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Gallipoli Barracks Hospital

Gallipoli Barracks Hospital

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The hospital at Gallipoli Barracks is served by a chilled water system comprising 2 air cooled chillers with primary ChW pumps and 39 ChW AHUs, (all but 4 fitted with 2 way control valves). The AHUs were unable to maintain close temperature control and the operating theatres had poor humidity control due to fluctuating ChW field SP differences. Additionally the existing hydronic arrangement in the plant room provided only primary ChW pumps while the field SP control strategy called for bypassing of chilled water back to the chillers at low load. This led to very low water temperatures entering the chiller and low field DP while some AHUs were unable to satisfy zone cooling and dehumidifying loads. Further, both existing reciprocating chillers were in very poor condition with frequent failures due to short cycling and very badly corroded condensers.

The scope of work completed by DTS was to consult, engineer, design and construct a new chilled water system to service the field, including 2 new 760kW Carrier air cooled screw chillers, 2 new duty and 1 standby primary ChW pumps, duty and standby secondary ChW pumps with VSD, upgrade of electrical distribution system for the mechanical services including new MSSB and BMS. The trick was to relocate the field DP sensor to the far end of the ChW index run and control the secondary ChW pump speed via the VSD to maintain a constant field ChW DP. This provided the all zone ChW control valves with reliable DP and so the ChW valves gained authority. This provided the ability to closely control zone temperatures and humidity in the operating theatres. The two new screw chillers each had a dedicated primary ChW pump which maintained a constant ChW flow rate through the chillers. This allowed the chillers to operate one at a time or together if the load was sufficient. Each primary chilled water pump draws water from a 2000Litre buffer tank which is fed by the return ChW from the field.

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The long term benefits are that:

  1. Building conditions of temperature and humidity are maintained in full Summer load through to the lightest winter load without failure
  2. Chillers have a constant flow and do not short cycle and when called run for a good length of time even in light load  conditions because on board chiller controls are exploited to optimum effect
  3. Field ChW pumping energy requirements only need to meet that which is actually required without deliberately wasting energy on bypass