The MultiPACK project, an EU-funded project to develop integrated transcritical CO2 (R744) HVAC&R systems, has found integrated CO2 heat pump systems to be a “reliable” solution for hotels, reporting COP values of up to 6 during field tests in two northern Italian locations.
The results were published in an article in Industria & Formazione magazine, published by Centro Studi Galileo, in April. The article was written by Italian OEM Enex, a partner in the MultiPACK project.
“The MultiPACK project provided the opportunity to install and monitor integrated HVAC systems for hotel installations,” said the authors from Enex. “The experimental campaign validated their operation and performance while demonstrating the reliability of the individual components and the entire unit.”
The first integrated CO2 heat pump system was installed in a hotel located near Lake Garda in Northern Italy. It provides space heating, cooling and domestic hot water. The heat source is groundwater, and the cooling capacity is 20kW at 12/7°C (5.7TR at 53.6/44.6°F). The heating capacity is 20kW at 30/55°C (86/131°F), and the hot-water capacity is 30kW at 65°C (8.5TR at 149°F). The system is equipped with a two-phase multi ejector and two evaporators – one with natural circulation and the other located in the suction line of the multi ejector feeding the heat exchanger.
In natural circulation the evaporator is not fed directly by the expansion valve, but from a low-pressure liquid receiver, which is in turn fed by the expansion valve. Using a low-pressure liquid receiver is advantageous as it ensures the whole surface is wet, and therefore the efficiency is higher. The liquid receiver feeds into the evaporator using the gravity principle where the less dense vapor from the outlet is returned to the same receiver.
The system also has a hydronic module consisting of three-way valves that can change the water flow according to the needs of the building. The hydronic system provides the space heating and cooling using fan coils. The hot water is stored in two storage tanks connected in series to facilitate stratification.
The second installation is an air-to-water system located in the Dolomites in Italy’s northeastern mountainous region. The unit functions as a chiller, providing cooling and hot water by using the integrated heat recovery. It has a cooling capacity of 150kW at 12/7°C (42.7TR at 53.6/44.6°F). The hot water is supplied to tanks, and the chiller is coupled with a system based on fossil fuels.
The system has the same two-phase multi ejector and evaporator design as the first installation and is equipped with a gas cooler to reject the unwanted heat outside in case hot water is not needed.
Data from the Dolomites installation was collected from June to August 2020, measuring pressure, temperature, capacity and water flow within the circuit. The system achieved a COP of 6 in stable conditions with ambient air at 15°C (59 °F) and a COP of 3 when the ambient temperature is around 30°C (86°F). The cooling capacity was between 50 and 60kW (14.2 and 17TR) with the temperature range between 10 and 20°C (50 and 68°F).
In 2020, the five-year-old MultiPACK initiative presented preliminary results showing that these integrated CO2 systems are also suitable for supermarkets in a southern European climate.
The MultiPACK project aims to demonstrate the performance and efficiency of the next generation of standardized CO2 cooling and heating installations for commercial and public buildings. It is funded by the European Union’s Horizon 2020 program, and project partners include the Norwegian University of Science and Technology (NTNU), Sintef, CNR-ITC, Danfoss, Enex, Sonae and retailer RACE. The project is led by NTNU.
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