New Lift Control Gives Improved Efficiency and Operation at Swiss Hospital

The renovation of a bank of six lifts at Frauenfeld Hospital in the region of Thurgau in Switzerland has improved energy efficiency and increased lift capacity by 30%.  The retrofit solution for the lifts, was devised and carried out by AS Aufzüge AG (AS) working with Control Techniques Switzerland.  The upgrade was carried out with minimal disruption to hospital routine.

Frauenfeld Regional Hospital belongs to Spital Thurgau AG which is sub-divided into four operations based at three sites: Münsterlingen Psychiatric Hospital, the St. Katharinental rehabilitation clinic in Diessenhofen as well as Kantonsspital Frauenfeld, the regional hospital in Frauenfeld.  The hospital (Kantonspital) has 265 beds, and is operated at a capacity of up to 95%. The high-rise building dates from 1974 and experiences a very high frequency of lift usage because the three passenger lifts and three bed lifts (one bed lift being designed as a fire brigade lift) transport patients, visitors, heavy beds with equipment and medical personnel from one floor to another, and to the operating theatres and/or the intensive care stations – places where, often, every minute counts.

Frauenfeld Hospital has 19 storeys, four below ground -level, and the design of this building makes one thing abundantly clear - without absolutely reliable lift systems, the hospital is unable to function properly.  The original lift control system was installed in the 1980s and it was time for the complete renewal of the system. The system chosen was lift systems built by AS Aufzüge AG (AS) combined with individual, custom-built drive solutions supplied by Control Techniques. 

Claus Wittel, the Technical Services Manager at the hospital, compiled a specification document which itemised the key requirements that any renovation of the lift control system on the existing AS lifts would have to take into consideration.  "The main points about this renovation project conducted jointly with AS were threefold: the very short conversion time available during normal ongoing operations at the hospital, the ability to increase capacity for individual journeys by lift, and to optimise the power consumption of the system.” 

Michael Moser, Project Manager of MDC modernisation at  AS, comments, "We have been working with Control Techniques for a long time now because we wish to offer an open system which presents no problems at all in terms of maintenance. 

 “The recuperation of energy across the board is already a standard feature within the industry and here, as in so many other cases, we have once again pioneered new avenues with Control Techniques.

The Unidrive SP AC drive system with regenerative capability was proposed for the six electrically interconnected lift systems (three passenger lifts, each rated for loads of 630 kg, two bed lifts, each rated for loads of 1,800 kg, and a fire brigade lift, also rated for loads of 1,800 kg.)  The 4-quadrant power regenerative mode was selected instead of using the more conventional arrangement of brake resistance units that generate heat and waste energy.  These resistors are only used for operations during major overhauls, and to mitigate any peak load periods that may arise.  The modular design of this lift system can be disconnected from the mains power supply when not under load and can be operated independently and without DC intermediate circuit network.  This assures high levels of operational reliability and simple expansion of the system without the need for any adaptation. Thanks to the feedback system that recycles power via a common DC bus, energy can be returned to the power supply network.  The high performance factor (cosφ=1.0) of Unidrive SP, which offers an optimised ratio of standby to effective current, substantially increases the efficiency rating of the entire lift system.

Activation of drive commands and position management, all displayed on the screens in the reception area and in the machine room, takes place within the lift control system and is transmitted in the form of digital signals and DCP-04 BUS communication to the Unidrive SP drive.  Employees are able to reach their destinations directly in batch mode, after which the lift takes its other passengers to each storey selectively, i.e. to their desired destination, with optimised stops along the way. Michale Moser describes the drive concept from an AS viewpoint:  "The synchronous motors on these six lifts have no gearboxes and are operated by a self-teaching, self-optimising piece of software.  A special fast-start function makes it possible for the brake to cause the doors to re- open during the closing operation, and to be 'held in position' by the inverter (fast start) – this saves one to two seconds of time, thus enabling the cabin to restart immediately.

The lift control units (Böhnke BP306 with CANopen technology) make it possible to respond to individual customer’s wishes and the collaboration between all three parties involved has, to date, been very good indeed.

"The conversion work, all carried out during normal operations at the hospital, was carried out by the specialists from AS and Control Techniques with only very brief interruptions in service with a view to maintaining an emergency service at all times." adds Claus Wittel.

The finished refurbishment has given the hospital authorities a system with less maintenance and downtime through the self-optimising group control function and energy saving through the regenerative feature and the linked DC intermediate circuit.  The autonomy and high level of availability of the lift system has had a positive impact on the service life of the entire system – crucial in a hospital. 

Claus Wittel summarises:  "We have demonstrated that we can release the 30% latent capacity within the system through the use of this new control system.  The secondary objective was to save energy and we estimate this to be in the region of a cost saving of roughly €2,700 per annum.  Overall, a very successful project!"