Heat, power and cooling for India’s commercial developments

What’s the best option for supplying heat, cooling and reliable power supplies to the large commercial developments, many of which incorporate IT services, springing up in India? Engine-based cogeneration, argues Nandkumar Pai, provides the most flexible and cost-effective solution.

India has, in recent years, emerged as a key player in the global IT market. As a result, the country is attracting international investments and new, efficient, business parks are springing up everywhere. This has given rise to an unprecedented boom in real estate development, especially in its commercial segment, notably office park developments catering to Information Technology/Information Technology Enabled Services (IT/ITES) and other such mega-complexes, as well as to the growing number of large commercial malls, all of which are heavy electricity consumers.

Energy requirements of commercial spaces

The energy requirements of commercial spaces can be classified under three broad headings: power and comfort cooling, reliability and compact layout.

  • Power and comfort cooling Requirements will vary from day to day and throughout the year, and are application driven. For example, a 24 hour IT/ITES facility with a built-up area of close to 186,000 m2, will have a more or less stable power requirement in the range of 6″8 MW throughout the day, whereas the comfort cooling requirement will see a wide range of fluctuation from 2000 TR to 8000 TR. (TR stands for tons of refrigeration). A commercial mall, on the other hand, will typically have a 12″16 hour daily operating pattern with comfort cooling peaking during weekends.

  • Reliability These facilities need 24/7 power without interruption, since they are driven by the application sensitivity such as server loads in an IT complex, business sensitivity such as retail outlets in a mall, as well as safety considerations. Hence these facilities are designed with redundancy factored in for both power and comfort cooling sources.

  • Compactness Layout is quite important as it allows the real estate developer to use the available land effectively, and to maximize the rental space.
  • A facility developer has two options for meeting his energy requirements. He can choose either a conventional solution, or a combined cooling, heating and power (CCHP) solution, both of which are discussed and compared below.

    The conventional solution

    In this case the power is sourced from the local state electricity board, and redundancy is built-in with 100% back-up power by installing high-speed diesel generators. Comfort cooling is provided by electrical chillers with a built-in redundancy in the configuration. For example, for a facility with 8000 TR of design comfort cooling requirement, nine (eight working and one standby) 1000 TR electrical chillers can be installed. The electrical chiller can be of reciprocating type, rotary screw type or centrifugal type.

    The final combination of electrical chiller equipment varies according to operating conditions, space constraints, water availability, and so on. The specific power consumption of these chillers will vary from 0.5″0.9 kW/TR. Centrifugal chillers are the most efficient at full load conditions, having a 0.55″0.65 kW/TR power:TR ratio.

    Though the conventional solution would appear to be the most lucrative option with the least investment needed, this is not always the case on account of the following:

    • Poor reliability of power supplied by the Indian state utility boards makes it necessary to operate expensive diesel sets during power interruptions. In some states the power supply situation is so poor that the end customer is forced to endure power interruptions for approximately 30% of the time, year-round. In such cases, the effective power cost to the end user shoots up by 30%”40% of the base electricity tariff.
    • Recent trends in India show that the power tariff to commercial establishments is increasing, and is in the range of 30%”80% above the industrial tariff.

    These factors are causing developers to evaluate setting-up their own captive power plants to cater to the energy demands of their upcoming commercial establishments.

    Combined cooling, heating and power

    The combined cooling, heating and power (CCHP) solution for such commercial spaces depends, among other things, on the location, the availability of fuel, the operating pattern and space constraints, and every solution will be unique for a given case. For the purpose of detailed evaluation, this article is limited to a CCHP solution with natural gas as the primary fuel. However, this concept is equally applicable for liquid fuels.

    The basic concept in a CCHP case will be to improve efficiency of the solution and thereby reduce the operating cost, by using the free ‘waste’ heat from exhaust gases and the hot water circuit in the absorption chiller for chilled water generation.

    In an absorption chiller, the free heat from the engines is used to separate water from the absorbent i.e lithium bromide, solution. Water acts as a refrigerant. A concept diagram of an absorption chiller is given in Figure 1.

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    Generally in a commercial space, comfort cooling constitutes about 40%”50% of the overall energy requirement, i.e. of power plus comfort cooling. The chilled water recovery potential through an absorption chiller of Wärtsilä medium-speed engines is in the range of 170″210 TR/MW. This means that TR recovered from the absorption chiller through engine waste heat is not sufficient to meet the total comfort cooling loads of such facilities, and hence some amount of chilled water has to be recovered through electrical chillers.

    The redundancy factor can be considered, based on the criticality of the application, by having one or two additional engines as standby. However with piped gas, which cannot be stored, as the primary fuel, one has also to consider operating the facility on an alternate fuel such as diesel. This is especially true in countries like India where the gas supply agreement one enters into with the gas supplier, allows for 15″21 days of annual gas outage. Thus, with this in mind, with pure gas engines one has to consider equivalent standby capacity through high speed diesel sets. Alternatively, dual-fuel engines, which are a better option on account of compactness of layout and lower capital cost, could be considered.

    With a dual-fuel option, gas turbines (GT) also qualify as a possible option, especially considering their potential for recovering higher TR through an absorption chiller using free exhaust gases. Generally, for such applications, considering a comparatively limited power requirement, normally less than 50 MW, and a multi-unit solution addressing the need of redundancy and load variations, industrial turbines are preferred. The TR recovery potential from a GT through an absorption chiller is in the range of 500″700 TR/MW depending upon the electrical efficiency of the GT, i.e. the higher the electrical efficiency, the lower the TR recovery potential, and vice versa. The energy balance from a GT is quite close to the energy balance of a commercial space. And when trying to equate the electrical efficiency and thermal efficiency from both options, then one can conclude that the efficiency of a GT is better than an engine, after recovering the total heat for TR generation (see Table 1).

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    With this background, it would be obvious to conclude that in such spaces GT is a better option than a reciprocating engine. However, this is not so and the fact is that reciprocating engines are the clear and natural choice because of the following factors.

    Comparing efficiencies

    Chilled water can be generated through reciprocating chillers, screw chillers, centrifugal chillers or vapour absorption machines (VAMs). Except for absorption chillers, which need heat, all other machines consume electricity to generate chilled water output. When comparing these machines for performance, the term coefficient of performance (COP) is often used, which is nothing but efficiency (efficiency terminology is not used as COP most of the times exceeds 1), and is defined as: COP= chilling output/heat input, with both the numerator and denominator measured in the same thermal unit, i.e. TR, kcal, kJ, etc.

    For example, the COP of a centrifugal chiller consuming 0.6à‚ kW of power for delivering 1 TR per hour of heat, will be: 1 TR = 3024 kcal, 1 kW = 860 kcal. Hence, the COP of the machine equals 3024/(0.6 x 860) = 5.86.

    The COP of reciprocating, screw and centrifugal chillers varies from 4 to 7. Whereas, for an absorption chiller it is 0.65 to 1.3, depending upon whether the absorption chiller is of single-effect or double-effect (single-effect will have a COP of 0.65, whereas the double effect COP will be almost double, a little less than 1.3). This clearly explains that an absorption chiller needs more heat input to deliver the same TR when compared with electrical chillers.

    This is precisely one of the reasons why engines are the clear lead runners for combined cooling, heating and power solutions in the commercial segment. With engines, the balance shortfall in TR can be made good by efficient electrical chillers, having a higher COP as compared to an absorption chiller. Though the generated electrical power with engines will be higher, the overall operating cost will still be lower compared to a turbine.

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    This conclusion is substantiated by the calculation given in Table 2. Here is a case where the energy balance suiting a gas turbine is considered for evaluation. The numbers given are based on a kW:TR ratio of 1000:550, and the analysis will hold good for similar ratios for a commercial facility, such as 20à‚ MW of power and 11,000 TR, or 30 MW of power and 16,500 TR, and so on.

    It is evident that Wärtsilä dual fuel (DF) engines have a superior operating cost, even when compared with the best energy mix suiting a GT. Hence, any hybrid solution i.e. mixes of GT and engines, cannot be better than a pure engine solution.

    Apart from this advantage, a mix of electrical chiller and absorption chiller reduces the overall chilled water equipment cost for meeting a given TR requirement, compared to that of a pure absorption chiller solution. Also, the design TR load is only needed during peak summer times ” say, approximately 100 hours per annum. For the rest of the year the TR requirement is low, on an average 50%”60% of design value. This automatically suits the engine case since the absorption chiller with engines act as baseload machines, while for peak requirements, the electrical chillers can be switched on and off, thereby lowering the actual electrical load on the engines and reducing the gas consumption. In the case of GT, excess TR can only be avoided by bypassing heat to the stack, which does not lower gas consumption. This will further improve fuel savings in favour of engines.

    Other factors

    It should also be noted that irrespective of the type of chiller, electrical (vapour compression type) or absorption type, a cooling tower is needed for supporting its operations. However, to generate the same amount of chilling (TR), an absorption chiller needs a bigger cooling tower than an electrical chiller. Although the absorption machine is quite expensive as compared with an electrical chiller of equivalent capacity, the difference in cooling tower sizes further widens the differential investment costs between absorption and electrical chiller systems.

    Unlike a GT, engine life is not affected by daily starts and stops resulting from daily load variations of a 24-hour facility or a daily on and off facility such as a commercial mall. Also, the carbon footprint with an engine is the least among all fossil fuel power generation technologies, and is even lower than a CCHP gas turbine solution.

    In the case of the real estate developer having land/space constraints, the entire plant room i.e. the engines, the absorption chillers and electrical chillers, can be located in an extended basement of a commercial facility.

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    Initial investments will vary based on the energy mix of a given facility. When a developer is considering engine-based CCHP solutions purely from the point of view of returns on investment, then his decision will depend on two externalà‚ variables such as cost of natural gas (fuel) and the equivalent power tariff from a conventional source (including the standby power cost). Figure 2 shows an indicative CCHP viability curve based on these two variables. As per Wärtsilä’s analysis, the minimum built-up area of a commercial space beyond which the CCHP solution becomes viable is about 90,000″140,000 m2.

    CONCLUSION

    It is evident from the above that a Wärtsilä engine-based CCHP solution meets the requirements of large commercial spaces for the following reasons:

    • flexibility to take care of the varying load pattern
    • inbuilt redundancy in the configuration
    • multi-fuel capability to ensure a 24/7 energy supply
    • compactness of layout and possibility of a basement installation
    • lowest operating cost among all alternatives
    • environmentally friendly on account of its carbon footprint being the smallest.

    This provides the real-estate developers with a serious alternative for meeting the energy requirements of commercial spaces.

    Nandkumar Pai is Associate Vice President, Sales, Power Plants, Wärtsilä in India
    e-mail: nandkumar.pai@wartsila.com


    International Tech Park, Bangalore (ITPB)

    The 69-acre (28 ha) ITPB is the first high-tech park of its kind in India, and is designed to provide a complete ‘work-live-play’ environment for IT and technology-related businesses. It fully integrates a practical amalgamation of office, production and retail space. To date, the Park has a total built-up area of close to 214,000 m2.

    ITPB currently has six multi-tenanted buildings that are fully occupied and has land available and ready for further expansion. It is one of the first business space facilities in India to house a shopping mall and to organize regular fun and fitness events for its occupants. The mall offers fully functional banks, ATMs, foreign exchange facilities, courier, lifestyle stores, a laundry service, a wide range of food and beverage outlets, medical clinic and a health club, thereby offering a wide range of conveniences to the occupants. Truly a ‘World in a Park’, ITPB houses more than 145 companies employing over 20,000 people.

    Businesses located at ITPB are involved in key growth industries, including information technology, biotechnology, electronics, telecommunications, R&D, financial services, and other IT-related services. Over 26 acres (10.5 ha) of land within ITPB has been notified as an IT/ITES Special Economic Zone and earmarked for further development for multi-tenanted and built-to-suit buildings.

    The success of this landmark development has made the Park an iconic benchmark for other Indian states vying to set up world-class infrastructure of their own to attract investments. Since it started operations in 1997, ITPB has won accolades for its ability to attract global corporations to Bangalore.


    A view of the ITPB
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    Power to the ITPB Bangalore property is produced by a liquid fuel-based Wärtsilä combined cooling, heating and power (CCHP) solution, comprising three Wärtsilä 9R32 generating 9 MW and one Wärtsilä 18V32 engine of 7.5 MW capacity, with chilled water recovered from engine waste heat totalling to 7560 kW chilling (2150 TR) through absorption chillers. The remaining comfort cooling requirement is generated through electrical chillers.

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