The heat medium in the Fresh air handling unit heat exchanger is water (surface cooling: 7~12℃; Heating to 70-90℃ or steam heating) In winter in the north, when the temperature drops below 0℃, whether it is a commercial clean air conditioning unit or a fresh air ventilation unit, the maintenance of the fresh air handling unit needs regular maintenance and periodic inspection. Especially in cold winter, prevent the copper pipe of a surface cooling coil of the fresh air handling unit coil from freezing and cracking.
This is the same as the principle of the fan coil unit, which brings warmth and coolness into the room through the copper pipe cold water/hot water medium in the surface cooler to improve the balance of indoor air temperature.
The fresh air handling unit, which is the same as the fan coil unit, is mostly installed on the indoor roof. Once there is water leakage, the indoor equipment will be damaged. Compared with the fan coil unit, the fresh air treatment unit has stronger adaptability to the use environment.
Causes and prevention methods of the freezing crack of pipes using fresh air handling unit in winter.
On the one hand, the freezing and heat preservation of the copper pipe of the Fresh air treatment unit or the fan coil unit is caused by freezing, and there are several other important reasons:
1. Dirty blockage
The dirty blockage is common.
Common blocking substances are iron filings, dust, silt, weeds, etc.
Workaround:
Usually, in order to maintain the stability of water quality, a proper amount of sodium hexametaphosphate should be added to the system, but it is easy to dissolve a small amount of oxygen into hot water, resulting in corrosion of metal pipes and equipment and rust.
After the rusting system is recycled for a period of time, the substances precipitated from the water, together with the accumulated dust, microorganisms, and so on, stay in some parts of the pipeline and equipment with the circulation of hot water, and accumulate to form a dirty blockage, which blocks the passage of some fan coil units exhaust valve automatic devices.
2. Gas blockage
Air blockage in a copper tube of the surface cooler.
A, part of the air in the cleaning and water filling stage is not discharged.
B, the air overflowing from the water and the evaporated water vapor in the heating stage
C, changing water quality many times leads to the increase of gas content in the system.
D, Some automatic parts of the exhaust valve are damaged, and the exhaust system is ignored.
3. No antifreeze sensor is installed or the installation position of the antifreeze sensor is wrong.
A, The antifreeze sensor should be installed at the backwater of the windward side of the hot water coil; Only the antifreeze alarm is displayed remotely, but not linked with the fresh air fan and electric fresh air valve. Apart from the above points, there is another common problem in the ERV system.
B. In areas with low temperatures in winter, when residential buildings adopt total heat exchangers and the fresh air volume is larger than the exhaust air volume, the fresh air temperature will increase slightly. When the outdoor temperature drops suddenly and the initial room temperature is low, the outlet air temperature of the ERV device will be lower than 0℃;
C. In the initial stage of heating, the water flow in the hot water system is not smooth, so fresh air is directly introduced into the fan coil return bellows for reheating, and the fresh air blows directly on the coil surface, which may cause the coil to freeze and crack.
The above three conditions meet at the same time, which will inevitably lead to the freezing crack of the coil of the air handling unit.
