Application of total heat exchanger in Engineering

Talking about the application of total heat exchanger in engineering

1 overview

the energy consumption of buildings in China accounts for about 18% - 25% of the total energy consumption in the country, and this proportion will increase with the continuous improvement of people's living standards. In the energy consumption of buildings, the energy consumption of HVAC accounts for more than 60%. Therefore, building energy conservation, especially HVAC system energy conservation, is a major demand for national economic and social development. At the same time, with the improvement of people's attention to the quality of life, indoor thermal comfort and air quality have been paid more and more attention by consumers. Therefore, the design of HVAC system should be based on the theme of energy conservation, and try to reduce system energy consumption while improving indoor thermal comfort and indoor air quality

this paper takes a university experimental building in Fujian as an example. The floors are 4 ~ 6 floors, and the building height is less than 25m. According to the engineering characteristics, this design adopts frequency conversion multi connected air-cooled central air conditioning system. Combined with the total heat exchanger, the purpose of not only saving the energy consumption of the air conditioning system, but also improving the indoor air quality and thermal comfort is achieved

2 application of enthalpy recovery technology in this project

2.1 characteristics of enthalpy recovery technology

building energy conservation, especially HVAC system energy conservation, is a major demand for national economic and social development. At the same time, with the improvement of people's attention to the quality of life, indoor thermal comfort and air quality have been paid more and more attention by consumers. As the airtightness of modern air-conditioned buildings is getting higher and higher, its indoor air quality can only rely on centralized delivery (2) because the jaws of material testing machines often use outdoor fresh air into the room to ensure

in the total energy consumption of air conditioning system, the energy consumption of handling fresh air load accounts for a large proportion. In actual operation, many buildings artificially reduce the amount of fresh air introduced into the building in order to reduce the energy consumption of air conditioning system, which is obviously insufficient. More and more attention has been paid to the ventilation safety of air-conditioned buildings due to the insufficient supply of fresh air. The SARS crisis in the spring of 2003 sounded an alarm for the ventilation safety of air-conditioning systems. The fundamental to solve the problems of indoor air quality and ventilation safety of air-conditioned buildings is to increase the outdoor fresh air volume of air-conditioned rooms and minimize energy consumption. It is a feasible method to set up energy recovery equipment in the fresh air/exhaust system

people spend 90% of their lives indoors. With the continuous improvement of living standards, more and more people will put forward higher requirements for indoor air quality (IAQ). The total heat exchanger can comprehensively and thoroughly solve the three elements of humidity, cleanliness and air flow, and play the function of regulating and recycling the temperature

Figure 2 energy saving capacity and investment payback period of the best 15 energy-saving technologies

as shown in Figure 2, enthalpy recovery technology ranks second among the best 15 energy-saving technologies promoted by the U.S. Department of energy. Because it does not need to drive energy during operation, its investment payback period is about 2 years. Therefore, this technology has great application prospects

Figure 3 structure of total heat exchanger

Figure 3 is the structure and principle diagram of total heat exchanger. Total heat exchange includes sensible heat and latent heat exchange

exchange of temperature (sensible heat)

when air with different temperatures flows through both sides of the medium, heat is exchanged by conduction

humidity (latent heat) exchange

humidity exchange is carried out through the following two mechanisms

① conduct humidity exchange through the differential pressure of water vapor on both sides of the medium

② there is a step hole in the center of the water vapor disc on the high humidity side, which is absorbed by the hygroscopic agent and released to the low humidity side through the capillary action of the paper fiber

2.2 application of enthalpy recovery technology in this project

as the laboratory is also the place for students to attend classes, the personnel are relatively concentrated and the number is large. If there is no fresh air, the air quality is very poor, resulting in dizziness, chest tightness and low efficiency. In addition, the laboratory has requirements for exhaust air, which cannot be penetrated through the cracks of doors and windows like general office buildings, and a certain amount of exhaust air must be guaranteed. The discharged air is indoor air with low temperature (26 ℃), and the fresh air temperature that needs to be supplemented (35.2 ℃). This will inevitably cause a wave of energy. At this time, the discharge outlet is in the middle and upper position, which is not conducive to energy conservation

due to the requirements of fresh air and exhaust air, we can recover the heat of exhaust air. Choosing total heat exchanger to pre cool the fresh air is a good treatment method

now, some manufacturers' total heat exchangers can basically achieve a heat recovery rate of 75%, and the total energy-saving effect is as high as 70%, thus reducing the load of air conditioning by 20%, and the investment can be recovered in a few years

the total heat exchanger has various forms and specifications. The large one can be equipped with several rooms, and its air volume can reach more than 100om3/h, while the small one is equipped with one for each room. Therefore, its location and type selection should be unified and coordinated with the interior decoration. At the same time, when arranging the air outlet and air inlet, we should not only prevent the short circuit of the air inlet and exhaust flow, but also consider the conflicting requirements of the construction profession, sometimes the latter has greater restrictions

the flow chart of the air conditioning process with total heat exchanger is shown in Figure 4

Figure 4 air treatment process diagram

the I-D diagram of summer treatment process is shown in Figure 5

Figure 5 summer air treatment process

1. Determination of W1 state point after enthalpy recovery:

(subscript 1 is the outdoor state point, 2 is the state point after the problem of heat exchange accuracy, and N is the indoor state point)

the apparent efficiency of the runner total heat exchanger is:

get T2 = 27.8 ℃

the latent heat efficiency of the runner total heat exchanger is:

get D2 = 14.5g/kg (dry)

2 After enthalpy recovery, the reduced cooling load of fresh air is reduced:

3. The cooling load of fan coil is reduced:

L point is to = 13 ℃ and φ＝ 95% intersection,

il=34.5kj/kg

conclusion

this design is based on improving indoor thermal comfort and indoor air quality while minimizing system energy consumption. In view of this design idea, this design: (1) the air conditioning system adopts VRV system, which can flexibly control and save electric energy; (2) The air conditioning fresh air system adopts total heat exchanger to recover the energy of exhaust air, which is conducive to improving the comfort of indoor air and reducing the air conditioning load by about 20%

in this system design, the VRV air conditioning system is organically combined with the total heat exchanger, which saves the energy consumption of the air conditioning system, reduces the operating cost, improves the indoor air quality and improves the comfort. According to the manufacturer's research