CIOB Innovation Achiever’s Award Winner – The Oxypod: How it works

The CIOB’s Innovation Achiever’s Award recognises outstanding industry-based innovation that has improved upon – or extended beyond – current expectations of best practice, in the built environment. The Award aims to celebrate individual excellence in innovation. The 2014 Premier Award winner in this category went to Robert Harris and Stanley Whetstone for their innovation ‘Oxypod: A Clear Solution to Energy Efficiency’. The Oxypod is an egg shaped device developed by Stanley Whetstone from an original idea formulated by builder Robert Harris. The development received financial support from The Goodwin Development Trust. Used in closed-looped heating systems, the device removes trapped and dissolved air from the system, boosting energy efficiency by as much as 30%. The following text is a technical piece provided by Stanley Whetstone describing how the Oxypod works (copyright Stanley Whetstone):

Water that enters a sealed or open vent system contains roughly 2.5% of dissolved air. When the heating system fires up and the water begins to heat, it can no longer hold this air in solution and it precipitates out. It forms in insulating barrier between the outside of the water and the inside of the pipework and heat exchangers.

Many engineers believe that an auto air vent placed high in the system will get rid of the dissolved and entrained air as it will naturally float to the highest point in the system. Our research and the eventual field trials and more latterly formal testing of this has borne out that most of the air cannot come out of the system because of the Nitrogen, which makes up 78% of the air. When this noble gas is precipitated out of solution, along with the Oxygen, which is around 18% of air, it forms bubbles that are microscopic and have no buoyancy. The problem is then exacerbated by the fact that the Oxygen and Nitrogen are partially bonded by their co-valent electrons. This prevents most of the Oxygen from exiting the system through the air vent placed high in the system. The only way to get rid of the air, is to cause a pressure drop. This is what Oxypod does and this is why heating systems corrode.

 

Within the body of Oxypod, instead of the primary water simply forming a vortex, it cannot, because of the shape of the Oxypod, which is egg shaped. It causes the water to literally “implode” in on itself. This has the effect of stripping away the surface tension of the water which stops air from coming fully out of solution. As the water is driven downwards by the circulation pump it enters a low pressure zone just under a dip tube. This has proven to be a drop of approximately 30 kilopascals. It was demonstrated by computer fluid dynamics testing and modelling conducted by Hull University. The air expands very rapidly and it can be heard escaping the system in the very early period after recommissioning. It’s similar to the opening of a bottle of a carbonated drink for the first time.

 

As the water is driven by the circulation pump downwards in the pipe work, a vortex forms. This then aids the elimination of air as within the centre of the vortex in the pipework, there is still a low pressure zone, created by the centrifugal forces in the vertical pipe. As the remaining air is driven downwards, the bubbles of air enlarge enough to gain their own buoyancy. It is a known fact that air and solids can travel against the direction of flow in a vortex, therefore the air can easily rise out of the primary system through natural phenomena created by the vortex.

The first thing that is noticed is that the system begins to run very quietly. This is due to the removal of air which is the cause of cavitation. Within the first 20 minutes, the water will heat up to 10°C hotter, so the boiler is turned down. This happens quicker with oil boilers than gas boilers. The whole pattern of the boilers’ performance changes as the air is eventually eliminated from the system. We think we are achieving a reduction of air in the system to down below 1:5 parts per million (ppm).

Our research has also proved that cold sections in a heating system, after a short time, achieve the same temperature as the rest of the system. This is explained by the fact that once air has been totally removed from a primary system, the systems resistance to flow is greatly reduced. Another discovery revealed through our research is that the primary waters’ viscosity is also reduced. These two factor contribute to the elimination of cold spots as the water is flowing through the system much faster, yet, is placing less stress on the circulation pump which is running vibration free.  The most obvious fact in all this is that the primary water returns back to the boiler much hotter, in fact, we have measured the primary temperature entering Oxypod and also leaving it. We have found that there is a 2°C rise in the primary flow. This has been repeated with the same result many, many times.

There are many engineers that will say that a very small ΔT will cause inefficiencies in the boiler. We have not found this to be so. In the 15 properties we data logged, it was recorded that the ΔT is only 1°C. Yet, in one property, it is producing an annual gas consumption less than 10,000 kW/Hrs per year, with a Carbon dioxide output of 1.85 Tonnes, where the average Carbon output is close to 4 Tonnes.

Once the system has stabilised, particularly with the newer condensing boilers which modulate, we have data logged two systems in two very different properties, but the result was almost identical. In a 15 year old 3 bedroom semi-detached house where the boiler’s set point was left at 75°C, from the middle of the afternoon, it ran between 36-48°C, yet, maintained 21°C throughout the property. The other logging we did was in a new 3 bedroom end of terrace house. This property had to be kept warmer for longer periods as the tenant has health problems. The boiler was actually set to 45°C, yet it ran between 32°C and 42°C and maintained a temperature of 24°C. This phenomena occurs because the radiators are now full of water devoid of any air and work in a slightly different way. The heat is more evenly distributed across the radiator and the heat can be felt from much further away. In lower temperatures, such as those run by heat pumps, the effect is the same, therefore contributing toward increasing the heat pump’s coefficient of performance.

Thermal image of a radiator before Oxypod is fitted   Thermal image of a radiator after Oxypod is fitted

When the Oxypod was submitted to Hull University’s Engineering and Acoustics Department the modelling threw up something totally unexpected. It showed that the flow velocities that the little unit at 80 mm dia. would accept, is up to 200 litres/minute. We then installed the Oxypod in systems over 88 kilowatts and got the same result as a small terrace house, yet the primary flow was up to 54 mm. We have recently installed Oxypod in the stations of the North East Ambulance Service and got an immediate drop in gas consumption of 20%. In a hotel with 24 bedrooms, we installed Oxypod and now the boiler is turned down to minimum. The reduction in gas consumption has now been recorded at 40%.