Monday, January 2, 2012

Turbocharging thoughts

2 Jan 2012: Most of us use the expression Turbocharging in the context of motor car engines, although the expression is frequently used more loosely in other contexts, such as in the economy, sport or teaching. It's commonly used to mean "a short term burst of energy to improve dramatically the performance or quality of ........... above normal expectations". It normally involves the release of energy from an external source, such as a spinning flywheel (in the Formula 1 KERS system), water stored at high altitude (hydroelectric) or in theatre, getting an experienced actor for a few weeks to boost the amateurs, or in football, the brief novelty effect of a new manager, and all the players desperate to impress the new boss.
    In engines, a small turbine driven by the exhaust gases can inject fresh air to the combustion process, more quickly than normal air pressure would provide. This boosts acceleration. Just when you need more oxygen, the exhaust cases are moving faster, and the turbine is giving the engine that extra oxygen.
    In our case, we have a free high performance energy input that comes when the sun shines, and helps the GSHP work more quickly and more efficiently. Normally our GSHP is working from a large volume of low temperature stuff called the earth, which it then has to convert to higher temperature. It does this by refrigerating liquid that is sent below to retrieve heat by coming back about 3 degree warmer. If it does not have to refrigerate so much, but still gets as much heat as it expected, then it is working more efficiently. When we get direct sunshine on our Sunbox even on cold days, there is a short term boost - and I see this in the figures at the end of the day - reduced House energy (because the PV was reducing electricity import) and reduced GSHP energy consumption (because the workload was reduced). This works better on cold sunny days (analogous to the accelerating engine) because the GSHP is required to reduce the outgoing refrigerant temperature, and thus the delta-T between refrigerant and Sunbox is even better. As the GSHP discovers that the liquid is coming up warmer than calculated, it can refrigerate less severely.
    I mentioned it in an October'11 posting called Turbo charge and here are some figures to illustrate it, sampling from two recent sunny and cold days.

Date27.12.1127.12.112.1.122.1.122.1.122.1.12
Time110012301045111511451230
Sunbox temp26.7º27.4º19.2º22.0º22.1º23.3º
Up to SB from GSHP4.4º5.8º2.7º2.2º2.2º4.6º
Down from SB to BH6.0º7.6º4.1º3.4º3.6º6.5º
From Borehole In7.7º9.9º5.5º5.8º5.8º8.4º
Ext Air Temp9.2º9.0º4.1º4.5º5.0º5.6º
GSHP activityHeatingHeatingHeatingHeatingHeatingHeating
Weather Sunny coldSunny coldSunny coldSunny coldSunny coldSunny cold

  We can see the process here, whereby a significant proportion of the heat required is gained from the Sunbox. The GSHP is calculating outgoing temperature based on the temperature it hopes to get from the ground, but as it gets more heat than it expects, it can reduce the amount by which it refrigerates the outgoing glycol. By doing this, it is cooling the ground less, leading to future energy savings.
   The nature of 'turbo' is to be a short term burst of energy boosting the main mechanism above the normal levels of activity. If the sun shone every day, then that might become the new normality, but in real life, the weather is a mixture of seasons, containing sunny days and grey days. If the sun shone every day, we could dispense with the borehole altogether and manage with solar-air panels only.

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