How green is my Oxford college?: Nicholas Kurti, who remembers when the city was black, welcomes its new enthusiasm for the environment

IT IS REFRESHING to see that Linacre College, Oxford, is determined to create in its new hall of residence probably the 'greenest' university building in Britain. It will save energy by better management and by the use of materials requiring less energy for their manufacture; it will save water because the lavatories will be flushed with a mixture of rainwater and purified waste water from baths, etc; and it is even claimed that the 40 tons of carbon dioxide the building will emit per year will be matched by the carbon dioxide absorbed by the 40 acres of Tasmanian eucalyptus forest which the college has saved from the chainsaw for a capital outlay of pounds 10,000.

Sadly, this last claim is wrong. The college seems to have been taken in by an enthusiastic but ill-informed environmentalist. A fully developed rainforest absorbs on average 1kg of carbon dioxide per square metre annually; however all but a small fraction is returned to the atmosphere. If the college really wants to nullify its carbon dioxide emission it should 'adopt' an appropriate acreage of the Forestry Commission's sustainably managed forests, with the proviso that all the trees felled be stored, in perpetuity, underground in one of our many disused coal mines.

When I arrived in Oxford in 1933 it was a grey, almost black city. Centuries of persistent atmospheric pollution, mainly the black smoke emitted by countless open fireplaces, gave the buildings a sombre, venerable look, but at the cost of masking many architectural and decorative details.

All this changed after the war. Periodic coal shortages and increasing labour costs led to the adoption of more efficient heating methods and, most importantly, the Clean Air Act of 1956 curbed the emission of black smoke. The cleaning of buildings ceased to be a wasteful, thankless task and Oxford turned into a golden city. Most people welcomed the change, though there were a few who bemoaned the removal of the 'patina' and regarded it as an even greater calamity than the advent of mixed-sex colleges.

It took some time to persuade architects to plan sensible heating systems. For instance, when in the 1960s it was discovered that the central heating boiler could not provide enough heat for a newly built college extension, the architect, instead of improving the thermal insulation by using double-glazed windows, decided to instal electric heaters placed under built-in seats. The idea that the flimsy dress of an occupant might catch fire was dismissed as unscientific scaremongering. A few weeks later, when fortunately not a dress but a cupboard door got badly scorched, the heaters were relocated.

In those early post-war years there was at least one forward-looking college when it came to the three Es of ecology, energy and environment. When Nuffield College was being planned it was decided to heat it with one of the most energy-efficient methods, a heat pump. This is similar to an air conditioner, except that instead of cooling a building by drawing heat from it and discharging it into the environment, the heat pump draws heat from the environment and, having 'pumped' it to a higher temperature, supplies it to the building.

A large source of heat was needed. But the obvious choice of using air for the source had to be abandoned because in winter the system would frost up. It was hoped instead to use water from the nearby Oxford canal. But because its temperature occasionally fell to nearly 0C, the same icing-up of the heat exchangers would occur.

The scheme was saved by the discovery that one of Oxford's main sewers passed near the college and would be an ideal heat source, since its temperature never fell below about 18C. A heat exchanger was accordingly installed in a small building near the college. But, alas, the system was used for only a few years, mainly because the college, instead of choosing an electric motor to drive the heat pump, opted for the greater thermodynamic efficiency of a diesel engine, which turned out to be unreliable.

To the best of my knowledge Nuffield's brave and laudable shot at more efficient heating has not been imitated in any other college or university building. But it is to be hoped that other colleges will now follow Linacre's example and remember the three Es (without forgetting the fourth, economics).

But surely Oxford - the city and its two universities - could come up with something more ambitious. It is generally agreed that the most energy efficient way to heat a building is by the waste heat from a power station run in the combined heat and power (CHP) or co-generation mode.

An ordinary power station rejects heat at about ambient temperature, which is useless for house heating. However, one can allow the heat rejected to rise to a sufficiently high temperature for it to be used for domestic heating - although this results in a slight reduction of the station's output.

An government inquiry in 1977-79 found that if one-third of the country's dwellings were heated by waste heat from power stations - which is economically feasible, even profitable - our annual carbon dioxide emissions would be reduced by nearly 100 million tons, or about one- eighth of the total.

Didcot power station is about 12 miles from Oxford, and a second power station is to be built. Could not one of these be run partly in the CHP mode and heat the houses, colleges and offices of Oxford? Various reports published by the Department of Energy between 1976 and 1980 provide a detailed model for a feasibility study which could be carried out as a multidisciplinary team project by students.

Even if such a study found that CHP district heating for Oxford was uneconomical, the project would not have been a waste of time. Not only would the students have been engaged in a timely study of topical importance but they would have learnt about the life of the community of which they are a part during their four years in Oxford.

The writer is emeritus professor of physics at the University of Oxford.

(Photograph omitted)