Recirculating Chiller: Cooling Capacity and Min Temp

A recirculating chiller is sized by two numbers that only make sense together: its cooling capacity and the minimum temperature it can hold. Capacity falls as the set point drops, so a unit rated to -30°C delivers less cooling near -30°C than at room temperature. Choose by capacity at your real working point.

What do cooling capacity and minimum temperature actually tell you?

Cooling capacity is the heat a chiller can remove per unit of time. Minimum temperature is the lowest set point the sealed refrigeration circuit can hold in continuous operation. Neither number means anything on its own. They are two halves of one specification, and we treat them that way on every unit we build.

Look at how the nameplate reads on our DLSB sealed series. The DLSB-50-30 is specified as a temperature range: -30°C to room temperature. That range is an operating envelope, not a performance figure. The same machine removes different amounts of heat at different points inside that envelope, which is why a single capacity figure quoted with no temperature attached tells you almost nothing when you are trying to size a purchase.

When we size a unit for a customer, we work from five inputs, and everything in this article maps back to them:

• Your target temperature — the real set point, not the deepest number on the datasheet.
• The cooling capacity at that target point — not at room temperature.
• Reservoir volume — the buffer the loop gives you.
• Pump flow and lift — whether the coolant actually reaches your equipment.
• Connection size — the plumbing the whole loop has to pass through.

Get those five right and the chiller will do its job. Get the first two wrong and nothing downstream rescues the installation.

Why does cooling capacity collapse as the set point drops?

The physics is simple once you strip it down. A refrigeration circuit moves heat from a cold side to a warm side, and the compressor does the lifting. The deeper you set the coolant temperature, the bigger the temperature lift the compressor works against. Refrigerant mass flow falls, efficiency falls, and the capacity the machine can deliver at the cold side falls with them. At the same time, the colder your loop runs, the more ambient heat leaks into hoses, tanks, and jackets — so the load rises while the capacity shrinks.

This is the sizing error behind most undersized chiller purchases we are asked to fix. A buyer compares two units on a room-temperature capacity figure, picks the bigger number, and then finds the chiller cannot pull a reactor jacket down to the actual set point under load. The unit was not defective. It was sized at the wrong point of its envelope.

How much capacity falls depends on the refrigerant circuit design, the compressor staging, and where in the envelope you operate — so we will not print a generic derate percentage here and pretend it applies to every machine. What we will say is a hard rule: never sign off a chiller on one capacity figure. Ask the manufacturer for the capacity at your working point, or at minimum at two points on the curve. On our side that is a standard part of the quotation process, not a special request. If a supplier cannot or will not give it to you, that tells you something about the supplier.

DLSB-50-30 vs DLSB-50-40: what do the real spec tables show?

Here is the comparison most competitor pages never put on one screen: two sealed 50-class chillers from the same platform, one floored at -30°C and one at -40°C, with the parameters that actually separate them.

Read the table the way we read it. The two units share the same sealed platform: the same 17 L expansion tank, the same PT100 sensor, the same 20 L/min pump working against a 20 m lift, the same DN20 connections, the same LCD display with digital buttons showing cooling, circulation, set temperature, and real-time temperature. Both ship on four brake casters with the full protection set.

What changes is the floor — and the electrical cost of holding it. The DLSB-50-40 sealed recirculating chiller rated from -40°C to room temperature draws 4.6 kW and 9.3 A where the DLSB-50-30 sealed recirculating chiller rated from -30°C to room temperature draws 4 kW and 7.9 A on the same 380V, 50Hz supply. Deeper refrigeration is not free. You pay for it in power draw every hour the machine runs.

So the judgment is direct. If your process floor is -35°C, the -30 model is simply out — no capacity argument rescues it. If your batch never goes below -20°C, buy the -30 model and take the lighter electrical draw. Skip the deeper unit unless your process actually needs the depth.

How low should you go: -30°C, -40°C, or deeper?

Buy to your real target temperature with sensible margin, not to the deepest number on the shelf. Every step deeper costs you power draw, and — because capacity falls toward the floor — it changes what the machine can actually deliver at your working point. A chiller floored far below your need is not a safety margin. It is an oversized electricity bill.

When the process genuinely runs below -40°C, you leave the standard DLSB range and move to the low-temperature line. Our low temperature recirculating chiller built as a closed, non-volatile coolant loop covers the deeper bands for external reactors, condensers, and laboratory process systems:

Do not spec -80°C because it sounds safe. The deeper the floor, the more the capacity-at-working-point question matters, and the more carefully the loop has to be engineered around it. Send us the real target temperature and we will tell you which band the process actually sits in — sometimes the honest answer is that you need less machine than you thought.

Which pump, tank, and connection specs decide whether the loop actually works?

Capacity at the chiller outlet is not capacity delivered at your jacket. The pump and the plumbing decide how much of it arrives, and this is where otherwise correct selections quietly fail in the field.

On the DLSB-50 pair the pump delivers 20 L/min against a 20 m lift. That lift is the budget for your entire external loop: hose length, connector losses, and any height difference between the chiller and the equipment it feeds. The units ship with DN20 inlet and outlet connectors and one 3.8 m circulation hose, which suits a chiller sitting close to the load. Stretch the run, add narrow tubing, or lift the coolant two floors, and you spend that 20 m budget fast. Keep runs short and keep to DN20 throughout — necking the line down to save a fitting costs you flow every minute the loop runs.

The 17 L expansion tank gives the coolant volume somewhere to expand and buffers the loop against temperature swing as the load changes. The PT100 sensor is what the controller actually regulates against, so the real-time temperature on the display is the loop temperature at the sensor — not necessarily the temperature inside your reactor. The longer and lossier the loop, the wider that gap runs.

Judgment: if your equipment sits well above the chiller or the loop is long, tell us the height difference and the run length at inquiry stage. That is the information that decides whether 20 m of lift is enough, and it is far cheaper to confirm before delivery than after.

How do you match a chiller to a reactor, condenser, or rotary evaporator?

This family is commonly matched with reactors, condensers, and rotary evaporator cooling loops, and each load behaves differently enough that one sizing habit does not fit all three.

A reactor jacket is the demanding case. The duty depends on the reaction heat and on how fast you must pull the batch down — an exothermic addition can spike the load well above the steady state, and the chiller sees that spike with no warning. Give us the batch size and the heat profile, not just the vessel volume. A 50 L vessel running a mild temperature hold and a 50 L vessel absorbing a fast exotherm are two different chillers. We walk through the reactor-specific side of this in our guide on choosing a recirculating chiller for laboratory reactors.

A condenser cares about vapor load. Starve a condenser of coolant flow and recovery falls — the vapor you paid to make goes out the vent instead of into the receiver. The duty depends on how much solvent you are evaporating and how hard you run the reflux, so the flow side of the spec matters as much as the temperature side.

A rotary evaporator is the gentlest of the three: it wants steady flow and a stable set point more than extreme depth. Do not buy deep refrigeration for a load that only needs dependable cooling.

The rule across all three: the vessel size never sizes the chiller. The heat does.

What should you send us before we quote a recirculating chiller?

Quotations go fastest, and come back right the first time, when the inquiry carries the five-point selection basis up front:

• Target temperature. The real set point of the process, plus any pull-down requirement below it.
• Cooling capacity at the target point. If you know your heat load, give it to us; if you do not, describe the batch, the solvent, or the vapor duty and we will work it through with you.
• Reservoir volume. How much buffer the loop needs for your cycle.
• Pump flow. The flow your jacket, condenser, or instrument expects, and the layout it has to push through.
• Connection size. The fittings already on your equipment, so the loop matches on day one.

Two more things worth confirming in the same message. First, your site supply: the DLSB-50 models run on 380V, 50Hz and draw 7.9 A or 9.3 A depending on the temperature floor, so check the panel before the crate arrives. Second, whether the process needs heating as well as cooling — if it does, a chiller alone is the wrong box, and our comparison of a heating-cooling integrated machine versus a recirculating chiller lays out where each route fits.

Fragen und Antworten

Is a chiller’s cooling capacity the same at every temperature?

No. Capacity falls as the set point drops toward the unit’s floor, because the compressor works against a larger temperature lift. Always ask for the capacity at your actual working point — a figure quoted without a temperature attached is not a sizing number.

Is a -40°C recirculating chiller always a safer buy than a -30°C model?

Not automatically. The -40°C model holds a deeper floor, but it draws more power to do it — on the DLSB-50 pair, 4.6 kW and 9.3 A against 4 kW and 7.9 A. If your process never approaches -30°C, the shallower unit is the better buy. Match the floor to the process, not to fear.

What is the lowest temperature a recirculating chiller can reach?

On our low-temperature line, the sealed options step down through -40°C, -60°C, -80°C, -100°C, and -120°C, using DLSB and DFY series systems with air-cooled or water-cooled configurations and PID or PLC control depending on the model.

Can one recirculating chiller cool more than one device at a time?

It depends on the combined duty. Add the heat loads of every device on the loop, then check the sum against the capacity at your set point and against the pump budget — on the DLSB-50 models that is 20 L/min against a 20 m lift. Two gentle loads can share a loop; one heavy load plus one gentle load often cannot. Send us both duty profiles and we will tell you which case you are in.

What electrical supply do the DLSB-50 chillers need?

Both models run on 380V, 50Hz. The DLSB-50-30 draws 7.9 A total current and the DLSB-50-40 draws 9.3 A. Confirm the site supply matches before delivery.

The short version of everything above: pick the minimum temperature first, from the process and not the shelf; then confirm the cooling capacity at that temperature, not at room conditions; then make sure the pump, tank, and connections can actually deliver it to your equipment. You can browse the full recirculating chiller range for reactor, condenser, and rotary evaporator cooling loops on our category hub, and the parameter documents behind these tables are collected in our company catalog. Send us your target temperature and duty, and we will come back with a size rather than a guess.