The task of any split system is efficient and quick cooling of the room air without unnecessary energy costs. Conclusion: when choosing a household air conditioning system for an apartment or a private house, it is important to determine the refrigeration capacity of the air conditioner. The calculation is carried out in two ways - using the online calculator or manually, both options are presented in this guide.
Online Refrigeration Calculator
To independently choose the power of a home air conditioner, use the simplified calculation method for the area of the cooled room, implemented in the calculator. The nuances of the online program and the entered parameters are described below in the instructions.
Note. The program is suitable for calculating the performance of household chillers and split systems installed in small offices. Air conditioning in industrial buildings is a more complicated task, solved with the help of specialized software systems or SNiP calculation methods.
Instructions for using the program
Now we explain step by step how to calculate the power of the air conditioner on the presented calculator:
- In the first 2 fields, enter the room area in square meters and the ceiling height.
- Choose the degree of illumination (insolation) through the window openings. The sunlight penetrating into the room additionally heats the air - this factor must be taken into account.
- In the next drop-down menu, select the number of residents staying in the room for a long time.
- On the remaining tabs, select the number of TVs and personal computers in the air conditioning area. In the process, the specified household appliances also generate heat and must be accounted for.
- If a refrigerator is installed in the room, enter the electric power value of the household appliance in the penultimate field. The characteristic can be easily found from the product instruction manual.
- The last tab allows you to take into account the supply air entering the cooling zone due to ventilation. According to regulatory documents, the recommended magnitude of the multiplicity for residential premises is 1-1.5.
For reference. The rate of air exchange shows how many times in one hour there is a complete update of the room air.
We will explain some of the nuances of correctly filling in the fields and choosing tabs. When specifying the number of computers and televisions, consider the simultaneity of their work. For example, one tenant rarely uses both electrical appliances at the same time.
Accordingly, to determine the required power of the split system, a unit of household appliances that consumes more energy is selected - a computer. The heat transfer of the TV receiver is not taken into account.
The calculator contains the following heat transfer values from home appliances:
- TV - 0.2 kW;
- personal computer - 0.3 kW;
- since the refrigerator converts about 30% of the consumed electricity into heat, the program includes 1/3 of the entered figure in the calculation.
Tip. The heat dissipation of your equipment may differ from the indicated values. Example: the consumption of a gaming computer with a powerful video processor reaches 500-600 watts, laptop - 50-150 watts. Knowing the numbers embedded in the program, it is easy to select the desired values: for a gaming PC, select 2 standard computers, take 1 TV receiver instead of a laptop.
The calculator allows you to exclude heat from the supply air, but choosing this tab is not entirely correct. In any case, air currents circulate around the house, bringing heat from other rooms, for example, the kitchen.It is better to play it safe and include them in the calculation of the air conditioner, so that its performance is enough to create a comfortable temperature.
The main result of the power calculation is measured in kilowatts, the additional - in British Thermal Units (BTU). The ratio is as follows: 1 kW ≈ 3412 BTU or 3.412 kBTU. How to choose a split system based on the numbers received, read on.
Calculation methodology and formulas
On the part of a scrupulous user, it’s quite logical not to trust the numbers obtained on the online calculator. To check the result of calculating the power of the unit, use the simplified methodology proposed by the manufacturers of refrigeration equipment.
So, the required performance of a domestic air conditioner in the cold is calculated by the formula:
Explanation of symbols:
- Qtp - heat flow penetrating into the room from the street through building structures (walls, floors and ceilings), kW;
- Ql - heat from residents of the apartment, kW;
- Qbp - heat input from household appliances, kW.
It is easy to find out the heat transfer of home electrical appliances - look in the product passport and look for the characteristic of the consumed electric power. Almost all of the energy expended is converted to heat.
An important point. An exception to the rule is refrigeration units and units operating in start / stop mode. Within 1 hour, the refrigerator compressor will emit into the room an amount of heat equal to 1/3 of the maximum consumption indicated in the instruction manual.
Heat receipts from people are determined by regulatory documents:
- 100 W / h from a person at rest;
- 130 W / h - while walking or performing light work;
- 200 W / h - during heavy physical exertion.
For calculations, the first value is taken - 0.1 kW. It remains to determine the amount of heat penetrating outside through the walls according to the formula:
- S - quadrature of the cooled room, m²;
- h is the height of the overlap, m;
- q - specific thermal characteristic, related to the volume of the room, W / m³.
The formula allows you to perform an integrated calculation of heat influx through the external fences of a private house or apartment using the specific characteristic q. Its values are accepted as follows:
- The room is located on the shadow side of the building, the area of the windows does not exceed 2 m², q = 30 W / m³.
- At average illumination and glazing area, a specific characteristic of 35 W / m³ is taken.
- The room is located on the sunny side or has many translucent structures, q = 40 W / m³.
Having determined the heat input from all sources, add the numbers obtained using the first formula. Compare manual results with online calculator metrics.
When it is necessary to take into account the heat input from ventilation air, the cooling capacity of the unit increases by 15-30%, depending on the rate of exchange. When updating the air environment 1 time per hour, multiply the calculation result by a factor of 1.16–1.2.
Example for a room of 20 square meters. m
We show the calculation of power for air conditioning of a small apartment - a studio with an area of 20 m² with a ceiling height of 2.7 m. The rest of the initial data:
- illumination - average;
- number of residents - 2;
- Plasma TV panel - 1 pc.;
- computer - 1 pc.;
- refrigerator electric power consumption - 200 W;
- air exchange rate without taking into account periodically working kitchen hoods - 1.
Heat dissipation from residents is 2 x 0.1 = 0.2 kW, from household appliances, taking into account the simultaneity - 0.3 + 0.2 = 0.5 kW, from the refrigerator side - 200 x 30% = 60 W = 0.06 kW. Medium-light room, specific characteristic q = 35 W / m³. We consider the influx of heat from the walls:
Qtp = 20 x 2.7 x 35/1000 = 1.89 kW.
The final calculation of the power of the air conditioner looks like this:
Q = 1.89 + 0.2 + 0.56 = 2.65 kW, plus cooling consumption for ventilation 2.65 x 1.16 = 3.08 kW.
Important! Do not confuse general ventilation with ventilating the home.Air flow through open windows is too large and changes due to gusts of wind. The cooler should not and cannot properly air-condition a room where an uncontrolled volume of street air freely passes.
Power conditioner selection
Split systems and cooling units of other types are produced in the form of model lines with products of standard performance - 2.1, 2.6, 3.5 kW and so on. Some manufacturers indicate the power of the models in thousands of British Thermal Units (kBTU) - 07, 09, 12, 18, etc. The correspondence of the climate units, expressed in kilowatts and BTU, is shown in the table.
Reference. From the designations in kBTU went the popular names of cooling units of various cooling capacities - "seven", "nine" and others.
Knowing the required performance in kilowatts and British units, select a split system in accordance with the recommendations:
- The optimal power of a domestic air conditioner lies in the range of -5 ... + 15% of the calculated value.
- It is better to give a small margin and round the result upwards - to the nearest product in the lineup.
- If the cooling capacity determined by the calculation exceeds the capacity of the cooler from the standard series by a hundredth of a kilowatt, it should not be rounded up.
Example. The calculation result is 2.13 kW, the first model in the series develops 2.1 kW cooling capacity, the second - 2.6 kW. We choose option No. 1 - a 2.1 kW air conditioner, which corresponds to 7 kBTU.
An example of the second. In the previous section, we calculated the performance of the unit for an apartment - a studio - 3.08 kW and fell between 2.6-3.5 kW modifications. We choose a split system of higher performance (3.5 kW or 12 kBTU), since the rollback to a smaller one does not fit into 5%.
For reference. Note that the power consumption of any air conditioner is three times less than its refrigeration capacity. A 3.5 kW unit will “pull” about 1200 watts of electricity from the mains in maximum mode. The reason lies in the principle of operation of the refrigeration machine - “split” does not produce cold, but transfers heat to the street.
The vast majority of climate systems can operate in 2 modes - cooling and heating in the cold season. Moreover, the heat output is higher, since the compressor engine, which consumes electricity, additionally heats the freon circuit. The difference in power in cooling and heating mode is shown in the table above.
In conclusion on industrial premises
The above calculation is not suitable for industrial buildings due to the discrepancy between the specific thermal characteristics q and various types of building structures. Although the methodology proposed by SNiP is also based on the summation of all heat receipts.
The algorithm for determining refrigeration capacity for air conditioning a production room looks like this:
- Determine the amount of heat flux through the external fencing by calculating the thermal resistance of the walls, roof and floor. The methodology is described in detail in the publication on calculating the heat load for heating - from the point of view of heat engineering there is no difference.
- Find out the number of staff, count the heat from office equipment and people depending on the intensity of work.
- Summarize the heat transfer of all electric motors and other equipment, taking into account the simultaneity and frequency of switching on.
- If hot technological tanks, furnaces or parts are located in the workshops, it will be necessary to determine the amount of heat flux from the heated surfaces.
- Find out the amount of supply air supplied by ventilation units, calculate the energy consumption for cooling it.
Air conditioning of some industrial premises (server rooms, large offices, cafes) is easier to calculate - there is less heat gain. The master installer will tell you about this technique in his video.