few solar questions

[Diver]

I hope someone can help me with few questions I have regarding solar heating.

I have a pretty simple set up right now - pump, filter and the pool The flow is about 52-55 GPM for the pump on high (measured by flowmeter, confirmed by filter gauge and pump vacuum gauge). I'm thinking 8 Aquasol 4x10 panels. They will be located right next to the pump/filter on the same level, so their head loss will be minimal. Looking at the panel tech sheet and my pump curve, I expect the flowrate to drop jsut a bit resulting in about 6GPM flow thru each panel (48 GPM, 8 panels) or maybe 5.5GPM.

The tech sheet says 4GPM is ideal flow, 10GPM is max. Should I bother with bypass to lower the pressure in the panels??

What is the simplest way to control solar? My pump run time is fixed and all I want is to open solar when sun shines and close it when it's not. I assume I can't get away with just a three way valve, actuator and temp sensor, I will still need a controller, right? Is Hayward GL-235 the simplest one for this purpose?

And the last Q. The panels will be mounted at about 40 degree angle. Is it ok to keep the top headers align horizontally without any tilt and simply put a vacuum breaker on the opposite side of the solar exit? The tile is recommended to prevent a possibility of air lock, but I wonder if have vacuum breaker on one top corner and solar exit on opposite would be enough for that purpose?

On this pic the problem is shown for panels tilted the wrong way. I think placing the breaker in the location omarked with an arrow would solve the problem. Especially if panels are not tilted at all.

Thanks!

 

[jblizzle]

I would not worry about a bypass, just use a 3-way valve that you can divert all or most of the flow to the panels. With this setup, diverting all should be fine.

I think that Hayward is about the simplest controller, but you might consider going a little better to something that will be able to switch the pump speed to high for solar and low when solar is not needed. I think there is a Pentair that will do that.

The breaker is not so much to let air out as it is to let air in, then the name vacuum release valve. If there are horizontal, you will not likely have a problem, but even a very minor tilt could help. Are you going to have all 8 panels in a row? Even an inch of tilt over the 32 feet would be enough.

BTW, you will want a check valve right after the fitler, then the solar 3-way and then another check valve on the solar return. That is all the valves you need.

 

[Isaac-1]

I would say you probably don't need a bypass, but you should measure back pressure going into the filter once you have it installed just to be safe, easiest way is to plumb in a T with a pressure gauge after the filter, but before the solar panels and screw in a low pressure gauge, 30 PSI sold at tftestkits for around $10 would work good, 15 psi or lower would be better as you ideally want to make sure there is only 1-2 psi going into the panel. (mine is at the pad, and reads around 7 psi, but I must also account for the water column going up to the roof top panels which accounts for about 5.5 psi to the inlet, 14.7 psi for every 34 ft of height).

As to the controller the GL-235 is the cheapest on the market, it is also a basic controller with no readout, just a vaguely calibrated warmer or cooler adjustment knob, overall a very popular work horse model, probably due to its price and reliability. There are certainly fancier controllers on the market, but they all cost more.

 

[Diver]

Guys,

Thanks for you quick responses.

I wouldn't really built a bypass, I would just use the three way valve for that purpose and set stop cams on the valve actuator to allow for some water to bypass. But just for simplicity of the conversation I mentioned bypass. If I know I need it, I would either install a flowmeter for the solar loop or a pressure gauge as Isaac suggested to make sure the adjustments to the flow are proper.

The panels will be in a row. I understand the purpose of the vacuum breaker but it would also allow the air to escape when panels are filled with water. So I figured if it's 100% horizontal it will be ok, if it's tilted accidently properly sloping up to the exit, it wouild be good. If by accident of lack of my workmanship I ended up tilting it wrong, placing vacuum breaker on that corner would help it as well.

It might be stupid, but having something crooked even intentionally will bug me

 

[chiefwej]

I'm using the Pentair SolarTouch controller. It cost $225 and came with everything you need for solar except the panels and plumbing. The kit includes the controller, sensors for both the panel and water temp, the control valve and actuator. Simple to hook up and if you ever add a two speed or VS pump, the controller will support it. When you consider the cost of all the individual parts, the kit is a pretty good deal.

The vacuum breaker will not bleed air out of the system, it's there only to let air in when it's shut down. That prevents water from staying in the panels and getting boiling hot or a vacuum from forming that might collapse the panel. Any air that's in the panels on startup will bubble up in the pool as its pushed out by the water coming in.

 

[Diver]

but you should measure back pressure going into the filter once you have it installed just to be safe, easiest way is to plumb in a T with a pressure gauge after the filter, but before the solar panels

Isaac,

wouldn't it make more sense to have that gauge in the actual solar loop? otherwise if it's before that it would measure back pressure for both solar and bypass, right? the only pressure one should worry about with solar is the pressure in the actual panels.

 

[mas985]

Pressure does not divide at common nodes (e.g. tees). So the pressure after the bypass will be about the same as right before the bypass. Flow rate however does split at tees so there is does matter where the flow meter is.

 

[Diver]

thanks Mark!

 

[Diver]

I had a 2+ feet interchangeable section of the pipe with unions on both sides right after the filter. I have a section with a flowmeter there and a section with inline chlorinator (for bumping CYA). so it looks like i could get another section with a preasure gauge, i could use that to dial in the correct bypass amount.

Mark, with pressure/flowrate numbers before the solar tee, is there a way i can calculate the flow rate thru the actual panels?

 

[pooldv]

+1 on the Pentair Solartouch. Pics of my solar install in build thread in sig.

 

[mas985]

IMHO, I don't think you really need a separate pressure gauge. If you set the bypass when the filter is clean, you can get a pretty good estimate of pressure at the roof, which is really what matters for the VRV.

To determine the flow rate through the panels, I would need a couple of measurements. Basically, the flow rate and filter pressure without solar, the flow rate and filter pressure with 100% going through solar. I can then tell you the target pressure for a given flow rate.

 

[Isaac-1]

For a good understanding on pressure issues on solar panels read this Hot Sun Industries Case Study Rigid Solar Pool Heating Panel Issues with Pressure and Variable Speed Pumps

ps you might also want to read this for some good general installation issues http://www.h2otsun.com/polypro/Powerpro.pdf even though it is targeted to their specific brand there is still a lot of good generic information, the same can be said about the older Elm/Aquatherm installation manual (Not their newer powerpoint slideshow looking manual) and the Techno-Solis manual, just less so.

Ike

ps to me it seems like it is easier to slope up a fraction of an inch per panel than to have to go back and fix things later if you have trapped air, this can be confirmed by using a simple cheap water level at time of installation How to Use a Water Level - 8 Easy Steps (with Pictures)

 

[Diver]

To determine the flow rate through the panels, I would need a couple of measurements. Basically, the flow rate and filter pressure without solar, the flow rate and filter pressure with 100% going through solar. I can then tell you the target pressure for a given flow rate.

Mark,

thank you for your offer, but this is still in design phase, I'm just thinking ahead I'll come back to you with some number hopefully next year.