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Case study of a Karachi building G4 Mega Corporate Tower.

Byline: Farhan Mehboob

Introduction

Buildings use about 40% of global energy, 25% of global water, 40% of global resources, and they emit approximately 1/3 of Green House Gas emissions. Given that buildings are large contributors in impacting our environment, resources and health, and the fact that buildings offer the greatest potential for achieving significant GHG emission reductions, at relatively minimal cost, in developed and developing countries, the Green Building Industry has flourished. A Green Building refers to a structure using a process that is environmentally responsible and resource efficient throughout a building's lifecycle. Energy consumption in buildings can be reduced by 30 to 80% using proven and commercially available technologies resulting in a sustainable, healthier and productive environment. Green Buildings enjoy the benefits of saving energy by reducing CO2 emissions into the atmosphere.

It also saves water by using rain harvesting or grey water reuse techniques, reduces vehicles miles travelled by choosing the location near public transport and conveniences which helps in reducing gasoline consumption. Material resources are factored in and an improved indoor air quality sought by reducing VOCs and air impurities through appropriate ventilation strategies. Along with an improved indoor lighting and thermal quality which serves to enhance comfort, well-being and productivity. Leadership in Energy and Environmental Design (LEED) Green Building Rating System developed and managed by non-profit U.S. Green Building Council (USGBC), is the most widely used rating system nationally and internationally. Buildings are given ratings of platinum, gold, and silver or "certified", based on green building attributes.

Pakistan's construction industry is seeing an increased activity with high rise buildings sprouting across the country, yet Pakistan also faces one of the worst energy and water crises in the world. There has consequently been an increased awareness amongst building owners and construction industry to move towards building Green Buildings and pursuing a building rating certification. Imperial developers and builders intended to build a high quality Shell and Core, Commercial Office building by applying sustainable development principles in a practical, well-planned and cost effective manner aiming to achieve a LEED Silver rated Building, the first in Pakistan. This building has now been built and certified as LEED Silver with 50 points. The Building has been designed to save 12% of energy and 45% of water use.

Energy savings have been achieved through improved envelope performance that includes a high performance glazing system with low U values, high performance chillers with better performance, a dedicated outdoor air system with energy recovery, UFAD systems for tenant spaces, a better lighting density and lighting control system and a state of the art automated Building Management system controlling HVAC, Electrical and Lighting Systems. Water saving strategies include use of low flow fixtures. As per LEED requirements for fundamental commissioning, the Building also employs a detailed commissioning process from pre-functional and functional testing procedures and documentation. This paper investigates how the G4 Mega Corporate Tower Building was able to achieve a LEED Silver Rated Building, the first in Pakistan, by employing Green Building Strategies focusing primarily on its MEP System design.

This building will act as a case study for potential of green building designs in Pakistan, not neglecting any cost implications that may accrue. The LEED process LEED was launched in an effort to develop a 'consensus based, market driven rating system to accelerate development and implementation of green building practices.' It includes a set of rating systems for design, construction, operation and maintenance of green buildings, from homes, schools, hospitals, data centers to neighborhoods that aim to help building owners and operators to be environmentally responsible and use resources efficiently.

Under LEED v3 2009, there are 100 possible base points distributed across six credit categories: 1. Sustainable Sites, 2. Water Efficiency, 3. Energy and Atmosphere, 4. Materials and Resources, 5. Indoor Environmental Quality and 6. Innovation in Design. Up to 10 additional points may be earned: four additional points may be received for Regional Priority Credits, and six points for innovation in design (which include exemplary performance credits for existing credit categories). Every credit category has pre requisite credits which must be complied for earning certification. Buildings can qualify for four levels of certification: Certified: 40-49 points, Silver: 50-59 points, Gold: 60-79 points and Platinum: 80 points and above. LEED certification is granted by Green Building Certification Institute (GBCI), which handles third-party verification of a project's compliance with LEED requirements.

The certification process for design teams is generally made up of two consecutive applications: one the design phase credits, and two, construction phase credits. The design credits include those that are the purview of architects and engineers and are documented in the official construction drawings. It allows the project team to submit credits early so that they can gauge whether or not those credits are on track for approval or not. It's a courtesy review by the GBCI, which is usually taken advantage of. Construction credits include those that are predominantly under contractor's purview and are documented during construction and commissioning of the building. These credits can only be submitted after the project administrator has attempted all pre-requisites and minimum number of credits required for certification. Alternatively, the submission may be made a single combined review. After Final Construction Review results are accepted, the project may be denied or certified as LEED.2.

The project The G4 Mega Corporate Tower, Karachi, is a 28 storey commercial office building with a total area of 411,000 sq ft of which 205,356 sq ft are air conditioned for cooling load of 2074 occupants and their equipments. Three Water Cooled Centrifugal Chillers of 308 TR cooling capacity each, two working and one spare chiller, cater for the building's cooling load, providing chilled water that is distributed through constant flow primary pumps and a variable flow secondary pumping system. Three Cooling towers with dedicated condenser flow pumps are used for heat rejection. A dedicated outdoor air system with energy recovery wheels, provide buildings fresh air requirements. Tenant spaces were designed using an Under Floor Air Distribution System (UFAD) which saves additional energy and is the first for a high rise in Pakistan.

LEED and MEP design through G4 buildings

The table below summarizes MEP related pre-requisite and design credits, applicable for a Core and Shell Building under LEED v3 2009. It is evident that over 50% of total possible credits lie within MEP designer's scope. Most of these points are achievable through an overall building energy performance model and are in the energy and atmosphere category. The rest are largely in Water Efficiency and Indoor Air Quality categories. The table also indicates the points that G4 Mega Corporate Tower is targeted for and how it achieves them. Table 1: LEED Scorecard for G43. Compliance with ASHRAE Standards As seen in Table 1, pre requisites of EA and IAQ category of LEED v3, 2009 assume a baseline compliance with the following ASHRAE standards:

* ASHRAE 55, 2004: Thermal comfort conditions for human occupancy, Section 5.2 o Operative Temperature 67.3 to 82.2 F o Humidity ratio limit 0.012 o Max Air speed 40 fpm at occupant level o Local thermal discomfort - radiant temperature symmetry, draft, vertical air temperature difference, floor surface temperature o Allowable Cyclic Operative Temperature variation = 2 F

* ASHRAE 62.1, 2007: Ventilation for Acceptable Indoor Air Quality, Sections 4-7 o Minimum Ventilation and Exhaust Air flow Rates o Air Cleaning Devices with appropriate MERV Ratings depending on Outdoor Air Quality Particulate Matter

* ASHRAE 90.1, 2007: Energy standard for buildings except low rise residential buildings, Sections 5.4, 6.4, 7.4, 8.4, 9.4 and 10.4.

o Building Envelope Compliance: U value of Building Envelope, climate zone wise, Zone 1-8

o Minimum equipment efficiencies for a. ACs and condensing unitsb. Heat pumps c. Water chilling packages d. Packaged Terminal and Room ACs and Heat Pumps e. Furnaces, Duct Furnaces and Unit Heaters f. Boilers g. Heat Rejection Equipment

o Service Hot Water Heating a. Equipment Efficiencies

o Power a. Feeder conductors shall be sized for a maximum voltage drop of 2% at design load.b. Branch circuit conductors shall be sized for a maximum voltage drop of 3% at design load.

o Lighting a. Automatic Lighting Control b. Exterior Building Lighting Power

o Electric Motor Requirements a. EPACT 1992 (not applicable for 50Hz, however using NEMA premium efficiency motors will save energy)

4. The energy model Also evident from the table above are maximum possible points achievable under any category and all credits 21 under EAc1 Optimize Energy Performance. Up to three points may be achieved following prescriptive compliance path of Advanced Energy Design Guide or Advanced Building Core Performance Guide. Thereafter, design teams have the option of achieving higher points doing a whole building energy simulation by building an Energy Model where points achieved are correlated with percent predicted energy cost savings, demonstrated by difference between design and baseline energy models. A minimum energy cost savings of 12% is awarded 3 points with 48% savings rewarded a maximum 21 points. The energy model must follow the modeling methodologies outlined in Appendix G of ASHRAE 90.1, 2007. This methodology's goal is to provide a baseline building to use as a reference point to compare the design building.

It is a way to standardize the baseline, while putting weight on important factors that heavily influence building energy consumption (e.g., location, geometry and occupancy patterns). This analysis uses the Building Performance Rating Method to quantify performance and determine energy cost. It presents a comparison between baseline building and proposed building. Guidelines require that the team makes two energy models: one representing the 'proposed' building as designed and second as 'baseline' building. Both sets of simulations (proposed and baseline) use identical climate data, layout, geometry, occupancy, loads and schedules. Depending on climate and building size, the standard provides requirements for HVAC system type, and wall and window definitions. An energy analysis was performed for G4 Mega Corporate building based on Appendix G of ASHRAE 90.1, 2007.

Baseline building chosen was based on System 8 from the "Appendix", which states the use of a VAV with Parallel Fan Powered (PFP) boxes and chilled water system. The envelope requirements were based on ASHRAE minimum values for building located in Climate Zone 1. The proposed design complied with the mandatory provisions of Standard 90.1-2007 (without amendments) and included all the energy costs within and associated with building project. The simulation was performed using the building's actual orientation and was then rotated 90, 180 and 270 degrees as per ASHRAE requirements. An average result of these simulations defined the baseline for the building. All models are approximate of reality and are based on many sets of assumptions. The software is considered less effective at producing absolute estimates of energy use than it is at producing relative comparisons between two different building features or systems.

Relative comparisons tend to mitigate the impact of model assumptions by holding assumptions constant between two different simulations. Absolute energy and cost results should be used only, if actual utility data is available and if the model can be calibrated to reflect measured information. Table 2 shows a summary of proposed and baseline parameters for G4 building. Table 2: Proposed and Baseline Parameters for Energy Simulation 5. Energy saving measures The table below shows energy analysis comparison between baseline and proposed G4 Mega Corporate building based on the parameters shown above: After incorporating all energy conservation measures of a better building envelope, better equipment efficiencies and improved lighting efficiency, the proposed building is predicted to save 12.45 % compared to baseline building.

However, since the building simulation was not carried out after the final detail design stage and the fact that actual savings usually fall short of expectations, the project had safely attempted for 3 points for a 12% savings during precertification stage. A revised energy model is underway to estimate final predicted energy savings of the building for submission during final LEED Review. The savings of Energy Conservation Measures employed in this building are tabulated below:

5.1. Building Envelope: Building envelope has improved with better U values achieved for the floor, walls and glazing as compared to mandatory values of ASHRAE 90.1, 2007. The glazing used is double glazing with low e glass.

5.2. Equipment Efficiency

To be continued
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Publication:Pakistan Engineering Review
Geographic Code:9PAKI
Date:Apr 15, 2017
Words:2168
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