Systems using solar thermal energy in combination with heat pumps 1 st concept paper

Transcription

1 Systems using solar thermal energy in combination with heat pumps 1 st concept paper to be presented at the 64 th ExCo meeting November 19-21, Winterthur, Switzerland Prepared by Hans-Martin Henning and Marek Miara Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2, Freiburg, Germany Phone +49/761/ Fax +49/761/ hans-martin.henning@ise.fraunhofer.de Contents 1 Introduction and background System examples and trends Why a systematic treatment is needed Why an IEA activity? First ideas of a Task structure and possible outputs Next steps Issues for the Executive Committee...8

2 Report history Date Version Author/s Major changes Hans-Martin Henning Hans-Martin Henning, Marek Miara First version Version sent to ExCo page 2

3 1 Introduction and background In the last years an increasing number of systems for house heating and/or domestic hot water production has been developed which use a combination of solar thermally energy systems and vapour compression heat pumps. Prototypes have been presented at major trade fairs and first commercial systems were put on the market from various manufacturers. Manufacturers originate either from the solar energy field or from heat pumps, i.e. most manufacturers exhibit a background in one of the two main involved technologies. This is also the reason for different general approaches: - Main system components are just placed one beside the other and do not interact. Solar energy is mainly used to reduce the electricity demand for hot water preparation. These systems are mainly offered by heat pump manufacturers. - The main purpose of the heat pump is understood as a method to increase the energy gain of the solar collector system. The heat pump allows to use solar energy even if the temperature of the gained heat has a temperature level below the required temperature of the demand side (heating system, hot water). - Overall system concepts are developed in which solar energy and heat pump either work in parallel or interact in a sense that solar heat is used as heat source of the heat pump either directly or indirectly, i.e., decoupled by heat storage. The used heat storage may be sensible or latent (PCM, ice) and short term or longterm (e.g. ground). No systematic analysis of the different systems and their application potentials in different sectors and under different boundary conditions has been made. Also these systems are not yet covered in norms or standards. 2 System examples and trends Examples of systems using a combination of heat pumps and solar collectors will be presented below. The skims are limited to main system components. To simplify the illustrations, the connection with the space heating system is for all systems the same. System type 1 One beside the other (typically offered by producers of heat pumps and/or solar collectors like Viessmann, Vaillant, Nibe, Bosch Thermotechnik, ) - System components are placed one beside the other and do not directly interact page 3

4 - Simple design; control systems for a heat pump and for a solar collector usually work separately - Use of solar energy solely for the domestic hot water production - The main advantage of the system (beside producing hot water partly with solar thermal and thereby decrease the heat to be delivered by the heat pump) is the decrease of the required average inlet temperature of the heat produced by the heat pump. This contributes to the increase of the SPF (Seasonal Performance Factor) of a heat pump and to the reduce of the electricity consumption of the system - In case of ground used as heat source there is no active regeneration of the ground heat source by the solar energy but only a reduced heat extraction mainly during summer due to the solar hot water production System type 2 Active regeneration (examples IDM Energie Systeme, Immosolar, Schüco, Roth Werke) - Components and benefits of the system are similar to the system 1, and additionally: - Active use of the solar energy for the support of the ground heat source regeneration, - The active regeneration causes the dehydration / drying-off of the ground around the borehole. This fact constitutes a (perhaps small) disadvantage in view of a subsequent natural regeneration. Another problem by the active regeneration is an outflow of the accumulated energy with the ground water. This process can significantly reduce the advantage of the active regeneration of the borehole and depends on local conditions. - System allows increasing of the solar gains and the prevention from the solar collector stagnation by a high irradiation and a small heat demand in summer. page 4

5 System type 3 Big buffer storage (examples Chemowerk CEMO, Soltex, Thermosolar) - The buffer storage has a big volume (e.g. 800 l) and serves as a heat source for the heat pump, in case of a lack of energy inside the buffer the heat pump uses the borehole heat exchanger - As a result of many hydraulic components (among others two storages) the system requires more place, higher cost and a sophisticated control system - No active support for the regeneration of a ground heat source foreseen - System allows higher inlet temperature for the evaporator of the heat pump and the increase of the solar gains System type 4 Maximal integration (example SolvisMax - SOLVIS) - The heart of the system is the (patented) multi-level storage tank - The condenser of the heat pump is placed directly in the storage tank - Solar collectors (often bigger field then usually) take the leading role in the system; heat pump plays an additional role - There is no active support for the regeneration of the ground heat source and no solar boosting of the heat source. The combination of the solar energy and a heat pump is similar to the system 1 one beside the other but integrated in a main buffer storage (solar combi-system approach) - Very compact and space-saving system with one control device for the whole system page 5

6 - Preparation of domestic hot water arranged with an external heat exchanger System type 5 Unglazed collector (several examples in different configurations) - The system uses the unglazed solar collector solely to increase the inlet temperature for the evaporator of the heat pump and for active regeneration of a ground heat source but not for active domestic hot water heating - Use of the unglazed solar collectors reduces the costs of the system and allows good integration of collectors with the shape of a house - Similar to other systems with active regeneration of the ground heat source, there is a potential for shortening of the borehole System type 6 Solar heating system (SOLAERA Comsolar), other similar systems using ice-water storage (Aquasol, terra sunenergy) - The main components of the system are special made hybrid solar collectors with air-exchanger, heat pump, water storage tank and ice-water storage tank page 6

7 - The ice-water storage accumulates very efficiently the energy conducted by the hybrid collector. The heat pump uses the energy accumulated in the ice storage and produces heat for the heating system and for domestic hot water - The low temperature of the ice storage allows almost losses-free accumulation of the energy - No ground heat exchanger (e.g. borehole) is required for this system - The hybrid collector uses the solar irradiation or the heat of ambient air System type 7 Ambient air heat pump (SOLution, ratiotherm) - The main components of the system are solar collectors, air-to-water heat pump and water multi-storage tank - The heat pump uses the energy from the solar collectors or ambient air (but not with the solar collector used as air heat exchanger like in system type 6) and produces heat for the heating system and for domestic hot water - No ground heat exchanger (e.g. borehole) is required for this system 3 Why a systematic treatment is needed The increasing number of offered systems using a combination of solar thermal energy and heat pumps and the high expectations about their contribution to energy efficient heating, hot water (and possibly cooling) of buildings give reason for a systematic treatment. A systemic comparison of existing systems is needed from the economical and environmental point of view. In addition, it is highly advisable to adjust various systems to distinct boundary conditions, for instance diverse buildings standards or climate zones. Merely a systematic approach, including the modeling, simulations and field-testing of the joint use of solar thermal energy and heat pumps, allows optimization and further development of the relevant systems. After all only a high quality of offered systems will ensure a sustainable development of markets for this type of combinations of solar thermal systems and heat pumps. This high quality needs a common, agreed approach for system characterization, bench-marking and standardization. Otherwise danger is given that examples of installations with bad results and unsatisfied users do not only affect the market for combined systems (solar thermal + heat pumps) but also the markets for heat pumps and solar thermal energy use. page 7

8 4 Why an IEA activity? The IEA Solar Heating and Cooling Programme provides an excellent platform for the development of common understanding of the different systems offered in different countries and using different schematics as shown in section 2. This includes the development of performance figures, economic figures, identification of potential applications (building standards, building types, climates) and pre-normative work aiming at the development of methods which could become standards later. In addition a joint international activity which involves industries (manufacturers, system suppliers) will help in the development of the technology and possibly bring up new or optimized solutions. Finally many of the companies involved in this technology field are internationally active and thus an international collaboration seems helpful and efficient. 5 First ideas of a Task structure and possible outputs The Task should be a joint Task with the IEA Heat Pump Programme (HPP). A possible structure might involve 4 subtaks: A Overview about solutions and generic systems B Performance figures and performance assessment C Modeling and simulation D Dissemination and pre-normative work Main outputs might be - Technical report on system schematics - Proposals for implementation into standards (for heat pumps and/or solar thermal systems) - System models including models for new components which may be not available so far (e.g. solar collector / air heat exchanger; storage with integrated condenser of the heat pump) - R&D roadmap - 6 Next steps We suggest that a Task Definition Workshop is organized. Participants should be composed of experts from R&D institutes and from companies involved this technology field. Experts should also be invited through the IEA Heat Pump Programme. Main questions to be addressed: - Need for an IEA Task/Annex? - Main wishes/needs from industry side? - Possible Task structure and contributions 7 Issues for the Executive Committee - Discuss concept paper - Check national interest - Decide on next steps (Task Definition Workshop) page 8