The development and calibration of a generic dynamic absorption chiller model

Although absorption cooling has been available for many years, the technology has typically been viewed as a poorly performing alternative to vapour compression refrigeration. Rising energy prices and the requirement to improve energy efficiency is however driving renewed interest in the technology, particularly within the context of combined cooling, heat and power systems (CCHP) for buildings. In order to understand the performance of absorption cooling, numerous models are available in the literature. However, the complexities involved in the thermodynamics of absorption chillers have so far restricted researchers to creating steady state or dynamic models reliant on data measurements of the internal chiller state, which require difficult-to-obtain, intrusive measurements. The pragmatic, yet fully-dynamic model described in this paper is designed to be easily calibrated using data obtained from the measurements of inflows and outflows to a chiller, without resorting to intrusive measurements. The model comprises a series of linked control volumes featuring both performance maps and lumped mass volumes, which reflect the underlying physical structure of the device. The model was developed for the ESP-r building simulation tool. This paper describes the modelling approach, theory and limitations, along with its calibration and the application of the model to a specific example

Communal residential laundry washing and drying : can it provide demand-side electrical load flexibility?

Changes in lifestyle have led to increased use and ownership rates of domestic appliances resulting in increasing electrical consumption in the residential sector. An important element of this consumption is due to domestic washing and drying of laundry. Given current and predicted ownership rates, the market for drying facilities is still not fully saturated and electrical demand for these functions will therefore increase. This paper looks at energy loads for laundering in high density housing such as blocks of flats and explores the benefits of communal facilities. Benefits of such facilities include reduced high humidity levels and the mitigation of decreased indoor air quality associated with indoor drying of laundry in individual dwellings. However from the perspective of integrating microgeneration into buildings, communal facilities may facilitate increased flexibility in the electrical demand profile, hence better complementing low carbon and localised energy supplies. In order to investigate the possible effects on the electric demand load profile, this paper presents the scenario of a hypothetical housing block and analyses the effect of moving from washing and drying in individual households to communal facilities. The study includes the effects of appliance energy-efficiency improvements and increased ownership rates. Results obtained show that communal laundering is successful in terms of time-shifting and hence lowering of peak electrical demand but is ineffective in reducing consumption

A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta

The present case study sets out to investigate the potential and limitations of passive building design in a typical Mediterranean climate. The Maltese Islands were taken as the case study location. Assuming a fully detached, cuboid-shaped, generic multi-storey office building, one representative storey was modelled by means of the building energy simulation code WUFI®Plus. Thermal comfort was analysed based on the adaptive acceptable operative room temperature concept of EN 15251 for buildings without mechanical cooling systems. Assuming neither artificial heating nor cooling, the free-running operative room temperature was evaluated. By means of a parametric study, the robustness of the concept was analysed and the impact of orientation, window to wall area ratio, glazing, shading, thermal insulation, nighttime ventilation and thermal mass on the achievable level of thermal comfort is shown and discussed. It is concluded that in a well-designed building and by means of decent insulation (present case: Uwall = 0.54 W/(m2 · K)), double glazing, variable external shading devices and passive cooling by nighttime ventilation, a high level of thermal comfort is achievable in this climate using only very minor amounts of energy for artificial heating and cooling or possibly even none at all.peer-reviewe

Building sustainably : a pilot study on the project manager’s contribution in delivering sustainable construction projects - a Maltese and international perspective

Despite ample technological advancements, the building industry is still seen as an unsustainable activity. To counteract this, building development is now being requested to be more sustainable. Due to the increasing complexity of sustainable projects’ criteria, the project manager’s role, tasked with the overall management of a building’s different development phases, is changing, becoming increasingly crucial for the attainment of pre-established sustainability goals. Based on this premise, the research presented in this paper is a pilot study set to preliminarily establish and identify a set of project management processes and supporting practices from existing literature, and gauge their significance and possible added value provided. This was done via a purposely designed questionnaire distributed locally, in Malta, and globally amongst established project managers. Notwithstanding the preliminary nature of the study some interesting results were obtained. Among the main outcomes of the study, it is observed how all respondents are very aware about sustainability issues and that their decision-making role places them in an optimum position to bring forward a sustainability agenda for a particular project. In terms of intervention, pre-construction (43%) and construction (28%) were considered to be the main stages were a project manager usually gives the highest input. However, various challenges were also highlighted by the respondents, including clients’ refusal to commit increased capital (34%), the requirement for further training (33%), and the lack of incentives aimed towards increasing the sustainability of projects (22%).peer-reviewe

A feasibility study on CHP systems for hotels in the Maltese Islands : a comparative analysis based on hotels’ star rating

In Europe, the energy consumed for heating and cooling purposes by the hospitality sector is significant. In island economies such as that of the Mediterranean Island of Malta, where Tourism is considered essential to the local economy, energy consumption is perhaps even more significant, and energy‐efficient systems, or the use of renewable energy, are often listed as possible solutions to counter this. Based on this premise, the research contained in this paper presents an investigation on the technical and financial feasibility of using Combined Heat and Power (CHP) and Combined Cooling, Heating, and Power (CCHP) systems for the hospitality sector in Malta. Using a supply– demand design methodology, the research made use of the software package RETScreen to model the electrical and thermal demand of a number of hotels ranging from 3‐ to 5‐star hotels. Based on these modelled hotels, different scenarios were simulated to analyze the technical and financial implications of installing a CHP in these modelled hotels. A number of parameters, including thermal size matching, presence of financial grants, electricity tariffs, feed‐in tariffs, and fuel prices, were tested out for a total of 144 scenarios. Results showed that the parameters having the highest impact were those of a financial nature. Specifically, the study showed that the 4‐star hotels considered were the hotels which would benefit the most from having such systems installed.peer-reviewe

Energetic, environmental and economic modeling of a solar-assisted residential micro-trigeneration system in a Mediterranean climate

Reducing energy consumption in buildings has become a priority for most countries. However, designing energy-efficient buildings is not a straightforward task - the increasing demand for high comfort standards, provided by conventional ‘energy-hungry’ cooling and heating devices conflicts with the need for demand reduction. Trigeneration, the simultaneous production of electricity, cooling and heating is often viewed as a means of improving energy-efficiency in large and medium sized buildings whilst still delivering thermal comfort. For hot climates, the benefit of utilising the waste heat emitted from an engine unit to power a thermally driven cooling device provides scope to utilise an otherwise wasted energy stream. However, in smaller sized residential buildings, the relatively low and intermittent energy demand coupled with high capital costs, has stifled the uptake of the technology - although the potential for substantial energy savings exists. Moreover, it is very common for home owners in hot climates to opt for other energy-saving devices such as solar water heaters (SWH), which would tend to reduce further the possible demand for space and water heating, possibly making the simultaneous use of both micro-trigeneration and SWH unfeasible. This paper compares the performance of a residential micro-trigeneration system to a hybrid micro-trigeneration/SWH system. The performance of both systems was simulated using a whole building simulation tool run at a high time resolution. The results obtained were then used to quanti fy the energetic and environmental performance of both systems; and also to assess their financial viability against the effect of varying fuel prices, electricity tariffs and a varying Feed-in Tariff (FIT). Results show that whereas the solar aided micro-trigeneration system obtains an overall higher (though marginal) energetic and environmental performance, the financial performance for the same fiscal parameters (fuel prices and electricity tariffs) deteriorates. Moreover FIT, plays an important role in the financial feasibility of the system.peer-reviewe

A comparative study of the energetic performance of climate adaptive facades compared to static facade design in a Mediterranean climate

Energy-efficient design of building façades has so far predominantly been confined to static rigid forms. Recently however, attempts have been made to design environmentally responsive façades, hereby called Climate Adaptive Façades. These have the potential to better address the occupant's requirements, while also reducing energy demand. The present paper focuses on adaptable glazed façades, in a Mediterranean climate. It investigates the simulated energy performance of three types of climate-responsive façades that could be retrofitted to an existing glazed façade, in the process comparing the results to using comparable static façades solutions. Modelling dynamic façades is not an easy task and currently no single building performance simulation package appears to be capable of completely modelling the behaviour of these façades. For this reason a number of simulation packages had to be used to determine the energy demand required to achieve comfortable indoor thermal and lighting conditions. Through the results obtained, it was possible to compare energy demand of a dual-façade design approach, dynamic vs. static, thus identifying general trends. The results also highlight the fact that in order to improve over the predicted performance further studies using specialised tools capable of modelling such novel technologies are required.peer-reviewe

Humidity distribution in high-occupancy indoor micro-climates

The general consensus among academics is that the spatio-temporal humidity distribution is more or less uniform in an indoor space. This has, for the large part, not yet been proven by an academic study; subsequently, this paper aims to demonstrate that this is not always true. The paper makes use of a validated transient CFD model, which uses the Low Reynolds Number k-ϵ turbulence model. The model simulates people in a room at a constant skin temperature and emitting a constant source of humidity using source terms in the species equation. The model is eventually used to predict the implications of having a high source of humidity, in the form of occupancy, on the micro-climate’s spatio-temporal humidity distribution. The results for the high-occupancy case show that different locations experience various amounts of humid air, with a 31% difference between the lowest and highest locations. The amount of water vapor in each person’s proximity is deemed to be highly dependent on the flow of the inlet jet, with the people farthest from the jet having an overall less mass of water vapor in their proximity over the two-hour experimental period. This paper has concluded that there are, in fact, cases where the humidity non-uniformity inside an interior environment becomes substantial in situations of high occupancy. The results of this paper may be useful to improve the design of HVAC systems.peer-reviewe

The effect of shank-space on the thermal performance of shallow vertical u-tube ground heat exchangers

One parameter that may affect the performance of a ground source heat pump is the shank-space, the center-to-center distance between the two branches of a vertical U-tube used in a ground heat exchanger. A 3D steady-state computational fluid dynamics (CFD) model of a U-tube ground heat exchanger was used to investigate the influence of varying shank-space on the thermal performance of two isolated vertical shallow U-tubes, one 20 m deep and the other 40 m deep, given that most existing research focuses on systems making use of deeper boreholes. The models adopt an innovative approach, whereby the U-junction at the bottom of the U-tube is eliminated, thus facilitating the computational process. The results obtained show that, although the temperature drop across the U-tube varies for different shank-spaces and is lowest and highest for the closest and the widest shank-spaces, respectively, this temperature drop is not linear with increases in shank-space, and the thermal performance improvement drastically diminishes with increasing shank-space. This indicates that, for shallow U-tubes, the temperature drop is more dependent on the length of the pipework.peer-reviewe

A preliminary computational study of flat roof convective thermal resistance in the presence of photovoltaic panels

The effect of roof mounted photovoltaics on the heat transfer performance of roofs has primarily been investigated in the context of the resulting shading effect. The convective heat transfer coefficient will change as a result of the blockage caused by the photovoltaic panels. In this work, a quantification is given of the differences between heat transfer coefficients on a bare roof and a roof with photovoltaic panels having a specified configuration. A computational fluid dynamics approach is used. The study is only preliminary and hence a standard k-e turbulence model is used. The presence of photovoltaics is found to increase the convective heat transfer coefficients by around 26% for a north wind. The influence on the U-Value depends on the type of roof construction but for summer conditions an increase in U-value is observed which has positive cooling effects.Bajada New Energy, Bitmac ltd., Econetique, Energy Investment, JMV Vibro Blocks, Solar Engineering.peer-reviewe