Performance Comparison
X-FLOW Solar Collectors
Comparison of performance with traditional EPDM-hose systems
The X-FLOW solar collectors have a particularly high level of performance when it comes to heating efficiency. This depends on a number of factors including first and foremost:
- the advantages of the unique x-channel system inside the collectors
- low weight/thickness and small water volumes
- large and flat absorption surface
The x-channel system
The design of the x-channel system inside the X-FLOW collectors means that a very turbulent water flow is achieved even at low water flow rates. This turbulence means that there are no temperature shifts in the solar collector. A solar collector that has a lineal flow of water has problems with friction against the wall/surface of the water conductor which means that the outside water in closest contact with the surface of the hosing flows considerably slower than the water in the middle of the hosing. This is effectively a system design fault that means that the water is not able to effectively transport the warmth away from the heat-absorbing surface of the collector system. As a rule of thumb, one can say that when the solar collector’s surface becomes more than 6-8 degrees warmer than the pool water, that emission losses increase considerably. Another significantly affecting factor is wind but even here the X-FLOW collector system has inherent advantages since it does not exhibit any temperature differences i.e. lower temperatures at the absorbing surface.
One can also achieve a turbulent water flow in lineal solar collectors and improve the heating efficiency through increasing the speed of water flow through the collectors to approx. 2 meters/second. Such a solution will however require either a very large separate pump or a significantly reduced filtration effect.
Low weight/thickness and small water volumes
The thinness of the X-FLOW solar collector material combined with the small momentary water volume means that X-FLOW has an extremely short heating time. This is a particularly important factor in variable weather conditions in which case the solar collector system may start and stop as often as 30 times during the course of a day.
Large and flat absorption surface
The flat surface of the X-FLOW solar collector means that it has the same angle for solar irradiation across the collector’s entire absorption surface area.
If one thinks about the arched nature of the surface of an EPDM-hose system, in this case it is no more than 20% of the surface of the hosing that can be considered to have a good angle for solar irradiation.
X-FLOW is a partial flow system
One of the big advantages with X-FLOW is that it does not require a separate pump but can be connected to, and utilise part of the flow from, the pool’s existing circulation system.
If one draws the water from between the pump and filter, and returns the water after the filter, one is utilising the pressure drop over the filter in order to achieve circulation through the solar collectors. In this case the operation of the solar collectors is effectively free and the only potential loss is that one may lose a couple of percent of the filtration capacity. The “disadvantage” with this type of installation is that it is vital that the user is very careful to back-wash the filter regularly. If one allows the filter to become very dirty then the pressure drop over the filter will increase and therefore the pressure and flow in the solar collector system will increase.
If one has a pump that is powerful enough to handle a pressure drop of 0.5 bar after the filter and without losing too much of the filtration capacity, then that is a good connection alternative. If one connects the solar collectors after the filter and the filter is allowed to become dirty then the pressure and flow in the solar collectors will be reduced.
How much temperature gain is achieved with X-FLOW momentarily?
As with all so-called “low temperature” solar collectors that are so particularly suitable to an application such as the heating of swimming pools, it is important not to operate with too high temperatures as this will very quickly cause a drop-off in the operating efficiency of the collectors. Not to mention possible problems with keeping the pool water clean e.g. build up of algae at higher temperatures, etc.
If one takes a “typical” X-FLOW installation of 10-12 collectors, then the momentary flow of water through the collector system will be around 60 litres/minute (or 3600 litres/hour). With each pass through the collectors the water will be heated by approx. 5-6 degrees. If we assume favourable conditions so that the collector system is operational for 10 hours during the day, then in one day a total water volume of 36 m³ will pass through the collector system.
To a typical pool (say, 8 x 4 x 1,5 m) that has a total water capacity of 45 m³, then approx. 80% of the pool’s total water volume will circulate through the collector system during the day. This should achieve a temperature increase in the pool of approx.6 degrees during one day with favourable weather conditions as in the case explained above.