Taking flexibility into account in designing beam systems

Transcription

1 Taking flexibility into account in designing beam systems Risto Kosonen and Maija Virta Halton Oy Corresponding SUMMARY In a modern office environment, balance is sought between working as individuals and the interaction between employees. It must be possible to appropriately combine various work methods, which means that partition walls and workstations should be flexibly adaptable, in order to best match the business model of each customer. The adaptability of office space is one of the central premises in designing a beam system. The systems must adapt to changed loads and partition wall locations. For a room system, adaptability means taking changes in the supply air flow, cooling effect and throw pattern of the supply air device into consideration. It must be possible to adjust the air flow supplied by the room device, which enables managing the maximum and average velocity in the occupied zone and thus reducing the risk of a draught. INTRODUCTION Recent studies have clearly proven the correlation between indoor air quality and the work performance of employees [1, 2]. Similarly, it has been demonstrated that the thermal conditions of the room have a significant impact on the productivity of work [3, 4]. Employee salaries and the potential change in productivity amount to many times the cost of a building technology system. The studies indicate that an investment in a better indoor environment is a profitable one, even with very minor productivity changes [5]. In addition to the indoor environment, the functionality of the workspace significantly affects the productivity of employees. Often a compromise must be made among the needs of the employee, team and organisation when arranging workspaces. Addressing the interaction and privacy needs of employees, both of which are important considerations in organisations, is particularly challenging. In general, it can be stated that, from the perspective of dispersing silent information (views, experiences, intuitions), fully autonomous workspaces do not support the business models of most companies. On the other hand, reducing the autonomy afforded by individual workspaces reduces acoustic privacy, which disturbs concentration. Organisational changes in most companies are continuous and require flexible changes in work methods and workspaces. The traditional one-person office areas, or cells, and open offices, or hives, seen in traditional offices are today changing into spaces that are more suited to team work, referred to as dens or clubs (Table 1) [6]. In addition to this, information technology contributes to independence of time and location, transforming offices more into meeting places for sharing information. The office space must be utilised efficiently, and therefore a dedicated workstation is no longer deemed necessary for a worker who spends only a few hours a day at the office. Working at several workstations and at customer sites is becoming more common.

2 Table 1. Adapting space types and business processes in office buildings. Space Interaction Autonomy Operation Example Hive low low customer call centre service Cell low high support tasks financial administration Den high low team work media Club high high expert work consultancy The supply air flow required in office buildings is relatively low (1.5 2 l/s per m 2 ), with the exception of meeting rooms and similar spaces. On the other hand, cooling (50 70 W/m 2 ) is required for attaining a good indoor environment. A beam system offers the possibility of achieving the above objectives within economical life-cycle cost limits. Therefore, the beam system has become the most common system in office buildings. It should be borne in mind that the various systems should be applied according to the requirements in each space. For example, variable air systems should be selected for meeting rooms and displacement ventilation for auditoriums and common spaces. Thus can an optimal overall solution be obtained with respect to expenses, energy use and environmental impact [7]. This paper discusses the flexibility requirements imposed by changing office processes for a beam system and covers certain solution models that help to improve the adaptability and flexibility of the system as well as the indoor conditions in the room. FLEXIBILITY IN A BEAM SYSTEM In Scandinavian design, ventilation beams are typically installed without a suspended ceiling in the room space, in the longitudinal direction. The basis for the system is the column spacing (e.g., 8.1 m), which can accommodate three one-person office rooms or two larger rooms (Fig. 1). This is possible because the beam is located at the side of the room instead of in the middle of the room module. Figure 1. Typical Scandinavian office building module division. The ventilation ductwork should be designed for constant pressure, which enables demand-based air flow control in meeting rooms. Pressure adjustment is implemented per

3 zone or by individual ventilation device. It should be taken into consideration in the management of air flows in a meeting room that the pressure level in a beam system is Pa and the pressure level of a typical variable air system (MIV) is considerably higher than this. The variable air unit installed in the system must operate at the pressure level of the beams. When the location of partition walls changes, the size of the room space and the supply air flow of the room device change as well. The typical office module division can result in three different cases: 1) one room device produces supply air for one room module, 2) it does so for 1.5 room modules, or 3) two room devices provide the required supply air flow for 1.5 room modules (Fig. 2). For maintaining a constant supply air flow (2 l/s per m 2 ), an adjustment range of l/s is required of the room device. This range increases to l/s if it must be possible to convert a one-person office room into a meeting room Room / Beam Space Type Primary airflow rate Nozzles HAQ Total 1 / 5 l/s 20 l/s 2 / 30 l/s 3 / Unit A 0 l/s 3/ Unit B 0 l/s 3 / Units A &B Meeting room l/s l/s 6 l/s,m2 Figure 2. Impact of room module division on the office and meeting room air flow. Ready adaptability of air flow and space arrangements also increases the need to manage air distribution such that it reflects the various space solutions. It must be possible to reduce the total air flow from a beam in situations where, for example, the room device is close to a partition wall and the distance of the workstation from the wall is short (Figure 2: room module 1). It should also be noted that, owing to individual differences between people, some people perceive even low air velocities as a draught. This means an increased need to manage the individual room conditions.

4 It is important to remember that the majority (70 80%) of the air flow distributed to the room is recycled indoor air induced by the ventilation beam through the thermal exchanger to obtain the required cooling effect. The supply air flow provided by the fans is only 20 30% of the total air flow. This means that if the supply air flow is 2 l/s per m2, the volume of air continuously recycled in the room is 8 l/s per m2. Therefore, an efficient way of managing room space air velocities is to reduce the induction ratio of the room device to an appropriate level. Figure 3 presents the principle of operation for the induction ratio adjustment in a ventilation beam. 1 2 Figure 3. Principle behind induction ratio adjustment: 1) induction ratio adjustment on and 2) induction ratio adjustment off. Figure 4 presents the impact of the induction ratio adjustment on the flow range of a CFD-simulated example room. The simulations indicate that induction ratio adjustment allows for reducing air velocities in the proximity of a window wall and at floor level. In Figure 4, induction adjustment is used on both sides of the beam. In practice, only one-sided induction ratio adjustment can be used, which lowers the effect of induction ratio adjustment on the room temperature. Figure 4. Impact of two-sided beam induction ratio adjustment on the air velocity for a sample room (threshold velocity: 0.25 m/s) and its temperature. Left: Induction ratio adjustment off. Right: Induction ratio adjustment on. Case-studies carried out in laboratories examined the significance of induction adjustment in a situation where beams installed in a suspended ceiling were perpendicular to the window. According to the measurements made, induction adjustment could significantly reduce air velocities in the proximity of the employees (Fig. 5) [8].

5 Figure 5. Impact of induction ratio adjustment on air velocity in laboratory tests. Top image: Induction ratio adjustment off. Bottom image: Induction ratio adjustment on. Induction ratio adjustment simultaneously affects air velocity and the cooling effect of the room device (by 5 15%). Depending on the design solution, the cooling effect of the room device can be decreased or increased on site depending on the induction adjustment position in the design situation. In comparing induction adjustment to adjusting the water flow in the beam, it can be determined that, when the goal is to reach the same air velocity, water flow adjustment results in a greater change in the cooling effect than induction adjustment does [9]. In addition to the maximum air velocity, induction ratio adjustment can reduce the average room air velocity. Figure 6 presents the impact of induction adjustment in a sample case on the average and maximum velocity [10]. SUMMER 0,3 v in m/s 0,2 0,1 Vave Vmax Setting (Relative) Figure 6. The impact of the total air flow supplied in the room on the maximum and average air velocity in the occupied zone as a function of the relative change of the induction ratio adjustment.

6 DISCUSSION In a modern office environment, balance is sought between work performed by individuals and in interaction between employees. It must be possible to appropriately combine various work methods, so partition walls and workstations should be flexibly adaptable if they are to best meet the business needs of individual customers. Adaptability of office space is one of the central requirements in the design of a beam system. The systems must be adjustable to address changed loads and partition wall positions. In design of a room system, this flexibility means taking account of supply air flow, cooling effect, and supply air device throw pattern changes. In addition, adjustability entails requirements concerning room automation, actuators and sensors. It must be possible to adjust the air flow supplied by the room device, which enables managing the maximum and average velocity in the occupied zone and thus reducing the draught risk. ACKNOWLEDGEMENT The writers should like to thank Tekes for funding this project. Special thanks go to Panu Mustakallio for the CFD simulations and to Harri Itkonen for constructive comments on the text. REFERENCES 1. Wargocki, P., Wyon, D. P., Baik, Y.K., Clausen, G., Fanger, P.O. (1999). Perceived air quality, SBS symptoms and productivity in an office at two pollution loads. The 8 th International Conference on Indoor Air Quality and Climate, Edinburgh. 2. Kosonen, R., Tan, F. (2004). The effect of perceived indoor air quality on productivity loss. Energy and Buildings 36, pp Wyon, D.P. (1996). Individual microclimate control: required range, probable benefits and current feasibility. In Proceedings of Indoor Air 96, Institute of Public Health, Tokyo. 4. Kosonen, R., Tan, F. (2004). Assessment of productivity loss in air-conditioning buildings using PMV index. Energy and Buildings 36, pp Hagström, K., Kosonen, R., Heinonen, J., Laine, T. (2000). Economic value of high quality indoor air climate. In Proceedings of Healthy Building 2000 Conference (held 6 10 August 2000, Espoo, Finland). 6. Flexibility Ltd., Cambridge, UK, at 7. Kosonen, R., Hagström, K., Laine, T., Martiskainen, V. (2003). A life-cycle study of an office building in Scandinavian conditions: a case-study approach. In Proceedings of Healthy Building 2003 Conference (held 7 11 December 2003, Singapore). 8. Zhoril, V., Melikov, A., Kosonen, R. (2006). Air flow distribution in rooms with chilled beams. 17 th Air-Conditioning and Ventilation Conference May 2006 in Prague. 9. Ruponen, M., Streblow, R., Mustakallio, P. (2005). Room velocity control for a room ventilation device. Paper presented at 8 th REHVA world congress CLIMA 2005 (held in Lausanne, Switzerland, on 9 12 October 2005). 10. Streblow, R. (2003). The effect of secondary volume flow in induction units on room air velocities. Hermann-Rietschel-Institut fur Heizungs-und Klimatechnik, Technical University of Berlin, Diploma Thesis no. 343, 2003.