How to select the cooling fan in the floor heating and air conditioning system

How to select the cooling fan in the floor heating and air conditioning system

For many dealers in the north, the heating end may be familiar, but they are not very confident in the cooling end. In our WeChat group, dealers often consult related questions. Among them, issues such as how big the election should be and how to choose are often mentioned.

　　 wind plate with big or not with small

　　 Regardless of whether it is the mainframe selection or the end selection, there is an optimal value, but in fact, it is difficult for us to be just right, to be satisfied without wasting, it is too difficult because there are too many factors affected. Take the selection of the fan as an example, the enclosure structure and the flow of people can affect the selection of the fan. So, when we select the wind plate, should it be better or smaller?

If the fan is too large, there are many disadvantages: firstly, it will increase the initial investment, and the operating energy consumption will also increase. The user may make a slight remark that the air source heat pump product is not energy-efficient; secondly, the noise of the fan is too loud. It will be larger, which will affect the user experience; in addition, the installation space will be crowded after the wind disk is large, and it will also affect the after-sales maintenance.

　　 In addition, if the fan is too large, it will make the temperature in the room difficult to control, resulting in a situation-it is cold when it is turned on, and hot when it is turned off, users will frequently switch on and off. The consequences of a too small fan plate are easy to predict, and the cooling capacity will decrease, especially when the weather is very hot, users will complain that the temperature in the room is not low enough.

　　 From the analysis of their respective disadvantages, it seems that the harm caused by the wind is bigger. In fact, it is not. The above problems will only occur when it is too large, such as 50% or more, but customers who are less than 5% may complain that it is not cold enough, and now there are more and more extreme climates, and cooling is the most basic function. From this point of view, it is more secure if it is appropriately larger.

　　Two methods for selecting wind plate

　　The fan coil has two main parameters: cooling (heat) capacity and air supply, so there are two ways to choose the fan coil:

　　 One is selected according to the circulating air volume of the room

　　The product of room area, floor height (after ceiling) and the number of air changes in the room is the circulating air volume of the room. The fan coil model can be determined by using the circulating air volume corresponding to the rated air volume of the fan coil;

　　Second, it is selected according to the heating and cooling load required by the room According to the load per unit area and the area of the room, the required heating and cooling load values of the room can be obtained (or it is very convenient to use general HVAC software to calculate it. You can learn it by yourself or participate in some special training courses). Use the room The cooling heat when the cooling and heating load corresponds to the high-speed air volume of the fan coil can determine the fan coil model.

The selection of air discs for general household applications is sufficient to meet the requirements of cold and heat. Special occasions that have requirements for circulating air volume and fresh air volume, such as wards, operating rooms, etc., must be strictly in accordance with the design specifications, and the air volume must be met at the same time And heat and cold requirements.

It is important to note that in the cooling capacity of the fan, there are two indicators: total heat cooling capacity and sensible heat cooling capacity. In conventional household applications, sweating is also a way for us to cool down, and sweat becomes condensed water to be consumed. Cooling capacity, so select according to total heat cooling capacity.

　　 The selection of wind disks by area is actually an empirical estimation method, not a strict design method

(In fact, the calculation method in the design manual is also an empirical calculation method, but this method has been more verified, and the logic is relatively strict.) The estimation by area is indeed very rough, but it is very fast and practical, so it is very unacceptable Professionals are welcome.

　　The design manual also gives some methods and data for estimation by area. Usually these data are conservative and can be used boldly. The disadvantage is that the cost is slightly higher. The climate is very different across the country, this value cannot be applied to all places, and in the same place, fat people and people have different requirements for air conditioning, so the estimation method really depends on the designer’s personal experience, a bit like the old TCM doctors take the pulse and suggest that those who enter this industry at the beginning should use software to strictly follow the design manual to calculate, and when they have accumulated enough experience, they can estimate by area.

　　How to calculate specifically?

　　The specific calculation of the fan selection can be done like this

　　According to the indoor and outdoor air design parameters, calculate the room cooling load Q and wet load W values, and then determine the fresh air volume of the room and the state point after the fresh air is processed according to the design requirements, and calculate the fresh air load;

　　According to the room cooling load Q and wet load W, as well as the fresh air volume and the status point after the fresh air is processed, the air supply volume and air supply status point of the room are obtained;

　　According to the sample of the fan coil unit, find its nominal cooling capacity and nominal heat quantity, and obtain the cooling and heat quantity of the fan coil unit under actual working conditions according to the air volume correction, working condition correction and dirt correction;

　　 When it is greater than or equal to the calculated cooling load, the requirements are met, and when it is less than the calculated cooling load, the fan coil must continue to be checked.

For example, it is known that the indoor cooling load of a room in summer is Q=5.38KW, the wet load W=0.22g/s; the indoor air design temperature is tn=27℃, ψ=60%; the outdoor air dry bulb temperature tw=34℃ , The relative humidity ψw=65%; the temperature rise of the fresh air unit and the air supply duct t=0.5℃, the fresh air volume required for this room is Gw=0.08Kg/s. It is proposed to use a fan coil unit and an independent fresh air system. The fresh air will be processed to the point L on the relative humidity line of 90%, and the fresh air will be sent to the point K on the isenthalpic line with the indoor air after the temperature is increased by 0.5℃. 　　 When selecting the wind plate for this case, the calculation steps are as follows:

1. Indoor load heat/humidity ratio ε=Q/W=5.38/0.00022=24500KJ/Kg, cross point N to make 24500 line and =95% line intersect with air supply point O (mixed fresh air and indoor air), then total delivery Air volume G=Q/(hn-ho)=5.38/(61.5-51.5)=0.538Kg/s;

　　2. Fan coil air volume Gf=G-Gw=0.538-0.08=0.458Kg/s=1410m3/h;

　　3. The specific enthalpy value of the air at point M at the outlet of the fan coil is hm=(G.ho-Gw.hn)/Gf=(0.538*51.5-0.08*61.5)/0.458=49.8KJ/Kg;

4. According to the specific enthalpy value 49.8kJ/kg of the outlet state point M of the fan and the indoor humidity ψ=60%, check the humidity chart to find that the outlet temperature of the fan is 18.2℃, then the apparent cooling capacity of the fan is Qs= Qf.Cpa(Tn-Tm)=0.458*1.01*(27-18.2)=4.07KW;

　　 5. The latent heat of the fan is QL=Q-Qs=5.38-4.07=1.31KW;

　　6. ​​Therefore, the basic parameters of the selected fan should be selected comprehensively to meet these conditions: air volume Gf≧1410m3/h, total heat Q≧5.38KW, and sensible cooling capacity Qs≧4.07KW.

　　The heat and moisture treatment capacity of the fan coil is only related to the inlet air parameters, air volume, cold water temperature and water flow. In the air conditioning design, although the heat and moisture processing capacity of the fan coil can be changed by adjusting the above parameters, this change is limited.

As the terminal device of the centralized air conditioning system, the fan is used in various occasions. Different occasions require different heat and moisture treatment processes. This can only be calculated and checked by calculating the air handling capacity of the fan-coil air conditioning system under the design conditions. The error between the expected design conditions and the standard conditions is within a certain range, so that the selection can meet the design requirements.