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High School Yards, Edinburgh

Condensing gas boilers - energy efficiency in higher education buildings

Overview

High School Yards was part of Edinburgh University’s estate, now the site of the Edinburgh Centre for Carbon Innovation.

In the late 1980’s, the High School Yards complex was home to the Geography Department and Department of Dentistry. The complex includes three separate buildings, forming a courtyard in the centre.  The total floor area was 400,000m2, housing facilities for 14,000 students.  All three buildings are sandstone construction, with pitched slate roofs and single glazed wooden framed windows.

Heating was provided by two, old, coal-fired, Lancashire steam boilers, each rated at 4,000lbs/hour. This study details the switch to a condensing gas boiler system.

Approach

In the early 1990’s, higher education buildings were found to use about 3,300 kWh/student  each year in providing space heating and hot water, accounting for around 65% of the total energy consumption in these buildings.

The old coal-fired boiler system at High School Yards operated 24 hours per day and had to be constantly manned to meet demand. They produced a lot of dirty soot and were difficult to control.

To improve efficiency, the heating system was gradually replaced by low temperature hot water (LTHW) circuits. Three new central gas-fired boilers replaced the coal-fired Lancashire steam boilers – one 349kW condensing boiler and two further efficient conventional boilers at 232kW each. These boilers had low standing losses, and took up considerably less space than the existing coal-fired boilers and the coal store.

Controls were installed to ensure that the condensing boiler was always used as a priority. Timers were also used to set the heating period from 07.30 – 16.30 five days a week.

Performance

Annual energy consumption dropped from 2,291,700kWh with the old boilers to 917,200kWh with the new boilers. The overall modernisation programme (including new boilers, the move from steam to LTHW and improved controls) resulted in a 60% saving in fuel consumption. The University anticipated a 4 year payback for the upgrades.

Lessons

The University Engineer was closely involved in the design and installation of the new plant. His view was that the design was straightforward and maintenance simple.

The University staff were very pleased with the reliability and performance of the new system.

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