Heat Meters

Heat Meter Industry 
Heating companies in many European and Asian countries use heat meters to measure how much heat
their customers use to warm their living spaces. These meters must be calibrated to accurately measure
how much heat is consumed.


Background 
For years, many European, Nordic, and Northern Asian countries have heated buildings with heated
fluid (usually water) that is pumped from a central boiler. This boiler usually supplies many customers–
–sometimes entire communities or very large apartment buildings––with heat and hot water.
The buildings are heated with heat exchange circuits (radiators, etc), which circulate a heat-conveying
fluid from the central boiler through each circuit. A heat meter is used to measure the amount of heat
used in a particular circuit. The customer is then billed for the amount of heat he or she has used.
The heat meter indicates heat in legal heat units. The calibration of heat meters is regulated by
government agencies and is usually subject to local and/or international guidelines. See the “additional
references” section of this document for examples.


Temperature Measurement Critical to the Heat Meter Industry 
In order for a heat meter to measure the amount of heat used in a room or building, a technician
measures the temperature of the heated fluid as it enters the circuit and then again as it exits the circuit.
The technician takes the difference of the two temperature measurements, along with the pressure and
flow measurements of the fluid, and computes how much heat was sent to the customer.
The meter utilizes a pair of calibrated PRT sensors to compare temperature differences of the entering
and exiting fluid. Technicians calibrate the PRT probes at a minimum of three points over the range of
5°C to 160°C, depending on the actual temperature range of the individual heat fluid system. They
obtain resistance values for the probes, which are used to calculate temperature coefficients that are
programmed into the heat meter.
According to one customer who calibrates heat meters, the sensor pairs only need to be reasonably
accurate in their measurement of absolute temperature (+/- 2 °C), but they must be more accurate in
measuring temperature differences (+/-0.2°C). Measurement standards call for at least ±0.01°C
repeatability.
source :  Hart Scientific Fluke Company