Flow meter hire sizing is the decision that determines whether a hire deployment commissions in hours or goes back on the truck. Pick too large a bore at low flow rates and the velocity drops below what the meter can read. Go too small and the signal saturates, pressure drop climbs, and the liner starts wearing faster than it should. Neither outcome is recoverable without pulling the unit off site and sourcing a replacement — which costs commissioning time that most projects don’t have to spare. This guide covers the engineering basis for correct sizing using the Aircon Rentals EFM and Magflo electromagnetic flow meter hire range, so the right unit arrives on site ready to connect.
How electromagnetic flow meters work
Electromagnetic flow meters operate on Faraday’s Law of electromagnetic induction. A conductive fluid moving through a magnetic field generates a voltage proportional to its velocity. That voltage — typically in the millivolt range — gets sampled by the electrodes and converted to a 4-20 mA output signal, readable via Modbus or direct instrumentation.
The measurement is purely velocity-based. Pipe bore directly determines whether the meter resolves a meaningful signal. The operating principle is Q = v x A: flow rate equals velocity multiplied by cross-sectional area. The meter measures velocity. You select bore to keep that velocity inside the instrument’s linear operating range.
For a hire deployment this decision happens before the unit leaves the Aircon Rentals depot — not on site. A correctly specified unit commissions in hours. One that arrives at the wrong bore goes back on the truck. Getting flow meter hire sizing right upfront is what separates a smooth deployment from an expensive one.
The velocity window — the number that drives sizing
Every electromagnetic flow meter has a functional velocity envelope regardless of brand. For the Aircon Rentals EFM and Magflo hire range:
| Parameter | Value |
|---|---|
| Minimum velocity | 0.3 m/s |
| Recommended operating range | 1–3 m/s |
| Maximum velocity | 10 m/s |
| Accuracy (typical) | ±0.5% |
At 1–3 m/s the signal-to-noise ratio stays high, electrode fouling is less of a concern, and head loss stays negligible. Drop below 0.3 m/s and readings become unreliable. Above 10 m/s the liner — typically rubber or PTFE — starts eroding and the meter’s turndown ratio is exceeded.
Matching meter bore directly to pipe bore without checking velocity is the most common flow meter hire sizing error. A DN100 meter on a DN100 pipe at low flow rates will almost always sit under-range. The Aircon Rentals technical team confirms velocity against your flow data before dispatch. If the numbers don’t land in the 1–3 m/s band, a different bore gets specified before anything leaves the depot.
Step-by-step flow meter hire sizing procedure
Step 1 — Start with normal operating flow rate
Use the flow rate the system runs at 80–90% of the time, not the design maximum. Peak flow is used only to confirm the upper velocity limit isn’t breached at the top end. Sizing to the design maximum almost always results in a unit that runs under-range during normal operation.
Step 2 — Calculate the required bore diameter
Rearrange Q = v x A. Targeting 2 m/s: A = Q divided by 2, then D = 2 times the square root of that result divided by pi. Q must be in m³/s before running the numbers.
Worked example: a system running at 5 L/s (0.005 m³/s) targeting 2 m/s gives A = 0.005 / 2 = 0.0025 m², then D = 2 x √(0.0025/π) = approximately 56 mm. The nearest standard bore below that is DN50.
Step 3 — Round down, not up
Select the nearest standard bore and round down. Rounding down increases velocity and produces a better signal. A result sitting between DN50 and DN100 means trialling DN50 first and confirming velocity stays under 10 m/s at peak flow. If it does, DN50 is the right hire unit.
Step 4 — Verify fluid conductivity
The fluid must exceed approximately 5 µS/cm. The EFM and Magflo range is rated for water and glycol — process water, chilled water, and condenser water all qualify. Deionised water and hydrocarbons do not. Contact Aircon Rentals to discuss alternative metering options for those applications.
Step 5 — Check straight-run requirements
A minimum of 5x bore upstream and 3x bore downstream of any elbow, valve, or pump discharge is required before locking in the installation position. Skipping this step accounts for a large share of field calibration errors that get blamed on the meter itself rather than the installation position.
Step 6 — Account for reducer head loss
If bore size has been reduced with a reducer fitting, calculate the additional head loss and confirm the pump curve has room to absorb it before the hire unit is confirmed.
If flow data isn’t readily available, the Aircon Rentals technical team can work through sizing from system documentation, chiller performance curves, or BMS data. That conversation happens before the hire order is confirmed — not after the unit is already on site.
Selecting the right hire model
The right model for your flow meter hire is the one where your normal operating flow rate sits at 10–50% of the maximum flow column. That placement keeps velocity comfortably in the 1–3 m/s band throughout the hire period and gives the meter room to handle flow variations without dropping out of range.
| Model | Connection | Min Flow | Max Flow |
|---|---|---|---|
| EFM-50-M | 50 mm | 0.59 L/s (14.8 kW) | 19.63 L/s (493 kW) |
| EFM-100-M | 100 mm | 2.36 L/s (59.2 kW) | 78.33 L/s (1,968 kW) |
| Magflo-100 | 100 mm | 2.36 L/s (59.2 kW) | 78.33 L/s (1,968 kW) |
| EFM-200-M | 200 mm | 16.7 L/s (419 kW) | 277.8 L/s (6,978 kW) |
The kW figures represent thermal energy flow rate from the energy meter output, not electrical power draw. All units run on 240V AC single phase at 50 Hz, carry an IP67 rating, communicate via Modbus, and output a 4-20 mA signal. Operating temperature range is -20°C to 150°C.
All four models are available on short-term hire — from a single day for a system diagnostic through to several months for ongoing commissioning or performance monitoring programs.
Physical dimensions and site logistics
Confirming site access before the hire unit is dispatched avoids the same problem as getting the bore wrong — equipment that arrives and can’t be positioned correctly wastes the same commissioning time.
| Model | Connection | Frame Size (mm) | Weight |
|---|---|---|---|
| EFM-50-M | 50 mm | 580 x 1,160 x 730 | 91 kg |
| EFM-100-M | 100 mm | 580 x 1,740 x 780 | 134 kg |
| Magflo-100 | 100 mm | 680 x 1,730 x 725 | 118 kg |
| EFM-200-M | 200 mm | 580 x 2,320 x 910 | 252 kg |
All units ship on skids from Aircon Rentals depots in Sydney, Melbourne, Brisbane, and Perth. Victaulic or flanged connection options are available depending on configuration. Confirm connection type, pipe material, and site access dimensions with the Aircon Rentals technical team before dispatch — particularly for below-ground plant rooms or sites with restricted access.
Common hire applications and model fit
Chiller hire flow monitoring — EFM-100-M or EFM-200-M
For medium-to-large tonnage chiller hire deployments, the EFM-100-M or EFM-200-M covers the load. Verify chilled water flow against chiller performance curves before settling on a size. The energy meter output gives real-time thermal performance data throughout the hire period — useful for commissioning verification and performance documentation.
HVAC commissioning — EFM-50-M
Smaller air handling unit hire and fan coil unit circuits suit the EFM-50-M. Confirm design flow rates are achieved before issuing test and balance reports. The 50 mm bore covers most smaller AHU applications without oversizing the meter for the circuit.
Pump optimisation — any model
The real-time 4-20 mA output connects to a BMS or data logger to build pump curve overlays and catch efficiency losses before they compound. Model selection follows the flow rate calculation rather than the application type — run the numbers first.
System diagnostics — short-term hire
Temporary inline installation isolates flow imbalance, confirms bypass valve function, or validates BMS flow signals against a calibrated reference. Short hire, specific purpose. The Aircon Rentals technical team can advise on installation position and straight-run requirements before the unit is dispatched.
These meters are not suitable for deionised water, hydrocarbons, steam, gas, or any fluid below 5 µS/cm conductivity. Contact Aircon Rentals to discuss alternative metering options for those applications.
Flow meter hire sizing — FAQs
How do I size a flow meter for hire?
Start with normal operating flow rate, target a velocity of 1–3 m/s, rearrange Q = v x A to get bore diameter, and round down to the nearest standard bore. Confirm the upper velocity limit isn’t breached at peak flow. If flow data isn’t available, the Aircon Rentals technical team can work through sizing from system documentation before the hire is confirmed.
What is the rule of thumb for electromagnetic flow meter sizing?
Keep normal operating flow rate at 10–50% of the meter’s maximum rated flow. That keeps velocity in the 1–3 m/s range where accuracy is highest and fouling risk is lowest. Operating consistently at the top of the meter’s range increases liner wear and reduces measurement reliability over the hire period.
What straight run does a flow meter need before installation?
A minimum of 5x bore upstream and 3x bore downstream of any elbow, valve, or pump discharge. This is the most commonly skipped step on hire deployments and the most common cause of calibration errors that get blamed on the meter rather than the installation position.
What fluids can an electromagnetic flow meter measure?
Any conductive fluid above approximately 5 µS/cm — process water, chilled water, condenser water, and glycol solutions all qualify. Deionised water, hydrocarbons, steam, and gas do not. Confirm fluid type with the Aircon Rentals technical team before the hire order is confirmed.
How quickly can electromagnetic flow meter hire be deployed in Australia?
From depots in Sydney, Melbourne, Brisbane, and Perth — most metro requests are fulfilled within 24–48 hours of a confirmed order with sizing details provided. Regional sites allow additional transit time depending on distance from the nearest depot.
Can Aircon Rentals help with flow meter hire sizing if I don’t have flow data?
Yes. The technical team can work through sizing from chiller performance curves, system documentation, or BMS data. Provide what you have and the sizing conversation happens before the hire order is placed — not on site.
Aircon Rentals provides electromagnetic flow meter hire across Australia — EFM-50-M, EFM-100-M, Magflo-100, and EFM-200-M available for short-term and long-term hire with technical sizing support included. Call 1800 626 996 to speak with a technical specialist, or contact us online to discuss sizing before confirming a hire order.