Employing two ammonia chillers of 0.5 MW cooling capacity each, a cooling system installed at a London hospital caters for the cooling needs of its operating theatres, maternity and intensive care units. The hospital authorities opted for the system thanks to its efficiency and distinguished safety characteristics.
Gate 4, Homerton University Hospital, London
The ammonia-based system at Homerton University Hospital in Hackney, London, UK replaced an existing one running on R22. Designed, built and installed by J&E Hall, the new system allowed for a 50% increase in cooling capacity compared to the replaced system, while fitting in the existing plant room.
The system features:
- Two ‘Aquachill’ ammonia chiller units of 0.5 MW cooling capacity each that cool water from 12°C to 6°C.
- U-tube suction separators fitted to the chillers: Supplied by Alfa Laval the suction separators allow for a refrigerant charge reduction by a third. Applied to a plate evaporator, the advantages of a thermosyphon system are retained, while keeping the refrigerant charge volume in the chiller similar to that of a DX unit.
- A safety shutdown programme ensuring that any leaks are contained within the system: an ammonia scrubber has been installed behind the system, as well as extract fans to remove the motor heat and an ammonia detection system near the exhaust fan. As a result, in the occasion of the smallest amount of ammonia release, the extract fans will shut down and the air scrubber will start. A water pump producing water spray is then activated allowing the ammonia passing through it to be absorbed into the water. Even in the unlikely event that the entire ammonia charge leaks, the air scrubber can absorb it all in the water.
Decommissioning of the R22 system
J&E Hall had to decommission the previous 340 kW R22 cooling system. More than 300 kg of R22 were removed from the old system and replaced with about 50 kg of ammonia in the new system.
