Efficiency direct.
In Depth Real World Energy Efficiency Case Studies

This project marked the start of our involvement with this large university NHS Trust. Having spent some time on site we realised that the plant in the hospital clearly lacked maintenance, was in need of repair or upgrade and was no longer under the control of the Trend BMS.

It became immediately clear that main AHU plant was being forced by increasing setpoints to deliver air at more than 20°C to compensate for defective reheater battery controls all over the hospital.

Our approach proposed to take a single plant room as the model for our energy saving initiatives that could be rolled out to all other plant rooms throughout the hospital. The plant room chosen was P3 containing six large AHUs’ feeding areas in the hospital which included the main kitchens, a hydrotherapy pool, outpatients, rehabilitation and geriatrics and the hospital administration department.

The project which was entirely managed by Efficiency Direct was split into two phases.

Phase 1 concentrated on improving the core plant and its controls within P3.

Phase 2 achieved the same thing within the areas supplied from P3 and would target the reheater batteries and improve their valves, actuators and controls to achieve reliable, correctly and efficiently controlled heating in their supplied areas.

The initiatives were:

• All associated BMS Outstations were interrogated and their control loops re-engineered to provide optimum performance and efficiency.
• As there were no time schedules programmed into the Trend BMS controls to turn off plant during silent hours when it was not required. Time schedules were agreed and set up and programmed for the six AHU’s within P3.
• Many of the mixing valves within all of the plant rooms were defective and were not controlling correctly. Many were missing actuators, were seized, or were simply no longer functioning. It was agreed with the NHS Trust that all mixing valves and actuators would be replaced within P3 for a standard type that would later be used throughout the hospital.
• All sensors and dampers for each AHU were checked and calibrated.
• Air flows within the AHU’s were severely restricted due to dirty and blocked frost coils, heating and cooling batteries. These were thoroughly cleaned by a professional duct cleaning contractor provided by Efficiency Direct to help create improved air flows through the AHU’s.

• Danfoss VLT FC102 Variable speed drives were installed to all supply and extract fan motors to reduce the speed and therefore power as necessary. They are controlled by the Trend BMS and respond to changes in outside air temperature, duct pressure and supply temperature. This provides the versatility needed for the challenging requirements of the environment found within a hospital.
• A new North Systems control loop was added to each of the 15 heater batteries supplied from P3. This system was then connected to the Trend BMS and allowed operators, for the first time ever, to adjust local temperatures around the hospital as necessary.

The chart of energy usage below shows the dramatic reduction in consumption before, during and after VSDs’ were fitted.

The installation in the plant room has not only improved the hospitals internal environment in the areas served, but has resulted in a reduction in the electrical consumption in the plant room of more than 50%.

This has been quantified in P3 as an annual saving of £48,000, equating to 533,000 kWh of electricity and 279 Tonnes of CO2. 

The Trust subsequently ordered a further 88 identical VSDs’ for its two major hospitals in Sussex.

The North Systems controls installation on the local reheat batteries has led to further energy savings, particularly in gas usage, and a large reduction in the number of temperature related complaints received by the helpdesk. This work is only recently completed and data is eagerly awaited to confirm the savings although we are confident that they are being achieved.

Once the rollout of the model was completed to all hospital plant rooms, further work was completed involving the replacement of 14 defective zone valves and actuators throughout the hospital. This work has recently been completed and has allowed the BMS to be re-programmed to impose time schedules on many of the new zone valves allowing those which feed areas that are not occupied out of hours to be set back (Temperature set point reduced) or isolated  altogether overnight.

A further benefit of this work has been the greatly improved environmental control in all areas of this large teaching hospital and the almost complete elimination of temperature related complaints received by the hospitals help desk.

NHS Trust Energy Manager Dawn Moss said “The work completed in Princess Royal forms part of a series of major energy reduction projects being undertaken by Efficiency Direct. The systems installed have proved to be reliable, versatile and efficient, and the project has been successfully extended and rolled out across the entire hospital.”