Yokogawa 212 Heat Calculator - Manual (Page 5)

1. OVERVIEW
The Model 212 Heat Calculator is designed to measure the energy consumed in
both heating and cooling (air conditioning) systems. The instrument is normally
supplied complete with temperature probes and power supply, and will interface
to a wide variety of flowmeters, including positive displacement and inferential
water meters, magnetic flowmeters with pulse outputs, turbine flowmeters &
paddlewheel flowmeters.
The Model 212 measures the temperature in the feed and return flow lines and
uses this information to calculate the density and enthalpy of water. By also
measuring the volume of water flowing in the system, the Model 212 will then
determine the energy used. Power is calculated as:
P = V x
ρ
x
(
h
TV
- h
TR
)
where P = Power (W)
V = Volumetric Flow rate (m 3 /sec)
 = density (kg/m 3 )
h
TV
= Specific Enthalpy (J/kg) at Feed Temperature
h
TR
= Specific Enthalpy (J/kg) at Return Temperature
The Model 212 is designed to be used in typical water heating or cooling systems
where pressures do not exceed 16 bars.
The temperature in both the feed and return lines is measured via two PT100
resistance temperature devices (RTDs). For maximum accuracy, four wire RTD
measurement is used and internally corrected for non-linearities which are
inherent to an RTD.
The Model 212 complies with OIML R75 and EN1434 standards and includes
Meter-bus and an infra-red data transfer option.
The Model 212 includes separate peak and off-peak registers as well as the ability
to compute charge and discharge energy in systems where heat may be stored in
underground tanks. The Model 212 also includes an RS485 communications link
with Modbus RTU protocol.
Overview 3