Steptank Thermal Driven Heatpump

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What is it?

The “Steptank thermal driven heatpump” is a heatpump that runs on high temperature heat instead of electricity. It is far better than old school thermal driven heat pumps, such as absorption heatpumps, Vuilleumier pumps( Thermolift ) and Boostheat heatpump (

How is the new technology different:

The Steptank technology is an improvement on the existing Boostheat technology. Boostheat uses a 3 stage Stirling like compressor to compress CO2 from 40 bar to supercritical 75 bar pressure. This is optimal for use as “high temperature” operation. (Fig 1 left)

The new Steptank heatpump has a Boostheat like compressor with up to 5 extra (step) tanks, connected via valves to the hot chamber. (Fig 1 right) These step tanks are filled and emptied in a particular order. This filling and emptying reduces the flow through the regenerator, and also reduces the pressure lifting that has to be done by the thermal part of the compressor.

When we compare the Pressure Volume diagrams (Fig 2), we see that these steptanks take care of the great deal of the compression. As a result, we do no longer need the 3 stages of the Boostheat compressor. If we take only the thermal part of the compression into consideration , we see that a 1 stage Steptank compressor has smaller compressor ratio then a 3 step Boostheat compressor.

Why is this better?

  • The COP is far better, typical 3.2 at 80°C output, instead of the existing best in class Boostheat 1.9 at 65°C output. This is due to the regenerator load which is 5 times less.
  • The Steptank heatpump has a 1 stage compressor instead of the 3 stage of Boostheat. This is so because of the steptanks are doing most of the pressure lifting. This reduces the cost dramatically.
  • The combination of COP 3.2 at 80°C is exceptional, even compared to electrical driven high temperature machines.

Does it work?

The Steptank way of doing things was evaluated by Prof Michel Depaepe & Prof Steven Lecompte of the University of Ghent (=nr 66 in Shanghai Ranking worldwide). They created a new simulation and validated all my claims in a paper. Feel free to ask for a copy of this paper. (Fig 3)

Can it be made?

Yes, the biggest challenge was finding valves that are fast and durable enough. Valves used in the pneumatic sorting machines industry (e.g. Mac Valve) can cope easily.

What are the consequences of the new technology?

This is the tipping point of the heat driven heat pumps market. COP and cost of the new machines are so much better that they can become mainstream. The high COP, especially at high temperatures makes it also possible to use the technology with electricity or gas depending on the availability. This can partially replace the need of seasonal peak energy storage. Operation at even higher output temperatures and heat recuperation looks promising. This technology will also change the economics of the "cogeneration" business.


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    Jan Lietaer
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