SleepBreeze personal cooler
First of all why do we need to consider cooling. Basically, the habitability of a shelter will be governed by the ambient environment (solar load, ambient temperature and humidity, local air movement) and also by the number of occupants and any equipment (e.g. a stove) that gives off heat and moisture.
Solar load[edit | edit source]
This can be highly variable. It will depend on the angle of the sun as it impinges on the shelter's walls and roof. The location of the shelter is key to this. Obviously the angle of the sun is greater closer to the equator. Shape factors of the shelter are also worth consideration. For example, if the shelter has a long and a short axis there could be an advantage in a specific orientation of the shelter in relation to the sun as it progresses across the sky. So, to minimise heat gain, think about minimising the area exposed to the sun. The building materials used and the ability of their surfaces to reflect heat are important. Note, the traditional shiney space blanket has a plastic coating to it, so it's not as "reflective" as you may think. So, shiney doesn't necessarily equate to reflective.
Ambient temperature[edit | edit source]
Without active cooling, misting or heating the internal shelter is only ever going to follow the external temperature. During the day it will be be warmer than ambient and at night its temperature will drop in line with ambient temperature. The insulation provided by the shelter's walls determines how hot/cold it will get, and also how soon this will happen.
Ventilation (aka "fresh-air make-up") will accelerate temperature equilibrium with the outside. Fresh air is of course necessary to remove heat, moisture, CO2 and body odour derived from the occupants as well as, cooking odours, wood smoke and the waste products of fuel combustion.
Humidity[edit | edit source]
Along with local air movement this determines how effectively we sweat. Humidity is present in the air, but clearly without some fresh-air make-up in the shelter humidity levels will rise and the conditions become less tolerable. Note, apart from having an impact on our ability to thermoregulate, excess humidity in a shelter may also lead to mould growth in bedding and on the building fabric.
Vinay Gupta has documented an attempt in his Hexayurt to reduce the shelter's air temperature by misting the air (water droplets are sprayed into the shelter - the energy required to evaporate these droplets is derived from the air). The result was a temporary success. However, heat gain from the shelter walls and the occupants soon negated the effect. Also, the added humidity reduced the effectiveness of sweating. The bottom line is that misting does work, but you have to accompany this with a through-put of ambient air.
Furthermore, it is not uncommon in poorly ventilated shelters for a phenomenon known as "Shelter Rain" to occur. This is where condensation forms on the roof and walls which then falls as a precipitate onto the occupants.
We now turn to internal heat and moisture gains:
In a refugee shelter the occupants will be the main sources of heat and moisture. At rest each occupant will yield approximately 70 watts of heat into the shelter. In addition moisture will be derived from sweating and respiration. Moisture derived from sweat will depend on the amount of physical work undertaken and the ambient temperature. [insert figures]
Additional heat and moisture will be also be derived from cooking stoves. [insert link to stove's page].
Ventilation Solutions[edit | edit source]
From the discussion above it is probably a given that some degree of ventilation is needed in a shelter. We also accept that minimal power is available to achieve this. Hence we first look at adapting the shelter to achieve a throughput of fresh air. An obvious, but often neglected, requirement is that air must be let "out" of a shelter as well as "in".
Provision of a chimney and ventilation slats[edit | edit source]
Taking the Hexayurt as an example we suggest that a chimney placed close to the apex of the roof could easily be incorporated, along with ventilation slats cut into the shelter's walls. A short rectangular chimney could be formed from similar material to the Hexayurt's walls and duct taped together. Preventing rain entering through the chimney could be prevented by incorporating a cowl on top of the chimney. Ventilation could be controlled by raising the chimney when needed, the cowl "sealing" it when in the lowered position.
Rectangular slats might be cut into the walls of the shelter, with duct tape used as a hinge. The position of these slats would be no less than 0.5m from the base of the shelter as air temperature is higher close to the ground due to heat gain from the soil. Orientation of the shelter was discussed in the earlier section on solar heat gain. In terms of ventilation slats these might be positioned to utilise prevailing wind direction.
Active ventilation[edit | edit source]
In an earlier section the efficiency of sweat evaporation was discussed. Sweat evaporation from the skin surface is determined by local air flow velocity as well as humidity.
Where there is no power available, and natural ventilation is insufficient, a punkah could be used. This is an early type of ceiling fan with its origins in India. The punkah was operated by a rope by a wallah, often a child. Whilst undoubtedly effective at creating a throughput of air, this technique raises the issue of the appropriate use of manpower. Bearing in mind that we wish to raise refugee populations from menial labour to more sustainable economic activity, this technique may not be ideal in the long term.
Where minimal power is available the techniques mentioned above can be enhanced with a small fan cooler, such as our own SleepBreeze personal cooler http://web.archive.org/web/20180925042715/http://sleepbreeze.co.uk:80/. This is why fanning a heat casualty is always advocated. Further enhancement of this active ventilation technique are to wet the skin surface using tepid water. Caution is urged, however, to ensure that the water used is of a standard where misting it over a person would not contribute to the spread of disease. [insert link to potable water, water sanitation section]
In theory, the fan unit could also be used to provide active ventilation of the shelter, although the effectiveness of this would be dependent upon the size of the shelter. [insert link to stoves section]
In situations where the refugee camp is more settled then further enhancements can be made to heat / cool storage. I'll be updating this section soon.
Summary[edit | edit source]
In this section we have outlined the basics of shelter habitability and proposed some simple ventilation techniques.
To learn more about coping with heatwaves follow the link below which gives the UK's Department of Health guidance on the subject, much of which is highly applicable to the refugee shelter situation:
Authored by Andy Buxton, SleepBreeze Ltd.