Air Conditioning Calculations:

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Calculate the power conditioner

Air Conditioning Calculations

Floor area, square meter         Consider ventilation ?
Ceiling Height, meter    
Insolation (degree of light rays of the sun)  
Number of people  
Number of computers  
Number of TVs  
Power of the rest of household appliances, Watts  
Estimated cooling capacity Q:
Recommended range of values Qrange:

If you decide to purchase an air conditioner, then the first thing you need to do is calculate its capacity. Most often, the adopted standard formula of 1 kW of power is designed for 10 m2 of the room area. But this formula is not accurate, because there are many other factors that have a direct impact on the calculation. It should take into account the amount of light coming into the room, the outside air temperature, the number of electrical appliances, etc. Let's consider the basic provisions that will help to make an accurate calculation of the power of the air conditioner.

Units of power

Quite often, in addition to the usual units of power measurements, others are used. For example, the British thermal unit, which is measured in BTU / h. It is determined by the amount of heat that needs to be heated for one pound of water per degree Fahrenheit.

With the SI system, it has the following relationship:

  • 1W = 3.4 BTU / h
  • 1000 BTU / h = 293 W
Quite often, the models are called "nine" or "twelve", because they are labeled with a mention of these and other figures, and performance measurement is performed in BTU / h.

How to calculate the power of the air conditioner

Power (more precisely, the cooling power) Is the main characteristic of any air conditioner. Estimated calculation Cooling capacity Q (KW) Is carried out according to the generally accepted procedure:

Q = Q1 + Q2 + Q3, where
Q1 — Heat inflow from the window, walls, floor and ceiling.
Q1 = S * h * q / 1000, where
S — Area of the room (sq. M);
h — Height of the room (m);
q — A factor of 30-40 W / cu. M:
q = 30 For a shaded room;
q = 35 At medium illumination;
q = 40 For rooms that receive a lot of sunlight.
If direct sunlight gets into the room, then the windows should be bright Curtains or blinds.
Q2 — Amount of heat influx from people.
Heat influx from an adult:
0,1 KW — In a calm state;
0,13 KW — With easy movement;
0,2 KW — At physical exertion;
Q3 — The sum of heat inflows from household appliances.
Heat inflow from household appliances:
0,3 KW — From the computer;
0,2 KW — From the TV;
For other devices, we can assume that they give off in the form of heat 30% of the maximum power consumption (i.e., it is assumed that the average power consumption is 30% of the maximum).

Power of selected air conditioner Should be in the range from -5% to +15% Of the calculated power Q . Note that the calculation of the air conditioner by this method is not very accurate and is applicable only for small rooms in the capital buildings: apartments, separate rooms of cottages, office space up to 50-70 square meters For administrative, commercial and industrial facilities other methods are used that take into account a greater number of parameters.

Example of calculating the power of the air conditioner

Calculate the power of the air conditioner for a living room area of 26 sq. M. M with a ceiling height of 2.75 m/s in which one person lives, and there is a computer, a TV and a small refrigerator with a maximum power consumption of 165 watts. The room is located on the sunny side. The computer and the TV do not work at the same time, because they are used by one person.

  • First, we determine the heat influx from the window, walls, floor and ceiling. The coefficient q is chosen to be 40 , since the room is located on the sunny side:
    Q1 = S * h * q / 1000 = 26Sq. M. M * 2.75 m * 40/1000 = 2.86 kW.

  • Heat inflows from one person in a calm state will be 0.1 kW .
    Q2 = 0,1 kW

  • Next, we will find heat inflows from household appliances. Since the computer and the TV do not work at the same time, only one of these devices must be considered in the calculations, namely the one that emits more heat. This is a computer with a heat release of 0.3 kW . The refrigerator emits about 30% of the maximum power consumption, ie 0.165 kW * 30% / 100% = 0.05 kW .
    Q3 = 0,3 kw + 0,05 kw = 0,35 kw

  • Now we can determine the estimated capacity of the air conditioner:
    Q = Q1 + Q2 + Q3 = 2,86 кВт + 0,1 кВт + 0,35 кВт = 3,31 kw

  • Recommended power range Qrange (From -5% to +15% of the calculated capacity  Q):
    3,14 kw  <  Qrange  <  3,80 kw

Additional parameters to consider when selecting an air conditioner

There are many factors that have a significant influence on the choice of air conditioner. First of all, it is necessary to take into account the role of the inflow of fresh air at the opening of the window. Simplified methodology for calculating the power of the air conditioner does not take into account the opening of windows for ventilation. This is due to the fact that even in the operating manual of the system it is indicated that the air conditioner should only work when the windows are closed. In turn, this creates certain inconveniences, since it is possible to ventilate windows only when the device is turned off.

Solve this problem is not difficult. Airing the room with the air conditioner on can be at any time, but do not forget to close the entrance door to the room (not to create drafts). It is also necessary to take into account this nuance when calculating the system's power. To this end, we increase Q1 by 20% to compensate for the heat load from the supply air. It is necessary to understand that with increasing capacity, the cost of electricity will also increase. For this reason, air conditioners are not recommended for use during the ventilation of premises. At the highest possible temperature (summer heat), the air conditioner may not support the set temperature, since the heat inflow may be too strong.

If the cooled room is located on the top floor, where there is no attic, the heat from the heated roof will be transferred to the room. The thermal inflow of the ceiling will be much higher than that of the walls, so we increase the power Q1 by 15%.

A significant role is played by a large area of glass windows. It is quite easy to follow this. It is enough to measure the temperature in the solar room and compare it with the rest. During the normal calculation, there is a window in the room, up to 2 m2. If the glazing area exceeds the permissible value. Then for each square meter of glazing, an average of 100-200 watts is added.

For operation in a wide range of thermal loads, the inverter air conditioner is well suited. It has a variable cooling capacity, so it is able to create comfortable conditions in this room.

Matching model series and capacity of the air conditioner in BTU and kW

Lineup BTU kW
7 7000 BTU 2.1 kW
9 9000 BTU 2.6 kW
12 12000 BTU 3.5 kW
18 18000 BTU 5.3 kW
24 24000 BTU 7.0 kW
28 28000 BTU 8.2 kW
36 36000 BTU 10.6 kW
42 42000 BTU 12.3 kW
48 48000 BTU 14.0 kW
54 54000 BTU 15.8 kW
56 56000 BTU 16.4 kW
60 60000 BTU 17.6 kW
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