THERMAL ENVIRONMENT IN OFFICE ROOM SERVED BY TASK/AMBIENT AIR-CONDITIONING SYSTEM WITH NATURAL VENTILATION T. Ushio1†, S. Horikawa1, K. Sagara2, T. Yamanaka2, H. Kotani2, N. Mishima3, and T. Yamashita4 1

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Nikken Sekkei Ltd., Japan Department of Architectural Engineering, Osaka University, Japan 3 The Kansai Electric Power Co. Inc., Japan 4 Sanki Engineering Co., Ltd., Japan

ABSTRACT A task/ambient air-conditioning system with natural ventilation was installed in a high-rise office building in Osaka, Japan. This paper will report the results of the field measurements of indoor thermal environment and natural ventilation opening performances. From the thermal environmental aspect, the office is properly divided into working “task” zones and a general “ambient” zone so as to ensure both occupants’ comfort and energy savings. Task air-conditioning is for satisfying individual thermal preferences by using floor outlets. Ambient air-conditioning for the ambient environment is moderately controlled with ceiling outlets. Natural ventilation substitutes for ambient air-conditioning during good weather conditions. Natural ventilation openings are so shaped to diffuse the air along the ceiling and send it as deep into the room as possible. The air flow from task floor outlets makes small temperature differences between the upper space and the lower space in the task zones and gives occupants thermal comfort. Sufficient ventilation can be ensured by this type of natural ventilation openings, and the differences in the room temperature are small among various places due to air flow along the ceiling surface. Heat consumption by ambient air conditioning was reduced by the natural ventilation by 1/3 for the measurement period.

KEYWORDS task/ambient air-conditioning, natural ventilation, thermal environment, thermal comfort

Introduction The task/ambient air conditioning system intensively controls thermal environment of the task area in the office environment and mitigates that of the ambient area to ensure both occupants’ comfort and energy savings. Natural ventilation can be utilized as ambient air conditioning for a long time in a cycle of a year. In an office room introducing the task ambient air conditioning system with natural ventilation, we measured the indoor environment in a case where natural ventilation was used alternatively for air conditioning in the ambient area (task air conditioning with natural ventilation), a case where the air conditioner was used (task/ambient air conditioning) and a case where only the ambient air conditioner was used (ambient air conditioning). We will report the field measurement results and the natural ventilation opening Photograph 1: performances. The high-rise office building

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Corresponding Author: Tel: +81-6-6203-2361, Fax: +81-6-6203-4278 E-mail adress: [email protected]

Main Application Total floor space Typical floor space Number of floors, Height Location Completion A/C system on typical floor

Table 1: Outline of the building Office, district cooling and heating facility Approx.106,000 m2 2 2 Approx. 2,000 m （effective area: Approx.1,400 m ） 5 basements and 41 floors above grade, 195m Nakanoshima, Kita-ku, Osaka City, Japan December, 2004 Task/ambient air-conditioning system using natural ventilation

Outline of natural ventilation Figure 1 shows the typical floor plan. Natural ventilation was performed on the 14th to 17th and 27th to 35th floors (13 floors in total). For natural ventilation, Twenty-six openings of 0.4 m2 were provided on each floor. The total opening space of 10.4 m2 (= 0.4 m2 x 26) corresponded to approximately 1/135 of the floor space that was rather large in a high-rise building. Figure 2 shows the concept of natural ventilation and task/ambient air conditioning. The following devices were provided about natural ventilation openings to prevent invasion of gust on upper floors, introduce the wind deeply into the room and save energy consumption. 1) Traps were installed in eaves to prevent rainwater and mitigate the strong wind. 2) The natural ventilation outlet had such a shape as to introduce the wind along the ceiling surface. 3) Natural ventilation openings were automatically controlled according to the indoor and outdoor conditions. Table 2 shows the opening condition of natural ventilation openings. The natural ventilation was automatically controlled to reduce as much energy consumption as possible. Photograph 2 shows the external view and internal view around natural ventilation openings. Table 2: Opening condition of natural ventilation openings 1) Indoor-outdoor pressure difference : 50 Pa or less when open 150 Pa or less when closed 2) Outside air temperature: 18ºC or more 3) Outside air humidity: 90% or less 4) Outside air enthalpy: Less than indoor enthalpy 5) Room temperature: Preset temperature between -2 ºC and +1 ºC -> Partly open Preset temperature between +1ºC and +3 ºC -> Fully open

Fig.1 Typical floor plan

Fig. 2 Concept of task/ambient air-conditioning with natural ventilation

Photograph 2: External and internal view of natural ventilation openings

Outline of task/ambient air-conditioning The working area was regarded as the task area, a general area was regarded as the ambient area, and each area was controlled separately. Task air conditioning is done by floor supply system. Figure 3 shows task floor outlet. Office workers can adjust the thermal environment by adjusting the task floor outlets. Office workers can easily change the air movement direction, air flow status (directional or diffusive) and air volume (high, low or OFF, 110 m3/h/outlet when high) of the task floor outlet. Ambient air conditioning is done by ceiling supply system. Mitigating ambient thermal environment (28ºC during cooling) could reduce energy consumption. Table 3 shows the outline of task/ambient air-conditioning.

Air conditioning Supply air volume Control

Fig. 3: Task floor outlet Table 3: Specifications of task ambient air conditioning Task Ambient 17.0 m3/h/m2 6.9 m3/h/m2 Constant supply air temperature and VAV control to constant indoor constant air static pressure control temperature

Outline of field measurements Field measurements were conducted on 30th floor (Measurement points: Fig. 1). On the Detailed measurement area (Fig.1, 16), we measured room temperature at 144 points, air movement velocity at 36 points, globe temperature and humidity at 4 points. Airflow velocity was measured at all natural ventilation openings. Table 4 shows the outline of field measurements. One hundred ten black lights (60 W) simulating the human bodies were installed at each desk. Personal computers were set in the standby status. The illumination was lit. Table 4: Field measurement conditions Pollen and noise Task A/C with natural Task ambient Ambient A/C Case measurement ventilation A/C ’05 Spring/Autumn: ’05 Summer: ’06 Winter: ’06 Spring: Measurement Apr.23 to May 1 Jul.16 to Jul. 22 Jan.19 to Jan.27 Apr.21to May 26 period Oct.23 to Nov. 4 Task A/C ON ON OFF OFF Task floor outlet Diffusive Diffusive*1 Holiday: OFF ON ON ON Ambient A/C Weekday: ON Natural ventilation Holiday Fully open Closed Closed Controlled openings Weekday: Controlled *1: Task air flows were changed in only detailed measurement area.

Field measurement results during task air-conditioning with natural ventilation Indoor airflow and temperature distribution The shape of the natural ventilation outlet was so designed as to introduce the wind deeply into the room. Figure 4 shows typical examples of constant velocity distribution at the air outlet in the environmental laboratory. We adopted the shape C that allowed airflow of 0.5 m/s to reach a position of approximately 7 m at the height of 1.1 m. Figure 5 shows the temperature distribution in the east-west direction created from the field measurement results of the west wind in autumn. The figure shows that the outside air supplied from the west to the office room is introduced and diffused along the ceiling deeply into the room until

Fig. 4: Constant velocity distribution in the laboratory (Supply velocity: 2 m/s, supply temperature difference: 6ºC)

approximately 15 m. Figure 6 shows visualized outside air flowing from the natural ventilation openings on the north side. The figure shows that the outside air is carried into the interior along the ceiling. Figure 7 shows correlation between the wind velocity by the Osaka District Meteorological Observatory and air change rate of indoor room by ventilation. Three to six air change rate by ventilation is assured when the wind velocity is 2 m/s and six to nine ACH is assured when 4 m/s. While the ventilation panel is partly open, air change rate of ventilation is approximately 70% of the case where the ventilation panel is fully open. When the north wind is blowing, the ventilation air volume is large against the wind velocity.

Fig. 6: Visualized airflow of north wind (autumn) (External wind velocity: 2 m/s, airflow velocity at natural ventilation opening: 1 m/s) Natural ventilation achievements and load reduction quantity Figure 8 shows the natural ventilation achievements. Approximately 50% of natural ventilation openings were opened. The temperature difference between the east and the west (①, ② and ④ in Fig. 1) was 0.2ºC on an average and 1.6ºC at a maximum, and there was not much difference between the windward and the leeward. Natural ventilation was not made on the 15th floor so that the natural ventilation performance could be compared. When the difference in heat quantity between the 15th floor and the 30th floor is regarded as heat quantity removed by natural ventilation because the internal load and air conditioning time are almost equivalent between the two floors, the heat quantity consumption was reduced by 36% mainly around the ambient air conditioner with natural ventilation during this period. Figure 9 shows the natural ventilation opening open time and the cooling load reduction quantity on an average between

Fig. 5: Temperature distribution at east-west section (autumn)

Fig. 7: External wind velocity and air change rate by natural ventilation

Fig. 8: Natural ventilation performance (October 24 to October 30, 2007)

the 15th and 30th floors for the year. Natural ventilation was used in April to June and September to November, and used for a long time in May and October. The annual total use time was 918 hours. The annual cooling load reduction quantity achieved by natural ventilation was 67,421 MJ/floor that occupied 13.3% of air conditioning on the typical floor. Indoor and outdoor pollen quantity Figure 10 shows the average outside air temperature from 9:00 to 18:00 by the Osaka District Meteorological Observatory and pollen quantity (mainly from Japanese cedar). The pollen quantity decreases drastically from May. When the minimum outside air temperature for natural ventilation is set to 18ºC, it is thought that pollen gives considerable effect only in the latter half of April because natural ventilation openings are opened automatically later April. We measured the indoor pollen quantity at a point of 0.75m above the floor, 3.6 m distant from the west window surface on the 30th floor (approximately 133 m in ground height) usually and at a point inside the natural ventilation opening on the same floor for last one week in the measurement period, and the outdoor pollen quantity on the roof (approximately 190 m in ground height) using a light scattering type pollen sensor. Figure 11 shows the pollen quantity on the 30th floor and the rooftop. Figure 12 shows the average pollen quantity on holidays and weekdays. The pollen quantity was larger on the 30th floor than the roof on weekdays when there were many workers, but the measurement result was reverse on holidays when there were a few workers. The difference in pollen quantity from the roof was smaller in the pollen sensor inside the natural ventilation opening than inside the room. It is postulated from the above results that the pollen quantity carried by people is larger than the pollen quantity coming in through natural ventilation openings. This item should be examined also in the future because the pollen sensor precision may give some effect. There have been no claims about pollen accompanied by opening of natural ventilation openings in the measured building.

Fig. 9: Natural ventilation opening open status and heat extraction by natural ventilation

Fig. 10: Daily average outdoor air temperature and pollen quantity

Fig. 11: Pollen quantity in the 30th floor and outdoor

Fig. 12: Average Pollen quantity on holidays and weekdays

Indoor noise Figure 13 shows changes in indoor noise when natural ventilation openings were open and closed on the 15th and 30th floors. Because the indoor-side chamber of natural ventilation openings had sound-absorption lining, noise was achieved to realize approximately 41 dB (A) (20 dB (A) decay) when natural ventilation openings were open, and approximately 36 dB (A) (25 dB (A) decay) when natural ventilation openings were closed while the outdoor noise was 58 to 63 dB (A). It is confirmed by this result that noise entering from the outside does spoil working conditions.

Fig. 13: Noise around natural ventilation opening

Field measurement result during task/ambient air-conditioning Figure 14 shows the task/ambient supply air temperature and indoor temperature during task/ambient air-conditioning. The temperature was lower in the interior than at the perimeter, the planar temperature difference was 2 to 3ºC, and the indoor temperature was kept in a range from 25 to 28ºC. Figure 15 shows visualized airflow blown out of the task floor outlet in the task area. Fig. 14: Task/ambient supply air temperature and This figure clearly shows airflow changes indoor temperature in summer given by changeover between “directional” and “diffusive” of the task floor outlet. Figures 16 and 17 show temperature and wind velocity distributions around an occupant in the detailed measurement area created from field measurement result. When the task floor outlet was closed, the temperature was 23.5ºC on the floor surface and 24.5ºC at the height of +1.1 m above the floor in the rear of an occupant. When the task floor outlet was open and set to “diffusive”, the low temperature area rose upward and task thermal zones was formed separately. When the task floor outlet was Fig. 15: Visualized airflow in field measurement in set to “directional”, the low temperature area office room was formed around the rear of an occupant toward which the blown-out airflow went. When the task floor outlet was closed, the temperature gradient between the floor and the ceiling temperature was small. The temperature difference was 1.2C between them. When the task floor outlet was open, cold wind was blowing to an occupant mainly at the height of +0.6 m above the floor. The airflow velocity was 0.15 m/s in the “diffusive” mode, and 0.25 m in the “directional” mode. It is expected that thermal environment can be changed by changing the mode. Figure 18 shows PMV at the height of +1.1 m above the floor near the rear of an occupant. The amount of clothing is set to 0.7 clo, and the quantity of metabolism is set to 1.2 Met. The PMV substantially changed depending on the open status of the task floor outlet. PMV was approximately 0.5 when the task floor outlet was closed, approximately 0.2 when the task floor outlet was open and set to “diffusive”, and almost 0.0 when the task floor outlet was open and set to “directional”. It is necessary to evaluate local thermal environment, but it is thought that the thermal environment can be changed when occupants manipulate their air outlets in the task area.

Fig. 16: Temperature distribution around an occupant

Fig. 17: Vertical distributions of temperature and airflow around an occupant

Fig. 18: PMV around an occupant (detailed measurement area)

Field measurement result during ambient air conditioning Task air conditioning is turned off and only ambient air conditioning is done in winter because there is few requests for cooling. Figure 19 shows the temperature at the indoor temperature measurement points ②, ③ and ⑤ shown in Fig. 1, ambient supply air average temperature, and return air average temperature on January 19 when the outside air temperature was lowest during the measurement period. There was much fluctuation in the supply air temperature while the air conditioning system was operating, but the indoor temperature was approximately 21ºC at the perimeter and approximately 23ºC in the interior. It can be seen that the temperature in the office room was almost kept in a range from 21 to 23ºC, and the thermal environment was stable while the air conditioning system was operating. Figure 10 shows the average temperature distribution in the detailed measurement area during the air conditioning time period (from 9:00 to 18:00). It can be seen that the temperature was approximately 20ºC and rather low on the floor surface near the window, but 21 to 22ºC around an occupant. It can be seen that temperature difference in the vertical direction was approximately 1ºC.

Fig. 19: Task/ambient supply air temperature and indoor temperature in winter (January 19, 2006)

Fig. 20: Temperature distribution around an occupant near a window (Average values from 9:00 to 18:00 on January 19, 2006)

Conclusion We have measured the indoor environment made by task/ambient air-conditioning with natural ventilation, and found the followings: 1. Natural ventilation openings developed at this time allowed external airflow to reach until approximately 15 m when the external wind velocity is 1.7 m/s and the indoor air blow temperature is 20ºC, and offered the sound shielding performance of approximately 20 dB (A) in the open status. 2. Because secured natural ventilation openings corresponded to approximately 1/135 of the floor space, the assured ventilation air volume corresponded to 3 to 6 ACH by ventilation when the external wind velocity was 2 m/s, and 6 to 9 ACH by ventilation when the external wind velocity was 4 m/s. 3. The achievements in the year were as follows: - Natural ventilation openings were open for 918 hours. - The heat quantity of 67,412 MJ per floor was removed by natural ventilation. 4. It is expected that the thermal environment of each person can be adjusted by manipulating his/her air outlets on the floor in the task area. 5. The temperature in the office room was controlled in a range from 21 to 23ºC during ambient air conditioning in winter. 6. The difference between the maximum temperature and the minimum one was approximately 1ºC, and the thermal environment was 21 to 22ºC around an occupant near the north window surface.

REFERENCES Tomoaki Ushio et al. 2006. Task Ambient Air Conditioning System with Natural Ventilation for High Rise Office Building(Part 1), Proceedings of Healthy Buildings 2006, Vol.4, pp.269-274 Hisashi Kotani et al. 2006. Task Ambient Air Conditioning System with Natural Ventilation for High Rise Office Building(Part 2), Proceedings of Healthy Buildings 2006, Vol.5, pp.135-140 Eunsu Lim et al. 2007. Airflow Characteristics in Room with Hybrid Air-conditioning System of Task Air Supply and Natural Ventilation, ROOMVENT 2007 Eunsu Lim et al. 2007. CFD Analysis of Airflow Characteristics in Office Room with Task Air-conditioning and Natural Ventilation, IAQVEC 2007