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

More documents

Recommendations

Info

have also an increased complexity that renders it harder to analyse the building’s performance.Analysing a building’ energy consumption down to room level requires a high amount ofmeasurement equipment, such as sensors and meters in each single room. Therefore, detailed buildingperformance analysis is often hampered by high monitoring cost, and practitioners often requestalternative cost-efficient methods (Jagemar, L. and Olsson, D., 2007).This paper develops an estimation algorithm in Section 3 to analyse building’s energyconsumption down to room level. The algorithm is adjustable in its information intake to differentsensing and metering equipment available in a building, providing a flexible usage with roughestimations using few sensors to detailed computations using a high density sensing deployment. Thealgorithm can be used for offline data analysis and for online monitoring as a so-called virtual sensor(a model-based sensor) to estimate the heat flows in rooms. Section 4 uses the algorithm’s output andcompares it to the reached user comfort level to evaluate actions improving the building’s energyconsumption. Both approaches provide a broad set of performance metrics to support buildingperformance analysis, monitoring, and optimisation (Augenbroe, G. and Park, C.-S., 2005).The approach is validated using the ERI building as an existing low-energy building with a hybridHVAC system that is introduced in the next section.2 The Environmental Research Institute buildingThe Environmental Research Institute (ERI) is a 4500 m² low-energy building, located in the maincampus of University College Cork. The building is used as “Living Laboratory” by the InformaticsResearch Unit in Sustainable Engineering (IRUSE) and the Irish strategic research cluster ITOBO(ITOBO, 2007) to serve as a full-scale test bed for Intelligent Buildings demonstrating buildingperformance concepts (Keane, M., 2005).CoolingCircuits P-12SolarThermalArrayHotWaterGas-firedBoilerHeat PumpUnderfloorHeatingPumpP-7MMeter HPMeter FH MUnderfloorHeatingManifoldsWater from culverttoriverFigure 1. High Level Schematic of the Mechanical System for the ERIThe building is equipped with a wireless sensor network of about 100 devices and a wiredBuilding Management System (BMS) system consisting of about 180 sensors and meters that monitorindoor and outdoor conditions. The ERI covers various HVAC requirements for laboratories, cleanrooms, cold stores, offices, open offices, and seminar rooms used by multiple research groups frombiologist, chemist, engineers, and computer scientists.The building is heated by an under-floor heating system that is primarily supplied by a geothermalheat pump that taps into a water supply fed from a culvert running adjacent to a nearby river. Thewater is preheated by heat recovered from the cold stores and heat generated by the solar thermalarray. The under-floor heating operates at a maximum temperature of 40ºC. A condensing gas boiler
is sized to act as a complete back-up system. The hot water is provided by an 84 m² solar thermalcollector array, where the rest of the requirement is provided by the boiler. See Figure 1 for aschematic of the mechanical system. The heat pump and boiler are separately controlled. Both havetimetable dependent set-points. They ensure that heating and domestic hot water are provided overworking hours.3 Estimating the room heat consumptionTo identify rooms with unusual high heat usage the room’s heat consumption needs to be analysed.But, instead of installing heat meters in each room to measure the individual heat consumption, theroom’s heat intake is estimated from the overall heat consumption of the underfloor heating system bycreating a virtual sensor model using knowledge about the room heating controls.In case of the ERI, each room has an individual temperature closed-control loop consisting of atemperature sensor, a decentralised controller and one to four on/off-valves operating separateunderfloor heating circuits. The temperature values are logged by the BMS. However, exactinformation about the control values at the valves is not available in the BMS system. This is notuncommon as often only measurements are seen as important are logged, but it is the control valuesthat define the room’s and building’s heat consumption. The temperature closed-control loops areactivated all of the time in the ERI; but, the central heating system provides heat only at specific times.The basic assumption for the estimation is: that only these rooms consume heat, which valves areopen and allow the hot water to circulate through the underfloor circuits. Let be defined as theabsolute heat flow of the underfloor heating system measured by the heat meter FH in Figure 1 in caseof the studied ERI. The heat flow is computed in the heat meter from the mass flow rate in thepipes and the temperature difference of the water going in and coming out of the underfloor circuits as · ; ; . The mass flow rate is controlled in case of the ERI by the centralunderfloor heating pump in Figure 1. The temperature difference depends on the heat consumption(flow) of the rooms. Let be the heat flow of any room in the set of rooms connected to theheating system. Assuming further that the underfloor heating system has no further losses beside inthe rooms, then the overall heat flow in time step is the sum of all room’s flows and each room takes a percentaged share =/ in the overall consumption, thus · ; ; . (1)Due to the basic assumption, a room’s heat flow depends on the valve opening 0 100%.Which is insofar correct, as the valve opening limits the individual mass flows in the underflowcircuits of each room. Hence, if the valves in a room are closed ( = 0%) then the mass and heat flowas well as will be zero. But, if the valves are open ( > 0%) then the percentaged share can be inthe range of 0 1 as long ∑ 1 holds as given by eq. (1). Thus, considering the valveopening only allows determining the rooms heated, but the share these rooms take of the building’sheat consumption is still unknown.Therefore, it is assumed that for each room a relative heating coefficient can be defined that is ameasurement of the room’s heating capacity in relation to other rooms if all valves are fully open.This can be for example the sizes of the room’s underfloor heating circuits. Let the actual heatingcoefficient of a building be further the sum of all room’s coefficients linearly depending ontheir valve opening such that · . (2)
Page 1: Model-based virtual sensors for roo
Page 7: 5 ConclusionThe introduced approach

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?