thermostat heating system type algorithm

[montreal]

My Honeywell programmable thermostat for central furnaces allows the system type parameter to be set.

The options are:
1 = gravity or steam system
3 = hot water, high efficiency furnace, or single stage heat pump
6 = gas or oil forced air
9 = electric

With these different types of furnaces come different performances, in that some deliver a high temperature output soon after coming on, others need more time to build up heat. Some can be ordered off shortly after turning on, others need to stay on for a minimum time in order to be energy efficient.

In other words, if a particular heating system uses an electric furnace, the thermostat may generate heating cycles that rapidly cycle on and off the electric element which will result in the home temperature staying within a tight band.

On the other hand, if an oil furnace has to stay on for a minimum amount of time, the thermostat may tolerate some over and under shooting of the home temperature. In this case, the thermostat may attempt to calculate a duty cycle that will generate the best comfort over a time frame of an hour or more.

Because my furnace is a custom built hybrid, I need to choose the best heating strategy that keeps my furnace consuming a steady amount of energy over a long time frame of several hours.

It would useful if I understood better how the thermostat behaves depending on the different types of heating systems for which it has been designed for.

In being forced to choose from the list of system types, I would prefer to identify a system for which the heat takes longer to start up and longer to shut down. If my thermostat is smart enough, it should then be able to anticipate the long term cycle rates that minimize temperature over and under shooting and minimize the corresponding swings in the amount of energy consumed during a particular time frame.

When I chose the option for electric furnaces, I noticed that my home temperature stayed between a degree or so, but the energy consumption oscillated more dramatically over time because the thermostat was constantly chasing after a rising and falling temperature target that was never quickly achievable.

If I now opt for another system type, my hope is that the thermostat will be a little more patient and chose a moderated duty cycle based on a longer learning curve.

Thanks in advance for any suggestions.

[wgauci]

Assuming you're looking for longer duty cycles where your unit takes a long time to heat up and stay at operating temperature. I would probably go with the first option, Gravity/Steam. The HE and regular gas options are really just going to try and maintain a specific amount of cycles per hour and the electric as far as I remember is just going to give you the option to energize the blower motor when W1 energizes. Most heating stats assume the blower is energized by the furnace heating circuit so the electric option just tells the stat to bring the blower on through the G terminal.

[montreal]

Thanks for your suggestion.
Yesterday I switched from the electric type to the heat pump type.

My cycles have gone from about 400 seconds to 1600 seconds and my duty cycle no longer swings from 20 to 40 percent over 12 hours.

During last night, the duty cycle held fairly close to 20% over the same period in spite of a different exterior temperature.

I have to be careful when evaluating the data as my kitchen refrigerator, which is located about 8 feet from the wall mounted thermostat, can go into a defrost mode and throw a bundle of heat into the space and fool the thermostat.

At least with a heat pump type, the thermostat knows that the pump can only generate so much heat depending on the outdoor temperature and therefore the stat should be more tolerant to over or under shoots in the heated space.

Maybe next week I`ll try the first option (gravity steam).