A multi-level modelling and evaluation of thermal performance of phase change materials in buildings

Integration of phase-change materials (PCMs) in building envelopes is a way to enhance heat storage capacity of buildings and thereby to rationalize the use of energy for heating and cooling of buildings. This work presents a numerical model of a building envelope with PCMs, verifications of the model according to a normative benchmark and measurements and a tentative case study that exemplifies the effects of such a building envelope on the thermal performance of a whole building. Simulations have been carried out using a modular environment of the International Building Physics Toolbox in Simulink®. As for the effects of PCMs in buildings, it is concluded that they are rather case sensitive; in the tentative case study, the annual savings of total energy for heating and cooling vary between 5% and 21%, depending mainly on the thermal comfort and the placement of PCM in the building envelope

Optimization of Night Cooling of Commercial Premises Using Genetic Algorithms and Neural Networks

This paper investigates if it is possible to optimize night cooling control setpoints and ventilation schedule regarding energy consumption and indoor climate. A retail store, located in Gothenburg, was used as a case study. The investigation was done by numerical modelling and simulations. It started with development and calibration of a building energy model for the store with data collected from the field. Afterwards, the calibrated model was used in the optimization of the night cooling. Initially, a genetic algorithm was applied to find the global minimum of the problem and further refined with a local search algorithm. The optimization speed was increased by neural networks, as they can approximate results faster than the building energy model. The study suggests that the cooling and fan energy consumption can be reduced by 16% in the studied facility, compared to the currently used trial-and-error schemes. The project concludes that the use of logged control data in combination with genetic algorithms and neural networks are an efficient way for both calibration and optimization of building energy models. The industry moves towards an increase of available logged control data. As such, it is important to be able to properly utilize the data, for improving the accuracy of building energy simulations and improving the results

Early-stage concentrations of formaldehydes and TVOCs in a new low-energy building

This paper deals with temporary discomfort caused by characteristic odours from new objects and materials in office buildings. Earlier investigations have shown that increased ventilation rates in residential buildings decrease the indoor concentrations of non-occupant-related indoor air pollutants such as aldehydes and total volatile organic compounds (TVOCs). To study how this basic principle for the control of indoor air pollutants complies with a demand-controlled ventilation, which is an important energy efficiency measure in modern office buildings, the authors have designed and conducted a serial of field tests. Concentrations of aldehydes and TVOCs have been measured in two newly built and identical meeting rooms under different ventilation strategies. By overruling the existing demand control ventilation and increasing gradually but differently the air change rates in the rooms over a course of five weeks, the concentration of formaldehyde and TVOCs decreased for about 75 % from the initial values of ca. 45 μg/m3 and ca. 400 μg/m3 respectively. Impact of door openings on instantaneous indoor air quality has been studied in parallel by combining CO2 measurements and numerical simulations. Good agreement was found between the simulated and measured CO2 concentrations and thereby the door opening model was verified

Co-Heating method for thermal performance evaluation of closed refrigerated display cabinets

In this study, an application of the adapted Co-Heating methodology for thermal performance evaluation of closed refrigerated display cabinets (RDCs) has been presented. A novel test series comprising three experiments has been developed and demonstrated on a commercial RDC with four doors to evaluate the envelope heat transfer coefficient, thermal inertia, infiltration at idle state and dynamic infiltration caused by door operations. The latter two experiments were conducted in parallel with the condensate collection method for validation of the results for infiltration. It was concluded with good (<10%) conformance between the methods that the infiltration at idle state for the tested RDC is approximately 0.022kg/s and that one 15s door opening causes approximately 0.94kg of ambient indoor air to infiltrate. Additionally, the time, equipment and associated costs for running the tests were compared, and it was concluded that the adapted Co-Heating methodology could substitute the condensate collection method for the evaluation of infiltration while providing additional results on the thermal performance

Techno-economic assessment of thermal energy storage technologies for demand-side management in low-temperature individual heating systems

The combined use of\ua0thermal energy storage\ua0(TES) technologies and\ua0heat pumps\ua0in building energy systems has been approved to achieve demand-side management. Although there is an increasing number of case studies about the TES applications, crosswise techno-economic evaluations of different technologies are rare, especially for applications in individual heating systems where the storage temperature range is less than 20\ua0K. Hence, in this study, three TES options; water tank (WT),\ua0phase change material\ua0tank, and\ua0building thermal\ua0mass (BTM) are simulated and compared. A\ua0systematic analysis\ua0approach was proposed to assure impartial comparisons of the energy performance and the life-cycle costs (LCC). Special focus was paid on practical issues such as restricted charging power for different TES technologies. It was found that the majority of LCC savings arises from the peak load reduction. The study also shows that BTM is the most cost-effective TES technology while the WT is the least attractive option, due to larger heat loss and lower storage density. Moreover, less discharged energy and cost savings were found in well-insulated buildings due to the restricted discharging power. Still, there could be more incentives for household TES technologies if additional prices or policies are implemented

Modelling VOC levels in a new office building using passive sampling, humidity, temperature, and ventilation measurements

New buildings often have high initial concentrations of VOCs that, although not necessarily harmful, may be disturbing and cause discomfort among occupants. In new buildings, running the ventilation system continuously and at full rate during the first year is common practice to reduce VOC levels. However, the drawback of such an arbitrary strategy is the risk of over-ventilating with unnecessary heat losses as a consequence. In this article, a new approach, a VOC-passport, is developed where early measurements of VOCs together with a calculation model are used to find an optimized ventilation strategy. The proposed calculation model is tested on two newly built office rooms where VOCs were measured using passive samplers, together with temperature, humidity and ventilation rates, and it shows good agreement with measurements. An example of how a daily ventilation schedule may look like if optimized with the prosed model is presented. The example illustrates that in buildings where VOC levels are allowed to increase periodically, VOC levels can be kept at acceptable levels during occupancy hours if the effective storage capacity is known. The proposed method has a potential to improve the indoor air quality in new buildings without compromising energy efficiency

Retrofitting of a listed brick and wood building using vacuum insulation panels on the exterior of the facade: Measurements and simulations

Many old listed buildings have an unsatisfactory thermal performance compared to the standards of today. The listing often limits the position and necessary thickness of an added insulation layer in the building envelope. Vacuum insulation panels (VIP) present unprecedented possibilities to reduce the required thickness of the insulation layer. The aim of this study is to explore the performance of VIP in the retrofitting of listed buildings. The goal is to improve the thermal transmittance and moisture performance of the wall and the thermal comfort for the occupants. Hygrothermal sensors were installed in the wall of a listed building insulated with VIP on the exterior. Sensors were also installed in a neighboring (non-retrofitted) wall as reference. Through a comparative analysis of the measured data it was concluded that the hygrothermal performance of the retrofitted wall was substantially better than of the reference wall. The measurement results were also compared to hygrothermal simulations to quantify the improvements in the thermal transmittance and moisture performance. A deviation was found between the measured and simulated relative humidity in the wall which was explained by vertical air leakage paths in the wall

Roadmaps for heating and cooling system transitions seen through uncertainty and sensitivity analysis

Future district heating systems should enable efficient and economic energy supply, which can be achieved by lowering the system temperatures and boosting it at demand-side. Current solutions include the ultra-low-temperature district heating (ULTDH) and fifth generation district heating and cooling (5GDHC) systems. The transition towards these systems is subject to multiple future uncertainties such as the energy price, investment cost, and demand changes, which were missing in previous works. To investigate the effects of these uncertainties on conclusions brought by established design roadmaps for future DHCs, a five-step framework, which combines the energy system optimization with stochastic simulations, uncertainty analysis and sensitivity assessment, is developed in this study. The framework is applied on a hypothetical 0.25 km2 square district with varying uncertain parameters. Based on stochastic cases, the index named cost-saving probability (CSP) is utilized to reflect the potential of being economic attractive when comparing the energy systems. For the transition towards the ULTDHC, 5GDHC, and individual systems, the most sensitive factors for the CSP are the area demand density, overlapping heating and cooling demand, and linear demand density, respectively. The investment in thermal energy storage (TES) becomes important only when the integration of a larger share of renewable energy is targeted. A roadmap summarizing the promoting and hindering factors for the system transition is provided, pointing out the future focus area for DHC design. The results from the sensitivity analysis also revealed the limited role of TES in integrating variable renewable energy in high-efficiency DHC systems