Abstract
(Englisch)
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Objectives
The aim of AIRLESS is to develop strategies, principles and protocols to improve and control the performance of air handling systems and components in buildings for incorporation in codes and guidelines.
The Swiss contribution is focused on the following items:
- The development of a diagnosis procedure able to quantify airflow rates, to detect and quantify leakage and shortcuts in air handling units. This procedures also allows to assess the overall ventilation efficiency in the ventilated space, and the power efficiency of fans and heat recovery units.
- To develop a testing protocol for rotating heat exchangers, allowing to quantify the transfer of contaminants from exhaust to supply air.
- To apply these diagnosis protocols to 10 air handling units and 5 rotating heat exchangers, and to use this experience to draft new maintenance strategies.
- To assess the effects of improved units and improved maintenance on energy use.
- To propose innovative solutions to improve the quality of supply air.
Results
The diagnosis procedure includes methods to measure the following quantities:
1. Main, secondary, and leakage airflow rates in air handling units, using multi-tracer gas dilution technique.
2. The mean age of air in the ventilated space and global ventilation efficiency in two-way air handling units.
3. The heat recovery efficiency by heat exchangers
4. The fan power efficiency.
5. The transfer rate of organic volatile compounds from exhaust to supply air through rotating heat exchangers
A PC-based computer program to help in planning and interpreting such experiments, initially developed within a national project , was greatly expanded and adapted to the purposes of AIRLESS. This tool helps in preparing the experiments and in interpreting the raw results to obtain the quantities mentioned in items 1 to 4 above.
Twelve units were measured according to this procedure. In one such unit, the CO2 generated by occupants was used, in parallel with tracer gas, to check this simple method.
The principles used in this test protocol and some results were presented to the scientific community and to professionals in several conferences . A 30 hours lecture on the method was presented (on invitation) at the National University of Singapore
The transfer rate of various volatile organic compounds by rotating heat exchangers was measured in two units and in different cases (with and without purging sector, at various temperatures, with and without filters). These measurements show that this transfer can be significant in some cases, in particular for low-boiling point compounds or when the heat exchanger is not well installed.
The effects of improved units and improved maintenance on energy use were assessed by numerous simulations, using a comprehensive model developed on purpose. One of the interesting results is that hybrid ventilation is very effective to ensure a comfortable indoor climate in office buildings at low energy cost. Another results from experiments on real units is that heat recovery can be partly or completely hindered by lack of building envelope air tightness or by parasitic recirculation.
Conclusions and perspectives
The results of the AIRLESS project were not just meant to be of a scientific character but were thought, and most of them also planned, to become tools for the intervention in the real world of the design, commissioning and maintenance of HVAC-systems for better IAQ.
From the point of view of source control, the first aim was to characterise the HVAC-components as potential pollution sources, and to understand why and how some components are more important as pollution sources than others. Protocols to assess the degree of cleanliness of the different components and to define a strategy for clean HVAC-systems are published. Then, the final aim was to be able to give relevant inputs to better design, better commissioning and better maintain air-handling units, under the IAQ perspective.
From the ventilation point of view, the issue was to evaluate what is the contribution of the HVAC-systems for the pollution load in a given space, in parallel with the occupants and the materials, and to determine what is the appropriate level of ventilation to cope with that load in order to keep the levels of indoor pollutants below a certain threshold. This requires the knowledge of the nature of the pollutants and the quantification of the pollutants emitted.
From the energy aspect, it was found that envelope air tightness is paramount for achieving good ventilation at low cost. Humidification and mechanical cooling are significant energy users. Mechanical ventilation, when used in conjunction with night natural ventilation for night cooling, can ensure a low flow hygienic air change, without the necessary high intensity cooling. In many cases, when applicable, naturally ventilated buildings do present similar heating demand than low flow mechanically ventilated systems and smaller electricity consumption.
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