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Heat Pumps Technology Guide SEAI Heat meter components must be installed correctly to ensure the accurate measurement of the target heat flow. Manufacturers will specify the requirements for each meter. Failure to observe these may lead to inaccurate measurements. For example: • Ultrasonic flow meters must normally be installed with the sensor head orientated within +/- 45 o of the horizontal. • Flow meters may also be sensitive to the direction of flow. In such cases, the flow meter will have direction marks on the body of the meter. These should match the direction of flow. • Heat meter manufacturers usually specify whether the flow sensor should be installed in the flow or return pipework. There may be restrictions on where flow meters can be fitted in the pipework system. Examples are: • Mechanical meters should not be located within five pipe diameters of bends or other disturbances, and the manufacturer’s instructions should be adhered to. • Ultrasonic meters should not be placed where there is a risk of air build-up, nor near a pump inlet or discharge point. Temperature sensors are supplied as matching pairs, and the serial numbers on the hot and cold temperature sensors should match. Temperature sensors should be correctly installed within their thermal pockets. Thermal paste can be used to ensure good contact between the sensor and the wall of the thermal pocket. The sensors should not be able to move once installed. It is good practice for the meter installer to fit the temperature sensors and calculators with security tags. This shows that the meter has not been tampered with. Such practices may be required by a financial incentive scheme. Temperature sensors and their leads are particularly susceptible to damage, so care should be taken in the choice of location for the thermal pockets, and in the positioning and securing of the sensor leads. The detailed design and installation must ensure that the temperature sensors are located to measure the intended heat flow. Incorrect positioning of one or both sensors will lead to erroneous heat measurement. 8.4. Maintenance and calibration Heat meters should be supplied with calibration certificates. Ideally, these calibration certificates should be valid for a set time period. However, manufacturers do not always state recalibration intervals or expected meter lifetimes, even on their calibration certificates, and there is no requirement in the Measuring Instruments Directive or EN1434 to do so. In the absence of guidance from the manufacturer, a period of no more than 5 years between recalibrations would be considered good practice. The calibration should be appropriate to the heating medium. For example, if it is to be used to measure the flow of a water/glycol mixture then the flow meter should have been calibrated for that mixture. Flow meters also require maintenance in order to ensure that they do not become less accurate over time. Recalibration usually requires that the flow meter is removed and returned to the manufacturer or a test house approved by the manufacturer. This will result in downtime for the installation (drain-down, refill and re- pressurisation) unless there is a way of by-passing the meter. It may be more economical to buy a new meter, perhaps as part of an exchange with the manufacturer. Records of all meter calibrations, repairs and changes should be maintained. 34PDF Image | Heat Pumps Technology Guide
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