Division Method 1: Using measurements

Under this method, the operator measures all relevant parameters, in particular temperature, pressure, state of the transmitted as well as the returned heat medium. The state of the medium in case of steam shall refer to its saturation or degree of superheating. The operator furthermore measures the (volumetric) flow rate of the heat transfer medium. Based on the measured values, the operator determines the enthalpy and the specific volume of the heat transfer medium using suitable steam tables or engineering software.

The mass flow rate of the medium is calculated as

Where ṁ is the mass flow rate in kg/s, V is the volumetric flow rate in m³/s and υ is the specific volume in m³/kg.

As the mass flow rate is considered the same for transmitted and returned medium, the heat flow rate is calculated using the difference in enthalpy between the transmitted flow and the return, as follows:

Where Q is the heat flow rate in kJ/s, h_flow is the enthalpy of the transmitted flow in kJ/kg, h_return is the enthalpy of the return flow in kJ/kg, and ṁ is the mass flow rate in kg/s.

In case of steam or hot water used as heat transfer medium, where the condensate is not returned, or where it is not feasible to estimate the enthalpy of the returned condensate, the operator shall determine h_return based on a temperate of 90 °C.

If the mass flow rates are known to be not identical, the following shall apply:

• Where the operator provides evidence to the satisfaction of the F1regulator that condensate remains in the product (e.g. in ‘life steam injection’ processes), the respective amount of condensate enthalpy is not deducted;

• Where heat transfer medium is known to be lost (e.g. due to leakages or sewering), an estimate for the respective mass flow shall be deducted from the mass flow of the transmitted heat transfer medium.

For determining the annual net heat flow from the above data, the operator shall – subject to the measurement equipment and data processing available, use one of the following methods:

• Determine annual average values for the parameters determining the annual average enthalpy of the transmitted and returned heat medium, and multiply with the total annual mass flow, using equation 4;

• Determine hourly values of the heat flow and sum up those values over the annual total operating time of the heat system. Subject to the data processing system, hourly values may be substituted by other time intervals as appropriate.