and Fall) and uses an artificial load to protect the water heating system from over-performing.

*) Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m²) or kilowatt-hours per square meter per day (kW·h/(m²·day)) (or hours/day))

An example of a heat rejection loop using a radiator:

  • The solar collector heats the solar storage tank through the bottom coil in the tank.
  • Heat rejection loop removes excessive heat when tank temperature (TT) exceeds its design limit.
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