[Greenbuilding] Triac Thermostats

Corwyn corwyn at midcoast.com
Mon Dec 19 17:13:43 PST 2011

On 12/19/2011 5:32 PM, John Straube wrote:
> You cant use a normal on-off thermostat with a modulating control.
> The simplest thermostat for use with an SCR or TRIAC would have what is
> called proportional control.
> For example, if the temperature fell below 68F by 0.1 F, 100W would be
> delivered to the heater, of the temperature dropped to 67.8F, 200W would
> be provided and if it dropped to 67F, 1000W would be delivered.
> Because a smaller amount of heat is added with small temperature drops,
> the temperature does not oscilate as much as an on-off control with a 3F
> deadband as described in the example.

But, it isn't, in fact, delivering 100W to the heater.  It is delivering 
1000W to the heater for 1 second out of 10.  Or perhaps 0.1 seconds out 
of 1 second.  I guess that is the point I am trying to make.

Since I have trouble believing that anyone *needs* within 0.1F stability 
in their house temperature; a thermostat upgrade will get most of the 
accuracy improvement anyway; and since no one has shown energy savings, 
I would recommend these only if the lifecycle benefits make them cheaper.

Thank You Kindly,


Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
topher at greenfret.com
(207) 882-7652

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