Points to consider when choosing a chiller for additional cooling and reasons for insufficient cooling capacity
If there is an increase in heat generation from surrounding equipment or a decrease capacity of cooling equipment, in addition to maintaining the cooling equipment or replacing it with a new product, forced additional cooling using a chiller will help prevent a decrease in factory operating rates.
This time, we will introduce the points to consider when considering additional cooling, using an existing hydraulic system as an example.
1. Points to consider when choosing an additional cooling method
First, we will introduce how to select an additional cooling method using an existing hydraulic system as an example.
There are several ways to add cooling equipment to an existing hydraulic system, so this time we will explain them in the following three scenarios.
- ・When the existing cooling equipment is attached to a different system from the hydraulic pump
- ・When equipment cooling is attached to the hydraulic pump return piping
- ・If there is no existing cooling system
When the existing cooling equipment is attached to a separate system from the hydraulic pump
If you want to use the existing cooler, install a new heat exchanger downstream and connect a chiller unit to provide additional cooling.
By placing the existing equipment upstream, the temperature difference with the hydraulic oil increases, maximizing the heat exchange capacity of the existing cooler. As the temperature of the working oil is lowered, the burden on the chiller is also reduced.
When the hydraulic pump return pipe is equipped with an existing cooling system
Similarly, if a cooler is installed in the return pipe of the hydraulic pump, a new heat exchanger is installed downstream of the existing cooler and additional cooling is provided by the chiller unit.
In the case of hydraulic pumps, it is important to note that pressures exceeding the withstand pressure of the heat exchanger may occur, which could cause the heat exchanger to burst.When installing, it is important to thoroughly check that the pressure in the return piping is below the withstand pressure of the heat exchanger and that there are no large pressure changes.
Without existing cooling
If you don't currently have cooling equipment, there are three ways to install it:
- ・Install oil chiller
- - New cooling circuit installed
- ・Heat exchanger and chiller unit installed on hydraulic pump
oil chiller installed
The least time-consuming option is to install oil chiller. Although it has less cooling capacity than a general-purpose chiller, it has the advantage of being easy to install and construct if capacity is sufficient.
New cooling circuit installed
Another option is to create a new cooling circuit that connects a pump, heat exchanger, and chiller.The key to selecting a circulation pump is to check that it has the appropriate capacity and flow rate.
Installing a heat exchanger and chiller unit on the hydraulic pump
Another effective method is to install a heat exchanger and chiller unit on the return pipe side of the hydraulic pump.Since the hydraulic pump generates pressure that exceeds the withstand pressure of the heat exchanger, be sure to pay close attention to pressure drops and pressure changes in the return pipe when installing.
2. Reasons for insufficient cooling capacity
From here, we will explain the reasons why cooling capacity is insufficient, using existing hydraulic equipment as an example.
For example, in the case of Air-cooling type cooling equipment, whose cooling capacity is affected by the ambient temperature, high outside temperatures can cause a decrease capacity addition, the influence of heat generated by surrounding prime movers and heat treatment furnaces can cause the temperature of the hydraulic oil to rise and cooling capacity to decrease.
Aging deterioration of cooling equipment is also a factor, which can be caused by factors such as clogging of cooling tower piping with scale, clogging in air-cooled radiators and chillers, refrigerant leakage, and deterioration of cooling circulation pumps.
3. How to calculate additional cooling capacity
Finally, we will explain how to calculate the missing cooling capacity required when installing a chiller for additional cooling. The required cooling capacity can be calculated by multiplying the "heat amount calculation formula" by a safety factor that takes into account factors such as heat intrusion from outside air.
[Calculation formula for required cooling capacity (calculation formula for heat amount)]
Vs×Cs×γs×ΔT÷t= Q [kW]
Example calculation of required additional cooling capacity
Let's assume that the temperature of 800L of hydraulic oil in the hydraulic oil tank rises from 30°C to 60°C in one hour, and calculate cooling capacity required at that time.
Using the unit conversion table and physical properties table, converting units and applying the values of hydraulic oil to the calorific value calculation formula will result in the following formula.
Q[kW]=①Vs×②Cs×③γs×④ΔT÷⑤t
| ①.Vs (volume of object) | 800L＝0.8m³ |
|---|---|
| ②.Cs (specific heat of the object) | 1.95kj/kg・℃ |
| ③. γs (density of the object) | 870kg/m³ |
| ④. ΔT (temperature difference of the object) | 60-30＝30℃ |
| ⑤.t (cooling time of the object) | 1 hour = 3600 seconds |
0.8×1.95×870×30÷3600＝11.3[kW]
Finally, as mentioned above, add safety factor of 1.2 (20%) to the heat calculation formula to account for heat intrusion, etc. safety factor is generally estimated to be 1.2 to 1.3 if the required heat amount is 3.5kW or more, and 1.2 to 1.7 if it is less than that. If the cooling is insufficient, a larger calculation is required.
11.3 x 1.2 = 13.6 [kW]
In other words, the heat load of 800L of hydraulic oil, which rises from 30°C to 60°C in one hour, is estimated to be 13.6kW, and the additional cooling equipment must have capacity to compensate for this.
Points to consider when calculating additional cooling capacity
The temperature rise of hydraulic fluid reaches its maximum immediately after the equipment starts operating and decreases over time. When estimating cooling capacity to be added, it is important to check the temperature change zone immediately after start-up, where the temperature change is large, as indicated by the red arrow in the diagram below.
４．まとめ
It is not uncommon to suffer from insufficient cooling during the summer when outside temperatures rise or due to aging. In such cases, additional cooling may be required to maintain operating efficiency.
When installing, carefully check whether there is any existing cooling equipment and the condition of the piping, and proceed in an optimal manner in terms of efficiency and safety.
