... complicate system, like system of solar collector,heat pump and heat recovery. Model PWTElectric water heater(100L-800L) The high ... high void-free polyurethane foam. * Various designs* Remarkably low heat loss * Non-CFC Polyurethane insulation* Elegance, good corrosion ... electric immersion heaters, or may use an external heat exchanger to heat water from another energy source such as district ...