In our series on the effects of solar pool covers we've looked at how much heat a solar pool heating system can add to a pool (with or without a pool cover), and we've also looked at how much heat a pool cover can add to a pool (with or without a solar pool heating system).
We also explained the synergistic effect between a solar heater and a pool cover, and lastly we've looked quantitatively at how much heat a solar pool heater used with a pool cover can add to a pool in total.
In this article we want to further explore this synergistic effect from a slightly different perspective this time. We ask the question: how much solar collector coverage alone do we need to get the same water temperature as a swimming pool that uses both a solar pool heater (with 50% coverage) and a bubble pool cover at the same time.
All calculations were performed using our new heat loading simulator (validated against the heat loading standards AS 3634-1989 and ISO TR 12596 1995 here). When we talk about solar pool heater coverage here we are talking about a standard traditional 8 tube, i.e. well spaced PVCu tube/mat/strip system. We use an ON time for the transparent bubble cover of 87.5% of the time, as that's more realistic than 100%, which implies basically the pool is never used.
Solar Pool Cover vs Solar Pool Heating System
Before we answer the above question, let's firstly look at how much solar heater coverage you need to produce the same water temperatures as a pool heated using ONLY a pool cover (on 87.5% of the time). Since we are specifying no shade, a solar pool cover does reasonably well here to heat a pool. This is a direct comparison between a solar pool covered swimming pool and a solar pool heated pool, both give the same water temperatures as shown in the table below:
(No Solar Pool Heating 0%)
Solar Pool Cover
Shows how much solar coverage you need for a pool that uses no solar pool cover to get the same water temperatures as a pool that uses just a transparent bubble pool cover on 87.5% of the time.
(We average the pool temperature over swimming pool heating season months only for all Australian capitals. All calculations were performed for a pool with light colored walls, normal wind sheltering, no shading, solar collector was installed using a 30° tilt facing North on a light metal roof, drawing from suction ports, using 3/L/min/m² flow rate.)
Solar Pool Cover + Solar Heater vs Solar Pool Heater ONLY
So a solar pool heating systems needs anywhere from 70% to 100% coverage to replace a transparent bubble style solar pool cover. (Note, as an aside: the larger solar sizing for warmer states we see in the table above, is as a direct result of the extra evaporation savings we obtain from using a solar pool cover). Now, let's add a mere 50% solar heater coverage to the swimming pool using the pool cover and work out what new solar heater coverage you need to get the same water temperature from solar heating ONLY. Since we're adding a mere 50% solar heating you'd be forgiven in thinking that as a first guess the required solar coverage for the solar ONLY pool, would just be the above, i.e. 70% to 100% + another 50% right? well wrong, by far...
When used with
Solar Pool Cover 87.5%
Solar Pool Cover
Shows how much solar coverage you need for a pool that uses no solar pool cover to get the same water temperatures as a pool that uses 50% solar pool heating coverage with a transparent bubble pool cover on 87.5% of the time. (We average the pool temperature over swimming pool heating season months only for all Australian capitals. All calculations were performed for a pool with light colored walls, normal wind sheltering, no shading, solar collector was installed using a 30° tilt facing North on a light metal roof, drawing from suction ports, using 3/L/min/m² flow rate.)
... because the actual answer is we need all the coverage from the first table + another 100% solar coverage, i.e. we'd need twice the amount. So Darwin for example, adding a mere 50% solar pool heating system coverage with a pool cover is equivalent to a whopping 200% solar pool heating coverage alone. In other words the heating input value of 50% coverage solar - when protected using a pool cover translates into 100% coverage solar when uncovered. Why? because a pool cover substantially decreases the heat loss equation for a pool and traps the gains from a solar pool heating system.
This example shows why even a 50% coverage solar pool heating system is worth it, but only when used WITH a solar pool cover. Again, with such plain results we can't stress this enough; if you have a solar pool heating system and you're not using a solar pool cover, at least in the shoulder months, you're really missing out on some amazing pool temperature gains.
It's important to stress we are not advocating 50% solar pool heater coverage, this is just an example to illustrate the power of combining solar heating + pool cover - solar pool heaters should be sized properly to provide reasonable results during swimming season months. However, it shows if you're not going to be using a solar blanket during shoulder months, be prepared to stump up much more for a much larger solar coverage collector array which will still not give you anywhere near as good a result as if you were to combine solar + cover.
Do you want to know how well a solar pool heating system will work for a specific set of conditions? Head over to our simulator and have a play with it :)