Evaporatif Klima Hakkında Bilgiler

www.erdincklima.com The Concept Evaporative cooling is a process in which hot dry air is cooled by evaporating water into it. Air naturally soaks up water. This water requires a great deal of energy to change from a liquid to a gas. This energy has to come from the air during this evaporation. The effect of this is that on a typical hot day in the UK, air at 30°C and 35%RH will be cooled down to 20 °C. This natural process is exploited by all mammals – sweat evaporates from the surface of the skin and the skin is cooled. For thousands of years it has been used to cool buildings and tents by hanging a wet cloth over an open door or window. As the air passes through the weave of the cloth the air is cooled and the atmosphere is made more comfortable.
	A modern evaporative cooler consists of a fan which draws hot air across wet filter pads and discharges the cool air to its point of use. As warm air passes over wet filter pads water naturally evaporates into the air. The air is cooled as it gives up the heat required to evaporate the water.
A more detailed explanation of the above is given in Section 9 Why does an evaporative cooler work in a UK Climate? The pattern of the relationship between temperature and relative humidity on a typical hot day in Northern Europe is shown below.
It can be seen that the highest temperature coincides with the lowest humidity. This gives the greatest cooling when it is needed the most. This also has a smoothing effect on the temperature of the air coming off the cooler which leads to more stable conditions. Comparison with Conventional Air Conditioning Evaporative Air Cooling Refrigerated Air Conditioning Uses only 10% of the electricity compared with conventional air conditioning Uses large amounts of electrical power because of compressor. As temperature rises efficiency improves As temperature rises efficiency reduces Cooling capacity is only limited by the air conditions. Up to 50KW of cooling can be achieved with only 1 KW of electricity used Cooling is limited by theoretical Coefficient of Performance which means a maximum of 3.5 KW of cooling for 1 KW of electricity consumed Open doors and windows do not affect performance Open doors and windows significantly reduce performance. Uses no harmful gases for its function. Uses environmentally harmful gases. Avoiding relative humidity below 50% significantly reduces static electricity problems Leads to low relative humidity which can create high static electricity conditions Few moving parts – one fan, one pump and three solenoid valves Many moving parts including complex and expensive components such as the compressor Easy and simple to service. More difficult and expensive to service. Always supplies 100% fresh air. Only supplies about 15% fresh air. 85% is re-circulated. It is not fresh. Air only cooled once. Air cooled many times. Has no upper limit on temperature High ambient temperatures can lead equipment to shut down due to compressor overload Lower purchase cost. Higher cost to purchase. Have bigger fans - pump large amounts of air. Smaller fans - pump less air. Temperature reduction limited by ambient Relative Humidity. At higher Relative Humidities cooling is reduced due to greater latent heat load compared to sensible load. Provides flow of fresh cool air. Provides cool, recirculated, stale air. Provides stable relative humidity levels which are more comfortable to work in Can lead to low Relative Humidity which is not comfortable. Simple to create positive pressure in buildings giving hygiene and control benefits More difficult to create positive pressure with recirculation systems Evaporative Cooling Performance Air and Water Air acts like a sponge to water. Just as spoe is limited in the amount of water it can absorb air is also limited. A key difference is the hotter the air the more water it can support before it becomes ‘saturated’ and can hold no more water. It can be seen from the data below that this amount of water dramatically increases as the temperature increases. The maximum amount of water supported by air at atmospheric pressure is: 0°C 10°C 20°C 30°C 40°C 5g per cubic metre 10g/m3 20g/m3 34g/m3 62g/m3 The term relative humidity refers to the actual amount of water in the air compared with its maximum or saturated value, and is stated as a percentage. e.g. Water at 30°C with 17g of water in it is 50% RH Many engineers use a Psychrometric chart to understand the relationship between air and water. This chart is explained in detail section 17 Theoretical Performance The performance of an evaporative cooler is dependent upon both the temperature and the relative humidity of the air passing over the pads together with the efficiency of the pads. The theoretical cooling is shown below. The higher the temperature and lower the relative humidity the greater the cooling effect Actual Performance The graph below shows an actual example of performance of a cooler. Legionnaires’ Disease Background It is estimated that there are 20 million evaporative cooling systems in the Western world. There has never been a documented case of Legionnaires’ disease associated with a wetted media evaporative cooler. Legislation in the United Kingdom is more stringent than anywhere else in the World. EcoCooling has developed the equipment and systems to comply with this legislation in a practical and relevant format. Specific Legislation Relating to Legionnaires’ Disease In addition to the Health and Safety at Work Act (HSWA), the Control of Substances Hazardous to Health Regulations (COSHH) and the Management of Health and Safety at Work Regulations (MHSWR) the HSC produce an Approved Code of Practice (ACOP) Legionnaires’ Disease: The control of legionella bacteria in water systems L8. It is the legal duty of employers and the responsibility of the managers of premises to comply with the above. Compliance with Legislation: The steps required in fulfilling statutory duties are: Completion of a Risk Assessment The preparation of a scheme for preventing or controlling the risk Implementation, managing and monitoring of precautions Maintenance of records Appointment of a responsible manager About Legionnaires’ Disease What is legionnaires' disease? Legionnaires' disease is a type of pneumonia. It was named after an outbreak of severe pneumonia which affected a meeting of the American Legion in 1976. It is an uncommon but serious disease. The illness occurs more frequently in men than women. It usually affects middle-aged or elderly people and it more commonly affects smokers or people with other chest problems. Legionnaires' disease is uncommon in younger people and is very uncommon under the age of 20. About half the cases of legionnaires' disease are caught abroad. The other half are the result of infections acquired in the UK . How do people get it? The germ which causes legionnaires' disease is a bacterium called Legionella pneumophila. People catch legionnaires' disease by inhaling small droplets of water suspended in the air which contain the Legionella bacterium. However, most people who are exposed to Legionella do not become ill. Legionnaires' disease does not spread from person to person. Where does it come from? The bacterium which causes legionnaires' disease is widespread in nature. It mainly lives in water, for example ponds, where it does not usually cause problems. Outbreaks occur from purpose-built water systems where temperatures are warm enough to encourage growth of the bacteria, eg in cooling towers, evaporative condensers and whirlpool spas (tradename Jaccuzi) and from water used for domestic purposes in buildings such as hotels. Most community outbreaks in the UK have been linked to installations such as cooling towers or evaporative condensers which can spread droplets of water over a wide area. These are found as part of air-conditioning and industrial cooling systems. What measures are there to control legionnaires' disease? To prevent the occurrence of legionnaires' disease, companies which operate these systems must comply with regulations requiring them to manage, maintain and treat them properly. Amongst other things, this means that the water must be treated and the system cleaned regularly. What are the symptoms? The symptoms of legionnaires' disease are similar to flu high temperature, feverishness and chills; cough; muscle pains; headache; and leading on to pneumonia, very occasionally diarrhoea and signs of mental confusion How is it treated? The illness is treated with an antibiotic called erythromycin or a similar antibiotic. The EcoCooling Approach to Managing Legionnaires’ Disease Evaporative Cooling System Design: The design of all EcoCooling equipment takes the ACOP guidance into account. This includes the following which would not normally be included on a standard installation of an evaporative cooling system: A water treatment system A process control system minimising build up of potential contamination Materials of construction which are corrosion resistant System Management: Work Space Cooling provides all clients with the following: A fully documented risk assessment package A prevention and control system for water management and equipment care based on the following principles Hygiene and Evaporative Coolers EcoCooling believes that hygiene is the most important factor in providing a safe and secure system which provides compliance with legislation and peace of mind. Hygiene The maintenance of a clean and safe evaporative cooler is achieved by the following: Avoidance of stagnant water Low water operating temperature Avoidance of corrosion and scaling No production of aerosols Maintenance Use of a biocide or UV Each of the above points will be detailed below Avoidance of stagnant water: Since no dead legs exist in the system no stagnation occurs during normal operation of an EcoCooling evaporative cooler. When a unit is switched off the system automatically drains. A low level probe constantly monitors the water level when shut down. When a system is first powered up the first operation is to empty the sump. Low water operating temperature: The temperature of the water circulating in the evaporative cooler is approximately the “wet bulb temperature” of the air passing over the filters. In practice this means that, in a temperate climate, the water temperature rarely goes above 20 0C as shown even when the air on temperature exceeds 35 0C It is generally accepted that Legionella is not a risk with water temperatures less than 20 0C Avoidance of corrosion and scaling: To prevent corrosion all water contact surfaces are either plastic or non-ferrous. EcoCooling evaporative coolers measure the water usage. When the water reaches a set point , determined on commissioning according to the local water quality, the sump empties automatically and replenishes with fresh water. This has the effect of preventing scale and removing of contaminants filtered from the air. During this drain cycle the sump empties completely to assist in the removal of any sediment which may be present in the sump. Use of Biocide: Growth of organisms filtered from the air is suppressed by supplying the evaporative cooler with water with a low level of biocide. No production of aerosols: The design of the EcoCooling coolers is such that only pure water evaporation occurs as the air passes over the filters. This removes the mechanism for the transmission of infections such as Legionnaires’ disease The maximum air velocity in an EcoCooling cooler is 1.9m/s. From the chart above it can be seen that the Munters maximum speed for avoidance of droplets is 3m/s. Thus a safety factor of over 50% is achieved. Maintenance: By the implementation of a programmed maintenance system the standards of hygiene are continued to provide a safe and secure system. Detailed maintenance procedures are provided to all users. Generic Risk Assessment The end user is ultimately responsible for performing their own risk assessments. This generic document is intended to provide technical details to support these assessments. Background The purpose of this document is to provide an understanding of the legionella control in EcoCooling evaporative coolers. Government guidelines which provide the basis for both design and risk assessment are explained. The prevention plan demonstrates the EcoCooling approach Government Guidelines With reference to the HSE publication ACoP L8: Legionnaires’ disease: The control of legionella bacteria in water systems, the following is the section which describes general methods of legionella prevention In general, proliferation of legionella bacteria may be prevented by: (a) avoiding water temperatures between 20 0C and 45 0C – water temperature is a particularly important factor in controlling the risks: (b) avoiding water stagnation, which may encourage the growth of biofilm; (c) avoid the use of materials in the system that can harbour or provide nutrients for bacteria and other organisms; (d) keeping the system clean to avoid the build-up of sediments which may harbour bacteria (and also provide a nutrient source for them); (e) the use of a suitable water treatment programme where it is appropriate and safe to do so; and (f) ensuring the system operates safely and correctly and is well maintained This document shall detail the approach taken to the above by EcoCooling in the design, commissioning, operation and maintenance of EcoCooling evaporative coolers. Note: This document is not intended to replace a risk assessment produced as a requirement of HSE ACoP L8 – Legionnaires’ disease: The control of legionella bacteria in water systems Prevention of Legionella in Evaporative Coolers Note that the following only applies to EcoCooling evaporative coolers. (a) Water Temperature Monitoring of the water the circulating water temperature shows that with air on temperatures to the cooler up to 40 0C the temperature of the water in the sump does not normally exceed 20 0C in the UK climate. Data demonstrating this is shown in the chart below: The above can be explained by the circulating water approaching the ‘wet bulb temperature’ of the air. In temperate climates the ‘wet bulb temperature’ rarely exceeds 20 0C and, in these rare instances, remains above this temperature for only a few hours. Note that when the cooler is switched off the sump automatically drains. This prevents the water rising to ambient temperature which may be in the 20 0C to 45 0C range. (b) Stagnation During normal cooling operation the water continuously circulates. The design of the cooler avoids any dead legs and so stagnation does not occur. When the unit is not operating the sump automatically drains. The unit is fully self draining and therefore no stagnation is possible. (c) Materials of Construction With the exception of the filter pads all water contact surfaces are manufactured from plastic or non ferrous materials. The Munters CelDek filter pads are manufactured from a cellulose material which is treated with ‘anti-rot' salts to resist biological deterioration and to give high absorbency. It is a rigid, self-supporting product. The pads are examined during programmed maintenance and replaced as necessary. (d) System Cleanliness As water evaporates both the levels of dissolved salts and solids increase. The volume of evaporation is measured using four level probes and, when a set concentration is reached, the sump is completely drained removing both the water which is approaching the scaling point and any other sediment or particles in the system. The sump is then refilled using fresh, clean water. Programmed maintenance includes cleaning of all water contact surfaces. (e) Water treatment programme Bromination can be added to provide additional microbiological security Whilst Legionella is not considered to be a risk below 20 0C other organisms can grow in these conditions. The purpose of a biocide or UV is to prevent the formation of bio-films which could play a role in the support of legionella bacteria. A brominator can be added which provides a residual minimum bromine level of 0.5 ppm in the sump. The process control system, using a system of level probes to calculate the concentration of water is set to prevent scale formation. (f) System Operation and Maintenance Operating instructions are provided with each installation. These include: Operating Instructions Brominator operating instructions Bromine level testing instructions EcoCooling can provide all chemicals and testing equipment required for the above. A detailed maintenance procedure is used for the cleaning, sanitisation and validation of the operation of the coolers. Summary The overall level of risk is dictated by the quality of the air being cooled. It is the air that can provide the seeding of legionella and nutrients for growth. With clean air the units are very low risk when all of the prevention and control activities described are adhered to. Generic Prevention and Control Plan Precaution Measure Action Avoid spray Design velocity of air over filter pads must not be exceeded No unauthorised or unspecified components to be used Water in unit must not enter fan Water level to be set to specification Unit to be installed horizontally Keep temperature of water below 20 0C Use fresh potable water Check on installation Drain when not in use Unit to be configured to drain when not in use. Avoid stagnant water Drain when not in use Unit to be configured to drain when not in use System must fully drain Unit must be installed horizontally Water presence must be monitored Use safe materials of construction All water contact materials shall be plastic or non ferrous (except pads) Use only specified components Keep water and system clean Do not allow salts to build up Use control system to monitor water concentration and drain automatically Do not allow solids to build up Solids removed as part of salinity control System should be cleaned of sediment as part of maintenance plan Minimise contamination from new installation Sanitise unit prior to use Prevent bio-films developing Use water treatment Prevent bacteria growth Use water treatment Use water treatment Biocide treat all incoming water Install brominator to treat all incoming water Maintain biocide concentration in system Make regular checks on bromine level Operate water system correctly and safely Adhere to instructions Provide end user with full documentation Installation Commissioning Operation Maintenance www.erdincklima.com