Optimal Use of Air Conditioner May 2015
Introduction The electric power is the most important requirement of modern contemporary life. Advanced countries witness enormous progress in this area. The Kingdom of Saudi Arabia, similar to other countries, had achieved tremendous leaps on the electric power utilization and managed to cover most of its territories. These services moved forward alongside great developments that the Kingdom is trying to accomplish in all its regions. The state had spent billions of Saudi Riyals to establish power generating plants, transmission and distribution substations aimed at delivering remarkable electric power services to all its customers and providing comfort to the citizens and residents of the Kingdom. Our valued customers, however, take the responsibility for utilizing these services moderately and conscientiously so that the benefits may cover all of their specific needs without waste or excessive use of this blessing from God among other greatest graces that God has bestowed upon mankind and avoiding extravagance or excessiveness in all aspects and affairs of life. The amount of electricity consumed and the amount of money we paid for this valued service are the results of our usage of electrical appliances. However, electric power rationalization means reducing the electrical loads in power plants and electric networks, thereby contributing to uninterrupted supply of electricity, saving large sums of money, and preserving the environment. Rationalization of energy consumption provides electricity to others. Air conditioning accounts for the largest segment of power consumption; the statistics on this issue indicate that 60% of the monthly power consumption during the summer months go for air conditioning, a percentage that is too high. 2
Definitions and Units Air Conditioning: This process is achieved by transferring heat energy from inside the room to the outside by means of an air conditioner. British Thermal Unit (BTU) It is the standard thermal unit of measurement and is defined as the amount of heat energy needed to raise the temperature of one pound of water (454 g.) by one degree F (0.55 degree C). Air Conditioning Capacity (by tons) It means the ability to transfer 12,000 BTUs per hour. An air conditioner with a 1.5 ton capacity is capable of transferring 18,000 BTU per hour at a certain temperature. Similarly, a 2-ton air conditioner transfers 24,000 BTU per hour, and so on. Energy Efficiency Ratio (EER) It is the result of dividing the maximum cooling capacity (BTU/hour) by the appliance total electrical input in watts which ranges between 5.4 to 11. The higher the ratio, the more cost effective the appliance will be. By properly employing this ratio, we can evaluate the appliance efficiency in terms of the consumed energy. Types of Air Conditioners and their Components: There are many different types of air conditioners. The following table shows the most frequently used types with their approximate BTUs. BTU Type of AC System Window Type Room A/C Split Type Air Conditioner Wheel Units Compact Central Units Central Air Handling Units Central Units BTU/hour 12000-24000 18000-30000 42000-120000 36000-192000 192500-741700 Ton 1-2 1.5-2.5 3.5-10 3-16 16-60 10-1600 3
It is worthwhile noting that the above BTUs depend on the exterior temperature upon which the design is made. For instance, the efficiency of a 24000 BTU/hr air conditioner at 35C ambient temperature will be much more once it operates at 50C external temperature. As mentioned earlier, there are many types of air conditioners using refrigerants which basically perform the same function and with almost the same components. We shall look into the most common type, the window type air conditioner. Window Type Air Conditioner: Window air conditioner consists of four main components: 1- The Compressor 2- The Condenser 3- The Evaporator 4- The Fans It is installed and fixed externally so that the compressor, the condenser, and the condenser fan are outside the building while the evaporator coil and evaporator fan are directed to the inner side of the building. Compressor To the room Air from inside the room 35 C Low pressure vapor High Low 25 C Exterior temperature 45 C High Pressure Vapor Heat expel coil 55 C valve Inside the room Outside the room 4
Window Type Air Conditioner Operation Period: The basic operation of an air conditioner can be summarized in the use of refrigerant as the main assistant in transferring heat from and into the building. And as the summer temperature inside the building is higher than the average human thermal level of comfort, we operate the air conditioner to cool down the heat inside the building. The compressor pumps the refrigerant to flow through the condenser coil where, with the aid of the condensing fan, the heat-expel process takes place causing the refrigerant to condense from gaseous state to liquid state. At this stage the refrigerant in liquid state passes through the evaporator coil. It is at this point when the evaporator fan allows indoor air to pass across the coil causing it to cool down. The cooled air is then delivered to the inside of the room. As this happens, the liquid inside the evaporator coil absorbs heat from the coil causing it to turn into gas state and returns to the compressor to replicate the same cycle while the air conditioner is in operation. The compressor pumps the refrigerant for longer periods as long as the temperature inside the room is higher than the desired temperature. The preferred temperature level can be freely set using a regulator called the thermostat. Thus, if we know that the compressor has a power consumption rating of 2,400 watts and that the air conditioner fan is rated at 200 watts, we can assume that the compressor s power consumption in one hour is equal to that of the fan s power consumption in over 12 hours. We then realize that the common cause of high electric bill from one month to another in the summer months is the compressor s running time. When the ambient (external) temperature is high e.g. at 45C level, it follows that the difference between the desired room temperature (25C) temperature and the ambient temperature will be high. And in order to decrease the difference in temperatures, the compressor has to run longer. Likewise, if a given ambient temperature is less than 35C, the resulting difference between the desired room temperature and the ambient temperature will be less. In this example, the power consumption is lower than the previous example. This difference can be well illustrated by approximation based on the compressor s capacity of 2.4 KW and the fan capacity of 0.2 KW as follows: At 45 C Temperature Period Compressor On Period Compressor Off Compressor Capacity (Watt) Fan Capacity Operation Hours 5
At 35 C Temperature Period Compressor On Period Compressor Off Compressor Capacity (Watt) Fan Capacity Operation Hours Temperature At 45 C At 35 C Ratio of compressor s running time against the total air conditioner s operating time 85% 55% Number of Operating Hours 12 Hours 12 Hours Power consumed during this period (the shadowed area in the figure) Power consumed during the month (12x2.4x.0.85) + (0.2x12) = 26.88 KWH 26.88x30 = 806 KWH (12x2.4x.0.55) + (0.2x12) = 18.24 KWH 18.24x30=547 KWH Cost of power consumpton for Residential Category at 5 halalas per KWH 806x0.05 = 40.3 Riyals 547x0.05= 27.35 Riyals 6
From the preceding example, we can conclude that the daily power consumption of an air conditioner at 45C temperature is higher by about 48% than the daily power consumption of the same air conditioner at 35C. This is due to the compressor s long run time at 45C which accounts for about 85% of the air conditioner s total operating time. On the other hand, at 35 C level, the compressor run time accounts for about 55% of the total operating time. This is reflected on the monthly bill i.e. the higher the ambient temperature is than the degree of desired comfort cooling, the higher the bill will be. That is exactly what happens in the summer months. Significance of the Energy Efficiency Ratio (EER) The air conditioner s Energy Efficiency Ratio (EER) is the ratio of the cooling capacity in BTU/hr to the power input or power consumption of the appliance in WATTS. To illustrate the significance of EER and its impact on the monthly electric bill, we present to our valued customers the following example of comparing two air conditioning units run by refrigerant and operating under the same conditions in terms of: - Capacity: 18000 BTUs - Operating time: 12 hours per day - Cost for each of the 1st and 2nd customer categories: 5 Halalas/KWH for the residential sector - EER of the first unit: 7.5 - EER of the second unit: 5 Unit One: EER = 7.5 Consumed power: 18000 7.5 = 2.4 KWH Daily power consumption: 2.4x12=28.8 KWH Monthly power consumption: 28.8x30 = 864 KWH Power cost based on the first and second customer categories: 864x0.05 = 43 Riyals Unit Two: EER = 5 Consumed power: 18000 5 = 3.6 KWH Daily power consumption: 3.6x12 = 43.2 KWH Monthly power consumption: 43.2x30 = 1,296 KWH Power cost based on the first and second customer categories: 1,296x0.05 = 65 Riyals 7
The higher the air conditioner s EER, the less electricity it will use to do its job. The abovementioned example illustrates an increase of power consumption cost to about 50% in air conditioning unit with low EER. Thus, we recommend that the customer, when buying an air conditioner, look for a model with a high energy efficiency rating even at a higher price than getting a cheaper unit with low EER. The Thermostat The thermostat knob-dials of air conditioners are numbered in various ways; some are numbered 1-7, others are from 1-10, and still other dials are numbered using different scales. They differ from one A/C to another. Yet, every scale means a certain degree of temperature. Therefore, it is recommended to turn the thermostat dial to medium setting for a moderate cooling effect and reasonable power consumption. However, the usual desired thermostat setting is between 18-32C for comfort cooling and moderate energy consumption. On/Off Ventilation Switch This is the switch that opens/closes the air conditioner s vent that switches it between using outside air and recycling indoor air. It is recommended that it be set in the OFF mode unless there are fumes you wish to expel from the room. A/C EER Consumption decreases the higher the EER is 8
Desert Air Cooler - How It Works The desert air cooler is the lowest energy consuming unit. It is typically used in the hot and dry areas to cool down the air inside buildings or open halls. It works by pulling in the outside air by a fan and then passing it through water-saturated straws. As the air passes the wet straws, evaporation takes place thereby causing the temperature to cool down. The cool air is then blown in the room/building by the fan. Desert A/C Power Consumption Water-saturated straws Fan 41 C 27 C 20% relative humidity 40% relative humidity By comparing this air cooling device to air conditioners (A/C), we find that A/Cs using refrigerants consume 8 times as much electricity than that of the desert air cooler. This proves that the desert air cooler has low power consumption rate, as shown on the following example. Comparison Aspect Air Conditioner Illustrative Drawing of the Desert A/C Desert Air Cooler Room Area(m 2 ) Capacity 25 18,000 units 25 1/3 hp Daily operating hours Air conditioner power consumption based on 45C ambient temperature which accounts for 85% of the total 12 hour running period. Power consumed per month Cost of power consumption using the tariff rate for Residential Sector equivalent to 5 Halalas per KWH 9 12 (12x2.4x0.85) + (0.2x12) = 26.88 KWH 26.88x30= 806 KWH 806x0.05= 40 Riyals 12 0.25x12 = 3 KWH 3x30=90 KWH 90x0.05= 4.5 Riyals
The example illustrates the importance of using desert air cooler during the summer season due to the significant savings it offers on power consumption as compared to a conventional air conditioner while taking into consideration the adequacy of water supply in a manner that does not go against policies on water conservation. Methods of Raising the Efficiency of Desert Air Cooler - Prevent accumulation of salts, dusts, and suspended particles by periodically changing the straws to improve the air cooler s efficiency. - Check and lubricate the water pump periodically. - Use the desert air cooler in open places such as halls and kitchens. Optimal Utilization of the A/C Systems. Valued customer: Listed below are special guidelines on the proper use of all types of air conditioning units to reduce power consumption and subsequently reduce the payable value of the electric bill. 1- Choose the right capacity and size of the air conditioner that best fit the size of the room. Cooling 1 m 2 of an uninsulated building requires about 800 BTUs, but only 600 BTUs required for an insulated building. 2- Buy the air conditioner with high EER to get more cooling output and lower power consumption. The study had proven that the A/C power consumption is reduced by 40% when its EER is raised from 5 to 7 at the same ambient temperature. 3- Maintain and clean the A/C unit once every year, at least, as the accumulation of dusts and sands reduces its efficiency. 4- Clean the air filter once every two weeks, as the accumulation of dusts and other particles impedes the passage of warm air from inside the room to the outside. As a result, the power consumption increases and the electricity bill correspondingly become higher. 5- Shade the air conditioner and lessen its exposure to the sun, as studies found that air conditioners with proper shading can be more efficient. 6- Set the thermostat at a moderate setting of 25C to reduce the temperature difference between ambient temperature and the desired temperature. This will in turn shorten the compressor s operating time and reduce energy consumption. Further, if the thermostat is set at higher degree, ice will form on the evaporator coil which then impedes air circulation inside the room. 7- Keep furnishings away from the air vents of the cooling system. Blocking the air flow impacts the functionality of the air conditioning system and leads to excessive power usage. 8- Use thermal insulation and double-pane glass to prevent heat loss through windows. In this regard, an insulated window is a good complement to thermal insulation in the building. 10
9- Install the air conditioner on the outer part of the room that has a constant flow of air to help dispel the heat coming from the unit to increase its efficiency. Avoid installing ACs in enclosed locations e.g. skylights and narrow spaces. 10- Turn off the air conditioner when leaving the building so as not to unnecessarily consume excessive amount of energy. 11- Seal the side openings or edges of the air conditioner to prevent air leaks. Preferably, apply in place insulation materials such as cork to prevent heat exchange. 12- Keep all windows and doors closed when air conditioning is on in order to maintain the desired air conditioning temperature and to keep warm air from entering the room. Further, we recommend the use of automatic door closers at building entrances that are more exposed to the exterior air. 13- Reduce ventilation when the central air conditioner is taking in more exterior air than required. In the case of window type air conditioner, keep the ventilation switch to off mode most of the time. 14- Use curtains or window blinds to prevent solar heat from penetrating the inside of the house during summer season. 15- In case of power outage, switch off the air conditioner in order to reduce the load and leave one light on to indicate that power has been restored. 11
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