Remove Your Pools Eyelet Socket to Increase Efficiency?

Sometimes when you install a brand-new solar pool heating system and run it for the first time, you can get pressure at the vacuum release on the return line that’s higher than advisable. This is especially common if the pump is a bit too strong or there's only one return port.

Normally, to drop the pressure you can install a bypass line that short-circuits some flow to the roof, diverting a portion of the water. However, before going to the trouble of cutting PVC lines, we advise customers to remove the constricting eyelet socket from the return port - especially if there's only one return.

We recently had a customer whose pressure was 32 kPa at the gauge on the return line. The gauge was ~1 m from the vacuum release, so the pressure at the vacuum release is approximately 32 kPa -10 kPa (1 m head) ≈ 22 kPa. Not ideal. We advised him to remove the eyelet socket and the pressure dropped to ~12 kPa, giving a pressure at the vacuum release of ~2 kPa (~20 cm head) - perfect!

That amount of pressure is just enough to close the vacuum release (preventing air from being introduced into the return line) but not high enough to slow the flow, put back-pressure on the pump, or increase pressure in the collector array.

His collector system now runs at the highest possible flow - and therefore the highest efficiency - while keeping stress on components as low as possible.

A higher turnover of water is critical not just for collector efficiency. The pool has its own "efficiency", as it collects energy throughout the day and develops a stratified layer. The more stratified the pool, the more heat it loses overnight.

In fact, did you know that removing just 1 °C of surface-to-bottom temperature stratification over 24 hours - thanks to better flow/mixing - can be equivalent to installing solar collectors with 20% coverage?

Yeap… hard to believe, but ~5 °C is a standard accepted increase for a 100% collector coverage system, (without a solar blanket), which implies ~1 °C for every 20% of coverage. In other words, all the energy from 20% solar coverage would raise the pool’s average temperature such that the surface is ~1 °C higher. Since the dominant heat-loss terms depend on the water surface temperature, we can achieve a similar effect by reducing the surface temperature by ~1 °C through improved mixing - reducing overnight heat loss.

Reduce the surface water temperature to increase the pool’s overall temperature - wrap your head around that. :)

Anyway, I thought I'd share this trick. You might do the same, it'll increase your collector efficiency, cut your pool's overnight losses, and lower the pressure on components - a win all around!