Saturday, April 24, 2010

Hour timer added, and relays for the DT500

23 April 2010: The sunbox system now has a Curtis 700L 'hour timer' underneath the thermostat. This (illustrated Left) will only display when the sunbox pump is on which will make evening readings a bit difficult. But overall, it will be useful to know how long the system is running for, and comparing that with the volume transmitted and energy harvested on the same day.
   The DT500 will also record the times when the pump and the GSHP come on and off. This is important because the sunboxes do not come on by themselves unless the GSHP starts up in the morning. This is because the pipe to which the Cold sensor is attached is inside the house and reaches room temperature overnight, about 21ยบ. And during the early hours, the sun is still too far in the east to heat up the Warm sensor in the sunbox to 5 degrees more than the Cold pipe.
    And during a cold day, the sunboxes turn off quickly, but come on again when stimulated by the GSHP. Similarly, the reason that the sunboxes are often working at 9 or 10 at night is that the GSHP is now doing a heating cycle (because evenings are cold) and they come on if there is residual heat up above (perhaps due to warmed up brickwork.) I would like to have been able to paint my brickwork with Matt black paint, but wasn't prepared to do this when the project was in its construction phase - in case it all had to be taken off.
  I assumed that the Datalogger would be able to detect a 230v AC ON/OFF, but it seems that this is not possible. So Dr Chris Wood tells me I have to take a 230v AC lead from the Sunbox Pump and another from the water pump inside the GSHP, and lead these all to relays like the Omron (illustrated Right), which simply open or close a circuit (can be DC or AC) when a 230vAC is applied, and this we will attach to the port of the datalogger to record the On and Offs. So the relays have been purchased and installed, and next time Blaise calls, we will wire them to the datalogger with speaker cable.

I am very grateful to Chris for educating me on relays. I have realised that if I want to power the pump in the loft, I don't need to run a power cable up there. I could just run a thin pair cable (capable of insulating 230vAC but not required to carry any current) up there which alerts the relay, and then permits the pump to use the power sockets in the loft. As I will have two pumps in the loft, for Sunboxes Mark 1 and mark 2, they can be alerted by relay. Until the Savita is installed, I will stick with the existing conventional power cable running up to the loft.

2012 Postscript: The Savita was never installed, as I didn't want to mess up my South wall any more, I re-used the components at East Leake, and I have decided to install a second system using high temperature collectors instead - evacuated tubes.

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