How to Choose a Chiller

The importance of chiller selection

To ensure stable operation of a chiller, it is important to select one that matches the device's operating conditions and facility usage. It is also important to pay attention to the chiller installation location, piping distance, and shape.

When selecting a chiller, it is important to match the conditions and circumstances of use with the chiller's functions, performance, and specification.
If this matching process is neglected, the expected performance may not be achieved once operation begins, or problems may occur with the equipment being cooled or with the chiller itself.
In addition to issues of the set temperature and heat quantity of the work (the object to be cooled), selecting a chiller model is not as simple as selecting other equipment, for example, as the head changes depending on the diameter, length, and shape of the piping connecting the work and the chiller.
Therefore, in this volume, we will provide a clear explanation of how to select the chiller that is best suited to your facility.

Four steps to confirm and decide on a chiller

As mentioned above, it is important to select a chiller that is suited to the equipment and work being cooled. Selecting the optimal chiller involves a process of confirming the conditions of use. Follow the four confirmation and decision-making steps below to select a chiller that is perfectly suited to your equipment.

Chiller and workpiece (cooling target) structure diagram

Chiller selection procedure 1: Determine the circulating water temperature

The circulating water temperature is determined based on the optimum temperature of the workpiece (the equipment or work that the chiller is intended to cool).

① Determine the optimum temperature for the workpiece to be cooled.
② Determine the temperature of circulating water.

Chiller selection procedure 2: Decide the installation location (outdoor vs. indoor) and cooling method (air-cooled vs. water-cooled)

3) Decide whether to install it indoors or outdoors, and whether to use air or water cooling.

Outdoor installation (PCU-SL series only)

• When you want to avoid exhaust heat being released indoors (in the case of air cooling)
• When you want to avoid air currents indoors (in the case of air cooling)
• If there is no space to install it indoors

Indoor installation

• When you want to operate a chiller near the equipment
• When you want to shorten the piping (reducing pressure loss and reducing piping costs)
• When you want to reduce installation man-hours

●Water cooling [circulating water]

• If cooling water (tap water, well water, cooling tower, etc.) can be arranged
• When exhaust and heat are a problem (when precise air conditioning settings are required, deterioration of the worker environment, etc.)

●Air-cooled [circulating water is cooled by heat exchange with outside air]

• When it is difficult to arrange cooling water (tap water, well water, cooling tower, etc.)
• When exhaust and heat dissipation by air cooling are acceptable

Features and internal structure of air-cooled and water-cooled chillers

Chiller selection procedure 3: Determine cooling capacity

(4) Calculate the capacity required for cooling based on the temperature change of the workpiece and the flow rate and temperature difference of the circulating water.
For details on how to determine cooling capacity for a chiller, please refer to Heat Rate Calculation Method.

Chiller selection procedure 4: Check the required head (check the pump capacity)

The required head (the pump's capacity to pump circulating water) will vary depending on the piping conditions below.
5) Determine the required "head" based on the pipe length, 6) pipe diameter, and 7) joints (number of bends), and confirm that the pump capacity of the chiller to be selected satisfies this requirement.
For details on how to calculate the required head, please refer to Head Calculation Method.

Calorific value calculation method

When selecting chiller capacity,
(1) Heat load heat amount < (2) Chiller cooling capacity
The heat load heat quantity and chiller cooling capacity are calculated using the formula below (calculation example and reference materials included).

(1) Calorific value calculation method

PCU series heat amount calculation method

Calculation example (1)

When the temperature of 800 L of hydraulic oil in a tank rises from 30°C to 60°C in 1 hour

From the physical properties table below, ②1.95, ③870, and ④60 - 30 = 30
Convert the units: ① 800 L = 0.8m3, ⑤ 1h = 3600sec

Substituting the above values into the formula,
(0.8 x 1.95 x 870 x 30 / 3600) x 1.2(safety factor) = 13.6 kW

Calculation example (2)

When the cooling water flowing into the equipment is IN: 26°C, OUT: 29°C, and the flow rate is 45 L/min

From the physical properties table below, ②4.18, ③998 ④29 - 26 = 3

If we break down the flow rate into a numerator and denominator and convert it into units based on the unit conversion table below, we get 36 L/min = 36 L / 1 min = 0.036 m3 / 60 sec. Therefore, ① 0.036, ⑤ 60
Substituting the above values into the formula,
(0.045 x 4.18 x 998 x 3 / 60) x 1.2(safety factor) = 11.3kW

*When the circulating solution is water, the temperature difference [ΔT] and flow rate [A] are calculated using the physical properties as coefficients.
It can also be calculated using the following formula:

Q[kW] = 0.07 × A[L/min] × ΔT[℃]

Calculation example (3)

After heat treatment, a 3 weight steel workpiece needs to be cooled from 250 to 40°C in 3 minutes.

From the physical properties table below, ②0.46 and ④250 - 40 = 210
Convert the units and get ⑤3 min = 180 sec

For ① and ③, the units can be converted as volume [m3] x density [kg/m3] = weight [kg], so ① x ③ = 3,

Substituting the above values into the formula,
(3 x 0.46 x 210 / 180) x 1.2(safety factor) = 1.93 kW

(2) How to check chiller capacity

Check the circulating water temperature (chiller set temperature), ambient temperature (if air-cooled), and cooling water temperature (if water-cooled), and calculate from the characteristics graph of the target model.

Example: Calculate cooling capacity of the PCU-3300R when circulating water temperature is 25°C and the ambient temperature is 20°C.

From the graph above, cooling capacity is calculated to be 3600W (selected at frequency 60Hz).

Lifting height calculation method

The pump power required to circulate cooling water can be expressed as "head."
The head varies depending on the condition of the piping connecting the chiller to the load (device), but the required head calculated from the pump capacity > piping is a condition. Below we will introduce how to calculate the head based on the piping conditions, etc.

Step 1: Determine the pipe length.

Length of piping from chiller to device:
3+5+4=12m×2(round trip)=24m…①

Step 2: Convert the fitting resistance to straight pipe length and add it to the pipe length.

Obtain the equivalent straight pipe length of the fitting from the table.

From the table...Threaded 90° short elbow 25A → 1.6m
1.6×4(places)=6.4m…②
①+②=24m+6.4m=30.4m…③

Since resistance varies depending on the shape of the joint, check the value converted into straight pipe length in the table above.

Step 3: Calculate the "head loss *Hf (m)" from the flow rate and pipe diameter and multiply it by the total pipe length from "Step 2".

When the flow rate is 30 L/min and the pipe diameter is 25 A, from the graph on the right, Hf = 0.04 Hf (m)…④
③×④=30.4×0.04=1.2(m)…⑤

*Head loss: Pressure due to pipe friction expressed per 1m of pipe length for each pipe diameter and flow rate.

※William Hazen Official
Hf=5.4775×10-3・C-1.85・D-4.87・Q1.85・L・α
(D: inner diameter of pipe, Q: flow rate, L: length of pipe, α: safety factor)

Step 4: Add the lift height from the chiller to the equipment to calculate the head.

Height from chiller to device: If 5m...⑥ ⑤+⑥=1.2(m)+5(m)=6.2(m)

The required lift is 6.2m…⑦

Step 5: Select a pump that satisfies the head calculated in step 4.

The chiller's head capacity shown in the graph is 35m (at 60Hz) when the flow rate is 30L/min.
Therefore, the head capacity of this chiller meets the required head (6.2 m).

35m > 6.2m

Example 1) When the circulating water flow rate is 30 m3/min, the head of the PCU-3310R is (when the required flow rate is greater than the rating flow rate).

*From the graph above, the head is calculated to be 35m.