Heating Classrooms With "Wasted" Heat: A Case Study

Many large organisations use CHP (combined heat and power) to produce electricity and hot water – but what about the “wasted” output of low grade heat?

In the majority of cases, this excess heat is just dumped into atmosphere – when it could be serving a useful purpose.

At the University of Dundee, the low grade heat from CHP has been harnessed to provide heating for its new Dalhousie Building by running around 150 metres of new pipework between the boilerhouse and the new building.

Excellent Energy Savings

Energy Manager, Derek Mitchell, says: “The ‘free’ low grade heating circuit is providing 60% of the total heating to the building.

“There is still however a requirement for top up to our domestic hot water which is kept above 60 deg C to prevent Legionella and in the very coldest days of the winter.”

The building is served by a mixture of air handling units, fan coil heaters, underfloor heating, radiators and domestic hot water. All heating plant was proportionally enlarged to accommodate the lower supply/return temperatures (47/37 deg C).

Reduced C02 Emissions

The new Very Low Temperature Hot Water (VLTHW) circuit saves around 100 tonnes of C02 per annum.

The VLTHW circuit resulted in an additional capital cost to the project of around £100,000. Initial payback was expected at around five years but thanks to rising energy prices, the payback period is now expected to be shorter.

Financial Benefits

“We originally estimated the savings for the ‘ free heat ’ which would have otherwise been provided with gas fired boilers at £15,000-£ 20,000 and subsequent evaluations through the heat meter fitted to the VLTHW circuit have proven this to be accurate.

“In addition to the VLTHW circuit we were also fortunate to have spare electrical capacity within the existing CHP Plant which provides some 80% of the electricity requirements of the Dalhousie Building with the remaining 20% supplied from the National Grid. This has resulted in C02 savings of 90 tonnes and financial savings of over £10,000 per annum,” said Derek.

Other environmental highlights of the Dalhousie Building include:

• Most rooms in the new teaching block have natural ventilation
• Mechanical ventilation is controlled through CO2 level sensors
• Enchanced u-values in excess of Building Regulation requirements
• Solar shading to minimise heat gain in summer
• Invertor drives on AHUs, larger fans and pumps
• Locally accessed building materials

The project has brought a lot of interest from other universities and Derek Mitchell says he feels sure that other organisations will be making use of this low cost energy source in the years to come.

The innovative project has already won Dundee a prestigious Green Gown environmental award from HEEPI (Higher Education Environmental Performance Improvement) which is funded by the HE Funding Council.

“Although the environmental and financial benefits were the main drivers for this project we have also found some additional benefits,” said Derek.

These include:

• Satisfied staff and students
• It has encouraged further investment by the University
• It helps towards legislative energy and carbon saving targets

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