Zone Simulators - There are four ZS's, each of which can be operated to represent the load in a zone. Each ZS contains a 5 kW (1.4 ton) electric heater, a steam spray humidifier capable of 1. 8 kg/h ( 4 lb/h) of steam, and a thermal mass coil. The TMC is used to emulate the thermal mass that exists in an actual zone due to construction materials, furniture, etc.