Optimization of Solar Water Heating System under Time and Spatial Partition Heating in Rural Dwellings
Abstract
:1. Introduction
2. Demonstration Project and Analysis Approach
2.1. Demonstration Project
2.1.1. Passive Solar Building
2.1.2. Solar Water Heating System
2.2. Time and Spatial Partition Heating Mode
2.3. System Thermal Performance and Economic Analysis
3. TRNSYS Modeling and Validation
3.1. Thermal Performance Simulation Model
3.2. Tests and Model Validation
3.2.1. Dynamic Thermal Performance Tests
3.2.2. Model Validation
4. Results and Discussion
4.1. System Comparison with Two Heating Modes
4.1.1. Heating Effect
4.1.2. System Performance Evaluation
4.2. System Optimization of TSPH
4.2.1. Solar Heating Area
4.2.2. Tank Volume
4.2.3. Auxiliary Heater Setting Outlet Temperature
4.3. Discussion of Optimal Operation of Active and Passive System
4.3.1. On/Off Operation Time of SWHS
4.3.2. On/Off Operation Time of Trombe Wall
5. Conclusions
- (1)
- The indoor heating effect and system performance evaluation were analyzed with CWSH and TSPH by means of TRNSYS dynamic simulation software. The results were validated by comparison with the test results of a demonstration building using CWSH in the period of 23–28 April. It was found that the average relative error in the temperature of the three rooms was 6.9%, and the relative errors of the accumulated heat energy collected by the solar system and solar fraction were within 6%.
- (2)
- The indoor air temperature of TSPH was already satisfied to a great extent, although the heating guaranteed hours with TSPH was lower than with CWSH. Compared with CWSH, solar fraction can be increased by 16.5%, auxiliary heating during the heating season can be reduced by 7390 MJ, and the annual operation cost can be reduced by 2010 RMB, with TSPH. Therefore, time and spatial partition solar heating technology was a better option for rural residence.
- (3)
- The indoor heating effect and solar fraction can improve if the solar collector area increased. When the solar collector area was 10–14 m2, the dynamic annual cost could be reduced to lower than 5200 RMB. Increased tank volume is advantageous for heat storage. The auxiliary heater setting outlet temperature had greater impact on the indoor heating effect, and this influence weakened when the auxiliary heater setting outlet temperature was higher than 50 °C.
- (4)
- Advanced opening and closing with 2 h of SWHS and increased heating time could improve the guaranteed hours of MB and LR. Increasing the heating time was unfavorable to system performance, and there were a suitable number of hours for advanced opening of SWHS. Closing of air vents hindered heat gain of the Trombe wall.
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
Ac | solar collector area (m2) |
cp | specific heat of the water (kJ/kg·°C) |
Cm | annual maintenance cost (RMB) |
COSTini | initial investment cost (RMB) |
COSTop | annual operation cost (RMB) |
COSTy | dynamic annual cost (RMB/Year) |
ELEaux | power consumption of auxiliary electric heater (kW h) |
ELEpump | power consumption of pump (kW h) |
f | solar fraction (%) |
i | bank loan interest rate (%) |
ILa | total tilted surface solar radiation (kJ/Hr·m2) |
m | mass flow of solar collector system (kg/Hr) |
n | service life of SWHS (Year) |
pele | electricity price (RMB/kW h) |
Paux | rated power of auxiliary electric heater (W) |
Qaux | auxiliary heating energy (kJ) |
Qsolar | useful energy gain of solar collector system (kJ) |
Qload | heat consumption of the building (kJ) |
taux | operation hours of auxiliary electric heater (h) |
Ta | outdoor air temperature (°C) |
Tair | indoor air temperature (°C) |
Tair,L | temperature of air layer (°C) |
T1 | outlet temperature of solar collector system (°C) |
T2 | inlet temperature of solar collector system (°C) |
T3 | temperature to heat source of tank(°C) |
T4 | temperature of tank (°C) |
T5 | temperature to load of tank (°C) |
T6 | outlet temperature of auxiliary electric heater (°C) |
T7 | indoor air temperature of second bedroom (°C) |
T8 | indoor air temperature of master bedroom (°C) |
T9 | indoor air temperature of living room (°C) |
Greek Letters: | |
η | collector efficiency (%) |
ηele | thermal efficiency of auxiliary electric heater (%) |
Subscripts: | |
all | heating in the whole day |
day | heating in the daytime |
j | number of functional room |
n | total number of functional rooms |
night | heating in the nighttime |
x | total number of functional rooms with heating in the daytime |
y | total number of functional rooms with heating in the whole day |
z | total number of function rooms with heating in the nighttime |
Abbreviations: | |
CWSH | continuous and whole space heating |
LR | living room |
MB | master bedroom |
SB | second bedroom |
SWHS | solar water heating system |
TRNSYS | transient systems simulation program |
TSPH | time and spatial partition heating |
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Component | Material | Thickness (mm) | Thermal Conductivity (W/m·K) | Density (kg/m3) | Specific Heat Capacity (kJ/kg·K) | U Value (W/m2·K) |
---|---|---|---|---|---|---|
Wall | Cement mortar | 40 | 1.34 | 1800 | 1.05 | 0.56 (S) 0.40 (N E W) |
Brick | 240 | 0.58 | 1400 | 1.05 | ||
XPS (S External) | 50 | 0.042 | 30 | 1.38 | ||
XPS (N E W External) | 80 | 0.042 | 30 | 1.38 | ||
Roof | Cement mortar | 20 | 1.34 | 1800 | 1.05 | 0.38 |
Reinforced concrete | 160 | 1.74 | 2500 | 9.20 | ||
XPS | 100 | 0.042 | 30 | 1.38 | ||
Floor | Cement mortar | 40 | 1.34 | 1800 | 1.05 | 0.51 |
Reinforced concrete | 150 | 1.74 | 2500 | 0.92 | ||
XPS | 60 | 0.042 | 30 | 1.38 | ||
Sandy soil | 150 | 0.59 | 1420 | 1.51 | ||
Window | Plate glass | 4 | 0.76 | 2500 | 0.84 | 1.30 |
Air layer | 16 | 0.0267 | 1.165 | 1.00 | ||
Plate glass | 4 | 0.76 | 2500 | 0.84 |
Types | Component | Descriptions |
---|---|---|
Trombe Wall | Air vent | The total number of air vents of size 200 mm × 200 mm is 5:3 and 2 located at the top and bottom, respectively. |
Glazing | The transparent glazing with a 4-mm-thick simple glass covers all the S external envelopes of SB and MB except the windows. | |
Coating | The thickness of the red corrugated sheet iron is 10 mm. | |
Air layers | The thickness of the air layer is 100 mm. | |
Attached Sunspace | Sunspace | The size of attached sunspace is shown in Figure 2. It has a window of size 1800 mm × 2100 mm in the partition wall. |
Glazing | The transparent glazing with a 5-mm-thick wired glass covers all the external envelopes. |
Heating Mode | Function Rooms | Heating Period | Heating Design Temperature (°C) |
---|---|---|---|
CWSH | All three rooms | 0:00–24:00 | 18 [38] |
TSPH | Second Bedroom | 0:00–8:00; 22:00–24:00 | 12 [39] |
Master Bedroom | 8:00–22:00 | 18 | |
0:00–8:00; 22:00–24:00 | 12 | ||
Living Room | 8:00–22:00 | 18 |
Name | Component | Main Parameters | Descriptions |
---|---|---|---|
Weather Date | Type 15-2 | Number of surfaces: 2; slope of surface-1: 45°. | The TMY-2 weather date of Gangcha. Used for the optimization analysis. |
Testing Weather Date | Type 99 | The measured meteorological conditions during the test were inputted. | Used for the model validation. |
Building | Type 56 | Room air exchange rate: 0.5 h−1; active layer of the three rooms were added. | The building model was built in Google Sketch Up, and imported to TRN Build for setting the parameters. Thermo-physical properties see Table 1. |
Tank | Type 534 | Tank volume: 0.2 m3, tank height: 0.9 m, number of tank nodes: 2. | The fluid used for the storage tank is water. There has a heat exchanger in the tank. |
Controller | Type 73 | Collector area: 14 m2, slope of collector: 45°; collector fin efficiency factor: 0.7; absorber plate emittance: 0.7; absorbance of absorber plate: 0.8. | The fluid used for solar collector is glycol solution. Thermal performance parameters obtained from the manufacture. |
Auxiliary Heater | Type 6 | Maximum heating rate: 10,800 kJ/h, efficiency of auxiliary heater: 0.95. | Used for supplying the auxiliary heater |
Trombe Wall | Type 36b | Wall height: 2.9 m, wall width: 1.5 m, wall thickness: 0.33 m, vent outlet area: 0.2 m2. | Used for calculating the energy of Trombe wall flow to MB and SB. |
Forcing Functions | Type 14h | Time parameters and corresponding temperature of 3 rooms were set. | Used for logical signal of time control. |
Vale | Type 3d | Maximum heating rates of three loops were set. | Pipe valves were replaced by pumps, and the influence of water temperature by pump was ignored. |
Equation | Equations (2)–(4) | Air temperature of the three rooms was inputted, and logical relation of the three control loops was set. | Used for controlling the on-off signal of pump (vale). The control logic was shown in Figure 3a. |
Parameters | Test Results | Simulation Results | Relative Error |
---|---|---|---|
Accumulated Heat Energy Collected by Solar System (MJ) | 123.66 | 125.42 | 1.42% |
Accumulated Heat Energy Provided by the Electric Heater (MJ) | 86.58 | 75.60 | −12.70% |
Solar Fraction f (—) | 58.82% | 62.39% | 6.07% |
Heating Mode | Monthly Auxiliary Heating (MJ) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
9 | 10 | 11 | 12 | 1 | 2 | 3 | 4 | 5 | Total | |
CWSH | 0 | 858.48 | 2849.65 | 5032.81 | 5011.89 | 3725.63 | 2071.64 | 388.20 | 182.08 | 20,120.38 |
TSPH | 14.14 | 570.83 | 1617.63 | 3326.66 | 3265.45 | 2288.97 | 1195.53 | 306.96 | 144.05 | 12,730.23 |
Serial Number | Description | Heating Guaranteed Hours (h) | Qaux (MJ) | Solar Fraction (%) | ||
---|---|---|---|---|---|---|
SB | MB | LR | ||||
Base case | The starting and closing time of loop equals the heating demand time | 5360 | 4565 | 3675 | 1275.11 | 40.30 |
1 | The starting and closing time of loop advanced 1 h to the heating demand time | 5337 | 4623 | 3748 | 1294.88 | 39.57 |
2 | The starting and closing time of loop advanced 2 h to the heating demand time | 5308 | 4686 | 3816 | 1324.29 | 38.36 |
3 | The starting time of loop advanced 1 h to the heating demand time, closing advanced 1 h | 5330 | 4671 | 3801 | 1348.69 | 37.87 |
4 | The staring time of loop advanced 2 h to the heating demand time, closing equals to heating demand time | 5294 | 4772 | 3919 | 1423.83 | 35.30 |
Serial Number | Description | Heating Guaranteed Hours (h) | Qaux (MJ) | Solar Fraction (%) | ||
---|---|---|---|---|---|---|
SB | MB | LR | ||||
Base case | Air vents always closed | 5360 | 4565 | 3675 | 1275.11 | 40.30 |
1 | Air vents always open | 5489 | 4869 | 3715 | 1188.65 | 40.26 |
2 | Air vents always open if Tair,L ≥ Tair, or else keep closed. | 5489 | 4873 | 3752 | 1111.20 | 42.60 |
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Liu, Y.; Li, T.; Chen, Y.; Wang, D. Optimization of Solar Water Heating System under Time and Spatial Partition Heating in Rural Dwellings. Energies 2017, 10, 1561. https://doi.org/10.3390/en10101561
Liu Y, Li T, Chen Y, Wang D. Optimization of Solar Water Heating System under Time and Spatial Partition Heating in Rural Dwellings. Energies. 2017; 10(10):1561. https://doi.org/10.3390/en10101561
Chicago/Turabian StyleLiu, Yanfeng, Tao Li, Yaowen Chen, and Dengjia Wang. 2017. "Optimization of Solar Water Heating System under Time and Spatial Partition Heating in Rural Dwellings" Energies 10, no. 10: 1561. https://doi.org/10.3390/en10101561