Hybrid heat pump for industrial applications: experimental characterization and optimal configuration

How to turn solar heat and industrial waste heat into useful cooling effect? Industrial processes are often energy-intensive and the need for their efficient decarbonization is now at the forefront of governmental and corporate policies worldwide. However, solutions for the green transition of the industrial sector should be:

  • Flexible
  • Widely applicable
  • Reliable

And should:

  • Minimize energy consumption
  • Reduce operational costs
  • Lower CO2 footprint

Is there a solution to all these answers? Heat pumps are the fit match to tackle these issues.

Within HYCOOL, CNR ITAE and Fahrenheit have developed a hybrid thermal heat pump for application in several industrial sectors where efficient and sustainable cooling is needed. But what is the hybrid heat pump?

The hybrid heat pump concept

HYCOOL system proposes the combination of a thermal heat pump with an electrical heat pump: the thermal heat pump exploits low-temperature waste heat (i.e. 70-90 °C) that is generally unused or dumped to the ambient. It can also be powered by renewable sources, such as solar heat and biomass. The electrical heat pump can exploit electricity locally produced (i.e. from PV panels or other sources) and thus further increase the share of renewables. The hybridization consists in the configuration of the two heat pumps: they can work in series, in parallel or in cascade by just changing the hydraulic connections. This makes HYCOOL configuration flexible and easily adaptable to different industrial cases.

In the framework of HYCOOL, two case studies are considered, which are shown in Figure 1:

  • At GIVAUDAN (chemical industry), process cooling at +5°C is needed. To achieve this target with an overall high efficiency, the base load is covered with an adsorption unit (80 kW nominal power) that cools down the fluid in the range 5-21°C. Peak load is supplied by a compression unit with a natural refrigerant (propane, R290), that is connected in series with adsorption unit.
  • At Bodedebò (food industry), cooling of food at -10°C is needed. In this case, the efficiency in cooling generation is achieved by using a cascade configuration: the thermal heat pump (adsorption) is used as topping stage for the electrical heat pump, in a two-stage system. This increases the efficiency of the electrical heat pump up to 40% at the expenses of renewable or even waste low-grade heat, so virtually without the need for extra cost.
Figure 1: HYCOOL flexible configuration of the hybrid heat pump.

Experimental evaluation of the hybrid heat pump

The hybrid heat pump was tested in the laboratories of CNR ITAE in Messina in design and off-design conditions (see Figure 2). The aim of the tests was to define the cooling power and electricity consumption of the hybrid heat pump in the different ambient and process operating conditions, as well as confirm the reliability under off-design conditions. To this purpose, more than 100 testing cases were evaluated, and the results were reported in form of performance maps, like those in Figure 3.

Figure 2: the hybrid heat pump installed at CNR.
Figure 3: performance maps of the hybrid heat pump tested at CNR.

Is HYCOOL solution feasible for you?

HYCOOL solution is widely suitable for a vast range of processes. To know whether solar cooling can be part of your industrial processes, a screening tool, based on process requirements and information on the solar radiation in your industry’s location, was realized and is accessible here:

The results of the experimental testing at CNR, instead, were used to compile a calculator to predict the refrigeration capacity and energy efficiency ratio (EER) of the cascade HYCOOL chiller for a given industrial cooling process. You can access the tool here:


Written by CNR-ITAE

Experimental Characterization of an Innovative Hybrid Thermal-Electric Chiller for Industrial Cooling and Refrigeration Application

Article pulished in Applied Energy (2020)

Title: Experimental Characterization of an Innovative Hybrid Thermal-Electric Chiller for Industrial Cooling and Refrigeration Application

Language: English

Authors: Giuseppe E. Dino (*1) , Valeria Palomba (*1), Eliza Nowak (*2), Andrea Frazzica (*1).

*1: CNR ITAE, Salita S. Lucia sopra Contesse 5, 98126 Messina, Italy
*2: Fahrenheit GmbH, Siegfriedstr. 19, 80803 Munich, Germany

Abstract: The energy demand of industries accounts for about 30–35% of world yearly energy consumption, a relevant percentage is due to the need of heating and cooling demand. Solar heating and cooling technologies can be integrated in industrial processes to reduce the fossil fuels consumption as well as the related greenhouse gas emissions. This paper reports the experimental analysis of a novel hybrid sorption-compression chiller for cooling and refrigeration purposes in cascade layout, which uses silica gel/water for the sorption cycle and a low Global Warming Potential (GWP) refrigerant, i.e. propylene for the compression cycle. The experimental results highlighted the flexibility of the system in terms of performances and operating conditions, these were compared to the theoretical performances and it was found out that electricity energy savings from 15% to 25% can be achieved when using the hybrid system over a compression one with the same cooling capacity. The results were converted in performance maps and processed in a statistical model, in order to get a simplified expression for
determining the overall performances of the hybrid system through variables that could be measured by a final user, such as the operating temperatures. Optimization strategies were identified for a further enhancement of the performance of the chiller, i.e. the reduction of the electricity consumption, by controlling the intermediate temperature (evaporation temperature of the sorption chiller) through sorption cycle management and the use of variable speed of the pumps in all the circuits to reduce the parasitic consumption especially at low part loads.

Experimental Evaluation of a Hybrid Adsorption-compression Cascade Chiller for Solar Cooling Applications in Industrial Processes

Title: Experimental Evaluation of a Hybrid Adsorption-compression Cascade Chiller for Solar Cooling Applications in Industrial Processes

Language: English

Authors: Valeria Palomba, Giuseppe E. Dino, Steffen Kühnert, Davide La Rosa, Andrea Frazzica.


The present work reports the experimental evaluation of the performance of a cascade chiller, having an adsorption cycle as a topping cycle and a vapour compression cycle as a bottoming cycle. An experimental testing campaign was carried out at CNR ITAE, focused on the definition of performance maps of the system under different operating conditions. In particular, heat source temperatures between 70°C and 85°C were evaluated, cooling temperatures between 22°C and 40°C and chilled water temperatures of -12°C up to 5°C, in order to reproduce the operation in different seasons, climates and user requests (i.e. air conditioning and refrigeration). Cooling powers from 18 kW (under air conditioning conditions) from 12 kW (for refrigeration conditions) were obtained for the lower cooling temperatures. Indeed, the cooling temperature has a great influence on the cooling capacity of the system, whereas heat source temperature has a smaller effect on the capacity of the system. Finally, the energy savings that can arise from such a configuration were calculated and up to 25% reduction, if compared to a standard vapour compression system can be achieved. A reduction in CO2 emissions up to 3.5 yearly tons were calculated as well.

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