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Mon Nov 24, 2014

A Tale of Two Cities (or one city and a sovereign city-state)

In September I went to Agadir, Morocco on holiday. Beautiful country, fantastic food and day after day of perfect azure skies. The temperature peaked between 28 and 30°C each day – it was sheer bliss.

The previous December my travels had taken me to Singapore. Beautiful country, fantastic food and day after day of perfect azure skies. The temperature peaked between 28 and 30°C each day – it was NOT sheer bliss.

Don’t get me wrong, I had a wonderful time and I have some amazing photographs – only none of them feature me. I spent the entire time looking frazzled. Frizzy hair, red in the face, puffing and panting – not the picture of elegance sipping Singapore Slings in the Raffles Hotel that I had previously envisaged. Every day felt like I’d just finished running a marathon.

Why such a difference?

The simple reason for these two extremely different comfort experiences is humidity. In Agadir the relative humidity (RH) averaged at 56% whereas in Singapore it was 82% or higher – in fact, one day it reached 96% and I spent most of the day darting in and out of air conditioned buildings.

Humidity is one of the major factors that affect our level of comfort. For instance, using the heat index calculator, 30°C with an RH of 82% feels like a stifling 38°C. However, the more comfortable RH of 56% in Morocco meant that the same 30°C felt only one or two degrees higher. At 46% it would have felt the same.

Why is high humidity such a problem?

The biggest reason for discomfort in high humidity is that your sweat (the body’s natural mechanism to cool down) cannot evaporate from your skin because of the high levels of moisture already in the air – the body continues to overheat which can lead to respiratory problems, cramps, drops in blood pressure, heat exhaustion and, in extreme cases, heat stroke, which can be fatal.

As well as the potential for overheating, high humidity in the home is also a great breeding ground for mould, dust mites, fungus and other nasties – it also exacerbates allergies and asthma and can cause damage to furniture and wooden floors.

There are many sources that have their own ideas about the optimal level of humidity in the home but, overall, they average out between 40 and 60% - which happens to be the range recommended by the Passive House standard. Outside of this range the potential for problems increases.

What can affect fluctuations in RH? 

  • Everyday domestic activities
  • Use of showers and baths
  • Natural transpiration of people, animals and plants
  • Temperature and weather conditions

How can we tackle this?

We need to design our homes so that the rising UK temperatures don’t cause discomfort and health concerns to their occupants. The greatest challenge is the cumulative causes of overheating, which involve accounting for the above listed factors causing high RH levels that are beyond our control.

Whilst we pay careful attention to the building design, we also need to ensure that any changes don’t adversely impact the energy efficiency of the dwelling.

There are certain cooling approaches, both passive and active, that can be investigated but we should keep in mind that humidity can have a far greater effect on human comfort than temperature so methods of dehumidification, including enthalpy, should be included in our discussions.

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