Glycol Loop Commissioning Checklist: Flow, Filtration, and Chemistry (Before You Blame the Chiller)

Why this glycol loop commissioning checklist exists

If you run rotary evaporators, condensers, cold traps, or wiped-film / short-path distillation, you already know the dirty secret: when temperatures drift or recovery slows, the first thing everyone blames is the chiller.

In reality, many “bad chiller” complaints are glycol loop problems—air, flow imbalance, filtration gaps, wrong glycol concentration, depleted inhibitors, or heat exchangers that slowly foul until performance collapses.

This post is a glycol loop commissioning checklist you can use before startup (and again after any major maintenance or expansion). It’s written for operations teams that need repeatable outcomes: stable condensing temperature, predictable solvent recovery, and fewer emergency service calls.

Along the way, we’ll connect the dots between loop issues and downstream pain: poor solvent recovery, higher kWh, unstable vacuum/distillation behavior, and avoidable downtime.

Scope: what counts as “the loop” in a lab/process cooling train

For commissioning purposes, treat the loop as everything from the chiller reservoir outlet to the equipment and back:

• Chiller / refrigerated circulator
• Supply/return headers
• Branch drops to each load (rotovaps, condensers, cold traps, distillation condensers, receiver jackets)
• Valves, hoses, quick-disconnects
• Strainers/filters and any air/dirt separators
• Heat exchangers (process condensers, external plate HX, jacketed vessels)
• Instrumentation: temperature, pressure, flow, conductivity/pH ports

The checklist below assumes you’re feeding multiple branches (even if it’s “just two rotovaps and a condenser,” it behaves like a small hydronic system).

Preflight checklist (before you add glycol)

1) Confirm the design intent (write it down)

Commissioning fails when “requirements” live in someone’s head. Put these in a one-page commissioning sheet:

• Minimum supply temperature needed at the most temperature-sensitive load (e.g., condenser inlet)
• Ambient conditions the system must survive (storage and operation)
• Number of loads, make/model, and expected duty cycle
• Target flow per branch and total target flow
• Target loop ΔT (supply-to-return temperature rise)
• Target glycol concentration (freeze/burst protection margin)
• Materials in the loop (stainless, copper/brass, aluminum, elastomers)

Why this matters: the same chiller can look “underpowered” if the loop is configured for a ΔT it can’t achieve or a viscosity it can’t pump.

2) Verify piping and hose realities (the hidden head loss audit)

Before filling, walk the system and document:

• Hose IDs and lengths (long small-ID hoses kill flow)
• Quick-disconnect type and bore size (some are surprisingly restrictive)
• Height changes (vertical lift)
• Number of elbows, manifolds, restrictive valves
• Any “temporary” reducers left in place

Commissioning tip: If you can’t easily calculate head loss, you can still avoid obvious mistakes—too-small hoses and too many restrictions are the #1 culprits in low-flow loops.

3) Verify branch isolation and balancing capability

You need to be able to:

• Isolate each branch
• Throttle/balance each branch
• Purge air at high points (manual vents or purge ports)
• Drain and flush without disassembling half the system

If you don’t have these features, you can still commission—but you’ll do it with more downtime and more guessing.

Glycol concentration: freeze protection vs viscosity (don’t over-glycol the loop)

Your freeze protection target should be driven by the lowest expected fluid temperature and the facility’s risk tolerance (power outage, overnight setpoints, etc.). But higher glycol concentration increases viscosity, which:

• Reduces flow for a given pump
• Increases pumping energy
• Reduces heat transfer (lower Reynolds number, worse convection)

That combination can masquerade as a “weak chiller.”

What to do during commissioning

• Select a glycol type appropriate to your environment and compliance needs (propylene glycol is common where incidental contact risk matters).
• Use manufacturer freeze-point charts for your specific fluid, not a generic rule of thumb.
• Measure concentration with a calibrated refractometer (not guesswork).

External references for concentration/freeze protection guidance:

• ChemAqua, “Guideline for Selecting and Maintaining Glycol Based Heat Transfer Fluids” (overview of inhibited glycol systems and degradation modes): https://www.chemaqua.com/en-gb/wp-content/uploads/sites/8/2024/07/Guideline-for-Selecting-Glycol.pdf
• Notes on viscosity impacts and pump performance concepts (and the need to reference viscosity at operating temperature): https://blog.craneengineering.net/the-effects-of-viscosity-on-systems-and-pump-selection

Commissioning rule: Use the lowest glycol concentration that safely meets freeze/burst protection. Over-glycoling is a common self-inflicted wound.

Chemistry documentation: pH, conductivity, inhibitor reserve (baseline or it didn’t happen)

A glycol loop is also a chemistry system. If you don’t establish a baseline at commissioning, you can’t tell whether you have:

• oxygen ingress
• corrosion activity
• contamination from process leaks
• glycol degradation (thermal, aeration/oxygenation, microbiological)

ChemAqua summarizes glycol degradation modes and emphasizes the need for proper inhibitor/buffer packages (and monitoring) in closed loops: https://www.chemaqua.com/en-gb/wp-content/uploads/sites/8/2024/07/Guideline-for-Selecting-Glycol.pdf

Commissioning chemistry checklist

At minimum, document:

• Glycol type and brand
• Concentration (refractometer reading + temperature)
• pH
• Conductivity (or TDS, depending on your program)
• Inhibitor reserve (nitrite/molybdate/triazole, per your glycol chemistry and materials)
• Visual clarity (haze/solids/oil sheen)

General closed-loop targets vary by formulation and metallurgy—follow your glycol/water-treatment supplier’s ranges. As a broad reference point, many closed hydronic systems target pH in a mildly alkaline range; for example, NTI’s water best-practices guidance for hydronic systems references pH 7–9 in typical closed-loop contexts: https://ntiboilers.com/wp-content/uploads/2023/08/Water-Best-Practices.pdf

Commissioning best practice: take two baseline samples

• one immediately after mixing
• one after the loop has circulated, been purged, and run under load for a day (this catches “first run” contamination and air release)

Filtration & strainers: the cheapest insurance you’ll ever buy

Why filtration matters in condenser-driven processes

Rotovaps and distillation condensers rely on stable heat transfer. Debris, pipe scale, gasket fragments, PTFE tape, and pump wear particles can:

• foul small passages in condensers
• stick valves partially closed
• reduce flow in a way that looks like a chiller issue

Commissioning filtration checklist

• Install a Y-strainer (or basket strainer) where it protects the most sensitive components.
• Confirm the strainer is accessible for blowdown/cleaning.
• Specify and record the mesh / micron rating you installed.

Micron recommendations are application-specific (and depend on HX geometry and acceptable pressure drop). The key commissioning action is to:

• start with a conservative strainer/filtration strategy,
• check differential pressure (or at least flow) during the first week,
• then optimize.

If you have plate-style heat exchangers or small-passage condensers, finer filtration may be warranted, but don’t “go fine” without understanding pump margin.

Startup flushing plan (what good looks like)

New loops (and recently modified loops) contain debris. A startup flush is not optional if you want stable operation.

A simple commissioning flush plan:

1) Mechanical inspection: confirm all strainers are installed and clean, all valves in correct positions.2) Fill with flush fluid: often clean water or a cleaning solution appropriate to your metallurgy (follow your water-treatment vendor).3) Circulate and purge: run pumps, open high-point vents, purge until air release stabilizes.4) Branch-by-branch flush: flush each branch individually at higher velocity if possible.5) Blow down strainers: clean strainers repeatedly until debris rate drops.6) Drain and refill with glycol mix: add inhibited glycol/water mixture.7) Document baseline chemistry: concentration, pH, conductivity, inhibitors.

For general hydronic cleaning/startup language, see “Cleaning and Start-up of Mechanical Piping Systems” (spec-style guidance on flushing, backflushing pumps/strainers, and removing debris): https://www.gov.nl.ca/ti/files/works-masterspec-230802.doc

Flow verification: prove flow at each branch (don’t assume)

This is the heart of a glycol loop commissioning checklist: verify real flow where it matters.

Why branch flow matters for rotovaps and condensers

Many rotovap/chiller issues are really “not enough coolant flow through the condenser,” which raises condenser temperature, reduces condensation rate, and forces:

• higher vapor load to the vacuum pump
• worse solvent recovery
• more frequent cold trap overload
• unstable boiling behavior

Manufacturers commonly call for meaningful coolant flow; for example, Heidolph notes roughly 8 L/min water flow through a condenser in one context: https://flavor.heidolph.com/en/blog/29490

Your equipment may need more or less, but commissioning should confirm you can actually deliver the required flow rate, not just “the pump is on.”

Branch flow commissioning steps

• Identify each branch and label it physically.
• Measure flow using one of:
• inline flow meters
• clamp-on ultrasonic flow meters
• timed bucket test (for open, safe configurations)
• With all branches open, record flow per branch and total flow.
• Close all but one branch and record flow again (this reveals balancing issues).
• Adjust balancing valves so critical loads receive guaranteed minimum flow.

Acceptance criterion example (adapt to your process):

• Each rotovap condenser branch achieves its minimum required L/min at the worst-case viscosity (coldest operating condition).

Setting ΔT targets (and why ΔT tells you the truth)

Loop ΔT (supply vs return temperature) is one of the most powerful diagnostics you have.

• If ΔT is near zero, you may have too much flow for the load, bypassing/mixing, or poor heat pickup.
• If ΔT is too high, you may have insufficient flow, fouled HX, or undersized pumping.

In building chilled-water practice, a common rule of thumb is around 10°F (about 5–6°C) ΔT for conventional systems, with variations depending on design. Practical references also tie flow to load using “gpm per ton” heuristics (context-dependent but useful for intuition): https://www.eng-tips.com/threads/chilled-water-gpm-per-ton.11873/

For lab/process loops, the “right” ΔT depends on:

• condenser approach temperature needs
• process stability requirements
• hose/piping constraints
• pump capability at glycol viscosity

A pragmatic commissioning approach to ΔT

1) Start with a conservative ΔT target (e.g., 3–6°C) to ensure good heat pickup without extreme flows.2) Under stable load, record supply temp, return temp, and branch flows.3) If you can reduce flow while maintaining process temperature stability, you often reduce pumping energy and improve controllability.

Remember: ΔT is not just a number—it’s a fingerprint of whether energy is being absorbed and moved effectively.

“Bad chiller” failure modes that are actually loop problems

1) Air in the loop (the silent performance killer)

Symptoms:

• gurgling/noisy lines
• erratic flow and temperature swings
• pump cavitation behavior
• fluctuating condenser temperature

Why it masquerades as a chiller issue:

• the chiller can be producing cold fluid, but air pockets prevent heat transfer and reduce effective flow.

Commissioning prevention:

• purge at high points
• maintain positive pressure where applicable
• recheck air release after first heat cycles (air comes out of solution)

2) Wrong glycol mix (too concentrated, too viscous)

Symptoms:

• low flow everywhere, especially at cold setpoints
• pump overload or poor pump curve position
• poor condenser performance even though chiller is “cold”

Why it hurts your operation:

• higher viscosity increases pumping power and reduces convective heat transfer.

Reference on viscosity measurement importance and pump selection considerations: https://blog.craneengineering.net/the-effects-of-viscosity-on-systems-and-pump-selection

3) Undersized pumps / underestimated head

Symptoms:

• good flow on a single branch, terrible flow when multiple branches open
• inability to hit minimum condenser flow
• chronic “we can only run one unit at a time” constraint

Commissioning prevention:

• calculate or estimate system head
• confirm pump curve at glycol viscosity and operating temperature
• verify flow with all loads online

4) Fouled heat exchangers (condensers, coils, plate HXs)

Symptoms:

• rising approach temperatures over weeks/months
• needing colder and colder supply setpoints to get the same result
• increased compressor runtime and kWh

Why it hits solvent recovery and stability:

• warmer condensing reduces capture efficiency; more vapor makes it past the condenser and into downstream traps/pumps.

Commissioning prevention:

• flush correctly
• install strainers/filters
• record baseline ΔT and approach temperatures for trending

How loop issues drive poor solvent recovery, higher kWh, and unstable processes

When cooling is unstable, the process compensates in expensive ways:

• Poor recovery: insufficient condensing leads to more solvent vapor load downstream.
• Higher kWh: chillers run longer and at lower setpoints to “brute force” around bad flow or fouling.
• Unstable boiling: fluctuating condenser temperature changes vapor pressure dynamics, increasing bumping/foaming risk.
• Maintenance spiral: vacuum pumps see more vapor, oil degrades faster, traps ice up, operators chase symptoms.

Commissioning is the moment to stop this cycle before it becomes “normal.”

Commissioning documentation pack (what to file for future you)

Create a simple, auditable record:

• P&ID or flow schematic marked “as commissioned”
• Branch list with measured flows and valve positions
• Supply/return temps under a known load
• ΔT target and actual ΔT under load
• Glycol brand/type and concentration
• Chemistry baseline: pH, conductivity, inhibitor reserve
• Strainer/filter location and mesh/micron rating
• First-week strainer cleaning frequency and findings

This becomes your troubleshooting and preventive maintenance foundation.

Preventive maintenance (PM) intervals to set during commissioning

Don’t wait for “something to go wrong.” Set PM cadence up front:

• Weekly (first month): strainer inspection/cleaning; record ΔT and supply/return temps.
• Monthly: verify branch flow (spot check critical branches), inspect hoses and QDs.
• Quarterly: glycol concentration check (refractometer) and visual clarity.
• Semi-annual: chemistry test panel (pH, conductivity, inhibitor reserve), inspect for leaks/oxygen ingress.
• Annual: deep clean as needed, calibration of sensors/flow meters, review load changes.

If your loop sees frequent top-offs, treat that as a red flag: makeup fluid introduces oxygen and shifts chemistry.

Product plug: a chiller that only performs if the loop is commissioned

If you’re feeding multiple lab/process loads and need a broad temperature range, the PolyScience AD15R-40 refrigerated/heated circulator (15 L, -40°C to 200°C class) is a solid option—especially when you pair it with a documented loop commissioning and PM plan.

Recommended gear (Urth & Fyre listing): https://www.urthandfyre.com/equipment-listings/refridgerated-chiller-ad15r-40-2-units

If you’re expanding capacity, note that this listing includes two units, which can be useful for redundancy, staging, or splitting critical vs non-critical loads.

Urth & Fyre angle: make cooling a solved problem, not a daily argument

At Urth & Fyre, we help teams:

• map cooling loads across rotovaps, condensers, and distillation trains
• right-size chillers and pumping for real-world viscosity and head
• standardize a glycol loop commissioning checklist and PM SOPs so performance is repeatable
• troubleshoot “chiller problems” that are actually flow, filtration, or chemistry problems

Cooling shouldn’t be your bottleneck—and it definitely shouldn’t be a mystery.

If you’re planning an upgrade, adding loads, or chasing unstable recovery, explore equipment listings and consulting support at https://www.urthandfyre.com.