Abstract This paper analyzes the relationship between fan coil unit, indoor heat and humidity ratio and fresh air. It is pointed out that the conventional design method is difficult to obtain satisfactory results in the actual design, and a fan coil plus fresh air system is proposed. Design method.
Keyword fan coil fresh air design fan coil and independent fresh air system is a widely used air conditioning form. The hotel building rooms, office buildings, hospital wards, etc. mostly use this system, and some designers also apply it. Go to restaurants, cafes, KTV rooms and more. Different room functions have different air conditioning load characteristics, that is, the required indoor heat and humidity processes are different. However, at present, when designing a designer, the fan coil is usually selected only according to the load size, and the fresh air is processed according to the recommended state of the fresh air treatment, without considering whether the indoor air treatment process is truly satisfied. Although there are many analysis processes for the fan coil and fresh air system in the manuals, textbooks, and journals, the heat and humidity capacity of the fan coils is less considered, and the design is less maneuverable. It is also difficult to apply it to the design to make the necessary calculations. This paper intends to analyze the effects of the heat and humidity process of air treatment on the air conditioning and the final state of fresh air treatment on the indoor heat and humidity ratio, and obtain a more reasonable and feasible design method of the fan coil and fresh air system.
First, the heat and humidity ratio of the heat and humidity ratio of the air treatment process of the fan coil is Erc. According to the sample of the fan coil, according to the determined indoor design parameters, the cold water temperature and flow rate and the operating grade of the fan coil, the fan is obtained. The total heat capacity Qt of the coil and the sensible heat capacity Qs, the heat-humidity ratio of the fan coil air treatment process is: different types of fan coils, when operating in different grades, for different indoor temperature and humidity conditions, The thermal performance of the fan coil (ie, the amount of cooling and dehumidification it provides) is different at different chilled water temperatures and flows. How to find the fan coil for air treatment, but only a few manufacturers have more detailed fan coil multi-case thermal performance data, while most manufacturers only have standard operating conditions (inlet air dry bulb temperature 1 :1.=27'(:, wet bulb temperature 1.=19.5' into 0 water temperature 1; 11.=71, inlet and outlet temperature difference 5 - the thermal performance data of the fan coil can not meet the multi-conditions Requirements: The author passed the thermal performance data of the carrier fan coil (four models: 002, 003, 004, 006, respectively, in six water temperatures: 510C, four water flows and eleven temperatures and humidity) Under the condition, about 2000 data are sorted and analyzed. The mathematical method of multiple regression is used to obtain the following full cooling capacity and sensible cooling capacity equation of the fan coil: Qs, the fan coil is in working condition and standard. The sensible heat capacity under working conditions: G, G0 fan coil water flow under working conditions and standard working conditions, kg/s; V, V-fan coil air volume under working conditions and standard working conditions , mVs; tl0 fan coil in the working condition, air inlet dry bulb temperature under standard working conditions, C; tsl, tsl0 wind Coil in use conditions, the standard conditions of inlet air wet-bulb temperature, c: twl, tmo fan coil in use conditions, the cold water inlet temperature standard conditions, I :.
eFC=2500/ thinks that the fan coil should only bear the changing cooling load (the cooling load of the envelope structure), and the new wind turbine group should take the stable cold load (personnel, lighting load) as the benchmark to determine the final state of the fresh wind. The final state point. It is believed that when the fresh air system is dispersed and the control point is more than L7 m1, the new wind should be treated to L1; when the fresh air system is set centrally and the control points are small, the new wind should be treated to L3. According to the fresh air temperature of the new fan unit and the cold water temperature of the fan coil, Moreover, when the fan coil is turned off and only the fresh air is sent, the principle that the indoor temperature and humidity do not change greatly, and the analysis shows that L5 is a reasonable new wind end state. They also analyzed from different angles (outdoor meteorological conditions, internal and external zones), and considered that L6 and L7 are better, so that the fresh air can bear the indoor wet load, and the fan coil can be operated in dry conditions, avoiding the long-term humidity of the condensate pan. The resulting sanitary problems, the coil ribs are less likely to accumulate dust and reduce the amount of cleaning work. The design manual also considers that 1 point is the most reasonable, the fan coil is dry, and the load is small, and the small one can be selected. However, the author believes that whether the fan coil is used for dry operation has nothing to do with the new wind. When the coefficient of moisture evolution of the fan coil is =1, the heat and humidity of the fan coil to the air treatment process is Ksre=, the fan coil is in dry condition; when >1, the sF, the fan coil is in wet condition. It can be known from formula (4) that the heat and humidity of the fan coil to the air treatment process is only related to the air inlet temperature and humidity conditions, the cold water temperature, the water flow rate and the air volume. When the fresh air is directly sent into the room, it is irrelevant to the fresh air, that is, the fan disk. Dry and wet conditions have nothing to do with fresh air. In the interior design parameter range H of the comfort air conditioner, the dry condition of the fan coil requires a higher cold water temperature, and the water temperature rises, and the cooling capacity provided by the fan coil will decrease. For example, the interior design parameters tN=25'C, cpN=50%, standard water volume, high-grade air volume, only the cold water temperature is higher than 11.5X: the fan coil is dry; and the fan coil cooling capacity at this time It is only 60% of the cooling capacity of the fan coil when the cold water temperature is 7'C (others are unchanged). Although the fan coil is responsible for part of the indoor load, the cooling capacity provided is much reduced. It is possible that the fan coil can not only choose the small one model, but instead asks to choose the larger one, which makes the cost increase and the installation inconvenient.
These practices have taken into account factors such as consistency of cold water, control and operation regulation, internal and external partitioning, and fan coil operation close to dry conditions. However, only the enthalpy difference provided by the fan coil (ie, the total heat and cooling capacity) is considered, and the cooling and dehumidifying capacity of the fan coil is not comprehensively considered, that is, the heat-humidity ratio of the fan coil to the air treatment process is often eFe. The rooms that cause different heat and humidity properties of water (such as hotel rooms and restaurants) use the same fan coil operating parameters and the same fresh air end state, which obviously cannot meet the requirements. The difference between the indoor heat and humidity process and the different fresh air treatment end states require that the cooling capacity and air handling process of the fan coil are different. From the rationale, very few people go to check whether the fan coil mee meets the requirements, but only pay attention to whether the total cooling capacity meets the requirements, and few people really investigate the indoor state (mainly humidity) of the fan coil air conditioner. Whether the requirements are met.
Third, the fan coil plus fresh air system design e value comparison method in the fan coil is often selected according to the cooling load, only consider the fan coil treatment ç„“ difference (full heat cooling) is greater than the cold load, and not Considering the dehumidification capacity of the fan coil, it is not considered whether the air treatment process of the fan coil meets the processing required for the interior design. The choice of the final parameters of the new wind also sets off the thermal performance of the fan coil, only from some of the aforementioned non-primary factors.
If the margin of total heat treatment capacity > the margin of heat treatment capacity, then the potential heat treatment capacity must have a margin; if the full heat treatment capacity of the author believes that the design and equipment selection of the fan coil plus fresh air system must be considered comprehensively The relationship between the indoor heat and humidity process, the new wind final parameters and the fan coil thermal performance. Here, a design selection method for a fan coil and a fresh air system is proposed. The method of use in the following is still called the s value comparison method. That is to compare the heat-humidity ratio required in the room with the heat-humidity ratio of the fan coil to the air treatment process, so that the two are similar.
Set the fresh air treatment to the state point L (L point is equal to the relative humidity line, according to the new wind turbine team is 95% or 90%), see Table 1. Known: f fresh air treatment final state point parameter Table 1 consider the fresh wind The indoor heat and humidity ratio is: the change of the indoor comprehensive heat and humidity ratio f is indicated as the fresh air state point changes. It can be seen that as the fresh air temperature decreases, the indoor integrated heat-humidity ratio becomes larger; when the fresh air state point is the intersection of the indoor heat-humidity ratio f line and cpt, = when the fresh air state point is 17 points (new wind burden indoor Wet load) When f, the temperature and humidity in the room will change. It is assumed that the cooling capacity provided by the fan coil just meets the sum of the indoor heat load and the fresh air load, and does not consider the heat capacity and wet capacity of the room. When ££>(;, it is equivalent to a small wet load, requires a high heat-to-moisture ratio (such as a hotel room), and the fresh air treatment end state is low, for example, the indoor temperature and humidity will change to the dry and hot directions. When "<f/ is equivalent to a large wet load, a low heat-to-moisture ratio (such as a restaurant) is required, and the fresh air treatment state is high, for example, the indoor temperature and humidity will change in the cold and wet directions.
The s value comparison method is to change the final state point L of the fresh air treatment along the line, so that the indoor comprehensive heat-humidity ratio is similar to the heat-humidity ratio of the fan coil to the air treatment process, that is, it is known from the analysis that when the indoor heat-humidity ratio is f is larger (such as hotel rooms), should choose a higher fresh air end state point, such as l2, l3a, so when the indoor heat and humidity ratio f is smaller (such as restaurant), you should choose a lower fresh air final state point Such as l6, l7a, make. Of course, it can be seen from equation (6) that it can also be changed by adjusting the fresh air volume. However, it is well known that the adjustment of the fresh air volume is limited. ; can be obtained by formula (1) or formula (4). Considering the load change and the operation adjustment, the situation that the indoor residual heat is reduced and the residual moisture amount is unchanged (hotel room) should have the same amount of residual heat in the room and the amount of residual moisture (restaurant) should be The above analysis shows that the design of the fan coil plus fresh air system can be divided into the following four steps: 1. Determine the final parameters of the new wind. According to the comfort or process requirements, the indoor design temperature and humidity parameters are reasonably determined, and the indoor cooling load and wet load are calculated; the water temperature and water flow of the fan coil are determined according to the cold source and the cold water system; the cold load due to the design is already Considering the maximum load of the most unfavorable situation, and the fan coil selection will be considered for correction, so the design is based on high-grade air volume; using the S-value comparison method, referring to the data of the new wind final parameters in Table 1, through trial calculation, select the appropriate The new wind end state point, so that it satisfies the formula (7).
2. Fan coil selection. According to the sum of the total cooling capacity of the fan coil is equal to or equal to the sum of the indoor heat load and the thermal load brought into the room by the fresh air, the 艮P:a correction coefficient, considering the effect of the accumulated dust of the unit after the coil on the heat transfer; Use: a In addition, it is considered here that the external residual pressure of the selected fan coil should be sufficient to overcome the wind resistance of the fan coil inlet and outlet. When the resistance of the inlet and outlet is greater than the residual pressure of the fan coil, the air volume and the cooling capacity will decrease, and these effects should also be considered when selecting (discussed in another article).
3. Air volume check. For summer comfort air conditioning, the specification specifies that the air supply temperature difference should not be greater than ior, and the number of air changes is not less than 5 times per hour.
Therefore, the air volume of the fan coil should be checked according to the number of room air changes not less than 5 times per hour. Or airflow analysis based on jet theory.
4. Selection of new wind turbines. According to the known total fresh air volume and outdoor meteorological conditions (new wind initial parameters) and the above-mentioned new wind final parameters and cold water temperature, according to the thermal calculation method of the surface cooler, the new wind turbine group selection design is carried out, and the model of the new wind turbine group is obtained. The number of units and the number of rows of cooling coils. A fresh air system is usually a supply of fresh air for several rooms, and it is impossible to design according to each room.
It can only be designed according to the typical room in which the typical room should represent the load characteristics of most rooms in the fresh air system.
1. Determine the final parameters of fresh air (1), know that the fan coil is 7t: cold water temperature, standard water flow G fan coil heat treatment ratio of air treatment = 250/=11468k/kg room heat and humidity ratio: test Calculate, determine the new wind end state point as team = 90%, indoor comprehensive heat and humidity ratio = 2, fan coil selection type carrier fan coil type 004 standard full heat cooling capacity is 3300kcal / h = 3838ww, calculate its title The total heat capacity under working conditions: 3, air volume check: 004 type Carrier. The fan coil high-grade air volume is 680 irVh, the mid-range air volume is 470 mVh, the air exchange frequency is 7.6 times/h when calculating the high-grade air volume, and the mid-range air volume is changed. The number of gas is 5.2 times/h to meet the requirements.
4. Selection of new air blower group (omitted) V. Conclusion Fan coil is a stereotyped product whose heat and humidity capacity is only related to imported air parameters, air volume, chilled water temperature and water flow.
In the air conditioning design, although the above parameters can be adjusted to change the heat and humidity capacity of the fan coil, the change is very limited. However, the fan coil is used as the end device of the semi-centralized air conditioning system in various occasions. Different occasions require different heat and humidity processes, so that the design requirements can only be met by adjusting the final parameters of the fresh air. Generally, the indoor heat and humidity ratio is high, such as a hotel room, requiring a high fresh air temperature; a low indoor heat and humidity ratio, such as a restaurant, requiring a low fresh air temperature.
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