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Four Flow Meters, Four Fluids: How We Instrumented an Ammonia Refrigeration Loop Industry : Industrial Refrigeration / HVAC | Fluids : Anhydrous Ammonia, Ammonia Solution, Demineralised Water, Chilled Water | Tags: FT-01 to FT-04
Flow meters for ammonia refrigeration and chilled water system
Quick AnswerA customer came to us with four flow measurement tags on single ammonia refrigeration and chilled water system. The fluids were anhydrous ammonia (FT-01), demineralised water (FT-02), 25% ammonia solution (FT-03), and chilled water (FT-04). Two tags needed Coriolis — not because it was specified by default, but because mass flow with totalising was a genuine process requirement. The other two got vortex meters. All four output 4-20 mA to PLC, AISI 316L wetted parts, ANSI flanged, IP55. |
Ammonia has been used as a refrigerant for over 150 years. R717 still outperforms most synthetic alternatives on thermodynamic efficiency, which is why it shows up in large cold stores, food processing plants, and absorption chiller systems. The trade-off is handling complexity. Ammonia is toxic above about 25 ppm in air, attacks copper and copper alloys on contact, and needs SS316L throughout all wetted components. Most engineers who specify ammonia systems know this. What they sometimes miss is the instrumentation side.
This particular system runs an absorption refrigeration cycle. Anhydrous ammonia is the primary working fluid. A 25% ammonia-water solution circulates on the distribution side. Demineralised water feeds the mixing stage. Chilled water goes to the load. Four flow measurement points, and the engineering team needed a different answer for each one — different fluid, different pressure rating, different accuracy requirement, different reason for picking one meter type over another.
The system is controlled by PLC. All four flow transmitters output 4-20 mA signals directly to the PLC panel. Power supply throughout is 220V AC. Area classification is safe (non-hazardous) for all four locations.
| Tag | Fluid | Type | Size | Flow Range | Pressure | Temp. | Accuracy | Connection |
| FT-01 | Anhydrous Ammonia | Coriolis | 1" | 100–3,000 kg/h | 25 bar | 100°C | ±0.1% | 1" ANSI 300 |
| FT-02 | Demineralised Water | Coriolis | 3" | 9,780–24,450 kg/h | 10 bar | 100°C | ±0.1% | 3" ANSI 150 |
| FT-03 | Ammonia Solution 25% | Vortex | 2" | 10–28.3 m³/h | 25 bar | 100°C | ±2.0% | 2" ANSI 300 |
| FT-04 | Chilled Water | Vortex | 4" | 40–240 m³/h | 10 bar | 100°C | ±2.0% | 4" Flanged |
FT-01 — Anhydrous Ammonia, 1" Coriolis, 100–3,000 kg/h
Coriolis flow meter for liquid ammonia measurement
Fluid: Pure anhydrous ammonia, liquid phase. Density 611 kg/m³ at 20°C, viscosity 0.14 mPa·s. Operating pressure 19 bar, design pressure 25 bar.
Coriolis was the correct choice here, not vortex. Anhydrous ammonia refrigerant flow needs to be measured in mass units (kg/h) because the refrigeration load calculation is energy-based. Volumetric flow is not useful without knowing the density at operating conditions, which varies with temperature and pressure. A Coriolis meter measures mass flow directly, regardless of fluid state changes.
The flow range is 100–3,000 kg/h on a 1" line. That is a 30:1 turndown — well within Coriolis capability. Accuracy is ±0.1% of reading. The totalising function is enabled on this tag, which means the PLC accumulates kg of ammonia passed for process accounting. ANSI 300 flanges match the high-pressure line class.
FT-02 — Demineralised Water, 3" Coriolis, 9,780–24,450 kg/h
Fluid: Demineralised water at 70°C, density 978 kg/m³, viscosity 0.40 mPa·s. Operating pressure 4.5 bar. Line 1003.
Demineralised water feeds the ammonia absorption mixing process. Precise mass dosing is critical here: the ammonia-to-water ratio directly determines the concentration of the ammonia solution output (FT-03). An error in the DMW feed rate produces off-spec ammonia solution, which affects the entire refrigeration cycle downstream.
This is why Coriolis was specified over electromagnetic flow meter, despite DMW being an electrically conductive liquid where magmeter would normally be the default. The process engineer required mass flow with totalising, not volumetric. The Coriolis meter on 3" ANSI 150 flanges delivers this directly. Flow range 9,780–24,450 kg/h at ±0.1% accuracy.
FT-03 — 25% Ammonia Solution, 2" Vortex, 10–28.3 m³/h
Stainless steel 316L Vortex flow meter for ammonia solution
Fluid: Aqueous ammonia solution, 25% NH3 by weight, 75% water. Density 916 kg/m³ at 10°C, viscosity 0.76 mPa·s. Operating pressure 16.45 bar, design pressure 25 bar. Line 1002.
FT-03 sits downstream of the mixing point. By the time the ammonia solution reaches this loop, the concentration has already been set by the FT-01 and FT-02 mass balance upstream. So volumetric flow is all you need here — there is no requirement to measure mass. We went with vortex on 2" ANSI 300, flow range 10–28.3 m³/h.
One point to note: ammonia solution at 0.76 mPa·s (0.76 cP) is low-viscosity. Vortex meters require a minimum Reynolds number, typically Re > 10,000 for reliable operation. At 10 m³/h on a 2" pipe, Re is well above that threshold. No concern on minimum flow. Totalising is not required on this tag.
FT-04 — Chilled Water, 4" Vortex, 40–240 m³/h
Fluid: Chilled water at 8.4°C, density 1,000 kg/m³, viscosity 1.37 mPa·s. Operating pressure 4 bar. 4" flanged line.
The chilled water distribution loop is the highest-flow circuit in this system at 40–240 m³/h. This is a 6:1 turndown range at utility-grade accuracy. Vortex flow meter is the cost-efficient and reliable choice for clean chilled water at these flow rates. No totalising function required.
NBR is listed as the line material on this loop — the load side piping uses standard rubber-lined construction rather than SS, consistent with lower-pressure chilled water distribution practice. The flow meter itself uses AISI 316L for the wetted parts, which is correct regardless of the downstream piping material.
Most engineers default to one meter type across a system if they can. It is simpler to stock, simpler to maintain, simpler to explain to procurement. But in this project, defaulting to Coriolis on all four tags would have been over-engineering on FT-03 and FT-04, and defaulting to vortex on FT-01 and FT-02 would have missed the mass flow requirement entirely. So two Coriolis, two vortex — and a clear reason for each.
| Parameter | Coriolis (FT-01, FT-02) | Vortex (FT-03, FT-04) |
| Measurement output | Direct mass flow (kg/h) | Volumetric flow (m³/h) |
| Accuracy | ±0.1% of reading | ±2.0% of reading |
| Totalising | YES — required by spec | Yes |
| Min viscosity limit | No moving parts, no limit | For low viscosity liquid |
| Fluid density | Measures density directly | Requires known density |
| Typical application | Accurate dosing, custody transfer | High-volume utility loops |
Put simply: if the process needs to know how many kilograms passed — for dosing, for energy accounting, for custody — use Coriolis. If you just need to know the flow rate on a utility loop where density is stable and accuracy requirements are modest, vortex does the job at lower cost.
Ammonia is incompatible with copper, brass, and most copper alloys. All flow meters in this project use AISI 316L as the wetted material. 316L (low carbon) is selected over 316 to reduce intergranular corrosion risk in welded joints exposed to ammonia at elevated temperatures.
The anhydrous ammonia and ammonia solution loops run at 25 bar design pressure — hence ANSI 300 flanges on FT-01 and FT-03. The DMW and chilled water loops run at 10 bar, allowing ANSI 150 on FT-02 and standard flanges on FT-04.
Design temperature is 100°C for all four instruments. The anhydrous ammonia line carries a dual design temperature specification of -50°C / 100°C, reflecting the cryogenic condition possible during plant shutdown or emergency venting. The Coriolis meters specified cover this range without material or seal issues.
If you have a similar multi-fluid instrumentation requirement — ammonia, refrigerants, process water, or chemical solutions — send us the following and we will recommend the correct meter type and size within 24 hours:
Contact Silver Automation Instruments: inquiry@silverinstruments.com | WhatsApp +86-18936759191 | Coriolis flow meter | Vortex flow meter
