Ultrasonic BTU Meter

The firmware reads three signals continuously: mass flow from the transit-time sensor, supply temperature from the supply PT100, and return temperature from the return PT100. It solves the energy integral E = ∫(ṃ × Cp × ΔT) dt and outputs the result in kWh, MJ, BTU, or kJ. Mass flow comes from volumetric flow times density. The firmware looks up density from the supply temperature on the on-board steam table, so no external density input is needed.

Two options. The CT-1 clamp-on pair (DN50 nominal, 100 ohm class 0.8, −40 to +160 deg C, 0.1 deg C resolution) mounts external to the pipes with coupling paste and stainless straps. No pipe cut needed. The in-line PT100 thermowell pair uses a threaded G1/2 well welded or screwed into the pipe wall. Faster response, more permanent, but requires a pipe cut. Both feed the same transmitter input; specify at order.

3 to 90 deg C across the supply and return pair. HVAC chilled water runs 4 to 12 K, condenser loops 8 to 15 K, DHW 30 to 50 K, and district-heat primary 40 to 90 K. Accuracy tightens at higher delta-T. At 4 K HVAC the PT100 0.1 deg C resolution dominates and energy accuracy sits in the 3 to 5 % range. At 50 K district-heat the same hardware delivers under 2 %. Below 2 K delta-T, use volumetric flow with separate temperature instruments instead.

RS-485 Modbus RTU is the native interface. The register map exposes energy rate, flow, supply and return temperatures, totalizer energy and flow, alarm status, and diagnostics. BACnet integrates through a Modbus-BACnet gateway (Loytec, Contemporary Controls, Cimetrics). KNX uses a Modbus-KNX converter. LonWorks goes through a gateway. M-BUS EN 13757 connects directly to the EU billing aggregator. Pulse output handles legacy register systems. The factory pre-configures the register map and slave address from the BMS spec at order.

Custody-transfer certificates are not shipped from the factory. EN 1434, MID MI-004, and OIML R75 are buyer-arranged with the local notified body. What ships standard is the ISO 9001 calibration certificate (serial number plus tested flow and temperature ranges), the EMC 2014/30/EU certificate, and a mill-cert traceability note. For custody-transfer billing; district-heat primary metering, EU tenant billing under EED; combine the calibration cert with the notified-body certificate. For non-custody HVAC sub-measurement and ISO 50001 reporting, the standard certificates are enough.

Three reasons. First, no moving parts on the flow side. No impeller wear, no bearing seizure on glycol blends, 10-year service life without recalibration walks. Mechanical BTU meters typically need 10-year replacement. Second, low-flow sensitivity. The transit-time signal reads accurately at HVAC trickle flows below the mechanical Q1 floor. Third, integrated PT100 input and BTU firmware in one transmitter, so no separate integrator is needed. Magnetic BTU is restricted to conductive water above 5 µS/cm and full-bore flanged install; ultrasonic reads glycol blends and supports clamp-on retrofit. Trade-off: ultrasonic costs more at DN15–DN25, with parity from DN50 up.

Lead time is 5 to 7 business days from order confirmation, factory direct. The kit ships with the IP65 wall-mount transmitter, the flow transducer pair sized for the DN, the CT-1 PT100 supply and return pair with coupling paste and stainless straps, up to 30 m of signal cable, and a pre-configured Modbus register map and slave address per the BMS spec. ISO 9001 calibration and EMC 2014/30/EU certificates ship with every meter. EN 1434, MID MI-004, and OIML R75 are buyer-arranged.