Introduction to current environment issues

There are 142 hazy days, in average, per year in big cities, and more than half of China is under the influence of haze, with 104 cities moderately polluted. PM2.5 is consistently deemed to be the chief culprit causing air pollution and affecting health. The smaller the particle is, the easier it is to enter the depths of the organs, and the greater its harm to health is. The particulate pollutants long hidden in the air may cause respiratory diseases, cardiovascular diseases, and even cancer. According to Tsinghua University’s research report, indoor pollution is more than four times of outdoor pollution, while we spend 80% of our life indoors, so the indoor air quality issue shall bring to special attentions. In addition to the intrusion of PM2.5 indoor, which is four times of that outdoors, there are also pollution problems like formaldehyde, excess carbon dioxide, oxygen deficit, more than 500 kinds of volatiles and more than 200 kinds of viruses. Without indoor ventilation, we will suffer from various diseases and hidden dangers, and keep in the sub-health state. 

1. Hazard of oxygen deficit: Oxygen deficit in human body may lead to abnormalities in the metabolism of various tissues, and even cause lesion to vital organs like brain and heart, and even death; oxygen deficit may also affect the body growth and mental development of infants.

2. Hazard of formaldehyde: International Agency for Research on Cancer (IARC) classifies formaldehyde as the category-one carcinogen that may cause nasopharyngeal cancer, nasal cancer, sinus cancer and even leukemia.

3. Hazard of carbon dioxide: in case of a concentration of carbon dioxide above 1,000ppm, we will feel drowsy and sick and have rapid heartbeat. In case of a concentration above 5,000ppm, it may cause cerebral injury.

The fresh air system is an indoor circulating ventilation system consisting of fresh air unit, fresh air pipeline, vent and an electric control. The system handle and regulate the outdoor fresh air in terms of purification, temperature and humidity regulation, and then introduce it into the house, and discharges the original indoor vitiated air, via vent and exhaust duct, out of the house. Through such continuous and effective circulation of indoor and outdoor air, the indoor air is kept as fresh and comfortable as that in nature.

Comparison between fresh air system and other environmental electric appliances

a.Opening window for ventilation This is natural ventilation and is greatly affected by outdoor environmental factors like outdoor PM2.5 pollution, raise dust, noise and temperature. In summer and winter, this way of ventilation also wastes a large amount of energy due to the presence of air conditioners and heating. What’s more, due to the blind wind direction and airflow, the needs of fresh air in the whole house cannot be met.

b.Ventilation fan This is a simple ventilation equipment used for short time local application, like the ventilation fan installed in the bathroom, with short design life, large noise, small blowing rate, no purification nor energy saving function, which cannot meet the needs of comfortable and fresh air in the whole house.

c.Air purifier It purifies the indoor air through long-time indoor air circulation, and it can purify fine particles like PM2.5. But as the indoor and outdoor air cannot be ventilated for a long time, the indoor oxygen content will significantly reduce, while the pollution indicators like formaldehyde, organic volatile and CO2 will significantly increase, so we must keep air ventilated and exchanged when using the air purifier.

d.Air conditioner Most air conditioners have no fresh air function, but only partial purification function. When using the air conditioner, we must keep the doors and windows closed to concentrate the energy and not to emit it; as a result, we cannot get more fresh air. Even if the air conditioner is provided with the fresh air function, it can only supplement limited amount of fresh air oxygen, and cannot guarantee the indoor air quality. Due to oxygen deficit and indoor pollution, the confined space may lower our immunity and even cause air-condition diseases in case of large temperature differences between indoor and outdoor air.

Significant functions of the fresh air system in the whole house

a.Purify indoor PM2.5 particles and sterilize effectively

b.Provide sufficient fresh oxygen indoors

c.Regulate indoor humidity and temperature effectively

d.Discharge effectively formaldehyde, organic volatiles, carbon dioxide, odor and other pollutants out of the house

e.Save significant indoor energies with the heat recovery unit

Power consumption of fresh air ventilator

The power consuming components of the fresh air unit are motor and control of the ventilator, with a power consumption equivalent to that of the fan. The household fresh air unit generally consumes about 100W of power, and is one of the indoor products with low power consumption, yet the heat recovery equipment of the fresh air unit can recover 70-96.5% of energy loss, actually saving large energy expenditures for the family.

Selection of fresh air ventilator

Key parameters of fresh air ventilator: fresh air volume, static pressure, noise, heat recovery rate, primary purifying rate of PM2.5, power;

Slight fresh air volume is the full name of fresh air volume, which meets the requirements of fresh air volume indoors based on related standards. The fresh air volume can be calculated in two ways:

a.Ventilation times: 0.5-1 time of ventilation to be generally selected for household; see relevant standards for the recommended ventilation times in other fields or environments.

b.Per capita fresh air volume: 30-50m3 fresh air volume per capita per hour for household; see relevant standards for the recommended ventilation times in other fields or environments.

Here is an example: a master bedroom with an area of 20m2 and a height of 2.8m.

The fresh air volume is calculated according to Method a to be 20*2.8*1=56 m3/hour

In case of two people in the master bedroom, the fresh air volume is calculated according to Method b to be 2*30=60 m3/hour

The larger one of the two calculation results is taken as the selection basis, i.e. 60 m3 fresh air volume is required per hour in this room. This method also applies to the remaining rooms, and the total blowing rate of all rooms is less than or equal to that of the selected fresh air unit. Different occasions require different fresh air volumes and ventilation times. For details, see the table below:

Modeling Guide

Heat recovery rate

The fresh air system has a heat recovery function achieved by the heat exchangers, which are generally divided into sensible heat and total heat. The sensible heat exchanger only exchanges the sensible heat or temperature, and the total heat exchanger exchanges both latent heat and sensible heat, or both temperature and humidity.

The heat exchange efficiency is an indicator for measuring the energy recovery effect. The higher the heat exchange efficiency is, the better the energy recovery performance of the equipment is, and the more obvious the energy saving effect is.

Static pressure is a concept in fluid mechanics. When air flows along the inner wall of the pipeline, there will be dynamic pressure and static pressure. The air molecules move irregularly and hit against the pipe wall to generate the static pressure, and when the air molecules hit against the pipe wall, the counteractive resistance will be generated by the pipe wall. To overcome such a resistance, the host shall be designed with adding external excess pressure, namely the static pressure of the host. The larger the static pressure is, the stronger the pipeline resistance that the host overcomes is, and the longer the pipeline system that can be connected externally is.

For specific technology consulting and academic communication, please contact NILAN Service .