Heat Anticipator

Bryan_13

This is a theoretical question, how is the Heat Anticipator Setting determined? Since the H.A. warms the thermostat so it is satisfied early, it compensates for the amount of heat that is released to the house after the fire stops to avoid overheating.

But this time might vary from house to house, due to radiator sizes, room sizes, insulation, windows, other heat loss, etc. So it seems that the H.A. might need to be adjusted to whatever works for each location to avoid overheating at the end of the cycle. But boilers (like Burnham's Independence) specify 0.8A, period. How do they come up with a hard number like that?

Chris V

Heat anticipator

The setting refers to the amperage draw of whatever control the thermostat is controling...zone valve, cad cell relay etc. You are correct when you say the anticipator needs to be adjusted differently for each house. The outside temperature and type of heat also effects the setting.

scrook_2

the initial setting

e.g. 0.8A reflects the actual current draw of the control on the boiler. The anticipator calibrations reflect the typical amount of heat required to shut off the t-stat in time to prevent overshoot, but, as you note, differences in insulation, radiation, piping, circulation, heating medium, etc. vary, so the setting may need to be tweaked a little from the initial setting.

J.C.A._3

Anticipator is set.....

With a milliamp tester. If using an oil primary, sometimes the rating is stated on the control, but it doesn't account for resistance or the lenth of the wire connected to the unit. I have a tester that measures Milliamps, and it seems to work well as a guide to a decent setting. As always, asking the homeowner will answer more than the meter. If they say it is cycling frequently, turning the anticipator setting up a bit makes for a longer cycle. If you've got a "set screw" type anticipator, it will help to read the manual and make the determination based on experience. Remember that most factory settings are for Gas/Warm air as a standard. The manual will explain how to set for something different. If you've got a steam system, I've been told to set them for the gravity hot water setting.(not too many new steam systems out there, but lots of replacement!) Chris

Unknown

Good question Bryan

You are correct in saying that the anticipator is set usually as a function of how long the devices the thermostat is controlling takes to operate so that the building does not over or under heat. Normally that will be a direct function of the amperage draw of the devices that are being controlled and normally this can be checked right at the thermostat by checking the amperage draw. In the case of the Independence boiler, we are using an isolation relay to isolate the thermostat away from the multiple devices we are now controlling such as the probe LWCO, Pressuretrol, Vent Damper, Blocked Vent Switch, Flame Rollout Switch and Ignition Device or Gas Valve. The current draw of the Isolation Relay is probably nowhere near 0.8 amps but we ask you to set the heat anticipator as to where it should be for a steam system which responds differently than a hot water or warm air system when it shuts down. Hope this clarifies this point a little.

Glenn Stanton

Burnham Hydronics

Bryan_11

That makes sense

...the only thing that isn't clear to me is why the amount of overheating that should be anticipated is a function of the amperage draw of the controls, unless the idea is to ensure that there is still enough current left available to operate the controls when the anticipator is energized...

Thanks!

Dale

Voltage is the issue

The heat anticipator is a series load, which is uncommon. voltage drop adds in series, so for instance 2 24volt valves in series would have 12 volts measured on each of them and neither would open. the anticipator is in series with the gas valve in the older equipment. The gas valve needs a nominal 24 volts to open, if the source tfmr is nominal 24 volts the heat anticipator must be and is designed to drop only a few tenths volts, and of course since it is a load it must be rated for safe amps. Amps is the same anywhere in a series circuit.Honeywell knows how much heat is needed. What they don't know is what amps will flow since they don't know what is the main load amps, so they have the heat anticipator set so that if you match the set amps to the actual draw enough heat will be supplied.

scrook_2

anticipator heating

the heat or power (in watts) generated by the anticipator is the current squared times the resistance of the anticipator (P = I^2 * R). I don't know why "I" is often used for current (or "E" for voltage) though.

Since the current for one control is differant than the current for another, you need to change the resistance to get the same amount of heat out of the anticipator -- double the current needs one quarter the resistance for example. Hence the adjustment.