A closed loop cooling system is a sealed circuit of water or glycol that picks up heat from process equipment or a building, gives that heat up at a heat rejection device, and returns to collect more, and Paul Industries designs, fabricates, installs, flushes, treats, starts up and maintains closed loop cooling systems in all 50 states. Because the fluid never meets outside air, the exchangers and jackets it serves stay clean and its chemistry holds steady. This page is for the plant engineer or facility manager who has to specify a loop, rescue a troubled one, or hire the firm to carry the job. For the wider plant picture, see our process cooling systems page.
What is a closed loop cooling system?
It is a pressurized piping circuit in which one charge of treated fluid circulates continuously between the loads it cools and the equipment that rejects their heat. A workable closed loop cooling system definition has three tests: the fluid is isolated from the atmosphere, it is charged once and topped up only for small losses, and heat leaves by crossing a metal wall instead of by evaporating the circulating fluid.
The loads vary widely: injection molds and hydraulic oil coolers, air compressors, welders and induction furnaces, jacketed reactors and tanks, laser sources, variable frequency drives and transformers, and air handling coils. What they share is a need for clean coolant at a controlled temperature. A narrow water passage in a mold or drive plate tolerates very little scale, which is why plants move such equipment off tower water.
What is a closed loop water system?
A closed loop water system is any sealed water circuit that moves thermal energy from one place to another, whether for cooling, heating or both, without mixing that water with an outside supply. Water treatment professionals often define it by its makeup rate. A National Institutes of Health technical bulletin describes makeup as typically under 5 percent of total system volume in a year, and some practitioners draw the line at 10 percent. A loop taking on much more than that behaves like a leaking system, and the leak has to be fixed before any chemistry program can hold.
How does a closed loop cooling system work?
A pump pushes cool fluid through the loads, where it warms by a planned number of degrees, and the warmed fluid returns through a heat rejection device that lowers it back to the supply temperature. Since the circuit is full and sealed, the pump only overcomes friction; the water going up one riser balances the water coming down the other. That is a real energy difference from a tower circuit, where the pump also lifts water to the tower’s distribution level.
Three accessories make the circuit stable. The expansion tank gives the fluid room to grow and holds a reference pressure. The air separator removes the gas that comes out of solution as the fluid warms and depressurizes. The makeup line, with its meter and backflow preventer, replaces small losses.
Closed loop cooling system diagram, described station by station
Picture a rectangle read clockwise, drawn for a tower-and-plate arrangement. A dry cooler or fluid cooler simply takes the place of station 6.
- Expansion tank connection. A single line ties the tank into the return main, and the makeup line joins at or near this point. Pressure here stays nearly constant whether the pump runs or not, so it is known as the point of no pressure change.
- Circulating pump. Located just after the tank connection, so that it pumps away from the tank and adds its head to the loop instead of pulling the suction side down. Standby pumps sit in parallel with isolation and check valves, frequently on a factory-built pump skid.
- Strainer and side-stream filter. A basket or Y strainer protects the exchangers; a small filter on a bypass line keeps removing fine iron.
- Supply header to loads. Branches feed each machine, each with isolation, a balancing or control valve, and test ports.
- Return header and air separator. The warmed return passes through the separator, the warmest part of the loop, with vents at every high point.
- Heat exchanger to the heat sink. A plate heat exchanger passes the heat to tower water, and the tower loop is drawn as a second, separate rectangle.
- Back to station 1. Temperature and pressure sensors on both sides of the exchanger, a chemical pot feeder and a sampling point finish the drawing.
Open loop vs closed loop water system
The difference is whether the circulating water touches the atmosphere or a water body: an open loop water system either discharges its water after one pass or recirculates it through an evaporative tower, while a closed loop holds the same water sealed in pipe. Tower water scrubs dust, pollen and biological matter from the air, and its minerals concentrate as it evaporates, so everything it flows through is exposed to fouling.
| Factor | Open loop (tower water through the equipment) | Closed loop |
|---|---|---|
| Fouling at the load | Scale, silt and biofilm reach every exchanger and jacket | Load surfaces stay clean; only the heat rejection surface sees the outdoors |
| Water use | Continuous makeup for evaporation, blowdown and drift | Small top-up with a dry cooler or chiller; spray water use if an evaporative cooler rejects the heat |
| Chemistry | Scale, corrosion and biological control, plus Legionella risk management | Corrosion inhibitor, pH control and periodic bacterial checks |
| First cost | Fewer components | Adds an exchanger or a fluid cooler, expansion tank, air control and second pump set |
| Approach temperature | Tower alone, commonly about 5 to 10 degrees Fahrenheit above wet bulb | Adds an exchanger approach of a few degrees, or works from dry bulb with a dry cooler |
| Freeze exposure | Basin and outdoor piping need heaters or drain-down | Glycol in outdoor sections, or an indoor exchanger keeping the sealed loop warm |
Comparing a closed loop cooling system vs open loop plant on first cost alone misses the expense that shows up later: descaling, retubing, downtime, and the temperature control lost as surfaces foul. The open loop’s real advantage is that it delivers the coldest possible condenser or process water for its size, because no second exchanger sits in the way. Plants often run both, with the tower circuit open and everything downstream of a plate exchanger sealed.
Types of closed loop cooling systems
Five arrangements cover most installations, and they differ mainly in how the heat finally leaves the site and how cold that lets the supply run.
| Type | How heat leaves | Rule-of-thumb supply limit | Water consumed | Where it fits |
|---|---|---|---|---|
| Closed circuit fluid cooler | Spray water evaporates over a coil holding the loop fluid | About 5 to 10 degrees Fahrenheit above wet bulb | Spray evaporation and blowdown | Single-exchanger simplicity, moderate loads, outdoor siting |
| Open tower with plate exchanger | Plate exchanger hands heat to tower water | Tower approach plus a few degrees across the plates | Tower evaporation and blowdown | Large loads, existing towers, indoor loop free of glycol |
| Dry cooler | Finned coil and fans, air side only | About 10 to 20 degrees Fahrenheit above dry bulb | None for heat rejection | Warm-water loads, scarce or costly water |
| Chiller loop | Refrigeration circuit, then a condenser | Set by the machine, well below ambient | Depends on air-cooled or tower-cooled condenser | Tight or below-ambient temperatures |
| Hydronic building or plant loop | Central plant serves coils through distribution piping | Set by the plant | Depends on plant | Comfort cooling and mixed process loads |
A closed loop cooling tower system can mean either of the first two rows, so ask which one a proposal intends. The fluid cooler keeps the loop inside a single coil and removes the plate exchanger, and it typically costs more than an open tower of the same duty. The tower-and-plate version adds one exchanger approach, yet it scales more easily and allows the loop to be isolated for cleaning. Upkeep on the tower side is covered on our cooling tower cleaning page. Dry heat rejection, including adiabatic assist for peak hours, is explained in the dry cooler guide, and glycol selection and concentration on the glycol cooling systems page.
Closed loop chiller arrangements
Here the refrigeration machine’s evaporator sits directly in a sealed, pressurized circuit, or behind a plate exchanger that protects it. The term also separates this layout from packaged units with a vented reservoir, where the pump draws from an atmospheric tank and the fluid sees air on every pass. Three layouts recur: direct piping with an inline buffer tank; primary and secondary pumping, where a constant-flow chiller circuit is decoupled from variable-flow load pumps; and an isolated loop in which a plate exchanger separates a dirty or sensitive process circuit from the machine. Manufacturers commonly ask for 3 to 10 gallons of loop water per ton of nominal capacity to prevent short cycling, with more for tight temperature control. A 100-ton machine at 6 gallons per ton needs 600 gallons, so a loop holding 480 would get a 120-gallon buffer tank. Machine selection is on our process chillers page.
Closed loop system HVAC applications
In buildings, the closed circuit is the normal way to carry both cooling and heating: chilled water, hot water and condenser loops for heat pumps are all sealed piping. The closed loop hydronic cooling system serving air handlers and fan coils is the familiar case, and its plant is described on our chilled water systems page, with pipe layout in the hydronic piping guide. A two-pipe closed loop heating and cooling system changes over between seasons, and a four-pipe layout runs both at once.
A water loop system usually means the shared circuit behind water-source heat pumps. That loop commonly floats between about 60 and 90 degrees Fahrenheit, with a fluid cooler rejecting heat at the top of the band and a boiler adding it at the bottom, so that units cooling one zone can feed units heating another.
Closed cycle cooling water system and closed circuit: what the terms mean
These labels overlap, and a specification or permit can use them to mean different things, so it pays to confirm which is meant. In a power plant, the first label usually means the sealed auxiliary loop that serves bearing coolers, generator stators, air chillers and sample panels, typically filled with demineralized water and rejecting heat through shell-and-tube or plate exchangers to the main cooling water. Environmental rules use nearly the same words differently: under 40 CFR 125.92, a closed-cycle recirculating system includes wet, dry and hybrid cooling towers, because the regulation is concerned with how much water is withdrawn from a river or lake, and not with whether the circulating water touches air.
A closed circuit cooling water system, as equipment vendors use the words, is generally a loop whose fluid stays inside a coil or exchanger. Closed circuit also names the evaporative fluid cooler itself, sometimes sold as a closed circuit cooling tower. On a plant drawing, trace where the fluid meets air and the terminology will sort itself out.
Closed loop cooling system design inputs
The work starts from the heat load and the warmest supply temperature the equipment will accept, because those two numbers decide the heat rejection type, the flow and the pipe sizes.
| Input | What to establish | Why it drives the design |
|---|---|---|
| Load | Peak and minimum heat for every machine, and how loads coincide | Sets capacity and part-load control; a machine list beats a nameplate total |
| Supply temperature | Warmest supply each load tolerates, and its allowed swing | Sets whether evaporative, dry or refrigerated rejection can work |
| Delta T | Planned temperature rise across the loads | Larger difference, less flow, smaller pipe and pumps; check that each machine allows it |
| Flow | Gallons per minute equal 24 times tons divided by delta T, for plain water | Sets pipe, valves and pump head |
| Approach | Site design wet bulb or dry bulb, plus each exchanger’s approach | Each added approach raises the warmest supply on the hottest day |
| Fluid | Water or glycol mix, and the lowest ambient exposure | Glycol lowers heat capacity and raises viscosity, so flow and head rise |
| Expansion and pressure | Total volume, temperature extremes, static height, relief setting | Sets tank size and fill pressure |
| Air removal and makeup | Separator location, high point vents, metered fill | Keeps pumps and coils free of air, and makes leaks visible |
Take a 200-ton load at a 10-degree difference: 24 times 200 divided by 10 gives 480 gallons per minute, or 2.4 million Btu per hour. With a design wet bulb of 78 degrees Fahrenheit, a 7-degree tower approach and 3 degrees across a plate exchanger produce roughly 88-degree supply on the hottest day. At 95 degrees dry bulb, a dry cooler with a 15-degree approach gives about 110. If the molds or drives need 85, the options are a chiller, trim cooling on peak days, or a reselected load. Closed loop cooling water system design is mostly the discipline of doing that check early, against site weather and real machine limits. Plant-wide headers, insulation of below-dew-point pipe (see mechanical insulation) and spare capacity for future machines come next.
Closed loop cooling thermal expansion and the tank
Because water is nearly incompressible, a sealed loop needs a compressible gas cushion to absorb growth. Chilled circuits are the easy ones to get wrong: the largest expansion occurs when the plant shuts down and the fluid drifts up to room temperature, so the sizing range runs from coldest fill to warmest idle, and not just across the running temperatures.
Here is a worked example for a 3,000-gallon carbon steel water loop filled at 50 degrees Fahrenheit that can reach 100 degrees when idle. Water density falls from about 62.41 to about 61.99 pounds per cubic foot, a growth of about 0.68 percent. The steel grows too, by about 0.10 percent in volume, leaving about 0.58 percent, or 17 gallons, of net expansion. If 55 feet of static head plus a 5 psi margin at the top of the system sets a 30 psig fill, and the maximum allowed at the tank is 60 psig, then the diaphragm tank’s acceptance factor uses absolute pressures: 1 minus 44.7 over 74.7, or about 0.40. The tank needs about 17 divided by 0.40, or 43 gallons, and the next larger standard size is selected. Pressurized tanks of this type are commonly built to ASME Section VIII. Glycol mixes expand more than water, so their properties replace the water figures. The relief valve is then set above the maximum, at or below the rating of the lowest-rated component it protects.
Materials, water quality and corrosion inhibitors
Closed loop cooling water protects metal through a corrosion inhibitor program matched to the metals present, kept in alkaline pH, with oxygen kept out by keeping the loop tight. Most large loops are carbon steel, welded or grooved, with copper in coils and stainless steel in plates; process duties and high-purity fluid call for stainless pipe. Galvanized steel is best kept away from inhibited glycol, since the zinc can react with the inhibitors and drop out as sludge. Fill water quality matters as well: softened or demineralized water brings far fewer minerals than raw supply.
Common inhibitor families are nitrites, molybdates and azoles, the last added where copper is present. Each comes with a trade-off. Nitrite is effective on steel, yet some bacteria consume it as a food source, so a falling nitrite reading can be a biological problem. Molybdate relies on some dissolved oxygen to work. Oxidizing biocides such as chlorine are normally kept out of sealed loops, because they attack the inhibitor and the metal; where a biocide is needed, a non-oxidizing product is chosen. Target concentrations belong to the chemical supplier’s written program for that loop’s metals. The open tower chemistry beside it is a separate program, explained on our cooling tower water treatment page.
Do closed loop cooling systems use water?
They use a one-time fill and a small top-up, and any further water use depends entirely on the heat rejection equipment. The sealed circuit itself evaporates nothing. A dry cooler or air-cooled chiller adds nothing to that. An evaporative fluid cooler keeps the loop fluid sealed, yet its spray water evaporates at about the same rate as a tower handling the same heat, so the site’s water bill looks much like an open tower’s.
Worked example: how much water does a closed loop cooling system use?
A sound 3,000-gallon loop should take less than about 150 gallons a year in makeup, using the 5 percent benchmark, while a leaking one can lose far more: the same bulletin notes that 25 percent of volume per month, here 750 gallons, is not unusual. For contrast, take the 200-ton example above with the heat going to an evaporative device. Evaporation runs at about 1 percent of circulating flow for each 10 degrees of cooling, so about 4.8 gallons per minute, or nearly 6,900 gallons a day at full continuous load, before blowdown.
In data centers the same logic applies at a much larger scale, and it is treated separately: our data center cooling systems page covers rack and facility loops, and the data center water usage guide puts numbers on the water side.
Makeup and leak detection in practice
A totalizing water meter on the makeup line is the cheapest leak detector a sealed loop can have, and it needs a person or a building automation point reading it. An automatic fill valve left open with no meter hides a leak indefinitely while fresh oxygen and minerals keep arriving. Conductivity, pH, alkalinity and inhibitor falling together also point to water loss. Common culprits are pump mechanical seals, valve packing, expansion tank overflow and relief valves that weep. A chemistry shift with no makeup at all suggests something different: a cross-leak at a plate exchanger, with the higher-pressure side pushing into the other.
Flushing, passivating, filling and commissioning sequence
A new loop is cleaned before its first real charge, in a fixed order, because construction debris, mill scale and cutting oil will otherwise end up in the smallest passages. Sensitive equipment stays out of the circuit until the water runs clean. Owner specifications set the numbers: flushing velocities in published guides and contracts range from a 3 feet per second minimum during chemical cleaning to an 8 feet per second minimum using temporary pumps.
| Step | What gets done | Acceptance point |
|---|---|---|
| 1. Walkdown | Check supports, vents, drains, valve positions and the piping drawings | Punch list closed |
| 2. Pressure test | Hydrostatic test of new piping; ASME B31.9 calls for at least 1.5 times design pressure, limited by the weakest component | No leaks; signed record. Flush soon after, as standing test water starts corrosion |
| 3. Isolate and bypass | Bypass chillers, plate exchangers, molds and control valves; install temporary strainers | Temporary jumpers in place |
| 4. Flush | Circulate at the specified velocity, section by section, draining from low points | Strainers stay clean; water runs clear |
| 5. Chemical clean | Cleaner chosen for the metals, removing oil and mill scale | Readings level off between samples |
| 6. Rinse | Drain and rinse until the water approaches fill water conductivity and pH | Rinse results logged |
| 7. Passivate | Dose inhibitor straight away so the clean steel forms a protective film | Inhibitor at the program level, no bare steel left wet |
| 8. Fill and vent | Remove bypasses, fill from the low point, vent high points, set tank precharge before pressurizing | Target pressure at the top of the loop |
| 9. Start up and balance | Prove pump rotation and flow at each branch, verify exchanger and cooler performance | Flows within tolerance |
| 10. Turn over | Baseline chemistry, pressure, flow and makeup reading, with the operating instructions | Records in the owner’s hands |
The testing itself is described on our hydrostatic testing page. Skipping steps 4 through 7 is how a new loop ends up plugging strainers for its first months of life.
Sealed loop maintenance schedule
A sealed loop needs far less attention than a tower, but its failures develop out of sight, so scheduled readings are what catch them. These intervals are common practice, adjusted to the manufacturer’s instructions and how the loop trends.
| Interval | Tasks |
|---|---|
| Weekly | Read and log the makeup meter, loop pressure and supply and return temperatures; test inhibitor level and pH, and test more often if levels are dropping |
| Monthly | Check strainer differential pressure, pump seals, air vents and exchanger pressure drop; confirm the standby pump runs |
| Quarterly | Pull corrosion coupons after about 90 days in the rack; take bacteria samples, including low-flow spots and dead legs; review the makeup trend |
| Annually | Check tank precharge with the water side isolated and relieved; test the relief valve per the owner’s program; calibrate sensors; clean or inspect plate exchanger and cooler surfaces; test glycol concentration and reserve inhibitor |
| As condition requires | Open the plate pack and clean it, replace filter media, clean the loop chemically if corrosion products are restricting flow, repair insulation |
Paul Industries builds these tasks into preventive maintenance programs, with the logbook and trend charts kept where the plant’s engineers can see them.
Troubleshooting a sealed cooling loop
Most sealed loop problems reveal themselves through pressure, makeup or chemistry readings before any machine trips, and the combination of symptoms usually names the cause.
| Symptom | Probable cause | Corrective work |
|---|---|---|
| Makeup meter climbing | Leak at a seal, packing, relief valve or a concealed section | Isolate sections, repair, then restore chemistry |
| Relief valve lifts on warm-up | Tank undersized, waterlogged or with a failed diaphragm; low precharge | Check precharge, replace or enlarge the tank |
| Pressure falls sharply on cooldown | Low tank volume or precharge, or a slow leak that the fill valve is hiding | Tank check, then a makeup trend review |
| Gurgling, noisy coils, erratic flow | Air in the loop, low pressure at the high point, separator misplaced | Raise fill pressure, vent, relocate or add the separator |
| Supply temperature drifting up | Fouled cooler or plate exchanger, low flow, added load, weather beyond design | Clean surfaces, verify flow, recheck the load |
| Rising exchanger pressure drop | Plates or tubes plugged with iron or debris | Backflush or open and clean; add side-stream filtration |
| Inhibitor falling, makeup flat | Bacteria consuming nitrite, or a cross-leak at an exchanger | Bacteria test, non-oxidizing biocide, exchanger pressure test |
| Black or rust-colored water | Active corrosion, low inhibitor, oxygen entry | Coupon and iron checks, filtration, cleaning and repassivation |
| Chiller short cycling or low-flow trips | Small loop volume, plugged strainer, staging problem | Buffer tank, strainer cleaning, control changes, chiller repair |
What to ask closed loop cooling system companies
A proposal shows how a contractor thinks through the full life of the loop, so ask for these specifics before award:
- The supply temperature calculation at site design conditions, showing every approach in the chain.
- The expansion tank calculation with fill temperature, warmest idle temperature, fluid and pressures.
- A written flushing, cleaning and passivation procedure, naming what stays bypassed and until when.
- Pressure test records to the governing code, ASME B31.9 for building services or ASME B31.3 where the engineer calls for it.
- Where the air separator, tank connection, makeup meter and sample points go, shown on the drawing.
- The inhibitor program and how its test results reach the plant.
- Who answers the phone on a Sunday night when the loop loses pressure.
How Paul Industries carries a closed loop cooling job
Paul Industries takes the job from a load list to a loop that holds its temperature for the life of the plant. Our engineers calculate the load, flow, supply temperature and expansion. We supply the fluid coolers, dry coolers, chillers, towers and plate exchangers; fabricate pump skids, headers and spools in the shop and in the field; install, wire and insulate; pressure test, flush, clean and passivate; fill, balance and start up; and then treat, service, repair, replace and maintain everything on the loop. Crews work in all 50 states, with same-day emergency response when a loop goes down. Request a quote for a new system, a conversion from tower water or a loop that keeps losing water.
Standards referenced: ASME B31.9 · ASME B31.3 · ASME BPVC Section VIII · ASHRAE Handbook: HVAC Systems and Equipment · 40 CFR 125.92
Frequently asked questions
Do closed loop cooling systems lose water?
Yes, in small amounts. Seals weep, samples get drawn, maintenance drains a section and relief valves occasionally lift. Those losses should stay a small fraction of system volume each year, and steady losses beyond that mean a repairable leak.
What fluid goes in a closed cooling loop?
Indoor loops usually run treated water, ideally softened or demineralized, with a corrosion inhibitor. Any section exposed to freezing outdoors takes an inhibited ethylene or propylene glycol mix, and food plants generally choose propylene.
Is a closed circuit fluid cooler the same as a cooling tower?
It looks similar and also rejects heat by evaporation, with one key change: the loop fluid stays inside a coil while separate spray water runs over the outside. The spray circuit still needs tower-style water treatment and cleaning, but the fluid in the coil stays clean.
How often should closed loop water be tested?
Weekly testing of inhibitor level and pH is a common baseline on industrial loops, with lab analysis and bacteria sampling at longer intervals. A loop with stable readings and flat makeup can be reviewed less often if the treatment supplier agrees.
Why does closed loop water turn black?
Black water usually means fine iron oxide from corrosion under low oxygen conditions, while reddish brown water points to rust formed where more oxygen is present. Either color calls for checking inhibitor level and the makeup rate, and then adding filtration to remove the solids.
What pressure should a sealed cooling loop run at?
Enough to keep the highest point positive, typically static height converted at 0.433 psi per foot plus a few psi of margin, and below the rating of the lowest-rated component. High points that fall below atmospheric pressure pull air in through vents and seals.
Where does the expansion tank connect?
Usually on the pump suction side, with the pump discharging away from the tank connection. Connecting there lets the pump add pressure to the circuit, which helps vents expel air and keeps pump suction from dropping.
Can an open tower loop be converted to a sealed loop?
Yes. A plate heat exchanger is installed between the tower water and the plant, and the plant side receives an expansion tank, air separator, chemical feeder, new pumps and a full cleaning, since old piping usually holds years of scale. The extra exchanger approach is checked against what the loads can accept.
Does loop water ever need replacing?
Well-treated water can stay in service for a very long time, since the inhibitor is what gets topped up. Replacement comes when contamination, biological fouling or wrong-fluid mixing makes correction impractical, and the loop is then cleaned before refilling.
Why would a sealed system need a makeup line at all?
Filling, venting and replacing small losses all require a controlled connection. With a meter and backflow preventer, the makeup line also becomes the loop's main diagnostic point, because every gallon it passes equals a gallon lost somewhere.
Does a closed loop need biocide?
Sometimes. Sealed loops can grow denitrifying and sulfate-reducing bacteria, especially around dead legs and low-flow branches, and these can cause fouling and corrosion under deposits. Testing guides the decision, and a non-oxidizing product compatible with the inhibitor is the usual choice.
What is the difference between a closed loop and once-through cooling?
Once-through cooling takes water from a source, runs it through the equipment one time and discharges it warm, so withdrawal is large and permits often apply. A sealed loop keeps the same charge indefinitely and needs a device to reject its heat.
What does a side-stream filter do on a sealed loop?
It continuously cleans a small slip of the circulating flow, gradually removing the fine iron that passes through a basket strainer. Plate exchangers, narrow machine passages and control valves all benefit, and a pressure gauge across the housing tells the operator when to change media.
How is a leak found in concealed or buried pipe?
Sections are isolated by valves and held under pressure to see which one falls, then listening equipment, thermal imaging or a tracer narrows the location. Comparing makeup against pressure over a period when the plant is idle helps confirm the size of the loss.
What sets the installed price of a sealed cooling loop?
Heat rejection type, capacity, supply temperature, pipe material and length, the number of connected machines, standby pumps, controls and whether work happens around running production. Conversions add cleaning of old piping, and water, chemical and downtime savings are part of the comparison.
Can new machines be added to an existing loop?
Yes, provided flow, heat rejection and expansion volume are rechecked. New branches are flushed separately before joining the main, hot taps or planned shutdowns make the tie-in, and the inhibitor is raised to cover the added volume.
How are plate exchangers protected in a sealed loop?
They stay bypassed during flushing, get a fine strainer on the inlet, and are monitored by pressure drop so plugging is seen early. Keeping the two fluids at a known pressure relationship also makes any plate leak easier to read from chemistry trends.
What happens when air stays trapped in the loop?
Air pockets block coils and machine passages, cut heat transfer, cause noise and can make pumps lose prime or cavitate. Oxygen carried in with that air also drives pitting in steel, so persistent air is treated both as a flow problem and a corrosion problem.
Does a process loop need insulation?
Pipe carrying fluid colder than the room's dew point needs insulation with a vapor retarder to stop condensation and drips. Warmer loops are often insulated only for personnel protection or heat gain, and outdoor glycol lines may also need jacketing against weather.
Which is better for a plant: a dry cooler or a fluid cooler?
It comes down to the supply temperature the machines need against the site's weather and water cost. A dry cooler uses no water but is limited by dry bulb temperature; a fluid cooler reaches colder water on hot days at the price of spray water treatment and consumption.
Related: Data Center Cooling Systems · Chilled Water Systems · Glycol Cooling Systems · Cooling Tower Water Treatment · Cooling Tower Cleaning · Dry Cooler · Request a quote