The implementation of European Measuring Instrument Directive 2204/22/EC (MID) has regulated approval and placing on the market for heat meters and other measuring instruments, throughout Europe. As well as heat energy for heating, cold energy for air conditioning and cooling is now also gaining importance, so that this form of energy also has to be precisely measured for accurate billing.
The European directive itself only recognizes the heat meter as a
measuring instrument, but not a cold meter. Until the MID came into
force, the area of cold measurement in Germany was covered by heat
meters. These were approved and verified for Germany in accordance with
PTB Directive K7.1.
With the implementation of MID into national legislation, this
regulation for the cold meter ceased to apply, so requirements and
approvals have been defined for the cold meter and its sub-assemblies in
an additional directive, K7.2.
But it had become apparent that in practice, not all heat meters were
equally good at meeting the high requirements of cold measurement.
Sometimes small temperature differences of 2°C occur, which still have
to be measured and recorded by a temperature sensor with accuracy and
long-term stability. There is also the fact that the temperatures to be
measured can be below the dew point. If during operation, temperatures
change and fall below the dew point, a temperature sensor that is not
designed for this will begin to “breathe”. Moisture can get inside the
instrument. Even slight traces can cause an electrical shunt and
therefore measurement error. To prevent this, the material and design
requirements for a temperature sensor have been increased by one.
The extended requirements have been redefined by PTB Directive K7.2 and
in the context of cold approval under approval number 22.77, temperature
sensors are type-tested for compliance with the more stringent
requirements and are approved for national cold verification. The
temperature sensors then meet the statutory requirements for billing in
contractual transactions. The quality of the cold meters is ensured by
the test and approval standards of the PTB, under Directive K7.2.
As the temperature sensors have to demonstrate different design
approvals (national or MID approval), subject to their application in
cold or heat meters, JUMO has developed a uniform sensor design that is
approved for both applications. So it is possible to mark the sensors
with both approvals and to market them in nationally verified versions,
as well as in CE and metrologically-marked versions. The user then has
the unlimited advantage of using a single temperature sensor, regardless
of whether this is connected to a cold meter, a heat meter or a
combined cold/heat meter.
