May 1937: West end debut for innovative air conditioning system

An attempt to attract affluent movie goers saw air-conditioning installed in a London cinema

Rotary water vapour refrigeration plant
Rotary water vapour refrigeration plant - The Engineer

Aficionados of Britain’s cinemas will know the name of Oscar Deutsch, the son of a successful scrap metal merchant who opened his first picture house in Perry Barr, Birmingham in 1928.

Those same enthusiasts will know that Deutsch created ODEON Cinemas, which in the space of nine years had grown to 250 movie theatres.

Deutsch’s publicists are purported to have pushed ODEON as an acronym for Oscar Deutsch Entertains Our Nation, but it is equally likely the chain took its name from the Greek word ōideion, which is ‘a building for musical performance’, an altogether more appropriate description of the old Alhambra Theatre in Leicester square, London, which Deutsch acquired in 1936 as the site of his company’s prize cinema.

The old Alhambra was demolished to make way for what is now the ODEON Luxe Leicester Square. According to ODEON Cinemas Group, art deco architecture became synonymous with Odeon, as did the latest technology and in 1937 The Engineer ran a report on air conditioning installed in Deutsch’s flagship venue in the heart of London’s West End.

Deutsch wanted to attract a more affluent class of cinema goer and followed a trend that saw ‘increased consideration…being given to the incorporation of air-conditioning equipment in order that the occupants may enjoy clean comfortable, and healthy atmospheric conditions, regardless of the prevailing exterior weather.’

Installed by Vacuum Refrigeration, Ltd, the plant was designed to give a constant dry bulb temperature inside the building of 68oF [20oC], with 57 per cent relative humidity, when the outside shade temperatures vary between 80oF and 30oF.

Each occupant will be supplied with 1200 cubic feet of fresh air per hour

“Should the outside summer shade temperature at any time exceed 80oF [27oC] a corresponding increase will be provided in the theatre, so that the difference between the inside and outside dry bulb temperature will not be more than 12oF, otherwise patrons would experience discomfort owing to the wide divergence,” The Engineer said, adding that the percentage of humidity would remain unaltered.

The new theatre could accommodate 2,300 movie goers and in designing the equipment it was necessary ‘to take into consideration the amount of heat and humidity liberated by so many people’.

“Each occupant will be supplied with 1200 cubic feet of fresh air per hour,” The Engineer reported. “The heat gains make it essential for refrigeration to be incorporated in the service in order that excess moisture may be condensed out of the air.”

The rotary water vapour refrigerating plant comprised a centrifugal water vapour extractor and compressor (similar to a normal turbine blower), which could be driven by an electric motor operating through a speed increasing gear, or by the direct application of a steam turbine, a flash type water evaporator, a surface vapour condenser, a dry vacuum pump for air extraction, and a cold-water extraction and delivery pump arranged integral with the flash evaporator.

Our reporter added: “The action of the surface condenser and dry vacuum pump will provide an absolute pressure in the evaporator about 1.5in to 2in, depending on the temperature and quantity of the condenser water available. The action of the rotary vapour compressor further decreases the absolute pressure in the evaporator to some predetermined value, at which the temperature of the water to be cooled is obtained.


“In addition to this duty, the vapour compressor extracts and compresses the water vapour to the pressure existing in the condenser to which it is passed, the condensate then being returned to the evaporator feed. Since the vapour volume varies largely with a slight difference in temperature, the plant automatically regulates itself and practically floats on the load.”

According to The Engineer’s report, the Alhambra plant was designed to eliminate 2,400,000B.Th.U. per hour, described as the equivalent to melting 200 tons of ice per 24 hours at 32oF, the compressor being operated at full load by a 185HP electric motor.

“The chilled water leaves the evaporator at a temperature of 45oF and is circulated to the spray washing plant at the rate of 800 gallons per minute,” The Engineer said. “The whole of the air admitted to the theatre will be thoroughly washed, cleansed, and dehumidified by a spray type air washer. Before entering the auditorium, the air will be suitably heated as conditions may demand, and the relative humidity adjusted. The complete plant will deliver 1.5 tons per minute of correctly conditioned air to the theatre. The air extracted will conveyed by ducts situated under the balcony steppings and stalls seats, and also through the proscenium arch and stage extracts. In total it will constitute some 75 per cent of the air admitted, the balance of 25 per cent being used to maintain a slight pressure inside the auditorium, thus preventing cold draughts from entering in winter.”