Comparison of solar thermal and solar electric space heating and cooling systems for buildings in different climatic regions

Solar Energy 188 (2019) 545–560

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Comparison of solar thermal and solar electric space heating and cooling systems for buildings in different climatic regions

T

Osama Ayadia, , Sameer Al-Dahidib ⁎

a b

Mechanical Engineering Department, The University of Jordan, Amman 11942, Jordan Department of Mechanical and Maintenance Engineering, School of Applied Technical Sciences, German Jordanian University, Amman 11180, Jordan

ARTICLE INFO

ABSTRACT

Keywords: Solar electrical cooling Solar thermal cooling Solar cooling simulation Primary energy ratio Solar heating

Solar thermal and Photovoltaic (PV) systems can save significant amount of non-renewable energy that are utilized to satisfy the energy services for buildings. The falling prices of PV in recent years increased the attractiveness of PV systems. The purpose of this research is to develop a systematic methodology for fair technical and economical comparison of reference and solar assisted systems. For this reason, the annual energy requirements for heating, cooling and DHW for a selected dormitory building under five representative climatic conditions were evaluated using the Hourly Analysis Program (HAP). At the same time, solar thermal and PV systems have been designed and simulated for the same building using Sketchup, Trnsys and PVsyst. Finally, a systematic comparison between the solar systems and five conventional systems have been carried out in terms of primary energy ratio, and Levelized Cost Of Energy (LCOE). For the case of Amman, solar thermal and electric systems achieved a non-renewable primary energy savings of 29% and 100%, respectively, whereas, they achieved LCOE savings of 15% and 62%, respectively compared to the best conventional system. The selection of the best solution for a given project requires a full understanding of the system performance and the interaction of its components rather than the technology efficiency only. This system performance depends on the building envelope, load patterns, availability of solar radiation, roof area availability, energy prices, and policies. Thus, a case-by-case analysis should be done for each project in each climatic region.

1. Introduction Most people spend the majority of their time inside buildings, and since thermal comfort in buildings is generally achieved by mechanical heating and cooling systems, the energy requirements for buildings represents the highest energy-consuming sector worldwide. About 40% of the total energy demand in the EU and Australia is utilized for buildings, and a similar share of 39% in the US and 25–30% in China (Klepeis et al., 2001) (Schweizer et al., 2006) (Odeh et al., 2016) (économiques, 2013) (Harish and Kumar, 2016) (Ramesh et al., 2010) (Anisimova, 2011; Boyano et al., 2013; Buyle et al., 2018; The U.S. Energy Information Administration (EIA), 2017, 2011; U.S. Department of Energy (2011). Energy consumption in building sector across different climatic regions differs significantly. In addition to the climate, this variation is related also to other attributes such as the building size, thermal characteristics of the buildings, occupancy density, income, energy cost and the difference in behavior and preferences. For instance, in cold climates, the highest portion of buildings energy consumption is used

⁎

for space heating followed by electric appliances. While for moderate warm climates, water heating and cooking are the main consumers. In both climates, Domestic Hot Water (DHW) presents a significant player (économiques, 2013) (D’Agostino and Parker, 2018). Among the energy consuming services in the building, the demand for air-conditioning of indoor air has increased at a high rate worldwide during the last few decades, even in heating-dominated climates. The main reasons for the increasing energy demand for summer air-conditioning are the increased internal loads due to the increased use of electric and electronic equipment, increased living standards, occupant comfort demands and architectural characteristics and trends, such as an increasing ratio of transparent to opaque areas and to the growing popularity of glass buildings (Henning et al., 2013). And this upward trend in energy demand is assured to continue in the future (PérezLombard et al., 2008). This energy demand increase for building services is already putting enormous strain on electricity systems in terms of energy consumption and peak demands during summer months, especially in hot climates. This will increase the need of new power plants to meet peak power

Corresponding author. E-mail address: [email protected] (O. Ayadi).

https://doi.org/10.1016/j.solener.2019.06.033 Received 30 January 2019; Received in revised form 11 June 2019; Accepted 13 June 2019 0038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved.

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O. Ayadi and S. Al-Dahidi

Nomenclature

SC SH SHC H&C LPG LCOE SPF PER NRE ETC HP HR HVAC VCC SPB ε Η PERNRE , ref

Notation and list of acronyms DHW PV HAP CDDn HDDn DB MCWB Lat Long Elev Global Irrad KPI IEA VRF EER CCHP COP PGU Abs. CPC STC LCC

domestic hot water photovoltaic hourly analysis program cooling degree-days heating degree-days dry bulb temperature mean coincident wet bulb temperature latitude longitude elevation global irradiation on horizontal surface per year key performance indicators international energy agency variable refrigerant flow energy efficiency ratio combined cooling heat and power coefficient of performance power generation unit absorption chiller compound parabolic concentrator standard test conditions life cycle cost

PERNRE Qel Qin el and Tm* fsav.NRE

in

space cooling space heating solar heating and cooling heating and cooling liquefied petroleum gas levelized costs of energy seasonal performance factor primary energy ratio non-renewable energy evacuated tube collectors heat pump heat recovery heating ventilation and air-conditioning system vapor compression chiller simple payback period primary energy factor efficiency non-renewable primary energy ratio of reference system non-renewable primary energy ratio electricity thermal inputs primary energy conversion factors reduced temperature difference non-renewable energy savings

2008) and (Paitazogou et al., 2015) presented systems for hotels and a hospital in Morocco and Jordan. (Edwards, 2011) presented the performance of a solar cooling plant for housing in Ontario. (Dalibard et al., 2009) presented a large scale solar cooling plant in Germany. Solar cooling systems for industrial application in a diary and beverage factories in Morocco and Tunisia were presented by (Ayadi et al., 2008) (Ayadi et al., 2009). Bermejo et al. (2010) presented a solar cooling plant for the Engineering School of Seville in Spain. The utilization of solar PV for DHW, heating and cooling is also a promising technology, especially nowadays with the drastic drop of PV prices. Regarding the utilization of solar PV for DHW, from technical perspective, it was early in 1994 when (Fanney and Dougherty, 1994) patented a solar PV hot water system. Matuska and Sourek (2017) showed that the efficiency of a solar thermal system for DHW is more than 3 times higher than a direct coupling of PV solar array to a Direct Current DC resistive heating elements for identical hot water load and climate conditions. However, when PV system is connected to an energy efficient heat pump, (Good et al., 2015) showed that it is more efficient to use PV in combination with heat pumps for residential buildings than it is to use solar thermal collectors for a Norwegian residential building he studied. From economical point of view, early in 1997 (Fanney and Dougherty, 1997) mentioned that even though solar PV hot water systems were more expensive than the existing solar thermal water systems, it is expected that solar PV water heaters would offer the promise of a less expensive system within the next decade. Currently, (Meyer, 2015) and (Holladay, 2014) showed examples that favor solar PV water heating compared to solar thermal collectors from economical perspectives. Recently, the economic performance of PV systems for DHW is becoming more attractive, not only because of the lower costs of PV, but also due to vital rule that DHW and thermal energy storage can play to increase the pv integration and self-consumption in buildings (Thür et al., 2018) (Schwarz et al., 2018) (Roselli et al., 2017). Regarding the utilization of solar PV for cooling applications, a range of authors performed in-depth studies for comparing different solar cooling configurations, considering both thermally driven and solar electric systems (Lazzarin, 2014) (Lazzarin and Noro, 2018)

demand (The Future of Cooling, 2018) (Sarbu and Sebarchievici, 2017). The utilization of solar energy for heating and cooling applications seems to be an attractive solution that can participate to increase the renewable energy shares in building energy consumption while reducing the consumption of fossil fuel and the environmental impacts of conventional systems. One of the main motivations of the investigation of solar cooling systems is the coincidence of energy availability (solar radiation) and the cooling demands of most buildings (Osama Ayadi et al., 2012b; Montagnino, 2017; Montenon et al., 2016; Motta et al., 2006). Basically, solar cooling can be realized by two general methods; the first method relies on solar thermal collectors that produce heat, this heat is then drives a thermally driven chiller, that can be absorption, adsorption or desiccant cooling system. The second method entails utilizing Photovoltaic (PV) solar panels that convert solar radiation directly into electricity, this electricity is used to drive the motor that rotates the compressor of a vapor compression chiller. Solar thermal cooling systems has increased slowly from one thousand systems installed worldwide in 2011 (Henning, 2011) to nearly 1200 systems in 2014 as estimated by (Mugnier and Jakob, 2015). While the lack of awareness and technical knowledge about solar thermal systems creates a barrier against a wider deployment of this technology, the real main challenge is the lack of economic competitiveness. Within the framework of IEA SHC Task 38, 135 SHC systems installed worldwide have been surveyed. With respect to the end use typology, more than the half of these systems are dedicated to the airconditioning of office buildings. For this type of buildings, the DHW demand is low and often produced by decentralized small electricity driven water heaters. About 9% of the considered installation are applied at education centers, 6% in industry, and only 5.2% and 3.7% were installed for hospitals and hotels where the DHW loads are significant (Henning et al., 2013). A number of experimental studies have been carried out to test solar thermal cooling systems for different end use applications. (Osama Ayadi et al., 2012b) presented an example of the design, installation and monitoring results of a pilot plant for a solar heating and cooling system for an office building in Italy. (Asmar, 2008) (Krüger et al., 546

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(Eicker et al., 2015) (Mokhtar et al., 2010) (Infante Ferreira and Kim, 2014) (Kim and Infante Ferreira, 2008) (Neyer et al., 2018a) (Neyer et al., 2018b). For example, one of the first scientific contributions is due to Kim and Infante Ferreira (2008) in which authors compared solar thermal including solar thermo-mechanical, absorption, adsorption and desiccant systems as well as solar electric systems, at that time (2008), authors concluded that single-effect LiBr–water absorption system achieved the lowest cost. However, since 2008, prices of PV systems decreased significantly, and in a more recent study in 2014, the same authors of the previous study found that solar electric cooling system has become the most feasible solution (Infante Ferreira and Kim, 2014) (Comello et al., 2018). Mokhtar et al. (2010) proposed an evaluation methodology for the techno-economic performance of different solar cooling configurations based on the weather conditions and cooling load profile of a building in Abu Dhabi, UAE. Applying this methodology, they systematically evaluated 25 possible configurations of solar collecting systems coupled to different cooling technologies including solar electric and solar thermal cooling options. Based on the overall efficiency, vapor compression chillers driven by electricity from multicrystalline PV cells were found to be the most efficient option. Fong et al. (2010) compared five different solar cooling system configurations for an office building in Hong Kong in terms of a year round primary energy consumption, solar electric cooling system showed the lowest consumption, followed by absorption refrigeration system. Hartmann et al. (2010) compared solar thermal and PV options for small office building in two different European climates (Madrid and Freiburg), and found that the solar electric system outperforms the solar thermal system in the current and the future scenarios in terms of primary energy and economical savings. In 2012, Henning and Döll (2012) mentioned both of the solar thermal and PV solutions for the active solar systems for heating and cooling of buildings. However, they focused in their study on solar heating and cooling systems using solar thermal collectors only. Additionally, they mentioned that PV based solutions were still scarce and no general trends on their design and operation strategy were existing. However, they expected that future work will certainly include design studies for PV based systems. In 2014, Lazzarin (2014) compared the overall system efficiency of solar thermal and electric cooling systems during one day of operation. Within the solar thermal category, Lazzarin (2014) investigated different solar collectors, sorption chiller technologies and heat rejection systems. The highest cooling effect for a given solar radiation was achieved by double effect absorption chiller driven by evacuated tube collectors, followed by a PV driven system. Eicker et al. (2015) compared the overall performacen of solar electric cooling with solar thermal absorption cooling systems for an office building in six locations with different climates. Results showed similar primary energy savings for both systems. However, it was found that if the surplus electricity produced by the PV system is injected into the grid, the primary energy savings of solar electric cooling system would be higher. SPF Testing (2016) introduced an innovative approach for the design of solar thermal and photovoltaic systems in a typical nearly ZeroEnergy Building. It is based on simplified models and set of equations for performance prediction of both building and system components. They mentioned that Future works will be aimed at applying simulation-based optimization techniques to relevant case studies. In 2018, Lazzarin and Noro (2018) showed that from a technical perspective, the solar thermal configuration in which Parabolic Trough Collector drives a double effect absorption chiller could reach a similar efficiency to that of a PV cooling system. However, from economical point of view, this solar thermal system would roughly cost the double compared to the PV driven technologies (Lazzarin and Noro, 2018).

While previous studies about solar cooling systems investigated solar thermal and solar PV cooling, none of them investigated systems used for cooling, heating and DHW preparation. Eventhough, the DHW consumption can be responsible for a substantial share of the total building energy use. DHW production accounts for approximately 15% of the total energy consumption in the residential sector in the USA and EU (Pérez-Lombard et al., 2008). It has to be mentioned that compared to solar cooling only, solar thermal systems that are designed to supply heating, cooling and DHW for buildings maximize the utilization of the collected solar energy to the maximum extent (Ayadi et al., 2012) (Kiwan et al., 2016) (Neyer et al., 2018b). Also, these systems could demonstrate better primary energy savings and may become more competitive than solar PV cooling systems. A systematic comparison between solar electric and solar thermal cooling, heating and DHW in terms of primary energy, based on a detailed simulation that covers a full year of operation, is still missing and it is done in this paper. 2. Methodology The objectives of the present work are two-fold: (i) to systematically analyse the performances of five conventional heating, cooling and DHW system configurations, and (ii) to compare them with solar electric and thermal assisted systems. For all systems, the electricity and fuel consumption are evaluated, and the primary energy ratio is calculated. These analyses are carried out for full year of operation in five different climates. The following procedure is developed and applied for the energetic evaluation for full year of operation of all the systems: 1. The building’s heating, DHW, and cooling demands are analysed for five climatic regions by dynamic building simulations using the Hourly Analysis Program (HAP) developed by Carrier (Carrier corporation, 2018); 2. The proposed building is modelled using SketchUp (Trimble Inc., 2017); 3. Skelion plugin is employed to define the maximum number of solar collectors and PV modules that can be installed on the building’s rooftop without self-shading (Skelion, 2017); 4. PVsyst software is employed to evaluate the predicted power output and electricity savings that can be achieved via the PV system (PVsyst SA, 2012); 5. TRNSYS software is employed to evaluate the solar thermal heating and cooling systems’ performances; 6. The unified monitoring procedure developed by the International Energy Agency (IEA) Tasks 38 (Sparber et al., 2008) and updated by IEA Task 53 (Neyer et al., 2018a) is applied to evaluate the nonrenewable primary energy ratio for the conventional systems and the non-renewable energy savings by the solar thermal and electric assisted systems. 7. An economic assessment and comparison for the reference and the solar assisted systems for a dormitory building in a selected region is carried out. 3. Building loads With respect to the selection of the most appropriate building typology for the comparison between solar systems, the selected building should have a significant energy load profiles. While the consumption for the DHW all year around could be high in buildings such as hotels, hospitals, dorms and sport centers, as oppose to buildings such as offices and commercial centers. This might be beneficial to investigate the powerful of solar thermal systems with respect to PV assisted system. A dormitory building is chosen in this study. It is worth mentioning that the indoor environment of a dormitory will, indeed, effect students’ health, comfort and productivity, and thus, it influences their learning 547

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Fig. 1. Front view of the building (left) and its modeling using Sketchup (right).

Fig. 2. Plan view of the dormitory floors.

and working efficiency. Therefore, the investigation of the thermal environment of a dormitory is of paramount importance (Chen and Liu, 2017). The building model considered in this analysis is based on a real dorm building located at the University of Jordan (latitude 32°00′47″N, longitude 35°52′35″E, elevation 1003 m), which is one of the four interior dorms for female students at the University campus. The selected building is a five floor building, and the area of each floor is 1246 m2. Each floor consists of 24 double rooms with a total number of 240 students. The front view of the building, its modelling using Sketchup as well as the typical floor plans are shown in Figs. 1 and 2, respectively. Fig. 3 shows the detailed characteristics of the building envelope. The overall heat transfer coefficient (i.e., U-value) of the walls, ceiling and windows are 0.48 W/m2K, 0.48 W/m2K and 3.4 W/m2K, respectively. This study investigates the building in five representative climatic regions (New York, Milan, Amman, Abu Dhabi and Jakarta) that cover a broad range of climatic conditions from strongly heating dominated climates to strongly cooling dominated climates. This selection is based

on Köppen climate classification (Peel et al., 2007) that divides climates into five main climate groups, with each group being divided based on seasonal precipitation and temperature patterns. The five selected cites cover the following main groups A (tropical), B (dry), C (temperate), and D (continental), whereas it excludes only the E (polar) climate. The cooling and heating energy demand of this dorm was simulated dynamically using the HAP software (Carrier corporation, 2018). The heating and cooling design conditions as well as the heating and cooling degree-days of the selected locations were obtained from ASHRAE (Owen and Kennedy, 2009), while the global irradiation on horizontal surface were obtained from Meteonorm 7 (METEOTEST Genossenschaft, 2015). The annual mean temperatures and the global horizontal irradiances of the five locations under study are summarized in Table 1. Fig. 4 presents the monthly energy consumption for cooling in the different climatic regions, it can be seen that cooling load is highest in Abu Dhabi and Jakarta. However, the load profile differs significantly between these two locations; in Abu Dhabi, the peak cooling load occurs in summer while in Jakarta the load profile is almost flat all over

Fig. 3. Wall and ceiling construction. 548

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Table 1 Heating and cooling design conditions, CDD, HDD and the global horizontal irradiance of the five locations under study. Location

Lat.* (°)

Long.* (°)

Elev.* (meter)

Heating DB* (°C)

Cooling DB* (°C)

Cooling MCWB* (°C)

CDD* (°C-day)

HDD* (°C-day)

Global Irrad.* (kWh/m2)

Abu Dhabi Jakarta Amman Milan New York

24.43 N 6.12 S 31.98 N 45.43 N 42.75 N

54.65 E 106.65 E 35.98 E 9.28 E 73.8 W

27 8 779 103 89

11.5 22 1 −5.1 −18.8

44.9 33.8 35.3 33 31.7

23.2 25.7 19.1 24.1 22.8

3565 3398 1037 588 329

30 0 1291 2265 3671

2027 1660 2045 1125 1409

Monthly energy consumption for cooling [kWh]

* Lat: Latitude, Long: Longitude, Elev: Elevation, DB: Dry bulb temperature, MCWB: Mean coincident wet bulb temperature, CDDn: Cooling degree-days base 18.3 °C, HDDn: Heating degree-days base 18.3 °C, Global Irrad: Global irradiation on horizontal surface per year.

and the relatively high solar radiation during the cooling season.

AbuDhabi Jakarta Amman Milan NewYork

250000 200000 150000

4. Systems comparison In this section, the Key Performance Indicators (KPI) adopted for the technical assessment of different solar systems are presented. Moreover, different routes for satisfying6+ the heating, cooling and DHW demands of the building are presented and discussed. These systems include five reference systems as well as solar electric and solar thermal systems.

100000 50000 0

0

1

2

3

4

5

6 7 month

8

9

10

11

12

13

Monthly energy consumption for heating [kWh]

Fig. 4. Monthly energy consumption for cooling [kWh].

180000 160000 140000 120000 100000 80000 60000 40000 20000 0

4.1. Technical assessment criteria AbuDhabi Jakarta Amman Milan NewYork

0

1

2

3

4

5

6 7 month

8

9

The technical comparison between conventional and solar thermal and PV assisted heating, cooling and DHW systems is complicated. This complexity resulted from the vast variety of components and system configurations, the possibility of utilizing energy sources with different qualities (heat and electricity), and the climatic conditions under which the systems are operating. Several attempts have been made to develop KPIs that ensure a fair comparison between various systems working under different climatic conditions. One of the major contributions in this field was the unified monitoring procedure of solar heating and cooling systems developed within the framework of Task 38, of the International Energy Agency (IEA) Solar Heating and Cooling Programme (Sparber et al., 2008) (Napolitano et al., 2011). This procedure was further extended and developed within Task 48 (Menegon and Fedrizzi, 2015) and Task 53 (Neyer et al., 2018a). Based on the aforementioned KPIs, the Non-Renewable Primary Energy Ratio of reference system (PERNRE , ref ) was selected in this work and applied for the reference systems; as it gives more in-depth information under the economic/environmental point of view. The energy ratio is based on the entire useful heating and cooling energy (Qout ) and is compared to the non-renewable primary energy effort of the system within a certain interval of time (in this study a whole year is used). Larger values of the PERNRE entails that both of the heating and cooling services can be obtained with a relatively small amount of fossil derived energy, and that the system is environmentally friendly (Neyer et al., 2018a).

10 11 12 13

Fig. 5. Monthly energy consumption for heating [kWh].

the year. Fig. 5 depicts the heating load of the five climatic regions: New York and Milan have the highest energy consumption for heating, while the loads in Jakarta and Abu Dhabi are negligible. Fig. 6 presents the relative H&C and DHW energy consumption of the building in the five selected climate regions. Jakarta have the highest share for cooling, while New York have the highest share for heating. The share for DHW ranges between 7 and 15% of the total energy consumption of the buildings. It has to be mentioned that, even though the CDD and the HDD for locations like Amman are close to each other, 1037, 1291 respectively, the relative cooling energy consumption is much higher 67% compared to 18% only for heating. This occurs due to the high internal heat gains

Fig. 6. The relative heating, cooling and DHW energy consumption of the building in the different selected climates. 549

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PERNRE , ref =

(

Qout Qel, in el

+

Qin in

)

(1)

Electricity (Qel ) and other thermal inputs (Qin ) are converted to nonrenewable primary energy units with the primary energy conversion factors ( el and in ). Such factors for heat and electricity from fossil fuels have been defined as follows, on the basis of the European Directives (European Parliament, 2006):

• •

= 0.4 (i.e., kWh of electricity per kWh of primary energy) = 0.85 (i.e., kWh of heat per kWh of primary energy, considering the boiler efficiency) el

in

Fig. 7. First reference system based on electrically driven heat pump for (heating and cooling) and electric water heater for DHW.

4.2. System description and performance assessment

1.8

In this section, both reference and solar assisted system configurations are described, and the results obtained from their performance evaluation based on the adopted KPIs is presented.

1.6 1.4

PERNRE,ref

1.2

4.2.1. First reference system This system utilizes electricity from the electric grid to drive a variable refrigerant flow (VRF) reversible heat pump for satisfying the heating and cooling demands of the space. At the same time, electricity is used to power an electrical water heater to supply the required DHW for the building occupants. A simple energy flow chart of this system is depicted in Fig. 7. The design Energy Efficiency Ratio (EER) and COP of the heat pump were entered in the HAP software and they were used to determine the condensing unit input power at the design rating point. Input power is then corrected on hourly basis as operating and environmental conditions change.

1 0.8 0.6 0.4 0.2 0

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

Fig. 8. Primary energy ratio for the first reference system in the five different climate regions.

• For cooling, condensing unit input power is calculated as a function •

of outdoor air dry-bulb temperature, indoor unit entering wet-bulb temperature, part-load ratio, refrigerant line length, refrigerant line maximum vertical distance, compressor type, and, if applicable, heat recovery operation; For heating, condensing unit input power is calculated as a function of outdoor air dry-bulb temperature, indoor unit entering dry-bulb temperature, part-load ratio, refrigerant line length, refrigerant line maximum vertical distance, compressor type, defrost operation and, if applicable, heat recovery operation.

Primary Energy Ratio (PER) results of this system are shown in Fig. 8. The highest value was obtained in Jakarta (i.e., 1.41), where the system was working mainly for cooling in favorable ambient temperatures with a Seasonal Performance Factor (SPF) of the VRF in the cooling mode of 4.8. While the lowest was in New York (1.05) where the system was mainly working in heating mode and the SPF of the VRF system in heating mode was (3.06).

Fig. 9. The second reference system based on electrically driven heat pump for (heating and cooling) and air to water heat pump for domestic hot water. 1.8 1.6 1.4

PERNRE,ref

1.2

4.2.2. Second reference system The second reference system depicted in Fig. 9 is similar to the first reference system. However, DHW is produced by an air to water heat pump. The monthly average water temperature received from the mains were evaluated. PER results for the second reference system are presented in Fig. 10. Since the heat pump is consuming less energy than the electrical heater to prepare the DHW, the primary energy ratio of this system is higher than that of the first system. The highest value was obtained in Jakarta (1.78), while the lowest was in New York (1.3).

1 0.8 0.6 0.4 0.2 0

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

Fig. 10. Priamary energy ratio for the second reference system in the five different climate regions.

550

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Fig. 11. The third reference system based on electrically driven heat pump for (heating and cooling) and diesel fired hot water boiler.

Fig. 13. The fourth reference system based on electrically driven chiller for cooling and diesel fired hot water boiler for space heating and domestic hot water.

1.8

fourth reference system is expected to be lower than that of the first three reference systems. PER results for the fourth reference system are shown in Fig. 14. The highest value was obtained in Jakarta (1.3), and the lowest was in New York (0.87).

1.6 1.4

PERNRE,ref

1.2 1 0.8

4.2.5. Fifth reference system The fifth reference system (depicted in Fig. 15) is based on the combined cooling heat and power (CCHP) concept. Basically, the CCHP systems is composed of power generation unit (PGU) and waste heat utilization equipment. Researchers have investigated various CCHP systems configurations theoretically and experimentally (Afzali and Mahalec, 2018; Deng et al., 2011; Li et al., 2018; Yan et al., 2016) (Wu et al., 2014). A simple yet energy efficient system configuration was selected in this study, it is based on a gas-fired CCHP that burns gas in the power generation unit (PGU) and produces electricity and usable heat simultaneously, heat is used for the DHW preparation, and the produced electricity drives a variable refrigerant flow reversible heat pump for satisfying the heating and cooling demands of the space. When the electricity required by the heat pump is not met by the CCHP production, the remaining part is covered by the public grid. PER results for this system are shown in Fig. 16. The highest value was obtained in Amman (1.8), and the lowest was in Abu Dhabi (1.39).

0.6 0.4 0.2 0

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

Fig. 12. NRE Priamary energy ratio for the third reference system in the five different climate regions.

4.2.3. Third reference system The third reference system depicted in Fig. 11 is similar to the first reference system. However, DHW is produced by a diesel fired hot water boiler. It is worth mentioning that gas boiler is more efficient, and that the cost of heat produced by gas is lower under the condition that a gas distribution network is available in the desired location. For instance, for cities such as Amman this gas network is not available, and users have to buy their own bulk storage, which makes the cost similar or higher to that of diesel. Notice that, for utilizing a gas fired hot water boiler, only the calorific value of the fuel and the efficiency of the boiler have to be modified. This can easily be done, and the trend of the results would be marginally affected. PER results for the third reference system are shown in Fig. 12. Results demonstrated the same trend as for the first reference system. However, since the primary energy ratio for the DHW heating process is higher using a diesel boiler that using and electrical heater, the PER of this system is higher. The highest value was obtained in Jakarta (1.64). While the lowest was in New York (1.24).

4.2.6. Comparison of reference systems Figs. 17 and 18 present the non-renewable primary energy ratio of the five reference systems under the five climatic regions, the main findings are:

• The first three systems utilized reversible heat pump for heating and 1.8 1.6 1.4

PERNRE,ref

1.2

4.2.4. Fourth reference system The fourth reference system (depicted in Fig. 13) is utilizing electricity from the grid to power a vapor compression chiller to meet the cooling load demand of the building. While a diesel fired hot water boiler is used to provide the thermal energy required by the space heating load and the domestic hot water demand. In this system, the chiller used for cooling is working with a lower SPF (3.2–3.4) compared to that of a VRF system working in the cooling mode (3.8–4.8). Moreover, the diesel boiler used for space heating in this system configuration is also working with a lower PER (0.95) than a VRF system working in heating mode (1.2–1.7). Thus the PER of the

1 0.8 0.6 0.4 0.2 0

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

Fig. 14. NRE Priamary energy ratio for the fourth reference system in the five different climate regions. 551

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Fig. 15. The fifth reference system based on CCHP concept. 2 1.8 1.6

PERNRE,ref

1.4

Fig. 19. Solar thermal systems supplies heat to the thermally driven chiller, space heating and domestic hot water.

1.2 1 0.8 0.6 0.4 0.2 0

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

•

PERNRE,ref

Fig. 16. NRE Priamary energy ratio for the fifth reference system in the five different climate regions.

2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

• • System 1 Abu Dhabi

System 2 System 3 System 4 Reference systems Jakarta

Amman

Milan

System 5

4.2.7. Solar thermal cooling and heating system In this system (shown in Fig. 19), solar thermal collectors installed on the rooftop of the building. The thermal output of these collectors will cover part of the thermal demand of the space heating during winter, as well as they will supply thermal energy required by the absorption chiller during the cooling season. These collectors will also supply domestic hot water for the building all the year around. Single and double effect absorption chillers are commercially available. While the double effect absorption chillers have higher COP compared to the single effect chillers; they require high driving temperatures in the range of (140–180 °C) for operation under the high temperature lift conditions (Henning et al., 2006), such as the cases in Abu Dhabi and Amman. These high driving temperatures can only be achieved by utilizing concentrating collectors (at least single axis tracking one). Concentrating collectors allow the production of heat at higher level of temperatures matching the inlet temperature requested by highly efficient multi effect thermally driven chillers. However, less than 3% of all solar cooling plants worldwide utilize these collectors. The main barriers against a wide application of concentrating collectors are: (i)

NYC

PERNRE,ref

Fig. 17. Comparison of PERNRE,ref for systems in the different climatic regions.

2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

Abu Dhabi

System 1

Jakarta

System 2

Amman System 3

Milan

NYC

System 4

System 5

cooling, since the performance of the heat pump depends on the temperature difference between the ambient the space to be heated or cooled, their best performance was noticed in the favorable ambient temperatures during the cooling mode in Jakarta. Whereas, due to the high temperature lift during the heating mode in the cold climate of New York, the PRE was the lowest. The variation between the first three systems are based on the technology applied for the DHW. And since the heat pump applied in system 2 is more efficient than the electrical heater (system 1) and boiler (system 3), the overall PER of the second system was the highest in the five climatic regions. The fourth reference system is based on a typical chiller and boiler configuration. Since the energetic performance of these components is lower than that of the VRF reversible heat pump, the overall PER of this system is the lowest among the five reference systems in the five climatic regions. The PER in the cold climates was improved using the cogeneration system (the fifth system), Its best performance was obtained in the moderate climate of Amman.

Fig. 18. Comparison of PERNRE,ref for different systems in the five climatic regions.

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Fig. 20. Schematic diagram of the solar thermal heating and cooling system.

the requirement of a tracking system, which is associated with higher initial and maintenance costs. (ii) the requirement of high direct solar radiation levels, which is not the case of some locations in this study (Ayadi et al., 2012) (Henning et al., 2013). In order to achieve high temperatures by the solar field while avoiding the restrictions of the concentrating collectors, a fixed Compound Parabolic Concentrator (CPC) solar thermal collectors were selected in this study. These collectors combine the ability to achieve relatively high temperatures with good efficiency, while they are fixed. Fig. 20 shows the schematic diagram of this system. It presents the solar thermal heating and cooling system configuration. Depending on the local needs, the operating mode of the systems is changed automatically. In this system, Compound Parabolic Concentrator (CPC) solar thermal collectors deliver their heat either to the hot storage, where it could be used for space heating and preparation of the DHW, or to the absorption chiller to produce part of the required cooling demand of the space. Chilled water produced by the chiller is delivered to the 2-pipe distribution system that cools the spaces via fan coil units in the rooms. Heat rejected from the chiller to the ambient via a cooling tower. A backup boiler is connected to the hot storage to supply any deficit

heat requirements, and a vapor compression chiller is connected to the cold storage to satisfy the building cooling requirement when the output of the absorption chiller is low. In order to investigate the potential of solar thermal system on the building’s roof; the building layout was drawn using Sketchup software (Trimble Inc., 2017) (Fig. 21), and the solar systems design plugin for Sketchup “Skelion” (Skelion, 2017) was used to evaluate the maximum possible roof area that can be utilized for the CPC collectors considering that no mutual shading occurs between 10:00 am–2:00 pm during the winter solstice. The optimal configuration of CPC collector was achieved by installing the CPC collectors with the same building orientation, i.e., azimuth (24° east of south). Based on the previous graphical analysis, a solar thermal system consisting of 230 CPC collectors was designed at the rooftop, with a total of 500 m2, collectors are installed 24° toward southeast, with optimal slope for each location. CPC collectors were selected due to their high efficiency at high output temperatures compared to flat plate collectors. High temperatures are required to ensure a good COP of the thermally driven chiller. Reviewing the “SPF Institute for Solar Technology” testing report of CPC collectors, “Sunerg HV12” collector was selected for this system, its

Fig. 21. Layout of the CPC collectors to be installed on the roof of the building. 553

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Fig. 22. Collector efficiency (left), and its construction (right).

A rational selection of the reference system to be considered for the comparison with the solar systems is the one with the highest PERNRE, which was the second reference system in this study. Fig. 23 presents the non-renewable energy savings achieved by the solar thermal system compared with the second reference system. While the solar thermal system achieved some non-renewable primary energy savings in Amman (29%) and Abu Dhabi (10%), its performance was worse than the reference systems in New York and Milan due to the low performance of the solar thermal collectors in the cold climates with low solar radiation. At the same time, there was no NRE primary energy savings in Jakarta, where the main contribution of the solar thermal collectors was utilized to drive the single effect absorption chiller which has a low coefficient of performance (COP).

Table 2 Standard operation conditions of Bumble Bee absorption chiller. Parameter

Unit

Nominal cooling capacity Heat demand Reject heat COP

160 208 374 0.79

kW kW kW –

Chilled water

temperature inlet temperature outlet volume flow pressure drop max. pressure

21 16 27.7 0.25 6

°C °C m3/h bar bar

Hot water

temperature inlet temperature outlet volume flow pressure drop max. pressure

90 72 9.7 0.36 16

°C °C m3/h bar bar

temperature inlet temperature outlet volume flow pressure drop max. pressure

30 38 39 0.57 6

°C °C m3/h bar bar

Reject heat water cycle

4.2.8. Solar PV system The solar PV system (depicted in Fig. 24) is similar to the second reference system. However, the main part of the required electricity is supplied by the grid-connected PV system installed on the rooftop of the building. When the electricity required by the system is not met by the PV production, the remaining part is covered by the public grid. While, the surplus electricity from the PV system is injected into the grid when the demand is less than the PV system production. In order to investigate the potential of solar PV system on the building’s roof; the building layout was drawn using Sketchup software (Trimble Inc., 2017) (Fig. 25), and the solar systems design plugin for Sketchup “Skelion” (Skelion, 2017) was used to evaluate the maximum possible roof area that can be utilized for the PV panels considering that no mutual shading occurs between 10:00 am–2:00 pm during the winter solstice. The optimal configuration of PV panels was achieved by installing the PV panels with the same building orientation, i.e., azimuth (24° east of south). This orientation enables the installation of 230 modules of the selected PV panels “Sun power – SPR- 400E-WHDT”. The nominal output

technical data were obtained from test report published at SPF website (SPF Testing, 2016). Fig. 22 (left) presents the efficiency of the collector based on its aperture area with respect to the reduced temperature difference Tm*, which presents the difference between the average temperature of the collector and the ambient temperature divided by the irradiation on the collector plane- on the x-axis, whereas Fig. 22 (right) presents the collector’s construction. After reviewing the commercially available absorption chillers that are compatible with the required cooling load of the building and the available driving heat from the solar collectors, the single effect water/ lithium bromide Bumble Bee absorption chiller was selected. Its cooling capacity is 160 kW at standard operation conditions. Table 2 gives an overview about the operation of the chiller at standard conditions (Kühn, 2013).

45% 35%

4.2.7.1. Performance assessment of the solar thermal heating and cooling system. The performance of the SHC system is basically evaluated based on the non-renewable primary energy ratio (PERNRE) which is calculated in a similar way to that of the reference systems. Moreover, in order to evaluate the savings achieved by using the solar system, the non-renewable energy savings (fsav.NRE) is calculated comparing the PERNRE to the PERNRE.ref as shown in Eq. (2), and, thus, respectively the NRE primary energy savings of the solar system are compared to the reference system.

fsav . NRE = 1

s

.

25%

5% -5% -15% -25%

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

PERNRE . ref PERNRE

15%

Fig. 23. Non-renewable energy savings achieved by the solar thermal system compared with the second reference system in the different climate regions.

(2) 554

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Table 3 Main technical specifications of the Selected PV module (Sun power – SPR400E-WHDT) at STC. Parameter

Fig. 24. On-grid PV system supplies part of the electricity for the first reference system.

Unit

Electrical Data Peak Power Rated voltage Rated current Open circuit voltage Short circuit current Peak efficiency

400 72.9 5.49 85.3 5.74 18.5

Wp V A V A %

Temperature coefficients Power Voltage Current

−0.38 −0.23 0.06

%/K V/K %/K

Mechanical data Number of solar cells Module length Module width

128 2067 1046

Monocrystalline Silicon mm mm

Table 4 Technical specifications of the selected inverter (Sunny Tripower 20000TLEEJP).

of this panel at Standard Test Conditions (STC) is 400 Wp, and it measures 2.07 m by 1.05 m. The tilt of these panels was adjusted based on the location. The electrical and mechanical specifications of the PV panels are reported in Table 3. The global power of the solar array at nominal STC is 94.2 kWp, the total module area is 497 m2. For this system, four inverter units of 20 kWac from “Sunny Tripower 20000TLEE-JP” were selected. The technical specifications of the inverter are reported in Table 4. The PV system was modeled using PVsyst simulation software (PVsyst SA, 2012), the system is composed of four “Sunny Tripower 20000TLEE-JP” inverters and 230 “Sun power – SPR- 400E-WHDT” PV modules. This is the maximal number of modules that can be installed on the rooftop of the building area due to space limitation. The tilt angles of the PV panels systems were optimized to achieved the highest annual production of the system for each location. The monthly production of the PV system of the selected climate regions is presented in Fig. 26. While, the selected optimal tilt angles and the annual energy production are reported in Table 5. Based on the obtained results, Amman demonstrated the highest annual yield of the PV system, due to the high solar radiation and the moderate ambient temperatures. While Abu Dhabi is blessed with solar radiation levels as well. However, the performance of the PV system is declining during summer months due to the high temperatures affecting the PV panels performance. Fig. 27 presents the non-renewable energy savings achieved by the solar PV system compared with the second reference system. The solar

Parameter

Unit

Input (DC) Maximum recommended PV power Maximum DC voltage Rated MPPT voltage range Maximum input current/per MPP tracker input

20,450 1000 580–800 36

W W V A

Output (AC) Nominal AC rated power Nominal AC rated line voltage

20,000 400

W V, 3 phase

Maximum efficiency

98.5

%

PV system achieved high non-renewable primary energy savings starting from 39% in Jakarta and reached 100% in Amman. The higher the PV system yield, and the lower the energy consumption in the building would result in higher non-renewable energy savings. 4.3. Economic assessment The utilization of SHC systems leads to much higher investments compared to conventional systems due to the extra components required in these systems (solar collectors, PV panels, thermally driven chillers, larger cooling towers, etc.). However, they require less energy and thus lower operation costs. As a result, a fair economic comparison has to compare full life cycle cost (LCC) of the different systems.

Fig. 25. Layout of the PV panels on the roof of the building. 555

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18

AbuDh abi Jakarta

16

Amman

Energy output [MWh/month]

20

14 12 10 8 6 4 2 0

1

2

3

4

5

6

7

8

9

10

11

12

Month Fig. 26. The monthly production of the PV system of the selected climate regions in MWh/month.

solar assisted systems, it also shows a breakdown of the cost of the systems used for space cooling (SC), space heating (SH), and the DHW. It is worth mentioning that the cost considered in Table 6 is the “turnkey cost” including the investment-material of main and the auxiliary components (pumps, pipes, insulation, etc.) and the planning and installation costs. The maintenance and the replacement costs were neglected in this analysis. For systems utilizing a reversible heat pump for heating and cooling, the cost of the heat pump is calculated based on the higher capacity required, (cooling in the case of Amman). If the heat pump’s cooling capacity meets the system’s load, then its heating capacity will certainly meet the system’s heating load.

Table 5 The optimal tilt angle and the annual energy production of the PV system in MWh.

Optimal tilt Annual output

[°] [MWh]

Abu Dhabi

Jakarta

Amman

Milan

New York

24 171.9

11 133.9

30 181.4

35 101.3

40 134.0

100% 90%

)

80% 70%

.

50%

_(

60% 40%

4.3.2. Energy consumption based cost Electricity, diesel and liquefied petroleum gas (LPG) prices in Jordan are shown in the Table 7 for March 2019. It has to be mentioned that for electricity price in Jordan, the tariffs are constructed in a “block” structure with various consumption thresholds and charges are increasing with higher demand (NEPCO, 2017) (Ministry of Energy and Mineral Resources., 2017) (Ministry of Energy & Mineral Resources (MEMR), 2019).

30% 20% 10% 0%

Abu Dhabi

Jakarta

Amman

Milan

NYC

Climate region

Fig. 27. Non-renewable energy savings achieved by the solar PV system compared with the second reference system in the different climate regions.

4.3.3. Levelized costs of energy – LCOE The Levelized Cost Of Energy (LCOE) is typically used to provide a figure which expresses the total cost per unit of energy taking all cost items over the whole lifetime of the system into account (Henning et al., 2013). In order to calculate the LCOE, the annuity method is used, the initial investment (or total system cost) is spread over the life-time of the system in constant annual quantities, then the annual energy cost is added to the annual system cost. This is presented in the Annual cost column in Table 8. The main two assumptions used for the calculation of the annualized values are the period under consideration (20 years), and the interest rate of (5.75%) based on the Central bank of Jordan. The LCOE is then calculated by dividing the Annual cost in Euros by the energy utilized by the system in kWh. This is presented in the LCOE column in Table 8.

In this section, the economic assessment of the reference and solar assisted systems for the building under consideration in one climatic region (Amman) is carried out. This procedure can be applied for other locations, yet, several factors have to be taken into consideration; the variation of energy prices, the differences in equipment cost (including customs and taxes), PV integration policy applied (net metering, feed in tariff, self-consumption, etc.), and these factors might lead to significant deviations between the results of different locations. 4.3.1. Investment costs The investment cost of a system includes in addition to the specific cost of the main components, the planning, assembly, construction and commissioning. Specific costs for the main components include also economy of scale price; the greater the capacity of a certain component the cheaper is the specific investment cost. These economic data are based on several resources including a comprehensive local market study (Neyer et al., 2018a) (Mokhtar et al., 2010) (Henning and Döll, 2012) (Henning et al., 2013) (Oppelt et al., 2013) (Ayadi et al., 2018). Table 6 presents the total costs of the five reference and the two

4.3.4. Simple payback period Simple Payback Period (SPB) is an economic indicator that calculate the time required to pay the difference between the initial cost of the proposed solar system and the reference system from the annual operation cost saving. The expression of the simple payback period is written as: 556

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Table 6 Costs of different solution. System

Service

Equipment name and type

Main parameter (capacity)

Unit cost

Cost [€]

Total cost [k€]

1

space cooling space heating DHW

variable refrigerant flow reversible heat pump variable refrigerant flow reversible heat pump hot storage + electrical heating element

250 kW 235 kW 2400 L, 125 kW

712.8 €/kW

178,214

181.6

1 €/liter, 8 € /kW

3400

2

space cooling space heating DHW

variable refrigerant flow reversible heat pump variable refrigerant flow reversible heat pump hot storage + air to water heat pump

250 kW 235 kW 2400 L, 100 kW

712.8 €/kW

178,214

1 €/liter, 410 € /kW

53,743

3

space cooling space heating DHW

variable refrigerant flow reversible heat pump variable refrigerant flow reversible heat pump hot storage + hot water diesel boiler

250 kW 235 kW 2400 L, 125 kW

712.8 €/kW

178,214

1 €/liter , 49.4 € /kW

8571

4

space cooling space heating DHW

vapor compression chiller diesel Boiler hot storage + hot water diesel boiler

250 kW 235 kW 2400 L, 125 kW

427 €/kW 71 €/kW 1 €/liter , 49.4 € /kW

106,929 16,721 8571

132.2

5

space cooling space heating DHW

variable refrigerant flow reversible heat pump variable refrigerant flow reversible heat pump hot storage + power generation unit + heat recovery

250 kW 235 kW 2400 L, 208 kW PGU, 125 kW

712.8 €/kW

178,214

535.3

1 €/liter , 1630 € /kW , 125 € /kW

357,143

space cooling

90 kW 160 kW 176 kW, 500 m2 , 7200 L

428.5 €/kW 1000 €/kW 71 €/kW, 165.6 €/m2 , 1 €/liter

38,565 160,000 12541, 82800, 7200

301.1

space heating, DHW

vapor compression chiller vapor absorption chiller diesel boiler + solar thermal collectors + storage

space cooling space heating DHW Solar

variable refrigerant flow reversible heat pump variable refrigerant flow reversible heat pump hot storage + air to water heat pump Solar PV system

250 kW 235 kW 2400 L, 125 kW 94.2 kWp

712.8 €/kW

178,214

326.1

1 €/liter, 410 € /kW 1000 €/kWp

53,743 94,200

6

7

Table 7 Electricity, diesel and natural gas prices for March 2019.

SPB =

Electricity

(€0.01/kWh)

First block : from 1 to 160 kWh/Month Second block : from 161 to 300 kWh/Month Third block : from 301 to 500 kWh/Month Fourth block : from 501 to 600 kWh/Month Fifth block : from 601 to 750 kWh/Month Sixth block : from 751 to 1000 kWh/Month Seventh block : more than 1000 kWh/Month

5.3 11.5 13.6 18.1 21.1 23.8 32.0

Diesel LPG (bulk) for Central Distribution

0.7 (€/Liter) 721 (€/ton)

Total system cost (k€)

Annual system cost (k€)

Annual energy cost (k€)

Total annual cost (k€)

LCOE* (€/kWh)

1 2 3 4 5 6 7

181.6 231.9 186.7 132.2 535.3 301.1 326.1

15.5 19.8 15.9 11.2 45.7 25.7 27.8

80.1 54.0 56.4 69.8 32.5 35.9 0

95.6 73.8 72.4 81.1 78.2 61.7 27.8

0.134 0.103 0.101 0.113 0.109 0.086 0.039

Cinitial, ref

Cannual, ref

Cannual, sol

186.7

(3)

where Cinitial, sol and Cinitial, ref are the solar and reference initial costs, respectively, and Cannual, sol and Cannual, ref are the solar and reference annual operating costs, respectively. Table 9 presents the SPB of the solar thermal and PV systems compared to two reference systems; (i) the reference system with the lowest capital cost (reference system number 4), and (ii) the reference system which has the lowest LCOE (reference system number 3). 4.3.5. Economical assessment results Fig. 28 gives an insight about the economical results of the studied systems. This is important since it presents the initial cost of the system together with the associated LCOE, thus, one is not deceived by the low initial cost of a system alone. The main findings from Tables 6, 8 and 9 and Fig. 28 are:

Table 8 economic comparison of the equipment and energy cost for the different systems. System

Cinitial, sol

231.9

• System number four (chiller and boiler) has the lowest investment • •

* LCOE Levelized Costs Of Energy.

cost of 132,221 €, this explains the wide application of this system. However, its LCOE is 0.113 €/kWh which is the second highest value. The first system utilized reversible heat pump for heating and cooling, this system is more efficient and expensive than system number 4. However, because this system relies on an electrical heater for the DHW preparation, the cost of electricity consumption, and it has the highest LCOE of 0.134 €/kWh. The annual energy consumption of the cogeneration system (system number 5) is the lowest among the reference systems, However, due to the high investment cost of 535,357 €, the LCOE is still high

Table 9 Simple payback period of the solar systems in years.

Solar thermal Solar PV

SPB with respect to reference system with the lowest initial cost

SPB with respect to reference system with the lowest LCOE

5.0 2.8

5.6 2.5

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0.160 0.140

500

0.120 400

0.100

300

0.080 0.060

200

0.040 100 0

LCOE (€/kWh)

System cost (x1000 €)

600

0.020 1

2

3

4

System number

System cost (€)

5

6

7

0.000

LCOE (€/kWh)

Fig. 28. System cost and LCOE for the reference and solar systems.

0.11 €/kWh.

significant share of the total energy consumption of the buildings, in this study the share ranges between 7 and 15%. In order to compare solar thermal and solar PV systems. It was also necessary to study reference systems that are typically utilized for such a building. Seven systems have been investigated technically and economically, including the two solar thermal and PV assisted systems. The non-renewable primary energy ratio for the reference systems and the non-renewable energy savings by the solar assisted systems were evaluated. And the LCOE was assessed to ensure a fair technical and economical comparison among the different systems. The simple payback period was also calculated for the two solar systems. Among the five reference systems, the second system utilizing VRF reversible heat pump for heating and cooling, and an air-water heat pump for the DHW showed the highest PRE in hot climates. While the cogeneration system performed better in the cold climates. As mentioned earlier, most previous studies about solar thermal cooling did not consider the DHW demand in the analysis, while it has to be mentioned that compared to solar cooling only systems, solar thermal systems that are designed to supply heating and DHW for buildings maximize the utilization of the collected solar energy and improves the non-renewable primary energy ratio. Compared to the second reference system with the highest PRENRE, solar thermal heating and cooling system achieved a non-renewable primary energy savings ranged between 10% and 29% in Abu Dhabi and Amman respectively. While it did not achieve any PRENRE savings in the other three locations. Solar PV driven heating and cooling systems became very attractive during the last few years due to the unexpected drop of solar modules costs. Through decentral electricity generation from RE sources, e.g., PV, the cooling electricity demand can be covered significantly and, consequently, the stress on electric networks can be reduced. The solar PV system achieved non-renewable primary energy savings starting from 39% in Jakarta and reached 100% in Amman. The higher the solar resource availability, and the lower the energy consumption in the building would result in higher non-renewable energy savings. A fair economic comparison of different systems has to compare their full life cycle cost (LCC). A detailed economic analysis for the different systems was carried out under the for the warm and temperate climate of Amman, the solar thermal system has high initial cost compared to reference systems. However, it achieved 29% non-renewable energy saving. This resulted in low energy based cost, and the LCOE decreased to 0.086 €/kWh, which is 15% less than the lowest reference system. A simple payback period of the solar thermal system compared to the cheapest reference system (system 4) is calculated to be 5 years. While compared to the system with the lowest LCOE, the PBP is 5.6 years. The solar PV system has an initial cost similar to that of the solar thermal. Nevertheless, since it is connected to heat pump with high

• The second system utilizes the energy efficient heat pump for all • •

•

required services, its energy cost is the lowest among reference systems. However, due to its high initial cost, its LCOE is not the lowest. The third system combines the utilization of the energy efficient heat pump for heating and cooling, and the DHW boiler having a low energy based cost. This lead to the lowest LCOE among reference systems. The solar thermal system has high initial cost compared to reference systems. However, it achieved 29% non-renewable energy saving. This resulted in low energy based cost, and the LCOE decreased to 0.086 €/kWh, which is 15% less than the lowest reference system. A simple payback period of the solar thermal system compared to the cheapest reference system (system 4) is calculated to be 5 years. While compared to the system with the lowest LCOE, the SPB is 5.6 years. The solar PV system has an initial cost similar to that of the solar thermal. Nevertheless, since it is connected to heat pump with high efficiency, this system managed to achieve 100% non-renewable energy savings. And the LCOE was the lowest 0.039 €/kWh. A simple payback period of the solar PV system compared to the cheapest reference system (system 4) is calculated to be 2.8 years. While compared to the system with the lowest LCOE, the SPB is 2.5 years.

5. Discussion and conclusions Heating, cooling and DHW for buildings present a substantial share of global energy demand and peak loads. The utilization of solar assisted HVAC systems has the potential of reducing the consumption of non-renewable energy, hence, reduce operational costs and environmental impacts. In this study, a systematic methodology for fair technical and economical comparison of reference and solar assisted systems has been developed. This procedure was applied for a dormitory building under five climates that cover a broad range of climatic conditions from strongly heating dominated climates to strongly cooling dominated climates. Heating and cooling loads analysis emphasized the need of an hourly load analysis, and not just annual energy demand, for example Jakarta and Abu Dhabi have the similar annual energy requirements for cooling, however, the load curve in Jakarta is almost flat all over the year, while the load of Abu Dhabi has a strong summer peak. The hourly analysis of the heating and cooling load profiles of buildings showed these variations and allowed for optimization of the heating and cooling systems required for each type of load. While most of the previous studies about solar cooling and heating have not considered the DHW, it was found that this load can present a 558

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energetic performance, this system managed to achieve 100% non-renewable energy savings. And the LCOE was the lowest 0.039 €/kWh. A simple payback period of the solar PV system compared to the cheapest reference system (system 4) is calculated to be 2.8 years. While compared to the system with the lowest LCOE, the PBP is 2.5 years. Considering the current systems costs, energy prices and policies for the warm and temperate climate of Amman, this study favors solar PV coupled with VRF reversible heat pump over solar thermal with absorption chiller both technically and economically. This is especially true for a situation with net metering PV integration policy. The selection of the best solution for a given project requires a full understanding of the system performance and the interaction of its components rather than the technology efficiency only. This system performance depends on the building envelope, load patterns, availability of solar radiation, roof area availability, energy prices, and policies. Thus, a case-by-case analysis should be done for each project in each climatic region.

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