T-Stat CPH

Bergy

Can anyone explain how the CPH work on a thermostat? How does it affect the run times of first, second and third stage heat for a geothermal heat pump with electric strips as third stage?



Thanks



Bergy

Jean-David Beyer

I have a thread about this already going.

I have made guesses, as have others. So far, no one has supplied an authoritative answer. When it gets colder, I might try to guess it better.



The thread is called "How does a digital thermostat really work inside?"

Magnehelic

Quite Simple really

CPH controls the first stage contacts on a multistage t-stat.  The common settings are 3 (high mass hydronic or steam) 6 forced air gas, and 9 (heat pump).  the thermostat will monitor the internal thermistor this many times in an hour.  A "smarter" stat will only cycle the device for a very short period 1.5 - 2 minutes) if there is any drop in temperature at all measured at the thermistor.  A "less smart" stat will cycle the device no matter what at whatever CPH setting is in there.  this was an "electronic" compensation for the old "mechanical" anticipator settings.  Most I have set up have worked pretty well.  I almost always used the 3 CPH settings even on forced air gas, because hearing that jet engine of an inducer blower come on every 10 minutes drove me insane.

Mike Kusiak_2

Another Thread

Here is another thread which winds up going into some detail on the way CPH is implemented.



http://www.heatinghelp.com/forum-thread/128816/VisionPro-Thermostat-Problem



Of particular interest is a link to a Honewell document which goes into some detail about control strategies and thermostat operation.



http://customer.honeywell.com/TechLit/pdf/77-0000s/77-E1100.pdf