Air-conditioning apparatus with simultaneous heating and defrosting modes

1. An air-conditioning apparatus comprising:

a plurality of outdoor units through which refrigerant flows, the plurality of outdoor units each including a compressor and an outdoor heat exchanger;

at least one indoor unit through which a heat medium flows, the at least one indoor unit including an indoor heat exchanger;

a plurality of relay devices to which the plurality of outdoor units are connected independently, and to which the indoor unit is connected, each of the plurality of relay devices including a heat medium heat exchanger configured to exchange heat between the refrigerant and the heat medium; and

a controller configured to control action of the plurality of outdoor units, the indoor unit, and the plurality of relay devices,

the controller being configured to

determine the necessity for a defrosting operation for each of the plurality of outdoor units,

responsive to determining that the defrosting operation is necessary, compare an indoor unit total load with an outdoor unit total capacity, the indoor unit total load indicating an air conditioning load during a heating operation, the outdoor unit total capacity indicating a capacity of an other outdoor unit excluding a target outdoor unit where the defrosting operation is necessary, and

responsive to determining that the indoor unit total load is greater than the outdoor unit total capacity as a result of comparing, control an operating frequency of the compressor of the other outdoor unit to increase the outdoor unit total capacity.

2. The air-conditioning apparatus of claim 1 , wherein

each of the plurality of outdoor units further includes

an outdoor-side outlet temperature sensor configured to detect a refrigerant outlet temperature of the refrigerant flowing out from the outdoor heat exchanger during the heating operation, and

the controller determines that the defrosting operation is necessary in a case where the refrigerant outlet temperature is equal to or below a set temperature set in advance for the refrigerant outlet temperature.

3. The air-conditioning apparatus of claim 1 , wherein

the indoor unit further includes a suction temperature sensor configured to detect a suction temperature being a temperature of air in an indoor space, the air being to be supplied to the indoor heat exchanger,

the controller obtains the indoor unit total load based on the suction temperature and a set temperature indicating a target temperature of the indoor space, and

the controller obtains the outdoor unit total capacity based on the operating frequency of the compressor of the other outdoor unit.

4. The air-conditioning apparatus of claim 1 , wherein

the indoor unit further includes

an indoor-side inlet temperature sensor configured to detect a heat medium inlet temperature of the heat medium flowing into the indoor heat exchanger, and

an indoor-side outlet temperature sensor configured to detect a heat medium outlet temperature of the heat medium flowing out from the indoor heat exchanger,

the controller obtains the indoor unit total load based on the heat medium inlet temperature and the heat medium outlet temperature, and

the controller obtains the outdoor unit total capacity based on the operating frequency of the compressor of the other outdoor unit.

5. The air-conditioning apparatus of claim 1 , wherein

each of the plurality of relay devices further includes

a bypass valve provided to a bypass that bypasses the heat medium flowing through the heat medium heat exchanger, and

a pump configured to cause the heat medium to circulate,

the indoor unit further includes an indoor fan configured to supply air to the indoor heat exchanger, and

in a case where a temperature of the heat medium flowing through a relay device of the plurality of relay devices that is connected to the target outdoor unit is lower than a water temperature threshold set in advance as a comparison result from the load determination unit, the controller brings the bypass valve of the relay device connected to the target outdoor unit into an open state, reduces a wind speed of the indoor fan of the indoor unit or stops the indoor fan, and increases a flow rate in the pump of each of the plurality of relay devices.

6. The air-conditioning apparatus of claim 2 , wherein

the controller is further configured to determine an order of priority in performing the defrosting operation for all of the plurality of outdoor units in a case where the defrosting operation is necessary for all of the plurality of outdoor units as a result of a determination.

7. The air-conditioning apparatus of claim 6 , wherein

the controller determines the order of priority such that an outdoor unit with a lower refrigerant outlet temperature has a higher order of priority.

8. The air-conditioning apparatus of claim 6 , wherein

the controller is further configured to determine a defrosting time for each of the plurality of outdoor units in performing the defrosting operation for all of the plurality of outdoor units.

9. The air-conditioning apparatus of claim 8 , wherein

the controller determines the defrosting time such that an outdoor unit with a lower refrigerant outlet temperature has a longer defrosting time.

10. The air-conditioning apparatus of claim 8 , wherein

the controller determines the defrosting time, using a defrosting time determination table where the defrosting time is associated in a stepwise manner with every set range of the refrigerant outlet temperature, such that an outdoor unit with a lower refrigerant outlet temperature has a longer defrosting time increased in a stepwise manner.

11. The air-conditioning apparatus of claim 1 , wherein the plurality of outdoor units are connected in parallel.