Danish Climate Conditions Research Articles

Climate data for moisture simulations: producing a Danish moisture reference year and comparison with previously used reference year locations

Buildings comprise of complex systems, and various materials in combination. Different materials have different expected service life, and degradation processes start as soon as a building is put into operation. Degradation processes are often accelerated with the presence of moisture. To build robust and moisture safe buildings, hygrothermal simulations are used to predict hygrothermal conditions in constructions, and especially areas of risk. Simulations are useful tools for prediction of moisture accumulation, and results can further help predict the risk of moisture damage, i.e., frost damage or mould growth. The external climate can therefore have a significant impact on the service life of constructions. Due to the lack of a sufficient Danish climate reference year, including precipitation, hygrothermal simulations of Danish constructions are currently performed with either Danish climate data without precipitation (primarily for energy and indoor climate conditions), or with climate data from closest locations in either Sweden or Germany which include rain. Therefore, a complete Danish reference year, including precipitation, will inevitably enhance the value of hygrothermal simulations of buildings in Denmark. This paper presents the method used to develop full climate datasets based on Danish conditions, including precipitation. To integrate the climate datasets in the hygrothermal simulation programs, the climate datasets contain the following parameters: temperature, relative humidity, wind direction and speed, solar radiation, rain, as well as estimations for cloud cover and longwave radiation based on the other climate parameters. The climate datasets generated and presented in this paper, represent a Typical Meteorological Year (TMY), without extreme events, generated according to EN ISO 15927-4:2006. The climate datasets are based on Danish climate data from the period 2001-2019, provided by the Danish Meteorological Institute, DMI. By prioritizing climate parameters, and through statistical analysis, representative 1-year reference climate datasets were generated based on Danish climate conditions. The climate parameters of the 1-year reference climate datasets are compared with the traditionally used Swedish and German datasets, and a Danish Design Reference Year (DRY) from 1995.

Performance and dye-stability of semi-transparent dye-sensitized solar cell pavilion modules after six years of operation

A solar pavilion with 248 commercial 30 × 30 cm semi-transparent DSC modules were built at Roskilde University campus in 2016. After five years of operation under Danish climate conditions, and again one year later, two representative modules one from the south side and one from the north side of the pavilion facades were removed and their electrical performance relative to new modules was obtained. In addition, the respective dye degradation and triiodide bleaching was investigated. The south oriented module showed a decrease in efficiency of 85% and the north oriented module of 34% after 5 years. The degradation products of the applied ruthenium dye Z907 were typical thermal degradation products in which one or both of the thiocyanate ligands in Z907 had been substituted with the electrolyte components 3-methoxypropionitrile and or iodide. The degree of dye degradation in the south and north oriented modules after five years were 73% and 50% and the I3− concentration decreased 63% and 33%, respectively. The decrease in electrical performance Δη = 16%/year of the south module is within the same magnitude as performance loss of similar large-scale outdoor DSC installations. Such relatively high efficiency losses pr. year needs to be reduced if building integration photovoltaics based on the dye-sensitized solar cell technology should be commercially successful.

Performance and control strategy development of a PCM enhanced ventilated window system by a combined experimental and numerical study

This study proposes a PCM enhanced ventilated window (PCMVW) system for ventilation preheating/precooling purposes for building energy conservation. It is designed into a summer night cooling application and a winter solar energy storage application using different control strategies. An EnergyPlus model of the PCMVW is built to investigate the control strategies. Next, a full-scale experiment is conducted to study the working principle of the PCMVW and to validate the model. With the validated model, the thermal and energy performance of the PCMVW is compared to 2 other ventilation systems and shows that the PCMVW can greatly decrease the cooling/heating energy demand for both summer and winter applications. Finally, the paper proposes control strategies for residential applications under Danish climate conditions. The developed control strategy for summer night cooling application is to use between-glass reflection shading, ventilate directly from PCM heat exchanger to the room while applying VW self-cooling for ventilation pre-cooling mode, and heat the room with air from VW to prevent overcooling of the room. The developed control strategy for winter solar energy storage application is to use between-glass absorption blind, make use of the hot air in VW, and to cool the VW by self-cooling and bypass ventilation to prevent overheating of the room. With the developed control strategies, the building energy saving is up to 62.3% and 9.4% compared to the primitive summer and winter control strategies respectively.

A Comprehensive Approach for Modelling Horizontal Diffuse Radiation, Direct Normal Irradiance and Total Tilted Solar Radiation Based on Global Radiation under Danish Climate Conditions

A novel combined solar heating plant with flat plate collectors (FPC) and parabolic trough collectors (PTC) was constructed and put into operation in Taars, 30 km north of Aalborg, Denmark in August 2015. To assess the thermal performance of the solar heating plant, global radiation, direct normal irradiance (DNI) and total radiation on the tilted collector plane of the flat plate collector field were measured. To determine the accuracy of the measurements, the calculated solar radiations, including horizontal diffuse radiation, DNI and total tilted solar radiation with seven empirical models, were compared each month based on an hourly time step. In addition, the split of measured global radiation into diffuse and beam radiation based on a model developed by DTU (Technical University of Denmark) and the Reduced Reindl correlation model was investigated. A new method of combining empirical models, only based on measured global radiation, was proposed for estimating hourly total radiation on tilted surfaces. The results showed that the DTU model could be used to calculate diffuse radiation on the horizontal surface, and that the anisotropic models (Perez I and Perez II) were the most accurate for calculation of total radiation on tilted collector surfaces based only on global radiation under Danish climate conditions. The proposed method was used to determine reliable horizontal diffuse radiation, DNI and total tilted radiation with only the measurement of global radiation. Only a small difference compared to measured data, was found. The proposed method was cost-effective and needed fewer measurements to obtain reliable DNI and total radiation on the tilted plane. This method may be extended to other Nordic areas that have similar weather.

Analysis and validation of a quasi-dynamic model for a solar collector field with flat plate collectors and parabolic trough collectors in series for district heating

Abstract A quasi-dynamic TRNSYS simulation model for a solar collector field with flat plate collectors and parabolic trough collectors in series was described and validated. A simplified method was implemented in TRNSYS in order to carry out long-term energy production analyses of the whole solar heating plant. The advantages of the model include faster computation with fewer resources, flexibility of different collector types in solar heating plant configuration and satisfactory accuracy in both dynamic and long-term analyses. In situ measurements were taken from a pilot solar heating plant with 5960 m2 flat plate collectors and 4039 m2 parabolic trough collectors in series in Taars, Denmark from Sep.2015 to Aug.2016. The simulated thermal performances of both the parabolic trough collector field and the flat plate collector field have a good agreement with the measured performances. The thermal performance of the hybrid solar district heating plant is also presented. The measured and simulated results show that the integration of parabolic trough collectors in solar district heating plants can guarantee that the system produces hot water with relatively constant outlet temperature. The daily energy output of the parabolic trough collector field can be more than 5 kWh/m2, while the daily energy output of the flat plate collector field is less than 5 kWh/m2 under Danish climate conditions. The simplified and validated TRNSYS model can be a useful tool to simulate and optimize thermal performance of solar heating plants with both flat plate and parabolic trough collectors.

Computational prediction of the effective temperature in the lying area of pig pens

Using solid floor instead of drained or slatted floor in the lying areas of pig pens has distinct advantages in relation to animal welfare, odour abatement and ammonia emission, energy consumption and reduced building costs. However, pig producers often opt out of providing a solid floor due to the risk of manure fouling in the lying area during warm periods, fouling that may increase work load, reduce animal welfare and degrade the indoor environment. The risk of fouling the lying area increases as indoor temperature increases, and it is therefore recommended that the indoor temperature should be maintained at around 13°C during the last part of the growing period if diffuse air intake is used. Undesired higher indoor temperatures still occur during about 40% of the time each year, even in the relatively cold Danish climate (where outdoor temperatures average about 8°C).This study aims to investigate the potential benefits of using a hinged ceiling flap inlet to control the air velocity and experienced thermal environment for pigs in the lying area of finisher units. A new equation for the effective temperature (ET) has been developed and used to express how temperature, humidity and velocity, individually contribute to the combined effect of the thermal condition raising pigs are exposed to. Computational Fluid Dynamics (CFD) simulations were conducted to estimate the relevant parameters and, finally, the ET. Furthermore, the developed ET equation was implemented in the CFD model as a Custom Field Function to calculate the distribution of ET in the animal occupied zone. It was assumed that a traditional diffuse ceiling air inlet would deliver the required airflow rate as long as the outdoor temperature was below 10°C. At higher outdoor temperature, a ceiling-jet inlet above each pen was opened gradually depending on the cooling requirements. When the inlet was only slightly open, it formed a wall jet attached to the ceiling. After reaching the end wall, the jet of air was deflected toward the lying area. When the jet inlet was more fully open, it sent the jet directly to the lying area.Our investigations showed that the ceiling-jet inlet could be used to control air speed in the animal occupied zone and generate the same ET in the preferred lying area at a 9-degree higher outdoor temperature than if the same ventilation rate were delivered though the defuse ceiling only. This indicates that the periods of undesired high indoor temperature can be reduced from 40% to 5% of the time under Danish climate conditions. In addition, the results showed that the largest cooling effect was obtained when the ceiling-jet inlet was opened less than 30% due to the generation of the jet’s being attached to the ceiling.

Annual measured and simulated thermal performance analysis of a hybrid solar district heating plant with flat plate collectors and parabolic trough collectors in series

Flat plate collectors have relatively low efficiency at the typical supply temperatures of district heating networks (70–95°C). Parabolic trough collectors retain their high efficiency at these temperatures. To maximize the advantages of flat plate collectors and parabolic trough collectors in large solar heating plants for a district heating network, a hybrid solar collector field with 5960m2 flat plate collectors and 4039m2 parabolic trough collectors in series was constructed in Taars, Denmark. The design principle is that the flat plate collectors preheat the return water from the district heating network to about 70°C and then the parabolic trough collectors would heat the preheated water to the required supply temperature of the district heating network. Annual measured and simulated thermal performances of both the parabolic trough collector field and the flat plate collector field are presented in this paper. The thermal performance of both collector fields with weather data of a Design Reference Year was simulated to have a whole understanding of the application of both collectors under Danish climate conditions as well. These results not only can provide a design basis for this type of hybrid solar district heating plants with flat plate collectors and parabolic trough collectors in the Nordic region, but also introduce a novel design concept of solar district heating plants to other high solar radiation areas.

Beyond nearly-zero energy buildings: Experimental investigation of the thermal indoor environment and energy performance of a single-family house designed for plus-energy targets

A detached, one-story, single-family house in Denmark was operated with different heating and cooling strategies for 1 year. The strategies compared during the heating season were floor heating without ventilation, floor heating supplemented by warm air heating (ventilation system), and floor heating with heat recovery from exhaust air. During the cooling season, the house was cooled by floor cooling and was ventilated mechanically. Air and globe (operative, when applicable) temperatures at different heights at a central location were recorded. The thermal indoor environment, local thermal discomfort and overheating were evaluated based on EN 15251 (2007), EN ISO 7730 (2005), and DS 469 (2013), respectively. Energy performance was evaluated based on the energy production and HVAC system energy use. The thermal indoor environment during the heating season was satisfactory but it was not possible to reach the intended operative temperature when the outside temperatures were very low. During the cooling season, the cooling demand was high and overheating was a problem. Although the house was designed as a plus-energy house, it did not perform as one under the Danish climate conditions. It would be possible to decrease the heating and cooling demand during the design phase through careful consideration of parameters such as the orientation, glazing area, solar shading, and thermal mass. With a lower demand, plus-energy levels can be achieved even with the minimum contribution from the energy producing components.

Operational strategy, economic and environmental performance of sludge treatment reed bed systems - based on 28 years of experience.

Sludge treatment reed bed (STRB) systems have been used for dewatering and mineralisation of sludge in Europe since 1988. STRB systems provide substantial environmental, economic, and operational benefits compared to mechanical sludge dewatering solutions such as belt presses and centrifuges. They require less energy, no chemicals, reduce the sludge volume and produce bio solids with dry solid contents up to 20-40% under Danish climate conditions, depending on the sludge quality. Experience has shown that sludge treated in STRBs represents a high quality product with a low content of pathogens and hazardous organic compounds, qualities that make it suitable for recycling on agricultural land. The upfront capital cost for STRBs are often higher compared to mechanical dewatering devices. However, the operational expenses (OPEX) (including energy, chemicals, bio solid handling) are significantly lower compared to conventional mechanical dewatering devices, delivering an economic break-even of about 3-5 years. This paper provides an overview of the operation and maintenance costs and environmental benefits of a typical STRB based on the experiences gained from the operation of a large number of STRBs with yearly treatment capacities between 100 and 3,000 tonnes of dry solid up to approximately 250,000 PE in Denmark and Europe.

Long term thermal energy storage with stable supercooled sodium acetate trihydrate

Utilizing stable supercooling of sodium acetate trihydrate makes it possible to store thermal energy partly loss free. This principle makes seasonal heat storage in compact systems possible. To keep high and stable energy content and cycling stability phase separation of the storage material must be avoided. This can be done by the use of the thickening agents carboxymethyl cellulose or xanthan rubber. Stable supercooling requires that the sodium acetate trihydrate is heated to a temperature somewhat higher than the melting temperature of 58 °C before it cools down. As the phase change material melts it expands and will cause a pressure built up in a closed chamber which might compromise stability of the supercooling. This can be avoided by having an air volume above the phase change material connected to an external pressure less expansion tank. Supercooled sodium acetate trihydrate at 20 °C stores up to 230 kJ/kg. TRNSYS simulations of a solar combi system including a storage with four heat storage modules of each 200 kg of sodium acetate trihydrate utilizing stable supercooling achieved a solar fraction of 80% for a low energy house in Danish climatic conditions.

Photoperiodic effect on flowering and seed development in quinoa (Chenopodium quinoa Willd.)

Sensitivity to photoperiod in quinoa (Chenopodium quinoa Willd.) was studied under controlled conditions to enhance crop adaptation to environments outside its centre of origin. Two varieties, a traditional variety from Bolivia (Real), which will not mature under Danish conditions, and an early maturing variety (Q52), developed for Danish climatic conditions, were used in this reciprocal transfer experiment. Plants were moved from a short daylength of 10 h (SD) to a long daylength of 18 h (LD) and vice versa at set intervals from sowing to 100 days after sowing (DAS). A reaction of LD in time to flowering was observed only in the Bolivian variety Real. Under SD both varieties flowered after 39 DAS. For Real the LD regime resulted in a moderate increase in time to flowering to 44 DAS. The non-sensitive, juvenile period in Real was estimated to be approximately 16 days. In Q52 a moderate increase in the number of leaves was formed on the main stem after flowering at LD, which indicates that some daylength sensitivity remains. The most striking difference occurred during seed filling, when going from SD to LD. In Q52 the time from the end of flowering to maturity increased from 39 to 52 days. Under SD, Real had a seed-filling period similar to Q52, but at LD Real remained with green leaves during seed filling. Hard seed was observed in the still green perigonium 57 days after end of flowering. At this moment re-shooting occurred from the inflorescence, and seed maturity was not reached at the termination of the experiment at 150 DAS. This study shows that flower induction is not a major problem for adaptation of quinoa to North European conditions but that a very strong, daylength sensitive, stay green reaction is the main cause of the late maturity of South American introductions.

Habitat and prey preferences of the two predatory bugs Anthocoris nemorum (L.) and A. nemoralis (Fabricius) (Anthocoridae: Hemiptera-Heteroptera)

The annual occurrence and distribution of the predatory bugs Anthocoris nemorum and Anthocoris nemoralis between apple, pear and herbal vegetation, was assessed in three apple orchards in 2001, and in two apple and two pear orchards in 2002. In the laboratory anthocorid prey preference was assessed in two-choice experiments with key pests of apple and pear including pear psyllid, apple psyllid, green apple aphid, rosy apple aphid and red spider mites. Anthocorid predation behavior towards pear psyllids was assessed. Anthocorids were the dominant early season predatory bugs. A. nemorum dominated in apple, while A. nemoralis dominated in pear. A. nemorum was also common in herbal vegetation, especially in mid-summer. Anthocorid numbers were correlated with numbers of collembola, psyllids and aphids in apple, and with numbers of psyllids in pear. A. nemoralis preferred pear psyllid to green apple aphid, while A. nemorum preferred green apple aphid . Both species preferred psyllids to spider mites. The success rate of A. nemoralis in attacking pear psyllids was higher than that of A. nemorum. A. nemorum had two generations in both 2001 and 2002 proving that it can be bivoltine under Danish climate conditions. The mid-summer move by A. nemorum from trees to herbal vegetation suggests that herbal vegetation may maintain A. nemorum in orchards at times of low prey numbers in the trees. Habitat and prey preference trials both identify A. nemorum as a biological control agent of special importance in apple, whereas A. nemoralis is of importance in pear.

Microclimate Prediction for Dynamic Greenhouse Climate Control

Greenhouse energy-saving and biocide reduction can be achieved through dynamic greenhouse climate control with computerized model-based regimes. This can be optimized when next to greenhouse macroclimate (i.e., the aerial environment) also, the crop microclimate is predicted. The aim of this article was to design and apply a simple deterministic microclimate model for dynamic greenhouse climate control concepts. The model calculates crop temperature and latent heat of evaporation in different vertical levels of a dense canopy of potted plants. The model was validated with data attained from experiments on dynamic or nondynamic (regular) controlled greenhouse cultivation. Crop temperature was with a 95% confidence interval of 2 °C or 2.4 °C for sunlit or shaded leaves, respectively, accurately predicted in a simple greenhouse with predefined climate set points. With a more dynamic greenhouse control also including assimilation lighting and screens, the prediction quality decreased but still had a 95% confidence interval of crop temperature prediction of 3.8 °C for sunlit leaves. Simulations showed that controlling greenhouse temperature according to the predicted crop temperature rather than according to the air temperature can save energy. Energy-saving is highest during winter and 12% energy saving was attained during January under Danish climate conditions.

Methane Production during Storage of Anaerobically Digested Municipal Organic Waste

Anaerobic digestion of source-separated municipal organic waste is considered feasible in Denmark. The limited hydraulic retention in the biogas reactor (typically 15 d) does not allow full degradation of the organic waste. Storage of anaerobically digested municipal organic waste can therefore be a source of methane (CH4) emission that may contribute significantly to the potential global warming impact from the waste treatment system. This study provides a model for quantifying the CH4 production from stored co-digested municipal organic waste and estimates the production under typical Danish climatic conditions, thus quantifying the potential global warming impact from storage of the digested municipal organic waste before its use on agricultural land. Laboratory batch tests on CH4 production as well as temperature measurements in eight full-scale storage tanks provided data for developing a model estimating the CH4 production in storage tanks containing digested municipal organic waste. The temperatures measured in separate storage tanks on farms receiving digested slurry were linearly correlated with air temperature. In storage tanks receiving slurry directly from biogas reactors, significantly higher temperatures were measured due to the high temperatures of the effluent from the reactor. Storage tanks on Danish farms are typically emptied in April and have a constant inflow of digested material. During the warmest months the content of digested material is therefore low, which limits the yearly CH4 production from storage.

Characterisation of production of organic rich topsoil from sludge

The stabilisation of a sludge-mineral soil mixture and a method to evaluate the state of stabilisation were investigated. The organic matter and nitrogen content are reduced up to 50% during a stabilisation process of three months under Danish climatic conditions. The stabilisation was shown to be an aerobic process limited by oxygen transport within the mixture. The degree of stabilisation was evaluated by oxygen consumption in a water suspension and the results showed that a stable product was achieved when oxygen consumption was stable and in the level of natural occurring aerobic soils (0.1 mgO2/(g DS*hr). The study thereby demonstrates that a stability of a growth media can be controlled by the oxygen consumption method tested.

Prospects for controlling animal parasitic nematodes by predacious micro fungi.

Resistance against anthelmintics is widespread, particularly in parasitic nematode populations of small ruminants. Several new techniques or supplements have been developed or are under investigation. Biological control (BC) is one of these new methods. The net-trapping predacious fungus Duddingtonia flagrans produces thick walled resting spores, chlamydospores, which are able to survive passage through the gastrointestinal tract of cattle, horses, sheep and pigs. Under Danish climatic conditions it has been shown that the number of parasite larvae on pasture and the worm burden of the grazing animals is significantly reduced when animals are fed spores during the initial 2-3 months of the grazing season. Work with D. flagrans in France, Australia, USA, and Mexico has confirmed the strong BC potential of this fungus. Today much work is going into development of suitable delivery systems for grazing livestock worldwide. Ultimately, BC should be implemented in integrated parasite control strategies, both in conventional and organic livestock production.

Extended Nutrient Removal in Small One-Tank Activated Sludge Plants

The general Danish standards for discharge from municipal waste water treatment plants larger than 5000 PE require extended nitrogen and phosphorus removal to 8 mg/l total-nitrogen and to 1.5 mg/l phosphorus. In many cases the local authorities require that the same standards have to be met by smaller plants down to 500 PE. In some cases even tighter standards are set. As plants for extended nitrogen and phosphorus removal for smaller communities should not necessarily look like the large plants, new concepts have been developed. Combined nitrogen and phosphorus removal based on one activated sludge tank and one clarifier has proved to be advantageous both technically and economically in order to meet the above mentioned standards given under the Danish climate conditions with water temperatures of 38°C during winter. Six plants ranging from 600-2,500 PE and further three plants from 4,000-7,300 PE are now in operation. This paper gives a general description of the design and the operation of these plants. The plants operate by means of simultaneous precipitation and a special intermittent operational strategy or nitrification/denitrification. Operational results from the five plants with up to 4 years of operation show average concentrations of nitrogen and phosphorus of 5-6 mg/l and 0.4-0.8 mg/l, thereby leaving a rather large margin to the general Danish standards. As regards competition, the concept has proven to be very competitive in the range of 1,000-10,000 PE.