DE102004058857A1 - Solar energy system with heat exchangers to transfer heat from solar panels to a heat pump cycle for heating or cooling of buildings and for storing heat - Google Patents

Abstract

A solar energy system has solar panels connected to heat exchangers to transfer heat into a heat pump cycle, e.g. Organic Rankin Cycle (ORC), for heating or cooling buildings and for charging heat storage elements. The system is driven by an electrically powered heat pump which drives a fluid through a compressor, expansion throttle and heat exchangers. The system is optimised for Summer and/or Winter operation.

Description

The solar radiation offer of the sun is enormous: Every year the earth reaches 3.7 × 10 ²⁴ Joule. That is more than 10,000 times the world's primary energy consumption. The sun delivers the same energy that all earthlings consume in the course of a year in just 40 minutes.

The German households consume about 30% of the total energy requirement. There are also commercial, industrial and public buildings.

The Government of the Federal Republic of Germany has decided to reduce CO ₂ emissions by 25% by 2005 compared to 1990 levels!

With the heat pump and energy recovery via an ORC steam process, it will not only be possible to save considerable amounts of fossil energy and CO ₂ emissions in the future, but also generate more electrical energy than is needed to provide heat, especially if the building is well insulated.

The solar radiant heat or energy is used much better and on expensive long-term storage and an additional heating can be dispensed with

Last but not least, the technology described below can save significant amounts of CO ₂ , which significantly improves the environmental situation and makes an important contribution to achieving the Kyoto target.

Worldwide could the need for fossil fuels for heating purposes and power generation through the use of solar energy strong be reduced.

• – Auftreffwinkel der Sonnenstrahlung (Tages und Jahreszeit)
• – Intensitätsänderungen durch wechselnde Entfernung Erde – Sonne
• – Atmosphärische Veränderungen: Abschwächung durch in der Luft befindliche Moleküle, Wasserdampf und Verunreinigungen (Stäube)

Solar radiation consists of direct and diffuse radiation. The direct radiation is received directly (without change of direction). The intensity of direct sunlight depends on the following factors:

• - Impact angle of solar radiation (day and season)
• - intensity changes due to changing earth - sun
• - Atmospheric changes: attenuation by airborne molecules, water vapor and impurities (dusts)

The diffuse radiation is the (energetically less valuable) proportion the solar radiation, the earth's surface only after previous reflection reached by clouds and scattering in the atmosphere. On a clear On sunny days the diffused radiation consists mainly of the blue of the sky.

The direct and the diffused radiation together make up the global radiation. The global radiation is the total energy radiated by the sun on a m ² horizontal earth surface during a certain period of time.

The The following tables give the long-term averages for the daily global radiation at.

Tabelle 1 Tägliche Globalstrahlung (horizontal) in Wh/m²d für den Standort Berlin

Table 1 Daily global radiation (horizontal) in Wh / m ² d for the location Berlin

Tabelle 2 Jährliche Globalstrahlung an verschiedenen Orten

Table 2 Annual global radiation at different locations

Solar systems, where mirrors or lenses are used (high-temperature systems), can only use the use direct radiation. They usually have to be the sun tracked become and come only in very sunny areas of the earth Application.

The better adapted to the climatic conditions of Central Europe. or vacuum collectors work at a lower temperature level. You can, however convert both direct and diffuse solar radiation into heat.

today are solar thermal systems mainly for water heating and at best for heating support used.

The desired Temperatures are 45 - 60 ° C. The temperatures heating support systems conventional type are usually much higher (except low temperature or underfloor heating) and can - especially in the winter - not can be achieved by the solar system alone. A solar system can So (so far) only a certain proportion of the total required heating and hot water energy cover.

In As a rule, the bivalent mode of operation was economically optimal. By bivalence is meant the interaction of different Heating systems, such as a solar system with a conventional Gas or oil heating. These systems are now widely used, technically mature and often work on the verge of profitability.

Solar room heating with heat pump and energy recovery in summer

The Use of solar energy for the purpose of space heating with a low-temperature heating (if possible underfloor heating or large area radiator surfaces) other requirements for system design than for hot water.

at In this concept, the solar system is regarded as the primary source of energy. The collector area is at least a quarter of the living space to be heated and the Sollarwärmespeicher reach / reach a few cubic meters of water. An extensive one Coverage of the heat demand in the annual transitional periods is only possible with well-insulated houses.

Regarding the selection of a suitable heating system in conjunction with a thermal solar system is mentioned that a flat collector system on average flow temperatures from 55 ° C supplies (vacuum collectors much more). It thus becomes clear that one Low temperature heating (e.g., underfloor heating) much better is suitable as a conventional radiator heater (flow temperature 70 - 90 ° C).

The dimensioning of a solar heating system must be carried out taking into account all occurring in individual cases building and usage data. Particular importance is attached to the quality of the thermal insulation and thus the heat demand of the house. An estimate provides the following values .: collector area: 1.5 - 2.5 m ² per 1,000 kWh annual heat consumption Contents of the hot water tank: 1 m ³ per 10 m ² collector area

A Doubling of the solar area only yields about 10 - 20 % more heat output with direct heating, over the solar system, the building. Using a heat pump and a big one heat storage However, this amount is much higher.

A significantly larger solar system can, as described below, a significant proportion of heat and Take over hot water supply and doing excess energy feed back.

So long the irradiated solar energy is large enough, the solar system provides the space heating system and the water heater with heat. Excess solar energy enters the solar heat storage (Buffer memory) and is on days with low solar radiation to disposal.

As soon as a sufficient amount of space for heating space and water heating from the collectors can no longer be supplied, the heat pump their operation on.

The heat pump removes heat from the solar collector circuit during low-level radiation and lowers it Thus, the collector working temperature up to a value of about 2 - 10 ° C (depending on the outside temperature and sunlight). As a result, the heat losses of normal collectors are greatly reduced and thus made a much larger proportion of the irradiation harnessed. The collector temperature in this case is usually well above the outside temperature, but below the required flow temperature for the heating circuit.

The annual average coefficient of performance (efficiency) of the heat pump becomes compared to conventional Applied technology (use of geothermal energy via earth collectors or geothermal probes) significantly improved.

Then you can the heat pump if necessary, get their heating energy from the buffer tank.

Enough also the stored heat here not out (for example, permanent snow cover of the solar system), then will the needed Thermal energy the environment (for example geothermal energy, Groundwater or outside air). The with the heat extraction of the soil associated large surfaces have so far the main costs for a heat pump system turned off. So far, almost exclusively this or in "lack of space" even more expensive geothermal technology applied.

With the technique described here and the use of a heat pump can Compared to conventional technology (additional boiler) considerable Saving energy.

The heat pump

Heat pumps are machines that provide useful heat by dissipating ambient heat through the evaporator ( 4 - 1 ) at a low temperature (eg from the ambient air, the soil or groundwater) and at a higher temperature than useful heat to the capacitor ( 2 - 3 ) again. The energy expenditure for this "pumping process" ( 1 - 2 ) is at small temperature differences between heat absorbing and donating side significantly lower than the output useful heat.

more lower the temperature difference between heat source (evaporator) and the flow temperature (condenser) for the heating system the more the heat pump works more economically.

The Coefficient of performance ε calculated from the ratio ε = net power / expended power

Quality Heat pumps reach at a temperature difference of 25 ° C (10 ° C evaporation temperature, 35 ° C condensation temperature) a figure of merit of on average 5.2 - 5.6!

The energy concept

at a complete roofing with as large as possible and inexpensive Solar modules (future also finished solar modules according to the modular principle) can accordingly high solar coverage rates are achieved.

So far the solar surplus heat could not be used during the "summer half - year" on the contrary, had to be taken to ensure that the solar system does not overheat and thereby possible damage takes. A cooling However, the collectors are hardly possible with "charged" "hot water storage".

Not Most recently, the previously installed systems were made out of this and out cost reasons rather lower than oversized and were mainly used for hot water.

The let solar energy surpluses However, make good use of energy generation. Reach solar plants Standstill temperatures of up to 200 ° C in summer With an ORC process (reversal of the heat pump) can now while the "unused" summer time the same amount of electrical energy or more, as in winter for the Operation of the heat pump needed becomes. The solar thermal system can be used in conjunction with a heat pump and an ORC process not only heating but also in addition Generate electricity.

The ORC process is based on the water-steam process similar method with the difference that instead of water, an organic working medium (hydrocarbons such as iso-pentane, iso-octane, pentane, perfluoropentane, toluene, silicone oil) or an ammonia-water mixture (Kalina process) is used.

These Working media have cheaper ones Evaporation properties at lower temperatures and pressures.

The Excess heat generated in summer the solar system is over a heat transfer medium or better directly (direct evaporation of the working fluid without additional Heat exchanger) transferred to the ORC steam engine process.

organic Work equipment stands out against water by cheaper Evaporating properties. They evaporate and overheat at lower temperatures and lower heat input. The vapor pressure is low, the steam volume, however, correspondingly large!

The Collector fields of the solar roof can be directly on the roof construction are located and thus replace the roofing. Furthermore can with well-insulated large collectors waived a thermal insulation (especially if the roof area is uninhabited or for storage is being used).

When heat storage serves a good heat-insulated Buffer memory, designed for a bad weather bridging time from about 4 - 10 Days (depending on the outside temperature).

For the condenser cooling of the ORC process ( 2 - 3 ) should be used if possible groundwater, as at maximum solar radiation significant amounts of cold water as possible are needed.

With a maximum solar radiation of about 1,000 watts / m ² , a collector efficiency of about 50% at a temperature of 100 - 120 ° C and a process efficiency of about 7 - 12% falls a cooling or condensation heat of about 450 watts / m ² Collector surface on. (At a condenser inlet temperature of 10 ° C outlet temperature 20 ° C). The ORC steam process generates an output of approx. 35 - 60 W / m ² .

This "peak power" can be reduced via an intermediate heat store to provide constant power generation at lower power and to minimize the size and cost of the ORC steam plant., Also, some of the heat of condensation can be recovered via a recuperator by preheating the condensed working fluid. The recuperator (heat exchanger) is located in front of the condenser ( 2 ( 2 ' - 4 ' )). Following is a further preheating and possibly evaporation via the buffer memory possible. Further evaporation and / or overheating of the working fluid takes place via the solar collectors.

is the use of groundwater (over a fountain) not possible so can the cooling also about the outside air (favorable solution but efficiency loss due to higher ambient temperatures) or over-dimensioned, Rainwater cistern introduced into the ground, which makes sense also for the irrigation of the land, Toilet flushing, Washing machines and the like is used (about 50% of the water needs). The cistern is in permanent Exchange with the ambient heat of the soil at approx. 10 ° C (Summer as well as winter) and should have as large a surface as possible to the earth environment with sufficient Have depth. It can thus both summer as a capacitor for power generation Serve, as well as in winter, with insufficient solar heat yield (rarely) contribute to heat production Afford. An icing must necessarily be avoided.

The used refrigeration and ORC equipment must of course be completely environmentally friendly and non-toxic, although the circuits separated by a heat transfer medium are. (except with direct heating or cooling (in the future possibly Kalina process).

power generation and power consumption

A economic consideration leaves present difficult to perform, because empirical values, especially in the energy and electricity generation not available, a rough estimate Here, however, shows very good results and positive future prospects.

Since about 75% of the annual solar radiation (average 1040 kWh / m ² ) is generated in the summer half-year (from April to September), it can be estimated that 780 kWh / m ² a solar radiation can be used for the ORC work process. If only 1.5 to 4% of this is converted into electrical energy (80% collector efficiency, 30% heat loss, ORC efficiency depending on temperature 2 - 9%), then a total current reduction of about 12 - 31 kWh el./m ² im Year.

The remaining 260 kWh / m ² are radiated during the winter months and converted into heat in the absorber of the solar system to about 50%.

(efficiency Solar collector approx. 80%, heat losses and inclination angles of the sun together make up about 50%). The remaining 130 kWh / a will be over the heat pump used for heating and hot water.

The total heat demand of a low-energy house including water heating is about 70 kWh / m ² a (7 liters of heating oil / m ² ). This heat requirement can be provided with sufficient collector area about 50% of the solar system. The remaining heat must be pumped with the help of the heat pump to a temperature of "only" 35 ° C. Hot water to about 55 ° C.

For the remaining heat requirement, with an average annual heat pump capacity of about 7, only about 5 kWh of electricity / m ^{2 are} required.

aim

The The goal of this energy concept is a significantly better utilization the solar heat by integrating new technology while reducing costs and increase efficiency compared to existing systems.

One An essential step in the development of this technique is the Interaction of an electric heat pump and an ORC steam process using common technology. Thus, e.g. the electric motor (Three-phase asynchronous motor), which is used to drive the compressor also serves as a generator for the ORC process.

For this is one common shaft, a clutch and possibly a translation required.

Over a Star-delta connection can be the motor or power generator in two Power levels are operated.

Furthermore can change the speed and power via a pole change in two or more stages (e.g., 1,500 and 3,000 U / min). This results in power levels of e.g. 1/1, 1/2, 1/3 and 1/6 of the rated power for Generator and engine.

For the ORC steam process For now, a modified or retrofitted piston or screw compressor heat pump serve (development and improvement).

measurement Control technology is for an optimal and economical Operation inevitable.

The future Development goals should also focus on further improvement the achievable efficiency and the further development of environmentally friendly organic work equipment for focus on low temperature ranges.

at direct heating of the working medium the solar collectors, the ORC steam process achieves a higher efficiency, because the heat losses of the heat exchanger omitted.

Becomes the solar fluid replaced by the working fluid (e.g., perfluoropentane), the entire But withstand a pressure of up to 6 bar, which is guaranteed by many manufacturers today. The Working medium boils under normal or ambient pressure at about 30 ° C and can thus already at low temperatures and low vapor pressure make a contribution to power generation.

By Further development and cooperation with heat pump manufacturers still considerable Potentials for significant efficiency improvements and cost reductions to reach.

Larger objects and old buildings with lower thermal insulation and higher Temperature level and heat demand can with a gas or heating oil heat pump be operated, here in addition the cooling and exhaust heat (until condensation) of the engine can be used. Of course it should Again, not on a power generation during the summer time waived become.

Of the generated electricity can be fed into the power supply network.

Claims (4)

Thermal solar system with a heat pump and an ORC steam process, consisting of one or more solar collectors, and one or more heat accumulators, characterized in that the heated by the solar panels via a respective heat exchanger on the ORC steam process, the heat pump, the / Heat storage or directly to the flow of the heating system is transferred. The ORC steam process takes place via an expansion machine, a piston or screw motor. The electric drive for the heat pump (DC alternating current or three-phase motor) serves as a generator for the ORC process. The condensation of the working fluid via a heat exchanger in the condenser or condenser. The coolant is cooled by outside air, geothermal, well or groundwater. If the storage tank temperature is insufficient, the coolant serves as the heat source for the heat pump. The coolant can also be used in the summer for cooling the building by cooling the heating circuit via a heat exchanger. Thermal solar system with a heat pump and an ORC steam process according to claim 1, characterized in that that the work equipment for the ORC process directly via the solar collectors is evaporated. The work equipment is added Heat requirement over one heat exchangers on the heat pump, the or the heat storage and transferred to the heating flow. Thermal solar system with a heat pump and an ORC steam process according to claim 1 and 2, characterized in that the working medium via a recuperator, which is located between the expansion machine and in front of the condenser, is preheated ( 1 ( 2 ' - 4 ' )). Subsequently, the working fluid can be further heated or evaporated via the heat storage before the working fluid is evaporated and overheated via the collector circuit. Thermal solar system with a heat pump and an ORC steam process according to claims 1 and 2, characterized in that that the heat pump has a Internal combustion engine is driven. The exhaust and coolant heat is used for heating purposes.