In the framework of an international bilateral cooperation between the Agence Marocaine pour l’Efficacité Energétique (AMEE) and the Italian Ministry for Environment, Land and Sea (IMELS), a freescoo Air Handling Unit has been installed at the library of AMEE in Marrakech in October 2016. The project is managed by the Italian University Politecnico di Milano and has been carried out with the collaboration of the company Pleion which delivered the solar evacuated tube collectors.
The system has a maximum air flowrate of 1500 m3/h, rated cooling power of 6,2 kW and supply fresh air to a room of 400 m3. The rated power needed is about 250 W. For driving the cooling process, about 2 lt/kWh of cooling energy is needed.
The operation of the system in summertime can be described as following:
In the wintertime the system provides also heating to the room when the sun shines and the required air change in the middle seasons.
In order to assess the energy consumption, an extended monitoring campaign has been performed during the 2017. For the heating mode data presented have been registered in January and February (59 days), whereas for cooling operation from May to September (159 days).
Energy performances are evaluated according to the monitoring procedure for solar cooling systems developed by the Task 38 and 48 of the International Energy Agency experts.
The analisys based on monitoring data shows that, for typical operating conditions in cooling mode, the electricity saving in comparison to conventional HVAC systems can be over 70%.
With regards of the cooling operation, two days of July are presented here below.
|Description||Value First Day||Value Second Day||Unit|
|Cooling energy delivered by the AHU||91||29||[kWh]|
|Average flow rate||881||376||[m3/h]|
|Incident solar radiation||52.9||43.3||[kWh]|
|Solar collector heat||31.9||24.1||[kWh]|
|Specific power consumption for ventilation||0.40||0.96||[W/m3/h]|
|Hours of operation||24||10||H|
|Solar collector efficiency||60%||56%||[-]|
The total incident solar radiation ranged between 50-60 kWh/day, and the cooling power produced by the AHU were between 2.5-5.5 kW, with a supply temperature of 19-22°C. First day is characterized by high solar radiation, extreme ambient temperatures (maximum value about 50°C).
Second day has lower solar radiation and ambient temperatures up to 40°C. System has been operated 24 hours during the first day, and 10 hours during the second day. In the first day, the cooling power of the AHU produced during the night is only due to the indirect evaporative cooling effect.
Daily energy performances of the AHU – July 2017
In this chart the daily performances in July are reported. The EER was always higher then 5, with peak values higher then 10, and an average value of about 7. Thanks to the very good performance of the evaporative cooling module of the AHU, the thermal COP of AHU varied between 1 and 2, with a strong influence of the external environmental conditions both in terms of temperature and relative humidity.
Monthly energy performances of the AHU – July 2017
In the second chart monthly performances of the machine have been depicted: the average air flow rate had a minimum value in the month of May, 400 m3/h and, whereas a maximum value of about 900 m3/h is reached in the month of August. The electricity consumption varied correspondingly both for the increase of the air flow rate and the daily working hours.
Seasonal and yearly performance results
|Thermal energy – AHU||5527||960||6487||[kWh]|
|Thermal energy – BUI||2250||1109||3359||[kWh]|
|Average flow rate||714||623||668||[m3/h]|
|Incident solar radiation||6859||2008||8867||[kWh]|
|Solar collector heat||3966||1235||5200||[kWh]|
|Mean daily water consumption||83||0||–||[liters/day]|
|Specific power consumption for ventilation||0.46||0.35||0.40||[W/m3/h]|
|Hours of operation||2524||412||2937||[h]|
|Days of operation||139||59||198||[day]|
|Solar collector efficiency||58%||61%||59%||[-]|
According to the results obtained, a comparison with the energy performances of a conventional AHU coupled with a vapor compression reversible heat pump has been assessed. The main hypothesis regarding the conventional system concern the energy efficiency ratio of the chiller/heat pump and the electricity consumption for the ventilation. Results show an electricity saving of 70 % over the year.
Calculated annual energy performances for a conventional AHU coupled with a vapor compression reversible heat pump
|EER for the chiller/HP (assumed)||3||[-]|
|Electricity consumed by the chiller/HP||2162||[kWh]|
|Specific power consumption for ventilation (assumed)||0.30||[W/m3/h]|
|Electricity consumed by the AHU for ventilation||589||[kWh]|
|Total electricity consumed||2751||[kWh]|