Btu and Heat Rate Measurement

The errors of the various Btu and heat flow detection sensors are as follows mechanical Btu—2-5% FS electronic Btu—0.5% FS and heat flow—1-2% FS. 

In all energy systems, including renewable, it is important to measure both the rate at which heat is flowing and also the energy flow that a fuel provides. The detection of the calorific values by calorimeters have already been discussed in Section 3.2.4. Here, first the heat flow sensors will be discussed. 

The efficiency of the overall utility distribution system is an indication of the losses that occur as a result of insufficient thermal insulation, leaking steam traps, etc. When considering an alternative optimization strategy, it is recommended to measure the energy consumption both before and after a particular strategy is implemented so that an accurate cost-benefit analysis can be made and the payback periods of the various strategies can be compared. 

In mechanical Btu meters, the volumetric flow is detected by positive-displacement or propeller-type sensors (Section 3.9.12) and is mechanically multiplied by the temperature difference across the exchanger. Transmitting attachments can also be provided wherever remote readouts are needed. These units are mostly used in HVAC applications and are not recommended if the temperature difference is under 3°C (5°F). 

In electronic Btu sensors, the flow sensor is usually a high-accuracy turbine flowmeter, and the temperature difference is usually detected by RTD transmitters which provide high repeatability and wide turndown. Their total error usually does not exceed 0.5% of full scale. 

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