Method and system for Determining flow rate in a pipe

A method for determining the flow rate in a pipe includes measuring a temperature difference between the pipe and the temperature of the surroundings of the pipe and dividing this difference by the difference between the temperature of the fluid entering the pipe and the temperature of the surroundings of the pipe. A non-linear conversion between the ratio derived in this way and the flow rate is used to estimate the flow rate. Also disclosed are methods for estimating the temperature of the fluid entering the pipe using either the temperature of the pipe or the local air temperature. The first method comprises: periodically receiving measurements of the temperature of the conduit; determining an extremal temperature of the conduit over a preceding time period of predetermined length; and using the determined extremal temperature as an estimate for the fluid temperature. The second method comprises: determining a rolling average of local air temperature over a preceding predetermined period; and using the determined rolling average of local air temperature as an estimate for the fluid temperature.