When the pump power is calculated, it is the product of the rated pump capacity and the pump efficiency. The pump power is not applied when there is not useful energy collected or there is not incident radiation present. Useful energy is defined according to equation 2.1.4 within the Technical Manual. Essentially, it’s the energy received by the collector minus losses from the collector to the surroundings.
So in summary, you should see non-zero pump power when “Q useful” and “Irradiance – Incident” are both non-zero. Otherwise, you should see zero pump power. The rationale behind this, is that the solar water heating pump cycle will not run to save energy while the resource is not available.
Regards,
Nick
