For several years the technology of chilled ceilings has been a favourite issue among HVAC technicians and underwent a boom in the past few years. According to the survey of a German technical journal, on March the first 1993, a total of 308,490 m² of chilled ceilings had been installed in German buildings, out of which 69 per cent had been installed in new buildings and 31 per cent in modernized projects. Cooling ceiling systems are the ideal.application where high demands are placed on comfort requirements and where the energy loads are very high compared to material loads.
Mechanical ventilation with heat recovery (MVHR) and passive stack ventilation (PSV) systems are both proposed as methods of ensuring satisfactory ventilation rates in UK housing. MVHR provides controlled ventilation in all rooms together with heat recovery, while the cheaper PSV system offers lower running costs, but without heat recovery and without a controlled air supply to all rooms. The relative energy consumption of the two systems depends on a number of factors that are difficult to predict.
For thermal comfort and energy conservation reasons, displacement ventilation and radiative cooling systems are increasingly used. Simulation programs are generally not able to correctly simulate such systems because of their one node approach for the air temperature. A procedure for creating DOE-2 inputs to simulate both system types each alone or in combination - without program code change - was developed, based on a more detailed new TRNSYS-Type, and validated against existing experimental data sets.
The continual reduction of the transmission heat losses of residential buildings causes an increasing importance of the ventilation heat losses. Energy saving can be achieved by using a mechanical ventilation system with heat recovery. A great improvement is the combination of heating and ventilation in one system. In this project such a combined system was developed to reduce the energy consumption of the fans, the operating expenses and also the investment costs in comparison to existing systems. In future a high market acceptance is expected for combined heating and ventilation systems.
In conjunction with IEA Annex 18, DCV-systems, a test on an auditorium in a school in Tyreso south of Stockholm has been carried out. The auditorium has 450 seats on a slightly sloped floor and a ventilation system with low impulse air supply devices placed at the lower (front) part of the auditorium. The system is intended to act as a displacement ventilation system during operation with heat load from people. The flow rate is governed by a CO2 sensor in the exhaust air device. In non-operational state, and if heating is necessary, the system operated with recirculation of air.
The paper presents a criterion to assess the performance of mechanical exhaust hoods for dome stic kitchens and a procedure to experimentally test them; an analysis of the relevant parameters which affect their performance is made, the test results are shown, and finally these are compared with the results of a numerical fluid dynamic code. Experiments were performed using the tracer gas technique, and attention has been drawn rather on the hood efficiency in the removal of pollutants than on the IAQ in the test room.
A test room which was built at a scale 1:5 to the original one has been used to investigate air-conditioned rooms. The original room was specified by the international project IEA ANNEX 20. A lot of experiments were made on different inlet geometries and air change rates. Velocities and turbulent quantities were measured not only in the inlet plan but also in the room itselfby means of hot wire anemometry. The ammonia absorption method according to Kruckels has been applied to determine the heat transfer coefficients at the walls. Qualitative results were obtained by laser light sheets.
The efficiency of removing excess heat by employing mixing ventilation is based on the properties of jets. Therefore the behaviour of jets in enclosures is important. A correct supply design is essential otherwise the jet will separate from theceiling and drop into the occupied zone. This will give rise to unacceptable high velocities. the basic properties of jets in ideal situations like an infinite space are well known. However, in a room the jet interacts with the room air and the room surfaces.
A new miniature mechanical ventilation system with both supply and extract air and an air-to-air heat exchanger has been developed in Great Britain and Denmark. The system which is intented to ventilate a single room has the dimensions of a shoe box and can be placed/installed on the inside wall in an existing air vent. The system can operate with two air flows, 40 or 70 m³/h. At the low speed the noise is insignificant, intended to be "not disturbingN in sleeping rooms.
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