Water heating issues!

Since yesterday we are trying to tackle down the problem of the water which gets too hot during the day. Yesterday the water in the tank started from 28.8 oC and after 8 hours the water temperature rose to 31.8 oC. Initially we tried to put a dozen of icepacks inside the black 1m3 tank. However, as expected this showed no difference to the temperature, some icepacks are not enough to cool 1 m3 of water!

 putting icepacks in the tank

Today we tried another solution: We made the pipe of the concentrate stream to pass from a bucket full of icecubes and icepacks before ending in the 1m3 tank. we hoped that the ice could cool down the concentrate stream before it returned to the tank.However, the material of the pipe proved to be a good isolator, and heat exchange with the ice was not achieved.

concentrate stream (in a spiral configuration) inside a bucket full of ice

we have to think about a heat exchanger solution probably using a spiral coil, placed inside the 1m3 tank.

One week in Creta - day devoted to PV power

Today we close one week since the system reached the laboratory where we are placed. It was a very intensive week, full of hard labour work. Andres may disagree with this, but this is the experience of an unfit person like me. We managed in one week to do lots of things concerning installation, setting up things, cleaning rooms, bringing things into place, modify tanks and pipes. Right now everything seems to be in perfect place, datalogger was installed and calibrated yesterday, solving also some problems in electronics connections.

It is 9:00 and we are waiting for the sun to go up since its still somewhat below 200 W/m2. Today the day is devoted to desalination powered by the sun and datalogging the results.

Still there are issues which are not resolved:

- For the 3rd time of operation the permeate quality we get is not satisfactory (around 680 mg/l when the maximum limit for drinking water is 500 mg/l, assuming the same relation as Brett Ibbotson was using for conductivity and TDS). As a result yesterday night we didnt flush the system with very pure water, and as a consequence the concentrate of the membranes after flushing had a concentration of 1210 mg/l. Note that the membranes are considered clean when the concentrate current is not more than 1000 mg/l.Of course the assumption for the relationship between the TDS-electrical conductivity has to be changed and be calculated for the specific seawater sample we get in chania).

- Second issue is that the power cable of the pearson motor has a copper ring end which doesnt fit from the opening of the fusebox (when powered by the PVs). For the time being, Andres has used a piece of a copper raw cable to extend the original power cable, in order to manage to connect it in the fuse box. However, we are not sure if this can give more resistance, and influence the calibration to the datalogger (when measuring the voltage and the current of the motor).

Sun is rising higher, i will post more at the end of the day :)

1st operation with the PV system for one hour!

On Saturday after the long "running" procedure powered by grid, we connected the system with the PVs! It was around 17:00 and it worked perfect, with no a lot of fluctuations until 18:00. 

desalination with PV!

no grid, only sun!

First water from the sun!



Feed flow = 5gpm
Permeate flow = 1 gpm
Membrane pressure= 55 bar
ΔP at prefilter = 1 bar
Permeate conductivity = 1200 μS/cm corresponding to 780.96 mg/l.


The permeate quality is an issue we have to deal with today.

At 18:00 the irradiation fell abruptly because of heavy clouds, and then we had to stop the system. 

Today we are starting operation with PVs and see how it will go!

1st long running to observe the system operation - still by grid!

Using the configuration which is already described, we removed 150 l of permeate to a tank above the 1m3 tank, and then permeate was returning to the 1 m3 by overflowing. as a result the system reached steady state not at 37000 mg/l (which is the real salinity of the seawater of the region), but at a higher salinity of around 44775 mg/l.

On Saturday, we ran for around 4 hours the system (powered by the grid), to observe how it operates.
We observed the following in the beginning:
Feed conductivity= 68.8 mS/cm which corresponds to: 44775 mg/l                               at 27.4 C
permeate conductivity= 1149 μS/cm which corresponds to 747 mg/l                              at 27.5 C
concentrate conductivity= 75 mS/cm which corresponds to 48810 mg/l.
membrane pressure= 56 bar
ΔP of prefilter = 1.2 bar
Qfeed = 5 gpm
Qpermeate = 0.95 gpm

flux= 14.6 lit / h*m2   (Membrane total area = 14.8 m2)



After 4 hours we observed:
Feed conductivity=67.5 mS/cm which corresponds to: 43929 mg/l                               at 28.8  C
permeate conductivity= 1187 μS/cm which corresponds to 772 mg/l                              at 28.9  C
membrane pressure= 55 bar
ΔP of prefilter = 1.2 bar
Qfeed = 4.8 gpm
Qpermeate = 0.95 gpm

flux= 14.6 lit/h * m2  


in the course of 4 hours the temperature rose 1.4 C, and also the permeate conductivity rose instead of falling. Its considerably high compared to the results in the lab.

At the end of the day we flushed with 200 l of demineralised water, making sure that the membranes were totally clean. We will see today if we have any differences in permeate quality.

We decided also to dilute the seawater in the tank with demineralised water,  so that after filling the 140l permeate in the small tank, the steady state of the system would reach the salinity of the  real seawater in chania (around 37000 mg/l).