Ground-Coupled heat pumps with low-temperature heat storage: Some Swedish experiences

A large research program in the field of solar-coupled heat pumps with seasonal storage in the ground, using vertical pipes to a depth of 10-40 m, has been going on for several years in Sweden. In this paper, some main results from two experimental plants are presented. As well, results from a technical-economical optimization study are discussed. In these calculations comparisons are made among systems using ambient-air natural convection heat exchangers, lowtemperature solar collectors, and II conventi ona 111 amb i ent-a i r heat pumps wi thout storage.One of the experimental plants heats a school and consists of low-temperature solar collectors on the roof, four diesel-driven heat pumps, and a storage system with vertical pipes in clay, depth 35 m. Seasonal performance factors (SPF\u27s) are 3.6 (heat pumps) and 1.7 (total system). The other plant is an experimental one for a single-family house with an electrically driven heat pump, natural convection heat exchangers on the roof, and a storage system in clay, depth 10 m. Annual SPF\u27s are 3.0 (heat pump) and 2.5 (including all auxiliary electricity consumption). Systems evaluation calculations indicate optimal sizes of the three main components, although the optimas are flat. The differences in economy between systems with solar collectors and with natural convection heat exchangers are small. However, systems with solar or ambientair heat collectors and storage systems cannot today compete economically with ambient-air heat pumps without storage systems, at least if Swedish conditions are assumed

Optimization of a combined heat pump/storage system with solar or convective heat collectors

A large computer program simulating space heating systems in large multifamily houses or small district heating systems is presented. The system consists of a heat collector, either an ambient-air natural convective collector or a solar collector, a heat storage with vertical pipes in the ground, and an electrically driven heat pump. The most important technical and economical design parameters are the size of the collector, the storage, the heat pump, and the system control. The influence of these parameters on the annual COP and the heat supply ratio has been simulated and is discussed. This influence is presented in a generalized way. With the aid of the technical results an economic optimization is made of the system. The optimum is flat but sensitive to the combination of the system parts. A sensitivity analysis on the optimum is made to show the influence of investment and energy costs. Finally the system is compared with a heat pump without storage which is found to be somewhat more economically advantageous

Technical and economical design of a combined heat pump/low temperature storage system. Results from system simulations.

A computer program simulating a whole heating system for space heating in large multifamily houses or small district heating systems is presented. The system consists of an ambient-air natural convective heat collector, a heat store with vertical pipes in the ground, and an electrically driven heat pump.The most important design parameters from both a technical and an economical point of view are the sizes of the storage, the ambient-air heat collector, and the heat pump. The influence of these parameters on the technical result is discussed. With the aid of computer simulations it is shown how this influence can be presented in a generalized way. From this presentation a method to optimise this kind of system is outlined. Using typical costs for Sweden the total annual cost for some designs is calculated and a cost comparison is made with an oil fired burner.In the optimisation calculations optimum values for the main parts were determined. For the heat collector and the storage size flat optimums were found. The heat pump size shall in most cases be as large as is practically possible, when such aspects as freezing of the soil have been taken into account. Compared to an already existing oil fired burner and to a heat pump without storage this system was found to be more expensive. Decreasing investment cost and increasing energy costs in the future can however make the system economically favourable

Learning from experiences with Industrial Heat Pumps

This publication is the twenty-third in a series of Analysis Reports. These reports are specifically designed to increase awareness of a particular energy-saving technology or technique, applicable in the end-use sector, thereby facilitating its market introduction. The reports are designed to inform end-users of the characteristics of suecessful applications, and also to indicate those aspects requiring detailed assessment prior to implementation

Learning from experiences with Industrial Heat Pumps

This publication is the twenty-third in a series of Analysis Reports. These reports are specifically designed to increase awareness of a particular energy-saving technology or technique, applicable in the end-use sector, thereby facilitating its market introduction. The reports are designed to inform end-users of the characteristics of suecessful applications, and also to indicate those aspects requiring detailed assessment prior to implementation

Design of a vertical earth heat pump system. Results from system simulations.

In the paper technical and economical aspects of introducing a vertical pipe heat storage with natural convection heat collector and heat pump in an existing building are discussed. The technical influence of the design parameters is studied with a big computer program which is briefly presented. The general influence of the design parameters is presented with special interest in the occurrence of freezing in the vicinity of the storage pipes. Some examples are given which show that an economical optimum storage/collector combination can be found. In this optimum storage freezing will occur. The reduction of total annual cost can be considerable compared to a non-freezing storage