Cycles per Hour vs. deadband vs. heat anticipators

Kevin_in_Denver_2

OK, heat anticipators were never the right solution, and we can forget everything we ever knew about them, and replace any thermostat we see that has one.

The Honeywell vision Pro 8000, for example, recommends one cycle per hour for a steam system. But it also claims to regulate temperature to within plus or minus 1 degree. On a cold day with only one cycle per hour, wouldn't the deadband tend to be larger than 2 degrees?

I realize it depends on a lot of factors, but I don't understand how you can program both a small deadband and a low cycle rate. What am I missing?

Any thermostat designers out there?

John Ketterman

You're right. It can't be done. It's false advertising.

Nothing wrong with anticipation, though. In "PID" terms the anticipation is the "D", it sees how fast you're approaching the traffic light and puts the brakes on a little before you need to stop. Mixing metaphors here. Too bad anticipation has gone the way of the dodo. Honeywell assures us that anticipation is the same as cycles per hour, but it isn't.

Mitch_4

I agree

I do NOT like CPH stats, I dont want them, I want longer run times, adjustable temp differentials, especially in condensing appliances, slightly wider ranges increase run times leaving the appliance in condensing mode longer and saving $$$.

Dont like em!

Stuart Oglesby_2

HO question

Hopefully this isn't a threadjack, but I am having a problem in a similar vein.
I recently put in a new Honeywell programmable T-stat for a 28 year old Weil McLain boiler connected to cast iron radiators. Now the boiler runs more than ever. Literally within two minutes of startup the T-stat is reading at the correct temp, runs for about ten more minutes, then shuts off. Yet the radiators aren't even warm in the room the T-sat is in. It comes back on about 15-20 minutes later, again shuts off before radiators are warmed up. This goes on and on until the room is finally warm.
I believe the default for hot water boilers seems to a setting of 3 cycles per hour, and Honeywell says(as above) a +/- 1 degree. Is all this related?
If I should be starting a new thread please let me know, just that some of the above discussion sound very familiar, and I don't know whether to call Honeywell or my heating contractor.

Thanks,
Stuart

Plumb Bob

You are saying the radiators aren't very warm, but then you are saying the stat is reading the right temperature, so why shouldn't the stat shut off? If it waited for the radiators to be warm, its reading would be much higher than the setting.

Simply from the limited info supplied it seems that your stat is doing its job perfectly, but it may not be in the right location. Maybe it is getting warm before the house as a whole is warm. You want it in a place that is representative of the whole house.

Or you could change the stat to 1 cycle/hr and that should cause it to cycle less, but you'll get a bigger temperature swing.

Long Beach Ed

Tekmar Thermostats

Tekmar makes a neat little thermostat in the #507 - 512 Series. Beautiful piece of engineering.

The problem is that it varies cycle time with temperature change, right down to a minute cycle.

Put one of them on a steam boiler and listen to it suck fuel on a warm day with those 60-second cycling.

Geez....

Long Beach Ed

Stuart Oglesby_2

Stumped

That's what is confusing. The thermostat is set for 68, if it still says 68 but then runs for heat, why is it coming on at all? That's for a heat call, _not_ for maintaining boiler temp.And how is the temperature rising that fast if the rads are sometimes still cold to the touch? It's in a central room on an inside wall(plaster & lathe) and this happens both in the am and pm, so I don't think it'solar gain as the room gets no sun after noon.

I'm expirementing this season with no/very little setback as the house is all masonary(plaster, block, and stucco) and not well insulated(though we're working on that). Setting it at a constant 68 seems to make the short runs worse, so I am trying a simple program of 67 when not home, 68 when home.

What is also confusing is simply the cycles per hour setting. Is that to limit how often the burner will run or will it make the burner run that many times/hour?