Book - School of Science and Technology

Building regulations 621It is essentially the desire to achieve energy savings that may lead sometimes to aproliferation of controls; nevertheless, such an objective is fundamental to good practiceand may include:. limiting plant operating periods. economical control of space conditions. efficient plant operation to match the load.The main objectives of the building energy management part of the system may besummarised as:. monitoring system performance. optimisation of system interrelationships with the building and its occupants. centralisation of fault reporting.The importance of economical use of energy is emphasised by some of the basicprovisions incorporated into recent legislation.Building regulationsThe current Building Regulations, 1991, (Part L), make it mandatory that space heatingor hot water systems in buildings, other than very small installations, are provided withautomatic controls, such that:. Space temperatures are controlled by thermostats.. Systems are provided with a timeswitch (or optimum start control) to ensure that theyoperate only when the building is occupied.. Boiler plant is controlled in an efficient manner and switched off when no heat isrequired.. Hot water supply storage is thermostatically controlled, and the heat supply is shut offwhen there is no demand.With increasing environmental awareness, further revisions to the Building Regulationswill increase the statutory requirements on control systems.Elementary componentsThe nature of heating and air-conditioning systems is such that, for the majority of theperiod of operation, plant and system capacity will exceed demand and the order of thisexcess varies with time: steady state conditions may be assumed never to occur. It followstherefore that, if the plant were to be uncontrolled, the conditions in the occupied spacewould be outside the desired range in consequence of which some means of control is afundamental requirement.A simple control system, Figure 22.1, comprises a sensing device, to measure thevariable, a controller, to compare the measured variable with the desired set-point andto send a signal to the control device, which in turn regulates the input. In such a system, atemperature sensor (sensing device) in the flow pipe from a heat exchanger measures thetemperature of the water (controlled variable) and signals the information to the controller.The controller compares the flow temperature with the desired temperature (setpoint) and passes a signal to the control valve (control device) to open or close, therebyregulating the amount of heat introduced to the heat exchanger. This is an example ofclosed loop control, where feedback from the controlled variable is used to provide a