PhD Thesis - Energy Systems Research Unit - University of Strathclyde

Control Loop 6DescriptionTime – basedcontrol schemeBypass valve cooling coil 1 controlControl scheme used to control the amount of chilled water passing through orbypassing cooling coil 1. Based on a proportional control which senses thetemperature of the air return from the ground floor apartment the valve variesbetween fully open (F.O) and fully closed (F.C.).00.00-08.00 Hours Valve varies between fully open and fully closed whenair temperature varies between 24ºC-21ºC respectively.08.00-18.00 Hours No control18.00-24.00 Hours Valve varies between fully open and fully closed whenair temperature varies between 24ºC-21ºC respectively.Controls 1 to 4 are used to ensure that the system works within user definedspecifications. Sensors and actuators were all positioned within the plant system;sensing a parameter within a part of the plant network and sending feedback to anactuator in another part of the plant. For example, control loop 1 operates the CHPunit via an ‘On’/‘Off’ control strategy featuring a 10ºC ‘dead band’ which ensuredthat the contents within the hot water storage tank were continuously within acontrolled 10°C temperature range. Set back control is employed during theafternoon (between 10.00 and 14.00 Hours) when demand is low. In parallel theauxiliary boiler was controlled (using loop 2) in such a way that if a shortfall in thesupply hot water temperature was detected, the boiler would switch ‘On’ tosupplement the heating energy provided by the CHP Unit.In addition to mimicking the classical control seen in buildings and systems, controlin building simulation can also be used for more abstract purposes. Control loop 5 forexample was used to mimic the draw on the hot water tank using one-minute profilesgenerated using the approach described in Chapter 2. In this case the controller setsthe flow from the tank (modelled using a pump) to be equal to the flow rate in theprofile (refer to Figures 2.38 and 2.39).Finally loop 6 is an example of a control loop which creates an interaction between aplant system component and the building. In this case the sensor is positioned in theexhaust duct of the ground floor apartment, sensing the return air temperature fromthe ground floor apartment and sending feedback to the bypass valve of the coolingcoil. Based on the temperature sensed, the bypass valve of the cooling coil increases101