AIVC, Air Infiltration Review, Volume 20, No. 1, December 1998
Ventilation Technologies in
Urban Areas
19th Annual AIVC Conference Report
at Hotel Rica, Holmenkollen Park, Oslo, Norway
The theme of the 19th Annual AIVC Conference this year was 'ventilation technologies in urban areas'. The conference, held between 28th-30th September, 1998 at Hotel Rica, Holmenkollen Park, Oslo in Norway, was attended by 76 delegates from 19 countries, who presented a total of 54 papers and posters.
Keynote Speech - Energy Efficiency Measures in Norway
The keynote speaker at the conference was Roar Brunborg, Deputy Director General of the Norwegian Ministry of Petroleum and Energy. Mr Brunborg stressed that although Norway is an energy rich country, measures still need to be taken to avoid wasting energy. He indicated that about half of the country's energy supplies are derived from renewable energy sources.
The following energy efficiency measures were indicated by Mr Brunborg to currently exist in Norway:
- information and training,
- introduction of energy efficient technologies and renewable energy sources,
- creation of networks -- an industrial energy efficiency network, and- a network for the building sector,
- normative measures, and
- research and development.
As well as the aforementioned measures, Norway is an active participant in international research projects, such as the IEA Energy Conservation in Buildings and Community Systems Programme.
Displacement Ventilation Theme in Best Paper and Best Poster
For his contribution to the conference, "A Semi-Empirical Flow Model for Low-Velocity Air Supply in Displacement Ventilation", Eimund Skaaret (NBRI, Norway) won the Best Paper award. Adding to available design methods for displacement ventilation, this model enables the calculation of the near zone for arbitrary air flow rate, supply air temperature and supply diffuser size of similar shaped diffusers. In addition, he has provided manufacturers with criteria on which to base performance documentation of air diffuser devices. Continuing this topic, the Best Poster, awarded to Magnus Mattsson (KTH, Sweden), was also concerned with displacement ventilation. In his poster, "Displacement Ventilation in a Classroom - Influence of Contaminant Position and Physical Activity", he showed how a single person walking around a classroom full of seated individuals can improve the air change efficiency. He based his conclusions upon experiments in a full-scale test room. Furthermore, he concluded that people sitting furthest away from the air supply might receive the least contaminated air, because a large proportion of the air reaching the breathing zone is reflected from the furthest wall from the supply.
The classroom with person simulators
Sketch of the set-up in the classroom
Natural Ventilation
Design
James Axley (Yale University, USA and Visiting Researcher at the AIVC) presented the initial results of work he undertook at the AIVC in summer 1998. (This work will be more fully documented in a forthcoming AIVC Technical Note.) His presentation showed how using 'pressure loop equations' may lead to feasible design solutions for natural ventilation systems. Also on the subject of natural ventilation design, Yuguo Li (CSIRO, Australia) has made a theoretical investigation of a building with two openings at different heights, a heat source, solar heat gain, and conduction losses (although no thermal mass). He showed how this can lead either to upward or to downward flow depending on the strength of the heat source. Furthermore, increasing or decreasing the heat source strength is shown to lead to flow reversals, in which the flow direction jumps suddenly from one direction to the other.
The Urban Environment
Natural ventilation in urban environments was considered by Matheos Santamouris (University of Athens, Greece). He presented the results of measurements made in ten 'urban street canyons', located in Athens, Greece, together with ventilation rate modelling results based on those measurements. From the modelling, it transpired that the flow reduction may be up to ten times that corresponding to a building without shielding, in undisturbed ambient wind conditions. He concluded that this may have implications for natural ventilation potential under those conditions.
David Etheridge (University of Nottingham, UK) gave an account of a wind tunnel experiment designed to study the effect of natural ventilation opening position on internal concentration of traffic generated pollutants. The experiment simulated the circumstance of a building situated next to a busy main road. The results suggested that by placing ventilation openings at roof level or on the leeward face of the building, a reduction of up to one third could be achieved compared with a cross ventilation strategy.
Another contributor also made use of wind tunnel experiments: Fernando Marques da Silva (LNEC, Portugal) reported how natural urban ventilation may be assessed through an integrated model. In his approach, wind information is transferred from an undisturbed area, such as an airport, by numerical modelling. This is then used as a boundary condition in wind tunnel experiments. These provide not only the pressure distribution for the specific building, but also the general patterns of flow around it. This pressure distribution is then integrated with internal building characteristics and internal heat sources or sinks in models to give an idea of the internal flow patterns.
NATVENT
In a session solely concerning the EU NATVENT Project, Søren Aggerholm (Danish Building Research Institute, Denmark) examined perceived barriers to natural ventilation in office buildings. These barriers have been identified through interviews conducted with leading designers and decision makers. Although in general the interviewees expected an increased uptake of natural ventilation in offices in future, they seemed to perceive a current lack of knowledge and experience with natural ventilation. Crucially, they commented that at present there did not seem to be enough information in existing standards and guidelines, case studies, or easy to use design tools available.
The same session also included a discussion of the control of night cooling with natural ventilation. AHC Van Paassen (Delft University of Technology, Netherlands) related how he has used sensitivity analysis to investigate various control strategy and ventilation opening configurations, for both high and medium thermal inertia buildings. For high inertia buildings, in order meet a given comfort criterion, the maximum allowable daytime heat gains were determined to be between 27 W/m2 to 32 W/m2, and 22 W/m2 to 26 W/m2 for medium inertia. An effective ventilation opening area of 2% of the net floor area, using cross ventilation, appeared to be the optimal solution.
Indoor Pollutants and their Control
Hiroshi Yoshino (Tohoku University, Japan) explained the principles behind the revised Japanese Ventilation Standard for Acceptable Indoor Air Quality (HASS-102) created by SHASE. The Standard specifies maximum acceptable indoor air concentrations for CO2, CO, suspended particulates, NO2, SO2, HCHO, radon, asbestos and TVOC's. It states that ventilation airflow rates to obtain these concentrations should be calculated for each one. For other unidentified pollutants, the ventilation airflow rate that provides 1000 ppm CO2 concentration is assumed to give acceptable indoor air quality. The overall basic ventilation requirement is then the maximum value among these airflow rates. When pollutants are not completely mixed with the indoor air, ventilation effectiveness is taken into account in the ventilation requirement calculations.
Yuichi Takemasa (ETH Zentrum, Switzerland) proposed a new concept for building performance evaluation, 'occupant contaminant inhalation' (OCI), that uses the total mass of pollutant inhaled by persons who occupy a building during its operational life. He also proposed a further, related concept of 'contribution rate of contaminant sources' (CRCS), for assessing the contribution of individual contaminant sources to indoor concentrations and OCI values.
Conference snaps: from top: AIVC staff and delegates at conference banquet; keynote speech presented by Roar Brunborg; Jean-Robert Millet discusses his poster with Marco Perino
Sometimes pollutants from exhaust air may unintentionally become re-entrained back into the intake air of the same or neighbouring buildings. Jerzy Sowa (Warsaw University of Technology, Poland) discussed different types of regulatory requirements for the prevention of re-entrainment of pollutants due to improper location of exhausts. He examined advantages and disadvantages of different types of models and their application in standards. Amongst his conclusions was that differing assumptions and simplifications made in the models cause widely varying predictions of pollutant dilution for the same distance between exhaust and air intake.
A new experimental method for the determination of the performance of air filters has been developed by Paolo Tronville (Politecnico di Torino, Italy). This is intended for filters for general ventilation applications. In his presentation, he stated that with this method, the fractional efficiency may be found for particles lying in the range 0.2 micrometres to 3 micrometres. Furthermore, he maintained that it improves on the traditional 'dust spot efficiency' method, by allowing more information to be obtained in a shorter time.
Mechanical Ventilation
The EU JOULE-TIPVENT Project, "Towards Improved Performances of Ventilation Systems", has a range of objectives, centring on: understanding the impact of air flow rate requirements in standards on the energy demand of residential and office buildings; monitoring case studies of mechanically ventilated buildings; impact of standards and regulations on performance, and performance checking and improved (smart) design of mechanical ventilation systems. Peter Wouters (BBRI, Belgium) gave an introduction to this project. (See also feature later in this newsletter.)
A case study building with an active envelope has been examined in detail by Dirk Saelens (KU Leuven, Belgium). This envelope incorporates forced convection and was designed to shelter the building from a high external noise and pollution load. It also acts as an active solar collector, decreasing cooling loads in summer, and operates as an air-to-air heat exchanger, recovering heat losses in winter. The general inference from this study was that good design and workmanship are essential to fulfil claimed performances of active envelopes.
Remediation and Renovation
Achim Trogisch (University of Applied Sciences Dresden, Germany) has made filtering and humidity measurements in dwellings of the exhaust air of bathrooms that lack windows. (Approximately 70% of dwellings in the eastern states of Germany are ventilated by natural window airing.) However, some occupants are reluctant to use the windows for ventilation due to the consequent energy cost. This may lead to mould growth. In his presentation, he suggested certain solutions to this problem.
The occupants of a block of flats in Finland were questioned about their perception of indoor air related problems before and after renovation of the ventilation system. Jari Palonen (Helsinki University of Technology, Finland) explained that the previous system, a mechanical exhaust only system without outdoor air inlets, had given rise to complaints, particularly about draught, traffic noise and dust from the street. After the installation of a new type of fresh air window, with air filtration as well as good acoustic performance, substantial improvements were found in the occupants' reactions.
Urban Transportation
Hoo Jee Poh (Nanyang Technological University, Singapore) has made a study, using computational fluid dynamics, on the effects of an air curtain upon heat and mass transfer by air movement in a bus. When the external temperature is 30 °C, and the internal temperature is controlled at 24 °C, opening of the door causes a rapid increase in internal temperature, requiring additional cooling energy and causing thermal discomfort. Using simulation, he determined that an air curtain blowing vertically downwards at 6 m/s between the interface of the hot and cold air (with a 5 s door opening delay) was best for maintaining the internal temperature.
Heat Recovery
Tests on five units combining supply and exhaust fans, filters and a heat recovery exchanger have been performed by Anne-Marie Bernard (CETIAT, France), in order to determine their thermal performance. The units are intended for use in balanced residential ventilation systems. Additionally, the influence of humidity and frost on their efficiency has been examined. The energy saving was found to be about 43% if the unit is positioned in the attic, or 66% if it is in the heated volume of the dwelling. Frost may lead to a decrease in efficiency, necessitating the use of a supplementary coil for its avoidance.
A simulation of infiltration heat recovery was reported by Max Sherman (LBNL, USA). In this study, a laminar flow model was used to simulate the air flow in various cavity wall configurations, both with and without insulation. He indicated that most heat recovery occurs at low air velocities and with long flow paths. This allows sufficient time for the heat transfer to take place. Therefore, in general, more heat recovery is observed when insulation is present.
Guest Speaker at the Conference Dinner and Closing Session
An entertaining speech was given by the Guest Speaker at the Conference Dinner, Dr Bent Børresen (Techno Consult, Norway). After the final session on the following day, the conference was summed up by Willem de Gids (TNO, The Netherlands). Then the Awards for Best Poster and Best Paper were presented by Martin Liddament, Head of the AIVC, before he closed the Conference. The AIVC would like to extend their thanks to all the contributors and participants in this year's Conference.