Model-based virtual sensors for room heat metering and energy ...

Then, is a measurement of the building’s actual active heating capacity, i.e. if representsthe room’s underfloor heating circuits size then is the actual size of active circuits in time stepk. As is defined as the room’s heating capacity in relation to other rooms, eq. (2) also allows toestimate the percentual share of a room in the overall heat flow from eq. (1) such that finally results · . (3) This equation (3) allows estimating the room heat flow from the relative heating capacity of aroom in comparison to the others. In the named example of using the underfloor heating circuit size as it will mean that a room utilises the same proportion of the actual heat flow as his heating circuitsize is in relation to the building’s active circuits . The benefit of equation (3) is that it easilyscales to different available knowledge levels by modelling and adequately.The valve opening depends on the control values computed by the room temperaturecontroller. If a detailed model is necessary then the specific characteristic curves of the valves can beused. In case of the ERI, simple on/off-valves are used and it can be simplified that 0, 1.The relative heating coefficient of each room can be individually adapted to the availableinformation about the building. In simple cases it can be set to the number of valves or radiators,which permits rough estimations. Better results provide the size of the underfloor heating system orradiators assuming that their size is proportional their heating capacity. For very precise results,detailed models of the heating system systems can be used that model also dynamic aspects such asthe dependence of the heat transfer on the temperature difference between the heating system androom air temperature.The estimation in its basic form in eq. (3) neglects any time delay behaviour in the heating systemsuch as the dead times of the water floating through the pipes as well as the delay behaviour of theheat transfer between the underfloor and the room air temperature. It assumes that the delay effectsare less relevant for the estimation considering the fact that large sampling intervals of 15 min arecommon in building performance analysis like in the ERI case. If the delay times are very large andnot neglectable the equation (3) can be extended to an difference equation considering also pastcoefficients with and .Summarising, a buildings room’s heating consumption can be estimated in each time step by the following algorithm:(1) Compute the room’s control value and valve opening for each room .(2) Compute the building’s actual heating coefficient with eq. (2) from .(3) Estimate the room’s heat flow for each room via eq. (3) from , .The proposed algorithm uses the control value for each room’s individual heating control. Asinformation about the control value is often not available like in the investigated ERI case, the controlvalue can also be computed by remodelling the control algorithm. In case of the ERI, the valvesare individually controlled for each room by a bounce control with a hysteresis of 0.3Cº arounda temperature set-point . This means, that if the temperature in a room drops below ( - ) the valves are opened ( 1) and the room is heated until the room temperaturereaches ( + ) at which point the valves are closed ( 0). Thus,1, ; 0, ; (4) 1, otherwise.If more advanced PID controllers are used the control value can be recomputed in a comparableway if the controller parameters are known. If the set-point is not known it partly can bereconstructed from the step response of the room temperature (Vasyutynskyy, V. et al., 2005) if thequality of control is good enough.