Solar fraction and electricity consumption

From the 282 operation hours in the cooling mode about 35.8% (101 hours) no solar operation was possible. On 148 hours (52%) a complete solar operation covering the whole hour was possible, on the remaining 33 hours the solar system could only provide a part of the driving heat. From an energetic point of view, 59.8% of the driving energy over the whole cooling operation period came from the solar system.

The electricity consumption over the whole cooling period was 10% of the cooling energy. This electricity consumption includes the electricity needs for the chiller itself, the heat rejection via the boreholes, the driving circuit and the cold distribution to the cooling coil in the air handling unit. But it does not include the pump of the solar loop.


temperature lift: T_MT_in — T_NT_out [K]

Подпись: driving temperature (T_HT_in) [°C]

Fig. 5. Frequency diagram of driving temperatures Fig. 6. Frequency diagram of temperature lifts.

(from heating net or solar system).

Calculating an electric COP for the whole system as the cooling energy produced per kWh of electric energy consumed, an electric COP of approximately 10 can be derived. It has to be noted however, that although energy efficient pumps have been used, all pumps operate at constant volume flows independently of the chillers output power. Thus a constant electricity consumption of about 500W is measured during operation. Optimising the control, e. g. using a flow rate control when low cooling capacity is needed may give potential for reducing the electricity consumption.