Reduced energy consumption for ventilation in buildings by integrated air cleaning and heat pump - task 2

This report summarizes task 2 of the Clean Air Heat Pump (CAHP) project - experimental validation and demonstration on the energy savings capacity of the CAHP for heating, airconditioning and ventilation. A prototype unit of the CAHP with air handling capacity of 250 L/s was developed for the test. The prototype unit includes a specially designed heat pump with two condensers, two evaporators and one silica gel rotor. The dual condensers and evaporators design was made to minimize the energy consumption of the CAHP operating in both summer and winter climate conditions. It also makes it easier to switch between different operation modes.

The prototype unit of the CAHP was tested in the laboratory at DTU. The test lab has an air handling system that can simulate climates of different seasons and climate zones. To make it comparable with the simulation made in Task 1 of the project, climates of the three cities i.e. Copenhagen (Denmark), Milan (Italy) and Colombo (Sir Lanka) were used for evaluating the energy performance of CAHP. The three cities cover mild-cold, mild-hot and hot & humid outdoor climates. Airflows of these climate conditions were established in the test room as outdoor air supplied to the CAHP and real energy consumptions of the CAHP were measured when it was operated at these climate conditions.

For the Danish climate (the mild cold climate), the measured energy saving of the CAHP system compared to the conventional heating/air-conditioning and ventilation system was around 59% in summer and 49% in winter. Considering that most of the heating systems in Denmark were not electric driven, the energy saving of the CAHP in winter was further compared by the cost of energy. Compared to a conventional heating and ventilation system which was gas driven, the CAHP system saved 25% in the cost of energy. Since the Danish summer climate is very mild, over 80% of the yearly energy consumption for ventilation is used during winter season. It is, therefore, estimated that more than 29% annual energy cost saving for heating/air-conditioning and ventilation is expected in Denmark using the CAHP ventilation technology. For the mild hot climate, e.g. the Italian climate, the measured energy saving of the CAHP was around 40% in summer season. For winter season, 22% reduction of the energy cost was expected. For the extremely hot and humid climate, e.g. Sri Lanka, cooling is required over the year. The energy saving was only measured for cooling and ventilation. The results showed that 30% of power saving could be achieved.

In general, the laboratory tests showed that CAHP technology is suitable for heating/airconditioning and ventilation in all kinds of climates around the world except for the hot and dry climate. The energy saving is expected in the range between 25% and 60% depending on the climate. This measured energy saving is little lower than it was calculated by the numerical simulation in phase 1 of the project. The reasons are discussed in the chapter of Discussion.

It is worth noting that the reference system that was used to compare for the energy consumption with the CAHP included an efficient energy recovery system for ventilation. Compared to such a ventilation system, the CAHP system could still save substantial amount of energy. Therefore, the technology is highly recommended provided that its air cleaning function is further validated by experiments.