*3.1. Room Temperature and Coe*ffi*cient of Performance (COP)*

As shown in Table 1, the temperature level was increased significantly (*p* < 0.05) in the house with the air heat pump compared to the control house. The highest and lowest temperatures in the AHP house were 26.1 and 19.9 ◦C, respectively (Figure 3). The COP value was reduced when the external temperature was decreased during the weaning period.

**Table 1.** Effect of the air heat pump system on inside temperature and coefficient of performance (COP).


a, b means that values with different superscripts within same row are significantly different (*p* < 0.05).

**Figure 3.** Temperature profile for control (conventional electric heating system) versus air heat pump (AHP) housing system during winter, at the entry, center, and back position of the rooms (average mean value at lower and upper positions). (**A**) Temperature profile during weaning period (four weeks). (**B**) Temperature profile during growing period (six weeks). (**C**) Temperature profile during finishing period (six weeks).
