A cooling tower is one of those purchases that is easy to get wrong in both directions. Oversize it and you pay for concrete, water treatment and fan power you never needed; undersize it and the line runs warm every summer afternoon, which shows up as gauge variation and rejected sheet. The method below takes you from heat load to a specific frame size in five steps.
Why an Extrusion Line Needs Heat Rejection at All
Screw extrusion converts motor power into heat, and a surprising amount of that heat ends up in the polymer rather than in the product. A three-roll calender stack, the cooling rolls that set sheet thickness, and the mould or die circuits all have to be held at a workable temperature. If that heat is not removed continuously, the sheet develops inconsistent gauge, the rolls lose their set point and the line drifts out of specification.
Two devices handle this in practice. A cooling tower rejects heat to the atmosphere and is the economical choice for large loads. A chiller uses a refrigeration circuit to hold water at a precise temperature. Most plants run both: the tower carries the bulk load, and a chiller trims the circuits that need accuracy.
Step 1 — Establish the Heat Load, Not the Tonnage
Buyers often start from a tonnage figure they remember from another plant. It is better to start from the load. Add up the motor power that becomes heat in the process, the heat taken out of the melt by the cooling rolls, and any hydraulic or gearbox losses that a heat exchanger is expected to carry. Express the total in kilowatts and keep the figure in front of you; every later decision follows from it.
Rating conditions matter as much as the number. Our published tower data is quoted at water entering at 37 °C, leaving at 32 °C, a 5 °C range, against a 27 °C design wet-bulb. If your site’s summer wet-bulb is higher, the achievable approach changes and the selection should be revisited rather than assumed.
Step 2 — Convert the Load Into Circulating Flow
Once the load and the temperature range are fixed, the circulation rate follows. A 5 °C range moving a kilowatt per second requires roughly 0.048 litres per second for each kilowatt, so a 250 kW load needs somewhere in the region of 12 cubic metres per hour before allowances. Add about five per cent for the pump to overcome pipe losses, and you have the figure the tower must be selected against.
This is why the flow column, not the model name, is the honest way to compare towers. A nominal 150 ton tower moving 117 m³/h is a very different proposition from a nominal 100 ton unit at 78 m³/h, and the gap between them is what decides whether one frame can carry your whole line.
Step 3 — Check the Wet-Bulb Before You Commit
The cold water a tower can produce is limited by the wet-bulb temperature of the air around it, not by the size of the fill alone. A tower rated at a 27 °C wet-bulb will fall short in a location that regularly sees 30 °C. The remedy is either to accept warmer cold water, to increase the range, or to step up one frame size.
Because this single figure can change the machine you order, it is worth measuring rather than estimating. Design wet-bulb data for the site is the most reliable input you can give a supplier.
Step 4 — Match the Pump and the Pipework
An open tower is normally served by a single clean-water centrifugal pump, usually sized for a flow about five per cent above the nominal circulation rate and a head of roughly 20 to 30 metres depending on how the pipework runs. Vertical inline and horizontal end-suction bodies both work; the choice is usually about floor space and access for maintenance.
Pipe size should be generous. Moving the same flow through a smaller bore raises velocity, and pressure loss rises with approximately the square of that velocity. A DN125 connection running at low velocity costs far less pump energy over a decade than a DN80 connection pushed hard.
Step 5 — Decide How Much Treatment You Need
An open tower exposes the water to air, so it collects dust, dissolves gases and grows biological film unless it is managed. At minimum, plan for a side-stream filter, a dosing regime and regular blowdown. Where a circuit serves a mould or a precision roll, a plate heat exchanger between the tower water and the process loop is a common compromise: the tower handles the bulk heat, and the closed loop stays clean.
The VihoX Cooling Tower Range at a Glance
Every frame below is a round counterflow FRP open tower built to the same rating conditions, so the choice between them is a question of flow and floor space rather than features.
| Model | Nominal Flow | Fan Motor | Matching Pump | Tower Size | Operating Weight |
|---|---|---|---|---|---|
| VihoX 40T | 31.2 m³/h | 1.5 kW | 4 kW | Ø1650 × H1800 mm | Approx. 550 kg |
| VihoX 60T | 46.8 m³/h | 1.5 kW | 5.5 kW | Ø2145 × H1960 mm | Approx. 1,250 kg |
| VihoX 80T | 62.6 m³/h | 1.5 kW | 7.5 kW | Ø2145 × H2040 mm | Approx. 1,280 kg |
| VihoX 100T | 78.1 m³/h | 2.2 kW | 11 kW | Ø2900 × H2370 mm | Approx. 1,650 kg |
| VihoX 120T | 93.7 m³/h | 2.2 kW | 11 kW | Ø2900 × H2500-2560 mm | Approx. 1,690 kg |
| VihoX 150T | 117 m³/h | 2.2 kW | 15 kW | Ø2900 × H2560-2670 mm | Approx. 1,700 kg |
Sizing Mistakes That Cost Money Later
Three errors recur. The first is selecting on tonnage alone without checking that the nominal flow matches the calculated figure. The second is ignoring local wet-bulb data and then discovering in August that the line runs warm. The third is under-sizing the basin and the pump together, which produces a tower that cycles noisily and never settles.
None of these are expensive to avoid. They simply require the load, the range and the site conditions to be written down before the order is placed.
Frequently Asked Questions
Does a sheet extrusion line need a cooling tower or a chiller?
They do different jobs. A cooling tower rejects heat to atmosphere and is the economical way to dump large heat loads. A chiller uses refrigeration to hold water at a precise temperature. Most extrusion plants run a tower for bulk heat rejection and a chiller where the process needs a tight set point.
How do I work out the flow I need?
Start from the heat load in kW, not from a tonnage figure. Dividing the load by the 5 °C design range and the properties of water gives the circulation rate, then add roughly five per cent for pipe losses.
What if my summer wet-bulb is higher than 27 °C?
The tower will not reach the same cold water temperature, so select one frame larger or accept a warmer cold water temperature. Send us your local wet-bulb and we will re-check the selection.
Can one tower serve several machines?
Yes, provided the combined heat load is added up and pipework is sized for the total flow. Ring mains with branch valves let individual machines be isolated without stopping the tower.
Why is the receiver or basin volume important?
It buffers the difference between what the machines draw and what the tower returns, and it holds enough water for make-up between evaporation and blowdown. Too small a basin causes the pump to cycle.
How much water does a tower consume?
Evaporation removes roughly one per cent of the circulation flow for every 6 °C of cooling range, plus a small drift and blowdown allowance. It is far less than the water a once-through system would use.
What maintenance does an FRP tower need?
Mostly water treatment and cleaning. Keep the fill free of scale and biological growth, check the float valve, inspect the fan and bearings, and clean the basin strainer on a fixed schedule.
Can the tower be installed indoors?
It can, but the discharged air must be ducted out and replacement air provided, otherwise the tower recirculates its own humid exhaust and performance collapses. Outdoor placement on a slab is simpler and cheaper.
Send Us Your Cooling Load
Give us the heat load in kilowatts, your local summer wet-bulb and a sketch of the circuits you need to cool, and we will come back with a frame size, a pump duty and a pipe schedule instead of a catalogue page. Browse the counterflow FRP tower range, or read the specifications of the extrusion lines that the tower will be cooling. Our engineers answer on WhatsApp at +86 147 7547 6896.