Building Services Engineering Research & Technology

Mechanical ventilation poses some challenges for control of pollutants in a fully enclosed dental clinic. Natural ventilation is used in some clinics because of its high exhausting efficiency and low non-renewable energy consumption. In this study, a dental clinic model was built using a computational fluid dynamics platform. The objective was to study the effect of natural ventilation on pollutant dispersion in this setting. The evaluations were conducted using the advanced turbulence model, large eddy simulation for the flow field and the discrete phase modelling for pollutant tracks. Three basic ventilation paths were identified, the ‘single narrow path’, ‘narrow path’ and ‘dispersive path’. The results show that the first of these had the highest efficiency, with an escape time of about 1/30 and 1/100 of the narrow and dispersive paths, respectively. Despite the position of the pollutant source and facilities such as bulkheads, escape time was significantly reduced when the ventilation flow rate was increased under the single narrow and dispersive paths. However, for the narrow path, these factors played a more dominant role in the escape time than the ventilation flow rate.

Practical application : This study is expected to provide information and guidance in understanding the pollutant spread in a naturally ventilated room such as a dental clinic.

The inclusion of soil freezing and snow cover within the context of a building energy simulation is explored. In particular, a method of including soil freezing within the simulation of heat flow from a building to the neighbouring foundation soils is considered. Non-linear thermal conductivity and heat capacity relations are explored that account for the effect of soil freezing. In addition, the work also considers latent heat generated by phase change that occurs as the soil water temperature reduces and ice forms. A simple approach to represent the insulating effect that snow cover may have on the net heat flow at the ground surface is also provided. The approach is illustrated by application to the simulation of a full-scale ground heat transfer experiment performed by others. The results provide a first indication of the potential significance of the inclusion of ground freezing within the context of modelling heat transfer from a full-scale monitored building. Overall transient temperature variations are shown to be dependent on ice content and latent heat effects. Non-linear, ice-content dependent, thermal conductivity and heat capacity are included in the work. Good correlation between measured and simulated temperature variations has been achieved.

Practical application: The principle application relates to the assessment of heat transfer from buildings through to the underlying foundation soils. In addition, the work is of direct relevance to a wider range of applications, for example, ground source heat pumps, thermo-active piles and foundations. The model lends itself to application with respect to utilisation of ground energy within the context of pavement design, particularly, in relation to the alleviation of winter ice problems. It also applies within the context of assessment of urban heat island phenomenon and heat and moisture transfer beneath freezer foundations.

The design of an elevator system heavily relies on the calculation of the round-trip time under up-peak (incoming) traffic conditions. The round-trip time can either be calculated analytically or by the use of Monte Carlo simulation. However, the calculation of the round-trip time is only part of the design methodology. This paper does not discuss the round-trip time calculation methodology as this has been addressed in detail elsewhere. This paper presents a step-by-step automated design methodology which gives the optimum number of elevators in very specific, constrained arrival situations. A range of situations can be considered and a judgement can be made as to what is the best cost–performance tradeoff. It uses the round trip value calculated by the use of other tools to automatically arrive at an optimal elevator design for a building. It employs rules and graphical methods. The methodology starts from the user requirements in the form of three parameters: the target interval; the expected passenger arrival rate (AR%) which is the passenger arrival in the busiest 5 min expressed as a percentage of the building population; and the total building population. Using these requirements, the expected number of passengers boarding an elevator car is calculated. Then, the round-trip time is calculated (using other tools) and the optimum number of elevators is calculated. Further iterations are carried out to refine the actual number of passengers boarding the elevator and the actual achieved target. The optimal car capacity is then calculated based on the final expected passengers boarding the car. The HARint plane is presented as a graphical tool that allows the designer to visualise the solution. Three different rated speeds are suggested and used in order to explore the possibility of reducing the number of elevator cars. Moreover, the average passenger travel time is used to indicate the need for zoning of buildings.

Practical application: This paper has an important application in allowing the designer to arrive at the optimum design for the elevator system using a clearly defined methodology. This ensures that the number of elevators, their speed and their capacity are optimised, thus ensuring that the cost of the elevator system and the space it occupies within the building are minimised. The method also employs a graphical method (the HARint) in order to allow the designer to visualise the optimality and the feasibility of the different design options.

A study was conducted to assess the energy performance of an optimal predictive control strategy for radiant floor district heating systems. A four-zone radiant floor heating system model was developed. The simulated performance of the optimal predictive control strategy was studied. The results showed 10% energy savings compared to a Proportional-Integral (PI) control strategy. Experiments were conducted in a laboratory radiant floor district heating system test facility. The description of the test facility, its operating conditions, and the results obtained are described. Experimental results further confirm the findings from the simulation study. Being simple and energy efficient, the optimal predictive control strategy is a good candidate control strategy for radiant floor district heating systems.

Practical application: Energy efficiency is a major issue of interest in the design and operation of sustainable heating systems. The radiant floor district heating systems have been successfully installed and operated in many countries resulting in significant energy savings. The optimal predictive control strategy proposed in this study further enhances the potential for higher energy savings from the district heating systems. The optimal control strategy is simple to implement as it relies on the predicted outdoor air temperature and computes future temperature set-points for the boiler water temperature. A suitably tuned Proportional-Integral (PI) controller can be used to track the optimal set-point thus realizing potential energy savings. A programmable logic controller or a supervisory control system would be appropriate to implement the designed optimal control strategy. The local control can be realized by using industrial PI feedback controllers.

The performance of a residential radiant chilled ceiling system combined with an outdoor air handling unit under steady operating conditions in summer was tested, and the stable operating characteristics of this system were analyzed. Indoor thermal environment parameters of room which employed this system were measured and analyzed and the thermal comfort evaluation of occupants was given. The results show that the composite system works well in summer, which can provide low- and high-temperature chilled water for the air supply terminal and the radiant terminal devices. Good thermal comfort can be achieved in room which employed this system, and no condensation risk occurs when it is applied in hot summer and cold winter zone of China. All the analysis provides a technical support for the popularization of the residential radiant chilled ceiling system combined with an outdoor air handling unit in China, and provides a reference for the further optimization of this system.

This paper describes a novel methodology to group building services into a single trunking system at minimal proximal distances between them. The study focused on solving the geometrical complexity encountered in conventional arrangements of building services, while taking into account thermo-physical and electromagnetic interactions between services together with building regulations. The potential solution for delivery and distribution of building services in any number of directions is an ‘onion layers’ type of design, using novel mathematical manipulations based on manifolds of spherical and cylindrical geometries joined using Bezier surfaces. Computer-aided design iterations were undertaken for channelling six building services into a single unit including water, air, electricity and data. It consists of concentric cylindrical-spherical shells superimposed at few millimetres gaps (channels) for which physical prototypes were produced.

Practical application: Successfully integrating building services such as water, air, electricity and data into a single trunking delivery system would offer an important advancement in reducing services installation cost, maintenance and the running cost of a building. Current design tools and techniques do not offer any solution for such integration; hence the current development of a multi-services trunking system. Subject to satisfactory compliance with health and safety requirements, plus maintenance issues, the system is proposed for embedding into building construction walls, panels or for placement into a confined space as a first step towards next generation building service. It is foreseen that many industries and business will be involved in the early stage of this development.

A novel control algorithm, named H-L control, for a direct expansion air conditioning system was previously developed, so that an improved indoor humidity control was achieved at a higher energy efficiency. However, a variable speed compressor was used, leading to a high cost of implementation for the control algorithm. This technical note reports on an experimental study, where two parallel connected single speed compressors were used to replace an expensive variable speed compressor to implement the novel control algorithm. Experimental results demonstrated that similar control performance may be achieved when using two single speed compressors, thus lowering the cost of implementation.