The main problems of operation of air conditioners in heating mode, at negative outside temperatures.
When cold weather sets in, many people start using air conditioners for heating. This desire is justified, since it is economically more profitable than heating with other electrical appliances, such as convectors or oil radiators.
Often, air conditioners are used as the main means of heating in offices, apartments, shopping pavilions due to economic reasons. However, the operation of air conditioners for heating in cold weather has a number of limitations, which are due to the design features and features of the physical principles by which air conditioners operate.
So what are the problems that users face when using air conditioners in the cold season? It:
- Reduced thermal performance of the air conditioner.
- Freezing of the outdoor unit of the air conditioner and as a result, an even greater decrease in the performance of the air conditioner, the risk of compressor water hammer.
- Risk of water hammer during compressor start-up due to the presence of liquid refrigerant condensed in the compressor.
- Violation of the condensate drainage system (condensate does not have time to drain and ice freezes in the tray of the outdoor unit, which can lead to jamming of the fan or its breakdown).
- Air conditioning does not warm the room.
Although the manufacturer supplies split systems that are completely charged with refrigerant, however, this gas station provides up to 3.6 (5.0) meters of a standard piping (depending on the manufacturer) and if the length of the route exceeds the standard, then installation requires refueling with freon in the amount indicated manufacturer. If refueling is ignored, the power of the air conditioner is lost, and the compressor may overheat.
The performance of the air heat exchanger and the entire system, namely the amount of heat that the refrigerant can give or receive, depends not only on its design, but also on the temperature of the air passing through it. The greater the difference between the temperature in the street and the temperature in the room, the more difficult and more energy-intensive the air conditioner is to transfer heat from the street to the inside. Technically, it looks like this: air with a low temperature lowers the evaporation pressure, which causes a proportional drop in the condensation pressure, respectively, the mass flow rate of the refrigerant decreases, and therefore the cooling capacity of the air conditioner, i.e. there is a drop in the performance of the air conditioner, and the lower the outdoor temperature, the greater the loss of air conditioning power.
Please note that the manufacturer usually always indicates two air temperatures (indoor and outdoor temperature), the operation of the air conditioner. And if the air temperature goes beyond the ranges specified by the manufacturer, then it is not recommended to operate the air conditioner.
Also in cold weather, especially during high humidity, especially if it rains or wet snow, users may encounter the problem of ice formation on the outdoor unit. This is due to the fact that the air conditioner works on the principle of a heat pump, i.e. removes heat from the street and pumps it inside when working for heating, or vice versa when working for cooling. At the same time, the temperature of the heat exchanger of the outdoor unit drops below the temperature of the outdoor air, which contributes to its freezing. This leads to a loss of power of the domestic air conditioner, (due to a decrease in the air flow of the heat exchanger), so the air conditioner is forced to periodically go into the defrost (defrost) mode of the outdoor unit. The frequency and duration of the defrost mode depends on the temperature and humidity of the outdoor air, weather conditions and the installation location of the outdoor unit.
What to do:
- pay attention to the length of the route, check with the installers if refueling was carried out with freon, if the length of the route exceeds the standard. If refueling has not been carried out, contact the installer or service center (operation is not covered under the warranty);
- Do not turn off the air conditioner at night (it is advisable not to turn it off at all), so as not to interrupt the defrost cycle;
- if we talk about inverter models of air conditioners, the air conditioner is controlled by the outdoor unit board, which analyzes the data received from the sensors of the outdoor and indoor units, user requests and, based on them, controls the compressor performance and the rotation speed of the fans of the outdoor and indoor units. In cases where the user sets the maximum rotation speed of the indoor unit fan, the air conditioning control system has to adjust the operating modes of the compressor and the outdoor unit fan, while deviating from the optimal operating parameters and ice begins to form more intensively on the outdoor unit heat exchanger, the air conditioner starts to defrost more and more often, and for longer periods, which does not allow the user to qualitatively heat the room. Therefore, it is recommended to set the operation of the fan of the indoor unit to AUTO mode in the air conditioner. In this case, the air conditioner, automatically adjusting the fan speeds and compressor performance, will work under optimal conditions and will not allow ice formation on the heat exchanger as much as possible. In this case, the frequency of transitions to the defrost mode will be minimal and the user will be able to optimally use the equipment for heating.
- make sure that the “coat” of ice on the heat exchanger of the outdoor unit does not become too thick (more than 1 cm), if the ice thickness is too large or the ice freezes on the heat exchanger unevenly (in stripes), then you must contact the installer or service center ;
Liquid refrigerant formation in compressor crankcase
During prolonged shutdowns of the outdoor unit (when it cools to ambient temperature), the liquid refrigerant is concentrated in the least heated elements of the outdoor unit, including and in the compressor. In this case, the liquid refrigerant partially dissolves in the oil and partially, like a heavier liquid, settles at the bottom of the compressor crankcase. At the next start-up of the compressor, the liquid refrigerant together with the oil enters the compressor compression chamber, and so on. the fluid does not compress, it can cause a strong water hammer. In addition, the oil pump instead of oil draws in liquid refrigerant from the bottom of the compressor crankcase, and it begins to flush the oil from rubbing surfaces, i.e. the compressor runs with virtually no lubrication. This leads to various mechanical damages (seizure in the bearings), often the compressor simply “seizes up”.
What to do:
Install the compressor crankcase heater. Even a slight difference in temperature between the compressor and other parts of the outdoor unit will eliminate the formation of liquid refrigerant in the compressor crankcase. The power of such a heater is usually small (a few tens of watts is enough) and it does not cause the compressor to overheat during operation in the summer, however, if desired, you can install either a thermostat or a self-regulating cable that changes its resistance depending on temperature.
Condensate drainage system malfunctioning
At low temperatures, strong winds and snowfall, clogging of the drainage hole, there is a chance that during defrosting the condensate does not have time to drain and ice freezes in the tray of the outdoor unit, which can lead to jamming of the fan or its breakdown.
What to do:
Install the heater in the pallet of the outdoor unit, which will prevent the formation of ice.
Air conditioning does not warm the room.
Often this problem is caused by:
- not choosing the right air conditioner for performance;
- the room is poorly insulated and has high heat loss;
- there is a large cross of people (doors are constantly open), the entrance is not equipped with a thermal curtain
- when using an air conditioner for heating in cold weather, in commercial premises, especially such as a shopping pavilion, at an indoor temperature less than + 16 ° C, difficulties may arise with access to normal operation. (check the operating temperature in the room in the user manual).
- there is not enough refrigerant in the air conditioner (split system).
What to do:
- if the equipment is selected incorrectly, it will turn to verified specialists to clarify the calculation of the required equipment capacity for this room. Replace or install a new air conditioner according to specified calculations;
- in case of poor thermal insulation (high heat loss), take measures to eliminate heat loss or add new heating equipment;
- with a large cross of people (doors are constantly open), equip the entrance with a thermal curtain;
- if the room temperature is below the range specified by the manufacturer, then the air must be heated with some additional heating device to the minimum working temperature inside the room (+ 16 ° ~ + 17 ° C). Then do not turn off the air conditioner.