Improvements on the standard DEC cycle

1.2. The adoption of the condensation coil

An improvement of the energy and exergy performance of a standard DEC system may be achieved if an additional heating coil is installed on the regeneration side, after the recovery wheel and before the traditional heating coil; in this paper it will be referred to as “condensation coil”. The amount of thermal energy recoverable from the “condensation coil” is limited by the temperature of the gas coming out of the compressor, which can be assumed as high as 75°C, in a chiller working with R-407C and a condensation pressure around 2 MPa. The saturation temperature of R-407C in the same operating conditions is as high as 45°C, but this potential thermal drop of 30°C can not be always exploited, as the temperature of the air coming out of the recovery wheel can be higher than 45°C, as shown in Tab.3.

Table 3. Inlet air temperature to the condensation coil (point F, see Fig. 1)

Trig = 70°C

Trig = 80°C

Trig = 90°C

46,1 (°C)

51,4 (°C)

56,1 (°C)

Fig.3 shows the results of the analysis as the percentage improvement achievable by using a condensation coil with respect to the corresponding standard DEC cycle. The results get better as both the regeneration temperature and the solar fraction decrease, as in this case the temperature of point C (see Fig. 1) increases, thus determining an increase of the temperature tF (see Table 3). As previously explained, this reduces the recovery potential of the condensation coil, which causes the limitation of the performance improvement to only 5% if solar energy is not used, against the 12% obtained with a regeneration temperature as high as 70°C.

Furthermore, the advantage of installing a condensation coil in a solar assisted DEC system seems not to be high, as the coil limits the potential left to the solar system.

10

0 0.2

Solar fraction

0 0.2

0.4 0.6 0.!

Solar fraction

0 0.2

0.4 0.6 0.

Solar fraction

5

0

1

Fig. 3. Improvements due to the adoption of a condensation coil

Actually, there is a different way of looking at these results, which is that the condensation coil allows a reduction of the collecting surface needed to achieve the same results in terms of overall energy savings; an economic analysis is required to decide whether to integrate the system with solar section.