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),

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

Taking these 4 Annexes both Programmes came to the result that

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.

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

Task 3 – deals with the improvement of components and systems
There are still improvements possible; the Task should deal with

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

Task 5 – Overcoming Economic Barriers
Overcoming economic barriers has to cover both economy for users and economy for the country. Measures can be

Task 6 – Increasing the Acceptance
Increasing the acceptance means improving the knowledge on ground source systems. Measures are

Results:

Results of this Annex will be

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.

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