cycles per hour - explain?

Mike T., Swampeast MO

Provided the room temp setting has not changed, the thermostat will limit the number of calls for heat in an hour to the setting.

For example, with a setting of 1 cph suggested for steam, you will get one heat call in an hour.

The length of that heat call will vary with the load on the system, e.g. the colder the weather the longer the call.

One cycle per hour with a steam system helps ensure a good, long and efficient steam production cycle at the expense of less "tight" temperature regulation. Fortunately the mass of the iron rads (particuarly if UNCOVERED) helps keep the temp fluctuation to a minimum.

I would presume that the lower the number of cycles per hour the greater the overshoot allowed above the thermostat setting.

The "brainier" thermostats likely start with an overshoot assumption and then measure the rate of temperature rise during a call for heat and the rate of temperature fall after the call ends. After collecting that data for a period of time and comparing differences in rates of rise/fall, it can adjust the allowable overshoot to keep temperature as near the desired setting as possible for the given cycle rate.

This is quite different than other electronic thermostats whose calls for heat are determined by a fixed deviation from the setpoint. The traditional mechanical thermostats with adjustable anticipation are similar to this sort of electronic but you must measure the current available through the t-stat to properly "zero" the anticipator.

Tom S.

Confused by the concept...

Can someone explain the concept of cycles per hour to me? I mean if my thermostat is set for 1 cycle per hour (steam), does that mean it will only cycle on once per hour even if there are two (or three) calls for heat in that hour?

Or if there are no calls for heat will it turn on once in that hour?

Thanks in advance,

Bill

ChasMan

You would think you could infinately adjust it.. Perhaps in their next version. I hate thermostats.

Tom S.

Thanks...

Thanks, that helps me understand it. I will (for curiousity's sake) keep my eye on how it all works - my Honeywell Digital is set for 1 cph, but it seems anytime I walk up to it and decide to bump up the temp, it responds. Perhaps that act of manual override takes precedence over cph settings, or perhaps I'm just hitting it at the right time.

Bill

Mike T., Swampeast MO

If you hate thermostats, use TRVs or FHVs! They offer automatic and inherently infinite adjustability.

scott75

Will cph affect efficiency/oil consumption? Also, most steam boiler have pressuretrols (I know you dont like them). If the 1 cph is long enough, it could cycle on the pressuretrol anyway, effectively giving you more than 1cph, correct? By the way, how does an outdoor reset work with steam? From what I understand with hot water, it adjusts the temp of the water. Can't really do that with steam though. So does it affect the cph instead? Sorry, I don't mean to hyjack the thread.

Scott

Mike T., Swampeast MO

Don't forget--the cycles per hour relate to an undisturbed thermostat.

Increase the t-stat setting and it will respond immediately--if it didn't people would **** to no end and they'd never be able to sell them...

Mike T., Swampeast MO

Scott,

You're getting beyond me with specific questions about the operation of steam systems. I've never even played with (let alone worked on) a steam system.

I kind of think that during normal operation (maintaining temp) that a well-sized and well-tuned steam system will condense steam just as fast as it can be produced with little or no cycling on pressure during a call for heat. I could however be VERY wrong in this.