Applying TABS to a Publishing Company Headquarters Using Integrated Design.
INTRODUCTIONJapan is hot and humid during summer, and offices located in urban areas tend to be more densely occupierd and have highter heat load than in North American and European countries. Therefore, radiant cooling systems are not as popular in Japan. However, this project achieved comfort and deep energy-savings by adopting increased insulation, Thermo Active Building System (TABS), and a desiccant air conditioning system. In addition, floor space was maximized in a dense urban area with strict regulations of site area and building height. By utilizing a concrete slab as &a radiant surface, TABS can reduce the heat source capacity by providing a peak load shift operation utilizing the thermal capacity of the slab. Moreover, direct costs can be reduced by omitting a finished ceiling, and indirect costs can be reduced by reducting the floor to floor height. This paper describes the key points of how this project applied TABS adopted in a publishing company headquarters building located in Tokyo, Japan, and explains the performance evaluation results during the construction and operation phases.
OUTLINE OF THE PROJECT
During the project planning phase, the operation of the existing publishing company building was carefully surveyed. In the publishing company bussiness, employees usually working during different time shifts. Since starting and ending times vary, depending on their tasks, the building is open day and night. Since heat loads were unevenly distributed both spatially and timely in this building, it would be necessary to keep the energy consumption of air conditioners as low as possible, while maintaining good comfort in the new building. In addition, for their editing and publishing business, the office space needed to have many walls rather than windows on which a variety of posters, advertisements and magazine covers could be posted. Furthermore, lighting with constantly high illuminance was needed for proofreading. Aside from the workstyle related requrements, the distance between the site border and the new building wall had to be 10m or more, due to urban planning regulations. In addition, the miximum height of the new building must be 40m or less. Therefore, the total floor area compared to that of the old building would be less.
Outline of the Building
Figure 1 shows the exterior appearance of the completed building. Architectural, structural and building services technologies are well integrated into this building. In response to the building height restriction, an exposed concave-convex ceiling was adopted, which will be introduced in detail later in the paper. Under the same conditions, a typical building with a suspended ceiling would usually have 9 floors above ground. This building, however, has 10 floors and maintains a 2.8m ceiling-height on each floor, thus maximizing the total floor area. For the cooling and heating, TABS was adopted becaouse the exposed ceiling can be used as a radiant surface to create a comfortable indoor environment. Concrete walls and ceiling are also utilized as interior finishing. Table 1 shows the building data, and a typical plan and section are shown in Figure 2. Typical office floors from the 3rd to 10th floor are astylar spaces where no columns or beams are visible in the rooms. To meet the requirements of maximizing wall area and high and stable illuminance nance discovered from the preconstruction survey, structural walls are located at the perimeter of the office space on all sides. Optimum design can be seen on the facade, where become smaller as they get closer to the lower and outer sides. "Low-E" double-glazing is used for the windows to reduce skin load. 485mm(19.01in)-thick insulation covers the outer concrete walls, taking advantage of the large thermal mass of the concrete, preventing the fluctuation of indoor temperature.
AIR-CONDITIONING SYSTEM AND HEAT SOURCE
As indicated in Figure 3, cooling and heating system in this building is provided through three systems: A desiccant air-conditioning unit, which treats outdoor air, a radiant cooling system, and an air-conditioning unit, both of which handle internal loads. The radiant cooling system has a cooling capacity of 40W/[m.sup.2] (3.72W/[ft.sup.2]) per installation area. Since the installation rate is 50%, the average capacity of the cooling system for the office area is 20W/[m.sup.2] (1.86W/[ft.sup.2]), and the surface setpoint temperature is set at 22[degrees]C (71.6[degrees]F). In the event of heavy internal loads, the air conditioning unit has a maximum cooling capacity of 80W/[m.sup.2] (7.43W/[ft.sup.2]). TABS was adopted for cooling, aiming for demand suppression by peak shift operation and mitigation of indoor temperature fluctuations. In addition, the heat source system consists of three types of heat pump chillers, in accordance with load characteristics. The chilled water outlet temperature is set at 12[degrees]C (53.6[degrees]F) for TABS, and 7[degrees]C (44.6[degrees]F) for the other systems. The hot water outlet temperature is set at 45[degrees]C (113[degrees]F). The chilled water for TABS is supplied at about 16[degrees]C (60.8[degrees]F) after heat exchange. For the dehumidification in summer, heat recovery chillers are used to regenerate the desiccant and increase energy efficiency. Chilled water extracted along with hot water is utilized to cool outdoor air and handle air-conditioning loads. Additional chilled water is supplied from module chillers when necessary.
CONCAVE-CONVEX SLABS AND PLANNING OF TABS
As indicated in Figure 4, the concrete slabs which also work as radiant surfaces for TABS have a unique shape. It is made up of normal and reversed beams. The normal beams support the slab load from under the slab, while the reversed beams support from above. Both structures are alternately arranged to form concave-convex slabs. The bottom surface of the concave slab works as a radiant surface for the lower floor, while the hollow space works as a passage for fresh air and supply air for the upper floor. On the other hand, the hollow space in the convex structure works as a passage for return air and smoke exhaust from the lower floor. The concave slab is installed with plastic pipes for supplying chilled and warm water, which are covered with a 30mm (1.18in)-thick mortar and 50mm (1.97in)-thick insulation. To minimize the time difference of heat transfer from the radiant pipes and slab surface, the thickness of the slab under the pipes is minimized, to as thin as 125mm (4.92in). In addition, water pipes are installed on top of the slab instead of inside it so that the risk of water leakage to the lower floor can be mitigated. Architectual design was integrated with the structural plan by installing linear-type lights in the slits for return air, efficiently treating waste heat from LEDs. In this way, all of the space formed by the concave-convex slabs are utilized for the building services.
TABS PERFORMANCE TEST DURING THE PLANNING AND CONSTRUCTION PHASES
During the construction phase, a partial mock-up of TABS was created in an environmental test room in order to confirm the following values: concrete surface temperature, the time required to reach the target temperature, and changes in temperature after it was turned off. Temperatures were measured at the points illustrated in Figure 5. The measured temperature of each point after the cooling system was turned off is shown in Figure 5. It was confirmed that it took about 20 hours for the room temperature to drop to the same temperature as that of the lower concrete surface. In addition, the temperature of the lower concrete surface increased by 1[degrees]C (33.8[degrees]F) three hours after the cooling system was turned off, and by 1.5[degrees]C (34.7[degrees]F) after another two hours. This shows that once heat is stored in the building structure, cooling can be provided even if the air conditioner is turned off for a certain amount of time.
ENERGY PERFORMANCE FEATURES
Energy performance for the first year after the completion of the building (from May 2017 to April 2018) was evaluated with BEMS data (Figure 6). The largest value of annual power consumption of each equipment, by the time of day, is seen at 15:00, and the smallest at 5:00. The smallest value was 53% of the largest value. Additionally, 58% of the energy was consumed in the daytime (8:00-20:00), and 42% at night (21:00-7:00). Since the whole building, including its heat source and air-conditioning systems, is used 24 hours per day, the energy consumption at night tends to be high. The annual primary energy consumption of the building was 1,501MJ/[m.sup.2] * year (132kBtu/[ft.sup.2] * year), which is less than that of a typical building in Japan, which is only used in the daytime. An ordinary building in Japan typically uses is 1,737MJ/[m.sup.2] * year(153kBtu/[ft.sup.2] * year).
EVALUATION OF INDOOR THERMAL ENVIRONMENT USING HEAT MAPS
A heat map is a two-dimensional representation of data in which indices of the indoor thermal environment by the time of day are represented by colors. In the heat maps, time is given along the horizontal axis, and dates along the vertical axis. Colored cells indicate data on an hourly basis. Heat maps visualize the trend of environmental factors. Figure 7 is a set of heat maps which shows room temperature, C[O.sub.2] concentration and power consumption of electrical outlets in the office space on a typical floor in winter and summer. C[O.sub.2] concentration and power consumption of electrical outlets each serve as an indicator of occuoant density and work intensity, respectively. While the building is used for 24 hours, both C[O.sub.2] concentration and power consumption of electrical outlets are lower at night and during holidays. On the other hand, desupite the fluctuaion of loads, room temperature difference during each day is very small in both summer and winter even when the radiant cooling and heating systems are turned off. This analysis revealed with the help of external insulation, heat stored in the building structure, which is a feature of TABS, could reduce fluctuation in the indoor temperature.
FIELD MEASUREMENTS AND POST-OCCUPANCY SURVEY
Field measurements and post-occupancy surveys were conducted in the summer of 2017 and the winter of 2018 to investigate the indoor thermal environment. A total of 204 responses were collected in the summer, and 206 responses in the winter. For both questionnaires, about 60% of the respondents were male, 40% were female. In addition to the gender and age, the questionnaire investigated the sensations of the thermal environment, humidity, and air flow as well as the satisfaction corresponding to the sensation. All the sensation and satisfaction were voted on a Likert scale of 1 to 7, with an exception of airflow sensation, which was voted on a 1 to 4 scale. As shown in Figure 8 a) and b), the indoor air temperature were within the range of 24.8 to 25.5[degrees]C (76.6 to 77.9[degrees]F) in both summer and winter. Since TABS was used, the ceiling surface temperature was between 24.3 and 25.0[degrees]C (75.7 and 77.0[degrees]F) in the summer. In the winter, it was almost the same as the room temperature because TABS was not used. The change of PMV over time is shown in Figure 8 c) and d). PMV was calculated on the assumption that the metabolic rate was 1.0 met, and clothing was 0.5 clo in summer and 1.0 clo in winter. During the night and morning in summer, there were some times in which PMV was lower than -0.5, which suggests that it was slightly too cool. In winter, it was well within the comfort zone. These results imply that the room temperature could be raised in summer.
Figure 9 demonstrates the results of the questionnaire. Results in the summer are shown above, and result in the winter are shown below. In summer, 90% of the votes were either neutral or on the cooler side. Regarding humidity, there were many dry sensation votes, despite the fact that the relative humidity was 40 to 50% RH, which was not very dry after all. Approximately 65% of the respondents felt no air flow. Moer than 70% of the responses were either satisfied or neutral with the thermal environment. In winter, about 70% of the votes were either neutral or on the warm side. Similarly to the results in summer, there were more than 60% dry sensation votes, despite the relative humidity being between 40 to 60% RH, which exceeds the set point humidity of 40% RH. This may have been a result of the air temperature being quite high. In addition, approximately 70% of the respondents felt no air flow, which was also similar to the results in summer. About 60% of the respondents were either satisfied or neutral with the thermal environment. About 75% of the respondents were satisfied or neutral with the humidity and the conditions of air flow.
HEAT BALANCE IN THE ROOM
Heat balance analysis of the office space was carried out for summer and winter based on BEMS data. Figure 10 illustrates the heat balance of the cooling and heating system and room. Data collected on weekdays of July and August 2017 were used for the analysis of the summer, and data collected on weekdays of February 2018 was used for the analysis of the winter. Table 2 describes the operation modes of each system: DOAS, AHU and TABS. As shown in the table, TABS was operated either continuously or intermittently during the summer and turned off or in intermittently operated during the winter. The heat balance equations are shown below, and the parameters for the analysis are shown listed in Table 3.
* Hheat balance of the system: -(qSA + qSOA +qSW) = qOS + qHU +qL1 + qL2 +qOA (2)
* Heat balance in the room: qOS + qHU + qL1 + qOA = -(qC1-c + qC1-r + qSA-UF) (3)
The calculated and measured heat balance of the system and room are shown in Figure 11. The load ratio in summer was close to assumption made during the design phase. However, the ratio of equipment heat load was lower than the assumption made during the design phase, while the ratio of lighting heat load was higher. During the summer, close values were seen in the input energy for continuous and intermittent operations. The ratio of heat extraction from the radiant surface, in the indoor heat balance was 39% for continuous operation and 29% for intermittent operation. Heat extraction here refers to the total value of radiation and natural convection from the radiant surface. In winter, internal heat gains in both the design phase simulation and measurement were larger than the skin load. Therefore, the operational demand is inclined to be on the cooling side. Overall, load ratios calculated in the design phase were close to the measured values. However, the ratio of lighting heat was higher for the measured values, likely to be due to the lower occupant density as compared to the design phase assumption. In addition, discrepancies were seen in the distribution of heat quantity during the winter. Though design phase calculations assumed that all the necessary cooling would be provided by TABS, the measured values indicate that 40% of the coolingwas provided by the DOAS.
CONCLUSION
This paper demonstrates a case study where a comfortable environment and energy savings are put into practice through the introduction of TABS in Tokyo, Japan, where the climate is hot and humid. Normal and reversed beams were alternately arranged to form unique concave-convex slabs for TABS, integrating building services spaces into the building structure and reducing floor height at the same time. Field measurements and BEMS data analysis after building occupancy suggested that this system could contribute to the comfort and energy saving performance within the building. In addition, the calculation of the system and room heat balance sheds light on the discrepancies between the design phase assumptions and BEMS data analysis. Based on the results from this study and further monitoring of the indoor environment and energy usage, improvements will be made to achieve more comfort and energy savings.
REFERENCES
Olesen, Bjarne W 2012. Thermo Active Building Systems--Using Building Mass To Heat and Cool. ASHRAE Journal 54 (2): 44-52.
Kosuke Sato, Ph.D.
Member ASHRAE
Eri Kataoka
Susumu Horikawa
Member ASHRAE
Shin-ichi Tanabe, Ph.D.
Fellow ASHRAE
Jun Shinoda
Student Member ASHRAE
Kosuke Sato is a general manager of the mechanical engineering department at Nikken Sekkei Ltd, Tokyo. Eri Kataoka is a mechanical engineer at Nikken Sekkei Ltd, Tokyo. Susumu Horikawa is a deputy head of engineering department and principal at Nikken Sekkei Ltd, Tokyo. Shin-ichi Tanabe is a professor at Waseda University, Tokyo. Jun Shinoda is a PhD student at Waseda University, Tokyo.
Table 1. Building Data
Location Tokyo, Japan
Occupancy Offices / Retail facilities
Structure Type Base Isolation / SRC and RC
Floors 10 (+3 BF, +2 PH)
Building area 1,661.71[m.sup.2] (17,886[ft.sup.2])
Total floor area 17,972.80[m.sup.2] (193,47,886[ft.sup.2])
Building height GL+51.39m (168.6ft),
RF height: 39.39m (129.2ft)
Typical floor height 3.75m (12.3ft)
Construction period Aug 2014 to Sep 2016
Table 2 Operation Mode
Period Summer Winter
A:2017/ B:2017/ C:2018
7/1~7/21 7/24~8/31 2/1~2/20
DOAS (*1) Cooling / Heating/humidification
Dehumidification
AHU (*2) ON OFF OFF
TABS Cooling Cooling OFF
Continuous Intermittent (*3)
Period Winter
D:2018
2/21~2/28
DOAS (*1)
AHU (*2) OFF
TABS Heating
Intermittent (*4)
(*1) DOAS: Desiccant Dedicated Outdoor Air System
(*2) AHU: Air Handling Unit
(*3) From 12 : 00 to 17:00 * * * OFF
(*4) From 11 : 00 to 16:00 * * * ON
Table 3 Parameters for calculation of heat balance
Symbol Name [W/[m.sup.2]] Type
qsA Air conditioning thermal input quantity 3
qsA = -(qsoA +qsw + qLi + qos + qHU + qoA + qL2 )
qsoA Input energy of outside air treatment air conditioner 3
qSOA = QoAC {1.2{[theta]oAC -[theta]r )/3.6)
qsw Radiative (TABS) thermal input quantity 1
qSA-UF Floor air conditioning thermal input quantity 3
qSA-UF = qsA + qsoA
qos Skin load, According to separate calculation 3
Symbol Symbol Name [W/[m.sup.2]]
qsA qHU Human heat load
qL2 Lighting heat load (in the ceiling)
qsoA (q)L1 Lighting heat load (room)
qoA Equipment heat load
qsw qa-r Ceiling (Radiant)
qcl-r = -h ([theta] r - [theta] c2 )*a
qSA-UF Ceiling (Convection)
qcl-c = qSW ~qci-r
qos
[Unit] thermal input quantity * load * heat generation - W/[m.sup.2],
Temperature - [degrees]C, Air flow - [m.sup.3]/h * [m.sup.2]
[Symbol] [[theta].sub.r]: Room temperature (1), [[theta].sub.c2]:
Ceiling surface temperature [[theta].sub.RA]: Return air temperature
(3), [[theta].sub.AC] :AHU supply air temperature (1), [[theta].QAC]:
DOAS supply air temperature(1),
QAC : AHU supply air volume (1) [Q.sub.oac] :DOAS supply air volume
(1), QRA : Return air volume (1), QEA : Exhaust air volume (1), h
Convection heat transfer coefficient (4.652W/ [m.sup.2] * K), a :
Radiation Pipe installation rate :0.5
[Type] 1 and (1)-Measured value, 2-Assumed value, 3-Simulated value
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| Author: | Sato, Kosuke; Kataoka, Eri; Horikawa, Susumu; Tanabe, Shin-ichi; Shinoda, Jun |
|---|---|
| Publication: | ASHRAE Transactions |
| Date: | Jan 1, 2019 |
| Words: | 3217 |
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