Crazy Science: Easing the Strain on the Energy Grid with Desiccant Packs

Scientists in Switzerland have kicked off a three-year project which uses a substance, similar to the silica gel desiccant packs often found in leather shoe boxes and electronics, to convert wasted heat from cloud data centers to cool air. The potential result, cloud data centers of the future might be able to cool themselves using their own waste heat.

The project is called THRIVE and it's goal is simple - to develop a heat pump powered by waste heat. If you have ever felt the hot air from an air conditioning unit or from the back of PC, this is waste heat. Waste heat can be very valuable and there is plenty of it coming from factories, power stations, data centers or other renewable sources such as solar power. It just needs to be harnessed and put to work efficiently.

A coated adsorber heat exchanger
tested at the Institute for Solar Technologies
at University of Applied Sciences Rapperswil.
Heat Pumps 101

Chances are you use a heat pump every day. They can be found in heating, ventilating, and air conditioning units to to convert environmental heat, the temperature of which lies between -5 and 15°C, into thermal heat for rooms or processes.

Traditional heat pumps draw warmth from the surroundings, such as from the earth or air, to vaporize a refrigerant in an evaporator. The vapor produced in the process rises into an electrically powered compressor, which condenses it and thus heats it up.

The vapor then turns back into liquid in an adjoining condenser and releases the heat into a heating cycle. This process can be used to produce both heat to air-condition rooms and cool air, like in a refrigerator.

Adsorption heat pump

A thermally powered adsorption heat pump works in a similar way – the major difference being that, in place of a compressor, it has an adsorption heat exchanger that uses heat at temperatures from 60°C as its driving energy instead of electricity.

During the so-called adsorption process, the adsorption heat exchanger adsorbs considerable amounts of vapor from the evaporator and compresses it inside the heat exchanger, thereby releasing heat. The refrigerant adsorbed beforehand is forced (desorbed) back out of the adsorption heat exchanger by the supply of driving heat from an external source.

The hot vapor released as a result turns back into liquid in the condenser and the corresponding condensation heat is released into the heating cycle. The adsorption heat pump can also be use to heat and cool.

These processes are supported by the desiccant or silca gel which will be filled in between the fins of the adsorber heat exchanger.

However, as the cooling or heat production takes place intermittently, at least two adsorption heat exchangers working in parallel are needed for it to run uninterrupted. Due to their low energy consumption, adsorption heat pumps achieve a much higher cooling or heat output in relation to the wattage used than conventional heat pumps.

In addition, pure water can be used as a coolant instead of refrigerants, which can sometimes be harmful for the environment. Another advantage of the technology is the fact that renewable heat sources can be used, such as solar-thermal systems, which typically generate temperatures of up to 90°C.

“Through the extensive use of the adsorption heat pumps we are looking to develop in THRIVE, it could theoretically be possible to reduce the electricity demand for heating and cooling purposes by up to 65% and the consumption of fossil fuels for heat production by up to 18% by 2040.” This would correspond to savings of around 1.8 million tons of CO2," says Dr. Bruno Michel, one of the THRIVE project leaders at IBM Research - Zurich.

Using a data center to heat and cool buildings  

By using heat, the adsorption heat pump is the ideal solution for many interesting applications where conventional heat pumps don’t make any sense. It could, for instance, use the waste heat from future, actively cooled, concentrated photovoltaic plants or cloud data centers that are cooled with hot water to provide air-conditioning for offices or residential buildings.

The Aquasar computer system developed by IBM researchers in collaboration with ETH Zurich in 2010 is a pioneer of hot-water cooling for computer systems, which not only massively reduces the energy demand for cooling in computer centers, but also enables the reuse of waste heat.

For the IBM researchers, THRIVE is the next step to make this a reality. Hot water-cooled data centers could then practically cool themselves using their own waste heat. 

THRIVE is a interdisciplinary team of partners including IBM Research – Zurich, the Hochschule für Technik Rapperswil, Empa, ETH Zurich, HEIG-VD, PSI, Zeochem AG, Danfoss, ETS Energie Technik Systeme AG, ewz, InfraWatt and MOF Technologies. The project is funded by the Swiss National Science Foundation (SNSF).

”In the THRIVE project, we have a unique opportunity to combine the latest findings from materials science, the technological optimization of heat exchangers and the merging of system and plant engineering from different disciplines,“ says Elimar Frank from the Hochschule für Technik Rapperswil and co-leader of the THRIVE project.

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