SIZING YOUR AIR CONDITIONER---A PRACTICAL GUIDE.pdf
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SIZING YOUR AIR CONDITIONER---A PRACTICAL GUIDE -- Measure the room volume (length × width × height) -- Choose the proper multiplier based on the room’s features. -- Multiply to get the needed cooling power. Male heat load (BTU) Female heat load (BTU)
SIZING YOUR AIR CONDITIONER---A PRACTICAL GUIDE.pdf
- 1. SIZING YOUR AIR CONDITIONER: A PRACTICAL GUIDE ABSTRACT This practical guide provides approach to sizing an air conditioner to achieve optimal indoor comfort and energy efficiency. Explains the key concepts of cooling capacity measured in BTU/hour and how these relate to air conditioner horsepower (HP). Outlines a step-by-step process: calculating room volume, window exposure, and heat sources, and defining the required cooling capacity air conditioner unit. Additional factors such as human heat load, appliance-generated heat, and sunlight exposure are also addressed to ensure a more accurate assessment. Conversions between watts and BTU are included to simplify equipment selection. By following these guidelines, homeowners and facility managers can avoid the drawbacks of undersized or oversized units, which can lead to poor performance and higher energy bills. This resource is intended to help consumers make informed decisions when investing in air conditioning systems for residential or light commercial use. Author Muhammad Rizwan Akram [email protected]
- 2. Research &Written by Mr. Rizwan Akram © All Rights Reserved 2025 Writer: Muhammad Rizwan Akram Department Manager Operations – Canon International, Lahore, Pakistan. Produced in June 2025 Sizing Your Air Conditioner: A Practical Guide The hot climate in our country makes it hard to relax comfortably, even with a ceiling fan running at full speed. The heat remained well into the night, leaving many of us unable to sleep properly. Installing an air conditioner in the bedroom or living room has therefore become the best solution to keep the whole family comfortable. In the past, have an air conditioner was seen as a luxury. But Today, however, it has become a necessity for most households in Pakistan. The development of energy-saving technologies, like DC inverters & Solar air conditioners are now more affordable and accessible. Popular brands on the market include Changhong, CHiQ, Hire, TCL, C-Life, Kenwood, Carrier, Gree, Orient, PEL, General, and O’ General. An air conditioner works by using mechanical components to absorb heat from a closed space and release it outside. A quality unit should regulate the temperature to a comfortable range (22–26 °C), maintain relative humidity (40%–60%), control air circulation, and deliver clean indoor air. The four main components of an air conditioning system are the compressor, condenser, metering device, and evaporator coil, blower fan, Thermostat Sensor, Electronic Control Board (PCB), Capacitor, and Outdoor Control Board (PCB) Air conditioners generally fall into two main categories: domestic and commercial. For domestic/ residential use, split-type units featuring both indoor and outdoor components are the most common. The wall-mounted split unit, capacity is measured in horsepower (HP), with common sizes including 1HP, 1.5HP, 2HP, 2.5HP, and 3HP. When you’re trying to figure out the right air conditioner for your room, you need to start by knowing its cooling capacity, which is measured in BTU per hour. Basically, this cooling capacity depends on how big the evaporator (or cooling coil) is, since that’s the part that actually does the cooling.
- 3. Research &Written by Mr. Rizwan Akram © All Rights Reserved 2025 A BTU- short for British Thermal Unit- is the amount of energy it takes to raise the temperature of one pound of water by 1 °F at sea level. In air conditioners, the BTU rating tells you how much heat the unit can remove from a room in an hour. The higher the BTU, the stronger the cooling power, and the higher the horsepower (HP) of the air conditioner needs to be. To give you an idea, a 1HP air conditioner normally removes about 9,000 BTU per hour. With newer technology, some models can go up to 10,000 BTU/hr even with the same horsepower. For a simple rule of thumb, you can think of 1HP as roughly equal to 9,500 BTU/hr. If you get the BTU estimate wrong, you might end up buying a unit that’s too small or too big for the room, which will affect its performance and your comfort. The easiest way to get it right is to use a BTU calculator, which many AC companies provide. But there are also other simple ways to estimate the BTU you need, so you can then match it with the proper HP rating for your air conditioner. Step 1: Measure the Room Volume First, figure out the size of the room you want to cool. To do this, measure its length, width, and height, then multiply these together to get the volume in cubic meters. For example, if your room is 6 meters long, 4 meters wide, and 2.5 meters high: 6 × 4 × 2.5 = 60 m³ That gives you the total room volume you’ll be working with. Method 1: Simple cooling capacity estimation using area only So, the suitable air conditioner capacity for this room is 1.5HP Cooling Capacity =Room Area x Heat Factor / BTU/hr Heat removed by 1HP Where, • Room Area =Length x Width = 14x12ft =1068ft2 • Heat Factor @ Coefficient =80 • BTU/hr heat removed by 1HP =9500 BTU/hr (reference to the above-mentioned) Cooling Capacity =168x80/ 9500 = 1.42 Method 2: Simple cooling capacity estimation using area and height Cooling Capacity = = (Room Area x Heat factor) + Room Height + Heat generated by person / BTU/hr heat removed by 1HP Where
- 4. • Room Area • • Heat factor (depends on room location).If the room is located on the main floor, the factor is 40; if the room is located on the second floor, the factor is 50 • Room Height. For each foot above an 8ft ceiling _ 1000 BTU/hr • Heat generated by person each person generates 600 BTU/hr of heat • BTU/hr heat removed by 1HP 168f2 50 (2nd floor room) 2000 (height is 10 ft, 2x1000) 1200 ( 2 Person Male) 9500 BTU/hr Cooling Capacity= (168x50) + 2000 + 1200 / 9500 = 11600/ 9500 = 1.22 So, the suitable air conditioner capacity for this room is 1.5HP Method 3: Air conditioning estimation – Rule of thumb Cooling Capacity = Room volume x Heat Factor) + Heat generated by persons / BTU/hr heat removed by 1HP Where • Room Volume = Length x Width x Heigh = 14 x 12 x 10 ft = 1680ft3 • Heat factor @ coefficient = 6 • Heat generated by persons = 1200 (two persons in room) • Btu/hr heat removed by 1 HP = 9500 BTU/hr Cooling Capacity= = Room volume x Heat Factor) + Heat generated by persons / BTU/hr heat removed by 1HP = (1680 x 6) + 1200 / 9500 = 1.19 Out of the three methods, all point to the same conclusion: a 1.5HP air conditioner is the most suitable capacity for the room shown in Figure 2. However, to get a more precise BTU estimate, you should also consider a few extra factors: 1. Heat from other appliances — such as lights, computers, or televisions that are in use. 2. Heat from people — the earlier calculations assumed only two people in the room; more occupants will generate more heat. 3. Window size and placement — larger windows or windows exposed to direct sunlight can increase heat load. 4. Air leaks — gaps or poor sealing in the room can affect cooling efficiency.
- 5. Research &Written by Mr. Rizwan Akram © All Rights Reserved 2025 Room Size (calculation example) The following reference values can be used as heat factors and additional considerations when calculating the required BTU: 1. Human heat load: typically, about 600 BTU/hr per adult person is used for simplicity, regardless of gender (men generally around 600 BTU/hr, women around 400 BTU/hr). 2. Lighting and electrical/electronic appliances: add (wattage × 3.5) BTU/hr. 3. Additional occupants: add 600 BTU/hr per person beyond the first two. 4. Direct sunlight: add 10% of the total BTU if the room is exposed to strong sunlight. 5. Open space: estimate room area (sq ft) × 120 BTU. 6. Kitchen areas: add about 4,000 BTU/hr due to heat from cooking appliances like stoves, ovens, and refrigerators. Additionally, using a ceiling fan can help reduce the cooling load by improving air circulation and distributing cool air more evenly.