Monday, July 10, 2017

Heatsink Water cooled

On upgrading my off-grid 24v system, I added more Photo-Voltaic Panels - 900W in total (150w x 6). I decided to sell this all this power instead of storing it into the batteries. I purchased two small grid-tie inverters - 500W peak  each and connected them to the solar panels and grid. They worked well however I noticed that the inverters were getting pretty warm! The inverters are installed in the garage which is South facing. Therefore the garage is exposed to long periods of direct sunlight, raising the room temperature significantly. I measured the temperature in the afternoon and the mercury hit 35 °C. This was forcing the inverters fan to run continuously besides that the inverters were still getting pretty warm.
I needed to find a way to keep the inverters cooler. One way to do this was to water cool them!
This required a lot of preparation because I needed to have a cold water supply next to the inverters, something which was not readily available.  The water cooling supply has been taken from the roof tank (2 stores higher) and thanks to gravity, I did not need a circulation pump to get the water circulating the inverters. The water after passing through the inverter heat-sinks is then dumped back in the well, thus there is no water wastage. The house water well pump would then switch on occasionally automatically (depending on the roof tank water level) and new cold water is pumped from the well to the tank.
I have this system running for the past month now and must say that I'm really satisfied with it's performance. The main objective has been reached in that the inverters are now running much cooler. A cooler inverter (electronics) will translate to a longer working life. The water is being circulated against the heatsink for most of the day but that's OK as long as the inverters are kept cool.

Built Details
The Inverters have been mounted on a 4mm aluminium sheet. A large heatsink has also been fitted to the back of the aluminium sheet to add in thermal mass. Thermal paste has been used to facilitate heat transfer between the two metals.
Two CPU water cooling blocks (as shown below) have been fitted to the 4mm aluminium sheet to allow cold water to circulate and cool the heatsink/inverters.

One Thermal switch has been fitted to the heat-sink. I have chosen a switch which will operate at 35 °C and reset at 20 °C. Therefore once the heatsink temperature reaches 35 °C , the thermal switch will turn on... switching on the water circulation solenoid.

The picture below is showing the underneath of the inverters heatsink. In the middle, I have attached the heatsink, on the left top corner, I have attached the thermal switch while CPU cooling blocks are the blue blocks attached to either side of the heatsink.

Water flow is controller using a 24v AC solenoid valve. A small transformer has been fitted to power the solenoid since it runs on AC! 
An AC solenoid runs cooler than a DC solenoid and that's why it has been chosen.

The picture below is showing the front of the aluminium sheet with the grid-tie power inverters installed.

The picture below is showing the inverters installed to the wall. On the left there is a consumer box with 2 separate double pole MCBs and a KW power meter to measure the amount of power generated by these inverters.
On the left of the inverters, there are the water connections, water feed and return showing also the solenoid box at the extreme right.

The solenoid box installed. A relay has been used to power the transformer which in turn will power the solenoid valve.

Therefore in summary;
The heatsink will warm up. On reaching 35 °C, the thermal switch will close and this will activate the 12v relay coil. The relay contacts will close and this will activate the 24v AC solenoid valve, opening the water flow.

No comments:

Post a Comment