My solar water heating system isn’t heating my tank
(the bottom of my tank)
Contractor leaves the job site satisfied that they have done a good job installing a solar hot water system only to be called back 2-4 weeks later to be told that the system doesn’t seem to be heating the customer’s tank. The homeowner has been keeping a detailed log of the temperatures in the tank as well as on the roof and shows you a log that never shows the tank
sensor getting hotter than 105 degrees. They say the system has been running and they haven’t noticed anything else unusual but clearly the system isn’t working properly with the solar only getting the tank this hot. What went wrong?
A modern differential control operates by measuring the temperature (via a temperature probe) in the bottom of the tank (T2) and the solar collector temperature at the outlet of the collector array (T1). Hot water tanks are constructed so they introduce any cold water into the bottom of the tank primarily via a dip tube that carries the cold water from the connection on
the top of the tank to the bottom of the tank. The Steca 0301U differential control (which represents greater than 50% of the control sales in the U.S.) only comes equipped with two sensors although it can take a third. In this case what the homeowner is seeing as the tank temperature is actually the temperature at the bottom of the tank (T2) where any cold water entering the tank is mixed with the solar heated water in the tank. The stratification in the tank allows the homeowner to have access to hot water (120 degrees +) at the top of the tank while only seeing “cold” water temperatures on the readout for the bottom of the tank.
solution: Supply the homeowner with a third temperature sensor that would then be mounted to the top of the tank showing what temperature the tank is actually delivering.
wendy:
could you help us trouble shoot problems with a new solar H2ot
22 May 2010, 5:09 pmwater heater?
The pressure changes from 0 psi at night to about 60 psi during the day.
The temp sensors say the top temp is 250F but the water coming down (based
on temp probe on the input pipe) is only about 110F.
our new system was working but is no longer. there was a leak that was repaired. now there appears to be little if any temp exchange from the roof to the hot water tank, but at night, if we heat the water in the tank with electricity, we will heat the solar pipes.
The pumps appear to be working (when we remove the screws we can see
turning as per the movies online).
Do you think we have air trapped in the system and if so, how can we get
it out?
thanks for any and all suggestions.
admin:
Wendy,
You have taken the correct first steps in the diagnosis of your system. Noting the temperature differences from your collectors versus the solar inlet side of the Solvelox, it sounds like there has to be a flow issue of some form. By checking the pumps to make sure the spindle is turning, this verifies that the pumps are not the issue. The fact that the inlet pipe is reaching 110 degrees indicates that there is at least some flow in the system. Air in the system is certainly a possibility. If air gets trapped around the impeller in the pump, it greatly diminishes the pumps ability to do its job and will ultimately cause a complete failure of the pump. Air in the pump makes a very distinct wooshing and crackling sound as it flows into the chamber and is blended in the water. Listen for this. If you do not hear this there is a good chance there is a blockage elsewhere in the system. If you do hear this, there is a coin vent located on the air trap below the pump on the solar loop. By turning the screw counter clockwise you will release any air that has gathered in the air trap. If your system is at 0 psi as you are observing at night, nothing will come out so it may be better to do this when you are observing some pressure in the system.
The best place to start looking for this is at the inlet of the Solvelox on the solar side. You will notice a Tee with a port (square headed plug) on this inlet behind the pump. There is a mesh strainer inside of this Tee that is designed to catch debris before entering the Solvelox heat exchanger. Occasionally pieces of insulation or other objects will get stuck in the pipes as they are installed. eventually they will find their way to the strainer and cause a blockage.
24 May 2010, 8:30 am