Objective
The construction and operation of a high-temperature heat pump of compact design using the compression principle and solution cycle.
Existing test-run measuring results do not give a clear picture of congruence due to the multitude of influencing parameters. It was tried to find a correlation for combined influences such an uniform correlation is possible and is described in the final report.
The project was finished with end of June, 1986. The long term test run has been performed end of 1986. This heat pump project has fulfilled all its major objectives.
The only major problem encountered was that the bearings in the compressor failed after about 150 hours of operation. This problem was marginally relieved by using rolling bearings with non-metal cages. However, the ultimate solution to this problem is to use hermetically sealed grease-lubricated ball-bearings.
Several smaller operational problems were encountered, the main one being that a steady-state of the plant could only be achieved with partial loads of under 30%. This was because of the insufficient suction height of the circulation pump. This problemwas overcome by installing the solution pump in a pit to increase the suction height. It should be noted that attention must be paid to selecting a pump that will operate with an extremely low suction height.
Some special conditions were found to apply to the starting-up of the system. Primarily, it was found to be necessary to ensure that nearly all the solution is contained in the desorber. If this is not the case then a spontaneous evaporation may occur when a load is put on the compressor causing a possible cut-off of the pump flow.
To shut down the system it is necessary to stop the compressor whilst leaving the solution pump running. The pressure gradient between the resorber and desorber will then take care of the solution flow-back to the desorber, thus ensuring the correct conditions for start-up.
In order to evaluate the operation of the heat-pump a special load-plant was constructed. Both the desorber and resorber had their own circulating water circuits. The heat supplied to the desorber is supplied from the absorber via controlled transfer lines. The surplus energy in the system, generated from the drive motor and pump, is removed by draining hot water from the system and replacing it with cold. By using this testing arrangement it was possible to measure the exact performance of the system.
The heat pump uses a binary combination of ammonia and water. This should improve on the efficiency of conventional units by between 20 and 50%. A further feature is that temperature increases of 100 deg. C are achievable. The output temperature can be up to 140 deg. C although in theory this type of plant should be able to operate with output temperatures of up to 150 deg. C and with a temperature difference of 100 deg. C. Units can be built with power capacities of between 200 and 1200 kW. The prototype has a power rating of 750 kW thermal.
The heat pump unit consists of 6 components :
- desorber,
- mono screw-type compressor,
- resorber,
- solution heat exchanger,
- solution pump,
- expansion valve.
The working solution is a mixture of ammonia and water.
The compressor is a standard screw type, number HS24 made by Hall, using ammonia-water solution as lubrication. The advantage of this type over others is that the displacement stars are fitted with ammonia-resistant plastic coatings which do not need oil lubrication. The gland is also cooled by the working solution. However for completely oil-free operation it was found necessary to modify the original ball-bearings with sealed gases lubricated types.
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Programme(s)
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Coordinator
13507 Berlin
Germany
The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.