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This system describes an integration on supply level for pre-heating of make-up water at a low temperature (<100°C). This application aims for a large temperature (lift over the collector) difference at the heat exchanger and a low collector inlet temperature. The make-up water is added about every 30 minutes, to compensate the mass loss within the system due to the open steam circuit.

Type | Flat plate collector |

Optical efficiency ηO | 0.811 [-] |

Linear loss coefficient a1 | 2.710 W/m²K |

Quadratic loss coefficient a2 | 0.010 W/m²K² |

IAM at 50° incidence angle | 0.91 |

Effective thermal capacity | 7050 J/m²K |

Primary loop between collectors and HX | Water-Glycol (35%, 980 kg/m³, 3.70 kJ/kgK) |

Secondary loop | Water (998 kg/m³, 4.19 kJ/kgK) |

Heat loss coefficient pipes | 3.5 W/m²K |

Pipe length collector – HX | (2x)100 m |

The pipe diameter is in each case determined as a function of mass flow.

Heat loss coefficient storage tank is 0.2 W/m²K. HX temperature spread for both heat exchangers at the solar and the distribution side is 5K. The tank diameter is in each case determined as a function of volume. The values for overall heat transfer coefficient of both heat exchangers vary depending on the collector area and heat demand.

The weekly and daily load profile is shown below.

This system describes a process level integration into a closed circuit system at low temperature (<100°C) with a small temperature difference at the heat exchanger. The daily load profile is assumed to be on full power at daytime and on only 20% at night time and at weekends.

Type | Vacuum tube collector |

Optical efficiency ηO | 0.687 [-] |

Linear loss coefficient a1 | 0.613 W/m²K |

Quadratic loss coefficient a2 | 0.003 W/m²K² |

IAM at 50° incidence angle | 0.91 |

Effective thermal capacity | 8780 J/m²K |

Primary loop between collectors and HX | Water (998 kg/m³, 4.19 kJ/kgK) |

Secondary loop | Water (998 kg/m³, 4.19 kJ/kgK) |

Heat loss coefficient pipes | 3.5 W/m²K |

Pipe length collector – HX | (2x)100 m |

The pipe diameter is in each case determined as a function of mass flow.

Heat loss coefficient storage tank is 0.2 W/m²K. HX temperature spread for both heat exchangers at the solar and the distribution side is 5K. The tank diameter is in each case determined as a function of volume. The values for overall heat transfer coefficient of both heat exchangers vary depending on the collector area and heat demand.

The weekly and daily load profile is shown below.

The system represents a steam generation and integration at higher temperature range (>100°C) for closed circuit systems. The system consists of a collector loop, an evaporator and a steam loop containing the condensate tank and the steam distribution line. The evaporator is typically a kettle type reboiler. The collector absorber is N/S oriented.

Type | LFC |

Optical efficiency η_{o} | 0.635 |

Linear loss coefficient a1 | 0 W/m²K |

Quadratic loss coefficient a2 | 0.00043 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

Type | PTC |

Optical efficiency η_{o} | 0.689 |

Linear loss coefficient a1 | 0.36 W/m²K |

Quadratic loss coefficient a2 | 0.0008 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

Type | LFC |

Optical efficiency η_{o} | 0.67 |

Linear loss coefficient a1 | 0.032W/m²K |

Quadratic loss coefficient a2 | 0.00018 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

The incidence angle modifiers IAM used in this study are presented in the following figure:

Therminol is considered as heat carrier within the solar loop. The dependency of its properties like density and heat capacity on the temperature is taken into account.

No storage tank is considered in this system. The evaporator model exhibits a steam/water volume that is related to the field size. It varies linearly between 1000ltr for 200m² and 2000ltr for 2000m².

The pipes from/to the evaporator are (2x)100m long whereas no field pipes are considered. The pipes’ specific heat loss coefficient amounts to 1W/m²K.

The steam boiler or evaporator is modelled as a boiler drum. A constant heat loss coefficient of 25W/K is assumed. The nominal thermal oil flow and the pipe diameter change according to the aperture. The Kvs value (aperture) of the steam release valve also varies according to the system size.

The system was considered to continuously have a solar fraction below 100%. The generated steam is directly fed to the heat sink. No demand profile is necessary.

I_dir: direct radiation on normal surface

Q_sol: solar heat transferred to boiler/drum

Q_process: solar heat transferred to process

Steam: quantity of steam

u_col: collector utilization ratio

u_sys: system utilization ratio

HTF flow: nominal flow in collector field

pipe dia: outer diamter of connection pipe

I_dir,s: specific direct radiation on normal surface

The system represents a steam generation and integration at higher temperature range (>100°C) for closed circuit systems. The system consists of a collector loop, an evaporator and a steam loop containing the condensate tank and the steam distribution line. The evaporator is typically a kettle type reboiler. The collector absorber is N/S oriented.

Type | LFC |

Optical efficiency η_{o} | 0.635 |

Linear loss coefficient a1 | 0 W/m²K |

Quadratic loss coefficient a2 | 0.00043 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

Type | PTC |

Optical efficiency η_{o} | 0.689 |

Linear loss coefficient a1 | 0.36 W/m²K |

Quadratic loss coefficient a2 | 0.0008 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

Type | LFC |

Optical efficiency η_{o} | 0.67 |

Linear loss coefficient a1 | 0.032W/m²K |

Quadratic loss coefficient a2 | 0.00018 W/m²K² |

Effective thermal capacity | 1000 J/m²K |

The incidence angle modifiers IAM used in this study are presented in the following figure:

A water/Steam mixture is circulating in the collector loop.

No storage tank is considered in this system. The drum model exhibits a steam/water volume that is related to the field size. It varies linearly between 300ltr for 200m² and 1200ltr for 2000m².

The pipes from/to the evaporator are (2x)100m long whereas no field pipes are considered. The pipes’ specific heat loss coefficient amounts to 1W/m²K.

A constant heat loss coefficient of 25W/K is assumed. The heat capacity of the metal parts is also considered. The nominal solar loop flow and the pipe diameter change according to the aperture. The Kvs value (aperture) of the steam release valve also varies according to the system size.

The system was considered to continuously have a solar fraction below 100%. The generated steam is directly fed to the heat sink. No demand profile is necessary.

I_dir: direct radiation on normal surface

Q_sol: solar heat transferred to boiler/drum

Q_process: solar heat transferred to process

Steam: quantity of steam

u_col: collector utilization ratio

u_sys: system utilization ratio

DSG flow: nominal flow in collector field

Absorber dia: outer diamter of absorber

I_dir,s: specific direct radiation on normal surface