System description

The AC-Sun system consists of two separate circuits: the driving circuit and the cooling circuit.

The driving circuit is in principle the same as in a thermal power plant. Heat creates steam that drives a turbine, but in the AC-Sun application the temperatures and pressures are lower. The circuits operates under vacuum allowing steam to be generated at low temperatures. 

The cooling circuit's process is similar to the basic refrigerator cycle, except that the media is water. To make water work as a refrigerant the pressures are also very low in the cooling circuit.

See animated demonstration of the technology here

                                [1] Buffer tank      [2]  Expander       [3]  Condenser

              [4] Compressor   [5]  Condenser     [6]  Evaporator     [7]  Heat exchanger


Cooling process in the driving circuit       Step  a)  to  c)

a)   Water is heated in the buffer tank [1] and evaporated to steam. The buffer tank holds no air, only water in the bottom and steam in the top. When temperature rises, pressure builds up but remains below atmospheric pressure.  

b)   On its way from the buffer tank to the turbine [2] the steam is superheated by a heat exchanger [7]. The steam goes through the turbine (expander) [2] that makes the turbine shaft spin. An expander is a turbine wheel designed for transforming pressure to rotation. The steam flows through the expander, expands and pressure and temperature drop. This makes the turbine wheel and shaft spin.

c)   Coming out of the turbine the steam flows to the condenser [3], where it condenses to liquid water, which is pumped back to the buffer tank. Condensation makes the pressure drop maintaining the pressure difference before and after the expander wheel. The condenser is a heat exchanger that cools down the steam with the surrounding air outside the building. 


The cooling circuit       Step  d)  to  g)  

d)   On the turbine shaft in the other end of the expander wheel, a compressor wheel is mounted [4]. The compressor is a turbine wheel designed to increase pressure when rotating. When the steam is compressed the pressure and temperature rises.

e)   After the compressor a heat exchanger [7] cools down the steam and uses this energy to super heat steam in the driving circuit. A heat exchanger is a device that can transfer heat (energy) from one circuit to another without mixing steam from the two circuits.

f)    The steam is then condensed in a condenser [5] similar to the condenser in the first circuit. In the condenser the steam cools down and is converted to water. This keeps the pressure low in the condenser. This condenser is also placed outside the building.  

g)    From the condenser liquid water flows to the evaporator [6] where pressure is very low. The pressure in the evaporator is low because the compressor is absorbing steam from it and the incoming water travels through a thin pipe. Due to this low pressure inside the evaporator, water will evaporate at 15oC. This creates the cooling effect. Heat is transferred from the air inside the building to the water in the evaporator, keeping the building cooled. A fan circulates air over the evaporator and into the building. An evaporator is a heat exchanger where a fluid changes phase from liquid to gas (from water to steam).  


The energy flow

The energy flow is shown in the picture below. Heat from a solar thermal collector is transferred to the buffer tank, where water evaporates (80-90oC). After the buffer tank the steam is superheated with heat from the cooling circuit by a heat exchanger [7]. In the expander pressure and temperature will drop. This means that the condensation will take place at a lower temperature (40oC) 

Through the compressor in the cooling circuit pressure and temperature increases. Heat from the steam is transferred to the first circuit to overheat the steam before the expander. After the compressor and the heat exchanger [7] steam enters a condenser and becomes liquid water. In the evaporator the water then evaporates and flows into the compressor.

This means that energy (heat) is added to the system in the buffer tank (could be by a solar thermal system) and in the evaporator in the cooling circuit. It is the evaporator that creates the cooling effect by removing heat from the air inside the building. 

Energy is removed from the system at the two condensers (one on each circuit). This waste heat could be transferred to air outside the building or used in another way (heating up a swimming pool). 

Energy is transferred internally in the AC-Sun system from the cooling circuit to the first circuit to overheat the steam before it enters the expander turbine. 


Placement for the components

The red circle in the picture below shows which components - turbines [2] and [4], the heat exchanger [7] and buffer tank [1] - are built together . The condensers [3] and [5] are placed outside the building to remove waste heat from the system and the evaporator is built into the ventilation system of the building.