The hybrid heat pump constitutes one of the core elements of the HyCool solution for solar cooling in industry and, therefore, its optimal design is crucial to achieving high performance of the overall system. Since the very beginning of the project, the Fahrenheit team has been working on a prototype of the hybrid heat pump with the goal of obtaining highest efficiency while keeping the machine simple and reliable. In the early spring of 2019, the first prototype HyCool XHHP01 was ready for testing. The results of the tests performed by CNR have shown a very good performance of the prototype and have indicated a few areas, which still needed improvement. Currently, the Fahrenheit team is making use of the time left before the installation of the pilot sites to optimize the functionalities of the hybrid heat pump. Three members of the team explain to us the general concept of the hybrid heat pump, how they want to optimize the prototype, and what challenges are still ahead of them.
The hybrid heat pump constitutes one of the core elements of the HyCool solution for solar cooling in industry and, therefore, its optimal design is crucial to achieving high performance of the overall system.
Eliza Nowak, Project Engineer at Fahrenheit GmbH, on the general concept of the hybrid heat pump
The term “hybrid” refers to a combination of two or more interconnected and co-operating heat pumps based on different principles of operation. In our case, the developed prototype consists of an adsorption and a compression heat pump connected in such a way that the evaporator of the adsorption unit cools down the condenser of the compression one. This lowers the condensation temperature below the one resulting from the outdoor conditions. Lower condensation temperature means higher EER (Energy Efficiency Ratio – ratio of the delivered cooling capacity to the consumed electrical power) of the compression chiller. Of course, to make this layout feasible, the savings of the electrical power consumption of the compressor due to higher EER should be higher than the additional power consumption of the adsorption unit and its auxiliaries.
Doreen Acker, Software Developer at Fahrenheit GmbH, on the prototype optimization
In terms of the control software optimization, we are implementing two changes in the HyCool XHHP01 prototype. The first one is the introduction of a free cooling mode, to allow the use of low external temperatures for cooling of the compression unit’s condenser. In brief, in the free cooling mode the condensation heat of the compression chiller is dissipated directly to the ambient air via the dry cooler. If the outdoor temperatures are low enough to ensure the condensing temperature of the compression chiller as low as or lower than with the use of the adsorption chiller, which happens mostly in winter and during night time, the system will operate more efficiently in the free cooling mode. The operation of the system resembles the standard operation of the compression chiller and saves the electrical power needed to drive the circulating pumps of the adsorption chiller. Thanks to the clever hydraulic connections in the adsorption unit, we can implement this new operation mode through a software update without the need to rebuild anything in hydraulics. The second change is the optimized start-up procedure. After the tests performed by the colleagues from CNR, they suggested that the compression unit should be started when the temperature in the cold water circuit of the adsorption unit reaches a specified threshold. In this way, we will ensure favourable conditions for the operation of the compression unit at all times.
René Weinitschke, After Sales & Factory Service Engineer at Fahrenheit GmbH, on the data logging and Cloud solutions
In order to evaluate the performance of the hybrid heat pump, we have to perform measurements and collect meaningful data. Some of the measurements will be carried out by the main control system based on the sensors installed on the pipelines but there are also quite a few sensors installed inside the prototype. The values from these sensors will not be sent to the main control system; rather we plan to collect them in the Cloud. We have not used this technology so far, but its implementation in our commercial projects is one of our priorities. It will not only help our After Sales services, but also contribute to our technology development. HyCool is a great opportunity for us to test this solution! From the beginning, we have to place great emphasis on the data security, especially because the pilot plants will be installed in “real-life” factories.
According to the current execution plan, the optimized prototype of the hybrid heat pump is going to be delivered to the Bo de Debó demo site in October 2019. After proper installation and commissioning, the operation of the hybrid heat pump will be monitored for 12 consecutive months. Based on the collected data the Fahrenheit team will evaluate its performance. It is expected that due to the optimization measures implemented, the prototype will show even better performance than what was achieved during the first tests at CNR.
Article by Givaudan
The idea was to test HyCool in at least two industries using significant amounts of cooling in their
processes and Givaudan offers a great profile to host one of the pilot sites as a representative of
the chemical industry. We couldn’t pass up the opportunity to participate in this innovative project.
HyCool is particularly attractive to Givaudan for two main reasons. First, our sustainability strategy
A Sense of Tomorrow includes ambitious environmental targets. This project will help us reduce
GHG emissions by a projected 3% for the site and decrease energy consumption in terms of
electricity and gas, helping us towards our goal of 100% renewable electricity by 2025. The
project is totally aligned with our sustainability strategy. Secondly, every Givaudan production
plant needs heating and cooling, and it would be relatively easy to replicate this technology.
HyCool should deliver refrigeration with 25% greater efficiency—this would provide Givaudan a
We have finished the conceptual phase: we have decided where and how to use the cooling
produced, where to install equipment and how to connect it. Now we are looking at detailed
engineering: how to best connect materials, figuring out the best design for the electrical
connections, etc. The one-year installation phase will then start this summer.
One issue was finding a place to install the solar collectors. They require more than 1, 000 m2 of
surface, preferably over a roof. Because of a lack of surface on our buildings, and for safety
reasons, mainly the presence of flammable products, this wasn’t possible, and we had to install
the solar field at ground level. This caused problems such as how to manage shadows of other
buildings that we had to solve.
We also have to comply with all EHS requirements including ensuring a good works plan for
execution. We expect a number of external contractors and companies on site during installation
and we will need to monitor all aspects of their work. We will need to ensure a pre-start safety
review, issue corresponding work permits and make sure we prevent injuries and accidents: we
want to ensure that “Everyone gets Home Safe Everyday”.
Givaudan, which itself has a target of reducing absolute Scope 1 and 2 GHG emissions by 30% between 2015 and 2030, is proud to host one of the project’s two pilot sites at its Sant Celoni plant.
During the initial phase, we worked closely with the equipment companies and engineering and
general contracting partners. This has been a real team effort.
The next steps are to finish the installation on time, on budget and safely and then to operate the
machinery and collect data on energy efficiency and ease of use. We have two years of hard work
ahead, but it will be stimulating. As to transferring the technology to other sites – why not? If it is
cost effective, we will be able to use it in countries with even more favourable weather conditions
such as Mexico, South Africa or Singapore.
Last September our colleagues Valeria Palomba, Andrea Frazzica, Steffen Kühnert and André Große
presented the following paper on Hycool at the Eurosun conference held in Rapperswill:
This paper presents the dynamic modelling of a hybrid cascade chiller for solar cooling in industrial applications driven by Fresnel solar thermal collectors. The chiller comprises an adsorption module, which is directly connected to the bottoming vapor compression chiller. This cascade configuration allows enhancing the overall electric COP, since the adsorption module is operated to dissipate the heat rejected by the vapor compression chiller, thus reducing the condensation temperature quite below the ambient temperature. The model was implemented in Dymola/Modelica, allowing describing heat and mass transfer phenomena inside each component. The complete model was then validated against experimental data obtained on a cascade chiller prototype at the CNR ITAE lab. Finally, a reference daily simulation was performed to evaluate the ability of the developed chiller in providing cooling energy to a typical industrial application
Keywords: Dymola/Modelica, cascade chiller, industrial solar cooling
The cooling demand is continuously growing worldwide in different sectors (Werner, 2016). Particularly, energy consumption and related emissions due to cooling processes in industrial sector are becoming a major issue. For this reason, the integration of renewable thermal energy sources inside industrial sites, for both heating and cooling applications is gaining a lot of attention (Farjana et al., 2018). Usually, it is accomplished with the use of thermally driven sorption machine, driven by thermal energy produced by non-concentrating solar thermal collectors (e.g. flat plate, evacuated tubes) (Murray et al., 2016). Nevertheless, this approach suffers of some weaknesses: first, when renewable source (i.e. solar energy) is not available, a backup system is needed to either operate the sorption chiller (e.g. gas boiler) or to directly produce cooling by means of standard technology (e.g. vapour compression chiller).
Secondly, the use of non-concentrating solar thermal collectors technologies often is not sufficient to properly drive the sorption machine, thus making it work under off-design conditions for several hours. Furthermore, these solar thermal collectors cannot be integrated as heating source in most of the industrial sites, since the achievable temperature level is usually not sufficient drive any process.
In such a background, the EU co-funded project HyCool (HyCool, 2018) aims at increasing the use of solar heat in industrial processes, integrating a concentrating Fresnel solar thermal collector technology, with a hybrid cascade chiller, to increase the share of renewable sources for heating and cooling applications in industries.
The present paper deals with the development of a numerical model, implemented in Dymola/Modelica, for the simulation of the innovative cascade chiller. The model describe heat and mass transfer phenomena in each component of the chiller, in order to accurately simulate its operation. Furthermore, it has been validated by means of experimental data measured at the CNR ITAE lab and it will be further used to evaluate optimal operating conditions and management strategies under typical working boundaries of an industrial plant.
2. The Hybrid cascade chiller
The hybrid heat pump is made up of two units, working in cascade mode: a thermal unit and an electric unit. The thermal unit is an adsorption chiller, based on the system already commercialised by Fahrenheit, which will be driven by the heat produced by a field of Fresnel solar thermal collectors, for the production of chilled water in the range of 16-22°C. This unit is hydraulically connected to the condenser of an electric vapour compression unit (i.e. cascading mode), which will provide chilled water to the user. In such a way, the adsorption unit is primarily meant for dissipating the condensation heat of the vapour compression unit. This operation allows increasing the overall electric COP, by reducing the temperature lift between evaporator and condenser of the vapour compression unit, thus limiting the compressor work.
Furthermore, the utilization of the cascading operation of the two units allows exploiting the benefits of the two types of systems, i.e. the low primary energy consumption of the thermal unit, which will be fed by renewable solar energy, and the fast response and good temperature control under different conditions of the electric unit (Vasta et al., 2018). A schematic of the hybrid heat pump operation and components as well as the different temperature levels is reported in Figure 1.
3. Dynamic modeling and validation
As shown in Figure 1, the hybrid heat pump is realized by hydraulically connecting the thermal and electric units. Consequently, the models for the two units were implemented and tested separately and then the overall model for the system was assembled and calibrated. […]