Sunday, February 6, 2011

Don't count chickens... unless they hatch

5 Feb '11: In my conversation with Dr Chris Wood a couple of days ago he reminded me of the importance of searching for ways to prove that there are real efficiency savings from the Surya Sunboxes.
    If you will permit me to use another Animal metaphor, I remember saying in an earlier posting that a ground source heat pump is rather like a hungry dog gobbling at its food. It just greedily sucks up heat without discriminating where it comes from - it only takes the heat it needs for heating the house above and no more, so why would that make it more efficient? This is the point he was making. If some of that heat is from a solar panel, and some for the ground, it does not automatically follow that it will make the GSHP more efficient! and would it save enough electricity to justify the cost?
   The general theory is that a 1 degree rise in the temperature of the primary source can add 3-4% to the COP of the heat pump. My deep ground is over 10º and rising gently when at the same time last year, it was about 5ºC and rising gently.   It does not necessarily follow arithmetically that 5 degree difference automatically multiplies that 5 times... although it might do - it is hard to verify, especially when I fear that the datalogger memory is full and therefore the real numbers for last Nov and Dec might be lost.

Timescale: Ground chilling is something that occurs over 5-10 years, and it would take that length of time to be really sure, to see if the performance in 5 years time is as good as when the machine was new. Our intention is to defrost the ground, not to make it hot!
  We installed the GSHP in Feb 2007, and should have started this then - who takes records that early, and who keeps records that long? I wish I had done so from week one! Doh!

Graphic representation: I showed him this diagram which is an unusual graphic interpretation, because it combines Degree Days with Kilowatt Hours on the same chart. They are different units, but proportional. The diagram is extended every month. It started from 1 October 2009 and currently ends at 31 Jan 2011.
  The diagram clearly shows that in a milder winter of 2009-10 (red curve), the blue curve of the heat pump consumption was vastly greater than it has been in recent months.
  There is a small inexactitude, that is to our credit, in that the blue curve also includes DHW and floor pump consumption. The Heating part of that would be lower than shown, and zero during summer.

Immersion Heater:  Another point is that most heat pumps have an emergency function which is a direct electric heater in case they are unable to retrieve enough heat from the main source. If this comes on, the electric consumption soars, because it is direct 1:1 heating. Our heat pump had to do this for the equivalent of 220 hours in 2007, and 220 hours in 2008, and in the winter of 2009-2010, it used 110 hours, mostly in the Spring when the ground was exhausted.
  In the winter of 2010-2011 including the severest December in recorded UK weather history, our heat pump has used only ONE hour - and that annoys me, how did that happen and why? I think I know, because this IVT model has a faulty algorithm that overheats the water, repeatedly, trying to pasteurise the water every day instead of every 3 weeks.  I have now beaten this by fitting a small Danfoss thermostat that stops it heating the water beyond about 58º.

Sunday 6 Feb '11: Electric consumption: This will always be a primary decider, because it can be directly balanced against the power generation of the Photovoltaic roof - electric kilowatt hours balancing electric kWh - and it can be directly costed in Pounds and Pence. It is also a final decider of whether we are 'Carbon Zero' or not.
   Every week, I do a meter reading and compute the full consumption of the House and of the GSHP. I am glad to say that we are advancing into unknown territory, seeing consumption levels lower than ever previously witnessed. The House annual consumption is less than 6,000 kWh (5,970), and the GSHP annual consumption is below 4,000 kWh (3,957) for the first time ever.
 (as each week of the cold Feb 2010 peels off and a warm week of Feb 2011 is added, this is not surprising. So I ask, will we stay below this line for the rest of the year?)

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