Air Cooled Chiller London Eye by Dunham-Bush Limited

The London Eye is a giant Ferris wheel on the South Bank of the River Thames in London, also known as the Millennium Wheel. Since mid-January 2015 it has been known as the Coca-Cola London Eye. London Eye was erected in 1999 standing at 443 feet (135m) tall with a wheel diameter of 394 feet (120m).

Operations and Requirements

There are 32 sealed and air-conditioned ovoidal passenger capsules, each approximately 10-tonne in weight holding up to 25 people. The wheel rotates at 26 cm (10 inch) per second, one revolution takes around 30 minutes. It does not usually stop to take on passengers; the rotation rate is slow enough to allow passengers to walk on and off the moving capsules at ground level. Capsule doors are opened for approximately 3 minutes during the embark and disembark period.

Challenges

Retrofitting the heating and ventilation systems is part of a £125 million upgrade project for this top rated tourist attraction. The London Eye cannot be shut down for extended periods as would have been preferable for such a large project. It was decided therefore that the capsules will be taken down one at a time and transported to a workshop in Worcester where upgrade works will take place. The empty slot at the wheel will be replaced with a "dummy" unoccupied capsule.

Capsule Environmental Design Conditions:

Indoor: 20°C @ 50% RH during summer and 18°C @ 45% RH during winter
Fresh Air: 240 L/s

There are four main criteria for the environment control:

  1. Humidity
  2. Temperature
  3. Fresh air circulation
  4. Visibility

Solution

The final design of Environmental Control System for Heating, Ventilation & Air—Conditioning of the capsules is a chilled water system with air-cooled chiller. The Environmental Control System consists of the following:

  • 1 x Air cooled chiller
  • 1 x Fresh air AHU (Air Handling Unit)
  • 2 x Recirculation FCU (Fan Coil Unit)

The DB IACS Air-Cooled Chiller is tailored made specifically to suit very limited installation space and accessibility constraints as it is situated beneath the passenger platform within the capsule. London Eye IACS chillers are designed to the following specifications:

Chiller Model : JACS —5QR
Compressor: 4 x scroll compressors
Refrigerant System : 2 independent circuit
Evaporator: 2 x Brazed Plate Heat Exchanger
Condenser: 6 x EC Fans
Controls : DB Vision 2020i intelligent controller

Results

Thermal momentum of the chilled water circuit helped to achieve excellent results in terms of capsule temperature and humidity control. Pre—set controlled temperature and humidity within the capsule can be achieved just a few minutes after the doors are closed.

Fitting an AHU for fresh air introduction and two FCUs at high level for air recirculation results in conditioned air being distributed evenly along the capsule to ensure all glass panels remain clear.

Refrigerant safety is further enhanced as, in the unlikely event of a refigerant leak, it would be confined to the chiller rather than leaking around the capsule or interconnecting pipework.

The service and maintenance downtime of the chilled water system is greatly reduced due to the innovative design which allows the unit to be removed and replaced quickly without breaking into the refrigerant circuit.