Estimation of the cooling water consumption for refrigerators
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I saw in other studies that, assuming the cooling capacity of the freezer is 200 KW and the power of the motor is 100 KW, the required cooling water flow rate was calculated using Cp 4.18； There are two different ways of calculating the temperature difference: 1) Total heat transfer amount = 200 + 100 = 300 KW; cooling water flow rate = 300/4.18/5 l/s. 2) Total heat transfer amount = cooling capacity = 200 KW; cooling water flow rate = 200/4.18/5 l/s. It seems that the first method is correct; please advise, fellow users. Additionally, after obtaining the results using the above method, what amount of margin is generally appropriate to include?
Of course, the first method is the correct one. As for the margin, around 5-10% should be sufficient
Generally, the second algorithm. A motor with a power of 100 kW does not mean that its heat generation is also 100 kW. Generally speaking, the heat generation of a 100kw motor is relatively low. Normally, it would be around 1–2 kW. There are usually clear requirements for the cooling water used in motors; if not, a slight margin can be added using the second calculation method.
As seen elsewhere, the two sea friends already have different opinions – is there anyone with a more authoritative explanation?
You can use the HYSYS software to simulate the chiller system; it is a system that consists of simple modules, and that’s exactly how the manufacturers design it as well – the parameters in it are quite clear. Only by knowing how to calculate can you have a stronger foundation! Please give me more points!
The second algorithm is the correct one; the cooling capacity is similar to that achieved by circulating water cooling, but a 20% surplus of circulating water is required. The motor power is primarily used to overcome the valve resistance and system resistance.
Reply to 1# heicafei: I replied so well – please give me more points. You have so much wealth, haha.
The first method: a little over ten percent
I don’t quite understand it, but I personally think the suggestion on page 5 is good – using the HYSYS software for simulation. There might even be unexpected rewards!
This post was last edited and replied to by zpg on 2011-4-12 at 16:31. Reply 1# heicafei: Here is a set of actual measurement data for McQuay chillers provided to the original poster. If I remember correctly, the compressors used are single-screw type: Cooling capacity Q1 (kcal/h): 254.73, 25.33, 79.65, 90.4; 219,144, 279,888, 326,608, 438,288. Number of motors × rated power (kW): 1×60, 1×75, 1×90, 2×60. Supply water temperature (°C): 30, 30, 30, 30. Return water temperature (°C): 35, 35, 35, 35. Cooling water flow rate (L/s): 14.85, 18.91, 22.16, 29.7; in m3/h: 53.46, 66.807, 679.77, 6106.92; in kg/h: 53,188, 67,730, 79,370, 106,376. Cooling water heat transfer capacity Q2 (kcal/h): 265,941, 338,649, 396,852, 531,882; in kW: 309.13, 393.64, 61.26, 18.2. Safety factor (1–Q2/Q1): 21.35%, 20.99%, 21.51%, 21.35%. Both the design data and the actual measurement data show that using the second method with an additional ~20% margin is sufficient; the first calculation method is completely unreasonable. . What the friend on the 3rd floor said makes sense – a 100kW motor doesn’t mean that its heat generation is necessarily 100kW, haha. Furthermore, the example figures you provided – a cooling capacity of 200 kW and a motor power of 100 kW – well, the COP is far too low, at only 2. The COP values listed in the table above are all above 4. For a unit with a cooling capacity of 254 kW, the power of its compressor motor is only 60 kW; in other words, one unit of electricity used can generate equivalent to 4 units of cooling capacity. No one would buy a cooling unit with a COP of 2.
I also think the motor power specified by the poster is a bit alarming. One only needs to calculate the cooling load; depending on the purpose for which cooling is required, a margin of 20-30% can be taken. If the motor has a cooling water connection, it should be used for cooling; however, a 100kW motor probably doesn’t have such a connection, so air cooling along with heat dissipation through the casing should be sufficient