In this phase of the work the aim was to create the hourly cooling load profiles of the diary Best Milk (Marrakech, Morocco). The necessary information has been provided by the factory personnel and through audits on the plant Best Milk uses raw milk provided by a vast number of farms in the area of Marrakech. Cows are milked early in the morning in small dairy farms in villages around Marrakech, then milk is collected in several collecting centres and transported by truck tanks to the diary factory in the city. Generally milk tanks reach the factory by midday and the milk temperature ranges between (9-28 °C) depending on the availability of refrigeration systems at the collecting centre and the ambient temperature. According to the process engineers, the milk has to be cooled after the first milking to 7.3°C or less within 4 h of the start of the first milking. In the existing system milk is cooled via two plate heat exchangers, supplied on their cold side with a chilled water at about 2°C. Moreover, even though with the dedicated financial resource for the project which allowed only to size the pilot system far smaller than the existing conventional one, the system design was done in a way to increase replication potential and it has been decided to work on a portion of the industrial process (i. e., a portion of the milk volume flow) which allows to speculate on the possible behaviour of the a solar refrigeration system correctly sized for the application (i. e., about seven times in capacity). A scheme of the process is given in

fig. 2. In order to investigate the opportunities of utilizing the solar cooling system in the fresh milk cooling process, both, the cooling load profile and the solar radiation for one typical summer day were studied; it was concluded that due to the mismatch between the two profiles an inertial component was needed. A cold storage has been selected to store cold energy in the phases when the availability of solar radiation allows cold production, without having concurrent cooling demand. Also, due to the existing system configuration — where there are two heat exchangers to cool milk, and they are used alternatively — it was decided to connect the solar cooled heat exchanger to play a role on cooling the return chilled water to the existing chiller as this is common between the two existing milk heat exchangers. The load profiles worked out — an example of a daily profile is presented in fig. 3 — highlighted, on a daily basis, that four operation phases take place as further described.

Operation phase:

1. Direct cooling: This is the default mode of operation of the system when there are simultaneous solar energy and cooling load.

2. Charging the cold storage: This basically happens early in the day when there is enough solar radiation to run the chiller but there is no cooling load as the milk didn’t arrived yet to the factory.

3. Discharging the cold storage: As soon as the supply energy by the solar radiation is not sufficient to run the chiller, the system turns to discharge mode, where cold energy started to be discharge to

4. System Off: Obviously, when there is no load and there is no solar radiation the system goes off, this mainly happens in the very late hours of the night and before sunrise.

4 System components and their models

4.1 Solar field

An essential requisite, to obtain good system efficiency, is the choice of the Solar Collector type and the working fluid, so that should be guaranteed the desired chiller operating conditions (feeding temperature, fluid flow rate etc.). As a result Roof mounted parabolic troughs RMT produced by IST and the diathermic oil were selected. In these collectors, solar energy focused and concentrated on a liquid-filled receiver dramatically reduces convection and conduction thermal

loses. The receiver/absorber is a steel tube coated with a selective blackened nickel surface and surrounded by glass. A single motor drives the collectors to track the sun continuously during the day.