Monday, 9 May 2016

Sanden "Eco®" Hot Water Heat Pump + Solar Panels Revisited

My Sanden "Eco®" Hot Water Heat Pump wasn't providing me with hot water 100% of the time because of the "blockout" settings I had programmed. The system is an engineering marvel, but, as I wrote about earlier, its software and control system seems pretty weak.

In that post, I discussed how I tried and failed to use my 315L hot water tank as storage for excess energy generated from my solar panels. My problem was that I had a narrow "blockout" time window programmed (starting at 3pm and ending at 11am). During the time window, I have "free" power form my solar panels and, for that reason, I want the system to recharge the tank, thus storing energy that I would have otherwise sold to the grid.

Back to the present. Over the weekend I looked at why my timings did not work. I came across a somewhat dated (2011) Service Technical Manual for the same heat pump model which includes the following description of the logic used to control water heating:
Conditions to start and end heating water are as stated below: 
  1. Tank TH A ≤ 45°C (Lack in residual hot water in tank)
  2. More than 24hrs passed since the last start of operation. (for anti-Legionella purpose)
  3. Memory of last operation is lost. (First run after delivery, ROM writing error, etc
  4. Electrical shutdown is occurred while HP unit is operating.
  5. The current time is 10.00 (24hr clock basis).
  6. HP unit was not operated by the condition (5) due to a limitation of HPU operation. HPU operation starts once the limitation is cancelled. The term limitation defines a condition where HPU cannot be operated due to the electricity cutoff or the blockout time setting.
HP unit starts when either of (1), (2), (3), (4), (5) or (6) above is satisfied. 
Condition to end, GC Inlet TH > 50°C.
If this logic still holds (the document is dated 2011), then I can't explain why we occasionally went without hot water: conditions 2 and 6 should have ensured tank recharge even if condition 1 was not met.

Nevertheless, I went up the ladder again, unscrewed the four screws, took off the top panel and fiddled and re-enabled blockout, widening the time range by two hours so that the heat pump can run between 10am and 4pm.

For the last two days, our heat pump has come on at exactly 10am.

I have no idea which of the six conditions listed above is being satisfied.  But I'll be keeping an eye on the system. With my previous blockout settings, I would expect point 6 to be satisfied and the system to come on at 11am, only it did not seem to.

Not content that I do not understand what's going on, I'm going to perform an experiment and change the system back to 11am through 4pm (best for my solar panels) and check for a regular 11am start.

In summary, the additional information provided in the technical service manual has left me more confused. However, for the present, all appears to be working on a blockout timer and that was my goal.

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