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1.
PREFACE
This advanced Project guidelines have been developed to assist designers, program planners, and evaluators to make informed decisions on the cost-effectiveness of energy saving measures.. There are two basic types of gas absorption chillers: absorption systems and gas engine driven chiller systems. This project report deals specifically with gas absorption systems. These guidelines are intended to be a step forward a comprehensive approach to design specifications, which encompasses the full range of efficiency options for all types industries.
This advanced project guideline is based on careful evaluation and analysis of gas absorption cooling to determine when it is appropriate, how it is best implemented, how cost effective it is, and how its energy savings are describied. These guidelines describe effeciency measures that are more advanced than standard practise, yet still cost effective in all, or select markets. Design guidelines are used by individuals and organisations interested in making industries more energy efficient.
It should be remebered that this project document deals primarily with the comparision of a single effeciency measure and its baseline. This means that the analysis assumes that all other features of the building are fixed. This is done primarily for clarity of the analysis, and allows one to focus on the advantages and economics of the single measure.
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2.
DESCRIPTION
2.1 The basic principle of absorption cooling
1.1 The two basic principles on which all air conditioning and refrigeration plants operate are: a. When a liquid evaporates, it absorbs heat and when it condenses it gives up that heat. This heat is called the latent heat of evaporation and latent heat of condensation respectively.
b. Boiling point of liquid a pressure. i.e. boiling point decreases if pressure decreases and vice versa
The absorption cooling works on the affinity of some pairs of chemical to dissolve in one another. For example, lithium bromide solution has affinity towards water, water hasaffinity towards ammonia etc. this affinity depends on two factors – temperature and the concentration of the solution.
2.2 HOW AN ABSORPTION MACHINE WORKS: In vapour absorption chillers, a low pressure (vacuum) is maintained in the evaporator. At this pressure the refrigerant boils at very low temperature. This boiling causes the refrigerant to absorb the heat from the medium being cooled, thus lowering the temperature. On absorbing the heat the refrigerant gets vaporized. The refrigerant vapours thus formed tend to increase the pressure in the vessel. This will in turn increase the boiling temperature and the desired cooling effect will not be obtained. So, it is necessary to remove the refrigerant vapours from the vessel. A liquid having affinity towards the refrigerant
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vapour is sprayed in the absorber which absorbs the vapour and maintains the low pressure in the shell. As the absorbent absorbs the refrigerant vapor, it becomes dilute & losses its capacity to further absorb refrigerant vapours. To maintain continuous cycle, it is essential that the absorbent is enriched to its original level of concentration and the refrigerant vapours are condensed to the liquid. This is achieved by pumping the dilute solution continuously from absorber to the generator. In the generator the addition of heat boils off the refrigerant from the absorbent and the absorbent regains its original level of concentration. The re-concentrated absorbent returns to the absorber to resume the absorption process.The refrigerant vapour released in the generator flows to the condenser. In the condenser cooling water is circulated through the coils, which picks up the heat carried by the refrigerant vapour and vapour condenses back to the liquid phase. The condensed liquid is returned back to the evaporator thus completing the absorption cycle.
2.2.1
The basic Principle of an absorption cooling machine may be illustrated with Figure 2.1. In its simplest design the absorption machine consists of the following components: Evaporator Condenser Absorber Generator Solution heat exchangers Solution pump
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Figure 2.1 schematic of the principle of an absorption cooling machine
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In an absorption cycle chiller, the absorber, the solution pump and the generator in combination, instead of a mechanical vapour compressor, effects compressing the refrigerant vapour. Vapour generated in the evaporator is absorbed into a liquid absorbent in the absorber. The absorbent that has taken up refrigerant, spent or weak absorbent, is pumped to the generator where the refrigerant is released as vapour. Which vapour is to be condensed in the condenser. The regenerated or strong absorbent is then led back to the absorber to pick up refrigerant vapour anew. Heat is supplied to the generator at a comparatively high temperature and rejected from the absorber at a comparatively low level, analogously to a heat engine. The words “ thermo chemical compressor” have actually been used in specialised literature to describe the function of the generator and absorber half of the absorption cycle.
Refrigerant and absorbent in an absorption cycle form what is called a working pair, many pairs have been proposed through the years but only two of them have widely used: ammonia together with water as absorbent and water together with a solution of lithium bromide as absorbent. The ammonia water pair is mostly found in refrigeration applications, with low evaporation temperatures, below 0 Deg C. the water – lithium bromide pair is widely used for air conditioning applications, where it is not necessary to cool below 0 Deg . the pressure levels in ammonia – water are usually above the atmospheric pressure and while the water – lithium bromide machines generally operate in partial vacuum.
The heat flows in the basic cycle are the following : Heat is supplied, and cooling is produced, at a low temperature level. Heat is rejected in the condenser at an intermediate temperature level. Heat is rejected from the absorber, also at an intermediate level. Heat is supplied to the generator at a high temperature level.
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The basic cycle illustrated in Fig1.1 may be modified in several ways. One is to utilise all possible opportunities fro heat recovery within the cycle in order to improve the heat economy within the cycle. For example, it is customary to heat exchange the streams of weak absorbent leaving the absorber with the regenerated or strong absorbent that is led back into the absorber. When all heat recovery opportunities that can reasonably be used have been incorporated into the design of a machine, one obtains a cooling coefficient of performance of approximately 0.7 for the water – lithium bromide system and approximately 0.6. Further improvements may be obtained if one cascades more efficiently the high temperature heat available to power the generator. The so called double- effect systems incorporate two generators- absorber blocks that are staged, see figure 2.2, in order to utilise the heat supplied more or less twice. Heat is supplied at 170 Deg C to the first generator and heat rejected by the corresponding condenser is used to power the second generator at a lower level, the temperature 100 Deg C of a single effect machine according to Figure 2.1. The co-efficient of performance of such a system with water-lithium bromide as working pair may be 1.2, which is significantly better than the C.O.P of 0.7 of the single-effect system. It is not double of the single-effect because of imperfect heat exchange between streams of solutions, to some extent, and because the heat of vapourisation of the refrigerant is necessarily larger when it evaporates from a solution than when it evaporates from a pure liquid.
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Figure 2.2 – Schematic cooling cycle of Double effect Absorption Chiller
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Types of Absorption systems: Absorption chillers are generally classified as Single effect absorption system Double effect absorption system Triple effect absorption systems In direct –fired units, the heat sources can be gas or some other fuel that is burned in the unit. Indirect – fired units use steam or some other transfer fluid that brings in heat from a separate source, such as boiler or heat recovered from an industrial process. Hybrid systems, which are relatively common with absorption chillers, combine gas systems and electric systems for load optimisation and flexibility.
2.3.1 Single – Effect Absorption System: The single-effect “cycle” refers to the transfer of fluids through the four major components of the refrigeration machine- Evaporator, Absorber, Generator and Condenser, as shown in the pressure – temperature diagram in figure 2.3
Figure 2.3 – Single – Effect Absorption refrigeration cycle
ix Single – effect LiBr/H2O absorption chillers use low pressure steam or hot water as the heat source. The water is able to evaporate and extract heat in the evaporator because the system is under a partial vacuum. The thermal efficiency of single – effect absorption system is low. Although the technology is sound, the low efficiency has inhibited the cost competitiveness of single – effect systems. Most new single-effect machines are installed in applications where waste heat is readily available. Single –effect chillers can be used to produce chilled water for air-conditioning and for cooling process water, and are available in capacities from 10 to 1500 tons.
2.3.2 Double – Effect Absorption System The desire for higher efficiencies in absorption chillers led to the development of double-effect LiBr/H2O systems. The double effect chiller differs from the single-effect , in that there are two condensers and two generators to allow for more refrigerant boil –off from the absorbent solution. Figure 2.4 shows the double effect absorption cycle on a pressure – temperature diagram. The higher temperature generator uses the externally supplied steam to boil the refrigerant from the weak absorbent. The refrigerant vapour from the high temperature generator is condensed and the heat produced is used to provide heat to the low temperature generator.
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Figure 2.4 – Double – Effect Absorption refrigeration cycle These systems use gas fired combustors or high pressure steam as the heat source. Double-effect absorption chillers are used for air-conditioning and process cooling in regions where the cost of electricity is high relative to natural gas. Double-effect absorption chillers are also used in applications where high pressure steam, such as district heating, is readily available.
2.3.3 Triple – Effect Absorption System :
The triple-effect cycles are the next logical improvement over the doubleeffect. Triple-effect absorption chillers are under development, as the next step in the evolution of absorption technology. Figure 2.5 shows the triple-effect absorption cycle on a pressure-temperature diagram. The refrigerant vapour from the high and medium temperature generators is condensed and the heat is used to provide heat to the next lower temperature generator. The refrigerant from all three condensers flows to an evaporator where it absorbs more heat.
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Figure 2.5 – Triple – Effect Absorption refrigeration cycle
Two different triple-effect absorption chiller cycles are capable of substantial performance improvements over equivalent double-effect cycles. One uses two condensers and two absorbers to achieve the triple effct. A second, the double condenser coupled(DCC) triple-effect, uses three condensers as well as a third condenser sub cooler.
2.4
Efficiencies
Efficiencies of absorption chillers are described in terms of coefficient of performance(COP), which is defined as the net refrigeration effect by the net heat input . Single – effect absorption chillers have COPs of approximately 0.6-0.8 out of an ideal Since the COPs are less than one, the single-effect chillers are normally used in applications that recover waste heat such as waste steam from power plants or boilers. Double- effect absorption chillers have COPs of approximately 1.0 out of an ideal while not yet commercially available, protype triple effect absorption chillers 1.0. have calculated COP’s from 1.4 to 1.6.
xii The COP metric is also applied to electric chillers. However, since COP is based on site energy, it is not good for comparing gas and electric chiller efficiencies. A better metric is the resource COP, which accounts for the source to site efficiency of the fuel, accounting for electricity generation and transmission losses. Fig 2.6 shows typical values for both electric chillers and absorption chillers
Chiller
Site COP
Electric
2.0 – 6.1
Source –tosite factor 0.27
Absorption
0.65 – 1.2
0.91
Resource COP 0.54 – 1.65 0.59 – 1.1
Figure 2.6 – Typical values of electric chillers & Absorption Chillers 2.5
Advantages and limitations of using Absorption chillers
The primary energy benefit of gas cooling absorption system is reduction in operating costs by avoiding peak electric demand charges and time of day rates. The use of gas absorption chillers eliminates the high incremental cost of electric cooling. Natural gas cooling systems have greater resource efficiency than similar to electric systems. Typical electricity generation and distribution results in an approximately 65% - 75% loss in the initial energy resource of fuel. In contrast, only about 5% to 10% of the fuel resource is lost with a gas system. Additionally, electricity costs per Kwh are typically three to four times the cost per Kwh for electricity, so the cost of a unit of output(refrigeration) can often be lower with an absorption system. Utilising waste heat that would otherwise be unused greatly increases the cost effectiveness of the systems, compared to consuming gas directly.
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2.5.1
Absorption systems have several non- energy benefits over conventional electric systems
Eliminations of the use of CFC and HCFC refrigerants Quiet, vibration free operation Lower pressure systems with no large rotating components High reliability and low maintenance 2.5.2
Recent Improvements to absorption chillers Since the 1960’s, several improvements have been made to absorption chiller, which include:
Automatic purge systems eliminating the need for manual purging and lowering the potential for corrosion.
Faster system response due to the use of electronic controls and solution concentration sensing
Electronic controls and sensors that make crystallisation of the chiller far less likely than in the past.
Lower water flow requirements. Absorption chillers can provide water temperature as low as 3.5 Deg C allowing for the use of reduced air flow and duct size in delivery systems.
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2.5.3
Limitations :
Cost is the primary constraint on the widespread adoption of absorption chiller systems. The low thermal efficiency of single effect absorption systems has made them non-competitive except in situations with readily available free waste heat. Even double effect systems are non cost effective in many applications. Although absorption chillers can be quite economical in the right situation, their exact economics must be worked out on a project-by-project basis.
Absorption systems also require greater pump energy than electric chillers. The size of condenser water pumps are generally a function of the flow rate per unit cooling capacity. They require cooling tower capacities approximately 1/3 greater than electric chillers of the same size.
The primary disadvantage of the absorption system are their size and weight and they are larger and heavier than the electric chillers of the same capacity.
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3. HISTORY AND STATUS 3.1 History Absorption systems have been used in air – conditioning applications for over 50 years. Ammonia – water absorption equipment was found to be well suited for large capacity industrial applications that required low temperature for process cooling. In the late 1950’s the first working double-effect lithium bromide – water absorption chiller was built. Lithium bromide –water absorption equipment is currently used to produce chilled water for space cooling and can also be used to produce hot water for space heating and process heating.
In the 1960’s the natural gas industry was very effective in promoting this alternative to electric – driven cooling. Absorption cooling and gas absorption chillers were successfully marketed on the basis of lower operating costs, and better system performance. Counteracting this, innovations in compressors, electric motors and controls increased the performance and decreased the cost of electric cooling systems. Additionally, and perhaps more importantly, the gas crunch of the seventies curtailed gas cooling promotion and forced prospective buyers to remain with conventional electric systems. Since 1987 when the Montreal Protocol first came into existence many issues surrounding electric cooling including the use of CFC refrigerants and electric utility rates, have become increasingly complicated. Coincident with these electric cooling issues, gas costs have remained relatively stable while the technology itself has improved.
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3.2
Current market share
Indian absorption chiller market for FY 06-07 is estimated at 350 nos and valued at Rs.106 cr with total TR capacity installed at 70,000
The total chiller market in India is estimated at 7,000 units and valued at Rs.1800 crores
The Indian absorption chiller market is largely driven by industrial process cooling application
Natural gas equipment accounts for 8 to 10 % of the market for larger chillers and this number is expected to grow
As a result of rising electric rates and the increased efficiency, reliability and accessibility of gas equipment Figure 3.1 shows the Absorption cooling market conditions from 2003 – 2006.
IN NOS
IN RS. CRORES 390
334 287
140 121 95
FY03-04
FY04-05
FY05-06
FY03-04
FY04-05
Figure 3.1 Absorption chiller market conditions
FY05-06
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3.3
Cost Benefit Analysis For Vapour Absorption Chiller
OPERATIONAL COST ANALYSIS CAPACITY TYPE OF ENERGY SPECIFIC STEAM CONSUMPTION TOTAL STEAM/ HR DAILY OPERATION TOTAL STEAM CONSUMPTION PER DAY COST OF STEAM TOTAL COST OF ENERGY/ DAY POWER REQD. FOR M/C PER DAY COST OF POWER COST OF POWER REQD. FOR M/C TOTALOPERATING COST PER DAY TOTAL COST OF OPERATION PER YEAR MAIINTAINANCE COST TOTAL OPEATIONAL COST
200 STEAM 4 800 22 17600 0.6 10560 85 4.5 383 10943
RT Kg/hr-RT Kg/ hr HRS Kg Rs/Kg Rs. KW Rs/KW Rs Rs
3994242 Rs. 25000 4019242
CAPITAL COST ANALYSIS EQIPMENT COST DEPRECIATION RATE DEPRECIATION AMOUNT SAVING IN CORPORATE TAX @ 35% EFFECTIVE COST
2683000 80% 2146400 751240 1931760
Figure No. 3.2 – Cost Benefit analysis of Vapour Absorption Chiller
Rs Rs Rs Rs
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3.4
Cost Benefit Analysis For Reciprocating Chillers
OPERATIONAL COST ANALYSIS CAPACITY TYPE OF ENERGY SPECIFIC ELECT CONSUMPTION
200 RT ELECTRICITY KW/TR/ 0.7 HR 140 KW 22 HRS 3080 KW 4.5 Rs/KW 13860 Rs.
TOTAL ELECT/ DAY DAILY OPERATION TOTAL ELECRTICITY CONSUMPTION PER DAY COST OF ENERGY TOTAL COST OF ENERGY/ DAY
TOTALOPERATING COST PER DAY TOTAL COST OF OPERATION PER YEAR MAIINTAINANCE COST TOTAL OPEATIONAL COST
13860 5058900 40000 5098900
Rs. Rs. Rs. Rs.
CAPITAL COST ANALYSIS EQIPMENT COST DEPRECIATION RATE DEPRECIATION AMOUNT SAVING IN CORPORATE TAX @ 35% EFFECTIVE COST
2100000 25% 525000 183750 1916250
Figure No. 3.3 – Cost Benefit analysis of Reciprocating chillers
Rs Rs Rs Rs
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3.5
Standards and Ratings Currently there are no state or federal standards that regulate gas absorption cooling systems. However, there are several metrics that are used to define absorption chiller efficiency, including:
• • •
3.5.1
COP IPLV APLV
Coefficient of Performance (COP) The performance of absorption system equipment is usually rated in terms of COP, defined as the cooling output, or refrigeration effect in BTU, divided by the energy input, in BTU. This same metric is applied to electric chillers, but since it is based on site energy, it is not good for comparing gas and electric chiller efficiencies. Gas absorption chillers, as well as electric chillers, are rated to Air conditioning and refrigeration Institute ARI-550-92 conditions as listed below: Chilled water conditions: • 44 deg F chilled water supply temperature • 54 deg F chilled water return temperature • 2.4 GPM/ton chilled water flow Water cooled condensers: • 85 deg F condenser water supply temperature • 95 deg F condenser water return temperature • 3.0 GPM/ton condenser water flow
Air cooled condensers: • 95 deg F air supply • 20 deg F temperature differential between air supply and condensing refrigerant • 2 deg F refrigeration system loss to the condenser
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3.5.2 Integrated Part Load Value (IPLV) Another measurement of chiller efficiency is integrated part Load Value, IPLV. It is an industry standard for calculating an annual COP based on a typical load profile and the part load characteristics of chillers. It was originally conceived as part of ANSI/ASHRAE standard 90.1 (standard for energy Efficient design of New Non
residential and High-rise Residential buildings) in response to need for directly comparing manufacturers part load data. The method assumes that the chiller operates at a specific part load for a specific number of hours during the year. According to the following equation:
IPLV =
1 ____________________________________ 0.17 + 0.39 + 0.33 + 0.11 _____ ____ ____ _____ A B C D
Chiller Load (%) 100 75 50 25
Chilled water Return Temp (F) 85 78.75 72.5 66.25
Mfgr Rated COP
Part Load Hours(%)
A B C D
17 39 33 11
Figure 3.4 – IPLV Calculation Assumptions
COP ratings A,B,C, and D at each part load condition are obtained from the chiller manufacturer and should be derived from actual chiller tests. Note that the calculation allows for a 2.5 Deg C reduction in the entering cooling water temperature for every 10% drop in cooling load. A lower entering cooling water temperature corresponds to part load (reduced) cooling demand, that results from a drop in ambient temperature. Although LPLV is a useful way to compare different manufacturer’s chiller models, it
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probably dosen’t represent actual operating conditions. For applications where cooling load is not significantly affected by ambient temperature conditions, ( e.g when cooling load is dominated by internal gains) this estimate of part load performance may not provide accurate results. Chiller performance should be modeled to actual building load profiles tailored to site- specific ambient conditions
3.5.3 Applied Part Load value ( APLV) The applied Part Load value, APLV is calculated using the same IPLV formula, except that actual chilled and condenser water temperatures and flow rates are used. The advantage of using the APLV over the IPLV, is that this rating more closely approximates actual operating conditions imposed on the chiller. The disadvantage is the additional performance data that needs to be collected
3.6
Economics/cost effectiveness The figure no. 3.3 shows the economics of absorption systems vs. electric chillers. They are driven by the additional investment cost and several factors influencing operating cost, including:
•
Relative costs of the electricity and gas, and their billing structures,
•
Relative performance characteristics
•
Operating characteristics
•
Relative maintenance costs.
The first three factors are discussed in the following sections and combined to produce estimates of annual energy savings. Annual operating savings include an energy component and a comparison of O & M costs.
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3.6.1 Energy rates and billing structure Energy rates and billing structures have major impact on economic evaluations of gas versus electric cooling equipment. Energy rates include:
• • •
Electric demand, Rs/Kw Electric energy, ϕ/Kwh Gas Energy rate, Rs/MMBtu ( or therms)
It is essential that the complete utility rates and rate structures are used for an accurate economic analysis. Utility rate structures may include one or more of the following:
Block rates : - The electric block rates may be in terms of kWh, with different rates for various levels of energy consumption. It may also be stated in kWh per kw of demand. In this case kWh rate is function of demand. A lower demand typically results in a large allowed amount of kWh at a lower rate. A high demand results in a smaller amount of kWh before the higher rate kicks in. typically, although not always, the unit price per kWh increases as demand increases.
Time of use rates – The electric rate may vary depending on the time of day. The time of use rate is typically described in terms of on-peak and off peak and sometimes partial peak.
Ratchets – The electric rate may include a demand which allows for a variation on how the demand kW is defined.
Seasons – Some utilities have different summer and winter rates.
Taxes – applicable taxes and franchise fees, which can be over 10% in many ares.
Special rates – For gas cooling equipment or special load-management electric rates
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are sometimes available. Using average electric and gas cost is rarely adequate to capture the cost of operating cooling equipment, especially when the rate structure includes demand charges or declining blocks. The marginal electric price for cooling has a larger demand component relative to usage, which drives up the unit price. The details of the actual electric rates must be considered in the total analysis of chiller system operating costs.
3.6.2 Operating Characteristics Operating schedules for building types vary. For example, HVAC equipment for office buildings generally are operated approximately 10-12 hours per day, five days per week. Equipment in hospitals will operate near full load for much of the day and at reduced, but still significant load for the remainder of the day. Annual energy savings need to be large enough to overcome higher initial costs fro gas- engine driven chillers to be cost effective. Annual energy savings will be a function of the operating schedule. An operating schedule that has a significant number of hours where the equipment runs at part load, favors gas engine-driven chillers because of their excellent part load performance.
However, operating schedules that require equipment to run at full load for relatively few hours and not at all for most hours will result in too little annual energy savings to realize an acceptable payback for most business requirements.
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3.6.3 Estimating annual Energy savings.: To estimate the annual energy savings, the performance characteristics of each chiller alternative must be carefully compared. The customary approach to analyzing chiller economics has been to employ” equivalent full load hour” methodology. Equivalent full load Hours (EFLH)Are defined as the total cooling load supplied over the cooling load duration )ton/hour0 divided by the cooling equipment capacity (tons0. Part load operation is modified to obtain the equivalent of running at full load. While this method does not reflect the efficiency of part load operation, it does simplify economic comparison.
Since the economics of gas cooling are highly dependent on operating hours, accurate analysis requires a detailed building simulation. A comprehensive analysis should be done with an hourly simulation model, such as DOE-2, HAP or TRACE, which predicts when, where and how much cooling is required for the building.
3.7
Sizes of Absorption systems
:
The following commercially proven absorption cooling systems, ranging in size from 40TR to 2500TR are widely available in the market. These systems come as stand-alone chillers or as chillers with integral heating systems. The following sections provide manufacturer specific information and examples of installations
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3.7.1
High Pressure Steam Fired Vapour Absorption Chiller*
Refrigeration Capacity
150 TR to 2500 TR (525 kW to 8,775kW)
Chilled water in / out 12 / 7 °C Cooling water in / out 32 / 37.5 °C Steam Pressure
8 kg / cm2, g
Figure 3.5 - High Pressure Steam fired Vapour Absorption Chiller
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3.7.2.
Low Pressure Steam Fired Vapour Absorption Chiller*
Refrigeration Capacity
95 TR to 1460 TR (333 kW to 5,125 kW)
Chilled water in / out
12 / 7 °C
Cooling water in / out
32 / 37.5 °C
Steam Pressure
1.5 kg / cm2, g
Figure 3.6 - Low Pressure steam fired Vapour Absorption Chiller
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3.7.3
Hot Water Driven Absorption Chiller*
Refrigeration Capacity
45 TR to 360 TR (158 kW to 1,264 kW)
Chilled water in / out
12 / 7 °C
Cooling water in / out
31 / 36 °C
Hot Water in/ out
81/ 86 °C
Figure 3.7 - Hot water driven Vapour Absorption chiller
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3.7.4.
Direct Fired Vapour Absorption Chiller*
Refrigeration Capacity
150 TR to 1200 TR* (525 kW to 4,210 kW)
Chilled water in / out
12 / 7 °C
Cooling water in / out
32 / 37.5 °C
Fuel
Natural Gas, LPG, Furnace Oil, Kerosene,HSD etc
Figure 3.8 - Direct Fired driven Vapour Absorption Chiller
* Reference : “ EBARA Vapour Absorption Chillers “
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3.8 EQUIPMENT MANUFACTURERS There are several manufacturers of absorption chillers, including:
•
Carrier Absorption chillers- 100 TR – 1500 TR
•
York Absorption Chillers – 100 TR – 1500 TR ( Single-effect systems only)
•
TRANE (USA) Absorption Chillers – 100 TR to 2000TR
•
THERMAX (INDIA) – former licensee of Sanyo – 40 TR – 2500 TR
•
EBARA ( JAPAN) – 50TR – 2500 TR
•
VOLTAS (INDIA) - 100 TR – 2000TR
•
BROAD (CHINA) Absorption chillers – 50 TR to 3000
•
Yazaki (JAPAN), Small capacity units only – 50TR to 250TR
•
McQuay (USA) Absorption Chillers
•
SANYO (JAPAN) Absorption systems
The list is certainly not exhaustive. Daikin(Japan) withdrew from the absorption cycle field in the 1980’s, but it seems from recent reports that some activities have been taken up again. In addition to these in the list, there are manufacturers that supply large units for Industrial use, e.g Hitachi Shipyard(Japan) Most Absorption systems based on the water – lithium Bromide working pair is designed for air cooling applications. For historic reasons capacities are given in US RT(refrigeration tons), one US ton of ice per hour, in literature from manufacturers. One RT corresponds to 3.516KW cold production.
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3.9
LIST OF EQUIPMENT INSTALLATIONS
Absorption cooling equipment is available for the following facilities *:
• Hotels • Commercial buildings • Education centers • Hospitals • Super markets • Pharmaceutical companies • Refineries & Petrochemicals • Chemicals • Electronics • Engineering Industries • Thermal Power Plants • Dairy and confectioneries
* Refer figure 3.9 for installation list
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* Reference: “ Thermax Ltd vapour absorption chillers installation list”
Figure 3.9 - World wide Installation list of Absorption chillers
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3.9.1
Industry wise TR Installation
3
> 500TR 200 - 500 TR < 200 TR
16 7 2
2 1 1
3 ci a
ls
s ta l H os pi
m ic al
4 1
C om m er
6 er y
w er Po
Te xt ile s
ic al ch em
O th
er s
4
6
14 4
8
R ef in
3 2
Pe t ro
d
Pr
oc es si n
g
5
Fo o
2
5
C he
5
8
5
4
el s
1
9
H ot
11
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4. DESIGN ANALYSIS 4.1
Overview Absorption chillers were compared to the following chiller options:
•
Standard efficiency electric – screw or centrifugal
•
High efficiency electric screw or centrifugal
•
Indirect – fired single effect absorption system The analysis is structured to provide “typical” values that can be used as a screening tool during schematic design of a building or as guidance on equipment efficiency code bodies. The results of a detailed energy and rates analysis for seven building types in ten cities, have been distilled to a series of graphs.
The cities and buildings are representative of the range of climates and building occupancies where gas cooling options would be used. The list of cities, sorted by cooling degree day(CDD) is provided in Figure 4.1. information on building type and size are provided in Figure 4.2. The economic analysis is of course dependent upon gas and electric rates. Building description and city specific utility rates are provided the appendix. The results are graphed for various gas rates and various electric rates. Due to The complexities of the interactions between fuel type usage and utility rates. It was not possible to develop “typical” gas to electric cost results. These graphs can be used, as will be shown by example in the following chapter to determine relative increase in gas consumption and relative decrease in electric consumption, when comparing a gas chiller to an electric chiller. The results of separate fuel type analysis can then be combined to provide a complete picture of the savings opportunities.
xxxiv CITY San Francisco Chicago Washington DC Los Angeles Atlanta San Diegeo New Delhi River side Miami
CDD 50 2.833 2.941 3.473 4.77 5.083 5.223 3.221 5.295 9.474
Figure 4.1 – cities used for cooling analysis
Figure 4.2 shows the building types included in the analysis, along with the building size in square feet, and the cooling equipment sizes represents the variation in cooling load for the cities analysed. The sizing of the cooling plant follows ASHRAE 90.1R ECB guidelines with a 20% over sizing margin.
Type Medium office Large office Hospital Hotel Out-patient clinic Secondary school Large retail
Size (Sq Fts) 49,000
Cooling (tons)* 100 – 143
160,000 272,000 315,000 49,000
408 – 573 384 – 519 645 – 891 90 – 111
50,000
90 – 205
164,000
165 – 393
Figure 4.2 – Building type and size *Cooling plant capacity includes 20% additional over sizing
xxxv As shown in figure 4.3, the type of electric equipment, either screw or centrifugal, used as a comparison, was dependent on size. Figure 4.4 shows the standard and high efficiencies assumed for the various types of chillers.
SIZE (TONS)
TYPE
100 – 300
Screw
> 300 – 600
Screw
> 800
Centrifugal
Figure 4.3 – cooling Equipment Type Based on Size
Because of the complexities and individual nature of Hybrid systems, results of any hybrid systems analysis cannot be generalized. They were therefore intentionally not included in this analysis. However, if the results indicate that a gas absorption chiller is cost effective, or even marginally not cost effective, a hybrid system under the same conditions, will typically be cost effective.
4.2
Energy Savings Energy savings were calculated using detailed DOE-2.1E building simulation models. The models provide comprehensive data on energy use and savings. The modeling included a complete comparison of system components, including auxiliary equipment such as cooling towers, fans and pumps.
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The graphs in the figure 4.5 present the energy savings for watch of the cities for a range of marginal gas and electrical prices. The graphs present the annual energy cost savings, in rupees per year, versus the marginal cost of gas, in rupees per therm, or the marginal cost of electricity in rupees per kWh. The marginal energy cost, gas or electric, is calculated as energy cost savings, in rupees divided by energy savings in therms or kWh. The marginal cost accounts for varying rates that may apply based on total usage.
4.3
Cost Effectiveness Cost effectiveness is based on the calculation of the savings to investment ratio(SIR), SIR is defined as the Life Cycle Cost (LCC) savings, in dollars, divided by the incremental measure cost per unit capacity, in rupees per ton capacity, as shown in the following equation:
SIR
=
LCC Savings Incremental Cost
The SIR uses an investment model over the life of the equipment rather than the simplistic and short range perspective of simple payback.
The LCC savings describe the present worth of the energy cost savings over the life of the investment. If the LCC savings are greater than the incremental cost, then the SIR will be greater than one and the measure is assumed to be cost effective. Savings to investment ratios(SIR’s) indicate the cost effectiveness of the equipment selection depending upon several factors including :
•
Building type,
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•
Equipment,
•
Climate,
•
Utility rate, and
•
Scalar ratio.
Specific equipment cost information is provided in the Appendix. Additional first costs for absorption systems were applied to the cost-effectiveness model, including:
Additional cooling tower capacity add Rs450 -Rs750/Ton
Additional boiler capacity adds Rs300 – Rs750/Ton
Another element of the first cost for gas absorption chillers is the potential savings from interactions with other building elements. For example, installing a gas absorption chiller may reduce the building’s electric service drop and load center. These savings could be significant, but are not included due to the variability between installations.
A scalar ratio is a mathematical simplification of life cycle costing(LCC) analysis. The scalar ratio is a single term that combines discount rate, period of analysis, fuel escalation and other factors. The first year savings are multiplied by the scalar to arrive at the life cycle savings. In technical terms, the scalar ratio represents the series present worth multiplier.
Figure 4.4 –Cooling Equipment Efficiencies
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4.4
Effective Utilisation of waste heat from Diesel Genset to Run Air conditioning Plant:
Load shedding is a common practice everywhere due to increased load power stations. Industries depending heavily on electrical energy are the most affected ones. Industries are encouraged to have their own captive power stations. Diesel generating sets are the most common captive power stations. The exhaust gases of these gensets have a very large amount of heat(about 700 Degree Celsius at full load), which is wasted, can be effectively exploited. Waste heat of coolant (about 120 Degree Celsius)from diesel gensets, equipped with evaporative cooling system can also be exploited. The waste heat of exhaust gas & coolant so exploited can run a central air-conditioning plant based on Vapour Absorption Chiller .
The present case study(theoretical) shows that a 30TR Vapour Absorption chiller based central air conditioning plant can be run by tapping waste heat of the exhaust (14.5TR) and coolant heat(15.5TR) of 125 HP genset. The practical implementation of such vapour absorption chillers by number of companies like THERMAX India Ltd. Kaltimex, etc are reported. Such system with combined heating & power (CHPC) is the need of time for conservation of the energy.
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Key words : Waste heat Utilisation, vapour absorption chiller , Gensets, Air conditioners,CHPC(combined heating power & cooling) Nomenclature:
4.4.1 Analysis of Performance of the Vapour Absorption chiller System ( case study for 125HP Genset)
• Diesel Genset Details
1. Rated Power output of Engine Considered = 125 Hp 2. Break Hp of Engine = ¾ X 125 = 93.75 kW 3. Heat Loss along with exhaust = 93.75 kW 4. Heat lost to coolant (latent heat) = 75kW
• Vapour Absorption Chiller Details :
Operating Conditions : for a water- lithium bromide chiller water plant for air conditioning are as follows:
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Generator Temperature = 105 ° C Condenser temperature = 45 ° C Chilled – water Temperature = 5 ° C Absorber temperature = 45 ° C Temperature of Solution entering Generator = 95 ° C
Thermodynamic Calculations : Condenser & Generator Pressure P K = 71.9 mm Hg( At 45 ° C) Flash Chamber & Absorber Pressure P o = 6.54 mm Hg( At 5 ° C)
4.4.1 A
Thermodynamic Conditions :
State 1 :
Saturated Condition state at
P = 71.9 mm of Hg & t = 91 ° C ξ
Li Br2
= 0.63 ( From h - ξ Diagram)
h1 = -50 kj/kg
Rich Solution Concentration of Water ξ = 1 -ξ
Li Br2
= 1 - 0.63 = 0.37
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State 2 :
Saturated Condition state at
P = 71.9 mm of Hg & t = 105 ° C ξ
Li Br
= 0.67 ( From h - ξ Diagram)
h1 = -22 kj/kg
Poor Solution Concentration of Water ξ = 1 -ξ
Li Br2
= 1 - 0.67 = 0.33
State 4 : t = 45 ° C
ξ
Li Br2
= 0.63
h 4 = -140 kj/kg
The Enthaly is read against temperature and composition. It may be noted that point 4 represents a sub cooled state at 6.54 mm of Hg pressures.
State 4 a :
Assume the same as 4
Specific solution circulation rates f = 1 – 0.33 / 0.37 - 0.33 = 16.75 kg/kg of vapour f - 1 = 15.75 kg/kg of vapour
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State 3. : energy balance of liquid –liquid heat exchanger specific solution circulation rates f ( h1 – h4 ) = (f –1) (h2 – h3)
h3 = h2 - [ f ( h1 – h4) / ( f – 1) ]
=
State 5 :
-22 – 16.75(-50+140) / 15.75 = -118 kj/kg
It is the water vapour at 71.9 mm Hg pressure and 105 ° C temp.at these conditions it represents a superheated state. The enthalpy of vapour above the reference state of saturated water at 0 ° C can be found either from steam tables or from the empirical relation.
h = (250 + 1.88t) kj / kg using the later procedure h = 2501 + 1.88(105) = 2698 kj / kg
State 6 : Saturated water at 45 ° C h6 = 4.1868 (45) = 188.4 kj / kg
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State 7 :
P = 6.54 mm of Hg & t = 5 ° C (liquid + water)
h7 = h6 = 188.4 kj / kg
State 8 :
P = 6.54 mm of Hg & t = 5 ° C ( saturated vapour )
h8 = 2501 + 1.88(5) = 2510 kj / kg
4.4.1 B
qo
Refrigerating Effect :
= h 8 - h 7 = 2510 – 188.4 = 2321.6 kj / kg
Heat is added in the generator per unit mass of vapour distilled
qb = h5 – h2 + f (h2 – h1)
= 2698 – 22 + 16.75 (-22 + 50)
= 3189 kj / kg of vapour.
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Coefficient of Performance :
COP =
qo / qb = 2321.6
=
4.4.1C
/
3189
0.728
Water Vapour distilled, D :
Heat available for vapour generation from Exhaust gas system of Diesel Genset
=
0.75 X 93.75
= 70 kW
Heat available for vapour generation from cooling system of Diesel Genset
=
70 + 75 = 145 kW
D
=
[ 145 kj/s ] / [ 3189 kj / kg of vapour ]
D
=
145 / 3189 X 2321.6 kj/s
=
105.56 kW
=
105.56 / 3.516
=
30 TR
[ 1 TR = 3.516 kW]
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Figure 4.5
- Layout of Vapour Absorption Chiller with Wasste heat of Diesel genset
With increased natural gas availability and ever widening demand supply gap for power, commercial / industrial users are shifting towards selfgeneration to meet their ever increasing power needs. Industries are utilizing the tri-generation systems which utilizes the waste heat from the engine Exhaust directly along with the jacket water to generate chilled/Hot water to cater to the Air conditioning / process cooling / Heating requirements.
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Following table shows cooling potential based on engine rating. (Data from Thermax Ltd.) Table 1 : Cooling Potential based on Engine rating
ENGINE RATING (kw)
COOLING CAPACITY on Exhust + Jacket water ( USRT) *
300
100 - 110
500
175 – 200
1000
300 – 350
1500
425 – 500
2000
525 – 600
*Indicative and may vary as per Engine waste heat Parameters
Figure 4.6 – Sankey Diagram for IC engine with & without heat recovery
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4.6
DESIGN ANALYSIS GRAPHS :
4.6.1 Using Graphs: The following graphs that describe the performance of gas absorption chillers in a variety of cities and building types. As described earlier, these graphs were developed from DOE-2.1E runs done for representative prototype buildings using the actual utility rate structures currently published for each cities.
4.6.2 Annual Energy Cost Savings Graphs
Two sets of energy cost savings are calculated for each building type. One is for a range of marginal gas costs and a fixed marginal electric cost. The other is for a range of marginal electric costs on a fixed marginal cost.
The top graph in figure 4.7 is typical of the annual energy cost savings Vs marginal cost graphs. The bottom graph is same for the same conditions showing the energy cost savings Vs marginal costs. These particulars are for the medium office building type prototype. The comparison is between a gas absorption chiller and a standard efficiency electric chiller.
The vertical y-axis shows the annual energy cost savings, between the base equipment and the gas Absorption Chiller. As shown on the top graph, as gas prices increase, the energy savings associated with an absorption chiller decrease. Conversely, as electric prices increase, savings from the Absorption Chiller increases, as shown in the bottom graph.
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4.7
Energy Savings Graphs
Figure 4.7 – Energy Cost Savings for Absorption Chillers vs. Standard Efficiency Electric chiller for Medium Office
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Figure 4.8 – Energy Cost Savings for Absorption Chillers vs. Standard Efficiency Electric chiller for Large Office
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Figure 4.9 – Energy Cost SavConfidential Page l 12/16/2008ings for Absorption Chillers vs. Standard Efficiency Electric chiller for Hospital
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5
REFERENCES & BIBILOGRAPHY
• ASHRAE 90.1 Code Compliance Manual, US DOE.
• ASHRAE,1998 Refrigeration Hand Book, Chapter 41.
• Roy J.Dosat (2001) “ Principles of Refrigeration”, Pearson Education Asia
• C P Arora “Refrigeration & Air Conditioning” Tata Mcgraw Hill, New Delhi
• K.K.Ramalingam, “Internal Combustion engines “, Scitech Publishing (I) Ltd
• American Gas Cooling Center (AGCC), Basic Engine and Basic Absorption Power Point Presentations. AGCC website (agcc.org)
• American Gas cooling Center (AGCC), April 1996, Natural Gas Cooling Equipment Guide 4th Edition
• Ebara Refrigeration & equipments Ltd, JAPAN ,www.ers.co.jp
• THERMAX Ltd, INDIA , website www.thermaxindia.com
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