Page 330 - Defrosting for Air Source Heat Pump

Technoeconomic performances 325

experimental results and calculations were collected and used in later technoeconomic
evaluations. Third, the equations were developed, including the first and subsequent
running costs at different operating stages. After a series of conditions were assumed,
a technoeconomic evaluation is given. Finally, the technoeconomic analysis on frost-
ing/defrosting operations for optimized ASHP units is undertaken. The methodology
of this economic analysis is illustrated in Fig. 10.15. The energy performance analysis,
working as the basis of this study, is shown in Section 10.3.1.1. The economic perfor-
mance was analyzed in Section 10.3.1.2, which is the focus of this study.

10.3.1.1 Experimental study
The experimental ASHP unit and the experimental procedures and conditions are the
same as the previous section mentioned. Two frosting experimental cases were
designed, with both valves installed. Two different FECs, FEC 1 and FEC 2 , were
reached with valves fully open and evenly adjusted, respectively. The frosting dura-
tion was fixed at 60 min. The frosting operation performance of an ASHP unit at dif-
ferent FECs could be obtained in the experiments. As the baseline for comparison, the
valves in Case F1 were fully open, and the FEC 1 was less than 100% due to the refrig-
erant and air being unevenly distributed. In Case F2, the valves were evenly adjusted,
giving an FEC 2 value of almost 100%. Thus, the effects of the valves were obvious in
the different cases. Information on the two frosting experimental cases is listed in
Table 10.2.
Similar to the previous section, the experimental results that form the basis for the
economic analysis process in this section mainly came from previous defrosting
experimental studies. Considering the different installation styles of trays and valves,
four typical defrosting conditions existed, as shown in Fig. 10.16. To compare, the
prototype condition is shown in Fig. 10.16A, without any change for an ASHP unit.
In Fig. 10.16B, trays were installed under each circuit, and thus the melted frost could

Step 1: Experimental study Step 2: Experimental results & calculation
• An ASHP unit selected • Frosting operation data collected: COP,
• A three-circuit outdoor coil made Indoor thermal energy supplied
• Four typical conditions designed • Defrosting experimental results obtained:
• Frosting/defrosting experiments undertaken at Defrosting duration, power consumption, and
different FECs indoor air thermal energy consumed

Step 3: Assumptions & equations
Step 4: Technoeconomic evaluation
• Fundamental assumptions
• Running cost analysis • Frosting/defrosting/cooling assumptions
• Total cost evaluation vs operating year • First cost: ASHP unit, valves and trays
• The best typical case chosen • Running cost: Stage 1, Heating season with
• Discussions on payback periods frosting formation; Stage 2, Heating season
without frost formation; Stage 3, Cooling
season

Fig. 10.15 Flow chart for the methodology used in this study.