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Covering the preconceptions of solar cooling

SolX Energy covers the common preconceptions associated with the process of solar thermal assisted cooling technology.

Examples of how solar heat energy impacts the refrigerant cycle.

SolX Energy chief executive Mark Crabtree says: “Acquiring and maintaining clients such as Mercedes-Benz, Toyota, Sodexo & Cable & Wireless to mention a few, over the last couple of years is something we are immensely proud of. That said, boasting over a megawatt of our VRF technology on a single Mercedes Benz facility does not necessarily give us the credibility we first anticipated when approaching potential new customers.

“The due diligence required by the engineers, technicians and advisors to those clients means not only do they want to see the evidence, they must also understand how the technology works in detail, in some cases prior to even sanctioning an evaluation, which could be a legally time-consuming process. Today, however, our IP boasts several fully granted patents in various countries, including the USA, and therefore we are in a significantly more comfortable position to release a more detailed understanding of how our technology delivers.”

If you heed the advice from the SolX technical folks, it seems that understanding the concept of solar thermal assisted cooling is equally about understanding today’s HVACR variable capacity technology. The ThermX technology can only be partnered with variable or modulating systems. Therefore, SolX maintains that the technician looking to appreciate said technology should hold at least a basic understanding of the variable capacity technology.

If this is not the case, SolX strongly recommends that steps are taken to grasp, at the very minimum, a familiarity of such, in particular the compressor and the associated logic controls of these systems. Essentially, knowledge of the variable flow system should be strong enough to allow the reader to step outside of the theories involved in the process of single, fixed-speed compressor technologies, having a fixed volume flow.

Chris Micallef, SolX’s group technical director adds: “Our experience attests that a lack of understanding on how the variable system differs from the classic, fixed speed system of yesterday, will almost certainly result in the reader failing to comprehend or appreciate the thermodynamics and/or physics of how solar cooling realises the additional efficiency.”

The SolX technical team has set out below the main four preconceptions regularly encountered regarding the solar thermal cooling process.

Preconception #1: Solar thermal adds heat to the refrigerant, which, in turn, the condenser is required to remove

Factually, within the solar thermal cooling process there is no relevant ‘additional’ heat added. In the majority of cases, the logic controls are designed to recognise and meter the thermal energy in today’s modern systems. This is accomplished via a thermistor sensor, rather than through the previous method of using a pressure transducer, thereafter the logic control of such required to calculate the temperatures. The thermistor linked control logic then modulates the required compressor’s speed accordingly and, as such, the process allows the solar array to replace an element of the heat that would normally be generated by the compressor/s.

The diagrams pictured illustrate examples of how the solar heat energy impacts the refrigerant cycle.

Solar thermal, when correctly integrated into the cooling process of a modulating system, along with true thermodynamic logic controls, will operate efficiently with most refrigerants. The added benefit derived from the renewable, readily available solar energy may vary in comparison to the above illustrations, dependent on the refrigerant in use, along with the normally anticipated variables within any cooling system.

The condenser transfers heat from the refrigerant to the ambient air. The rate of heat transfer in a condenser is a function of its design properties, mass flow of the refrigerant, pressure, condensation temperature and the temperature and saturation of the refrigerant.

The solar thermal supported system retains the above process. The primary difference now being that on a system with the ability to modulate, the method increases the refrigerants temperature following the discharge from the compressor, while maintaining the pressure generated via the compressor. This therefore improves the Delta-T at the condenser point with a lower energy consumption at the compressor.

The alternative to this would be a compressor working harder to raise the pressure, subsequently raising the condensation temperature, along with an increased condenser fan speed.

Preconception #2: Heat = pressure

Some consider heat to be essentially an unwanted by-product of the pressurisation process. This is also factually incorrect. The reality is that pressure is the unwanted, yet necessary pre-condition. Without heat, the cooling effect cannot be achieved. Pressure and heat are collectively vital sources in the refrigerant process, but it is also important to comprehend that in the modern-day modulation system, the thermodynamic method is vital for efficiency improvement. Therefore, these two factors rarely align for prolonged periods.

To further emphasise this point, the vast majority of today’s VRF/VRV/MDV systems are manufactured without a single pressure transducer linked to the operational logic controls. These are now predominantly thermistor sensors.

Preconception #3: Solar thermal HVAC works, but is only viable in high ambient temperatures

Although it is generally accepted by those who have an understanding of variable refrigerant technology that a solar thermal assisted system would be beneficial in high ambient temperatures due to the Delta-T benefits, a common misconception is that this would not be the case in the considerably more temperate or ‘normal’ ambient environments.

Consider the fact that when the sun is available, the thermal collector continues to provide thermal energy to the refrigerant. The variable system’s logic control recognises this fact via thermistor sensors, as if this added heat is provided by the compressor. For example, to achieve the required Delta-T (liquid production), the system’s logic control measures data supplied via the thermistor sensors located at the condenser. Let us postulate that this specifies an increase in compressor demand, which on this occasion equates to a discharge temperature of, say, 65°c (149°F), along with the equivalent mass flow via the compressor. However, the temperature generated from the compressor and the solar array combined is, say, 70°c (158°F), maintaining the mass flow. The condenser logic sensors reasonably assume that the discharge temperature and subsequent mass flow is born only from the compressor output.

The reality is that the actual temperature discharged from the compressor may only need to be 40/45°c (104/113°F) with the relevant expected mass flow, due to the solar thermal supplementation. As such, the logic control may conceivably communicate to the compressor to slow down or maintain its position dependent on the available solar input, while maintaining mass flow of the refrigerant from the compressor.

The temperature generated via the compressor is determined by the logic to have increased, allowing the compressor to reduce its workload while actually providing a Delta-T in line with what would normally be achieved with the compressor working at a higher energy consumption rate. Ultimately, this results in an improved liquid refrigerant mass flow through the metering device, with an observed, measured and recorded reduction in energy consumption. All this results in reduced flash gas, or, as in the majority of cases, zero flash gas. 

Of course, pressure remains an important and always required component in the liquefication process. In today’s modern thermodynamically determined systems, however, pressure is monitored primarily to ensure system protection, but rarely measured in relation to impacting the logic of the control’s decision-making procedure.

The solar assisted cooling system produces efficiency gains by allowing the compressor to slow down to stages as low as its lowest possible design point, due to the utilisation of the same method.

Mr Micallef says: “We have so far developed installations on six continents across 47 different countries over the last four years. kWh data covering a multitude of differing ambient conditions has been observed and recorded. Of course, an element of this data was collated by ourselves, but the vast majority was completed by the end users themselves, through their own in-house evaluation of this technology.”

Case studies and data covering a number of high profile end users, including an independent evaluation conducted by Toyota in partnership with Durban University of Technology, along with many individual or multiple corporations, have been compiled. Most of these are available on request.

SolX is also open to potential clients or partners requesting a visit to an existing installation and will be more than welcome to affix any level of measuring device, such as power, pressure, or thermal to the system in question. Where required and if possible, visitors will also be given the opportunity to converse directly and privately with SolX clients.

Preconception #4: A solar thermal array cannot produce efficiencies on a cooling system during the hours of darkness

The sheer nature and design of the technology dictates that the solar thermal collector would generate zero additional heat energy following the discharge from the compressor during the hours of solar blackout. Consequently, it would be reasonable to surmise that there are therefore zero additional efficiencies gained during this period.

To the contrary, the efficiencies achieved are now derived from the opposite effect, with the solar array now acting as an oversized condenser, dissipating an element of the refrigerant’s heat prior to the condenser. The solar panels essentially reverse their role, again resulting in an improved liquid refrigerant mass flow through the metering device, delivering an observed, measured and recorded reduction in energy consumption.

Mark Crabtree concludes: “In closing, I should cover a question we are regularly asked: Why is it the largest and most well-known HVAC manufacturers, such as Daikin, Mitsubishi, Trane, Carrier, and Toshiba, do not have this technology on their systems? 

“Our answer is always pretty straight-forward, using a many time referenced example from the aviation industry. First, the innovators brought us the airplane. Much later, several innovators introduced versions of the jet engine. The cumulative outcome of this was the aeronautic industry ultimately developing the jet aircraft.

“The next innovation to enter the aviation arena, however, was invented by neither of the original airplane inventors, nor the manufacturers themselves. Today, the wing flaps remain one of the most important elements on today’s commercial-sized airplanes. These vast machines would simply not get off the ground without them. It is this subsequent innovative technology which ultimately revolutionised the aviation industry”.

19 February 2018

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