a b s t r a c tIn this study, an experimental investigation is performed on a two-stage dehumidification water desalination system utilizing a humidification-dehumidification process that has been accomplished using heat pump. The air is heated by means of heat pump condenser to increase its ability to efficiently humidify, while condensation takes place at the heat pump evaporator section. Additionally, in order to enhance the dehumidification efficiency a per-dehumidification process was performed to the humid air, using a cooling water heat exchanger and that was utilized prior to the evaporator. Raw water is sprayed at a constant flow rate of 2.2 L/min using cross, counter, and parallel flow spraying systems. The mass flow ratio between water and air is varied from 0.091 to 0.14 via the change in the air flow rate. The inlet cooling water temperature of the heat exchanger dehumidifier is changed from 15 to 25°C. Results of the experiments showed that the parallel flow spraying system has the highest productivity in both single and two stage dehumidification with a productivity of 2.34 L/h and 4.44 L/h respectively. The results show an extra ordinary influence of the heat exchanger on productivity intensification. The maximum specific productivity including all power consumption elements is 2.02 L/kWh.

No abstract

In this paper an experimental investigation on a lab scale HDH water desalination unit using a Heat pump was presented. From the thermodynamic view, it was found that the electric heater has a coefficient of performance equal unity, while the heat pump has a coefficient of performance greater than one; in other words the dissipated heat has a high scale. In addition, the refrigeration effect could be used as a secondary benefit. The proposed system utilizes the heat rejected and the cooling effect of the mechanically driven vapor compression heat pump for fresh water production. A test rig consisting of a fan, condenser duct, water spray humidifier and evaporator duct was constructed to study the performance under different operating conditions. The effect of air flow rate variation and water spraying direction (cross, counter or parallel) in the humidification process were studied. Experiments were carried out under variable inlet air conditions. Air flow rate was varied from 0.076 m3/s to 0.4054 m3/s. Results showed that cross water spraying humidification tests yielded the highest production rate. The unit’s maximum production rate was found to be 2.8 Liters/hour at a power 1.4091 kW.

In cold climate regions, closed greenhouses with minimal ventilation minimize the energy requirement for heating compared to open-ventilated greenhouses. In this paper, a model of a closed greenhouse with Earth-Air Heat Exchanger (EAHE) heating is presented and simulations are performed using climate data of a representative day of the coldest month of the year (i.e. January) at the case study location, Hurghada, Egypt. A comparison is made between a closed greenhouse with and without EAHE heating. The simulations show that without heating the greenhouse interior temperature drops below the minimum temperature for cultivation (20°C) during the early and late hours of the day. Furthermore, at midday the temperature inside the greenhouse exceeded the maximum temperature for cultivation (30°C). The results showed that EAHE enabled the greenhouse interior to be maintained at a temperature suitable for plant cultivation, cooling during the day and warming at night. Further, the variability in relative humidity was reduced from 35% to 15%, simplifying the control of the humidity within the greenhouse. Additional simulations that cover the winter period (November to February), demonstrated that the EAHE is a viable sustainable method for temperature regulation without any requirement for additional heating.

In this paper, we present a validated thermal model of a greenhouse. Then summer climatic data of a location in South of Australia (Port Augusta), known to have dry and hot summer, is used to compare the potential of different cooling technologies in providing cooling to greenhouse indoor air while considering the minimization of water consumption. Several cases are examined and compared to a reference case which is a closed greenhouse without cooling. The operation cases considered for cooling purpose are 1 - Fogging system; 2 - Single pipe Earth-to-Air Heat Exchanger (EAHE); 3 - Multiple pipe EAHE; 4 - combined operation of Fogging system and EAHE. Results indicated that relying on shallow geothermal energy through an Earth-to-Air Heat Exchanger (EAHE) minimized the water consumption of the fogging system reducing it from 11.6 to 4.7 kg/day. Furthermore, the results show that cooling via EAHE is the best strategy in terms of reducing water consumption without significantly affecting the temperature reduction when compared to the water reliant cooling technology fogging system. The combined operation of EAHE and fogging system managed to keep the indoor air condition at the favorable plant cultivation temperature level (20–30°C) and relative humidity (70–80%).