Need a SHW Installer advice on current issue with system

27 Posts
Aug 22, 2010 01:59 pm
Need a SHW Installer advice on current issue with system

So, I have a closed loop system with QTY 2 4x8 collectors going to a 80gallon tank with heat exchanger, currently being pumped using a 24v 20watt PV setup running a Laing DC pump. Recently lightning struck near my system and blew the Laing pump (system wasn't grounded but will be soon.) So I replaced the Laing pump and recharged my system to about 35 psi, with the expansion tank at about 30 psi. I'm now experiencing large pressure swings in the system, seeing about 65 psi during the day (August in CO). The flow rate is at about 1gpm or slightly less. I used to see temps at about 160 and pressure fluctuation only about 10 to 15 degrees. Now after the Laing pump exchange I'm seeing pressure swings of 30 lbs and incoming temps at about 110 degrees. I took off the pressure tank before replaceing the pump to see if that was busted but no. Any ideas what might be giving me the large psi swings and lower temps? 

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462 Posts
Aug 22, 2010 11:03 pm
Re: Need a SHW Installer advice on current issue with system

hey ben, I normally do not run a system at such a high pressure. The pressure alone is enough to put strain on such a small pump. Specs show a pump head of only 9 ft. I usually install a 15 lb expansion tank and run the system around 15 lbs as well. If you have a 30 lb tank, the pressure should be around 20 lb. 
 sounds more like you have air in the system and it needs to be bled. If the pump was blown from the lightning, fluid could have sat stagnant and boiled out. Excess air will heat up and expand and cause an increase in pressure. You can even cause vapor lock where the pressure in the panels is to high for the pump to overcome in which case you have to force cold water into the panels and purge or let them cool and then purge.
  How did you pump your glycol in? If you used a secondary pump, then use that again. Pump water out of and back into a bucket, through the system. Add water if needed and circulate until all the air is out. Close the outlet and let the pump bring up the pressure. If the pump cannot bring up the pressure, use a washing machine or garden hose hooked up to house pressure and add water and pressure that way. be sure to bleed the hose of air before you connect and fill..
 you should consider using a regular 110 volt pump. A TACO pump, model 007, uses 1/25 HP or around 30 Watts. If you have a small PV setup with an inverter, your all set.....
« Last Edit: Aug 23, 2010 01:02 pm by Tom Mayrand »
 
27 Posts
Aug 23, 2010 10:36 am
Re: Need a SHW Installer advice on current issue with system

Hey Tom,
  Thanks for the reply. I recharged my system using a 3/4 jet pump and had circulated it for 15 minutes before closes the vales to close the system. I had the pressure before at about 20lbs and when recharged decided to follow Bob Ramlow's recommendation for 30lbs, but.......Good find on the Laing pump spec showing only 9ft of head in the flow chart. My system head is about 15 ft. I think you are right about the pump not being the right fit for the job. I'm thinking that switching to an AC pump and Diff controller being the right thing to do so I can increase my flow rate. I think i will also decrease the system pressure as well.

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Tel: 877.878.4060 x101  or +1.978.562.5858 x101
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27 Posts
Aug 23, 2010 10:41 am
Re: Need a SHW Installer advice on current issue with system

I just checked my expansion tank with an air pressure gauge and it was at 36 psi!!!! I just decreased it down to 25 and the system pressure went down in unison. Lt's see if that helps today....

The Alternative Energy Store
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Tel: 877.878.4060 x101  or +1.978.562.5858 x101
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462 Posts
Aug 23, 2010 12:57 pm
Re: Need a SHW Installer advice on current issue with system

...usually the head rating of a pump is based on an open system. Basically, if you hooked up the pump to a water source and let it run, the water will shoot up to it's rated height. In a closed loop system you can usually get away with using most any pump since the head pressure from the water column in the piping is enough to compensate for the additional pressure needed. The Taco 007 has a low head rating also which is why a lot of installers use a Grundfos pump. But the Taco is better quality and last a lot longer. I've seen enough cases where pressure in the panels has built up to overcome any pump, which is why purging the air out is important. did you install a float type air vent? This will remove any air that is in the system as the fluid circulates.
 Also on hot sunny days, when you use very little hot water, and the water in the tank is hot and the system does not turn on, the fluid in the panels can get very hot and build up pressure. I often tell customers to use up, dump or waste some hot water just to keep the system circulating to prevent stagnation.
 As far as the expansion tank goes, if it is a 30 lb tank, the internal pressure should be 30 lb. when empty or disconnected from the system or out of the box, and the system pressure should be less. The job of the tank is to absorb any excess pressure to keep the system pressure steady.
 
27 Posts
Aug 23, 2010 01:11 pm
Re: Need a SHW Installer advice on current issue with system

yup, air vent at top of loop above collectors. But you make me wonder if purging the air from the expansion tank while loop was under idle pressure of 36 just filled the expansion tank more with fluid even though system pressure went down, and wondering if I expanded the bladder too much letting out pressure that I may not have room for expansion now.....

The Alternative Energy Store
"Making Renewable Do-able"
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Tel: 877.878.4060 x101  or +1.978.562.5858 x101
Fax: 877.242.6718  or +1.978.562.5854
 
462 Posts
Aug 23, 2010 01:35 pm
Re: Need a SHW Installer advice on current issue with system

 Air vent at top of collector could be a problem. I usually remove them. Since that is the hottest area of the system and since it is exposed to the elements, they tend to go bad and either sieze up or leak. I usually install them near and above the pump on the return side and on top or near the expansion tank.
  If the vent is on top of the panels, outside, it too can heat up and each time it vents air it usually contains fluid, hot water vapor, which in turn removes fluid from the system. This is where the air could be coming from.
 the expansion tank is a sealed unit, so air in the tank cannot mix with the water, unless the bladder has broke, in which case the entire tank will fill with fluid. Reducing the internal pressure should not increase the amount of fluid in the tank by much since the volume of the tank that holds the fluid,(half the tank) doesn't really change, a couple of ounces at best.....
« Last Edit: Aug 23, 2010 01:43 pm by Tom Mayrand »
 
27 Posts
Aug 23, 2010 01:54 pm
Re: Need a SHW Installer advice on current issue with system

Interesting note on the air vent. My colleague has also install an air vent near the expansion tank. And even bringing down my system to 25 lbs, I already see the loop pressure at 60 lbs again in the full sun, even with 1gpm output from the pump. A swing of 35 degrees on a hot day cannot be right. Me thinks the system needs to be re plumbed to include a air vent and ball valve at the expansion tank instead of the top of the collectors. Bummer, air vent is only 3 years old.

The Alternative Energy Store
"Making Renewable Do-able"
http://www.AltEnergyStore.com/

Tel: 877.878.4060 x101  or +1.978.562.5858 x101
Fax: 877.242.6718  or +1.978.562.5854
 
462 Posts
Aug 24, 2010 10:56 pm
Re: Need a SHW Installer advice on current issue with system

definately sounds like you got air in the top of the system. the air will heat up much faster and expand causing the pressure increase. I bet the fluid isn't even circulating.
 Best to drain the system down, remove the vent on the roof and plug the hole with an 1/8" brass plug, install the vent somewhere near tank ( I usually put them at the highest spot vertically above the outlet of the pump using a tee ) and then the expansion tank on the branch side of the tee heading back to the panels.
 Then flush, fill and purge with water and bring the pressure up to 15-20 lbs. Then let it run for a few day or weeks and see how it goes.
 then you can pump in your glycol displacing the water. If you measure the water when you drain the system you can figure out how much glycol to pump in. I usually start with near 100%, just in case there is a leak or service is needed an a little fluid gets lost. Then you can just add water with a hose.
« Last Edit: Aug 24, 2010 11:16 pm by Tom Mayrand »
 
462 Posts
Sep 9, 2010 08:47 pm
Re: Need a SHW Installer advice on current issue with system

Hey Ben, just seeing how you made out. Hopefully you got the system running properly again...
 
27 Posts
Sep 10, 2010 02:20 pm
Re: Need a SHW Installer advice on current issue with system

Hey Tom,
  It turns out it was the Air Vent that failed. After replacing it the pressure swings stopped and has been running beautifully. Thanks for all your helpful advice. Best Regards---Ben

The Alternative Energy Store
"Making Renewable Do-able"
http://www.AltEnergyStore.com/

Tel: 877.878.4060 x101  or +1.978.562.5858 x101
Fax: 877.242.6718  or +1.978.562.5854
 
27 Posts
Sep 10, 2010 02:21 pm
Re: Need a SHW Installer advice on current issue with system

Oh, and I also installed a ball valve before the pressure tank and air vent so in the future will make for quick switches....Ben

The Alternative Energy Store
"Making Renewable Do-able"
http://www.AltEnergyStore.com/

Tel: 877.878.4060 x101  or +1.978.562.5858 x101
Fax: 877.242.6718  or +1.978.562.5854
 

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