Thermal Comfort and Energy Consumption according to the Indoor Control Logic S. Kim 1 and D. Song 2 1 Department of Civil and Environmental System Engineering Sungkyunkwan University, Suwon-si, Gyeonggi-do 16419, Korea 2 School of Civil, Architectural Engineering and Landscape Architecture Sungkyunkwan University, Suwon-si, Gyeonggi-do 16419, Korea SUMMARY Indoor thermal environment or thermal comfort is the result of a combination of various factors such as air temperature, humidity, air speed, radiant temperature, clothing, activity, age, gender and so on. In terms of indoor control logic, it is important to consider these elements. Set-point temperature control which is used in most of buildings may not be sufficient in terms of thermal comfort and energy saving. In this paper, indoor thermal environment and energy use characteristics according to the control logic such as set-point temperature control, PMV control, comfort domain control proposed by ASHRAE will be analyzed by simulation method. The results showed that indoor thermal environments of the analyzed control logics are controlled in PMV and ASHRAE comfort zone. Comfort domain control not only satisfies thermal comfort zone, but also achieves energy saving compared with the other analyzed cases. clothing insulation, and activity), and expresses thermal comfort as quantitative numerical value (-3.0 - +3.0) (ASHRAE 2013). ASHRAE suggests the comfort range as shown in Figure 1. The comfort range is proposed for the summer and winter season. Generally, psychometric chart shows the state point of the dry-bulb temperature. But ASHARE Comfort Chart shows the comfort zone based on the operative temperature (OT), that is considered the influence of radiation. Although ASHRAE comfort chart does not define the range of relative humidity, in this study, we consider RH 40 to 60% as a comfort humidity range in terms of not thermal comfort but health. Analyzed Cases In this study, the control behavior of indoor thermal environment and energy use profiles were analyzed. The analyzed cases were shown in Table 1. In Case 1, Set-point control was analyzed. PMV control with comfort range (-0.5 - INTRODUCTION Indoor thermal environment is the result of complex interaction between environment factors (temperature, humidity, air velocity, mean radiant temperature) and personal factors (clothing, activity, age, gender). Indoor environment is controlled by set-point temperature in most buildings because of its simplicity. However, this control method may arouse thermal discomfort with the narrow temperature range and result in excessive energy consumption. In order to maintain the indoor environment with comfort and energy efficient, it is necessary to consider the various factors and its interaction. Many researchers study thermal indexes to evaluate thermal comfort such as PMV, OT, ET*, SET*, ASHREA Comfort Zone, and Adaptive Model. PMV is a representative index that indicates human thermal comfort. ASHRAE Comfort zone recommends the comfort range with operative temperature and humidity. Figure 1. ASHRAE Comfort Chart In this paper, indoor thermal environment and energy use characteristics according to the control logic will be analysed by simulation. METHODS Comfort Index PMV(Predicted Mean Vote), a thermal equation derived from analytical and empirical formula based on heat balance model, represents human thermal comfort (Fanger 1970). PMV indicates the thermal comfort with six variables (temperature, humidity, air velocity, mean radiant temperature (MRT), Figure 2. Analyzed Model Floor Plan ISBN: 978-0-646-98213-7 COBEE2018-Paper133 page 363
Table 1. Control Cases Cases Case1 Case2 Case3 Set-point Control PMV Range Control Cooling Control Mode Variable Control Logic Dry-bulb Temperature (DT) Set-point Control DT, MRT, RH, Air Velocity Range Control Operative Temperature (OT), Wet-bulb Temperature (WBT) Initial Cooling (OT, 24 o C) + Step Control Range/Value 26 o C -0.5 - +0.5 23.5-26.5 o C (OT), 16-20 (WBT) Ventilation ERV ( Exchange Mode) Table 2. Characteristics of Wall Materials Thick ness Capacity Capacity Den sity Unit m kj/hmk kj/kgk kg/m 3 Exter nal Wall Interi or Wall Floor Concrete 0.200 5.86 0.88 2198 Insulating Files Granite Stone 0.006 0.14 0.84 12 0.030 12.60 1.00 2800 0.014 5.02 1.13 2019 Brick 0.200 2.92 1.00 1800 0.014 5.02 1.13 2019 Vinyl Tile 0.003 0.612 1.40 1200 Table 3. AC System 0.027 5.02 1.13 2019 Concrete 0.150 5.86 0.88 2198 Air 0.700 0.047(hm 2 K/kJ) Tex 0.006 0.76 1.13 400 Unit Frequency 60 Hz Performance Cooling 8.3 kw Power Consumption Cooling 2.15 kw Indoor Unit 50 W Air Flow Rate 21 CMM +0.5) was represented in Case 2. Comfort mode controlled the indoor environment with operative temperature range (23.5-26.5 o C, summer) (Case 3). The analyzed building is classroom with an area was 67.24 m 2 located at Gimpo, Korea which were shown in Figure 2. The construction of wall was shown in Table 2 which complied the Table 4. ERV System Max Unit Air Flow Rate 800 CMH Power Consumption 290 W Exchange Rate Table 5. Simulation Conditions Weather Data Simulation Period Zoning Site Sensible 71 % Latent 44 % Seoul, Korea (TMY2) 25 th July J High-school, Gimpo, Korea Area 67.24 m 2 Volume 174.82 m 3 Occupants 30 person Gain Person Sensible 65 W Latent 55 W Activity Seated, light writing Lighting 15 W/m 2 System Operation Schedule 09:00~17:20 (on) Other hour (off) Energy Saving Design Standards of Building in Korea (Ministry of Land, Infrastructure and Transport 2008). Multi Split Air-conditioner and Energy Recovery Ventilation system (ERV) were installed in the classroom. System performance and energy consumption were shown in Table. 3. Table.4. Set-point control adopts on-off control and operated the compressor and indoor fan unit according to the indoor temperature condition (Case 1). PMV range control (Case 2) operates compressor and indoor fan unit until PMV up to -0.5 (cooling mode), and then only indoor fan unit is operated up to PMV +0.5 (blower mode). Comfort control (Case 3) is similar to PMV range control logic and operates cooling/blower mode according to the operative ISBN: 978-0-646-98213-7 COBEE2018-Paper133 page 364
4th International Conference On Building Energy, Environment Operative Temperature( ) 28 27 26 25 24 23 Figure 3. Operative Temperature ( ) 65 Relative Humidity(%) 60 55 50 45 40 35 Figure 4. Relative Humidity (%) 1.00 PMV Value ( ) 0.75 0.50 0.25 0.00-0.25-0.50-0.75-1.00 Figure 5. PMV (-) temperature range (23.5-26.5oC). The compressor is adjusted by the partial load condition. Simulation Model The indoor thermal environment on July 25, and the energy consumption during July were analyzed using TRNSYS simulation method (TRNSYS Reference 2000). Table. 5 showed the simulation conditions. The specifications of Multi Split Air-conditioner and ERV were applied based on ventilation requirement of school building in Korea, 21.6 CMH/person (Jeo 2008) and 30 persons per classroom (Center for Educational Statistics Information 2015). Infiltration rate was set at 0.2 time per hours suggested by ISBN: 978-0-646-98213-7 Figure 6. Psychrometric Chart Korean Buildings Total Amount of Energy Consumption. Indoor air velocity was set at 0.1 m/s in static indoor air velocity. Clothing insulation and activity level were set at 0.5 clo in summer and 1.1 met, respectively (ASHRAE Standard 552013). COBEE2018-Paper133 page 365
RESULTS To analyze the indoor thermal environment and energy consumption by control method, a simulation was conducted on July 25. Indoor thermal environment Figure 3, 4 showed the indoor operative temperature(ot) and relative humidity distribution according to the control method in the analyzed classroom. The operative temperature was a sensible temperature considering the influence of radiant heat transfer between human and ambient of the classroom. The distribution of the operative temperature and relative humidity was almost satisfied with comfort range of operative temperature (23.5-26.5 o C) and relative humidity (40-60%) in all cases. Case 1 was controlled by on-off control and showed a narrow OT range of 26.1 o C to 26.4 o C, and 47.8 to 50.8% of relative humidity. The OT and relative humidity was 24.9-26.3 o C and 47.8-52.0%, respectively, in Case 2. In Case 3, OT was ranged 24.7-26.2 o C and RH 48.0-52.0%. The range of the OT and RH was controlled within the ASHRAE Comfort zone in all cases in this study. The indoor thermal environment was controlled in similar range in Case 2, 3. The indoor PMV distribution during the operation hours was shown in Figure 5. The average of PMV was 0.34 in Case 1, 0.09 in Case 2 and Case 3, and the indoor thermal condition of the analyzed cases were satisfied the PMV comfort range (-0.5 - +0.5). Case 2 and Case 3 showed a wide range of PMV distribution compared with the Case 1. Control behaviors Figure 6 showed a control behavior of indoor thermal environment in Psychometric chart. The OT moved up and down with on-off control in Case 1. The OT was changed with broader range in Case2 and 3 compared to the Case 1. Figure 6 showed the operation pattern of the air-conditioner in each case. 1 was cooling mode and 2 was blow mode in Case 2. 1 initial cooling mode, 2 blow mode, 3 2 nd cooling mode in Case 3. AC Operation Hours and Patterns Figure 7 showed the pattern of compressor operation. Figure 8 showed the compressor operation hour during class time (09:00-17:20, 8.4 hours). 1 cycle in case 1 was about 4.2 minutes (2.7 minutes was cooling and 1.5 minutes was off). The compressor operating hour in Case 1 was the longest among the analyzed cases, 5.4 hours (65.0% of the class time), because on-off was frequently repeated with the narrow range of OT. In Case 2, 1 cycle was about 26.3 minutes with the pattern of cooling (7.8 minutes) and blowing (18.5 minutes), and the compressor operating hours was 2.5 hours (29.8% of the class time). The 1 cycle in Case 3 was about 31.2 minutes with cooling (10.9 minutes) and blowing (20.3 minutes) and the compressor operating hours was 2.9 hours (35.0%). Case 2 showed the lowest compressor operation time. The compressor operation time in Case 3 showed about 0.4 hours longer than Case 2. It is because the cooling time was longer according to partial load operation in Case 3. PMVRange Control 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Figure 7. Compressor Operation Pattern AC Operation Hours(Hours) 6.0 5.0 4.0 3.0 2.0 1.0 0.0 5.4 2.5 2.9 Figure 8. Compressor Operation Hours Energy Consumption(kWh/m²) Compressor Indoorfan unit Outdoorfan unit ERV 5.0 4.5 4.39 4.0 3.5 0.08 3.0 0.08 2.35 2.5 2.19 2.0 1.5 3.04 0.03 0.03 1.0 0.14 0.5 0.14 1.00 0.84 0.0 Figure 9. Energy Consumption ISBN: 978-0-646-98213-7 COBEE2018-Paper133 page 366
Energy Consumption Figure 9 showed the energy consumption for cooling and ventilation in each case. ERV operating by heat exchange mode had same energy consumption ( kwh/m 2 ) in all cases. The energy consumption of Multi Split Air-conditioner was sum of indoor fan unit, outdoor fan unit and compressor which is the biggest energy consumption of Multi Split Air-conditioner. As a result, the energy consumption in Case 1 showed the highest about 3.2 kwh/m 2 because the air conditioner operating hours increased due to excessive on-off control. Case 2 consumed 1.2 kwh/m 2 and Case 3 consumed 1.0 kwh/m 2. Case 3 showed the lowest among the analyzed cased. Energy saving effects in Case 2 and 3 was 63.8% and 68.8%, respectively, compared with Case 1. The energy consumption of indoor fan unit in Case 2 and 3 was higher than Case 1 due to the blowing mode. The compressor was comparatively less operated through the cooling/bower mode in Case 2 and Case 3. Case 3 showed the lowest energy consumption by using partial load operation (inverter control) even though the operation hours of air conditioner was longer than Case 2. CONCLUSIONS In this paper, the effect of the control logic on indoor thermal environment and energy consumption in a school building equipped with Multi System Air-conditioner was analyzed. The indoor operative temperature, relative humidity, and PMV were satisfied with comfort range of PMV(-0.5 - +0.5) and ASHRAE Comfort zone(ot 23.5-26.5, RH 40-60%) in all cases. The control logic using ASHRAE Comfort zone could control the indoor environment more simply than the PMV control which the considering factors are various. Set-point control which most of buildings adopted controlled in a narrow range of operative temperature and relative humidity. In terms of energy consumption, PMV range control showed the lowest in the operation hours of air conditioner. The energy consumption of ASHRAE Comfort control was 1.0 kwh/m 2, about 68.8% of energy saving effects using partial load operation compared to Case 1. ACKNOWLEDGEMENT This study is the result of cooperative research by Urban Architecture Research Project of Ministry of Land, Infrastructure and Transport(MOLIT). (17AUDP-B099696-03) REFERENCES ASHRAE. 2013. ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of ing, Refrigerating, and Air- Conditioning Engineers, Inc. Center for Educational Statistics Information, Students per Class, 2015 Fanger P.O. 1970. Thermal Comfort analysis and application in environmental engineering, Copenhagen: Danish technical Press Jeo J.I. 2008. Zero-Energy Green School Model Development study(Ⅰ) Report, Korea Educational Development Institute Ministry of Land, Infrastructure and Transport (MOLIT), Energy Saving Design Standards of Buildings, 2008 Society of Air-Conditioning and Refrigerating Engineers of Korea (SAREK). Weather Data for Korea, 1998 TRNSYS Reference Manual 2000. Madison: Solar Energy Laboratory, University of Wisconsin ISBN: 978-0-646-98213-7 COBEE2018-Paper133 page 367