Projects
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RACA Journal
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RACA Journal
1 . Each hotel floor holds the necessary condenser units , masked within the building façade . This system proved a particularly useful choice when the building height was extended mid-construction .
2 . Each hotel room is fitted with hideaway units fed by the chilled water hybrid VRF system .
3 . An example of various fresh air outlets into the common space of the luxury offices .
passing savings onto the client . Although the cost of the hybrid solution is slightly more expensive , the benefits are realised by not needing all of the additional sensors and control methodology .
For the hotel section , all of the condensers are installed on each floor and hidden within the façade so as not to be visible externally . The refrigerant piping runs to the HBC controller ( or mini-chiller / hot water heat exchanger ) and then from there onwards , PEX piping is run for the water reticulation portion .
The use of PEX piping in the system reduced the risk of the usual loss-factor of stolen copper piping which is a major cause of losses on many construction sites . Pressure testing and vacuuming becomes quite simple as excessive long copper pipe runs are also eliminated . The use of PEX is further a low-skilled application so the contractor doesn ’ t need skilled welders or specialist heavy equipment on site .
A further aspect on VMGs selection of the hybrid VRF system for the hotel rooms was that there are no expansion valves . These can sometime be a bit noisy – in a hotel room you may sometimes hear the ‘ hissing sound ’ of the refrigerant though the unit . With the hybrid system this is eliminated because there is only water being pumped through , and these pumps are situated outside of the rooms in the HBC boxes , reducing noise levels .
Each installed unit or room has its own controller that can be set by the occupant . The building control that was installed is the Mitsubishi Electric energy management central controller . Set up on the ground floor it gives access to the service team or the building manager . This system is also connected to the network infrastructure of the building so it further allows the operation of the system to be viewed remotely . Further , if an office tenant on the second floor wanted remote
viewing of how their particular AC system was running , or the particular set points , they can be issued with their own IP access to their system . The control systems in this project were quite complex and allow monitoring of all aspects tied into the central control system . The systems were also connected to the primary gas and secondary diesel generators installed in the building , allowing the monitoring of all electrical usage . This is an important factor because the electrical demand on the building is highly sensitive due to the limited capacity that is supplied by the local council .
If the building ’ s electrical supply , for whatever reason , increases to the point of threshold , which is reaching 1000kVA in electrical supply , load control on the air conditioning system is implemented reducing the entire system to 50 % of demand to avoid the electrical supply tripping . The functionality also allows a timeframe to stabilise – running the AC system within a specific range until the electrical supply drops below the minimum range – then normalising back to 100 % operation .
The fire relay is also connected to the central controller and rather than linking the fire detection signal into every single unit in the building , if fire detection does occur , the controller permits all of the ACs to switch off .
At the point of first phase completion these control ranges and the methodology were theoretically laid out . Once the building has operated fully , there may be adjustments in terms of the parameters in which the system running is carried out , and this can be changed and re-programmed to suit the client needs at any time .
Turning to the building ventilation system , the 11 th and 12 th floors , with each floor plate being over 500m 2 , smoke extraction was implemented for these areas which operate on motorised dampers in conjunction with window actuators that are installed across the façade . If smoke extraction is activated , certain windows are actuated open to allow smoke to exit the floors .
The three-level basement of the building is also fitted with smoke extraction , split into an extraction system and general ventilation on a low level variable speed drive operating frequency allowing fans to ramp to 100 % capacity in a fire scenario to extract smoke out of the
www . hvacronline . co . za RACA Journal I February 2021 33