What Is a Cooling Load?

The definition of cold load is to maintain the building's hot and humid environment and the required indoor temperature. The heat that must be taken away from the room by the air-conditioning system is called the cold load of the air-conditioned room, or the amount of cold that needs to be supplied to the room at a time is called Cold load, cold load includes sensible heat and latent heat. In contrast, if the air-conditioning system needs to supply heat to the room to compensate for the room's loss of heat, the heat supplied to the room is called a heat load.

1. The heat storage characteristics of the building structure determine the relationship between the cooling load and the heat gain. The convective components of the latent and sensible heat in the instantaneous heat immediately constitute an instantaneous cold load, while the radiant components in the sensible heat do not immediately constitute a cold load. The radiant heat is slowly dissipated after being absorbed and stored by the objects in the room. Give indoor air.

2. The air conditioning load is to maintain the building's hot and humid environment. The amount of cold that needs to be supplied to the room at a certain time is called the cold load. In contrast, the amount of heat that needs to be supplied to a room in order to compensate for its heat loss is called the heat load.

3. The indoor cooling load mainly includes the following aspects: lighting heat dissipation, human body heat dissipation, indoor electrical equipment heat dissipation, the amount of sunlight entering the room through the glass window, heat transfer through the temperature difference of the glass window, and unstable heat transfer of the envelope structure.

4. In the summer of cooling, the cooling load should be calculated to provide matching cooling capacity; in the winter, the heat load should be calculated to provide matching heating energy. In other words, the cooling load depends on the cooling load, and the heating load depends on the heat load. ^[1]

The capacity of each device in the air-conditioning system is selected according to the principle of capacity redundancy, that is, based on the maximum heat and humidity loads that may occur in air-conditioned buildings. In the actual operation of air-conditioning, the air-conditioning load is dynamically changed, and in most cases Below is running under partial load.

When the air-conditioning system is in a stable state at some point during operation, the temperature of the air in the air-conditioned building remains constant, and the heat flowing out and flowing into the air-conditioned room is in a balanced state.

The external energy disrupts the original state of energy balance and causes changes in the adjustment parameters, so the adjustment process begins to change the input or output energy of the object to bring the energy to a new balance and return the adjustment parameters to a given value. The load of the air-conditioning system changes dynamically under the influence of various external factors. These external factors mainly include the following:

(1) Solar radiation. The solar radiant heat that enters the room through the outer window of an air-conditioned room will be affected by changes in cloudy and sunny weather.

(2) Outdoor air temperature. Changes in indoor and outdoor heat transfer due to changes in indoor and outdoor temperature differences cause changes in cooling and heat loads in air-conditioned rooms.

(3) Penetration of outdoor air. Outdoor air enters the room through the gaps in the doors and windows of the air-conditioned room, which affects the indoor temperature.

(4) Fresh air. In order to meet the indoor sanitary needs and positive pressure and exhaust air requirements, changes in the amount of outdoor fresh air are introduced, that is, the use of fresh air directly causes changes in indoor cold and heat loads.

(5) Changes in the number of lighting, electric heating and electromechanical equipment on, off and in use in the built environment.

(6) The increase or decrease in the number of workers in the built environment will directly affect the level of cold and heat loads.

(7) Changes in indoor humidity cause changes in heat load, and changes in indoor humidity also cause changes in cold and heat loads in the air conditioning system.

(8) The outer envelope of the building also has a significant impact on the cold and heat load levels of the air-conditioned area. ^[1]

The cooling load of the air-conditioning area is one of the basis for determining the air-conditioning air supply process of the building and the capacity of the air-conditioning equipment. The calculation of the cold load in each link includes: the calculated cold load of the air conditioning area, the calculated cold load of the air-conditioned building, the calculated cold load of the air conditioning system, and the calculated cold load of the air conditioning cold source. ^[2]

The building cold load is mainly composed of external and internal disturbances. Therefore, controlling the building cold load includes reducing the internal heat source and reducing the heat transfer of the envelope structure.

Cooling load reduces internal heat source

In summer, part of the cold load comes from internal heat sources. Such as human body heat dissipation, electrical equipment heat dissipation, cooking heat dissipation and so on. Therefore, it is important to reduce the cooling load to reduce the generation of internal heat. Among them, human body heat is uncontrollable.

1. Lighting control heat dissipation

The most common indoor heat source is lighting fixtures. Taking incandescent lamps as an example, the light efficiency of this kind of bulb is extremely low, ranging from 5% to 10%, and the remaining electrical energy is converted into thermal energy. Therefore, incandescent lamps are also called thermal bulbs. The use of highly efficient energy-saving fluorescent lamps and a new type of LED light source can effectively reduce the amount of heat dissipated by the camera.

2.Control of electrical equipment heat dissipation

Selecting energy-saving electrical products with low heat dissipation can effectively reduce the heat generated by electrical equipment. In addition, arranging appliances with large heat production in relatively isolated areas can also reduce the impact of unused heat production on the indoor thermal environment. ^[3]

Cooling load reduces envelope heat transfer

The heat transfer of the envelope structure is the main component of the cold load. Controlling the heat transfer of the envelope structure is also the basic way to reduce the cold load. The heat gain of the envelope structure mainly includes solar radiant heat, convective heat transfer between the same air and the structure around the building, and air penetration heat. Because the heat from the outside can significantly increase the cooling load, it is important to reduce the heating of the envelope in the passive cooling design. ^[3]