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The Standard Bank Building on 88 Commissioner street was opened for business in 1908 and by the 1930’s became the Bank’s Head Office. In 1978, it underwent a major revamp which included the installation of a central chilled water plant. This comprised a Carrier HR30 chiller plant located in the basement of the building with associated condenser and chilled water pump sets, distributing chilled water to the plant rooms on each floor. An air handling unit on each floor provided conditioned air to the floor via a ducted system and distributed it into space via re-heat constant volume diffusers.
Recently the building underwent some renovations and one of the major upgrades was the air conditioning system. Mitsubishi Electric Airconditioning Distributors was selected for the upgrade of the air conditioning system and First Cool to do the installation.
The project was initialised as the aging chiller and air handling equipment had reached its economical life. Therefore, a completely new, innovative system was designed to fit the architectural appeal and structure of the building. Mr. Craig Cumming from Adaptive Resources Engineers was commissioned to do the mechanical HVAC design. The client requested that the following criteria be met:
Being built during the 1900’s, the structure posed a particular restriction whereby re-using chilled water equipment or either by installing an air-cooled chiller on the roof or stripping and re-building the chiller in the basement would have been near impossible.
Due to the building’s layout, and good mechanical conditioning of the supply fans it was decided to re-use the plant rooms whereby pre-fabricated air handling units would be removed. In turn, they were replaced with new pre-fabricated air handling units with a single interlaced evaporator coil which was installed and linked to Mitsubishi Electric’s linear expansion valve (LEV), allowing for the correct capacity airflow mix as determined by the Adaptive resources consulting agency.
Interestingly, the old centrifugal fans were retained and now controlled by Mitsubishi Electric Speed Drives interfaced digitally between the condenser and LEV, speeding up and slowing down, depending on the space demand. Interlinkage into a BMS (Building Management System) was a seamless exercise due to the interface adaptors supplied by the Mitsubishi Electric Airconditioning Distributors team.
In addition to the above, large openings in the plant room walls were introduced with free cooling mechanical louvres which were installed in each plant room to provide a free cooling system that worked very well. When this phase of operation is in use, over pressurisation fans linked to the speed drives draw out return air at the same rate as outdoor air is drawn into the building to ensure free cooling is achieved.
The process of upgrading the air handling within the building was planned to the finest detail, as throughout the whole exercise, none of the training rooms were disrupted. This was achieved by decommissioning the old chiller equipment floor-by floor as well as after-hours change over from chiller to VRF.
The Mitsubishi Electric VRF (Variable Refrigerant Flow) system modulates the flow of refrigerant, depending upon the capacity requirements of the building. In the simplest form, a VRF system comprises an air-cooled outdoor unit and a series of indoor units that regulate the air temperature inside an internal space.
This ideal is achieved by maintaining digital feedback from the indoor unit, continuously changing the compressor’s frequency and the indoor linear expansion device ensuring a perfect indoor space temperature.
The project started in late September 2015 and was completed by mid-November. The first savings were recorded in November 2015. Since November 2015, the project saved 221,893kWh which is equivalent to 29% of the building’s total consumption. Extrapolated to a full year, annual savings of 532,544kWh is expected. In monetary terms, the annual electricity bill is expected to reduce by R862,722 which yields a project payback of 4.1 years.
During the month of March 2016, the electricity consumption was reduced by 50,048kWh to 97,501kWh. This is a reduction of 34% compared to the baseline value of 147,549kWh.
The total expected annual carbon emission reduction is 220 tonnes. In March 2016, carbon emissions were reduced by 50 tonnes
Below is a short Performance Evaluation Report of the air handling project which was implemented at the Standard Bank Chambers at the Commissioner Street building.
As the above summary clearly indicates, the Mitsubishi Electric Airconditioning Distributors has shown its worth over the very short period as measured, and will continue to do so.