Dear Chris

For many years dancers have endured excessive temperatures in the Blackmore Gardens marquee at Sidmouth. This is in part because organisers have not given sufficient attention to opening ventilation side flaps. The Ham concert marquee has also been the subject of similar complaints. It has been increased in size and is now one of the larger structures of its type used in the UK. It is also in a very sheltered location.

Back of envelope calculations suggest that as the size of marquees increases the central temperatures might be expected markedly to rise. Do any STS readers know of any calculations for similarly sized structures in areas of the world where ambient temperatures can be higher? In central Europe or the USA for example? The calculations are straightforward when designing air conditioning but I can find little relevant on the internet for naturally ventilated marquees - except references to my own website and the rather obvious advice to use removable or roll up walls (and on two opposite sides), something that has been avoided at Sidmouth to help prevent onlookers enjoying the concerts for free!

Given that 1200 people generate, when stationary, around 100 kilowatts and on a hot day and in bright sunlight the roof might attain well over 35C thus becoming a radiant 'ceiling heater', ventilation becomes critical. This is prevented to some extent by the closed bar area that is one of the latest additions. This end of the marquee faces a prevailing wind direction. If the venue were to be used for ceilidh dancing then 100 kW could increase to 400kW and with peaks of maybe 500kW or more. In strenuous exercise, metabolic rate can increase to ten times the sedentary value.

Other UK dance venues also suffer from marked overheating even on cool nights, like some of the church halls at Sidmouth where there are too few openable windows. The previous venue for the Bath ceilidhs at the Sulis Club was notorious (again in a sheltered location with predominantly single sided ventilation) and at Stroud ceilidhs it proves essential to use the air conditioning.

I learnt via STS that the old social dance venue at Broadstairs also overheated.Can anyone provide a plan of the building or some photographs? The Met Office has warned of hotter summers so these issues may become more important in preventing heatstoke and possible death. Medical advice includes "avoid vigorous physical activities in hot and humid conditions". Festival organisers take note!

The Ham marquee is a focal point of 'the Hub' of Sidmouth's FolkWeek yet basic physics may have been overlooked in the quest for a 'vanity building project'. It is not so many years ago that no side flaps or doors were allowed on the eastern side - the local council having ruled that people trying to escape a fire might rush headlong into the river!

The design of the marquee in 2013 allowed for some but maybe insufficient cross ventilation - mirroring the perennial problem in Blackmore Gardens.

Stephen Wozniak
Sidmouth