• Energy Research

In the present work, a typical combined cooling, heating and power (CCHP) system comprised of boiler, flat solar collectors, absorption chiller and heat storage tank was investigated. The described system was considered to supply the given electricity, cooling and heating demand of a residential building; with heating and cooling needs of 100 and 50 kW, respectively. To find the optimum hybrid configurations with high reliability, low costs, low fuel consumption and emissions, a computer program was provided by authors in FORTRAN language. Different fuel prices were considered in the present work. The results indicated that the optimal operation strategy changes with Boiler and NGG fuel prices while it also changes with increasing the number of solar collectors, heat storage capacity and consequently decreasing total annual emission.

The technical and economic analysis of the dual-purpose power/water Solar Rankine Cycle (SRC) coupled with Multi-Effect Desalination (MED) system was investigated. The influence of using Thermal Va...

Abstract The present paper deals with a comparative exergo-economic analysis among four different horizontal Direct-Expansion Geothermal Heat Pumps (DX-GHP) with Carbon Dioxide ( C O 2 ) refrigerant in transcritical cycle. The studied configurations include the cycle with (a) expansion valve (EVC), (b) with expander (EC), (c) with expansion valve and Internal Heat Exchanger (EVC + IHE), and (d) with expander and IHE (EC + IHE). The unit cost of heat ($/ k W h e x ) for each configuration was determined under two scenarios of a) constant Space Heating (SH) and b) constant Domestic Hot Water (DHW) loads with the peak of 8 kW. The results showed that the lowest unit cost of heat ( c q ) and the highest total exergy efficiency ( η e x ) are associated with the (EVC + IHE) and (EC + IHE) configurations, respectively. Also, it was shown that for the SH (or DHW) load, 20% (or 14%) increase in the η e x results in 21.5% (or 20%) increase in the c q considering the electricity cost of 0.025 $/kWh. For the electricity cost of 0.25 $/kWh, however, 11% (or 20%) increase in η e x results in increasing the c q by about 7% (or 13%). It was also concluded that the configuration with the highest η e x is not that with the lowest c q .

Abstract The thermodynamic analysis of a horizontal CO2 direct-expansion ground source heat pump in transcritical cycle was performed to investigate the influence of using thermoelectric sub-cooler and the ejector on the performance parameters of the cycle. A comparative analysis was conducted between the Base cycle and the cycles with ejector and thermoelectric sub-cooler considering the pressure drops in the gas cooler and the ground heat exchanger. The effects of compressor inlet temperature, soil temperature, thermoelectric sub-cooler length, thermoelectric sub-cooler cooling water mass flow rate, and ground heat exchanger outlet temperature on different performance parameters of the cycles were studied. The results demonstrated that the application of ejector exhibits a more stable operation of the cycle and increasing its COP by 16.5% as compared to the Base cycle considering the same ground heat exchanger length. Also, the length of ground heat exchanger is considerably decreased by using the ejector considering the same COP for the Base and EJR cycles. Besides, thermoelectric sub-cooler decreases the irreversibilities of the cycle by generation more power, thereby COP is boosted by 16% as compared to the Base cycle. Furthermore, the major irreversibility in the cycle with thermoelectric and ejector is occurred in the compressor and followed by ejector, ground heat exchanger, gas cooler, thermoelectric sub-cooler, and the expansion valve, respectively.

Abstract The integration of Multi Effect Desalination (MED) unit with and without Thermal Vapor Compression (TVC) system into the Linear Fresnel Rankine Cycle (LFRC) was investigated for different seawater temperatures when it is located at the regions with different solar radiation levels. A comparison was made between the fresh water costs of the dual purpose LFRC/MED (or LFRC/MED/TVC) plants and the case when the MED and MED/TVC systems use direct steam of the LF solar field to produce fresh water (LF/MED & LF/MED/TVC). The water production costs of the described dual purpose plants were compared with that of the LFRC/Reverse Osmosis (RO) plant (LFRC/RO). An exergo-economic analysis was performed to determine the water unit costs of the plants. The results show that the fresh water costs of the LF/MED and LF/MED/TVC configurations are higher than that of the dual purpose plants. Also, it was shown that the fresh water cost is more affected by solar radiation level rather than seawater temperature of a region. It was also found that at fuel prices of 0.23$/m3, the water production costs of fuel based dual purpose plants would be equal to that of the plants with solar thermal source.

Two solar polygeneration systems were investigated for electricity, cooling and fresh water production. In the first scenario ( LF PS ), the linear Fresnel (LF) solar field was used as thermal source of the Organic Rankine Cycle (ORC), absorption chiller (ACH) and multi-effect desalination (MED) unit. In the second scenario ( PV PS ), photovoltaic (PV) panels were considered as the electricity source to supply the electricity load that is required for lighting, electrical devices, compression chiller (CCH) and reverse osmosis (RO) units. A techno-economic comparison was made between two scenarios based on the land use factor (F), capacity utilization factor (CUF), payback period, levelized cost of electricity (LCE), levelized cost of cooling energy (LCC) and levelized cost of water (LCW). The calculations were conducted for four different locations in order to determine the effect of solar radiation level on the LCE, LCC and LCW of systems in both scenarios. The results showed that the LCE and LCW of PV PS is lower than that of LF PS and the LCC of LF PS is lower than that of PV PS . Also, the payback period of LF PS and PV PS systems are obtained as 13.97 years and 13.54 years, respectively, if no incentive is considered for the electricity sale.

ABSTRACT The application of Linear Fresnel (LF) solar field was technically and economically considered as the thermal source of a Multi Effect Desalination Thermal Vapor Compression (MED/TVC) system with a water production rate of 9000-m3/day. The analysis was made on the five years radiation data of Kish Island, located in the Persian Gulf at south of the Iran. The water production costs were considered for three different configurations of the MED/TVC/LF desalination system to determine the required sizes of LF solar field, system costs and also amount of annual fuel savings. The results of the present study shown that the water production costs of the MED/TVC/LF system is obtained as a value between 1.63 $/m3 and 3.09 $/m3 for the systems without thermal storage and with thermal storage, respectively. The thermal storage system would increase the costs of the water production by about 42% and 65% for 6 h and 12 h of thermal storage, respectively. It was found that the water production cost of the MED/TVC/LF system with 67.77% contribution of solar energy and without the thermal storage system is high (3.32 $/m3) as compared to the conventional fossil fuel powered MED/Desalination plants with a water production cost of 1.26 $/m3.

The compound parabolic concentrators (CPCs) are of importance due to their capability in absorbing the incident solar radiation in a wide limit. The present paper deals with the optical and thermodynamic analysis of a solar CPC applying the accurate solar ray-tracing analysis. To this end, the optical efficiency of the CPC was obtained for different geometric concentration ratios ( $C_t$) based on the CPC modified equations and considering the diffuse radiation effects. The results demonstrated that the highest solar radiation absorption is obtained for $C_t$ of 1.63. The outlet temperature ( $T_o$), energy and exergy efficiencies ( $\eta _I$ and $\eta _{II}$) of the stationary evacuated tube CPC were compared with those of two different evacuated tube solar collectors without a concentrator (with large or low distance between the tubes). Based on the results, the average incident solar radiation of the CPC collector is higher than that of two other solar collectors without a concentrator. Besides, $\eta _I$ of the CPC is higher than that of other collectors within the range of effective reflective angle of the CPC, while for the higher incident angles, $\eta _I$ is lower than or equal to the other two collectors without a concentrator.