Considerations in Selecting Packaged Air Conditioners and Their Heat Recovery Operations

Cabinet Insulation: To prevent dew formation on the outer shell of the cabinet, the national standard stipulates that the thermal resistance of the cabinet insulation layer should be not less than 0.68m²/kW. At the same time, it is necessary to prevent cold bridges from occurring at the joints of each section of the cabinet. Currently, PEF or polyurethane foam is often used as the insulation material.

Face Velocity: At present, in order to reduce the overall dimensions of their products, some manufacturers tend to set a relatively high face velocity of the air conditioner cabinet. This can lead to the problem of water carry - over after the cooling coil section of the air conditioner cabinet. If the water baffle is not designed reasonably, this problem will be even more serious. Therefore, when selecting, it is advisable to control the face velocity of the cooling coil within 2 - 2.5m/s.

Air Leakage Index: The national standard stipulates that when the static pressure inside the packaged air conditioner cabinet is 700Pa, the air leakage rate inside the unit shall not exceed 3%. In actual use, we have found that the air leakage rate of some on - site air conditioner cabinets can be as high as 10%. Through analysis, this is mainly caused by the following reasons:
(1) Poor performance of the sealing material.
(2) Unreasonable design of the unit structure.
(3) Poor on - site installation quality.
(4) The cabinet of large - volume air conditioner cabinets has poor rigidity and is prone to deformation during startup and shutdown.

Insufficient Cooling and Heating Capacity: The design and selection of the cooling coils by manufacturers are mostly based on the empirical formula obtained from small - sample test results for scaled - up calculations. There is inherently a certain error in this method. Moreover, some enterprises copy the relevant samples of other manufacturers due to their lack of test conditions. This is the main reason for the insufficient cooling and heating capacity of such products of many manufacturers. Therefore, when conducting on - site inspections of manufacturers, we must understand their product testing methods in person.

Condensate Pan Overflow: This is the most common problem in the use of air conditioner cabinets at present, and users have the strongest reactions. The reasons for this problem are as follows:
(1) Excessive face velocity.
(2) The cooling coil is in the negative - pressure section, and no water seal is installed when the unit leaves the factory.
(3) The length and depth of the condensate pan are insufficient. The problem of excessive face velocity has been mentioned before. Regarding the determination of the height of the water seal set in the unit and the values of the length and depth of the condensate pan, we should negotiate with the manufacturer according to the negative - pressure value of the cooling coil section when placing an order.

Precautions:
For packaged air conditioners with double fans, the air pressure of the supply fan should be greater than that of the return fan. Otherwise, fresh air may not be drawn in.
For the panel material of the air conditioner cabinet, steel plate (with outer surface sprayed) should be preferred. If FRP material is used as the panel, attention should be paid to the fire - prevention issue.
For large - volume units, it is advisable to consider combining some functional sections (such as combining the cooling coil section and the heating section) to reduce the length of the unit.

Rotary Type: The rotary wheel serves as the heat - storage core. Fresh air passes through one semi - circle of the rotary wheel, and exhaust air simultaneously passes through the other semi - circle in the opposite direction. The exhaust air releases cold/heat to the heat - storage core. The temperature of the exhaust air rises/falls, and the temperature of the core falls/rises. When the hot/cold fresh air comes into contact with the cold/hot heat - storage core, there is a temperature difference.

The core releases cold/heat to the fresh air, and the temperature of the fresh air falls/rises.

Plate - Type: Fresh air and exhaust air pass through the heat - storage core in a cross - shaped manner simultaneously. The exhaust air releases cold/heat to the heat - storage core. The temperature of the exhaust air rises/falls, and the temperature of the core falls/rises.