Abstract: A thermostat for heating or cooling, operative to maintain an indoor air temperature to a limited setpoint range, is provided with a comparison circuit to prevent tampering intended to exceed a setpoint limit. A first temperature sensor responds to ambient air temperature and can include a first thermistor. A second thermistor is partly thermally isolated from the air, and senses a reference temperature that lags temperature changes in the ambient air. The two thermistors form a voltage divider coupled to one input of a differential amplifier comparator, the other input of which is coupled to a fixed voltage reference. When the ambient and reference temperatures exceed a predetermined temperature difference, the differential amplifier operates a relay that breaks a circuit including the contacts. This occurs when locally cooling the ambient air to generate a spurious call for heat (or vice versa).

Abstract: A system of monitoring energy usage for heating or cooling separate units in a multi-unit structure employing thermostat means to control delivery of hot or cold fluid to the unit, an elapsed time meter, a first circuit interconnecting the thermostat with the power source and meter and a second circuit in parallel with the first interconnecting the means to control delivery of the hot or cold fluid to the unit with the elapsed time meter to provide a tamper-proof, economically installable and reparable system. The system will not meter time of usage when insufficiently hot or cold fluid is delivered to the occupancy unit even when called for by its thermostat. The system also includes a method of determining energy usage in each individual unit using the elapsed time meter reading.