Final answer:
The coils must be cooler than the air inside the house to allow for heat absorption and efficient heat transfer. Insulation contributes to energy efficiency by slowing down the rate of heat transfer, both in cooling and heating scenarios.
Step-by-step explanation:
When coils are accepting heat inside the house in a heat transfer situation like an air conditioner or a heat pump working in a cooling mode, they must be cooler than the air inside the house. This allows the coils to absorb the thermal energy from the indoor air as part of the refrigeration cycle. According to the principles of thermodynamics, heat flows from a warmer area to a cooler one. The coils in this scenario serve as a medium to transfer heat from the inside to the outside, thus they must have a lower temperature than the air in the room for heat to flow towards them.
Insulation plays a key role in maintaining indoor temperatures by reducing the rate of heat transfer. For example, wall insulation prevents airflow and decreases heat loss. Effective use of insulation can reduce the energy required to maintain a comfortable indoor environment.
Regarding the efficiency of refrigerators, air conditioners, and heat pumps, it is noteworthy that these systems operate most cost-effectively when there's a smaller temperature difference between the hot and cold reservoirs (Th and To), which is related to the device's coefficient of performance (COP).