Nicolas Kelly

Simulation-assisted control in building energy management systems

Technological advances in real-time data collection, data transfer and ever-increasing computational power are bringing simulation-assisted control and on-line fault detection and diagnosis (FDD) closer to reality than was imagined when building energy management systems (BEMSs) were introduced in the 1970s. This paper describes the development and testing of a prototype simulation-assisted controller, in which a detailed simulation program is embedded in real-time control decision making. Results from an experiment in a full-scale environmental test facility demonstrate the feasibility of predictive control using a physically-based thermal simulation program.

A technique for the prediction of the conditions leading to mould growth in buildings

Epidemiological evidence suggests that the presence of mould growth in buildings can have a detrimental effect on the well-being of occupants. Based on an extensive literature review, growth limits for six generic mould categories have been formulated in terms of the minimum combination of temperature and relative humidity for which growth will occur on building materials. These limits were incorporated within the ESP-r system for building energy and environmental simulation in order to provide a design tool which can predict the likelihood and extent of mould infestation. The systems new predictive capability has been tested against monitored data and mycological samples taken from a mould infested house.

Assessing heat pumps as flexible load

In a future power system featuring significant renewable generation, the ability to manipulate domestic demand through the flexible operation of heat-led technologies such as heat pumps and micro-combined heat and power could be a critical factor in providing a secure and stable supply of electrical energy. Using a simulation-based approach, this study examined the linkage between the thermal characteristics of buildings and the scope for flexibility in the operating times of air source heat pumps. This was assessed against the resulting impact on the end-user’s comfort and convenience. A detached dwelling and flat were modelled in detail along with their heating system in order to determine the temporal shift achievable in the heat pump operating times for present-day and future dwellings. The simulation results indicated that the scope for shifting heat pump operating times in the existing building stock was limited, with time shifts of only 1–2 h achieved before there was a serious impact on the comfort of the occupant. However, if insulation levels were dramatically improved and substantial levels of thermal buffering were added into the heating system, sizable time shifts of up to 6 h were achievable without a significant impact on either space or hot water temperatures.

Photovoltaic-integrated building facades

Photovoltaic (PV) cells, when integrated within a building facade, offer the possibility of generating electric power and heat for local use or export. This paper reports on a project to investigate the practical operational efficiencies that might be delivered from such facades. The results from laboratory experiments and computer simulations are presented: the former were used to develop an empirical relationship between cell temperature and power output; the latter were undertaken to assess operational efficiencies under a range of climate conditions representative of the UK.

Developing and testing a generic micro-combined heat and power model for simulations of dwellings and highly distributed power systems

This paper elaborates an approach to the modelling of domestic micro-combined heat and power (μ-CHP) using a building simulation tool that can provide a detailed picture of the environmental performance of both the μ-CHP heating system and the dwelling it serves. The approach can also provide useful data for the modelling of highly distributed power systems (HDPS). At the commencement of the work described in this paper no μ-CHP device model that was compatible with a building simulation tool was available. The development of such a model is described along with its calibration and verification. The simulation tool with the device model was then applied to the analysis of a dwelling with a Stirling engine-based heating system. Different levels of thermal insulation and occupancy types were modelled. The energy and environmental performance of the μ-CHP device was quantified for each case; additionally, the potential for its participation in the control and operation of an HDPS was assessed. Analysis of the simulation results indicated that the parasitic losses associated with the μ-CHP system balance of plant reduced the overall heating system efficiency by up to 40 per cent. Performance deteriorated with increasing levels of insulation in the dwelling, resulting in reduced thermal efficiency and increased cycling, though overall fuel use was reduced. The analysis also indicated that the device was generally available to participate in HDPS control for greater than 90 per cent of the simulation time. The potential length of the participation time ranged from 1 to 800+min and depended upon the state of the μ-CHP system thermal buffer and prevailing heat loads. Probabilities for different participation times and modes were calculated.

Integrating power flow modelling with building simulation

The inclusion of photovoltaic facades and other local sources of both heat and power within building designs has given rise to the concept of embedded generation: where some or all of the heat and power demands are produced close to the point of use. This paper describes recent work to simulate the heat and power flows associated with both an embedded generation system and the building it serves. This is achieved through the development of an electrical power flow model and its integration within the ESP-r simulation program.

On the integration of renewable energy systems within the built environment

Future cities are likely to be characterized by a greater level of renewable energy systems deployment. Maximum impact will be achieved when such systems are used to offset local energy demands in contrast to the grid connection of large schemes. This paper elaborates a method whereby passive renewable technologies are deployed locally to reduce energy requirements while active renewable technologies are deployed to meet a significant portion of the residual demand. A modelling system for the identification of suitable schemes is then described and its application to a real case reported.

Development of a Computer Programme for the Prediction and Control of Mould Growth in Buildings Using the ESP-r Modelling System

Based on an analysis of the best published data, critical limits for the growth of six commonly occurring indoor moulds (defined in terms of relative humidity and temperature) have been formulated into a mould prediction computer programme. The fungi were selected as representative of moulds which differ in their relative humidity and temperature requirements to sustain surface growth, and because several were known mycotoxin producing species and of potential health significance. Each growth limit curve was generated from a series of data points on a temperature-relative humidity (RH) plot and fitted using the third-order polynomial equation RH = a3T3 + a2T2 + a1T + ao. The model was incorporated within the Environmental Systems Performance research programme for transient simulation of the energy and environmental performance of buildings, thereby enabling the system to predict the likely occurrence of mould development for fungi which exhibit similar tempera ture/RH requirements to the reference moulds. The model predicts the inter active parameters which give rise to local environmental conditions that encourage mould growth. The systems predictive capability was tested via laboratory experiments and by comparison with monitored data from a moul dy building.

A Review of ESP-r's Flexible Solution Approach and its Application to Prospective Technical Domain Developments

Abstract This paper reviews the cooperating solver approach to building simulation as encapsulated within the ESP-r system. The application of the approach to the core technical domains underpinning building simulation is discussed along with its extension to the additional, diverse domains needed to support broader and/or more detailed analysis. The implications for computational overhead through expanding the repertoire of ESP-r are also considered. The paper concludes with an appraisal of the ability of the cooperating solver approach to cater for anticipated future application demands.

Assessment of highly distributed power systems using an integrated simulation approach

In a highly distributed power system (HDPS), micro renewable and low carbon technologies would make a significant contribution to the electricity supply. Further, controllable devices such as micro combined heat and power (CHP) could be used to assist in maintaining stability in addition to simply providing heat and power to dwellings. To analyse the behaviour of such a system requires the modelling of both the electrical distribution system and the coupled microgeneration devices in a realistic context. In this paper a pragmatic approach to HDPS modelling is presented: microgeneration devices are simulated using a building simulation tool to generate time-varying power output profiles, which are then replicated and processed statistically so that they can be used as boundary conditions for a load flow simulation; this is used to explore security issues such as under and over voltage, branch thermal overloading, and reverse power flow. Simulations of a section of real network are presented, featuring different penetrations of micro-renewables and micro-CHP within the ranges that are believed to be realistically possible by 2050. This analysis indicates that well-designed suburban networks are likely to be able to accommodate such levels of domestic-scale generation without problems emerging such as overloads or degradation to the quality of supply.