Designing Cooling &
Heating Systems

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Don’t forget that roof, Jim

Don't forget that roof, Jim

One large factory I looked around on a number of occasions had the “Don’t forget that roof, Jim,” scenario.

A big building – 100m x 25m x 6m tall – the construction? An Asbestolux roof with an air gap complete with plasterboard panels supported in a metal ceiling grid. Roof skylights gave a more ‘natural’ feel inside and helped illuminate the production lines beneath.

Lots of hot processes, essentially a bakery in one half and a packing hall in the other, modern equipment in an old building heating everything at one end and cooling it all down at the other.

That roof was the cause of so much grief, but every summer Jim and the company flogged on knowing they would lose production because the product wouldn’t set so they paid a night shift to make up for the time lost. Then the problem went away again until the next year.

Was it all down to the roof? I did some sums; the ‘U’ factor calculation came to

2.43W/m2K. My trusty chart showed that between June and September up to 90kW of heat transmission could be expected through the roof into the factory.

During June (highest solar aspect) 90kW would raise the internal air temperature by 4 to 5OC.

In winter, heat losses through the roof cooled the air around the ovens and reduced the gas burners efficiencies, they all needed ‘turning up’ so the product would bake. More gas, more money. So a Double Whammy!

Anyway the same roof, many years on – Jim who had stayed with the business, explained they had always had that roof problem – for the owners it understandably proved to be all too difficult; do they invest in the invariably oversized cooling system and possibly, heating solutions for the Winter – or ‘just’ replace that roof?.

Confused by U factors heat losses, call us  – apply some science and be sure!


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