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

Most temperature-control failures get blamed on the chiller. In practice, a surprising number of “chiller won’t hold setpoint” calls trace back to the glycol loop: air in the line, dirty strainers, undersized piping, the wrong concentration, biological growth, or corrosion from mixed metals.

If you’re supporting solvent recovery, rotary evaporation, wiped-film/short-path distillation, reactors, or cold traps, loop stability isn’t just a comfort issue—it’s uptime and product quality. Stable condenser temperatures support consistent vapor collapse, tighter cuts, and less stress on compressors, pumps, and seals.

This post is a facilities-first glycol loop commissioning checklist you can run before you blame the chiller. It’s written for lab managers, facilities teams, and maintenance techs who need predictable temperature control in regulated, high-throughput environments.

Why most “chiller problems” are loop problems

A recirculating chiller can only remove heat at its rated capacity if the loop can deliver:

• Enough flow to move heat from the process to the heat exchanger
• Enough pressure to overcome piping/head loss without cavitation or bypassing
• Clean heat transfer surfaces (no sludge, pipe scale, biofilm, or plugged strainers)
• Correct fluid properties (viscosity, freeze protection, corrosion inhibition)

When those are off, you see the same symptoms:

• Temperature hunts or overshoots
• Alarms for low flow / high temperature
• High ΔT (supply/return spread) with low heat removal
• Pump noise (cavitation) and foamy reservoir
• Frequent filter/strainer clogging or rapid corrosion debris

Commissioning goal: document a stable baseline

A commissioning checklist isn’t just “get it running.” It’s about creating a baseline so that three months from now you can answer:

• Did flow drop?
• Did head loss increase?
• Did glycol concentration change?
• Did chemistry drift (pH/inhibitors)?
• Did contamination begin (solids or microbes)?

Your baseline should include:

• Supply temperature setpoint and actual
• Return temperature
• Loop differential pressure (or pump discharge/suction pressures)
• Flow rate (measured, not guessed)
• Strainer differential pressure (clean vs dirty)
• Glycol concentration and freeze point
• pH and inhibitor reserve (for inhibited glycols)

Step 0 — Pre-commission design sanity checks (before you fill)

Before flushing or adding glycol, confirm the fundamentals.

Confirm materials compatibility

Mixed metals (for example copper + carbon steel + aluminum in the same wetted loop) can accelerate corrosion. Your loop should be designed around compatible wetted materials and a glycol that includes corrosion inhibitors suitable for your metallurgy.

If you inherit a loop of unknown history, assume you need chemistry validation and filtration.

Validate pipe sizing and head loss assumptions

Undersized piping is one of the most common root causes of chronic low flow. High-viscosity glycol at low temperature amplifies the issue.

Facilities takeaway: if the loop was sized for water and later switched to 30–40% glycol, you may have unintentionally increased pumping difficulty.

Confirm heat exchanger approach temperatures

If your condenser or process heat exchanger is undersized or fouled, the chiller may “look weak” even when the loop is fine. Commissioning should include a quick check that process heat exchangers are sized, clean, and valved correctly.

Step 1 — Mechanical cleaning and flush protocol (the non-negotiable)

New loops shed debris. Existing loops hold it. Either way, your first job is to remove solids before they plate out on heat exchangers or destroy pump seals.

Guidance from commissioning bodies like BSRIA emphasizes pre-commission cleaning and flushing for closed pipework systems to achieve a stable condition for commissioning and ongoing maintenance.

External reference: BSRIA commissioning guidance overview: https://www.bsria.com/uk/knowledge/bookshop/commissioning_guides/

Flush protocol (practical sequence)

Use this sequence as a field-ready workflow:

1. Isolate sensitive equipment during the initial dirty flush

• Bypass plate heat exchangers, small orifices, fine control valves, and instrument ports where possible.

1. Install temporary high-capture filtration

• Put a startup strainer or bag filter in a location you can service frequently.

1. Fill with water (not glycol) for the initial flush

• Water is cheaper, easier to drain, and better for carrying debris out.

1. High-velocity circulation

• Run pumps at the highest safe speed to mobilize debris.

1. Directional flushing

• If possible, flush in sections and reverse flow to dislodge trapped solids.

1. Drain and inspect

• Open strainers, check captured debris, record what you found.

1. Repeat until clean

• Your endpoint is not “looks better,” it’s “strainer loading stabilizes.”

1. Optional chemical clean

• If you see oil, sticky residues, or corrosion products, use a compatible cleaner per manufacturer guidance, then rinse thoroughly.

1. Final fill with inhibited glycol mix

• Only after the system is mechanically clean.

Facilities note: If you skip Step 1, you’ll pay for it later with plugged strainers, unstable flow, and fouled heat exchangers that look like “mysterious chiller underperformance.”

Step 2 — Air removal and pump protection (stop cavitation at the source)

Air in the loop causes three major problems:

• Heat transfer loss (air pockets insulate)
• Flow instability (two-phase flow and pump cavitation)
• Accelerated corrosion (oxygen drives oxidation)

Commissioning actions

• Bleed high points repeatedly during first circulation
• Confirm expansion tank pre-charge and location are correct for your pump arrangement
• Verify the reservoir level remains stable and doesn’t foam
• Listen for pump cavitation (gravelly sound) and correct immediately

A chiller pump that sounds “angry” is usually not failing—it’s being starved (restriction, air, or NPSH issues).

Step 3 — Filtration and strainer selection (mesh matters)

Filtration is not a one-and-done decision. You typically need:

• Coarse protection during startup to capture construction debris
• Ongoing fine protection to keep heat exchangers clean

Mesh selection (rule-of-thumb approach)

Because every loop has different risk (new build vs. retrofit; stainless vs. mixed metals; plate HX vs. jacketed vessel), pick filtration based on what you’re protecting:

• Startup / dirty flush: coarser capture first so you don’t blind filters immediately
• Plate heat exchangers and small channels: finer protection once the loop is clean

If you’re using strainers, record:

• Strainer type and screen size
• Clean strainer ΔP at baseline flow
• “Change/clean” ΔP threshold (your SOP trigger)

Facilities best practice: place strainers where you can actually service them without draining half the building.

Step 4 — Instrumentation: measure flow and pressure like you mean it

Commissioning without measurement is just optimism.

Minimum recommended measurements

• Flow rate in the main supply header (or at each major branch)
• Differential pressure across the pump or key equipment
• Supply/return temperatures near the load

Baseline recording (what to write down)

At stable operation (30–60 minutes after conditions settle), record:

• Chiller setpoint
• Supply temperature (at chiller) and supply temperature (at load)
• Return temperature (at chiller)
• Flow rate
• Pump speed setting (if variable)
• Strainer ΔP
• Ambient conditions if relevant (mechanical room temp)

These numbers become your troubleshooting map later. If supply temp is fine at the chiller but not at the load, it’s almost always a distribution/loop issue.

Step 5 — Glycol concentration: freeze protection vs. viscosity (don’t over-glycol)

A common failure mode is “more glycol must be safer.” But higher glycol concentration increases viscosity, which can:

• Reduce flow
• Increase head loss
• Increase pump power draw
• Reduce heat transfer coefficient

Set concentration based on real lowest temperature risk

Use a reputable freeze-point chart from your glycol supplier and set protection to a realistic minimum, not a guess.

External reference (example freeze-point chart for propylene glycol): https://corecheminc.com/wp-content/uploads/2020/06/Freeze-Point-Chart-GlycoChill-Propylene-Glycol-Heat-Transfer-Fluid.pdf

If you operate near or below 0°C, validate that your chosen concentration protects against your worst-case exposure (including outdoor lines, dock doors, or shutdown scenarios).

Commissioning checks

• Measure glycol concentration with a refractometer (and record it)
• Record the corresponding freeze point
• Confirm the concentration aligns with your lowest expected operating temperature plus margin

Step 6 — Chemistry checks: pH, inhibitors, and microbiological control

Glycol doesn’t “wear out” instantly, but inhibitor packages do get consumed—especially in loops with oxygen ingress, mixed metals, or contamination.

Many inhibited glycol operating guides emphasize monitoring pH and reserve alkalinity (a proxy for inhibitor reserve) to confirm continued corrosion protection.

External reference (example inhibited propylene glycol operating guide): https://lentusllc.com/wp-content/uploads/2025/02/DOWFROST-LC-Operating-Guide-1.pdf

Commissioning chemistry baseline

At initial fill (or immediately after switching to glycol), capture:

• pH
• Reserve alkalinity (or inhibitor level per your fluid vendor)
• Visual clarity (haze can indicate contamination)
• Conductivity (optional but useful for trending)

Microbial growth: the hidden performance killer

Biofilm acts like insulation and can foul small passages. It also contributes to odor and can accelerate under-deposit corrosion.

Commissioning actions:

• Use inhibited glycol designed for closed loops
• Fix oxygen ingress (leaks, frequent top-offs)
• If microbial risk is high, consult your fluid vendor about biocide strategy compatible with your process and materials

Facilities note: If you’re constantly topping off, you’re constantly adding oxygen and diluting inhibitors. That’s a loop integrity problem—not a chiller problem.

Step 7 — Operational checks that protect uptime (and process quality)

Once the loop is clean, filled, de-aired, and measured, run checks that directly correlate to uptime.

Condenser stability test

For solvent recovery and distillation, condenser temperature stability matters. Commissioning should include:

• A steady-state run at typical load
• Recording condenser inlet/outlet temperatures
• Checking that the loop holds setpoint without oscillation

When condenser temperature drifts, you can see:

• Reduced solvent recovery rate
• More vapor passing through (higher downstream load)
• Unstable distillation cut points
• More frequent operator intervention

Alarm and interlock validation

• Verify low-flow and high-temp alarms are enabled and correctly set
• Validate any flow switches at the load
• Confirm your bypass valves are not masking real restrictions

Step 8 — Preventive maintenance schedule (turn your checklist into an SOP)

Commissioning is the start of the lifecycle. Convert your baseline into a simple PM cadence.

Weekly (or per shift in high-debris environments)

• Inspect strainer ΔP trend
• Check reservoir level and look for foam
• Quick visual check for leaks and corrosion staining

Monthly

• Clean strainers/filters (or replace elements)
• Record flow/pressure vs baseline
• Confirm temperature stability under typical load

Quarterly

• Check glycol concentration (refractometer)
• Spot-check pH (and inhibitor metrics if available)

Semi-annual / annual (depending on duty cycle)

• Full glycol analysis through fluid vendor (recommended)
• Inspect pumps/seals and verify calibration of temperature probes

Product plug: a practical chiller option (and why the loop still matters)

If you’re running smaller to mid-scale loads—or you need precise control across a wide range—lab-grade refrigerated/heated circulators can be a strong fit.

Recommended gear: PolyScience Refrigerated Chiller AD15R-40 (2 units) (temperature range -40°C to 200°C; designed for precise control and connectivity).

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

Even with high-quality circulators, your results still depend on the loop: correct glycol concentration, clean filtration, stable flow, and controlled chemistry. Commission the loop first, then evaluate whether you truly need more tonnage—or just fewer restrictions.

When to redesign: shared loops, head loss, and right-sizing circulators

If you’re expanding or adding equipment, consider whether a shared glycol loop (with proper hydraulic separation and controls) can improve overall uptime. Shared loops can work well when you:

• Group loads with similar temperature requirements
• Design branches with balancing and isolation
• Size pumps for real head loss (including future expansion)
• Add serviceable filtration and instrumentation at the header

Urth & Fyre can help you:

• Design shared loops for multi-station operations
• Match circulators/chillers to actual head loss (not nameplate assumptions)
• Implement preventive maintenance programs and connect you with calibration/chemistry partners

Quick-reference glycol loop commissioning checklist (copy/paste into your SOP)

Use this section as your working glycol loop commissioning checklist.

A) Pre-fill

• Confirm metallurgy compatibility and seals
• Confirm pipe sizing and expected head loss
• Verify valves are labeled and normal positions defined
• Confirm filtration/strainers are installed and serviceable

B) Flush & clean

• Isolate sensitive equipment for initial flush
• Fill with water and circulate at high velocity
• Clean strainers repeatedly until debris stabilizes
• Drain, inspect, repeat as needed
• Final rinse if chemical cleaning is used

C) Fill & de-air

• Fill with inhibited glycol mix at target concentration
• Bleed high points; verify expansion tank function
• Confirm pump is not cavitating (noise/foam)

D) Filtration finalization

• Set operational strainer/filter mesh appropriate for protected equipment
• Record clean filter/strainer ΔP at baseline flow
• Define ΔP threshold for service

E) Baseline measurements

• Record supply/return temperatures (chiller and load)
• Record flow rate
• Record pump setting/speed
• Record loop pressures or ΔP

F) Chemistry baseline

• Record glycol concentration and freeze point
• Record pH and inhibitor reserve metric
• Note clarity/contamination signs

G) Performance validation

• Run steady-state load test
• Verify condenser stability and alarm thresholds
• Confirm no abnormal vibration, noise, or leaks

Next steps

If your facility is fighting unstable temperatures, don’t start by swapping chillers. Start with the loop. A disciplined commissioning and baseline process typically delivers faster improvements, lower downtime, and longer equipment life.

Explore equipment listings and get help with loop design, right-sizing, and PM programs at https://www.urthandfyre.com.