Case Study
G4 Mega Corporate Tower, Karachi
LEED compliant MEP design in Pakistan
By Mr. Farhan Mehboob
1. 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 (GHG) emissions. Given that buildings are such 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 VMT (Vehicles Miles Travelled) by choosing the location near by public transport and conveniences which helps in reduction of 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 this serves to enhance comfort, well-being and productivity.
The Leadership in Energy and Environmental Design (LEED) Green Building Rating System developed and managed by the 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 the construction industry to move towards building Green Buildings and pursuing a building rating certification.
Imperial developers and builders, IDBL, 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 with the aim to achieve a LEED Silver rated Building, the first in Pakistan. This building has now been built and pre 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 an improved envelope performance that includes a high performance glazing system with low U values, high performance chillers with better part load 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 the HVAC, Electrical and Lighting Systems. Water Saving strategies included the use of low flow fixtures. As per the LEED requirement for fundamental commissioning, the Building has also employed a detailed commissioning process from the pre functional and functional testing procedures and documentation being fulfilled.
This paper investigates how the G4 Mega Corporate Tower Building was able to achieve a LEED Silver Rated Building, a first in Pakistan, by employing Green Building Strategies focusing primarily on its MEP System design. This building will act as a case study for the potential of green building designs in the Pakistan Market, not neglecting any cost implications that may accrue.
2. THE LEED PROCESS
LEED was launched in an effort to develop a “consensus-based, market-driven rating system to accelerate the development and implementation of green building practices.” It includes a set of rating systems for the design, construction, operation, and maintenance of green buildings, from homes, schools, hospitals, data centers to neighborhoods, that aims to help building owners and operators be environmentally responsible and use resources efficiently.
Under LEED v3 2009, there are 100 possible base points distributed across six credit categories: Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality and Innovation in Design. Up to 10 additional points may be earned: four additional points may be received for Regional Priority Credits, and six additional points for Innovation in Design (which includes 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 the Green Building Certification Institute (GBCI), which handles the third-party verification of a project’s compliance with the LEED requirements. The certification process for design teams is generally made up of two consecutive applications: one the design phase credits, and the second that includes the construction phase credits.
The design credits include those that are the purview of the architect and the engineer, 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.
The construction credits include those that are predominantly under the purview of the contractor, and are documented during the construction and commissioning of the building. These credits can only be submitted after the project administrator has attempted all prerequisites and the minimum number of credits required for certification.
Alternatively, the submission may be made as a single combined review.
After the Final Construction Review results are accepted, the project may be denied or certified as LEED.
3. THE PROJECT
The G4 Mega Corporate Tower is situated in Karachi, Pakistan. It is a 28 storey commercial office building with a total area of 411,000 sft. of which 205,356 sft is air conditioned for the cooling load of 2074 occupants and various equipment.
Three Water Cooled Centrifugal Chillers of 308 TR cooling capacity each, with two working and one spare chiller, cater for the building 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 the buildings fresh air requirements.
Tenant spaces were designed using an Underfloor Air Distribution System (UFAD) which saves additional energy and is a first for Pakistan in a high rise building.
4. LEED AND THE MEP DESIGN THROUGH THE G4 BUILDING
The table below summarizes the MEP related pre-requisite and design credits, applicable for a Core and Shell Building under LEED v3 2009. It is evident that more than 50% of the total possible credits lie within the scope of the MEP designer. Most of these points are achievable through an overall building energy performance model and are in the energy and atmosphere category, the rest lying largely in the Water Efficiency and Indoor Air Quality categories. The table also indicates the points that the G4 Mega Corporate Tower has targeted for and how it has achieved them.
Table 1: LEED Scorecard for G4
LEED Credit Possible Points Points Achieved Remarks
Sustainable Sites
SSc8
Light Pollution Reduction 1 0
SSc9
Tenant Design & Construction Guidelines 1 1 Tenant Guideline issued with technical information that will enable the tenant to coordinate their space design and construction with the core and shell building systems.
Water Efficiency
WEp1
Water use reduction 20 % P P
WEc1
Water Efficient Landscaping 4 2 The client minimized landscaping and used plants with low water requirement.
WEc2
Innovative Wastewater Technologies 2 2 Potable water for use in building sewage reduced by 50% through water conserving WCs and sanitary ware.
WEc3
Water use reduction 4 4 Low flow Efficient plumbing fixtures and fittings reducing water use by 45%.
Energy and Atmosphere
EAp1
Fundamental Commissioning of Building Energy Systems P* P All HVAC Systems commissioned.
EAp2
Minimum Energy Performance P P Compliance with energy related mandatory provisions in ASHRAE 90.1-2007.
EAp3
Fundamental Refrigerant Management P P No CFC based refrigerant used. (R-134a)
EAc1
Optimize Energy Performance 21 3 Whole Building Energy Modelling with 12% savings.
EAc2
Onsite Renewable Energy 4 0 No scope for Renewable energy in this building due to limited roof space.
EAc3
Enhanced Commissioning 2 0 No/Limited 3rd part commissioning agents in Pakistan
EAc4
Enhanced Refrigerant Management 2 2 R134a with low ODP and GWP with a max refrigeration impact <100.
Fire Suppression System does not use CFCs/HCFCs.
EAc5.1
Measurement & Verification-Base Building 3 3 M&V plan for Calibrated Simulation.
EAc5.2
Measurement & Verification-Tenant Submetering 3 3 A centrally monitored electronic metering scheme allowing for a tenant M&V plan to be implemented.
EAc6
Green Power 2 0 No grid source renewable energy technology in Pakistan.
Indoor Air Quality
IEQp1
Minimum IAQ Performance P P Complying with minimum IAQ requirements of ASHRAE 62.1-2007.
IEQp2
Environmental Smoke Control P P No smoking building
IEQc1
Outdoor Air Delivery Monitoring 1 1 Outdoor Air Monitoring Stations installed in DOAS to maintain minimum outdoor airflow values within the spaces within an accuracy of +/- 10%.
IEQc2
Increased Ventilation 1 0 Not feasible in Pakistan given poor quality of outdoor air and increased energy usage in conditioning the additional ventilation air.
IEQc4.1
Low-Emitting Materials-Adhesives & Sealants 1 1 Included in specifications.
IEQc4.2
Low-Emitting Materials-Paints & Coatings 1 1 Included in specifications.
IEQc6
Controllability of Thermal Comfort 1 0 Specified in Tenant fit-out guide, ---, as this is a “shell and core” project this credit was not claimed
IEQc7
Thermal Comfort: Design 1 1 Thermal comfort conditions complied with ASHRAE 55-2004.
IEQc8.1
Daylight and Views-Daylight 1 0 Daylight Calculations showed this to be not feasible with glare becoming an issue – this is a constraint of the building architecture
56 24
*P – Pre requisite (i.e. mandatory)
5. COMPLIANCE WITH ASHRAE STANDARDS
As seen in the table above, the pre requisites of EA and IAQ category of LEED v3, 2009 assumes as a baseline compliance with the following ASHRAE standards:
• ASHRAE 55, 2004: Thermal Comfort Conditions for Human Occupancy, Section 5.2
o Operative Temperature within 67.3 to 82.2 F
o Humidity ratio limit of 0.012
o Max Air speed of 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. Air Conditioners and Condensing Units
b. Heat Pumps
c. Water-Chilling Packages
d. Packaged Terminal and Room Air Conditioners 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)
6. THE ENERGY MODEL
Also evident from the table above is the fact that the maximum possible points achievable under any category and any credit are 21 points under the EAc1 Optimize Energy Performance credit. Up to three points may be achieved following the prescriptive compliance path of the Advanced Energy Design Guide or the 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 the number of points achieved is correlated with the percent predicted energy cost savings, demonstrated by the difference between the design and baseline energy models. A minimum energy cost savings of 12% is awarded 3 points with 48% savings rewarded by the maximum 21 points.
The energy model must follow the modeling methodologies outlined in Appendix G of ASHRAE 90.1, 2007. The goal of this methodology is to provide a baseline building to use as a reference point to compare the design building against. 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 an energy cost. It presents a comparison between baseline building and proposed building.
The guidelines require that the team make two energy models: one representing the building as designed, the “proposed” building, and a second “baseline” building.
Both sets of simulations (proposed and baseline) use identical climate data, layout, geometry, occupancy, loads and schedules. Depending on location (climate) and building size, the standard provides requirements for HVAC system type, and wall and window definitions.
An energy analysis was performed for the G4 Mega Corporate building based on Appendix G of ASHRAE 90.1, 2007.
The 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 the building project.
The simulation was performed using the buildings actual orientation and was then rotated 90, 180 and 270 degrees as per ASHRAE requirements. An averaged result of these simulations defined the baseline for the building.
As all models are approximations 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 the 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.
The table below shows a summary of the proposed and baseline parameters for the G4 building.
Table 2: Proposed and Baseline Parameters for Energy Simulation
Model Input Parameter Baseline Design Input Proposed Design Input
Exterior Wall Construction U‐factor = 0.581 Btu/hr.ft².ºF U‐Factor = 0.448 Btu/hr.ft².ºF
Roof Construction U‐factor = 0.915 Btu/hr.ft².ºF
Roof reflectivity = 0.30 U‐factor = 0.915 Btu/hr.ft².ºF
Roof reflectivity = 0.45
Floor Construction U‐factor = 0.350 Btu/hr.ft².ºF U‐Factor = 0.30 Btu/hr.ft².ºF
Fenestration U value 1.22 Btu/hr.ft².ºF 0.297 Btu/hr.ft².ºF
Fenestration SHGC All directions‐0.25 All directions‐0.19
Shading Devices None None
Interior Lighting Power
Density(W/sf) Lighting Power Density using Space‐by‐ Space method from ASHARE 90.1-2007 : Table 9.6.1 17% reduction from ASHRAE 90.1‐2007
Receptacle Equipment
Power & Miscellaneous
Equipment Density (W/sft) 0.6 0.6
Primary HVAC system type VAY with Reheat, Fan Control‐VAV
volume, Cooling Type‐Chilled water,
Heating Type‐ Electric resistance Tenant spaces- same as base case
Other space - Constant Volume FCU and AHU
Economizer Control None None
Energy Recovery None Enthalpy Wheel and Heat pipe
HVAC parameters - Water cooled centrifugal chiller
- COP ‐ 6.1
- kW/ton ‐ 0.5765 at ARI conditions 550/590. - Water cooled centrifugal chiller
- COP-6.247
- kW/ton-0.563 at ARI conditions 550/590
Chilled Water loop & pump High efficient secondary pumps with VSD High efficient secondary pumps with VSD
Boiler Not Applicable Not Applicable
Hot water loop & pump None None
Cooling Tower - Type – Open, Single Cell
- Design Wet Bulb temp ‐ 78 ºF
- Capacity ‐ NIL
- Fan bhp/ton ‐ 0.0126
- Motor efficiency ‐ 90% - Type – Open, Single Cell
- Design Wet Bulb temp ‐ 78 ºF
- Capacity ‐ NIL
- Fan bhp/ton ‐ 0.0126
- Motor efficiency ‐ 90%
Condenser Water Loop &
Pump - Flow ‐ 3 gpm/ton
- CW Loop pressure drop ‐ 15ft
- Impeller efficiency ‐ 0.77
- Motor efficiency ‐ 90% - Flow ‐ 3 gpm/ton
- CW Loop pressure drop ‐ 77ft
- Impeller efficiency ‐ 0.77
- Motor efficiency ‐ 90%
7. THE ENERGY SAVING MEASURES
The table below shows the energy analysis comparison between the baseline and proposed G4 Mega Corporate building based on the parameters shown above:
Table 3: Energy Analysis Comparison
Alternative Lights Equip. Cooling Tower Pumps Fans Ext. Lights Total Saving
Base Case 1,165,438 874,655 889,213 71,009 40,069 401,330 29,404 3,474,401 0.10%
Base + 90 1,165,438 874,655 897,587 71,503 40,336 403,875 29,404 3,486,256 -0.24%
Base + 180 1,165,438 874,655 887,915 70,354 39,677 392,948 29,404 3,463,326 0.42%
Base + 270 1,165,438 874,655 899,977 71,158 40,108 404,030 29,404 3,487,344 -0.27%
Base – Avg 1,165,438 874,655 893,673 71,006 40,048 400,546 29,404 3,477,832 -
Proposed 968,460 874,655 751,572 51,783 76,188 290,900 29,404 3,044,854 12.45%
After incorporating all the 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 the 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 the precertification stage. A revised energy model is underway to estimate the final predicted energy savings of the building for submission during the final LEED Review.
The savings of Energy Conservation Measures employed in this building are tabulated below:
7.1. BUILDING ENVELOPE
The Building envelope has been improved with better U values achieved for the floor, walls and glazing as compared to the mandatory values of ASHRAE 90.1, 2007. The glazing used is double glazing with low e glass.
7.2. EQUIPMENT EFFICIENCY
The chillers installed in the building have a better COP of 6.217 and IPLV 0.563 kW/ton than the mandatory ASHRAE 90.1, 2007 value yielding additional energy saving.
7.3. ENERGY RECOVERY
An air to air energy recovery has been employed on the Dedicated Outdoor Air System (DOAS) using an enthalpy wheel and heat pipe.
The energy recovery efficiency of the enthalpy wheel is 58%, recovering 55 TR of the load, and with the heat pipe recovering 20 TR of the load, a total reduction of cooling load of 75 TR from a total outdoor air load of 95 TR has been achieved. In comparison, a DOAS with just a heat pipe would need to cool 120 TR and be only able to recover 25 TR of the total load.
7.4. INNOVATION: UFAD
An Underfloor Air Distribution is a relatively newer air conditioning system that uses the open space between the structural slab and the underside of a raised floor system to deliver conditioned air to supply outlets located at or near floor level within the occupied zone i.e. up to 6 ft of the space.
UFAD systems have several potential advantages over traditional ceiling-based air distribution systems. Well-engineered systems can provide:
• Improved thermal comfort. By allowing individual workers to have some amount of control over their local thermal environment, individual comfort preferences can be accommodated.
• Improved ventilation efficiency and indoor air quality. Some improvement in indoor air quality can be achieved by delivering the fresh supply air near the occupant at floor or desktop level, allowing an overall floor-to-ceiling air flow pattern to more efficiently remove contaminants from the occupied zone of the space.
• Reduced energy use. Energy use can be reduced through a variety of strategies including controlled thermal stratification, higher supply air temperatures, and reduced static pressures in the underfloor plenum.
In light of the above, Tenants of the G4 Mega corporate Tower have been advised to install UFAD Systems to realize these energy savings.
7.5. LIGHTING
The lighting loads for G4 have been reduced from the ASHRAE 90.1, 2007 baseline values by reducing the lighting density as well as by using energy efficient LED fixtures. Approximately 70 kW lighting load was reduced without compromising lux levels.
In addition to the above measures, the following energy saving methods were also employed.
7.6. METERING
This building has also targeted 3 points for the Measurement and Verification credit by employing a metering scheme. There are several advantages of metering which does include energy conservation benefits too and are all listed as follows:
• By utilizing submeters, landlords can charge each tenant for their exact consumption during that billing period, rather than making a manual, time-consuming estimation.
• Submetering will help us make informed efficiency decisions and advance sustainability initiatives. Meanwhile, these efforts also make buildings more sustainable and help equipment and machinery last longer. It helps collect data to establish baseline energy consumption, track progress and see the exact payback of each initiative. It also provides a look into how your building stacks up next to the competition.
• Increasingly, local governments are requiring benchmarking and making the results available to the public. As the movement for transparency grows, more buildings will likely be required to report accurate consumption data.
7.7. WATER EFFICIENCY
To achieve LEED Certification, it is important to reduce the water consumption as much as possible. This can be done through installing higher efficiency low flow fixtures. An Analysis was carried out to find out how much water reduction can be achieved.
Considering a total Full Time Equivalent (FTE) of 2496 total occupancy running 275 days a year with each day running an 8-hour single shift, an analysis was carried using different fixture types and the final design shows a saving of 45% over the LEED baseline.
8. THE COMMISSIONING PROCESS
The Commissioning of the HVAC System and Lighting Control is a pre requisite of LEED. The Enhanced Commissioning credit widens the scope to every system in the building including a design phase review by the Commissioning Agent, continuing with an involvement up to the operations stage, 10 months after substantial completion. Due to lack of availability of commissioning agents in Pakistan providing these services, this additional service was not targeted. However, pre-functional and functional testing has been carried out.
The commissioning process involves the formation of a commissioning plan and commissioning specifications that include pre functional testing and functional testing forms for every equipment and an Integrated System functional testing procedure that is based on the system’s sequence of operations. A final commissioning report has to be submitted with a summary of all the documentation.
The pre functional testing ensures that every piece of equipment and every system in a building is installed correctly and can start up and run properly.
The functional testing ensures that every piece of equipment and every system in a building is operating properly.
The Integrated System Test is the pinnacle of the commissioning program, and the performance of these activities demonstrates the performance of the facility as a whole against the owner’s project requirements. The commissioned systems are operated at various loads and in various modes to demonstrate fully automated operation and proper response to equipment failures and utility problems.
9. BUILDING METRICS
Some building metrics for the G4 Mega Corporate Tower are shown below making comparisons against a typical construction building in Pakistan and an ASHRAE 90.1-2007 mandatory complied building.
The cooling loads reductions are as shown below. The actual building can be seen to have saved 26% over a typical construction and around 15% over ASHRAE 90.1-2007 requirements.
The percentage savings based on ton hours are shown against a typical building construction in Pakistan and against an ASHRAE 90.1-2007 mandatory complied building.
Table 4: Annual Ton Hour Savings
No. DESCRIPTION ANNUAL Ton Hrs Ton Hr Savings % Savings
1 Typical Construction 1,934,234
2 90.1– 2007 1,468,925 465,309 24%
3 Actual Building 1,233,310 700,924 36%
A reduction in Ton Hours directly impacts the annual energy consumption per square foot of area in the same ratio.
A comparison of annual operating cost and capital cost was generated, as shown in Figures 6 and 7 below.
According to CBECS (2012), a building in the U.S.A with floor space between 200,001 to 500,000 sft consumes on average around 57.8 kBTU/sft annually. The climate conditions for this metric are temperate as opposed to Hot and Humid in Karachi, where the building is estimated to have an annual energy consumption of 72 kBTU/sft.
In terms of operational cost, the actual building will save 35% over a typical construction and 17% over an ASHRAE 90.1-2007 complied building. In addition, it also reduces the capital cost by 15% over an ASHRAE 90.1-2007 complied building for PFP systems.
10. CONCLUSION
The LEED Certification Process enforces Building MEP Designers to design and incorporate a level of energy efficiency and water conservation measures that translate to a more sustainable and greener building. Despite there being limitations in Pakistan to possibly achieving certain credits related to daylighting, renewable energy or outdoor air ventilation rates, there is still sufficient avenue where green buildings can be designed without a major cost impact, for example through better building envelopes, improved lighting efficiency and outdoor air energy recovery. Mandating minimum equipment efficiencies with better part load performances are also beneficial in this market where there exists no code enforcement for equipment efficiency. There is a marked reduction in water usage with the application of low flow fixtures and further potential for storm water recovery and sewage treatment plants. Finally, the commissioning process is an extremely valuable exercise in Pakistan where oftentimes the quality of construction of the building leads to marked differences between the actual operations of the building vs. the intended design. By commissioning the building, the systems are ensured to work as close as possible to the design, as well as ensure that the O&M team is sufficiently trained to operate the building and realize the potential operational savings that the building would have been designed for.
