Condensor; 22 kW Figure 1: Sketch showing AC-Sun used on an A/C-plant

The AC-Sun devise consists of a traditional thermal solar panel using water with temperatures between 75-95°C. An expander, based on a Rankine-process, uses the energy from solar panels to operate a compressor, which through a Carnot-process cools air in traditional air coolers:

The system only uses water as the cooling medium and there is therefore no source of pollution. The principle is to make vacuum in a small tank and thereby lowering the temperature on the water used to cool the evaporator.

A normal thermal solar collector makes hot water at a temperature from 75 to 95°C. This temperature range is very low but can be used as direct energy to the A/C-system in AC-Sun. The cooling system works all together without any use of electrical energy. The only electrical parts of the system are the ventilators and two small water pumps. Totally electrical energy used in AC-Sun is only 10% on normal A/C consumption.

10th October, Lisbon — Portugal /

The process uses water as cooling agents both in the expander and the compressor and therefore is environment friendly. The challenge comes from the use of water as a process agent. This means that the expander must be overheated minimum between 60- 80°C, as well as processing must be in two steps.

The water steam from the vacuum tank is compressed in a small compressor like a turbo compressor on a car. The power to the turbo compressor comes from an expander connected to the solar collector.

The expander and compressor works on the same spindle shaft. Energy from the solar collector makes the rotation on the expander which drives the compressor.

The hurdle is the temperature in the expander — the steam making the expander to rotate has to be overheated so the steam doesn’t condense at the end of the expander blade. If this occurs at working speed, the lifetime for the turbine blade will be told in hours/days because of possible cavitations on the surface of the blade and later devastating the structure in the material.

The “temperature-help” comes from the compressor. The steam produced in the evaporator gets compressed and the temperature rises to at least 230°C in the compressor outlet. Through a small heat exchanger the energy from the compressor outlet goes to the expander inlet making the expansion possible without cavitations. The cooling and heating process is illustrated in a log PH-diagram showing the expansion and compression.

In principle this will cause AC-Sun turning 1.0 kW heat from 0.8 to 1.0 kW cooling. Other processes have an energy efficiency value less than half this size. And the production prices for those plants are — in contrast to AC-Sun — significantly higher than the A/C market price. The energy transformation in the AC-Sun is 1.5 kW at 10 kW cooling capacity and can with higher inlet temperature make electrical energy in a generator. In addition it’s possible to draw sterile water from the system — it has only to be supplied with the same amount of untreated water.

Maximum capacity on AC-Sun occurs after noon when the sun heats the most and the plant is controlled by a simple electrical system with low energy consumption.

The pipeline layout including certain KEY-numbers is seen in figure 4.

The system has been modelled in EES [1] with the adequate thermodynamic equations giving the performance of the system under specific conditions.

Furthermore the EES is in the process of being integrated in a TRNSYS [2] model, which will be used to estimate the yearly performance of the systems under different climates, as well as to optimise the dimensions etc. of the overall system.

2. Manufacture

The AC-Sun is planned to be produced in unit sizes with a 10 kW cooling capacity each. Each unit can be mounted together to make a larger cooling capacity, multiplying numbers of AC — Sun units to satisfy the needs for air condition.

TOutside from 25°C to 45°C at 100% humidity

TInlet from 16°C to 24°C

Maintaining fixed temperature

10 kW each unit

Fans and pumps = 0.4 kW

10% on normal A/C consumption of electricity

Turbine: aluminum, cast aluminum, stainless steel

All other materials has a format like traditional air condition plants

12 kW capacity at TSun from 75°C to 95°C

Figure 5: A/C-unit using AC-Sun — Dim 1,2×0.8×0.6 [m] without solar collector Cooling capacity / Coefficient of Performance

FIGURE 5: COOLING CAPACITY

Figure 6: COP

The cooling capacity, fig. 5, depends partly on the condenser efficiency. This efficiency can be changed by spaying water in the air to the condenser and thereby raise the air humidity in the supply air.