Friday, September 20, 2013

thermostats, mental models, and physics

Six degrees of separation is "the theory that everyone and everything is six or fewer steps away."  In Saskatchewan, one or two steps in usually all that are needed.  Why do I bring this up?   As I started to put together a post about Activity 3.5 in Rogers, Sharp, and Preece's book (pages 86-87), I found that their reference (Kempton, 1986) makes reference to McCloskey, whose work is also referenced by Halloun and Hestenes (1985), which is described by Bain in the book that I wrote about yesterday. McCloskey wrote about the persistent models, or explanations, of physics that may people hold.

Kempton's discussion of folk theories of home heating gives me the chance to show my age and make a reference to Theodoric of York, Medieval Barber, a character played by Steve Martin on Saturday Night Live, who once said "You know, medicine is not an exact science, but we are learning all the time. Why, just fifty years ago, they thought a disease like your daughter's was caused by demonic possession or witchcraft. But nowadays we know that Isabelle is suffering from an imbalance of bodily humors, perhaps caused by a toad or a small dwarf living in her stomach."

Activity 3.5 deals with how we use mental models in everyday reasoning.  One part deals with increasing the temperature in order to cook food quicker. Not too surprisingly, I found some thoughtful discussion of this misconception. The other part of the activity deals with what happens when you turn up the heat on a thermostat: if a house in winter is too cold, do you turn up the thermostat as high as it will go, or do you set it at the desired temperature? Kempton describes the valve and feedback theories of thermostat operation. Neither is completely accurate, but the feedback theory is closer to the actual operation of the thermostat.  Interestingly, from the perspective of conservation and reducing consumption, the valve theory more readily explained the benefits of lowering the temperature setting at night.

Yet, 2011 is 25 years removed from 1986. Furthermore, the data upon which Kempton based his work is from 1976 (more than 35 years ago). In my house, I have a high-efficency furnace with a modulating gas valve: the value theory makes a comeback! Yet, these high-efficiency forced-air home heating systems are not installed everywhere. I found, through google scholar, a recent paper that cited Kempton. In the Applied Ergonomics journal, Revell and Stanton (2013, in press) look for examples of feedback, valve but also timer (set thermostat higher for longer operation) and switch (thermostat is merely an on/off switch) theories in the UK. Rogers et al. seem to promote the switch theory ("thermostats ... instead function based on the principle of an on-off switch").

Revell and Stanton talk about the importance of regarding the home heating system as a system instead of individual devices.  More transparency related to the operation of the home heating system could allow residents to relate their actions to their goals and to understand when those cannot be met by the home heating system.  This, in turn, could reduce consumption and enhance comfort.

There are plenty of opportunities for design here.   Solutions must also acknowledge the difficulties and expense of upgrading these home systems and provide support to people using the heating systems that they have in place.

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