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Up to now biorefinery concepts can hardly compete with the conventional production of fossil-based chemicals. On one hand, conventional chemical production has been optimised over many decades in terms of energy, yield and costs. Biorefineries, on the other hand, do not have the benefit of long-term experience and therefore have a huge potential for optimisation. This study deals with the economic evaluation of a newly developed biorefinery concept based on superheated steam (SHS) torrefaction of biomass residues with recovery of valuable platform chemicals. Two variants of the biorefinery were economically investigated. One variant supplies various platform chemicals and torrefied biomass. The second variant supplies thermal energy for external consumers in addition to platform chemicals. The results show that both variants can be operated profitably if the focus of the platform chemicals produced is on high quality and thus on the higher-priced segment. The economic analysis gives clear indications of the most important financial influencing parameters. The economic impact of integration into existing industrial structures is positive. With the analysis, a viable business model can be developed. Based on the results of the present study, an open-innovation platform is recommended for the further development and commercialisation of the novel biorefinery.

Within the last decade, research on torrefaction has gained increasing attention due to its ability to improve the physical properties and chemical composition of biomass residues for further energetic utilisation. While most of the research works focused on improving the energy density of the solid fraction to offer an ecological alternative to coal for energy applications, little attention was paid to the valorisation of the condensable gases as platform chemicals and its ecological relevance when compared to conventional production processes. Therefore, the present study focuses on the ecological evaluation of an innovative biorefinery concept that includes superheated steam drying and the torrefaction of biomass residues at ambient pressure, the recovery of volatiles and the valorisation/separation of several valuable platform chemicals. For a reference case and an alternative system design scenario, the ecological footprint was assessed, considering the use of different biomass residues. The results show that the newly developed process can compete with established bio-based and conventional production processes for furfural, 5-HMF and acetic acid in terms of the assessed environmental performance indicators. The requirements for further research on the synthesis of other promising platform chemicals and the necessary economic evaluation of the process were elaborated.

Energy efficient cooling systems are urgently required in order to face the increasing cooling demand of the building and industry sectors and comply with the ambitious EU target of greenhouse gas emission reductions. The present work aims to show that simple heat rejection control strategies can lead to significant energy savings. Different approaches of sequencing the operation of several cooling towers and a method to adapt the cooling water temperature set-point to the actual ambient conditions are proposed. These strategies are first investigated theoretically for an existing chilled-water plant of 13.7 MW installed cooling capacity. Up to 20% energy savings are theoretically possible depending on the used control strategy and the weather conditions. A variable cooling water set-point as a function of the wet bulb temperature allows for the most significant savings. After implementation of this measure in the existing cooling plant, 2 years monitoring results show that the overall system efficiency of the chilled water plant could be increased by 15% compared to the initial status confirming the results of the theoretical study.

Poultry farms with floor-standing poultry generate large amounts of poultry litter waste. The direct application of this waste as an organic fertilizer does not ensure sustainable and cost-efficient utilization of all waste fractions, and can also be linked to environmental hazards. Therefore, the development of new technologies is required for processing poultry litter into a safe product with higher added value. In this work, the characteristics of activated carbon derived from hydrochar, along with the liquid products obtained from hydrothermal carbonization (HTC) and the wet torrefaction (WT) of poultry litter, were investigated. Poultry litter (PL) was applied in a mixture with sawdust (SD) in the following ratios: 1:0 (PL/SD 1:0), 1:1 (PL/SD 1:1), 1:2 (PL/SD 1:2), and 2:1 (PL/SD 2:1). WT processing took place in an innovative fluidized bed system in a superheated steam medium with low overpressure (less than 0.07 MPa) at 300 °C and 350 °C for 30–45 min. Conventional HTC processing was performed in a water medium at 220 °C for 1–4 h. The hydrochar produced in the experiments was activated with steam for 1 h at 450–750 °C. The porosity characteristics of activated hydrochar were measured, including pore size, pore volume, and specific surface area, in view of potential industrial applications as an adsorbent. Additionally, the contents of 5-hydroxymethylfurfural (HMF), as high-value product, were determined in the liquid products obtained from HTC processing, as well as in the condensate obtained after WT processing. Specific surface areas of the activated hydrochars may still be too low for application as adsorbent material. Hence, its use as a biofertilizer and soil improver should be preferred. Interestingly, the liquid fraction obtained from the innovative WT process displayed a significantly higher 5-HMF content compared to the conventional HTC process.

This paper presents experimental results of a 5 kW Diffusion-Absorption Chiller (DAC). The chiller has been tested at varying inlet generator temperatures, inlet cooling water temperatures and inlet chilled water temperatures. The lowest driving temperature to keep the bubble pump running was about 90 °C with 3.6 kW cooling capacity and chilled water inlet temperature being set at 18 °C. The maximum cooling capacity and COP reached for the DAC was about 4.52 kW and 0.45, respectively. The prototype has demonstrated a good potential for air-conditioning applications, while not requiring electricity internally for its operation and allowing coupling with waste heat or solar thermal collector systems.

This article compares the annual energetic, exergetic and economic performance of a combined (hybrid) photovoltaic-thermal collector system (PVT) to that of a system with separate solar thermal and photovoltaic collectors. Furthermore, energy saving potentials through refurbishment of the building envelope are investigated. The analysis is based on simulations with an experimentally validated PVT model. The major novelty of the study is that the water based PVT collectors are also used for long wave radiative cooling. Three different residential case study buildings from Central to Southern European climate zones are investigated. Their heat, cooling and electricity demand, as well as their renewable supply, are determined along with savings through the envelope measures. In general, the performance of the PVT system varies strongly with the boundary conditions of the demand profile, climate situation and energy price levels. The results demonstrate that PVT collectors used for heat (primary DHW) and electricity offer approximately 6–7 percentage points higher exergetic efficiency than thermal and PV collectors equally sharing the available surface area. Raising the temperature level for cooling by 4 K increases the amount of renewable cooling by a factor 2–4. The analysis shows that the economic performance of the trigeneration PVT system is only better than separate generation if the additional electricity and cooling generate enough benefit to compensate the loss of heat gains. Especially in the Portuguese location of Almada, with high electricity price levels and high enough cooling demand, the application of PVT in a trigeneration system is recommendable from an exergetic and economic point of view.

Many installed solar thermally driven cooling systems suffer from high auxiliary electric energy consumption which makes them not more efficient than conventional compression cooling systems. A main reason for this is the use of non-efficient controls with constant set points that do not allow a chiller power modulation at partial-load and therefore lead to unnecessary high power consumption of the parasitics. The aims of this paper are to present a method to control efficiently solar thermally driven chillers, to demonstrate experimentally its applicability and to quantify the benefits. It has been shown that the cooling capacity of a diffusion absorption chiller can be modulated very effectively by adjusting both the temperature and the flow rate of the cooling water. With the developed approach and the use of optimization algorithms, both the temperature and the flow rate can be controlled simultaneously in a way that the cooling load is matched and the electricity consumption is minimized. Depending on the weather and operating conditions, electricity savings between 20% and 60% can be achieved compared to other tested control approaches. The highest savings are obtained when the chiller is operated at partial load. The presented method is not restricted to solar cooling systems and can also be applied to other conventional heating ventilation and air conditioning (HVAC) systems.

A new photovoltaic–thermal (PVT) system has been developed to produce electricity and cooling energy. Experimental studies of uncovered PVT collectors were carried out in Stuttgart to validate a simulation model, which calculates the night radiative heat exchange with the sky. Larger PVT frameless modules with 2.8 m 2 surface area were then implemented in a residential zero energy building and tested under climatic conditions of Madrid. Measured cooling power levels were between 60 and 65 W m −2 , when the PVT collector was used to cool a warm storage tank and 40–45 W m −2 , when the energy was directly used to cool a ceiling. The ratio of cooling energy to electrical energy required for pumping water through the PVT collector at night was excellent with values between 17 and 30. The simulated summer cooling energy production per square meter of PVT collector in the Madrid/Spain climatic conditions is 51 kWh m −2 a −1 . In addition to the thermal cooling gain, 205 kWh m −2 a −1 of AC electricity is produced under Spanish conditions. A comparative analysis for the hot humid climate of Shanghai gave comparable results with 55 kWh m −2 a −1 total cooling energy production, mainly usable for heat rejection of a compression chiller and a lower electricity production of 142 kWh m −2 a −1 .

Energy supply concepts for zero energy residential building (ZERB) in Shanghai (humid) and Madrid (dry) are discussed in this paper. Simulation is employed as the main research method. Two typical housing models are designed according to the real occupancy condition, the life schedule, the thermostats settings, etc., for the two cities. An energy analysis considering the annual balance of input from the grid and output from renewable power systems is made. Indoor comfortable comparisons between the two models are presented to show optimal design strategies for HVAC under different weather conditions. Also performed is the analysis on the primary energy payback time and the CO 2 equivalent saving in order to evaluate the performance of novel energy systems to verify the feasibility.

On the basis of the Number of Transfer Units (NTU) method a functional relation between electric power for fans/pumps and effectiveness in dry coolers and wet cooling towers is developed. Based on this relation, a graphical presentation method of monitoring and simulation data of heat rejection units is introduced. The functional relation allows evaluating the thermodynamic performance of differently sized heat rejection units and comparing performance among them. The method is used to evaluate monitoring data of dry coolers of different solar cooling field projects. The novelty of this approach is that performance rating is not limited by a design point or standardized operating conditions of the heat exchanger, but is realizable under flexible conditions.

This paper studies the primary energy optimisation potential of an existing large solar adsorption cooling plant (Festo company). This plant consists of 1218 m2 (net area) vacuum tubes collectors, 2 hot storage tanks of 8.5 m3 each and 3 adsorption chillers of 350 kW cooling capacity each. Measurements and previous simulation studies show a good optimisation potential especially regarding the electricity consumption of the cooling towers [1]. The purpose of this paper is to quantify this potential in terms of primary energy savings by using dynamic simulations. The work focuses on the heat rejection loop which consists of the chillers and the cooling towers. Different control strategies of cooling towers fan speed are simulated. Additionally, different hydraulics configurations of the heat rejection loop with or without buffer storage tanks are studied in order to see the effect on the fan speed control of the cooling towers. The electrical COP of the global system can be increased up to 30-40% with such controls with a minor decrease in cooling capacity. The use of a buffer store between the chillers and the cooling towers is meaningful since it smoothes the temperature wave and makes the control easier and more stable. Specific primary energy savings up to 0.25 kWhPE/kWhcooling can be achieved with simple changes in the heat rejection loop.

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.