As summer temperatures rise, concern rises also over the rising temperatures in the underground environment of overcrowded metro systems that include above and below ground sections and have no sub-surface cooling systems. Following on from his previous papers, Calvin Barrows, makes the case for painting trains with high-performance solar reflective paint and fitting low emissivity glass windows as a cost effective method of addressing the issues retrospectively in older metro systems.
Even though we all experience the effect of sunshine in summer, there does not appear to be more than a superficial appreciation of just how powerful solar irradiation can be. When the sun is at its zenith, direct sunlight at earth surface is about 1050 W/m2. This is supported by monitored and observational evidence. The power of the sun is also affected by the angle of incidence, which reduces its intensity when it is at shallower angles. For example, at a 45° angle of incidence, although solar radiation can cover a 40% greater area, it is then 30% less intense than when at its maximum angle of incidence of 90°. Consequently, how this changing intensity might affect trains also needs consideration.
Professors Piercarlo Romagnoni and Fabio Peron of the Università Iuav di Venezia produced a factsheet which examines the temperature impact of solar radiation on thermal insulation materials for roofing applications. Although some train roofs are not insulated, this factsheet gives an indication of the potential external skin temperatures.
I think I left a comment and link to a Calvin Barrows article on IanVisits website. Calvin Barrows thinks it`s the suns heat that causes overheating on the tube as the Glasgow Subway, 3rd oldest underground railway in the world opened in 1896, which has two lines completely underground unlike the tube had an average temp of 16°C in 2018 even during the 31°C summer heatwave, however I don`t understand why the average temp has risen from 14°C in 1900s to 30°C in the summer nowadays on the London Underground if his theory is correct unless there is heating from the sun and decades of gradual heating of the tunnels. Solar canopies could be installed at tube depots and even over the tracks which will also reduce the amount of snow and leaves that fall on the lines. New buildings built over the tracks should help however one New York Subway depot (Hudson Yard ?) with new office skyscrapers and other buildings, ventilation fans had to be installed because of the excess heat from the trains in a now enclosed space.
Solar reflective paint which reflects infra red heat but allows visible light through used by the solar cells, also increases the efficiency of solar panels which work better at lower temperatures,so trains with pv panels in Byron Bay, Australia and India could use the paint. I don`t know if it`s worth putting pv panels on tube trains that only run partly on the surface but the solar panels will function as insulators reducing heating.
Indian Railways now plans to use solar farms rather than put the pv panels on the trains due to the weight but I think heavy rooftop pv panels that are installed on houses are used after looking at photos of the trains and not the specially developed lightweight ones on the Class 600 train in Byron Bay and on some electric and hybrid cars. SNCF also announced a month or two ago a plan for new solar farms to power trains in France.
I don’t think he is denying that the heating up of the clay is relevant to the internal temperature. But he points out that there is a large difference between the interior temperature of the deep tube from winter to summer. So it must be heat entering the deep tube in the summer that is driving that seasonal temperature difference. If we can substantially reduce the seasonal factors that allow heat entry from outside, then we can reduce the seasonal cycle of interior temperatures, and the summer temperature will be nearer the winter temperature – and this doesn’t involve increasing the winter temperature. So I can’t fault the logic of that.
He claims we can make a large difference to the amount of extra heat entering in the summer, because it mostly enters in the form of piston action pulling in external warm air at the tunnel portal, and the solar heat acquired by the rolling stock and radiated when inside the tunnel. There are methods of substantially reducing both of those. So, taking such actions will make a large difference to the summer temperature in the tunnels, and also slow the year-to-year acquisition of heat by the clay. Given that the clay can conduct away a certain amount of heat, it might even suffice to get back to an equilibrium.
It occurs to me if the tunnel portal measures to reduce sucking in warm air were of the kind you could switch on and off, you might want to switch them off when the temperature was cool outside, like in the early morning in the summer.
Hi Jason and Ivan
Thank you for your comments. I’d be happy for you to contact me at
[email protected] to move this matter forward.
This is the link to Rail Magazine’s Guest Column, which raises a new point about ballast being irradiated and reflecting it to the undercarriage and underside of the train; it is based on my presentation for train manufacturers to deliver to their customers. https://www.railmagazine.com/special-reports/innovation-issue-881. It’s on pages 20 & 21
Please also see this link. https://www.bbc.co.uk/programmes/p07qyjl5
Regards
Calvin & the Moderators
A security & technical point …
May I respectfully suggest that putting a “home” email on an open board is a security risk?
And that if one wants to solicit communications, then please put in the form:
firstname DOT secondname AT isp_name DOT co DOT uk – with inserted spaces, as I have just demonstrated?
Thanks Greg T for your concern. I apologise if I broke ant rules about leaving my e-mail address in a comment.
Because I have wanted to encourage feedback i have made this particular e-mail address public in my papers as restricting it would only frustrate any responses. Hence this particular e-mail address is easily obtainable.
A simpler explanation! https://citymonitor.ai/community/public-health/london-undeground-overgound-heat