A.R. Day

Improved methods for evaluating base temperature for use in building energy performance lines

The use of degree-days in building energy monitoring and targeting has often given rise to misinterpretation of results, which has in turn undermined con” dence in such techniques. Anecdotal reporting has, by turns, suggested the use of degree-days either works very well, or does not work at all. This ambiguous position is not helpful to energy managers who need robust tools and clear guidance on their use. This paper presents evidence to show how energy/degree-day correlations i.e., building performance lines, can be properly identi” ed, while taking account of the correct (and practical) energy balance of the building. In doing so it shows how the correct building base temperature can be identi” ed from reduced data sets, while demonstrating that such a practice is desirable. Performance lines constructed in this way, where appropriate, give rise to greater accuracy and reliability of results, while forming the basis for improved diagnostics.

Degree-days: Comparison of calculation methods

The uncertainties associated with calculating degrees-days from traditional formulae and other approximate methods were examined. Comparisons were based on calculations using hourly temperature records. A definition of uncertainty for monthly degree-days and some typical errors in annual values are presented. The ranges of uncertainty are small for published degree-days, but could be significant for a small percentage of occasions. If the methods are used for base temperatures lower than the current standard then the uncertainties increase. Also shown are the effects of these errors on the regression analysis often used in building energy monitoring.

Identification of the uncertainties in degree-day-based energy estimates

A formal method has been developed for quantifying the uncertainties in degree-day-based energy estimates in buildings. Different interpretations of base temperature as a means of describing the building energy balance were investigated, with the result of an improved degree-day model that does not require the use of correction factors. This model has been tested using high-quality data from building simulations, and the outputs have been subjected to statistical uncertainty analysis. The results show that degree-day uncertainties diminish with longer time frames. The uncertainties also impact on regression techniques used in monitoring and targeting of building performance, and these uncertainties may exceed typical targets for energy efficiency improvements.

A new degree-day model for estimating energy demand in buildings

A new degree-day model for estimating energy consumption in buildings has been developed that removes the need for correction factors and allows the user more control over the inputs. The proposed method incorporates a model for determining mean internal temperatures of buildings. The model has been tested for accuracy and sensitivity to input variations. It has also been possible to quantify the uncertainty in the model, which allows the user to determine the usefulness of a result to a particular application.

Review Paper: Solar-assisted heat pump research and development

The main findings of a detailed literature search on solar-assisted heat pumps (SAHP) are presented. The various system types are described and the relevant performance criteria by which systems can be assessed are defined. Where possible different system performances are compared and specific conclusions drawn. While most work in the literature has focused on series systems there is no evidence that these can compete with parallel systems, either in non-purchased energy delivery or, more significantly, in cost. Efforts to improve control strategies for series systems are unable to achieve better performance. Technology is sufficiently advanced to exploit the best of these systems if the economic climate becomes favourable. Some suggestions are advanced as to where future research effort can make a useful contribution.

Heating systems : plant and control

Introduction. Part A. Heat Generation. Boilers and Burners. Types of Boiler and Their Needs. Alternative Means of Heat Generation. Flueing. Part B. Systems and Control. Room Heat Emitters. Heating Circuits. Hot Water Services. Sizing Central Boiler Plant. Matching Output to Demand. Energy Consumption of Heating Systems. Index.

An improved use of cooling degree-days for analysing chiller energy consumption in buildings

Cooling degree-days have not commonly been used in building energy analysis due largely to a lack of understanding of how they should be defined. The extra complexity of cooling systems, including the existence of latent loads, means that simplified energy analysis techniques have been deemed too crude to be meaningful. This paper presents a detailed analysis of measured cooling energy data from a large air-conditioned site in Perth, Western Australia, which builds on previous theoretical work to develop a robust definition of cooling degree-day base temperature. The results show that not only do cooling degree-days give results suggested by the theory, but that the use of cooling energy performance lines can be used for more sophisticated energy analysis. Practical application: The energy performance of buildings is becoming increasingly important to define. Energy monitoring and analysis techniques using degree days have usually been confined to heating systems. This paper sets out how cooling degree-days can be used to assess the operational performance of a refrigeration plant, using real data to demonstrate the potential of the method.

The development of a dynamic model to simulate boiler controls

There has long been the need to improve the guidance for the control of multiple boiler installations. The literature shows that there is no generic guidance on how boiler plant — as opposed to the heating system — should be best controlled, despite their widespread use and many years of experience with these systems. This paper presents a simulation model that enables detailed investigation of multiple boiler operation under different control regimes. Five different conditions are presented in this paper. The first three show that individual boiler firing patterns behave as would be expected under ideal conditions. The loads for these simulations were chosen specifically to test this, and to provide some verification of the model. Two further tests were conducted to show firing patterns that may occur under typical control regimes. The resulting firing patterns showed unnecessary cycling of both boilers, a cause of premature failure and reduced efficiency. Practical applications: This paper presents the first stages of an investigation into the setting up and operation of multiple boiler control systems. A review of academic and industrial literature shows there to be very little guidance on how such control systems should be configured, and how different configurations will affect the system performance. This work is developing validated boiler models that can be used to investigate how sensor positioning and switching differentials can affect firing rates and interactions between boiler modules. In this way control settings can be more appropriately specified and commissioned. Excessive boiler cycling can lead to early failure of boilers and increased energy use. The results presented in this paper show that interaction between boilers due to poor sequence control settings will lead to additional and unnecessary cycling of boilers under part load conditions. The guidance arising from this work will help to extend boiler life and reduce fuel waste.

Energy performance of building designs: Evaluation using the CIBSE Building Energy Code Part 2(a) on a spreadsheet

The CIBSE Building Energy Code was first published in 1981 but has not been widely used among architects, civil engineers or building services engineers. A full calculation will require about 60 separate data inputs with some 80 calculation steps; perceived complexity and opacity perhaps inevitably lead to reduction in confidence. It is however, an ideal candidate to transferring to spreadsheet format. This paper presents work developed from an educational programme which allows simplified use of an otherwise complex and time-consuming procedure. It also allows the building thermal demand targets to be calculated from first principles.

Reducing Carbon Emissions in London: From Theory to Practice

Publisher Summary This chapter highlights the findings of two studies, one conducted for the London Energy Partnership and one for the Greater London Authority, both of which were completed around March 2006. Although independently commissioned, and designed to serve different purposes, they both deal with the practicalities of reducing carbon emissions in London; one through a technical analysis, and the other through the use of policy instruments. The first identifies how best it is to achieve future carbon savings with different mixes of energy technologies, while the other analyses the impact of regional planning policy on renewable energy implementation. Together they provide a picture of what needs to be done to achieve carbon emissions reductions targets in a large city using distributed and embedded energy systems, both technically and through policy frameworks. The report “London carbon scenarios to 2026” investigated the possible mix of energy technologies that could be deployed at a local and regional level to meet target carbon emissions reductions. The paradigm of local and regional implementation must necessarily assume some local or regional coordination, with some degree of power to influence the energy system. It is becoming increasingly apparent that there needs to be a sufficient political will and leadership to help force the pace of change necessary to meet even the minimum targets. London has set itself clear policy objectives to reduce its carbon footprint, and move towards a new paradigm in energy delivery. The aim is to increase embedded energy generation substantially, while improving the energy efficiency of the building stock. It is clear that success in meeting percentage carbon reduction targets is heavily dependent on planners and developers understanding the requirements and setting up clear mechanisms to negotiate the final design.