Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand
Abstract
:1. Introduction
2. PVT Collector Description
3. Building Energy Demand and Solar PVT Cogeneration System Design
3.1. Target Building Overview and Energy Load Calculation
3.1.1. Statistical Calculation of Building Electricity Load
3.1.2. Calculation of the Building Heating Load
3.2. System Optimization Design
3.2.1. Thermal Modeling
- (1)
- The heat capacity of PVT collector has been neglected, and the system is in a quasi-steady state;
- (2)
- The system flow rate is stable, and the Reynolds number for the fluid flowing through the single collector is the same as in the collectors connected in series;
- (3)
- The energy collected by the system can be effectively used;
- (4)
- The correction of the total heat loss coefficient and the effective transmittance of module due to the heat loss of the inlet and outlet pipes have been considered;
- (5)
- The ohmic losses in the solar cell are negligible.
3.2.2. System Optimization Results
- (1)
- The total photovoltaic power generation of the system should be more than or at least equal to the electrical load demand of the building:
- (2)
- The total thermal energy generation of the system should be more than or at least equal to the heat load demand of the building:
- (3)
- The outlet water temperature should be higher than or at least equal to the heat supply temperature (it is set at 45 °C in this study):
- (4)
- The system is made up of the same kind of PVT collectors connected in series and in parallel, so the number M and N should be bigger than or at least equal to 1, as shown in Equation (27):
4. Adjustment and Control Method
4.1. Pipeline Switching and Auxiliary Heating Device Control Method
4.2. Circulating Water Pump Frequency Conversion Control Method
5. Experimental Study and Results Analysis
6. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
Qj | the heating load caused by heat transfer of the building envelope, W |
Ae | the area of the envelope, m2 |
K | the heat transfer coefficient of the building envelope, W/(m2·°C) |
Ta,c | the outdoor calculation temperature, °C |
To,m | the interior set temperature, °C |
b | the temperature correction coefficient |
ε1 | the towards correction coefficient |
ε2 | the outer door correction coefficient |
ε3 | the height correction coefficient |
Qi | the cold air penetration heat consumption, W |
cp | the specific heat capacity of air, kJ/(kg·°C) |
ρao | the density of air, g/L |
Qu | the heat gain of PVT collector, W |
A | the area of PVT collector, m2 |
Ai | the outer surface area of the inlet water pipe, m2 |
Ao | the outer surface area of the outlet water pipe, m2 |
FR | the collector heat transfer factor |
τ | the transmittance of the PVT collector glass cover |
α | the absorptivity of solar PV module |
It | solar radiation intensity, W/m2 |
UL | overall heat transfer coefficient of the absorber plate, W/(m2·K) |
Ti | inlet water temperature, °C |
To | outlet water temperature, °C |
Ta | ambient temperature, °C |
N | number of PVT collectors connected in series |
M | number of PVT collectors connected in parallel |
the rate of flow of water mass, kg/s | |
Cp | the specific heat of working fluid, J/(kg·K) |
ηth,N | the heating efficiency of the system |
ηCN | the temperature affected photovoltaic power generation efficiency of the Nth PVT collector |
ηC | the photovoltaic efficiency of the solar cell under standard test conditions |
TON | the outlet water temperature of the Nth PVT collector connected in series, °C |
TCN | the temperature of solar cells of the Nth PVT collector, °C |
TfN | the water temperature of the Nth PVT collector, °C |
TpN | the temperature of absorber plate of the Nth PVT collector, °C |
ηmN | the photovoltaic power efficiency of the Nth PVT collector connected in series |
Quel,N | the total power generation of the system, W |
Ud | overall heat transfer coefficient of the water pipe, W/(m2·K) |
β | the packing factor of PVT collector |
L | the length of PVT collector, m |
W | the width of PVT collector, m |
Utc,a | overall heat transfer coefficient from cell to the ambient from top surface, W/(m2·K) |
Utc,p | overall heat transfer coefficient from cell to the absorber plate, W/(m2·K) |
Utp,a | overall heat transfer coefficient from the absorber plate to the ambient, W/(m2·K) |
Tc | temperature of the solar cell, °C |
Tp | temperature of the absorber plate, °C |
τg | the transmittance of the solar PV module glass cover |
αc | the absorptivity of solar cell |
αp | the absorptivity of the absorber plate |
F’ | the collector efficiency factor |
hpf | the heat transfer coefficient from the absorber plate to the water, W/(m2·K) |
θPV | temperature coefficient of solar PV module, %/K |
Tref | temperature of standard test conditions, 25 °C in this study |
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Material | Thickness (mm) | Density (kg/m3) | Thermal Conductivity (W/m·K) | R Value (m2·K/W) | Heat Capacity (J/kg·K) | Heat Capacitance (J/m2·K) |
---|---|---|---|---|---|---|
Glass | 3.2 | 3000 | 1.0 | 3.2 × 10−3 | 500 | 4800 |
PV | 0.22 | 2330 | 148 | 1.5 × 10−6 | 677 | 355 |
EVA | 0.5 | 960 | 0.35 | 1.4 × 10−3 | 2090 | 1003 |
Absorber | 2 | 7280 | 64 | 0.3 × 10−4 | 385 | 5605 |
EPS | 50 | 80 | 0.04 | 1.2 | 1120 | 4480 |
Parameters (Unit) | Uoc (V) | Isc (A) | Pemax (W) | Ptmax (W) |
---|---|---|---|---|
Value | 33.2 | 6.1 | 195 | 300 |
Parameter | Value | Unit | Parameter | Value | Unit |
---|---|---|---|---|---|
A1 | 2 | m2 | Utc,a | 9.2 | W/(m2·K) |
Ai | 10 | m2 | Utc,p | 5.58 | W/(m2·K) |
Ao | 10 | m2 | αc | 0.9 | |
FR | 0.6 | τg | 0.95 | ||
τ | 0.95 | αp | 0.8 | ||
α | 0.8 | F' | 0.968 | ||
UL | 8.35 | W/(m2·K) | hpf | 100 | W/(m2·K) |
cp | 4180 | J/(kg·K) | Utp,a | 4.74 | W/(m2·K) |
Ud | 1 | W/(m2·K) | θpv | 0.5 | %/K |
β | 0.67 | Tref | 25 | °C | |
W | 1 | m | ηref | 0.18 |
Number of PVT Collectors Connected in Series (N) | Number of PVT Groups Connected in Parallel (M) | Outlet Water Temperature To (°C) | Total Thermal Energy Generation Qu (MJ) | Thermal Efficieny ηth (%) | Total Power Generation Qe (kWh) | Photovoltaic Efficiency ηe (%) |
---|---|---|---|---|---|---|
6 | 6 | 14.59 | 387.15 | 41.45 | 28.78 | 10.9 |
3 | 12 | 14.61 | 386.02 | 41.37 | 28.04 | 10.8 |
12 | 3 | 14.57 | 382.97 | 41.04 | 27.76 | 10.5 |
4 | 9 | 14.60 | 384.99 | 41.26 | 28.03 | 10.7 |
9 | 4 | 14.58 | 383.30 | 41.08 | 27.89 | 10.6 |
2 | 18 | 14.64 | 387.09 | 41.59 | 28.03 | 10.8 |
18 | 2 | 14.57 | 382.63 | 41.00 | 27.44 | 10.3 |
1 | 36 | 14.71 | 387.48 | 41.61 | 28.06 | 10.8 |
36 | 1 | 14.57 | 382.30 | 40.97 | 26.40 | 10.1 |
ecT | NB | NS | ZE | PS | PB | |
---|---|---|---|---|---|---|
eT | ||||||
NB | 5 | 5 | 4 | 3 | 3 | |
NS | 5 | 4 | 3 | 3 | 2 | |
ZE | 4 | 4 | 3 | 2 | 2 | |
PS | 4 | 3 | 2 | 2 | 1 | |
PB | 3 | 3 | 2 | 1 | 1 |
Parameters | Uncertainties |
---|---|
Ultrasonic flow meter | ±0.5% |
Pt100 temperature sensor | ±0.1 K |
Solar radiation intensity | ±5% |
Ambient temperature sensor | ±0.5 °C |
Ambient humidity sensor | ±2% |
Temperature self-recording module | ±0.1 °C |
Humidity self-recording module | ±1% |
Parameters | Unit | Values |
---|---|---|
Accumulated thermal energy generation in one day | MJ | 288 |
Average thermal efficiency | % | 23 |
Average temperature difference between inlet and outlet | °C | 3 |
Average photovoltaic power | kW | 6.1 |
Accumulated power generation | kWh | 32 |
Photovoltaic efficiency | % | 10 |
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Share and Cite
Zhou, C.; Liang, R.; Zhang, J. Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand. Energies 2017, 10, 1281. https://doi.org/10.3390/en10091281
Zhou C, Liang R, Zhang J. Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand. Energies. 2017; 10(9):1281. https://doi.org/10.3390/en10091281
Chicago/Turabian StyleZhou, Chao, Ruobing Liang, and Jili Zhang. 2017. "Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand" Energies 10, no. 9: 1281. https://doi.org/10.3390/en10091281