In a single duct variable air volume (SDVAV) system, the supply air temperature is usually set as a constant value. Since this constant setpoint is selected to satisfy the maximum cooling load conditions, significant reheat will occur once the airflow reaches the minimum and the heating load increases. Resetting the supply air temperature (SAT) higher during the heating season can reduce the reheat. However, air flow will increase when the SAT is higher which consume extra fan power. Therefore, to minimize the total operating cost of a SDVAV system, the supply air temperature is typically reset based on outside air temperature (OAT) with a linear reset schedule. However, the linear reset schedule is often determined based on the engineer’s experience and it may not represent the optimal reset schedule for each building. This thesis documents a study to determine the optimized supply air temperature reset schedule for SDVAV systems and analyzes the influencing factors under different operation scenarios. The study was divided into five main sections. The first section introduces the research background and objective. Literature review is documented after the introduction. The third section describes the methodology used in this study and the fourth section develops an in-depth discussion and analysis of the impact of the key influencing factors: minimum air flow ratio; ratio of exterior zone area to total floor area (i.e., exterior area ratio); internal load and the prices of the electricity; the cooling and the heating energy. The simulation results using EnergyPlus Version 2.1.0 for various operation scenarios are investigated in this section. The last section is a conclusion of the whole study. The optimized supply air temperature can be set with respect to the OAT. The study found that instead of a simple linear relationship, the optimal reset schedule has several distinctive segments. Moreover, it is found that the optimal supply air temperature reset schedule should be modified with the change of operation conditions (e.g., different minimum flow ratios and internal loads). Minimum air flow ratio has a significant impact on energy consumption in a SDVAV system. Exterior area ratio determines zone load distribution and will change system load indirectly. For buildings with small internal load, a more aggressive supply air temperature reset tactic can be implemented. In addition, the cost of electricity, cooling and heating energy can determine which end use energy (i.e., reheat energy and fan power) should take the priority.

No description available.

The atmospheric effect of greenhouse gas emissions is posing an increasing threat to the stability of the global climate. Like many developing nations, the western Africa nation of Nigeria faces risks from climate change, with potential effects on the environment upon which Nigerians rely and on broader social constructs, including the national economy. Nigeria's diverse topography, which stretches from dry northern regions of the sub-Sahara to lush southern rainforests along the Gulf of Guinea, accentuates susceptibility to a variety of climate-related hazards, including warming, irregular rainfall patterns, and extreme weather occurrences. Driven by the influence of tropical climates on the global climate system and the importance of climate variability and change specifically within Nigeria, this study of the Nigerian hydroclimate explicitly characterizes historical variability and change through analysis of in-situ daily climate data. Daily maximum and minimum air temperature and total precipitation data from 1982 through 2011 were obtained from the Nigeria Meteorological Service for 20 locations across the country. Given the limited temporal extent of the data, two popular satellite-derived precipitation products were tested for usability as supplements to the in-situ data. Each of the satellite-derived products depicts rainfall with an unrealistically high frequency and with a temporal trend that is opposite reality. Only in-situ data were analyzed further, beginning with a methodology to define the climatological wet and dry seasons across the country. The critical wet season across Nigeria was found to last between 120 days (north) and 200 days (south), beginning April/May and ending September/October, with wetness migrating from nearer the southern coastline northward through the country during the Northern Hemisphere summer, before retreating south again. As with seasonality, the spatial distribution of precipitation amount and frequency relates to distance northward from the southern coast. Wet season precipitation approaches 2500 mm from an average of more than 115 wet days along the coast, to only about 350 mm and 35 days across far northern Nigeria. Conversely, the dry season produces 300 mm from 30 wet days across the south, and only 80 mm from less than 10 days across the north. The wet season in Nigeria accounts for greater than 90% of annual precipitation and number of wet days. Nigeria experienced a warming and wetting of the climate during the 30-year study period, during both the wet and dry seasons. However, a change in the equitable distribution of precipitation across wet days (i.e., daily intensity) is not greatly evident, as it is for many other regions of the world. Thus, the likely benefit of greater precipitation does not appear to be mitigated by the risks associated with an increase in the frequency of high-intensity rainfall events. But tempering the positive precipitation signal is the likely detrimental effect of warming. Inter-annual variability in the wetness of the critical wet season is evident in the synoptic atmospheric expression of the inter-tropical convergence zone/discontinuity, but also in sea surface temperatures within the Gulf of Guinea. Historically, sea surface temperatures are considerably higher during the wettest wet season years compared to the driest years, possibly indicating a short-distance teleconnection that may offer seasonal predictability. / Master of Science / Nigeria is experiencing the consequences of global climate change caused by gases that trap heat in the atmosphere. Nigeria is endowed with a diverse terrain, with green rainy parts in the south and arid regions in the north. In Nigeria, the economy and the environment are both being impacted by climate change. Decades of climatic data from various regions of the nation were examined in this research. We discovered that Nigeria is generally becoming wetter and warmer. Most of the yearly precipitation falls during the rainy season, which runs from April to October. There hasn't been much of an increase in extremely heavy rain, though, because the intensity of the rainfall hasn't increased significantly. However, higher temperatures can lead to issues. The amount of rain that falls in Nigeria is also influenced by sea surface temperature in the Gulf of Guinea. This study sheds light on how Nigeria's weather is changing due to climate change, which may have negative effects on both people and the environment.

Hur mycket lufttemperaturen varierar på en plats på land beror till stor del av platsens avstånd till havet. Ju längre ifrån havet platsen ligger, ju mindre influeras dess lufttemperatur av havstemperaturen. Hav värms och kyls långsammare än land vilket innebär att maritima platser har en stabilare lufttemperatur i jämförelse med inlandet.             Syftet med denna studie är att undersöka lufttemperaturer på en liten ö för att bestämma i vilken grad havsavståndet påverkar temperaturvariationer på liten skala. Mätningarna skedde på ön Mefjärd i Stockholms skärgård. Mefjärd har en storlek på ca 3000 x 400 m och är belägen drygt 10 km från Sveriges östkust. Mätningar av lufttemperatur gjordes kontinuerligt mellan den 20/3 och 22/4 både vid strandlinjen och vid mitten av ön. Även havstemperatur, vind och solinstrålning mättes. Statistiska beräkningar genomfördes och grafer över temperaturer och resterande uppmätt data skapades. Resultaten visade bland annat att lufttemperaturen vid strandlinjen var stabilare och generellt sätt närmare havstemperaturen än vad lufttemperaturen mitt på ön var samt att lufttemperaturen mitt på ön var känsligare för skillnader i solinstrålning än lufttemperaturen vid strandlinjen. Dessa resultat var tydliga trots att studien utfördes på liten skala. / The amount of air temperature variation at some location on land depends to a large extent on the distance between the location and the sea. The further from the sea a place is located, the less is its air temperature influenced by the sea temperature. The sea is heated and cooled more slowly than land which means that maritime locations has a more stable air temperature compared to inland locations.             The purpose of this study is to examine air temperatures on a small island in order to determine to what extent air temperature variations are influences by distance to sea, on a small scale. Measurements were taken on the island Mefjärd in the archipelago of Stockholm. Mefjärd is about 3000 x 400 m in size, located 10 km from the eastern coast of Sweden. Measurements of air temperature was taken continuously between the 20/3 and 22/4 both by the shoreline and in the middle of the island. Sea temperature, wind and solar radiation were also measured. Statistical calculations were done and figures displaying air temperatures and other measured data were created. The result showed, among other things, that the air temperature by the shoreline was more stable and generally closer to the sea temperature than the air temperature in the middle of the island, and that the air temperature in the middle of the island was more sensitive to changes in sun radiation than the air temperature by the shoreline. These results were apparent even though the study was conducted on a small scale.

Das Jahr 1816 ist in die Klimatologie als das "Jahr ohne Sommer" eingegangen. Der 1815 erfolgte Ausbruch des Vulkans Tambora auf der indonesischen Insel Sumbawa führte im darauffolgenden Jahr in vielen Teilen der Welt zu katastrophalen Missernten. Während in Nordamerika daran besonders die außerordentlich tiefen Sommertemperaturen Schuld waren, scheinen in Europa dafür sowohl die unter dem Durchschnitt liegenden Temperaturen wie auch die überdurchschnittlichen Regenmengen verantwortlich zu sein. Zeitgenössische Berichte wie auch Niederschlags- und Pegelaufzeichnungen aus verschiedenen Teilen Europas belegen eine besonders hohe Niederschlagstätigkeit im "Erntemonat" Juli des Jahres 1816 und eine hohe Wasserführung der großen europäischen Ströme in den Jahren 1816 und 1817. / The year 1816 is known in climatology as the "Year without Summer". The eruption of the Tambora volcano on the Indonesian island Sumbawa in 1815 led to catastrophic crop failures over many parts of the world in the following year. Whereas in North America those failures originated from extraordinarily low summer temperatures, causes in Europe seem to have been below-normal temperatures as well as above-normal rainfall. Contemporary reports and also precipitation and river gauge measurements from different parts of Europe document enhanced precipitation in July 1816 ("Erntemonat") and high discharges of large European rivers in years 1816 and 1817.

In dieser Arbeit wird über Klimamessungen berichtet, die beide Autoren in den achtziger Jahren im Raum Leipzig durchgeführt haben. Damit wird ein erster Versuch der Darstellung stadtklimatologischer Differenzierungen in Leipzig unternommen. Anhand der mittleren Lufttemperaturen läßt sich die städtische Wärmeinsel nachweisen. Darüber hinaus wird eine kleinräurnige Niederschlagsverteilung von Leipzig angegeben.

Near-surface air temperature (SAT) over Greenland has important effects on mass balance of the ice sheet, but it is unclear which SAT datasets are reliable in the region. Here extensive in-situ SAT measurements are used to assess monthly mean SAT from seven global reanalysis datasets, four gridded SAT analyses, one satellite retrieval and two dynamically downscaled reanalyses. Strengths and weaknesses of these products are identified, and their biases are found to vary by season and glaciological regime. MERRA2 reanalysis overall performs best with mean absolute error less than 2 °C in all months. Ice sheet-average annual mean SAT from different datasets are highly correlated in recent decades, but their 1901–2000 trends differ in sign. Compared with the MERRA2 climatology combined with gridded SAT analysis anomalies, thirty-one earth system model historical runs from the CMIP5 archive reach ~5 °C for the 1901–2000 average bias and have opposite trends for a number of sub-periods.

The HAbitability, Brine Irradiation and Temperature Package (HABIT) instrument of the ExoMars Surface Platform will investigate the present day habitability of Mars at the near surface environment. This instrument includes three Atmospheric Temperature Sensor's (ATS's) which are similar to the ones previously used on the Rover Environmental Monitoring Station (REMS) of the Mars Science Laboratory (MSL) rover, that has now been operating on Mars for more than four years. The ATS of REMS is only used to provide the air temperature, however on HABIT it will be used furthermore to provide information about winds and heat transfer at the surface of Mars. The retrieval method needs to be further investigated and validated. This master thesis is aimed at three goals: 1) the development and testing of an Earth Scaled Atmospheric Temperature Sensor (ESATS) to test the retrieval concept; 2) the validation with other Earth-based standard wind sensing technologies under outdoors uncontrolled conditions; and 3) the analysis of the existing observations of the ATS of REMS on Mars to get a better understanding of its expected future performance on HABIT once it operates on Mars. The ESATS is an up-scaled semi-autonomous prototype version of an ATS which consists of a rod of different size and material to those that are used on REMS and will be used on HABIT. The rod shall be heated from the base where it is attached to. The temperature profile shall be measured at three different measurement points. All these temperatures are different from the one of the atmosphere to which the rod is exposed to. The temperature profile along the rod changes depending on the air temperature, air density and the wind speed because of the convective heat transfer. A preliminar analysis is used to define what is the ideal length of the rod, and what is the material that is best adapted for this experimental prototype. Since the air density is needed to retrieve the wind speed, the pressure will be monitored as well. In parallel, a second wind measuring technique based on the dynamic pressure changes detected in a Pitot tube is used as control. The measuring campaign is subdivided in several stages: 1) The first part will take place in a laboratory, where the system is exposed to static conditions with no heating and no wind, which means that there is no forced convection caused by wind. In this setup all sensors are calibrated against one another and with help of a reference resistor the temperature sensors are also calibrated to 273.15K. Additionally different Operational Amplifiers (OpAmps) will be used to observe how the noise level is affecting the measurements, so that the best one will be used in the end. 2) Furthermore, the best position to place the intermediate temperature sensor is investigated by testing one of the rods with different locations of the middle temperature sensor. 3) Next, also within the laboratory environment, the different rods are used to obtain the temperature profile and retrieve the air temperature and heat transfer values, solving the equations that describe the heat transfer problem under static conditions. 4) The second part of the measurement campaign will take place outdoors, where the ESATS is exposed to forced convection due to wind. In this setting first the influence of the Sun on the system is measured, as it is important to know, if the measurement can be performed when the illumination conditions change. 5) Next, the system is tested with the 50cm rod in long term tests with the reference measurement of a commercial weather station (HOBO) next to it. With the data obtained the convective heat transfer method is used and the retrieved wind speed is compared to the one received from the HOBO. Finally, to get a better understanding of its expected future performance on HABIT once it operates on Mars, the data of the ATS of REMS is used to perform the wind speed retrieval for Mars and to compare it with the data received from the REMS wind sensor. It is only operating during daytime and has still difficulties to retrieve a precise wind speed. The measurement campaign has given several information about ATS in general. First it was decided to place the temperature sensor in the middle at 1/4 of the rod length, which is optimal for the retrieval process and which is also coincident with the one chosen for HABIT and REMS. The measurements in the laboratory are providing good and constant temperature profiles with the chosen setup which correspond with the one expected from the equations that describe the heat transfer problem in a long rod. On the other hand, it is not possible to calculate a valid ambient temperature for the short rods, which is because of an overheated boundary layer around the rods due to the heating. For this reason, it is recommended to use the longest rod in the lab. For outside testing the influence of the Sun could be confirmed and was affecting the measurements of the copper rod. During the time span where the prototype was in the Sun, it was not possible to get any reasonable results. The next measurement campaign was defined in a shadowed area with diffuse light only. Finally, the tests of exposure to dynamic changes over time are in excellent agreement with the ones provided by the HOBO station and can even give a better resolution and sensitivity to small changes of wind magnitude. This prototype has confirmed experimentally, that under Earth conditions, this method can be used to retrieve the wind speed. Finally, the Martian data of the REMS ATS are analyzed and the comparisons suggest that the method is sensitive to wind changes on Mars as well, and shows better time and magnitude resolution than the existing REMS wind sensor. This confirms that this method can be successfully used for the HABIT sensor. In this work the methodology that shall be used on HABIT to retrieve the convective heat transfer and wind on the surface of Mars is validated for Earth outdoors conditions. It is recommended to verify the obtained results with tests in a wind tunnel and to see how the system will behave with a higher heating and different rod materials. Furthermore, the setup should be tested in a way which makes it possible to determine the different directions of the wind.

The focus of this study is to examine the mechanisms involved in the interactions among large-scale atmospheric circulation patterns and how they are related to surface air temperature anomalies in the North American Arctic. Historical temperature data sets of Fairbanks, Alaska and Montreal, Quebec have been analyzed with respect to large-scale atmospheric circulation index data sets to investigate surface temperature anomalies in winter during the period 1960 to 2002.

Not available / text