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The energy consumption for space heating and domestic hot water preparation are significant burdens of a polish household budget, especially in old tenement houses. Simultaneously, lowering the emission of pollutants is under the great importance and one of main goals to achieve in big cities. This policy results in the need of elimination of systems based on solid fuels. The article analyses the environmental and social consequences of the exchange of heat sources in such buildings in one of the quarters in Wroclaw. It presents how this change will affect the levels of low emission and costs of energy supply to tenement buildings.

The energy efficiency of air-to-water heat pump operating in an actual heating installation depends on many factors. In order to create a reliable model of the unit, it is necessary to include as many of them as possible. Unfortunately, the most common data provided by heat pump manufacturers are based on tests performed in accordance with the EN 14511 standard [1]. These tests are performed in steady-state conditions and do not provide reliable information on the impact of dynamic effects on the energy efficiency of the device. The solution may be the tests in quasi-dynamic conditions. The article presents the possibility of creating the characteristics of an air-to-water heat pumps based on operational data. The accuracy of the created model has been compared with the characteristics resulting from measurements in steady state conditions. It has been confirmed that dynamic test data, after proper selection, will allow to determine the characteristics of repeatable parameters and this can be an alternative to tests performed in fixed conditions.

In this paper the authors analysed the impact of the calculation method of the partial load conditions and the accuracy of the energy demand profile on the simulation results of the air/water heat pump operation supplying the heating system. All the analyses results were compared to the results acquired for the real installation of the air/water heat pump located in Poland. The authors assessed the inaccuracy of the unit’s efficiency estimation resulting from the simplified thermal load profile of the air/water heat pump. It has been showed that using the monthly energy demand as the input data gives satisfactory results. Inaccuracy of the monthly simulation results in relation to simulations carried out on the actual hourly energy demand by no more than 7% is acceptable. On average, this deterioration did not exceed 3%.

Operating in part-load conditions significantly affects the energy efficiency of the air-to-water heat pumps. The currently used method of testing the devices does not provide the necessary data for estimating the degradation of the device’s efficiency in part-load operating mode. The value of the degradation coefficient Cc = 0.9 adopted in accordance with the EN 14825 standard is generally used. However, this value often does not reflect the actual degree of the COP reduction. Hence the new quasi-dynamic model and the calculation approach to the degradation coefficient were proposed. The model reflects the real and overall reduction between the full and part-load COP, not only the energy consumption in the stand-by mode. The estimation was made using the field measurement data of the air-to-water heat pump supplying heat to the low temperature installation. It has been proved that the determination of the main parameter is possible using a relatively small amount of data without losing an accuracy.

The energy efficiency of air-to-water heat pumps used for central heating depends significantly on the correctness of the device choice. Under given climate conditions, the temperature of the bivalent point defines the amount of energy supplied from an additional source, usually an electric heater, in periods when the power of the heat pump is too low. Commonly overlooked fact is that excess capacity is also unfavourable and has significant, negative impact on the energy efficiency of such a system. In the article, basing on the measurement data of the real installation of the air-to-water heat pump, a significant decrease in the energy efficiency of the device during periods of low energy demand was shown. The average monthly value of SCOP in the warm months was similar or even lower than in the winter months. The reason of this is the operation of the device under partial load. Although the values of COP were very high in short periods of operation, frequent switching on and off of the heat pump reduced its energy efficiency. Also, the length of operation in stand-by mode, i.e. the length of the periods between successive heating cycles, had negative influence on energy efficiency.

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