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Requirements for cooling meters

In addition to the more established provision of “heat” for heating various public utility companies also offer “cold” for air conditioning. In response to the increasing economic importance of “cooling services”, the European standard for heat meters is complemented by requirements for cooling meters. Basis for these requirements were metrological investigations at PTB.

Household cooling meter with an integrated temperature sensor on the outlet of the flow rate sensor.

The main purpose of an air conditioner is to cool down the ambient air. To this effect it removes thermal energy and “supplies cool air.” Cooling meters which determine this thermal energy do not differ in principle from heat meters. Therefore, the European standard EN 1434 of April 1997 which so far only contained requirements for heat meters, is now valid for both types of meters. However, compared to heat meters, cooling meters operate in a clearly restricted temperature range from 3 °C to 20 °C and with lesser temperature differences reaching 20 K at most. The requirements for cooling meters which have now been drawn up (for water as a heat-conveying fluid) will complement the standard which itself will not distinguish between meters for household air conditioning and meters for industrial applications.

In type approval tests, each individual flow rate sensor in a cooling meter must be tested at at least one water temperature in the range of (15 ± 5) °C. For mechanical meters, additional tests at (5 ± 1) °C are prescribed.

If cooling meters are to handle similarly large quantities of exchanged thermal energy as heat meters they need flow rate sensors designed for large volume flows due to the smaller temperature differences. For the tests, PTB has measuring devices for water flow rates up to 1000 m3/h and for temperatures as low as 3 °C.

Air conditioning units often run only in partial load operation at small temperature differences down to 2 K. To assess temperature sensor pairs of cooling meters in metrological terms, testing de-vices with very small measurement uncertainties are needed. These devices are also available at PTB.