Some Aspects of HVAC Design in Energy Renovation of Buildings

It is well-known fact that air conditioning systems are responsible for a significant part of all energy systems in building energy usage. In EU buildings, the building HVAC systems account for ca 50% of the energy consumed. In the U.S., air-conditioning accounts on average about 12% of residential energy expenditures. The proper choice of air distribution systems and sustainable energy sources to drive the electrical components have a vital impact to achieve the best requirements for indoor climate including, hygienical, thermal, and reasonable energy-saving goals. The building energy system components that have a considerable impact on the demand for final energy in the building are design, outdoor environment conditions, HVAC systems, water consumption, electrical appliances, indoor thermal comfort, and indoor human activities. For calculation of the energy balance in a building, we need to consider the total energy flows in and out from the building including ventilation heat losses, the perimeters transmission heat loses, solar radiation, internal heat from occupants and appliances, space and domestic water heating, air leakage, and sewage heat losses. However, it is a difficult task to handle the above time-dependent parameters therefore an energy simulation program will always be used. This chapter aims to assess the role of ventilation and air-conditioning of buildings through the sustainability approaches and some of the existing renewable energy-based methods of HVAC systems are presented. This comprehensive review has been shown that using the new air distribution systems in combination with renewable energy sources are key factors to improve the HVAC performance and move toward Nearly Zero Carbon Buildings (NZCB)

Interferencia entre chorro de entrada de aire y superficies en una habitación ventilada: estudio de un modelo a escala

JUSTIFICACIÓN En los países desarrollados hasta el 95% del tiempo se pasa en lugares cerrados, viviendas edificios de oficinas, hospitales, centros comerciales, cines, industrias... Estos lugares cerrados son los lugares en los que trabajamos comemos tomamos un café y en general vivimos. El desarrollo de los sistemas de ventilación para edificios se desarrollo de manera intensa a partir de los 70 y la aparición en Suecia y otros países nórdicos de problemas respiratorios en las edificaciones de bajo consumo energético. Con sellados casi herméticos que no permitían la transpiración del edificio y bajos niveles de ventilación apareció el S.B.S. (Sick Building Syndrome). Los síntomas del edificio enfermo según el Dr. P. König´s son los siguientes. 1.- Tendencia a crear corrientes que provocan reumatismos fríos. 2.- Irritación en membranas mucosas, el tracto superior respiratorio, ojos y sensación de sequedad. 3.- Fiebre, dificultad, para respirar dolor en articulaciones y fatiga . 4.- Fatiga, falta de concentración, mareo, dolor de cabeza. 5.- Pobre calidad del aire. El primer síntoma se debe a una ventilación cuyas velocidades máximas son superiores a las adecuadas. El segundo se debe a una cantidad elevada de polvo, microbios alérgenos y esporas por una ventilación ineficiente que no consigue expulsar las partículas e introducir aire limpio. El tercer síntoma se debe a problemas tóxicos microbianos que se reproducen en los sistemas de humidificación. El cuarto y el quinto síntomas se deben a una insuficiente o ineficiente ventilación que no consigue renovar el aire de la habitación y por tanto los contaminantes que se producen en su interior se acumulan. ENTORNO El proyecto presentado se realizó en “El laboratorio para la ventilación y la calidad del aire de la KTH”. Este laboratorio ubicado en la ciudad de Gávle cuenta con un número elevado de investigadores dedicados al estudio de la ventilación en edificios. En este centro se realizan estudios sobre ventilación en Catedrales, Edificios de viviendas, aulas de escuelas, en modelos reales o a escala y mediante simulaciones por ordenador. En este centro de investigación una de las lineas de investigación llevada por el Dr. Taghi Karimipanah, consiste en el estudio del movimiento del aire en habitaciones mediante el uso de modelos a escala con el objetivo de diseñar en el futuro sistemas que permitan renovar el aire de habitaciones y edificios de forma eficiente. El estudio que yo realicé se hizo a partir de una maqueta que el centro de investigación acababa de construir para simular la ventilación por chorro en habitaciones. Queremos estudiar el movimiento general de aire en varios casos y llegar a conclusiones sobre si la ventilación es adecuada desde el punto de vista de la renovación de aire y el confort térmico. Queremos saber si el chorro de aire permite la renovación del aire en la habitación o si las partículas contaminantes se acumulan porque el sistema por chorro no permite la mezcla correcta del aire. Además queremos controlar y medir en que zonas el aire de la habitación se mueve a mayores velocidades. EJECUCIÓN Para hacer esto en el proyecto se realizan tres tareas consecutivas. 1) La primera es la observación directa del modelo a escala con técnicas de visualización de fluidos tipo PSV y PSP. Estas técnicas consisten en la medida de la velocidad del aire por grupos de partículas y por partículas individuales. Los grupos de partículas se visualizan mediante humo que proveniente de una máquina e introducido en el modelo. Las partículas individuales se visualizan mediante burbujas jabón y helio con una densidad similar a la del aire. Con la ayuda de un haz de luz plano y una habitación oscura, veremos qué configuraciones de ventilación por chorro son más adecuados y cuáles menos y que ocurre al variar el caudal de ventilación. 2) Conocidas estas primeras conclusiones sobre el movimiento del aire realizaremos medidas in situ sobre el modelo para llegar a conclusiones sobre qué caudales son los más adecuados para las distintas configuraciones del modelo. Estas medidas se realizan con la ayuda de los sistemas antes explicados de visualización y equipos de medida 3) Se realizarán medidas con un anemómetro “Láser Doppler” para confirmar las conclusiones iniciales sobre el movimiento del aire y el modo en que afecta el caudal a la velocidad del aire en distintos puntos que definiremos como críticos del modelo. El anemómetro Láser Doppler permite medir la velocidad del aire en sus coordenadas x e y mediante la medición de miles partículas individuales que pasan por el punto de medida del aparato en el tiempo de muestreo. CONCLUSIONES Las conclusiones de este proyecto nos permitirán entender de una manera más concisa cómo deben instalarse y configurarse los sistemas de ventilación para conseguir resultados eficaces más allá de caudales mínimos o máximos pues el objetivo de la ventilación no es introducir y extraer aire, sino renovar el del interior para mejorar la salud de los ocupantes. Específicamente en el proyecto se concluye que para el modelo en cuestión el valor de Reynolds (calculado según apéndice) del Chorro debe ser mayor de 2600 para conseguir una mezcla correcta y que la orientación del chorro hacia paredes laterales produce corrientes fuertes en la zona ocupada

Análisis Energético de una Iglesia Histórica, Iglesia de los Marineros (Gävle - Suecia)

En este trabajo se estima el balance energético de un edificio singular, la Iglesia de los Marineros de Gävle (Suecia). Se calculan tanto sus pérdidas como sus ganancias energéticas y, tras analizarlas, se realizan una serie de medidas de ahorro tanto a nivel constructivo como de mantenimiento o comportamiento en el uso de los elementos eléctricos

Turbulent jets in confined spaces : application in mixing ventilation: experimental and numerical studies

The basis of mixing ventilation is the airflow supply to the room by means of jets initiatedfrom the ventilation diffusers. To avoid the draught problem, the design of mixing ventilationmakes uses the throw term, which is defined as the distance to the supply air terminal inwhich the jet centreline mean velocity is decreased to a given value. Traditionally, the throw ismeasured by the supply air device manufacturer. The throw is applied by designers to estimatethe velocity levels in the occupied zone. A standard for determining the throw is the CENstandard CEN/TC156/WG4 N86 "Draft Standard. Air terminal Devices. AerodynamicsTesting And Rating For Mixed Flow Application".The measurement of the throw is very time consuming even with the free jets and theinfluence of the room (the effect of confinement) is not considered. The objective of thepresent study is to give a basis for modifying the existing design and testing method used topredict the velocities in the occupied zone during the design process. A new method whichmay probably be more easier than the existing methods and at the same time give a betterprecision by including the confinement effect.In this thesis two methodological systems of experiment and numerical simulations have beenused. The numerical predictions are used in comparison with the measurements. Thereasonable agreement of the above mentioned methods is implemented to numerical study ofthe other room configurations which are not experimentally studied. This examining methodallows the possibility of studying a lot of configurations and in this manner generalising of theresults. Although the experimental part was made for both model-scale and full-scale testrooms, a large amount of data was obtained for a new test room whose dimension aresystematically varied. All of studies have been made for the isothermal case and themeasurements of velocities and pressures conducted along the room perimeters. The effect ofshort and deep rooms on the properties of the jet ( velocities, pressure, integral scale, jetmomentum, the rate of spreading of jet and turbulence intensities) have been carried out.Some old and recent investigations have been examined. Specially the concept of correlationsfrom open to closed rooms is criticised. It is also shown that the flow field in a confined roomis affected by many other factors than the Reynolds number. The surface pressure on theperimeters was used to calculate the reaction forces at the corners which causes recirculatingbubbles at corners. A study of the turbulent axisymmetric jet which is the basic element inturbulent shear flows and some restrictions of the traditional measurement techniques at theregion of interest in ventilation applications are discussed. The jet momentum is measured byweighing on a balance. Also a study of jets which collide with a wall , that is impinging jet,the effect of walls and confinement on the jet momentum have experimentally andnumerically been carried out. A new momentum balance model was developed for both thefree jet and confined one. An empirical relation has been found for estimation of the room’srotation centre which is used for validation of CFD results.Finally, it is found that the jets in a ventilated room which are a combination of free jet, walljet and impinging jet differ from the traditional wall jets. The rate of spreading of the jet andthe maximum velocity decay in a ventilated room are also different depending on the roomsize and its confinement

Miljöanalys för fordon

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Unsteady CFD simulations for prediction of airflow close to a supply device for displacement ventilation

Modern diffusers applied in the field of ventilation of rooms are often complex in terms of geometry, including perforated plates, dampers, guide rails, curved surfaces and other components inside the diffuser, with the intention to create satisfying thermal comfort for the occupants. Also connecting ducts can be different for the same diffuser in different situations, affecting the supply velocity profile. It is obvious that simulation of airflow and air temperature particularly in rooms with displacement ventilation is very troublesome, particularly if the near-zone of the diffuser is of interest. Experiments commonly indicate very high turbulence intensities in the near-zone of displacement ventilation supply devices, especially close to the floor where high mean flow gradient occurs. This indicates that the air flow from inlet devices designed for displacement ventilation might be very unstable; the position of the stream leaving the diffuser and entering the room is changing with time, hence diffusion of momentum and temperature are increased. This effect is not captured in RANS simulations, since it is performed with the assumption of time-independent conditions. In this paper URANS simulations were performed for prediction of velocity and temperature distribution close to a complex air supply device in a room with displacement ventilation. The presented study show that unsteady simulations with the realizable turbulence k-ε model generates too high eddy viscosity and therefore damps out the unsteadiness of the flow especially inside the diffuser

Investigation of flow pattern for a confluent-jets system on a workbench of an industrial space

A new air supply terminal based on confluent jets was installed on a workbench, in vicinity of a CNC machine, of an industrial space. The flow pattern and temperature field was carried out by CFD calculations and infrared camera imaging technique. A main goal of this technique is to save energy therefore the jet should distribute the air where it is desired. This is possible because the confluent jets system uses the benefits of both mixing (high momentum for better spreading of the air jet) and displacement (cleaner air in occupied zone). The results show that thermal comfort and air quality analysis relies on consistent facts and is in good agreements with the existed standards. It was shown that the supply terminal is able to spread the fresh air to the needed work area. This is an advantage of the high momentum air distribution system used in this investigation

Numerical investigation of indoor thermal comfort and air quality for an office equipped with corner impinging jet ventilation

This study investigates the feasibility of using only corner impinging jet ventilation (CIJV) for heating and cooling a medium-sized office space with two occupants while maintaining adequate indoor thermal comfort and air quality compared to traditional mixing ventilation systems. This study examines what impact various outdoor temperatures, ranging from −15°C to 25°C, have on an office environment in terms of indoor thermal comfort and air quality. Three different workspace positions were evaluated. The results show that the CIJV system meets the ASHRAE thermal comfort standards for all three positions. In terms of indoor air quality, CIJV performs better than traditional mixing systems, with improved mean age of air and ACE values. This study concludes that CIJV can be used both close and far away from the supply inlets and still provide adequate indoor thermal comfort and air quality during both cooling and heating season