Case Studies

The 55KW TASC Drive

An old TASC drive unit was in use to control the speed of a fan as part of a variable air volume system. A TASC drive controls a fan’s speed by means of a mechanical clutch. This process is inefficient as the electric motor runs at a constant speed, regardless of the actual speed requirement of the fan. The TASC unit was removed and replaced with a high efficiency motor and variable speed drive (VSD) thus permitting the speed of the fan to be reduced during periods of low demand. The improved operating efficiency of the motor and VSD reduced the fan’s energy use by more than 74% providing significant monetary and Carbon savings.

This supply fan serves the various office floors within the building. As part of the energy-based works on site, CO2 sensors have been installed throughout the building to determine the fresh air requirements of the space. By minimising the volume of fresh air drawn into the AHU during cold periods, there is potential to save energy by reducing the load on the heating coils.

In the car park, extract fans were found to be operating throughout the day despite the area being vacant for much of the time. The fans are now controlled using carbon monoxide sensors so that the fans will only run when exhaust gases exceed a threshold limit.

Inverter

During an energy survey undertaken by ACME, a number of pumps and fans were highlighted as being well suited for variable speed drive (VSD) control. It was agreed that a single pump would be used as a pilot scheme to prove the potential savings available from VSDs.

An ABB drive was installed to control the speed of the main LTHW pump (rated at 11kW). The drive was setup to vary the flow to maintain a desired return temperature setpoint. The running power consumption was found to reduced from 9.8kW to just 5kW. Savings on this one pump alone have been calculated to be in excess of £1,000 per annum.

DFE Building

ACME has maintained this site for a number of years and has recently completed a major project to design and implement a BEMS control philosophy that would provide significant savings.

The software strategy for the fan coil units was re-engineered to reduce loads on the heating and cooling systems at the beginning and end of normal occupancy times each day. This was achieved by automatically adjusting the deadband between heating and cooling setpoints throughout the day depending on the space temperature. The resulting saving was estimated by ACME to be just under £60k per annum from reduced operating hours of pumps and fans alone. This estimated saving does not include the additional savings achieved from reducing the running hours of the chillers and boilers. It would be easy to assume that this reduction of plant operating hours may have compromised occupant comfort. However complaints within the building actually reduced significantly and at the time of writing not a single complaint had been recorded.

Energy Survey

ACME has recently conducted BMS energy surveys at nine magistrates’ courts in and around London.

The surveys required a review of the software strategy, a walk-around of the site and an evaluation of the Supervisor and user interfaces. The surveys highlighted a number of ‘quick wins’ for reducing energy consumption such as minor software modifications, time setting adjustments and variable speed drive installations. A number of sensible recommendations were put forwards for each site and these were prioritised in terms of their potential payback period.

Department for Transport

ACME worked very closely with the end user and facilities team over 3.5 years to provide improved usability of the Supervisor and has achieved vast energy savings by modifying software and installing new hardware to ensure the plant operates more efficiently.

The energy saving applications on site have included software modifications to both the boiler and chiller plant, re-configuring of time clocks, calibration of various sensors and alterations to optimum start/stop control to ensure that the plant does not run for longer than is necessary.

ACME’s service contract commenced in 2007 and by the summer the energy consumption of the mechanical plant had been almost halved relative to the previous year’s consumption. The energy saving applications implemented on site are still providing continued energy savings to this day.