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C&G Unit 302: Principles of electrical science
Published in Trevor Linsley, Advanced Electrical Installation Work, 2019
During the period when the space heating or water heating is in the ‘on position’, thermostats based on the bimetal strip principle will maintain the room and water temperature at some predetermined level. Figures 3.67 and 3.68 show a wiring diagram for a domestic space and water heating system which circulates water through radiators to warm individual rooms. The Y plan uses one, three way water control valve. With this system the user may select hot water only or, hot water plus space heating. The S plan uses two separate control valves and therefore the user may select hot water only, space heating only or both together. The S plan gives the user more control and choice. In this type of system, energy conservation now recommends that each radiator be additionally fitted with a TRV (thermostatic radiator valve) to control the temperature in each room.
HVAC, renewable energy conversion and control systems
Published in J A Clarke, Energy Simulation in Building Design, 2007
In cases where the sensor or actuator has an inherent lag, it is possible to locate an additional equation-set within the system matrix equation. Consider a thermostatic radiator valve (TRV). The sensor is a wax filled capsule which expands against a spring to cause the valve to throttle water flow. The valve stroke is a continuous function of the sensed temperature deviation and so control action is proportional. Valve manufacturers will normally have data that describes the relationship between the sensed temperature and valve position, and between valve position and flow rate. These data can be re-expressed in the form of figure 6.16 allowing the proportional gain to be determined for any operating pressure.
Mind the Gap
Published in Kirsten M.A. Revell, Neville A. Stanton, Mental Models, 2017
Kirsten M.A. Revell, Neville A. Stanton
Figure 6.8 highlights the key control devices identified in the ‘compatible mental model’ (Figure 6.5). The interface of each control device may support, mislead or fail to reinforce the way devices function in the model in Figure 6.5. For example, the TRVs (Figure 6.8) are attached to each radiator, indicating custom control of the radiators within the system. The nature of the customization possible is misleading from the system image. The user is presented with a scale from 1 to 5 and set point adjustments are made by twisting a knob (Figure 6.8). There is no indication on the device of the relationship between the 1–5 scale and the temperature range at which hot water will be prevented from flowing into the radiator. Nor is there an indication that the device responds to changes in room temperature, or that this is a slow-responding device. Crossman and Cooke (1974) suggest that manual operators of slow response systems need to be taught the control characteristics in order to secure the best results. The name of the device (thermostatic radiator valve) contains reference to the ‘feedback’ function of the thermostat, as well as the control of fluid flow function of the valve which reflects well the device function. However, the device is not labelled by name, and the idea of a valve that users may have may relate to experience with those that offer fast-acting variable obstruction (like a gas valve) rather than a slow-responding control that functions by allowing or blocking flow. The idea of variable flow is reinforced by the twisting motion of the knob, similar to that used on other variable flow devices (e.g. gas hob control, tap). Together, these elements seem to communicate to the user a ‘natural mapping’ (as described by Norman 2002) between the 1–5 scale and heat output, rather than the ability to set a temperature range for automatic flow control.
Effective and scalable modelling of existing non-domestic buildings with radiator system under uncertainty
Published in Journal of Building Performance Simulation, 2020
Qi Li, Ruchi Choudhary, Yeonsook Heo, Godfried Augenbroe
Consider, for example, the case of large non-domestic buildings with radiator systems. Radiator heating is the most common type of hydronic heating system used in European non-domestic buildings. Radiator systems can have a considerable amount of heat delivered through radiant heat exchange with enclosing surfaces and internal objects (Sarbu and Sebarchievici 2016). Thus, the net heat delivery is more sensitive to the actual space layout and surface temperatures (Wallentén 2001). In addition, each radiator can generally be controlled individually via a thermostatic radiator valve (TRV), which modulates the radiator’s emitted heat based on a combination of user settings and local ambient air temperature. This autonomous and granular control strengthens the thermal coupling between radiator and its space, and as a result, enables large variations in user settings and resulted temperatures and heat balance across different spaces in a building. Therefore, detailed characterization of heat transfer phenomena and control mechanisms at individual space level becomes necessary. In addition, such detailed characterizations are critical for uncertainties to be accurately estimated and propagated into outputs of the entire building’s model through a bottom-up approach, as data that supports uncertainty quantification at aggregated levels are often not available. However, it becomes prohibitive to perform such detailed characterizations for large non-domestic buildings comprising hundreds of spaces because of the time cost of model setup and computational expense of the simulation model.