Dundee University Utility Supply Company (DUUSCO)

Introduction and history

The University was founded as a University College by local benefactors in 1881. In 1897 it became a College of St Andrews University and continued in this role until 1967 when by Royal Charter it was established as the University of Dundee.

Located on a site close to the City Centre the Campus has grown over the last 30 years until it now extends to some 42 hectares to serve the needs of over 7000 students.

The site has an extensive district heating network which has developed since 1962 and provides all the space heating, domestic hot water and process requirements of buildings ranging from halls of residence to recreational facilities, teaching to research laboratories. The latter category represents a very strong area of development which reflects the University’s world class standard of achievements in Life Sciences research; such buildings are services intensive with high levels of energy usage much of which is electricity.

The steady growth of demand for electricity was identified as being an area requiring close scrutiny and control as long ago as 1985. Unfortunately the end user determines how and when this energy is utilised and it was quickly realised that effective economic control would only be achieved by influencing the unit cost rather than limiting the degree of use.

Initial feasibility studies undertaken by the Estates & Buildings Engineering staff in 1988 suggested that CHP would be possible and several outline schemes were proposed. Financial constraints and uncertainties over interest rates resulted in the scheme being moth balled.

In 1995 an improved heat to electricity load profile, reduced gas prices and lower interest rates allied to steadily rising electricity costs served to rekindle interest in the CHP concept and the decision was taken to proceed with a 3MW Project.

The Project

Whereas earlier ideas had focused on a single engine scheme, as frequently founded on other sites, emerging plant options, and operational experience gained from other parts of the industry suggested that a multi-engine installation would achieve a better fit, whilst giving greater operational flexibility and a higher level of serviceability.

Tried and tested technology was considered a pre-requisite for the scheme and in order to minimise construction costs the plant was to be housed within the existing Boiler-house complex.

These objectives were realised by selecting generating equipment which had a proven track record in similar schemes in Europe whilst the removal of two 30,000 gallon stand-by oil tanks provided the 160 m2 of floor space required for the engine installation.

As the boiler plant forms part of an academic teaching building it was vitally important to avoid noise produced by the engines from entering the structure of the building. Considerable care was required in resolving the vibration isolation and noise containment issues and Messrs Vibronoise undertook the design and installation of both the acoustic enclosures for each engine generator set and the associated ventilation installations.

Similarly the proximity of the plant to adjacent residential property meant that a sound level of 37 dB(A) was specified to enable full radiator duty to be achieved at night without causing a disturbance to the neighbours. To achieve this sound level required the cooling units to be fitted with multiple slow running fans each having two silencers. Electronic speed control ensures that the fans start and speed up progressively to avoid any sudden changes in the perceived sound level.

Plant Description

The engine generator installation is comprised of three Jenbacher type J320G5-BO5 4 stroke 20 cylinder spark ignition gas fired engines running at 1500 rpm. The engine is coupled to a 3.3 kV alternator rated for 1500 kVA @ 0.8 power factor; under site MCR conditions output is 1002kW.

Heat recovery from exhaust gas, first stage turbo intercooler and jacket water is passed by plate heat exchangers into the returning district heating system water before it enters the existing boiler plant. When water conditions permit all the available heat is utilised in the pre-heating function otherwise some of the jacket heat is used to heat nearby buildings, any surplus being dissipated to atmosphere by the coolers.

A 4 MVA transformer interfaces between the alternators and the University’s 11 kV distribution network. A new switch room was formed to allow the incoming supply to be routed via the generator plant and includes the necessary protection devices which allow fully automatic operation of the installation.

The University’s boiler plant SCADA computer system is used to control the operation of the generators which operate in load following mode with output level set to minimise the electricity importation rate. Each engine generator unit is fitted with a comprehensive monitoring system which is connected via modem link with the system suppliers who are contracted for a long term maintenance agreement.

Procurement, Installation & Commissioning

The University established a wholly owned operating company Dundee University Utility Suply Company (DUUSCo) to undertake the procurement and long term operation of the installation as this would ensure the optimum tax relief throughout the life of the Project.

Rigorous economic modelling and cash flow analyses were performed to ensure the viability of the scheme under widely varying input cost conditions. After demonstrating its ability to withstand such sensitivity tests the University authorised the project and in Autumn 1995 McLellan & Partners, Consulting Engineers were engaged to prepare tender document and evaluate prospective suppliers.

The Estates & Buildings office undertook to co-ordinate the individual packages of work and the main contract for the supply of engines, generators, heat recovery equipment with erection was awarded to Machine Manpower Management in April 1996.

The site preparation, removal of oil tanks, civils work and infrastructure services alterations started in December 1995. Engines and the associated equipment were delivered in August 1996 and initial start-up took place at the end of September. Testing and demonstrating occurred during October and the plant was accepted for full commercial operation on 1 November 1996.

Reliable operation with a minimum of disruptions for maintenance stoppages was identified as being a major contributor to the overall performance of the undertaking. To obtain this objective a 10 year operational agreement was signed with the supplier which guarantees the level of serviceability throughout the period.

The overall cost of the undertaking is £2m and a 5 year payback period is envisaged.

Conclusion

The University identified that CHP represented the most realistic mechanism for controlling electrical energy costs. However, the translation of that decision into a working scheme demanded a considerable effort by the many disciplines within the Estates & Buildings office who co-ordinated the work of design teams and contractors whilst providing the essential linking knowledge of existing plant and facilities.

The contribution by the Client in achieving a successful outcome should not be underestimated as it is upon the quality of fit that depends the overall performance of a retrofitted installation such as this one.

The University stands to benefit for many years by virtue of reduced electricity costs whilst the ecology will benefit from the reduced CO2 emissions arising globally from the independent generation of power.