The Issue
IEN Consultants was brought in by this client not only to get the building to GBI (Green Building Index) GOLD and LEED GOLD certification, but also to provide technical guidance to the owner, designer and builders towards lowering the building energy usage by at least 30% compared to their previous building of similar nature and size.
To achieve higher energy efficiency and lower energy usage in retail building, there will necessary upgrades to not only the building energy systems, but also the building design as well as the construction of the building envelope. Upgrades mean additional capital expenditure. Although the client places high priority and importance on energy efficiency and reduction on operating energy, the additional cost to be spent to reduce energy usage must also be justifiable.
For this particular project, the client set the hurdle rate at 7years payback. This meant that we had to achieve the 30% energy reduction goal with energy conservation measures that would pay for itself in 7years or less.
The Approach
We started by setting up a benchmark for the energy usage of the existing retail store. This was done using information of the previous 24 month energy usage and maximum demand, store gross floor area and air conditioned floor area, visitor count and typical operational hours. The energy benchmark of the existing store formed the BAU (Business-as-Usual) scenario.
Utilizing the IES Virtual Environment dynamic energy simulation software, we predicted the energy usage of the new building if it was designed, constructed and operated just like the BAU scenario. We then set out to explore energy reduction strategies that would lower the energy usage by at least 30%.
There is no single silver bullet solution to achieve this. IEN proposed multiple energy conservation strategies, starting by reviewing building shape and envelope specifications, followed by optimizing for daylighting, strategies to make the lighting and cooling system more efficient and finally on the use of renewable energy to generate onsite clean energy.
For each of the proposed energy conservation strategies, we carried out whole building energy simulations.
For example – if we proposed that the roof insulation to be upgraded from 50mm thick mineral wool insulation to 100mm thick mineral wool insulation, we would carry out the whole building energy simulations for both scenarios and the difference in a whole year energy usage would be the predicted savings from this specific upgrade.
The Solution
In the case of this retail building, the shape of the building is very much dictated by the functional aspects of the internal store layout, which meant that the form of the building was already very simple and practical. Additionally, this client already has very high specifications for the building envelope construction. The external walls, windows and roof specifications are very well insulated. Therefore, there were limited opportunities to propose upgrades on this aspect. Our strategies primarily focused on daylighting, electric lighting and cooling system optimization.
Fig. 1 - Bar chart of projected energy reduction (%) for each energy reduction strategy
Although the energy reduction target was a priority, each proposed energy reduction strategy must still be demonstrated to bring sufficient savings to justify it’s additional investment.
To facilitate an informed decision by the owner, we compared the predicted energy cost savings (without accounting for future escalation rate of electricity tariff) against the estimated additional investment cost to determine the simple payback duration.
Any strategies with a payback of less than 7-years was recommended whilst any upgrades that resulted in a simple payback of longer than 7-years was dropped.
Fig. 2 - Tabulation of projected energy cost savings vs simple payback period of each strategy
Fig. 3 - Waterfall Chart of estimated Additional Investment Cost and Avoided Cost for each energy reduction strategy
The Outcome
With the cost, savings and payback clearly presented, the owner agreed to implement almost all of the energy reduction strategies that we recommended.
Upon completion and operation, the actual energy usage of the building was monitored. Initially the total energy of the building exceeded the set target. Through operational changes and fine-tuning of setpoints and control logic for building energy systems, the building energy consumption was progressively lowered and achieved the goal of being more than 30% reduction (normalized by building floor area) compared to the older building of the same function.
In fact this building went on to be declared the Winner in the Large Green Building Category at ASEAN Energy Awards 2019 as well as the Runner Up in the Energy Efficient (Green Building) Category, National Energy Awards 2019.
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