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Saturday, May 26, 2012

Tips For Choosing Air Conditioner For Home

Air conditioner or AC is needed in area where ambient temperature is above 25 Celcius degree or 77 Fahrenheit degree. This equipment uses substantial energy and sometimes running continuously for 24 hours.  Miscalculation when choosing AC will waste costs.

Few years ago window type of home air conditioner was very popular, until split type of home air conditioner came along which has separated evaporator and condenser. Evaporator serves to absorb heat from the room, and the condenser will dissipate that heat into air. For split type air conditioner, evaporator is placed indoor, and condenser is placed outdoor. The condenser has a component called compressor that serves to pump and compress the refrigerant that circulates to transfer heat. Photo above shows the condenser or outdoor unit, and the photo below is showing evaporator or indoor unit of split type AC.

BTU (British Thermal Unit) is a unit of heat which is used to measure the abilitly of air conditioner to transfer heat from inside the room to outside. The greater the BTU number the greater the amount of heat can be removed from the room by air conditioner. This unit of measurement is usually written on AC specification as BTU/h or BTU per hour.

For standard room ceiling height, about 3 meters or 9 feet, the estimation chart below can be used to determine the BTU number of air conditioner capacity. If using air conditioner with too small BTU capacity, then it will work extra hard. If using air conditioner with too large BTU capacity, the compressor would be too frequent on-off to adjust and keep temperature not to cold, this will waste so much electric power although the air conditioner is already set at a minimum.

If the room is exposed to sunlight or other heat source, then rise the BTU value of about 10%. If the room is in a shady place, then reduce the BTU value of about 10%.

If the room is occupied by more than 1 person then add 600 BTU per person.

For kitchen, add 4000 BTU to compensate heat of the stove.

For a large and complicated building, do not use estimation chart above in determining the BTU. But there is a procedure that considers the calculation of wet bulb temperature (without the influence of thermal radiation) and dry bulb temperature (heat radiation exposure), as well as air humidity. For home cooling system, the estimation chart above is suitable enough.

Beside BTU, air conditioner has horse power (hp) to measure performance. Horse power is actually used to measure the capability of AC compressor, and it is not cooling capability. One horse power is equal to 746 watts. Some air conditioner use PK (paardenkracht, Dutch) or PS (Pferdestärke) to measure compressor power. One PK is equal to 735.5 watts. Long time ago AC power was measured in PK or hp, and it was almost equal to the power measured in watts. But now as more efficient air conditioning, for air conditioner with cooling capacity 5000 BTU/h, the power is only 300 watts, no longer as high as 1/2 PK or 370 watts. In general, the relationship between PK and BTU are as below:

Other unit of measurement for AC is watt, this is a total required power to operate. Air conditioner needs electric power to drive compressor, blower in evaporator, and other accessories such as: control panel, timer, swing louver, etc. More accessories mean higher power (watt). So to determine the performance of AC should be referred to BTU and watt. The greater the BTU the cooler temperature, the smaller wattage the more efficient the air conditioner.

For those of you who are familiar with thermodynamics, please be a concern that for air-conditioning (AC) units of BTU/h is not equal to 0.2928104 watts as usually. AC has measurement by Seasonal Energy Efficiency Ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute.

Cooling Capacity per watt is ratio of heat transfer capacity to power (wattage), the larger the number is the better. Cooling Capacity per watt is also called SEER (Seasonal Energy Efficiency Ratio).

For LG Hercules Mini 4500 BTU/h and 260 watts power consumption, the Cooling Capacity per watt is 4500/260 = 17.31 BTU/Wh

For Panasonic Alowa 5000 BTU/h and 320 watts power consumption, the Cooling Capacity per watt is 5000/320 = 15.63 BTU/Wh

While Samsung AS05TSRN Virus Doctor has cooling capability 4991 BTU/h and consumes 310 watts, so the ratio is 4991/310 = 16.1 BTU/Wh

If your room has high ceiling, do not install air conditioner evaporator (indoor unit) too high. Because it will increase the volume of air to be cooled by AC, and make it works harder. AC evaporator mounting should be slightly higher than human head when standing, or about 7 feet from the floor. Cold air has heavier specific gravity than hot air, so cold air will gather at the bottom, and hot air will be trapped at top. This is why food refrigerator in supermarket has a door at the top (top loading) that can be left open, and cold food temperature still can be maintained.

There are holes at the top of the evaporator to suck hot air in the room. If evaporator position too close to ceiling, it will block hot air flow that will be cooled by the evaporator. Ensure installation of air conditioning evaporator is according to the manufacturer's instructions.

Furnitures and goods inside the room can affect the AC. The more and the bigger the furnitures and goods in the room, the less air volume to be cooled, so the AC works lighter. But if those furnitures and goods are blocking air circulation from indoor unit (AC evaporator) to the occupant and vice versa, the occupant will not get the cooled air.

Do not place the AC evaporator face to face with the door, because the cold air will easily escape out of the room when someone open that door to enter or exit the room. Insulate room well to ensure cold air does not easily escape.

A comfortable room temperature can be different for each person. For those who live in tropical regions the room temperature around 25 degrees Celsius (77 degrees Fahrenheit) is quite comfortable and healthy. For those who live in sub-tropic, comfortable temperature range is about 18-22 degrees Celsius (65-72 degrees Fahrenheit).

Some people like to set AC thermostat to get very cold room temperature, then use a thick blanket for sleeping. It is actually unhealthy and wasteful electricity. To sleep comfortably and soundly should use loose clothing and no blanket so you can easily breathe and move freely during sleep. Only use a blanket if you're sick. If the room is too cold, difference between room temperature and inside the blanket temperature can cause health problems. When sleeping with thick blanket in a very cold room, you will be easily awakened if your leg or arm out of the blanket and exposed to very cold room air. If you often wake up during the night, then your rest is become less effective and will cause health problems.

Outdoor unit (condenser) must be placed in open area with good air circulation to allow maximum heat transfer. Outdoor unit location must be accessed easily during cleaning and servicing. Although it is weather resistant, it should be placed in shady place to protect from dust and heat of the sun, and other heat sources.

It is recommended to use special electric line to supply power to AC, do not join with other electrical equipment. Especially if the AC is used continuously for 24 hours, in order to prevent heavy load for the grid to bear and can lead to excessive heat and burn. Thus, supply power to AC should use a special line or cable and special fuse.

Fuse and cable size are determined by the amount of electric current. The relation between current, voltage and power is:
           Current = Power : Voltage

So for AC with 220 watts power, and voltage of 220 volts, the current is 220/220 = 1 ampere. But when start, the AC will draw more current, could reach 1.5 to 2 times the normal current. Refer to your AC specifications to make sure how much current is required for your AC, in order to make sure the fuse and cable sizes to be used for that AC. Don't forget that AC also needs special electric connector for safety.

AC with inverter system is popular now. AC with inverter has compressor with adjustable speed depending to room temperature. The inverter name refers to motor control device that is used to drive the compressor. If without the inverter compressor will always work on the maximal capacity, and compressor regulates the temperature by on-off operation. But when start the compressor motor will draw about 1.5 to 2 times greater power than normal operation power. While AC with inverter, the motor is always working, and the speed is set to match the desired temperature, not necessarily always at full speed. As far as I know the smallest AC with inverter today is about 590 watts.


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