The function of the fresh air unit is to process the outdoor fresh air and send it into each room. In winter, the fresh air unit heats the outdoor cold air, that is, the surface cooler of the fresh air unit directly contacts the outside cold air, in order to prevent the surface cooler from being frozen when the heating is stopped. , An electric multi-leaf control valve should be added at the fresh air inlet and linked with the fresh air unit. When the fresh air unit is running, the air valve is opened, and when the fresh air fan is closed, the air valve is closed. This prevents the outdoor cold air from cooling the water in the surface cooler directly after the fresh air unit and the refrigerant water pump stop running, causing the water to freeze and freeze. Table cooler.