Defining a bivalent system in iSBEM?
A bivalent heating system is one in which the heating is supplied by two different types of heat sources. An example could be a heat pump with a gas boiler for backup. Within iSBEM, a fuel type and a seasonal efficiency have to be input in order for the SBEM calculation to produce the overall CO2 emissions per kWh of the total heating provided by the two heat sources. First, the proportion of the heating demand met by each heat generator needs to be estimated, in a manner that can be justified to Building Control. Then, an efficiency equivalent to the 2 systems based on their respective loads, efficiencies, and emission factors (obtained from ADL2A) needs to be calculated. Also, in order to ensure that the notional building is correctly defined (according to definition in ADL2A), if the fuel of one of the 2 generators is gas, it is necessary to define the fuel type for the equivalent heating system, which is entered into SBEM, as gas. Even if the calculated equivalent efficiency figure
