A Batch Solar Water Pasteurizer with Counterflow Heat Recovery: Lethality Priced from Thermal Death Kinetics and Daily Output Sized from Insolation

SIMULATED, NOT MEASURED. A batch solar water pasteurizer is specified in which each treated charge is discharged through a counterflow heat exchanger against the next raw charge, so the treated water's heat is recovered into the incoming batch. Lethality is priced from published-class thermal death kinetics (D and z values) for Escherichia coli, Salmonella spp. and an enteric-virus class represented by hepatitis A virus: the virus class sets the treatment, requiring a hold of 9.0 min at 65 C for a 6-log reduction, while a 1 min hold at 65 C gives it only 0.67 log. With heat-recovery effectiveness 0.70 at 65 C the net energy is 50.23 kJ per litre, 0.160 of the sensible heat of boiling from 25 C. At 5.0 kWh per square metre per day insolation and a collector efficiency of 0.50, one square metre treats 179.2 litres per day; a family unit of 20 litres per day needs 0.11 m2 of collector and a 10.0 litre batch tank in 2 cycles per day, and a school unit of 200 litres per day needs 1.12 m2 and a 50.0 litre batch tank in 4 cycles per day. All results are reproducible calculations from the deposited compute.py; nothing was built or tested.