An improved lumped parameter method for building thermal modelling

In this work an improved method for the simplified modelling of the thermal response of building elements has been developed based on a 5-parameter second-order lumped parameter model. Previous methods generate the parameters of these models either analytically or by using single objective function optimisation with respect to a reference model. The analytical methods can be complex and inflexible and the single objective function method lacks generality. In this work, a multiple objective function optimisation method is used with a reference model. Error functions are defined at both internal and external surfaces of the construction element whose model is to be fitted and the resistance and capacitance distributions are adjusted until the error functions reach a minimum. Parametric results for a wide range (45) of construction element types have been presented. Tests have been carried out using a range of both random and periodic excitations in weather and internal heat flux variables resulting in a comparison between the simplified model and the reference model. Results show that the simplified model provides an excellent approximation to the reference model whilst also providing a reduction in computational cost of at least 30%

CFD supported modelling of double skin facades in hot arid climates

Previous simulations predict the possibility of reducing cooling demands in office buildings in hot arid areas if a selective double skin facade is used. The reductions on cooling loads in rooms range between 19%-40% depending on the glazing thermal and visual performance characteristics of the exterior glazing of the double skin façade. However considerable uncertainty exists about the air flow rates and temperatures experienced within the channels of these facades. In this work a CFD model is used to predict these conditions for the case of an air-conditioned building in a hot arid climate. This case uniquely allows a CFD model to be applied to the facade independent of the simulation of the main building and its plant. Results show appreciable flow rates and temperatures generated mainly by buoyancy flow over the outer facade skin

A research study on Hong Kong's building services engineering profession: a review of the building services engineering profession in the United Kingdom

A review of the building services engineering profession in the United Kingdom is considered in this document. It provides supporting information for a comprehensive study into the profession in Hong Kong which is being conducted by Hong Kong Polytechnic University on behalf of the Hong Kong Institution of Engineers. The overall aim of the work is to investigate mechanisms for raising the profile of building services engineers in Hong Kong

Scheduling of Multiple Chillers in Trigeneration Plants

The scheduling of both absorption cycle and vapour compression cycle chillers in trigeneration plants is investigated in this work. Many trigeneration plants use absorption cycle chillers only but there are potential performance advantages to be gained by using a combination of absorption and compression chillers especially in situations where the building electrical demand to be met by the combined heat and power (CHP) plant is variable. Simulation models of both types of chillers are developed together with a simple model of a variable-capacity CHP engine developed by curve-fitting to supplier’s data. The models are linked to form an optimisation problem in which the contribution of both chiller types is determined at a maximum value of operating cost (or carbon emission) saving. Results show that an optimum operating condition arises at moderately high air conditioning demands and moderately low power demand when the air conditioning demand is shared between both chillers, all recovered heat is utilised, and the contribution arising from the compression chiller results in an increase in CHP power generation and, hence, engine efficiency

Numerical modelling of multiple standing column wells for heating and cooling buildings

A model for simulating clusters of standing column wells (SCWs) for use in geothermal heating and cooling systems is described in this paper. The model is three-dimensional, dynamic and solves the governing equations using a finite volume discretisation scheme with a fully implicit algorithm. The slower-acting field equations are solved using a wider time interval than that used for the faster-acting well equations and the two sets of equations are coupled through the field equation source terms. A groundwater bleed feature is incorporated. The model is applied to two evaluative test cases the first of which involves heating only and the second, heating and cooling. Results of the applications suggest that SCWs can deliver substantially higher rates of heat transfer than conventional closed loop borehole heat exchanger arrays especially when groundwater bleed is operational. An important practical consequence of this is that far less geotechnical drilling is needed when using SCWs than is the case with closed loop arrays

Modelling the robustness properties of HVAC plant under feedback control

Most existing building simulation programs fail to capture sufficient of the underlying dynamics of nonlinear HVAC plant and some have restricted room space modelling capabilities for low-time-horizon analyses. In this work, a simplified model of a room space with hot water heating and a chilled ceiling system is developed for the main purpose of analysing control system response. The room model is based on a new approach to lumped capacitance modelling and the heating and chilled ceiling emitters are modelled using third-order descriptions. Control system components are treated in detail and both controllers are ‘tuned’ at a nominal region of plant operation using a gradient-descent-based optimization procedure. Robustness qualities of the controllers are analysed with reference to extremes in plant operating conditions. A key feature of the work is the transparency of the modelling procedure, designed to have appeal to researchers as well as practitioners involved with HVAC control system design problems

Thermal comfort based fuzzy logic control

Most heating, ventilation and air conditioning (HVAC) control systems are considered as temperature control problems. In this work, the predicted mean vote (PMV) is used to control the indoor temperature of a space by setting it at a point where the PMV index becomes zero and the predicted percentage of persons dissatisfied (PPD) achieves a maximum threshold of 5%. This is achieved through the use of a fuzzy logic controller that takes into account a range of human comfort criteria in the formulation of the control action that should be applied to the heating system to bring the space to comfort conditions. The resulting controller is free of the set up and tuning problems that hinder conventional HVAC controllers. Simulation results show that the proposed control strategy makes it possible to maximize the indoor thermal comfort and, correspondingly, a reduction in energy use of 20% was obtained for a typical 7-day winter period when compared with conventional control

A fuzzy logic controller for temperature control of air handling plant

In this work the development of a three-channel fuzzy temperature controller for air handling plant is considered Sugeno inference mechanisms are used and their advantages for control type problems are highlighted The fuzzy controller is benchmarked against conventionally-tuned PID control It is demonstrated that the fuzzy controller is easier to set up than the PID controller whilst offering superior control tracking performance The work has made use of Matlab/Simulink as well as the Matlab Fuzzy Logic Toolbo

Modelling small-scale CHP plant under closed loop control

What is Matlab/Simulink ? Matlab-Simulink is a general tool for mathematical programming and dynamic simulation. This tool has originally been developed for control and automation applications, but it is at the same time a powerful tool for many problems in the field of engineering science. The tool also allows "hardware in the loop" simulations allowing to test real components by simulation. Using Matlab Simulink for HVAC applications ? The range of possible applications of the tool is very large - many fields of dynamic simulation and mathematical programming (cars, engines etc.). In the field of building and HVAC, the number of users of Matlab/Simulink has also been increasing in the last years. Why this workshop ? To date, there is very little exchange about modelling or simulation techniques using Matlab/Simulink in the field of building and HVAC simulation. The questions to be solved during this workshop are: how to improve information exchange and cooperation ? where is the tool of real interest and where not ? what are potential applications of the tool ? What kind of presentations are of interest ? Modelling and structuring in the graphical environment Simulink, Simulation and emulation (IAQ, comfort, control, energy consumption, ventilation), Visualisation techniques, Coupling with other Matlab toolboxes (CFD, Optimisation, control etc.) or other programs, Software demonstrations

Evaluation of domestic electrical demand and its effect on low voltage network performance

Electrical demand in a house depends on various factors mainly being the user’s behaviour and the rating of the appliances. Some researchers have used daily domestic electrical demand profile at half hour time resolution for the energy management. When data of half hour time interval is used for the analysis of on-site generation, it can lead to over/under -estimates of the proportion of generated energy used on site. As a consequence, this could lead to over/under-estimating in the import and export of power from and to the power grid. In this paper, domestic electricity use profile recorded at high time resolution of one minute is used to analyse the profile obtained at different time resolution and its effect on on-site generation. Daily load profile for summer and winter at time resolution of 30 minute is generated from a data set of 22 houses consisting data of a whole year which is then compared with the daily load curve obtained after diversity maximum demand from the literature. The generated daily load profile is then used to see effect on the low voltage network. For the analysis on the low voltage network, a typical UK low voltage network is developed in the Matlab/Simulink softwar