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Decentralized mechanical ventilation systems had a sustainable growth in the past ten years in order to guarantee air exchange in highly airtight renovated residential buildings. Smart control strategies could provide a solution to the tradeoff between energy efficiency, hygrothermal comfort and indoor air quality. In this paper, a novel fuzzy demand controlled ventilation strategy is proposed, using state-of-the-art sensors often available in ventilation systems. The proposed controller is tested using a co-simulation approach and is compared to other typical mechanical ventilation control strategies. Results show that this approach provides around 25% energy savings in comparison to a constant airflow strategy, and around 12% against typical smart ventilation systems. The obtained differences regarding hygrothermal comfort and indoor air quality are negligible, and the proposed controller succeeds on keeping the indoor environment in the acceptable range. Finally, the developed fuzzy controller could potentially allow control systems to adapt to different occupant preferences, by tailoring the membership functions to each user.

Heat pumps are expected to play a central role in decarbonizing heat supply, but face challenges in existing buildings due to high temperature requirements of existing radiator systems. This paper links the performance analysis of heat pump systems with methods to reduce temperatures of the space heating circuit. Field data and system simulations of air and ground source heat pumps show a linear correlation between the seasonal performance factor SPF and the mean heat pump temperature over a wide temperature range. Every Kelvin of reduced heat pump temperature increases the SPF by 0.10-0.13 points. Applied methods to reduce heating temperatures are demonstrated at existing multi-family buildings. Thermal insulation reduces the building's heat load, allowing a reduction of heating temperatures with the existing radiators. A further temperature reduction is achieved by analyzing the required heating power per room and identifying critical, undersized radiators. In a stu died building, the selective exchange of only 7% of all radiators is sufficient to reduce heating temperatures from 75°C/60°C -55 °C/45 °C. This corresponds to a reduction of the electricity consumption by 40-42%. However, the potential of these methods is specific for each building and depends particularly on its renovation state and installed radiator capacity. Nonetheless, an energy- and cost-efficient operation of heat pumps retrofitted in existing radiator heating systems is viable, if following the proposed system design method linking heat pump performance and reduction of space heating temperatures.

Mechanical ventilation systems acquired relevance in the past decades as a solution to guarantee air exchange in residential energy retrofit. The individualization of the control strategies to the user preferences could enhance the acceptance of innovative technologies and meet the energy efficiency targets for buildings. In this publication, a novel occupant-centered self-learning control strategy for decentralized ventilation systems is introduced. The controller has a standard-based default control profile, which learns the occupants’ preferences using a classification algorithm. The proposed controller is first simulated and compared to other available mechanical ventilation control strategies. A stochastic model for the manual operation of ventilation systems based on artificial comfort profiles is implemented in the simulation model. Results show that the proposed controller improves the indoor environmental conditions (measured with the relative humidity and CO2 concentration) without disregarding energy efficiency. The self-learning controller can successfully adapt itself to these profiles. The proposed solution was implemented in a real apartment. Measurements were carried out for three months, where two occupants operated the ventilation devices. The installed ventilation concept succeeded in maintaining an acceptable indoor environment, while the distinctive user profiles were learned in each room. The bedrooms were shifted towards lower air exchange rates, while in the rest of the rooms higher air exchange rates were preferred. This implementation confirms the individualization potential of this controller. Finally, the novel self-learning strategy provides an adaptive solution for residential decentralized ventilation controllers, targeting the occupant preferences regarding comfort, health and energy efficiency.

Decentralized regenerative mechanical ventilation systems have acquired relevance in recent years for the retrofit of residential buildings. While manufacturers report heat recovery efficiencies over 90%, research has shown that the efficiencies often vary between 60% and 80%. In order to better understand this mismatch, a test facility is designed and constructed for the experimental characterization and validation of regenerative heat exchanger simulation models. A ceramic honeycomb heat exchanger, typical for decentralized regenerative ventilation devices, is measured in this test facility. The experimental data are used to validate two modeling approaches: a one-dimensional model in Modelica and a computational fluid dynamics (CFD) model built in COMSOL Multiphysics®. The results show an overall acceptable thermal performance of both models, the 1D model having a much lower simulation time and, thus, being suitable for integration in building performance simulations. A test case is designed, where the importance of an appropriate thermal and hydraulic modeling of decentralized ventilation systems is investigated. Therefore, the device is integrated into a multizone building simulation case. The results show that including component-based heat recovery and fan modeling leads to 30% higher heat losses due to ventilation and 10% more fan energy consumption than when assuming constant air exchange rates with ideal heat recovery. These findings contribute to a better understanding of the behavior of a growing technology such as decentralized ventilation and confirm the need for further research on these systems.

Mechanical ventilation systems have acquired relevance in the past years in order to guarantee the hygrothermal comfort and indoor air quality (IAQ) in highly retrofitted residential buildings. The optimization of control strategies could provide a solution to this existing trade-off between energy efficiency, hygrothermal comfort and IAQ. In this publication, we propose a co-simulation approach (using EnergyPlus and Modelica) and a mathematical approximation of the discomfort of the occupant (namely, quadratic for relative humidity and exponential for CO2), and apply them to a demand controlled ventilation (DCV) scheme. Results show that this approach provides around 10% energy savings, while improving the thermal comfort, without compromising the humidity comfort or the IAQ. Finally, the developed functions could allow the control schemes to adapt to different occupant preferences, showing potential for future work.

In desiccant cooling systems, the desiccant material reduces the humidity in the process air by removing its moisture. The reduction of the temperature is achieved by heat exchangers, evaporative coolers or conventional cooling coils. These systems draw interest because they allow the use of low quality energy which can support sustainability through energy efficiency. The desiccant coated heat exchanger is a structure that allows the simultaneous removal of adsorption heat and dehumidification in a single element. This structure is a system element that can contribute extensively to the indoor air humidity control for new generation dehumidification in air conditioning systems. Besides, the dehumidification efficiency of this system has been found to be better than the conventional desiccant wheel. In this study, a desiccant coated small-scale heat exchanger is evaluated by simulation. Silica gel and aluminium fumarate are analysed as desiccant material coatings in this work. Simulations are performed according to two model configurations which are adiabatic and water-cooled cases respectively. Heat and mass transfer characteristics are determined for the two cases as well as the dehumidification and regeneration capacities. The performances of the two materials are compared based on the results of the simulations. Results of the study show the advantages of the water-cooled dehumidification over the adiabatic dehumidification and silica gel composite coating over aluminium fumarate coating.

In this work a novel solar driven dehumidification and cooling system is presented. The core components of this combined system are a sorptive dehumidification device based on high performance sorptive coatings and a novel evacuated tube solar air collector providing the driving heat. The essential part of the system is the coated heat exchanger. The chosen adsorbent is attached to the heat exchanger surface by a newly developed coating technique. Besides a brief description of the novel components and the experimental setup, the development of the aluminum heat exchanger, the coating procedure and scale up for geometries comparable to the heat exchanger in the dehumidification setup, as well as a first characterization of a small-sized coated heat exchanger regarding water uptake and dehumidification performance are presented. For estimating an overall system performance, a 2-dimensional thermodynamic model was applied, using the parameters in focus for the development of heat exchanger, coating and demonstration system.

The performance of a once-through solar desiccant cooling system, for air-conditioning a commercial office space, was modelled using the TRNSYS computer simulation software package. The study particularly focused on the potential for designing and operating a desiccant cooling system, without any thermal backup provided to mitigate for intermittent solar availability in three Australian cities. Increasing (i) indirect evaporative cooler effectiveness, (ii) air flow to the office space, and (iii) solar collector area were all shown to reduce the frequency of high temperature events inside the building occupied space. In the warm temperate climate of Melbourne (and to a lesser extent Sydney), high ventilation rates enabled comfort conditions to be maintained at or near acceptable levels in the occupied space, without the use of a backup thermal source. The synergy between evaporative cooling and solar desiccant cooling, observed in the warm temperate climates, was not evident in the tropical Darwin climate, suggesting that the selected ventilation desiccant cooling cycle is not appropriate for tropical climates.

Under tropical climate conditions, conventional air-conditioning systems consume a considerable amount of electricity in order to get rid of the high latent load (humidity) of the ambient air. This is due to the applied simultaneous dehumidification and cooling processes. Therefore, an idea of a separate handling of the latent and the sensible loads is investigated by applying series connected heat powered dehumidification and electricity powered cooling systems. A two-stage dehumidification system including a membrane-based heat and mass exchanger and an Evaporatively COoled Sorptive dehumidification system (ECOS system) is proposed to dehumidify the ambient air; the sensible load (cooling of dehumidified air) is handled by an efficient conventional cooling process operating at relatively high evaporation temperatures (14 െ 20 Ԩ). The aim of this study is to evaluate different conceptual system configurations and to find optimized systems for tropical climate conditions (air humidity and temperature are in the order of 20 g୴/kgୟ୧୰ and 32 Ԩ, respectively) by means of simulation calculations. The dehumidification capacity, the total specific removed enthalpy and the thermal coefficient of performance (COP) of the system are used as criteria for an assessment of the proposed concepts. The dehumidification system is mathematically modelled in MATLAB and linked with TRNSYS-17.1. Experimental data are used to validate the components models. Design and performance data of simulated air-dehumidification systems that are based on the concepts are presented. Results of the performance assessment show that using additional ambient air flow for the evaporative cooling process in the ECOS system can improve the dehumidification performance of the system and can reduce the cooling load of the cooling system significantly.

In the scope of the IEA Task 38 (Solar Air-Conditioning and Refrigeration) a comparative study of different simulation tools for solar cooling system pre-design was conducted. It aimed at identifying a range of uncertainties in simulation results which may be obtained by validated models from market available tools – and simulations performed by different experienced users. Tools applied in the simulation comparison comprise the fast pre-design tool EasyCool and the end-design tools TRNSYS, INSEL, SPARK and the TRNSYS-based TRANSOL. A model of a virtual office building in Palermo climate was used for the generation of a load file that was applied in all simulations. Further, a common system layout, component sizing and specifications, and a control strategy for the more advanced simulation tools were defined. The simulated solar cooling system is a chilled water system applying a 35kW absorption chiller by Yazaki (WFC 10). Results show that a margin of around 6 % deviation of the thermal performance parameters from their mean seems the best possible in the crosscomparison of the three closest baseline simulations – however the upper margin of around 20 % observed for all simulations may be more close to the real margin of variation. This reflects the high uncertainty in results of pre-design simulations and underlines the need of a good technical understanding by the user of simulation tools.

An enhanced evaporatively cooled open sorption cycle which can be driven by solar thermal heat is presented as an environmentally benign alternative to conventional air conditioning cycles. Experimental data of the core component- the desiccant coated heat exchanger - cooled by water evaporation is given. This evaporation of water in the heat exchanger leads to an increase in adsorbed water mass by 46% and an enhancement of the cooling capacity by factor 4.1 when compared to a solely air cooled process. The newly designed heat exchanger is then compared by a simulation analysis to data of an air cooled open sorption process published in earlier research. It is shown that the desiccant mass is used more efficiently in the more recent prototype. Further considering the evaporation in the heat exchanger underlines the more advanced performance that can be achieved with the new concept and prototype design.