18
$\begingroup$

I think, here is the main problem the difference between the internal and the external temperature.

For example, in Saudi Arabia, in 50 C, a passive house needed probably much sophisticated planning as in Paris.

Compared to the traditional cooling systems, in the second case is enough only to get a cooling system with bigger power. I think, they are much more scalable.

Is it anyways possible?

$\endgroup$
16
$\begingroup$

A yahkchal is an example of a type of passively cooled building in Iran

enter image description here

They utilise a combination of passive evaporative cooling and thick thermally insulating walls in order to keep the interior temperatures low enough.

First, wind is directed into underground aquifers known as qanat. They are then cooled due to the low humidity desert air causing water to evaporate. The cooled air then flows through the interior of the yakhchal, cooling the interior.

enter image description here

The thick insulating walls (filled with earth and various insulating materials such as straw and feathers) help to insulate the cool interior from the hot exterior, therefore maintaining a low temperature inside the yakhchal.

$\endgroup$
8
$\begingroup$

Insulation, shade, the use of low thermal conductivity materials and utilising any cool breeze at any time of the day are going to be key to passively cooling buildings in a hot climate.

Different solutions will be more applicable to houses than non residential buildings. The other thing to consider is whether the climate hot and dry or hot and humid.

In hot dry regions of Australia passive cooling measures used until the mid 20th Century included thick exterior walls, high ceilings, verandas, double roofs and where double roofs weren't used roof ventilators. The verandas and double roofs off shade.

In the hot humid parts of Australia houses were built on stilts, approximately 2m to 3m high. This continued until the late 1970s in Darwin. Such houses were also built to encourage airflow inside by have louvred internal walls and sometimes short height internal walls so the rooms looked like cubicles in modern day offices.

http://melbourneblogger.blogspot.com.au/2010/01/traditional-queenslander-house.html https://en.wikipedia.org/wiki/Queenslander_%28architecture%29 http://www.territorystories.nt.gov.au/handle/10070/19572

One thing that is sometimes overlooked in the passive cooling of buildings is the used green foliage gardens to offer shade and to reduce the amount of radiated and reflected heat reaching buildings.

$\endgroup$
  • $\begingroup$ +1 for foilage. just planting a tree in the right place can make a big difference. Where I live, houses are built partially into a hillside where possible. In the summer months, the rear part of the house remains cool due to the insulation caused by the earth. $\endgroup$ – user133 Jan 22 '15 at 13:25
4
$\begingroup$

Diurnal swings, i.e. temperature differences between day and night, are also an important consideration in hot climates.

If the temperature at night drops to something acceptable, you can use night purge to cool a thermal mass (e.g. concrete slabs or walls, phase change materials if you'd like to get fancy). This works well together with a well insulated envelop. In essence what @MarchHo talked about.

If on the other hand temperatures are high 24/7 (the tropics come to mind), you would avoid using thermal mass as it will stabilise the high temperatures and make it more difficult to cool down the building by other means. Your main source of passive cooling are breezes. Insulation to the roof and extensive shading will be important. If possible, the floor could be raised to allow breezes extracting heat from both sides. In addition to cooling loads, dehumidifications loads will be significant and are hard to deal with passively.

All this is based on common rules of thumb; there might be some smart design solutions that achieve comfort in different ways.

Alternatively you can go underground as for example in Coober Pedy. Find some images here.

$\endgroup$
3
$\begingroup$

Farther from the equator, a passive house is mainly a very well insulated house with good exposure to solar lighting for passive solar heating.

However in hot climate, one has to rethink completely the design.

Here what matters more is the way you can use the night "cool" air to cool the house.

Also you have to take great care to shading as best as you can all the exposed surface to the Sun.

Finally, active systems (like air conditionning) can help you reach the desired level of comfort.

Something else is equally important: you do not need to cool down the house as much as you think. A temperature difference around 10-15°C with the outside is already a lot.

$\endgroup$
  • 2
    $\begingroup$ I thought aircon systems were excluded by the passivhaus system? $\endgroup$ – EnergyNumbers Jan 21 '15 at 16:39
  • $\begingroup$ There is a difference between the passivhaus certification and passive house design. The first is german certification with requirements to be met, the second is a set of principles to apply to try and lower the energy use. $\endgroup$ – gromain Jan 27 '15 at 9:53
  • $\begingroup$ I understand: and doesn't the "passive" in passive house design preclude AC? $\endgroup$ – EnergyNumbers Jan 27 '15 at 10:03
  • 1
    $\begingroup$ Oh, yes, I get it. Well, it depends who you are talking to. Usually, yes. However in some cases it's not enough to be only passive and that's where active systems can come in. So, yes, you shouldn't have AC in a passive house, but an already passive house equipped with AC will perform way better and way more efficiently than a normal house equipped with the same system. $\endgroup$ – gromain Jan 27 '15 at 13:43
1
$\begingroup$

In order to build a passive house you have to limit the final energy use for cooling to 15 kWh/m² per year and your primary energy use for HVAC and lighting has to be less than 90 kWh/m² per year minus the deduction for compactness, so let's say around 70 kWh/m².

I guess getting to 15 kWh/m² final energy use for cooling (i.e. the heat extracted from spaces including all the insulation losses) in a climate like Saudi Arabia is almost impossible. In a classic building technique it would mean very thick insulation and small windows in order to limit solar heat loads through fenestrations.

The other criterion however, the primary energy use, would not be that difficult to meet because it represents the balance between the primary energy used and generated on-site by renewables (e.g. PV panels). So if your vapour compression cooling system uses 100 kWh/m² per year and your PV panels produce 40 kWh/m² per year (per m² of building net surface, not per surface of panels) you get to 60 kWh/m² in total which is quite good. If your PV panels create 100 kWh/m² then your balance is 0 and you have a net zero energy building.

So in conclusion, it does not make really sense to apply the 15 kWh/m² rule in Saudi Arabia. This rule (like the whole passive house concept) was made up in Germany and is a completely political choice which does not have any meaning (it could also be 10 or 25 kWh/m²). What is more important is the net primary energy use and this one you can keep in the passive limits. In fact, to build a building that has a low net primary energy balance Saudi Arabia is a good place because you have plenty of sun and you can generate a lot of green electricity on site with PV panels, something that is not possible in cold climates where the solar energy is not so abundant.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.