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Frontiers in Energy

Front. Energy    2019, Vol. 13 Issue (2) : 339-353     https://doi.org/10.1007/s11708-018-0596-5
RESEARCH ARTICLE
Heating energy performance and part load ratio characteristics of boiler staging in an office building
Da Young LEE1, Byeong Mo SEO2, Yeo Beom YOON2, Sung Hyup HONG1, Jong Min CHOI3, Kwang Ho LEE4()
1. Graduate School, Hanbat National University, Daejeon 305-719, South Korea
2. College of Design, North Carolina State University, Raleigh, NC 27695-7701, USA
3. Department of Mechanical Engineering, Hanbat National University, Daejeon 305-719, South Korea
4. Department of Architectural Engineering, Hanbat National University, Daejeon 305-719, South Korea
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Abstract

Commercial buildings account for significant portions of the total building energy in South Korea and thus a variety of research on the boiler operation related to heating energy in office buildings has been carried out thus far. However, most of the researches have been conducted on the boiler itself, i.e., the part load ratio characteristics and the corresponding gas energy consumption patterns are not analyzed in the existing studies. In this study, the part load ratio and the operating characteristics of gas boiler have been analyzed within an office building equipped with the conventional variable air volume system. In addition, the gas consumption among different boiler staging schemes has been comparatively analyzed. As a result, significant portions of total operating hours, heating load and energy consumption has been found to be in a part load ratio range of 0 through 40% and thus energy consumption is significantly affected by boiler efficiency at low part load conditions. This suggests that boiler operation at the part load is an important factor in commercial buildings. In addition, utilizing sequential boiler staging scheme can save a gas usage of about 7%. For annual heating energy saving, applying the sequential control boiler with a 3:7 proportion staging is considered to be the optimal control algorithm for maximum efficiency of boilers.

Keywords EnergyPlus      boiler      part load ratio      gas consumption      office building      boiler staging     
Corresponding Authors: Kwang Ho LEE   
Online First Date: 06 December 2018    Issue Date: 04 July 2019
 Cite this article:   
Da Young LEE,Byeong Mo SEO,Yeo Beom YOON, et al. Heating energy performance and part load ratio characteristics of boiler staging in an office building[J]. Front. Energy, 2019, 13(2): 339-353.
 URL:  
http://journal.hep.com.cn/fie/EN/10.1007/s11708-018-0596-5
http://journal.hep.com.cn/fie/EN/Y2019/V13/I2/339
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Da Young LEE
Byeong Mo SEO
Yeo Beom YOON
Sung Hyup HONG
Jong Min CHOI
Kwang Ho LEE
Fig.1  Study flow chart
Fig.2  Internal heat gain schedule
Representative day Terminal unit Boiler capacity/W Heating set-point/°C
17th April, 23rd January Conventional VAV box with reheat 290000 21
Tab.1  Simulation conditions
Fig.3  Simulation model (adapted with permission from Ref. [12])
Fig.4  Load distribution algorithm (adapted with permission from Ref. [12])
Field Input
Minimum part load ratio 0
Maximum part load ratio 1
Optimum part load ratio 1
Tab.2  Simulation input related to boiler part load ratio
Fig.5  Load distribution example
Field Equipment list Capacity/kW Operating priority Load distribution algorithm
1st 2nd
Case_1 Boiler_1 290 Boiler_1 *
Case_2 Boiler_1, Boiler_2 145 145 Boiler_1, Boiler_2 Uniform
Case_3 Boiler_1, Boiler_2 87 203 Boiler_1, Boiler_2 Uniform
Case_4 Boiler_1, Boiler_2 87 203 Boiler_1 Boiler_2 Sequential
Case_5 Boiler_1, Boiler_2 203 87 Boiler_1 Boiler_2 Sequential
Tab.3  Simulation cases
Fig.6  Boiler efficiency curve
Coefficient entry Input data
a 0.3822
b 2.2013
c -2.8237
d 1.3021
Tab.4  Boiler cubic curve input data
Fig.7  AHU heating rate and outdoor air temperature variations
Fig.8  Part load ratio (Case_1)
Fig.9  Part load ratio in intermediate period (Cases_2 and 3)
Fig.10  Part load ratio in intermediate period (Cases_4 and 5)
Fig.11  Part load ratio in heating period (Cases_2 and 3)
Fig.12  Part load ratio in heating period (Cases_4 and 5)
Case Total gas consumption/kWh Boiler_1 gas consumption/kWh Boiler_2 gas consumption/kWh
Case_1 517.9 517.9
Case_2 517.9 258.9 258.9
Case_3 508.2 225.7 282.5
Case_4 355.8 355.8 0
Case_5 470.3 470.3 0
Tab.5  Daily gas consumption data (intermediate season)
Case Total gas consumption/kWh Boiler_1 gas consumption/kWh Boiler_2 gas consumption/kWh
Case_1 1707.6 1707.6?
Case_2 1707.6 853.8 853.8
Case_3 1696.0 706.5 989.6
Case_4 1464.8 992.7 472.1
Case_5 1582.4 1494.4? ?88.0
Tab.6  Daily gas consumption data (heating season)
Fig.13  Gas consumption in each PLR (0≤PLR<40)
Part load ratio/% Case_1 Case_2 Case_3 Case_4 Case_5
Boiler_1 Boiler_1 Boiler_2 Boiler_1 Boiler_2 Boiler_1 Boiler_2 Boiler_1 Boiler_2
0≤PLR<10 747 747 747 474 1,035 251 123 550 47
10≤PLR<20 596 596 596 421 527 223 63 485 17
20≤PLR<30 251 251 251 366 175 210 40 353 7
30≤PLR<40 116 116 116 224 61 211 10 174 6
Total 1710 1710 1710 1485 1798 895 236 1562 77
Tab.7  Cumulative operation hours in each PLR (0≤PLR<40)
Fig.14  Gas consumption in each PLR (40≤PLR≤100)
Part load ratio/% Case_1 Case_2 Case_3 Case_4 Case_5
Boiler_1 Boiler_1 Boiler_2 Boiler_1 Boiler_2 Boiler_1 Boiler_2 Boiler_1 Boiler_2
40≤PLR<50 78 78 78 109 11 195 10 105 5
50≤PLR<60 16 16 16 84 19 171 17 73 3
60≤PLR<70 20 20 20 64 10 127 10 43 3
70≤PLR<80 16 16 16 37 12 97 12 19 5
80≤PLR<90 12 12 12 22 5 64 5 12 0
90≤PLR≤100 10 10 10 61 7 313 8 48 4
Total 152 152 152 377 64 967 62 300 20
Tab.8  Cumulative operation hours in each PLR (40≤PLR≤100)
Part load ratio/% Case_1 Case_2 Case_3
Boiler_1 Boiler_1 Boiler_2 Boiler_1 Boiler_2
Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh
0≤PLR<10 747 25.4 747 12.7 747 12.7 474 12.7 1,035 12.7
10≤PLR<20 596 49.2 596 24.6 596 24.6 421 24.6 527 24.6
20≤PLR<30 251 29.2 251 14.6 251 14.6 366 14.6 175 14.6
30≤PLR<40 116 17 116 8.5 116 8.5 7.35 8.5 61 8.5
40≤PLR<50 78 14 78 7 78 7 109 7 11 7
50≤PLR<60 16 3.4 16 1.7 16 1.7 84 1.7 19 1.7
60≤PLR<70 20 5 20 2.5 20 2.5 64 2.5 10 2.5
70≤PLR<80 16 4.6 16 2.3 16 2.3 37 2.3 12 2.3
80≤PLR<90 12 3.8 12 1.9 12 1.9 22 1.9 5 1.9
90≤PLR≤100 10 3.6 10 1.8 10 1.8 61 1.8 7 1.8
Total 1,862 155.2 1,862 77.6 1,862 77.6 1,645 77.6 1,862 77.6
Tab.9  Annual PLR date (Cases_1, 2, and 3)
Part load ratio/% Case_4 Case_5
Boiler_1 Boiler_2 Boiler_1 Boiler_2
Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh Operating hours/h Amount of consumed gas/MWh
0≤PLR<10 251 1.8 123 1.8 550 1.8 47 1.8
10≤PLR<20 223 4 63 4 485 4 17 4
20≤PLR<30 210 5.5 40 5.5 353 5.5 7 5.5
30≤PLR<40 211 6.9 10 6.9 174 6.9 6 6.9
40≤PLR<50 195 8.7 10 8.7 105 8.7 5 8.7
50≤PLR<60 171 8.8 17 8.8 73 8.8 3 8.8
60≤PLR<70 127 9.5 10 9.5 43 9.5 3 9.5
70≤PLR<80 97 7.7 12 7.7 19 7.7 5 7.7
80≤PLR<90 64 7.6 5 7.6 12 7.6 0 7.6
90≤PLR≤100 313 38.1 8 38.1 48 38.1 4 38.1
Total 1,862 98.6 298 98.6 1,862 98.6 97 98.6
Tab.10  Annual PLR date (Case_4 and 5)
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