Blowing hot and cold

Dave Wilson talks to Industrial Design Consultancy about a system that combines domestic space heating and air conditioning

Developing a new system doesn’t necessarily mean reinventing the wheel. More often than not, some of the most inventive systems are developed by engineers who are able to bring many existing, or previously disparate, areas of technology together and refine them to create an innovative design.

That is certainly the case at Datchet, Berkshire-based Industrial Design Consultancy (IDC), where a team of engineers recently unveiled a new heating and cooling system for use in domestic and commercial buildings.

The system is aimed at homes and commercial buildings

The system has been developed as the result of a combination of knowledge of the cooling cycle, the reworking of century-old jet-pump technology, and the deployment of modern passive solar thermal systems.

Most engineers will be familiar with the operating principle behind domestic refrigerators and air conditioners. In such systems, liquid refrigerant is fed into evaporator coils, whereupon the low pressure in the evaporator causes the fluid to evaporate, absorbing heat.

The vapour is then compressed by an electrical compressor and forced into condenser coils outside the cooled compartment or room, condensing the refrigerant into a liquid, at which point it loses the heat it previously absorbed.

But despite the fact that such systems have been effectively used for many years, IDC’s engineers were aware that these electromechanical systems represent an expensive and inefficient means to power them.

Some of the most inventive systems are developed by engineers bringing together existing technologies

What’s more, rather than design a system that would provide either heating or cooling, they wanted to develop a system for the home that would deliver both.

Bearing that in mind, they set about developing a system that would not only make use of new passive solar power systems as a source of energy for heating and cooling, but also replace the compressor with a jet pump.

The result is a system that they claim can provide homes with both space heating and air conditioning from one inexpensive thermal-energy source.

Stephen Knowles, managing director at IDC, said: ’The jet-pump technology used in the IDC system is not new – it was actually invented at the start of the 20th century to remove air from steam-engine condensers.

The system has been developed as a result of combination of knowledge of the cooling cycle, the reworking of century-old jet pump technology, and the deployment of modern passive solar thermal systems

The system has been developed as a result of combination of knowledge of the cooling cycle, the reworking of century-old jet pump technology, and the deployment of modern passive solar thermal systems

In operation, a high-pressure source of one fluid is forced through the inlet of the jet pump and through a tapered nozzle. As the fluid passes through the nozzle, it accelerates, causing an area of low pressure to be formed within the mixing chamber of the pump. This low pressure then causes a secondary fluid to be sucked into the diffuser section of the jet pump through a secondary inlet.’

Yet despite the fact that the jet pump itself might not be new, the way that the engineers at IDC have optimised its performance using computational fluid dynamics and then deployed it in their heating and cooling system is a departure from the designs of traditional heating or cooling systems found in the home.

That is because they have used the thermal energy generated from solar thermal panels placed on top of a building to provide heat to a vapour generator containing refrigerant. When the refrigerant is boiled to a temperature of 100°C, it is used as the high-pressure primary source to the nozzle of the jet pump. As the refrigerant is forced through a nozzle inside the pump, the speed of the flow of the pressurised refrigerant increases, creating a suction on an open end of the chamber that then draws cooler refrigerant from an evaporator into the pump chamber where it mixes with the hot refrigerant gas from the vapour generator.

Knowles said: ’The process of drawing refrigerant into the pump from the evaporator lowers the pressure of the refrigerant within the evaporator, causing it to boil off, creating a cooling effect. It is the rate at which the refrigerant is drawn into the jet pump from the evaporator that effectively determines the cooling capacity of the system.’

The use of the jet pump will allow us to realise a system at a price that makes it more widely acceptable

At the output of the pump, the two gases mix together, after which they are fed into a condenser not dissimilar to those found in more conventional air conditioners, where they once again become liquid. In the IDC system, the mixture then passes through a fluid reservoir, after which some of the fluid is returned to the evaporator through an expansion valve, while the rest is pumped back to the generator.

There, it is heated once more by the passive solar thermal system into a gas that is again forced into the jet pump to drive the system. ’By designing in some other novel features, the system can not only provide cooling during hot periods via the jet-pump cooling circuit, it is also capable of delivering heating via the same evaporator during colder periods,’ said Knowles.

According to Knowles, although solar electric systems have already been developed that employ vapour compression technology, because they require photovoltaic cells, batteries and charge controllers, they are expensive.

Passive solar thermal technologies, such as those developed by the engineers at IDC, on the other hand, should offer an attractive alternative due to the higher efficiencies of the passive solar system and its lower cost.

’Although solar-powered cooling technologies have been developed in the past, the use of the jet pump will allow us to realise a system at a price that makes the technology accessible to a wider range of customers,’ he said.
Based on its research and testing, IDC believes it would be possible to produce a system based on the new concept that will be capable ofdelivering 4.5kW of cooling during summer months and up to 4kW of space heating during colder periods.

In addition, the thermal energy generated by the passive solar system could be used to provide, or augment, existing hot-water systems. Furthermore, Knowles said, since the system is modular, customers could add additional units to the system should they need to increase the amount of heating or cooling required.

Extensive research and development has already been conducted into the system by IDC in partnership with solar-panel manufacturer Sertec Energy, renewable energy specialist Energy International Systems and London South Bank University. Grants from the UK government-funded Knowledge Transfer Partnership programme and EU collaborative research programme have also assisted in helping to develop the technology thus far.

IDC is planning to develop a proof-of-principle system, and will then work with investors and partners to turn the system into a commercially viable product that can be mass produced.from the room

The key facts to take away from this article

  • IDC has developed a system that combines heating and cooling
  • It makes use of passive solar-power systems as a source of energy
  • Instead of a compressor, the system utilises jet-pump technology
  • This will make the system more widely accessible to customers