Final answer:
Two-stage heating thermostats are utilized in heat pumps to run them cost-effectively by adjusting output based on temperature differences, thus maximizing COP and minimizing electrical consumption for heating.
Step-by-step explanation:
Two-stage heating thermostats are used on heat pumps because they allow the heat pump to operate more cost-effectively by maintaining temperatures closer to the desired setpoint without excessive cycling on and off. These thermostats enable the heat pump to run on a lower stage during milder conditions, which conserves energy and reduces wear and tear on the equipment. When the temperature difference between the inside and the outside (Th and To) increases, or when rapid heating is required, the second stage activates to provide additional heating capacity.
Heat pumps have a coefficient of performance (COP) that is directly related to the temperature difference they work against; smaller differences result in higher COPs, making the system more economical. By allowing the heat pump to adjust its output, a two-stage thermostat helps in maximizing the COP and reducing electrical consumption, which translates to lower utility bills and a smaller environmental footprint.