[Solution]
Passive ultra-low energy consumption buildings can provide sufficient, healthy and fresh air with extremely low energy consumption and constant indoor temperature when the outdoor environment is not suitable for natural ventilation by opening external windows through an efficient fresh air system. , the fresh air volume is not less than 30m3/(h·person) to ensure good indoor air quality. Therefore, passive ultra-low energy consumption buildings can provide sufficient and healthy fresh air.
Air handling units equipped with absorbent-coated rotary heat exchangers present significant opportunities to reduce energy and carbon emissions, while also improving the indoor environment. But what exactly makes them so beneficial? Below is a step-by-step guide to understanding what makes adsorption rotor technology so effective, with a particular focus on refrigeration applications.
Adsorption technology
Adsorbent coating materials have the ability to absorb moisture from the air when humidity is high and release it when humidity is low. This means that moisture is recovered; this means that we are also getting latent heat recovery as well as sensible heat recovery.
During the summer when the outdoor air is humid, the moisture in the outdoor air is absorbed and released into the exhaust air. During winter, the moisture content of outdoor air is lower, so adsorption coatings can recover moisture from the return air and release it into the supply air. This brings two benefits in cold outdoor conditions. Firstly, the increased humidity in the supply air is beneficial to the indoor environmental quality, and secondly, since the moisture is removed from the rotor, the risk of frost formation will be greatly reduced and the need for defrosting is more or less avoided. This means that the adsorption rotor saves some heating power for defrosting in winter.
During summer, when humidity is high, moisture is removed from the outdoor air and transferred to the exhaust. In winter, moisture is transferred from the exhaust air to the supply air.
Humidity transfer occurs when there is a difference in the moisture content between the exhaust air and the outside air. The amount of transfer is determined by the potential efficiency performance of the runner.
Supply air latent heat efficiency = (x22-x21)/(x11-x21 ) %
Where
x11= Exhaust air humidity g/kg
x21= Moisture content of outside air g/kg
x22= Supply air moisture content g/kg
Reduced cooling
Thanks to the latent heat recovery of the runner, we significantly reduce the cooling capacity requirement in the refrigeration system. Even with ordinary aluminum heat exchangers, we get reasonable cooling recovery.
Shows how much cooling energy recovery we get with the adsorption runner. This example is based on an outdoor air temperature of 30°C and a supply air temperature of 12°C. Sensible heat runners provide about 20% of the cooling, while adsorption runners provide about half the cooling. This will vary by conditions, but indicates a very significant reduction in the cooling capacity of the adsorption runner.
This latent heat recovery means that we can radically downsize refrigeration equipment. This means a much smaller chiller capacity and distribution system; this means significantly lower installation costs, smaller space requirements and fewer refrigerant charges.
Reduced cooling energy consumption
Of course, the reduction in cooling energy will depend on the duration of the warm weather. The following example has been calculated using the following conditions:
Air volume: 2 m3/s
Supply air temperature: 16 ℃
Exhaust air temperature: 22 ℃
- The adsorption rotor has a temperature efficiency of 82% and a humidity efficiency of 74% in summer.
- The aluminum runner has a temperature efficiency of up to 82% in spring and summer.
- The pressure drop of the adsorption runner is about 10Pa higher than that of the aluminum runner, so the difference in fan energy consumption is small.
- The first picture shows the cold energy recovery using an aluminium rotor and the second picture shows the cold energy recovery using an adsorption rotor.
In this example, the reduction in cooling energy consumption is close to 50% in the warmer climates of Milan and Frankfurt, and close to 20% in the cooler cities.
Adsorption rotors are relatively simple machines compared to refrigeration units, so we have the added benefit of much lower maintenance costs per kWh.
Peak power reduction
Occasionally, you will encounter weather with higher temperature and humidity than design values. Of course, this will cause the indoor temperature to rise. The recovered cooling power of the heat exchanger is proportional to the temperature and humidity difference, so when the outdoor conditions increase and the difference between the exhaust air and the outdoor conditions increases, we get more recovered energy.
Moisture Recovery
In cold weather, the humidity of the heated outdoor air is lower, so the indoor air becomes dry. In this case, the adsorption rotor recovers the moisture in the return air and returns it to the supply air; this means that the indoor air remains moist, more comfortable and hygienic. Humidification may be required to increase the humidity, then the adsorption wheel brings the benefit of a lower humidification load, so installation costs will be lower and running costs will be lower.
In this example, the cold air is heated by the rotor to 13 degrees Celsius and then reheated to 20 degrees Celsius.
When using the aluminum rotor, the relative humidity of the supply air produced is only 10%, while when using the adsorption rotor, the relative humidity is more than 25%.
Reduce humidification power
We can see that the humidification cost is significantly reduced. If we assume that the supply air needs 30% to 40% relative humidity, then we don't need to add about 5-6 grams of moisture per kilogram of air, we only need to add 2-3 grams of moisture, so the cost will be reduced by half using an adsorption runner . If an adiabatic humidifier is used, then the adsorption wheel can provide the benefits of reduced reheat power and reduced water consumption.
Leaks
The disadvantage of rotary heat exchangers is that there is an internal leakage problem between the return air and the supply air. With proper design and installation, leakage can be reduced to less than 1%. The runner needs to have effective seals, purge sectors, and the system needs to have the correct pressure balance set.
To get the correct pressure balance, the fan needs to be positioned correctly. The supply and exhaust fans are preferably installed upstream of the runners in their respective airflows. It is usually necessary to introduce a pressure reducing device in the return air.
Conclusion
The ability of adsorption runners to recover sensible and latent heat has a profound impact on both cooling power demand and cooling energy consumption. The refrigeration system is made smaller, saving space and cost. Smaller chillers also mean less refrigerant. Taken together, adsorption runners offer many significant advantages in terms of energy savings and lower investment costs, while ensuring greater comfort and health.
