# How to make a calculation of the capacity of the air conditioner and choose the right unit for your needs

Competent calculation of the power of the air conditioner is the key to effective, uninterrupted operation and durability of climate technology. The choice of performance is based on the overall dimensions of the room and related factors contributing to the accumulation of thermal radiation.

Taking into account all the parameters and nuances of operation allows you to provide the optimal power reserve, but do not overpay the split-system for over-performance.

## How much power should be oriented

The technical documentation for air conditioners indicates two or three types of power. The indicators characterize different operating parameters: cooling and heating performance, as well as the electrical power consumed by the split system.

The variation of the indicators can be misleading.In heating appliances, for example, a boiler or a radiator, the power of heat dissipation corresponds to the energy consumed. For air conditioning, these parameters are different.

Split complex, unlike a heater, does not directly convert electricity, but uses it to operate a heat pump. The latter is able to transfer heat energy much more than the electric power expended.

Cooling capacity is indicated in kW, the range of values of household equipment - 2-8 kW. In addition, many manufacturers in the technical descriptions use the British label - BTU (BTU).

The cooling capacity of the split should be adapted to the conditions of service. Otherwise, the normalization of the microclimate to the desired temperature will become an overwhelming task for the air conditioner and will outputtechnique out of order. Two scenarios are possible:

- low productivity - the work of the unit on the verge of possibilities;
- excess power - an increase in the number of on / off, which has a detrimental effect on the electric motor.

The ability to heat the room characterizes the thermal performance of the split. The heat output is always slightly higher than the cooling capacity. The difference between the indicators is the ratio of heat losses on the route of freon pumping in cooling and heating modes.

The heat output is especially relevant if the air conditioner is planned to be used as an inter-seasonal heat source. Split complex at times more efficiently electric heater.

## BTU value and label interpretation

BTU / BTU is a British thermal unit for measuring heat energy. The value determines the amount of heat spent on heating one pound of water per 1 ° of Pharyngate.

This unit expresses the cooling capacity of climate technology and is often present in product labeling.

Ratio between watt and btu / h:

- 1 Btu / h ≈ 0.2931 W, for convenience of calculation 0.3 W is used;
- 1 kW ≈ 3412 BTU / h.

Air conditioning - an American invention, which applies the Western system of measures. For practicality and clarity of display, the cooling capacity was decided to standardize and express in round numbers, for example: 7000 BTU / h, 9000 BTU / h, etc.

Understanding the digital designation in marking equipment, it will be possible to determine approximately which space the air conditioner is designed for.

## Self-calculation methods

There are several ways to calculate the performance of splits. The simplest, but not reliable enough - the calculation of the area. A more accurate one is the heat engineering method, which takes into account the design features of the room and the total thermal inflows.

### The choice of air conditioning on the service area

It is possible to determine the approximate capacity of the unit without mathematical calculations, appealing to the practical evaluation criterion - the floor area.

The average cooling capacity of the split is 1 kW per 10 sq. M of the serving room. This standard is relevant for residential premises with a ceiling height of 2.5-3 m.

Thus, when calculating the capacity of the air conditioner, the service area must be divided by 10. For example, a model with a capacity of 2.2 kW is suitable for a room of 22 square meters. The obtained value corresponds to the "seven" in the BTU system.

The design capacity is increased by 20% in the following cases:

- the location of the room on the sunny side of the house;
- the presence of panoramic windows;
- placing a large number of office equipment, electrical appliances.

The cooling capacity margin of 20% should be foreseen if there are many people permanently living or working in the room.

Due to the impressive dimensions, possible angularity and curvature, the air flows are unevenly distributed. In this case, it is advisable to install multisystem split-complexes.

### Heat calculation: typical formula and explanation

Thermal calculation is considered more accurate, taking into account the structural and operational features of the building. Determining factors:

- room dimensions: area and exact height;
- number of people;
- purpose of the room: gym, active work, rest, etc .;
- heat sources, household / office equipment;
- the presence of insulated facades and roofs.

The main emphasis in assessing the power of the air conditioner is on the total heat gain.

The greater the heat flow, the higher should be the cooling capacity of the split.

**Typical formula - Q = Q1 + Q2 + Q3**

Where:

- Q is the total cooling capacity;
- Q1 - heat gain from structural elements of the room;
- Q2 - heat leakage from people;
- Q3 - heat dissipation from technology.

**Calculation Q1.**Room heat excess is defined as follows: Q1 = V * g. The treatment of the formula: V is the volume of the room served, calculated by the product of square footage and the height of the ceilings; g is the calculated heat transfer coefficient.

The value of g depends on the orientation of the windows and the level of natural light in the room:

- 40 - sunny side, intensive insolation typical for southern, south-western, southeast orientation;
- 35 - moderate illumination of the east, north-west, west side;
- 30 - the prevalence of shading during the day is observed in rooms with windows facing north or northeast.

**Q2 Definition**. Heat production of people depends on their age and mobility. For an adult, the following heat emission characteristics are characteristic:

- resting state - 80 W;
- light work, moderate loads - 125 W;
- active activity - 170 watts.

When doing hard work and intense sports exercises, heat production reaches 250 watts.

However, this approach is justified when choosing a split system in children's institutions. Air conditioning is purchased for the future, so for a family, the heat transfer of children should be equated to “adult” indicators.

For an apartment cooling system, parameter Q2 is determined by multiplying the number of residents by the average value of heat generation - about 110 watts.

**Q3 value.**Heat surplus from electrical equipment is calculated by the formula:

**Q3 = N * m * i**

Where:

- N - power unit equipment;
- m is the number of household appliances;
- i - the conversion rate of electricity into heat.

In the calculations it is necessary to take into account the frequency of use of technology during the day, taking round-the-clock work per unit.

Summing up the total amount of heat leakage, you can determine the power of the air conditioner. It is acceptable to exceed the cooling capacity of the unit by 15% of the calculated indicator or its decrease - by a maximum of 5%.

### Step-by-Step Calculation Example

Calculated data to determine the performance of the split:

- room space - 24 sq.m, ceiling height - 2.8 cm;
- room with a standard window facing south;
- the number of residents - 2 people;
- equipment appliances: computer, TV, refrigerator (0.3 kW), incandescent lamp (0.1 kW).

Possible simultaneous operation of the listed electrical appliances.

**Step 1.**Determination of heat gains from windows, floors, walls and ceilings.

Q1 = 24 * 2.7 * 40 = 2592 watts.

The resulting value can be safely rounded to 2.6 kW. In the calculation, the coefficient g = 40 is used, since the room is well lit.

**Step 2.**Calculating heat gain from people. The heat production of an adult person we take for 110 watts.

Q2 = 2 * 110 = 220 W or 0.22 kW.

**Step 3.**Thermal inflows from the equipment are calculated for each type of equipment, taking into account the power conversion factor:

- computer - 0.3 kW;
- TV - 0.2 kW;
- electric bulb - 90 W (100 W * 0.9);
- the refrigerator is 100 W (300 W * 0.3).

Q3 = 300 + 200 + 90 + 100 = 600 W or 0.6 kW.

**Step 4.**Calculation of the cooling capacity of the air conditioner.

Q = 2.6 + 0.22 + 0.6 = 3.42 kW.

For comparison, it is possible to carry out an approximate selection of the air conditioner solely on the area without taking into account the number of resident and thermal inflows. For an area of 24 square meters, the estimated cooling capacity should be 2.4 kW, taking into account good illumination - 2.4 * 1.2 = 2.88 kW.

In this situation, the results of calculations by two methods differ. Priority - "thermal" calculation. The cooling capacity of the air conditioner should redeem all possible heat gains.

### Consideration of special operating conditions

The method described above in most cases does not need to be adjusted and gives an accurate result. Special attention deserves:

- the need for regular airing;
- the location of the room on the top floor;
- hot climate of the region;
- large glass area.

**Inflow of fresh air.**The documentation for split-systems usually stipulates that operation of the device with windows open is undesirable.

To maintain a normal microclimate without constantly moving the sash, you can leave the window in the micro-ventilation or install a supply valve. Both options do not provoke drafts when the entrance door is closed.

When operating the split in the conditions of gentle airing should be considered:

- In order to compensate for the additional heat load, the indicator Q1 should be increased by 20% when calculating the power of the air conditioner.
- Electricity consumption during the split operation will increase to 15%.

In hot weather, do not rely on the power reserve. With significant heat leakage conditioner will not provide the desired temperature.

**Top floor.**In the attic and apartment of the upper floors without an attic, the heat of the heated roof is transferred inside the room. The situation is exacerbated by the presence of dark-colored flat roofs.

**The hot climate of the region.**One of the rules of safe use of air conditioning is to comply with the permissible temperature difference outside and inside the building. The limit is 10 ° С. For example, if outside the window is 35 ° С, then the recommended temperature in the room is not lower than 25 ° С.

The rated power of the split-complexes is indicated taking into account operation in conditions up to 31-33 ° C. With an increase of up to 40 ° C or more, the cooling capacity of the unit is not enough to maintain the cherished 18-20 ° C.

Taking into account the climate predisposition to hot summer and own preferences for the level of coolness, the Q1 indicator should additionally be increased by 20-30% in the calculations.

**Big windows.**A typical formula assumes that a room has one window of standard dimensions - up to 2 sq.m. Multiple window openings or a panoramic design increases unrecorded heat leakage.

Adjustment of cooling capacity is based on each square meter of additional glazing:

- + 200-300 W - for the sunny side;
- + 100-200 W - moderate room insolation;
- + 50-100 W - the prevalence of shadow.

Light blinds or curtains will help reduce solar heat gain.

As noted above, in addition to the cooling and heating capacity, the power consumption is indicated in the passport of the split system. The value determines the power consumption. However, the coefficient and energy efficiency class are more informative.

In fact, the EER and COP coefficients show the amount of cold / heat produced while spending 1 kW of electrical power. The greater their numerical value, the higher the efficiency of the climate system and the lower the level of energy consumption.

That is, at EER = 2.5, the air conditioner at maximum cooling power consumes electricity Q / 2.5. Multiplying the result for the period of work, you can find out the daily power consumption.

Based on the ERR, splits are classified into energy efficiency classes. The category “A” includes the most economical copies, the “G” group is represented by air conditioners with the highest consumption of electricity.

## Additional criteria for choosing the air conditioner

In addition to the power characteristics of the system and the energy efficiency class, you should determine the following parameters before purchasing:

- type of air conditioner;
- the principle of operation of the unit;
- functionality;
- by the manufacturer.

Type of air conditioning. For home use used monoblocks and split systems. The first category includes window models and compact portable devices. Air conditioners built into the window have lost their former popularity.

The undeniable advantages of window "coolers": low cost and maintainability. This unit is more suitable for seasonal dacha use than for an apartment.

Mobile monoblocks are equipped with a flexible air duct that transfers heat to the street. A portable air conditioner is the optimal solution for a rented room.

Split systems confidently occupy a leading position among household air conditioning systems. The form of execution distinguishes two categories of splits:

- Two-block design.A pair of modules is connected to a freon closed line. The complex is easy to operate and virtually silent. There are various options for decorating the indoor unit, the case does not occupy a useful area in the room.
- Multi-system. External module provides two to five internal blocks.

The use of multi-complex allows you to set different parameters of air conditioning in separate rooms.

**Principle of operation.**Distinguish between conventional and inverter models. The order of the traditional split-system:

- When the temperature rises, the air conditioner turns on.
- After cooling to the designated aisle, the unit shuts down.
- Duty cycle on / off repeats continuously.

Inverter air conditioner operates more smoothly. After starting the room is cooled, but the device continues to work with reduced power, maintaining the desired temperature.

Due to the lack of "sharp" cyclical operation of the inverter air conditioners are low noise and durable.

**Functionality**Manufacturers, in an effort to win the location of customers, equip split systems with additional options. Well, if the air conditioner has the following features:

- fan distribution of air flow;
- automatic restoration of instrument settings;
- remote control;
- built-in timer

**Brand**In the ranking of leading manufacturers, foreign companies dominate: Daikin, LG, Sharp, Hitachi, Panasonic and General Climat.

## Conclusions and useful video on the topic

Practical recommendations of a specialist will help determine the power characteristics of an air conditioner:

A detailed video review of the types of climate technology, a comparison of the advantages and disadvantages of each solution:

Understanding the principles of calculating the performance of air conditioning systems, it will be possible to independently determine the range of permissible power.It is better to entrust the final calculation of suitable parameters to professionals - an experienced specialist will take into account all the operational nuances and select the optimal model of air conditioner.