technical description
Background:
Ground source heat pumps (GSHP) gain importance world-wide with respect to energy efficiency in heating and cooling operation. The ground acting as a store offers the possibility of damping the effects of the outside air temperature fluctuations, in colder climates it enables monovalent heating operation of the heat pump, and for utilities it is - compared with outside air operated heat pumps - a tool for demand side management measures.
Within the framework of the IEA, the Heat Pump Programme has carried out three Annexes on ground source heat pumps (GSHP),
- Annex 2: Vertical Earth Heat Pump Systems,
- Annex 8: Advanced in-ground Heat Exchange Technology for Heat Pump Systems, and
- Annex 15: Heat Pump Systems with Direct Expansion Ground Coils.
A completely different use of the ground happens in the case of large systems with both cooling and heating demand. In such a case natural recharging of the ground no longer works, i.e. the heat extracted through heating operation has to be recharged artificially, and an excellent solution is to use heat removal from cooling operation. However, taking this type of utilisation of the ground, the ground becomes a store, and the temperature changes in this store are the result of heat extraction/heat removal over the year. In this context the Energy Conservation through Energy Storage Implementing Agreement has carried out
- Annex 13: Design, Construction and Maintenance of UTES Wells and Boreholes.
Taking these 4 Annexes both Programmes came to the result that
- Ground coupled systems offer in the case of heat pumping systems stable operating conditions.
- Ground-coupled heat pumps are presently dominating the heating-only heat pump market in Europe.
- Ground coupled heat pumps have been also identified as an interesting and energy efficient solution for the heating and cooling market in North America; there is also a large interest from other countries like Japan and China in this technology.
- In the case of large systems the ground can be used as a store, which offers in the case of heating and cooling operation at least improved conditions at the beginning of both the heating and the cooling season. Additionally, direct-cooling becomes possible.
However, using this excellent heat sink/heat source, it is necessary to consider the system including the building – with small specific loads - the heat source and the heat sink system – a new approach is low-temperature heating and high-temperature cooling – the heat pump unit and the system control. Taking all these aspects as a whole, highly efficient systems can be realised.One problem of ground coupled systems compared with air based systems is the higher investment cost for making use of this excellent heat sink/heat source system. Therefore it is necessary to base such systems on a life cycle cost basis, where they really can show their advantages compared with other heating and/or cooling systems.
Scope:
Ground source heat pumps can be applied for different climates, different ground properties, for small and large systems, and for heating-only as well as heating and cooling applications.
Climate:
The climate has a strong influence on the ground temperature available and on the operating conditions of a heat pump systems (cold, moderate and hot climate, hot an humid climate, oceanic climate with small temperature fluctuations or continental climate with large temperature fluctuations).
Ground properties:
Ground properties are responsible for the type of ground utilisation and the heat disposal/heat extraction method, i.e. open or closed loop system. In the case of a closed loop system they are also responsible for the ground heat exchanger type used.
Small systems:
The common characteristic of small systems is natural ground recovery, mainly by solar radiation collected by the ground surface. Small systems are in use for heating as well as heating and cooling, they can be used, depending on the climate and the distribution system, for direct cooling (without heat pump operation), at least at the beginning of the cooling season.
Large systems:
For large system recovery of the ground has to happen by heat removal and heat extraction. Sometimes additional systems for recharging the store have to be provided. Heat removal can happen by direct cooling (without heat pump operation) and indirect cooling (with heat pump operation).
Objectives and Results:
This Annex applies to ground source heat pump systems for both heating-only as well as heating and cooling operation. Direct cooling is included.
- The first objective is a Market Analysis on state of the art installations in different countries and the development of a matrix of ground source heat pumps and improvements of components and systems
- The second approach is the development of design criteria and strategies to overcome market barriers and to support a wide spread application of ground source systems.
Project structur:
The objectives of IEA HPP Annex 29 are
Task 1 - should cover an
Investigation of the market situation in the participating countries and an
Analysis of systems/applications for different boundary conditions like building size and utilisation, climate and ground conditions.
Task 2 – is the development of a Matrix of ground source systems based on Task 1 and literature covering the topics
- Climatic Conditions
- Properties of the Ground
- Small Systems (with Natural Recovery of the Ground)
- Large Systems (using the Ground as a Store, including direct cooling)
- LowEx Systems (Low-Temperature Heating/High Temperature Cooling)
Task 3 – deals with the improvement of components and systems
There are still improvements possible; the Task should deal with
- Comparison of W/W, W/A, B/W, B/A and DX/W heat pumps for different applications using different refrigerants (with respect to National and EU proposals of new regulation on refrigerants)
- Analysis of control systems for DX heat pumps
- Investigation of ground Coils with CO2 as heat carrier (for example CO2 heat pipes)
- Field Tests of Large Systems for both heating, cooling and direct cooling
Task 4 – Overcoming Legal Barriers
Legal barriers are sometimes based on regulations and very often on concerns regarding ground and ground water pollution, respectively, caused by leaking refrigerants and heat carriers used in such systems. Measures to overcome such concerns are
- Monitoring of systems (small and large)
- Data Evaluation
- Development of design criteria for ground source systems
Task 5 – Overcoming Economic Barriers
Overcoming economic barriers has to cover both economy for users and economy for the country. Measures can be
- Reducing first cost through advanced ground coil systems
- Development of LCCA tools for ground source systems
- Contracting models
- Financing schemes, subsidies
- Special tariffs for ground source systems (DSM)
Task 6 – Increasing the Acceptance
Increasing the acceptance means improving the knowledge on ground source systems. Measures are
- Design criteria for small systems
- Hand Book for Large Systems
- Information of architects, planers, and consumers
Results:
Results of this Annex will be
- Final Report
- National Dissemination
- Workshops
- National Courses, Seminars and Conferences
These results should be a measure to increase the awareness of these excellent highly efficient systems, provide a wider market share and thereby contribute for reducing greenhouse gas emissions.