sorry if this has been covered before. looking at various heatpumps on heatpumpmonitor.org it would seem standard that heat meters only work in one direction - i.e measure heat going into the house - however when defrosting the heatpump - heat is taken out of the heating circuit as shown by the flow/return temps crossing. Is this leading to artificially high COP readings during defrost? just puzzles me a bit. typically during a defrost there will be a period where the flow temp is actually lower than the return temp - whilst the heatpump uses the heat from the water to melt the ice on the evaporator coil. This heat is then replaced by the heatpump when it restarts in normal heating after the defrost - but if the heat extracted is not accounted for then surely the COP is overstated. If the heat measure could go negative and the heatpump app deal with negative values (i.e heat leaving the building) then it would seem more correct to me.