Outdoor cooling is really a big challenge, particularly in hot climate regions. This is due to high ambient temperature, humidity and sun radiation.
What is outdoor cooling?
Outdoor cooling is the concept of cooling people or animals within open or semi-open areas. This can also be applicable to indoor areas and buildings where large volumes of fresh air (very high Air Changes per Hour (ACH) of 70 or more), are required.
Examples of instances where outdoor cooling would be needed:
Outdoor restaurant areas
patios
Smoking areas
Swimming pools F&B area
Bus stop stations
Zoo
Self and valet parking areas
Water parks
Construction sites
Outdoor shopping walkways
Stables
Milking station
Open to sky malls
Farms
Outdoor events and social media stands
School yards
Children playgrounds
Outdoor Sports
Jogging areas
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Why outdoor cooling is important
Increasing the comfort factor for people and animals is the key to having a successful outdoor facility operation. This will result in increased productivity and maintain customers’ satisfaction.
Take for example, smoking areas. As we all know, smoking is banned indoors, as per local regulations, almost all over the world. For the hospitality business it is very important to have outdoor smoking areas for their clients that still indulge. The big challenge is to obtain a reasonable level of comfort so that people can stay within those areas.
Another concept to consider is animal cooling. This will minimize the risk of heat stress and heat stroke. New studies results are confirming that cooling animals during summer will increase the productivity and profit, and can offer a significant improvement in their health.
Regarding Outdoor Sports, Events, and school yards cooling
It is essential to avoid heat stress in order to have successful activities outdoor. Children and the elderly are the most vulnerable sectors, but no group is immune to heat’s effects.
Outdoor cooling Challenge:
In reality outdoor cooling is difficult to achieve, but not impossible. Thermal convection between the surrounding (ambient) air dilutes the cold air stream form traditional cooling methodologies. There are other solutions which we will discuss below.
Completely controlled ambient air temperature is much easier to achieve in an indoor environment. Instead of cooling air that will quickly escape, the building acts like a container and retains the cool air, making the whole process far less expensive.
So is outdoor cooling a kind of “mission impossible”?
It is possible, with the right design, to cool zones or areas with continuous direct cold air streams, or, to put it another way, outdoor cooling is a form of extremely localized spot cooling.
Complications
Chilled air temperature will start increasing while traveling through surrounding hotter air; it will keep getting warmer until it attains ambient temperature.
Air flow attenuates quickly over short distances
Air velocity/flow-loss due to natural wind interference
Sun radiation
A cold air supply system running continuously would result in massive power consumption, more failure points and downtime
High velocity cooling systems can raise excessive dust
The sheer amount of air treatment required, with little chance for recirculation
Outdoor ducts and air devices, insulation, and thermal losses
Traditional air exchange rate (ACH) calculations not applicable
Condensation problems
Example from real life experience test:
In order to achieve reasonable thermal comfort zone for a simple 30 square meter area, as per traditional indoor cooling needs, requires about 5000 BTU at 100 Cubic Feet per Minute (CFM). In an uncontrolled outdoor scenario, you would need a minimum of 25,000 BTU /1000 CFM for the same effect.
In essence you would need to supply on the order of five times more cooling capacity, with ten times the original air flow to achieve the same effect. It is also notable that the effective range for cold air diffusion in an uncontrolled outdoor environment is only three to four meters, as seen in the following charts.
Temperatures vs. distance outdoor test (Dubai UAE) September 2014 with multi channels data loggers
Test 1: Ambient temperature (Dry bulb) 36; jet Diffuser Size 350mm
Distance In meters 0 1 2 3 4 6 7
Temp 19 21 23 26 29 33 36
Test 2: Ambient temperature (Dry bulb) 41; jet Diffuser Size 300mm
Distance In meters 0 1 2 3 4 6 7
Temp 23 25 28 34 37 41 41
Test 3: Ambient temperature (Dry bulb) 33; jet Diffuser Size 450mm
Distance In meters 0 1 2 3 4 6 7
Temp 21 22 24 26 29 31 33
Outdoor cooling solutions:
Dry Fans
Chilled Water System, District Cooling.
Portable or Packaged Air-conditioning Units
Evaporative Cooling Systems
Misting Systems, Wet Fans
Hybrid Systems
Dry Fans:
Dry fans are a low cost and effective solution for low to medium warm climate, but will not help much in hot climate. Directing air flow to people’s bodies will increase human body self-cooling with sweating evaporation and wind-chill effect. *fans must be IP rated for outdoor use.
Chilled Water System:
Chilled water system is a very good solution for outdoor cooling. chilled water supply from Local chillers or from district cooling supplier can be used with suitable chilled water coil cold air Diffusing systems with or without floor cooling system.
Portable or Packaged Industrial Air-conditioning Units (spot coolers):
The small off-the shelf portable air-conditioning units can’t be used because they are less than 18,000 BTU. Only industrial grade air-conditioners possessing powerful compressors, with large air flow and cooling capacity can be used.
Evaporative Cooling Systems:
Evaporative cooling systems are the best possible outdoor cooling solution known, due to low power consumption and possibility to provide large amounts of cold air.
Unlike using evaporative cooling for indoors, causing humidity increase problems, the humid air supplied with evaporative coolers is not a problem for outdoor cooling, since humidity will dissipate while mixing with ambient air.
Evaporative Coolers Types: Direct (DEC), Indirect (IEC), Indirect-Direct (IDEC)
Misting systems, wet fans:
Misting or fogging systems are a form of evaporative cooling system based on high pressure forcing water through very small orifice nozzles; this system produces very fine water drops (10 microns) which will evaporate very quickly, without the need for wet media such as those that are used in traditional air coolers.
Wet fans or mist fans are simply dry fans with mist.
Hybrid Systems:
The goal is to get the benefit from mixing all above solutions in order to obtain the max efficiency.
Examples:
using Chilled water misting
using Chilled water with indirect direct evaporative coolers
-using DX with Evaporative coolers
Outdoor cooling design concepts:
Direct air stream:
o Aligning the air stream to reach the destination area will guarantee people thermal comfort making sure they feel the cold air breeze
High Velocity air flow:
o Higher velocity will reach more distance and would help people to feel the cooling effect and get the benefit from wind-chill effect.
More air flow:
o Greater air flow will guarantee thermal comfort for larger spaces
Use of Wind barriers:
o wind barriers will help to reduce the hot air entering the site
o they will reduce the interference with your contained cold air stream
Use of sun shades and umbrellas: Shades will do three great jobs:
o first blocking the direct sun radiation heat
o it will insulate the area from top
o better containment of cold air
Avoid directing the cold air diffusers against the natural wind direction.
Minimize the distance to destination:
o Minimizing the cold air travel distance to destination area will reduce the Thermal convection while cold air stream is going through high ambient air temperature on the way to destination
Think smart / think green:
o Try to avoid wasting energy; remember that you are not going to cool the whole area
o try to distribute the diffusers only where people are sitting, walking or congregating
o avoid unused areas
Smart automation:
o By using automated dampers, louvers and solenoid valves, and splitting your system into smaller zones and sub-systems, vie using sensors and smart automation, you can make the system work only at the right place at the right time! This should result in an immense cost savings.
Insulation:
o Insulation strongly affects outdoor cooling systems efficiency and performance
o Study different materials, and efficacy
o Reusability should be a serious consideration
