It is the first question of almost every thermal control project, and the short answer disappoints everyone: it depends on the working temperature. The long answer is more useful, because the choice has consequences for maintenance, consumption and safety for the next fifteen years. We have been manufacturing both since 1978, so we have no commercial preference for either. Here's the criteria we apply, unvarnished, including cases where oil is a worse idea than it seems.
The decision table
| Criterion | Water | Thermal oil |
|---|---|---|
| Range of our range | 25–180 °C | Up to 300°C |
| With open tank | Up to 90°C | Up to 150°C |
| heat transfer | Far superior: more heat with less flow | Much worse: you need more flow for the same thing |
| Response time | Fast | Slow: more thermal inertia |
| Fluid cost | practically zero | High, and it must be replaced and changed |
| Maintenance | Lime and scale: requires water treatment | Oil degradation, filters, periodic analysis |
| Leaks | They dry | They get dirty, slippery and are a fire risk when hot. |
| cold start | Immediate | Slow: cold oil is very viscous |
| Energy consumption | Less than equal work | Higher: worse transfer, more pumping |
| Main risk | Scaling that ruins heat exchange | Fire and thermal degradation |
The summary in one line: If your process fits in water, it goes in water. Oil is not "the superior option", it is the option for when water no longer reaches it.
Where is the real border
Here the decision is made wrong more often. Many plants jump directly into the oil as soon as they go above 90 °C, when between 90 and 160 °C pressurized water is usually a better option in almost everything: it transfers much better, responds faster, does not degrade, does not smell, does not get dirty and does not burn.
| If you work at… | Choose | Because |
|---|---|---|
| 25–90 °C | Water with tank | The simplest, cheapest and most efficient. There is no debate. |
| 90–160 °C | Pressurized water (WDC or WIC) | You retain the thermal advantage of water without the drawbacks of oil. |
| More than 160°C | Oil | It is our selection threshold, and also the case of PEEK and PPS. |
| metal injection | Oil, always | The matrix works at 150–250 °C: it is not the domain of water. |
| Below ambient | Refrigerator (chiller) | A temperature control unit does not cool below ambient: it is not its job. |
Pressurized or open tank
Within each fluid there is a second decision that is overlooked, and it is the one set by the team family:
| open deposit | Pressurized / closed circuit | |
|---|---|---|
| Roof in water | 90 °C | 180 °C |
| Oil roof | 150 °C | 300 °C |
| Complexity | Minimum | Pressure control |
| Fluid oxygenation | Contact with air: promotes corrosion and degradation | Closed circuit: less oxygen |
| Cost | Minor | Higher at the start, better in the long run if you tighten the temperature |
A practical note about pressurized water: the minimum working pressure increases with temperature, around half a bar for every 10 °C above 90. At 150 °C that is about 4.5 bar. It is not a problem, but it conditions the installation and it is advisable to know it before, not after.
A temperature control unit is not a chiller
They get confused every day, and the confusion is expensive because the wrong equipment is purchased.
| Temperature Control Unit (TCU) | Refrigerator (chiller) | |
|---|---|---|
| What are you doing | Holds a setpoint: heats y cools | Produces cold: extracts heat |
| Range | Normally above ambient | Below the environment |
| Aim | Stability around a temperature | Cooling capacity |
| In an injector | Mold at constant 80°C | Cold water for the hydraulic group or the hopper |
The usual thing is to need both, and for them to work together: the chiller gives the cold, the temperature control unit decides the temperature of the mold. There is a case in which the chiller is no longer optional: if the cooling water enters at a temperature that is too close to the process temperature, the available jump is so small that cooling is no longer reliable. There you need a closed circuit with a chiller, not more power.
Frequently asked questions
Is a water or oil temperature control unit better?
The water one, as long as your working temperature allows it. It transfers heat much better, responds faster, consumes less and the fluid is free. The oil only compensates when you need to go above 160°C. Our water range reaches 180 °C and oil range up to 300 °C.
At what temperature do you need oil?
Our selection criterion is 160 °C. Below, if you have the choice, pressurized water is usually a better decision. Above, and always in injected metal or with PEEK and PPS, is oil.
Up to what temperature does a water temperature control unit go?
With open tank, 90 °C, because water boils at 100 °C at atmospheric pressure. With pressurized circuit, up to 180 °C.
Up to what temperature does an oil temperature control unit go?
Up to 300 °C in closed circuit. With open tank, up to 150 °C.
What is the difference between a temperature control unit and a chiller?
The temperature control unit maintains a set temperature and to do so it heats and cools, normally above the ambient temperature. The chiller only produces cold, below the ambient. They are complementary teams, not alternatives.
Does oil need more maintenance than water?
Different, not necessarily more. Oil degrades over time and temperature, and must be analyzed and changed. The water does not degrade, but it encrusts: without treatment, the lime ruins the heat exchange and the problem appears sooner than people expect.
Can I go from oil to water in an existing installation?
If your working temperature is below 160 °C, almost always yes, and it usually pays off in consumption and maintenance. The circuit must be cleaned thoroughly and gaskets and materials checked. It's a conversion we make frequently.
A manufacturer since 1978
We manufacture water and oil equipment, so we have no commercial preference for either: we have a preference for the one that makes your process last. Tell us the working temperature, the current fluid and what is failing you, and we will tell you what we would do. If you are also deciding on the setpoint, consult our mold temperature table by polymer, o talk to a technician.
Esta guía resume la decisión. Si necesitas el detalle técnico completo —rangos de trabajo de cada fluido, comportamiento por encima de 90 °C y criterios de dimensionamiento—, lo tienes desarrollado en agua o aceite térmico: cómo elegir el fluido.