In the HVAC industry, the heat recovery unit we commonly see has many forms: rotary heat recovery, plate-fin heat recovery, wheel channel heat recovery, heat pipe heat recovery and so on. These words need not be understood in detail, but just know about it.
In our most common fresh air system, the most common is the "plate-fin heat recovery" unit. There are also some imported products using rotary heat recovery, but usually high price, complex structure, inconvenient maintenance, less domestic application. Let's talk about the most common "plate-fin heat recovery".
Plate-fin heat recovery (classified by total heat and sensible heat) :
All-hot: Usually made from specially processed paper (such as kraft paper soaked in lithium chloride). Both heat transfer and moisture transfer.
Sensible heat type: usually made of aluminum plate (but also steel plate). So if you see a product advertised its heat exchange unit is made of aluminum, it is usually sensible heat recovery equipment.
Comparison of heat recovery effects:
In the process of heat recovery, because the all-heat equipment can exchange temperature and humidity, it is not easy to produce condensed water, because humidity will be exchanged and go into the air on the other side. In a simple way, if the indoor humidity is greater than the outdoor humidity, the indoor humidity will be transmitted to the fresh air and increase the humidity to the fresh air when the two air currents exchange heat. This is more obvious in winter, indoor humidity is large, outdoor humidity is small, exhaust air will humidify the fresh air. When the indoor humidity is lower than the outdoor humidity, the humidity of the outdoor fresh air will "run" to the exhaust wind, which is equal to the humidity of the outdoor fresh air. This situation often occurs in the spring and summer in the south. Due to the air conditioning, the indoor humidity is lower than the outdoor humidity. These two situations are favorable to improve the quality of fresh air.
For sensible heat equipment, only temperature can be exchanged, but humidity can not be exchanged. In the process of heat exchange, if the temperature difference between indoor and outdoor is too large, after reaching the dew point of the air, condensed water will be generated in the heat recovery unit. Therefore, drainpipes should be installed for all sensible heat equipment. So when you see a device with a drain pipe, you're pretty sure it's a sensible heat recovery device. What's wrong with condensate? When the condensed water appears in the heat exchange unit, it turns into water droplets in summer, which will block the air passage, seriously reduce the heat exchange rate of the equipment, and worsen the energy saving effect. In winter, frost will form, which will also block the air passage and affect the heat exchange effect of equipment.
Do you have some understanding of sensible and latent heat recovery methods? In fact, latent heat and sensible heat are both heat recovery methods, and their functions are roughly the same, but the principle of action is different.