Solar hot water

rene_3

Is 280 the boiling point glycol? Mine high limit is set for 160 right now but I may raise it to 180 like you did. My controller will also continue to run after hours to cool the water down to the set limit.

rene_3

Solar Loop keeps circulating hot water

I recently installed a solar hot water system using evacuated tube solar thermal collectors. It is a closed loop system system. There are 50 tubes. The solar loop goes through a coil in a 80 gal indirect SS hot water storage tank. The loop has a hot water circulator to move the water around the loop. The system is controled byn a teprature differential controller. I've been experiencing around 8 degrees heat lost at night from my domestic side of the tank. Just last week, I drained the solar loop down and installed glycol for the upcomming winter months in New England. That very same day is when my problem started. After the system shuts down at the end of the heating day, with the circulator off, the glycol in the closed loop continues to circulate slowly robbing heat from my 80 gallons of domestic water. I can stop it by shutting one of my in-line ball valves. I've gone back after the loop pipes are cold and opened the valve. Within 15 minutes, the pipe going back to the collectors starts heating up indicating that water is flowing discipating heat. In a matter of 4 to 5 hours, I'll loose anywhwre from 35 to 45 degrees in temperature from my domestic water in the tank. I believe this is called the capillary effect. I have a check valve in my loop, but the flow is in the other direction. From my basement to the collectors is around 45 feet away with a rise of about 18 feet. I could install a zone valve tied into the circulator which would close when the circulator shuts off thereby blocking the flow. I really don't want to install a zone valve for fear that the valve could fail shut if the selonoid went bad which could be dissaterous if I was not at home. I've heard of a heat loop trap or heat trap but I'm not familiar how it works and how to build it. Any help would be appreciated. Thanks.

RT

Steve_147

Why not put in another check valve to stop the flow? How hot does the tank get, my Two flat panels will heat 80 gal to 170 on a sunny day?

Metro Man

check

Make sure it is a spring check. This will get rid of your night time (or cold winter day) "thermosyphoning"

Take care that the expansion tank is not shut off from the collectors or ...... boom!

Metro Man

rene_3

I didn't know they had check valves that are spring loaded. What you're saying is that the circulator will override the spring during normal operation opening the check valve but will shut keeping the system blocked after shut down. In other words, thermosyphoning will not overide the spring.

Metro Man

yep

Ya ya betcha... That is exactly what it will do.

Standard equipment closed loop glyol systems.

Metro Man

hot_rod

dual checks

spring checks with a with a 1/2 psi pop pressure on both supply and return.
Those solar pump stations you see these days have checks built in behind the gauge ports.

Theyn also have a means (1/4 turn on the handle) to hold them open to drain the panels.

Both the expansion tank and safety relief valve must be above the checks and any isolation valves.

hr

Steve_147

Pump

Who Makes that pump station with that pump? is it DC?

hot_rod

A special

modification we made to the Laing D-5 strong that will be available in the Caleffi solar pump station. Let me know if you are interested.

hr

michael_34

Hey Hot Rod,
I would like to see the Liang/Caleffi combo if you have some pics.
Thanks
Michael

rene_3

Steve,
How high in temperature do you let your tank go to?

Steve_147

tank temp.

I have the controler set to 180 for the limit, it will still run the pump if the collector gets to 280 to keep it from flashing to steam. It will cool the tank by circulating at night.

hot_rod

Also, check with the tank

manufacturer to see what the highest temperature they allow. Some of the new solar controlers have a feature that will allow the tank to run up to 205F for collector overheat protection. Just below the 210F relief valve setting. Night time cooling can bring that temperature back down to a desired max.


Not all tanks will operate at that 205F temperature, from what i am told?

hr