Economic Factors Of Operating Solar Cooling Systems

Published Date: 02 Nov 2017

1.0 Introduction 3

1.1 Definitions 4

2.1.0 Solar thermal collectors: 4

2.1.1Solar collectors: 5

2.1.2 Stationary collectors 6

2.1.2.1 Flat-Plate Collectors (FPC): 7

2.1.2.2 Compound parabolic collectors: 6

2.1.2.3. Evacuated tube collectors……………………………………………….3

2.2.0 Solar Cooling Technologies: 5

2.2.1 Solar Electrical Cooling:…………………………………………………….17

2.2.2 Solar Thermal Cooling 17

2.2.3 Solar Combined Power/Cooling…………………………………………… 22

2.3.0 Effective mechanism of solar cooling systems………………………………… 24

2.4.0 Economic Factors of operating solar cooling systems:

2.4.1 Cost Parameters:…………………………………………………………… 25

2.4.2 Cost Effectiveness…………………………………………………………. 26

3.0 Methodology

3.1 Practicality of Solar Cooling Systems – Design and Mechanism…………. 27

4.0 Results and Discussion:

4.1 Capital Investments……………………………………………………………….. 34

4.2 Primaary Energy……………………………………………………………………..35

4.3 Running Costs……………………………………………………………………….36

4.4 Life Cycles Costs…………………………………………………………………..44

5.0 Economic evaluation of solar cooling systems in Greece…………………. 48

5.1 Economic feasibility of solar energy systems:……………………………… 48

5.2.1 Economic Evaluations……………………………………………………48

5.2.2 Economic Assumptions………………………………………………….56

6.0 Trends and Future Developments………………………………………………..60

7.0 Conclusion…………………………………………………………………………….63

8.0 References…………………………………………………………………………….65

Abstract:

The objective of this paper is to study and evaluate the viability of solar systems that can support chillers or refrigeration units. It looks into different kinds of collectors that are used and explores their different features. This paper then reviews three different kinds of solar cooling systems in terms of their advantages and disadvantages. It has the capability to calculate economic feasibility and determines in on the basis of the costs required to put forth such systems and also have a comparative analysis of the systems effectiveness and consummation. It then delves in to the methodology that was used to evaluate, which was based on calculations and formulas that determine the practicality and applicability of the designs and mechanisms used in the solar cooling system. In addition, a thorough analysis is done on the required economic criterion that includes the payback period and the net present value, which was implemented on these systems in the market of Greece. Furthermore, the paper provides a detailed picture on the feasibility of such a system by combining all the costs and comparing it with other technologies. The study then highlights that although such a system is not yet feasible when compared to the conventional technologies, however, the importance of environmental factors and the positive impact of such factors on the viability of the project should not be ignored. The paper then concludes that such solar cooling systems are the best alternatives when energy crisis and rocketing fuel prices are taken into consideration. Advancements in technology and further research in SE systems will portray the future picture for these systems differently, evolving it into a preferred choice.

Chapter 1.0 Introduction:

As a result of increased awareness among consumers about environment and energy prices, eco-friendly air conditioning and refrigeration have garnered a lot of attention. Since, the traditional method of vapor compression cycles required heavy usage of electric energy which is not only expensive, but leads to emission of harmful greenhouse gases, energy research agencies have set their aims to pursue and discover energy efficient methods and sources. Most certainly, the idea of using primary energy in the generation of cold sparked an interest in absorption equipment for air-conditioning. Hence, absorption cooling has become a serious contender and a wonderful opportunity to replace the CFCs or HCFCs cooling. This is especially true in the case of refrigeration, where thermally driven cooling, which consists of an assortment of different open or closed sorption technologies functioning at a range of temperatures, is at present, a popular topic.

The infrastructure of solar thermal collectors that exist today has made it feasible to reduce the cost of a solar based thermal cooling solution, since solar thermal collectors are widely used in different capacities for commercial and industrial heating purposes. Moreover, the ease of combining an array of high or low temperature adsorption (or absorption) chiller units into existing solar thermal units has further made it more feasible. For the past two decades, a large amount of research regarding the adsorption refrigeration technology, including the adsorption mechanism, has taken place. However, despite the technological developments in this area, the starting cost of a solar collector system is over the roof and not feasible. At present, this technology comprises of water cooling individual impact immersion chillers, where the temperature is in the vicinity of 90C. In the total investment, the preliminary total of a solar collector system that comprises of the greatest part of the investment budget, is proportional to its working temperature, there lies an opportunity for an even greater reduction in the initial investment of a water cooled system through low temperature driven sorption machines. The same is the case for an air chilled solar cooling system, which Is an upcoming kind of solar cooling unit, which will allow an increase in the solar collector’s efficiency and therefore an increased overall COP, in specific applications.

In this dissertation, I aim to investigate the adsorption/absorption chiller units, solar thermal collectors, as well as the economic and financial aspects of the proposals which combine the two units together to create the solar thermal chiller technology, concentrating more focus on the residential sector.

1.1 Definitions:

The key terms that will be used in this dissertation lie with the normal technical nomenclature, with not much need to explain the industry specific terminologies. However, there are quite a few unusual abbreviations. The following list mentions the abbreviations used in this proposal.

Ventilating, Heating and air conditioning HVAC - Air handling structures designed for humidity, temperature and level of air (Burton, 2006).

Air Handling Unit, AHU – A central unit designed to cool or heat air (Pita, 2002).

Energy Recovery Ventilator, ERV – a type of mechanical equipment that pre-conditions incoming outdoor air through heat. (Burton, 2006)

Return Air, RA –Air which has been returned from a conditioned area to the HVAC system (Burton, 2006).

Supply Air, SA – Air that is supplied to a conditioned space from the HVAC system (Burton, 2006).

Outdoor Air, OA – Fresh air that is mixed with return air (RA) (Burton, 2006).

Exhaust Air, EA – Air that is exhausted to the outdoor environment from the HVAC system (Burton, 2006).

Relative Humidity, RH – The ratio of the water vapor in the air to that of water vapor in saturated air. (Janis &Tao, 2008)

Percent of Outside Air, %OA – Percentage of total air supply from the HVAC system. (Janis &Tao, 2008)

Chapter 2.0 Literature Review:

The goal of this literature review is to evaluate the complete design and the mechanism of solar thermal collectors. Various solar cooling technologies, along with several economic factors of a solar cooling system from different literature sources are under discussion and evaluation and presented below. Moreover, solar thermal markets have also been analyzed.

2.1.0 Solar thermal collectors:

2.1.1Solar collectors:

Unique sorts of heat exchangers are solar energy gatherers. They are used to form internal energy using radiation energy. The solar collector is the chief constituent of the solar system. It is a device which first absorbs solar radiation, changes it to heat energy and then transforms it into a liquid which flows inside the collector. After that, solar energy is gathered and taken away from the flowing liquid to either one of two places, which are a utensil used for space conditioning or a storage reservoir for thermal energy. The two types of solar collectors are the stationary and concentrating collector and the non-concentrating collector. Comprising of a similar sized region for the taking in of solar energy is the non-concentrating collector. On the other hand, bowl-shaped reflective surfaces to absorb radiation in a small receiver for the increase of radiations is the sun tracking concentrating collector

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There are various types of collectors obtainable in the world and in this section detail of numerous kinds of collectors is provided.

2.1.2 Stationary collectors:

Movements such as single axis tracking and double axis tracking are used to distinguish the solar energy collectors. The type of collectors present are:

Flat plate collectors (FPC);

Stationary compound parabolic collectors (CPC);

Evacuated tube collectors (ETC).

2.1.2.1 Flat-Plate Collectors (FPC):

The solar energy passes through clear glass and reaches a darkened surface which then absorbs a lot of the energy and passes it through to the liquid tubes to the transfer medium for storage or consumption. The good insulation of the base of the absorber plate reduces losses through conduction. Liquid tubes are either joined to the plate or can act as an indispensable part of the plate. The liquid tubes are joined from both ends to the large width conduits. To minimize convectional losses through the absorber plates, transparent material is used. Along with that it helps reduce losses through radiations from the collector since the glass is see-through.

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FPCs are fixed in proper locations and do not need to search for the sun. Collectors should be placed in the direction of the equator. The collector needs to be put on a slant and to determine the best possible slant it firstly varies depending on the application and secondly it is equivalent to the latitude of the location, give or take 10-158 angle variations.

Fig 1 shows the components an FPC is made of:

Fig 1: View of a flat plate conductor

FPCs have been designed in various forms and from several different materials. Their main purpose has been to provide thermal energy to fluids such as water and can even provide it to air. Under the lowest cost, they are required to maximize the amount of solar radiation collected. Even with problems such as the adverse effects of UV rays, decay of substances, acidity leading to congestion, a rigid transfer fluid, ruptured glazing or other such causes. With the use of tempered glass, these causes can be diminished.

2.1.2.2 Compound parabolic collectors:

With the capability of reflecting the incident radiation to the absorber are the non-imaging concentrators called CPCs. Using a trough with parabolic divisions that face each other the moving concentrator will be able to keep up with the varying solar orientation. Fig 2 demonstrates that.

Fig 2: Diagram of a CPC with parabolic divisions.

Incoming radiation functions with CPCs at a variety of angles. To help radiation find the absorber surface, a lot of internal reflectors are placed to guide it to the bottom where the absorber surface is located. Fig 2 shows the range of arrangements such as being shaped like a tube.

The angle through which light moves through and find its way to the observer is called the acceptance angle. The usefulness of collectors increases if they are trough type concentrators or linear. A collector is placed in accordance to its acceptance angle (Fig. 2). Depending upon the collector’s acceptance angle the collector may be inert or tracking, A CPC concentrator’s opening is tilted at an angle in direction of the equator and the area’s latitude when it is extended along the axis. When the collector is placed along the North south direction, a collector has to change its axis to face the sun. Unless the collector doesn’t have the sun in the boundary of its acceptance angle it won’t receive radiation. When positioned to the east-west direction it is able to catch radiation easily due to the wide acceptance angle present.C:\Documents and Settings\ADU\Desktop\illustration_trough_sunlight.gif

Methods of approximation of ocular features and features about thermal energy of CPCs are shown in reference 46. The ratio of reflections to radiations passing through the CPC was determinable using a basic analytic technique Several arithmetical examples are shown that are beneficial in designing a CPC.

Typical CPC traits are shown in fig 1.1..

Tab 1.1: Traits of a typical CPC system

2.1.2.3. Evacuated tube collectors:

For warm and sunny weather orthodox flat-plate collectors were made. In unfavorable weather conditions, the benefits provided by these collectors are reduced.Early degeneration of internal materials is caused by atmospheric conditions such as condensation causing it to lose enactment and system crashes. As compared to other collectors in the market, the ‘evacuated hear pipe solar collectors’ operate differently.

Fig 3 shows a vacuum sealed tube with a heat pipe placed inside of it. ETC has established that the mixture of a selective surface and an impactful convection suppressor has a result of decent performance at high temperatures.

The vacuum envelope reduces losses through conduction; therefore, the collectors are able to function at higher temperatures in comparison to FPC. Similar to an FPC, ETC also gathers both direct and diffused radiation. But, the effectiveness is greater at low incidence angles. Therefore, this impact tends to provide ETC with an advantage over a FPC in day-long performance.

Liquid–vapor phase alteration materials are used by ETC to transfer heat at high efficiency. These collectors comprise of a heat pipe which is an exceedingly efficient thermal conductor, that is put in a vacuum-sealed tube. The pipe, is then attached to a black copper fin that fills the tube. A metal tip is coming out from the top of each tube which is joined with the sealed pipe.

Figure 3 Schematic Diagram of an Evacuated Tube Collector

The heat pipe has a little fluid quantity (e.g. methanol) which passes through a cycle of evaporating-condensation. What happens is that the the liquid is evaporated by the solar heat, and the vapors then moves to the sink area where the latent form of heat is given out after it condenses. The fluid which is now condensed is sent backward to solar collector and then this process repeats itself. As shown in Fig. 3, the metal tips up, when these tubes are fixed into a heat exchanger. Water passes the exchanger and absorbs the heat from the tubes.

The liquid which is heated then passes through one more heat exchanger and transfers the heat to the water which is stored in the solar storage tank. There isn’t a possibility of condensation or evaporation above the phase-change temperature, the heat pipe offers essential safety from overheating and freezing. This self-limiting temperature control is a distinct characteristic of the emptied heat pipe collector.

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The features of a typical ETC are shown in Table 2 below.

Table 2: Characteristics of a Typical ETC System

2.2.0 Solar Cooling Technologies:

Even though it seems counterintuitive at first, there are several methods and technologies that can be used for utilizing solar energy in HVAC systems for cooling. Since, cooling is basically required when the solar energy is freely available, solar cooling technologies seems to be an attractive and a viable option. Hwang, Radermacher, Alili, and Kubo (2008) present several methods of utilizing solar energy for cooling. As shown in Figure 4.1 Hwang et al. (2008) solar cooling equipment is divided into three categories. Most of these solar cooling technologies shown in Figure 4.1 will be discussed as well as the feasibility of utilizing each of these in buildings. However, since not all of the listed technologies will be discussed, the article by Hwang et al. (2008) would be a great source for any further questions on these technologies.

Figure 4.1 Solar cooling technologies overview. (Hwang, Radermacher, Alili, & Kubo, 2008)

2.2.1 Solar Electrical Cooling:

The primary of the three categories defined by Hwang et al. (2008) is "Solar Electrical Cooling". Solar electrical cooling is based on the use of photovoltaic panels which are used to convert light energy into electricity. As shown in Figure 4.1 the direct current (DC) electricity generated is supplied to either a Peltier cooling system or a standard vapor compression system like a traditional air conditioning unit.

Solar electrical cooling could be an option for the buildings as a PV array and electrically driven chiller are both utilized in the laboratory. The PV array could be used to power the chiller; however, the energy is already being utilized in the lab and simply switching the use of electricity would not be saving any energy as the currently supported system would then need to be supported using grid power. Additionally, the PV array is not tied into the electrical grid; therefore, the chiller would only be able to run when there was sufficient solar energy available or stored in the batteries. Finally, the existing PV array is too small to power the chiller already used in the laboratory.

2.2.2 Solar Thermal Cooling:

The second category presented by Hwang et al. (2008), "Solar Thermal Cooling" contains a vast number of technologies; however, only sorption cycles in particular absorption will be evaluated. Figure 7.1.1 shows the sorption cycles under "Closed Cycles", which primarily consist of absorption (liquid sorption) and adsorption (solid sorption) cycles. Both cycles are similar to a vapor compression cycle; however, they use a primary heat source and a sorption material to drive the cycle as opposed to a compressor. The buildings have previously investigated the feasibility of an indirectly fired absorption chiller using heat from the solar heating array. However, there are a few issues with utilizing a sorption process chiller in the buildings. First, the sorption processes typically have very low COPs. They also require higher temperature heat input than the current solar heating system in buildings can provide. According to Hwang et al. (2008) a single effect absorption chiller would require a heat input at 85 degrees Celsius and would operate with a COP of only 0.7. There is also the practical issue of obtaining an indirect fired absorption chiller. Currently, there are not many commercial products available and the few that are available are much too large for the buildings. Lastly, the buildings do not require year round cooling; this means that for a large portion of the year the system would not be utilized.

2.2.3 Solar Combined Power/Cooling

The third and final category presented by Hwang et al. (2008) : "Solar Combined Power/Cooling" cycles. This cycle incorporates the Rankine and absorption cycles to increase overall efficiency. The cycle is similar to a typical solar absorption cycle; however, instead of the metering device commonly used to reduce the temperature and pressure of the working fluid is a gas turbine. This gas turbine completes the task of the metering device while generating mechanical work which can be used to generate electricity.

The viability of utilizing a "Solar Combined Power/Cooling" has similar concerns to that of an absorption chiller. Just like with the absorption chiller, this technology is not commercially available in the market in a compatible size that would be practical for the buildings. While the power generation feature of the combined power and cooling systems does lift the COP a little, the COP of the cycle is still more or less the same as a typical absorption cycle. When not required, this system also generates cooling which would be wasted and hence for the majority of the year, the only useful output would be very little electricity.

2.3.0 Effective mechanism of solar cooling systems:

Numerous publications have investigated the controlling of the components in the solar cooling systems. The primary focus in this area of research lays in the control of absorption chillers that is the control of internal chiller processes. Another great aspect of this research looks into the control of large solar thermal systems and their performance and efficiency in regards to solar fraction and power consumption.

However, not much research is taking place on comprehensive control strategies for the total solar cooling system. One plausible reason for the lack of research on this subject matter could be the less number of existing solar cooling installations that are suitable for experimental testing. There are at present approximately 53 solar cooling systems functioning in Europe, but almost all of them are in daily use at fixed conditions and the range of the possible parameter variations in the control of these systems is very small (Paar and Heunemann, 2004). Due to this, extensive experimental researched needed in order to find suitable control strategies is restricted. Additionally, there are a small number of available simulation models for absorption chiller replication which further restricts a theoretical approach to the subject. The following literature references were selected to give a sense of precedent and contemporary research on control of solar cooling systems and their components.

Bong et.al. (1984) describes the control plan of a solar cooling system with chilled water storage in Singapore. The authors have made an attempt to reduce the variation of the temperature of hot water in the top part of the storage tank. The system is divided into three main control circuits: one circuit is from the solar collectors to the storage tank, another one is from the storage tank to the absorption chiller and one is from the chiller to the fan-coil units. The solar circuit is connected directly to the storage tank and there is no storage pump in the system. The solar circuit pump is controlled using a two-point control via the temperature difference between the collector field and the lowest layer of the storage tank. The storage tank in the system can be bypassed via an on-off three-sided regulator which is controlled according to the difference between the leaving temperature of the collector field and highest layer temperature of the storage tank. Thus water hot enough to charge the storage is only fed into the tank, otherwise the water re-circulates through the valve to the collector field again.

This setup was installed in order to prevent frequent pump cycling and fluctuating inlet temperature into the chiller. Present controlled operation of the absorption chiller for the time period from 8am to 5pm each day is used in the system. Outside this time period chiller and system pumps do not operate. The circuit control from chiller to fan-coils uses the level in the chilled water tank for controlling the chiller operation. If the level falls below a set level the chiller is restarted. The chilled water distribution pump in the fan-coil circuit is operated as long as the monitored room temperature is above 20.1 °C. The system performance has been compared to two other solar cooling systems and the authors report lower collector efficiencies and higher power consumption for the Singapore system. They relate this to the chosen storage tank charging and chilled water distribution strategies (Bong et al., 1987).

Yeung et.al (1992) describes a simple control mechanism for chilled and cooling water temperature in a solar air-conditioning system in Hong Kong. The chilled water temperature is being monitored and if it drops below a set point, the hot water supply to the chiller is cut off. The cooling water temperature is controlled by a differential controller in on-off mode. The fan of the wet cooling tower is being switched on if the cooling tower sump temperature exceeds 29.5 °C and switched off at temperatures below. These control strategies result in a fluctuating operation of the chiller with increased thermal losses due to a higher number of start-up and shut-down procedures. No information is given about the influence of this control strategy on the overall system (Yeung et al., 1992).

The experience with solar cooling systems shows that a large fraction of currently operating systems does not perform in the way they were designed to. Lower COP’s and cooling capacities as well as high standstill time are reported from system operators. The causes for this can be various. Inadequate planning and system design, mismatched system components, wrong hydraulic setup, untested operations or technical defects, to name only a few. However, repeatedly insufficient control strategies have been the primary cause of system faults. This was testified by Glaser for the absorption chiller in Freiburg, Germany.

The aforementioned example shows that, in order to achieve successful operational results, the control of a solar cooling system has to be carefully designed. All features appropriate for the optimum system performance have to be taken into consideration. All components that can be controlled actively should be incorporated in the system control. Therefore, the selection of precise control strategies is crucial for the system performance.

2.4.0 Economic Factors of operating solar cooling systems:

2.4.1 Cost Parameters:

The overall cost of capital comprises of the cost of the chillers, cooling water piping, cooling towers, electrical panels, solar collectors and fitting costs. However, the costs of the hot fluid pipework and insulation, the cost of using DC motor in place of the AC motor downstream of PV power supply, the gas burner and thermal storage / battery costs are not included. Moreover, as the cost of thermal storage is comparatively low as compared to the cost of other items in the total catalogue of solar cooling apparatus, therefore, it has been excluded. "According to a cost list of a solar collector and subsystem resources published by Garrison et al (1993), the price of a hot water tank was merely $1.1 - $1.4 (£0.7 - £0.9) per liter and may be even lower for larger volumes bought. The manufacturers of vapor compression equipment do not usually supply DC motors, therefore this cost is vague. Furthermore, since the total cost of the vapor compression chiller units are shown to be in the range of 9.3% to 13.2% (including AC motor), the extra DC motor costs are considered to be insignificant."

To calculate the cost of absorption of natural gas, the maximum range of thermal and electrical solar fractions, SOLFthe and SOLFw (0%-100%) were put under consideration. The following ratios indicate the solar input to total input of energy resources presented by equations 1 and 2, respectively:

(reference)11]

(Syed et al., 2002) (reference)12]

Vapor compression coolers display a substantial reduction in the level of primary energy mandate. Hence, for the full variety of thermal and electrical solar fractions, the main energy mandate of all chillers has been computed.

Maintenance costs of 1.1% and 4.1% of the total costs of the chiller, cooling tower and electrical panels and an interest rate of 5.1% and a repayment period of 11 years was assumed.

2.4.2 Cost Effectiveness:

The works provide sufficient proof, which suggests that out of numerous world-wide projects performed, despite their excessive potential for primary energy savings; there has been no proper cost controlled solar cooling installation currently operational.(Ziegler, 2002). Some critics have suggested that progress in terms of market tolerability of such systems might be probable through inventive design of collectors, chillers, or both (Mendes and Pereira, 1999 Henning et al. 1998). Nonetheless, this study has revealed that greater collector competence and / or cycle COP does not counterbalance the high capital investment required for solar collectors in specific. This is a major deduction to highlight the significance for the idea of a technologically, as well as economically achievable solar cooling system. The cost usefulness gap is shown in figure 5.

Figure 5 – Life Cycle Costs of Solar Cooling Systems as a Percentage of the Life Cycle Cost of a Conventional Centrifugal Chiller Plant

Figure 5 shows the fractional change in life cycle costs of solar cooling systems working on an annual basis with 100% solar fraction equated to an orthodox (non-solar) centrifugal compression plant working with grid electricity. It is shown that for solar cooling systems to become price effective with the orthodox yardstick, they must attain a threshold ordinate value of 100%. As explored by investigations and research, this is not predominantly the case with most technologies, therefore, it can be established that solar cooling system is not economically inexpensive and feasible on an annual basis, largely due to the high functioning cost of solar collectors. Moreover, it can also be seen that the lengthier the duration, this system is operating on solar power, the lesser the usefulness gap becomes, and the technologies that come nearest to being cost effective are the flat plate collector single-effect absorption and PV driven centrifugal vapor compression systems. On the contrary, at the other end, while sorption systems are operating at higher temperatures, the noticeably higher capital investment needed for emptied tube collectors, make these options unattractive.

Grounded on their current cost status, solar cooling system are believed to be uneconomical and unachievable compared to old-fashioned cooling systems. However, established on the study of the projected costs of solar collectors, it was possible to conclude the threshold cost at which the solar cooling systems could become economically feasible in comparison to the collector efficacy, cycle COP, and the least annual EFLH. Reading through Table 2, these threshold collector expenses can be recognized, which are summarized as follows:

FPC + SE (LT) Absorption: £57.1/m2

FPC + SE (MT) Absorption: £48.6/m2

ETC + SE (HT) Absorption: £97.1/m2

ETC + DE Absorption: £128.9/m2

PV + Air-Cooled Screw: £1.8/Wp

PV + Water-Cooled Screw: £1.857/Wp

PV + Centrifugal: £1.138/Wp

Chapter 3.0 Methodology:

Methodology to investigate the cost effectiveness of the solar cooling systems is discussed below. Our research is to shed light on the practicality and feasibility of the solar thermal collectors to power the chiller units.

3.1 Practicality of solar Cooling System -Design and Mechanism

In the past, authors have done an efficiency comparison on the temperatures of chilled water for several of the liquid and solid technologies of sorption, the vapour compression and the PV / solar collectors (Syed et al., 2002). Liquid chillers available commercially showed highest efficiencies for the Solar Coefficient of Performance (SCOP), and therefore for this reason they were selected for this study. Moreover, decreased capital cost systems for the cycles of jet refrigeration were also examined. Using a selection and pricing program, "the lowest capital cost chillers and cooling towers including the costs of their ancillary components were acquired, for a constant chilled and cooling water temperature difference of 6K" (York Opti, 2001). The chosen models of the cooling towers and the chillers were kept steady. ETC (Brunold, 2002), FPC (Bieri, 2001) and the PV (ASE Inc., 2001) costs of the capital were taken from literature that has already been published and through the communication with the suppliers.

Before measuring the costs of running, an analysis was done on the energy consumption for the chiller subsystems consisting of cooling tower and various pump duties. The former were attained from the selection data that the supplier provided, and the latter were calculated from equation (reference)13 and14]:

(reference)13]

where,

(reference)14]

The consumption of the electrical energy was determined for both the scenarios, that would acknowledge a thermal or mechanical compressor being present, that is, the former would have the volume of the electrical energy input as shaft power (Weflh) operating for an amount of EFLH and comparatively a smaller quantity of ancillary power (Wpoh) operating for 1.5 times longer than EFLH as shown in equation (reference)15]:

(reference)15]

The chiller ancillaries were taken to be functioning with grid electricity. Grid electrical energy cost, was taken as 0.04 £/kWh. The electricity consumption costs vary with ancillary plant power requirements and the compressor shaft power and according to equation (reference)16] EEN varies:

(reference)16]

Likewise, the natural gas consumption costs also vary with the generator heat requirement, Qg:

(reference)17]

Grid natural gas cost of 0.009 £/kWh was assumed at the higher value. Solar energy, was subtracted from the total energy cost as it was free. The specific energy cost is the ratio:

(reference)18]

The specific fossil fuel energy costs of cooling for the chillers were calculated by equation 19:

(reference)19]

For the capital costs, an interest rate of 5% was assumed along with a capital recovery factor of 0.13 (reference)Moran, 1989].

(reference)20]

Finally, specific system life cycle costs were determined by the ratio: