Pool solar panel pressure question

[marcandre]

I currently have 3 horizontal panels for a total of 170sqft. When the water is not going to the panels, I have about 4PSI at the filter. When I close the divert valve completely to send water to the panels, the pressure jumps to 14.5PSI and I barely have any water coming out.

For some reasons, when I open the valve a little (part of the water goes to the roof, other goes thru bypass) and bring the pressure down to 12PSI, there is a big big flow difference going to the pool. Although I have no way of measuring flow in the panels itself, I can 'hear' that there is much more water going thru the panels that if I closed the valve completely.

I'm curious as to why I have to partially open the divert valve to get good flow thru the panels. Pump too weak? My father has a similar setup and he can close the valve completely and only increase pressure by 3-4 PSI.

Also, I can 'hear' less and less flow thru the panels as I go up on the roof. I would like my panels to have the same flow thru them.

I attached a diagram of my setup.

Any help would be greatly appreciated

Untitled.jpg

[inetdog]

The only things that comes to mind are:
1. There may be a problem with cavitation in the pump which produces less pressure with strictly limited flow than with some flow in the bypass. Not sure if that could happen in real life though.
2. regarding less flow through upper panels, even though you are using a diagonal piping method that should help equalize flow across the three vertical spans, it is possible that the manifold piping is just too small where the three panel strings are connected. Or the system pressure could just be too low to actually fill the top level of panels (if the outlet of the top string is below the actual top of the panels.) Do you have an air bleed, or are you counting on turbulence to carry away any trapped air?

[russ]

Too much of a restriction in the panels - a small side stream to the panels is normal

[Naptown]

You do not have enough pump to overcome the head pressure of the additional height and static head of the panels
What is the pump yo are using and how high above the pool are the collectors?

[marcandre]

I currently have a 1hp pump that must pump to around 25ft

I was thinking of trying a 1.5hp pump but before I wanted to see ideas in case it would not solve my issue

[russ]

I currently have a 1hp pump that must pump to around 25ft

I was thinking of trying a 1.5hp pump but before I wanted to see ideas in case it would not solve my issue

It is pump internal design and not hp that give the required head.

[marcandre]

Yesterday I found a cheap used 1.5hp pump and decided to give it a try. It actually fixed my problem.

Russ, you are right, too much restriction in the panels. Since I have horizontal panels, water has to travel 20ft while it generally have to travel 10ft with vertical panels (more parallel flow = less restriction) such as my father system that I was comparing to. This is why I have to partially open my divert valve

My previous 1hp pump was strong enough to bring the water to the correct height since water was coming out of the highest point. I believe it was just too weak to purge air from the top (problem that would not exist on vertical panels since they would all be at the same height).

Moral of the story, avoid horizontal panels!

[thastinger]

I have a horizontal 9x30 array and kept my 1HP pump and everything works just fine.

You never mentioned what your pressure reads at the array itself but if you have 14 leaving the filter and a 20ft head then the pressure in the panels would be 5.34 and that is enough that you would have eventual leak problems. You need to check the pressure where you have your vacuum breaker and use the diverter valve to set it to about 2psi or less. Only a portion of the water is intended to flow through the array, it needs dwell time in the array to absorb the heat.

[inetdog]

...Only a portion of the water is intended to flow through the array, it needs dwell time in the array to absorb the heat.

The water only "needs dwell time" if you are trying to maximize the temperature increase of the water in the panels, as for domestic hot water heating.
For pool heating any increase in the amount of heat in the water, regardless of the mix of temperature versus volume, will end up heating the pool. And the heat will transfer from the panel to the water most effectively at higher flow rates.
What excess flow will do is cost you more energy using the pump, and opening the bypass valve will have the same effect if the pump is an impeller type rather than a positive displacement pump.

[russ]

1) The flow rate through the panels should be the design rate - there are many factors the designers take into account - none of which should be sound or feeling.

2) One should never use a positive displacement pump on a pool heater - things can go wrong. If there is a relief valve in the system it may or may not work at the moment it is needed.

3) The pump should be sized "right" to prevent excess flow and or excess pressure.