Aquastat DIFF question.

[4000xt]

Hi,

Just wanted to know if someone can answer this for me.

If the DIFF is set to 10F, does this mean when I am calling for heat and my high on the aquastat is set to 180 when and the pump is running and the water temp drops to 170 the burner will kick in again? and that will be the cycle till you stop calling for heat and the water temp can go down to 160 if that is the low setting and than when it hit 160 the burner kicks in to bring the water back to 170 and continues on that cycle till you call for heat.

After reading this I am confussed lol. I think I know what I am saying but want conformation on it from someone in the know. I was looking at honeywell info and that is what I was getting from what I was reading.

Thanks in advance.

 

[tool whore]

I am a little confused as well. If your aquastat is hooked to a recirc pump then the 10degrees is as you described for kicking the pump on. If your high and low are set 20 degrees apart 160-180 then your burner would kick on close to the low. Some of the newer ones with a board will actually kick on early to maintain or to bring the temp up slowly in an effort to save fuel/ cycle time.

 

[4000xt]

Now I am even more confused!!!

 

[4000xt]

But does the diff selector not select the temp the burner kicks in when calling for heat and when it gets to the low setting to keep the water temp up??? Has to do with the burner not the pump. Or maybe both.

 

[trythis]

Your thermostat should operate the indoor loop pump (radiant tubing, I assume), the aquastat should control the heat pump or boiler. If you have a tank, the aquastat could be set to keep the tank temp within the Diff and the max temperature(for heat) In this case, it still controls the heat pump, boiler whatever.

The house/shop temperature drops, the thermostat will indicate a demand condition, the radiant tubing loop pump kicks on to pump the hot water from the tank (if you have one.)
If the tank somehow has enough heat energy built up to supply the radiant with enough heat energy to warm up the room without dropping the tank temp 20 deg. and the thermostat warms up removing the heating demand, your boiler/heat pump may not even turn on during that heating cycle. In this unlikely case, the aquastat would not go into a demand state and not turn on the boiler.

 

[4000xt]

Great thanks for the info

 

[tool whore]

But does the diff selector not select the temp the burner kicks in when calling for heat and when it gets to the low setting to keep the water temp up??? Has to do with the burner not the pump. Or maybe both.

Alot more info could be given for clarity. Without it we seem to be going in an infinite loop. I guess it depends how you have it set up. Since we dont know we can assume or guess.

In my infinite experience of using aquastats they have been used primarily to control recirc pumps mostly on hot water return lines and also on storage tanks that dont have a burner at all. We cant know how you use yours but hopefully it is not also wired to a burner as your thermostat should handle that.

Your thermostat should operate the indoor loop pump (radiant tubing, I assume), the aquastat should control the heat pump or boiler. If you have a tank, the aquastat could be set to keep the tank temp within the Diff and the max temperature(for heat) In this case, it still controls the heat pump, boiler whatever.

This may be the case, but is back-asswards IMO. No offense to anyone who wires it this way. The thermostat is for controlling temps. This would be the low and the high in whatever you are regulating with said thermostat, be it a furnace, water heater, boiler, radiant loop? or anything else that heats air, water, oil, refrigerant. Again, this is my opinion. As stated above, my use of an aquastat has been limited to mostly recirculation pumps.

In schools or large buildings where a water heater is in one corner and the water service is throughout or covers a large area, the hot water is usually run in a loop. As it makes the loop it cools. Sometimes it cools alot and others not alot. An aquastat is placed in line and when a particular desired temp is read, the pump kicks on and circulates the water effectively raising the temp to some desired level. The aquastat does not cause the burner to come on, it only causes the pump to run, which does raise the temp (through circulation only). IF the circulation causes the thermostat to drop, IT kicks the burner on. Sometimes the pump may cycle several times before the burner lights a single time. The aquastat can be placed anywhere a thermostat can be placed (this can cause confusion on their uses) but generally are at or near pumps, tanks (storage) and sometimes in-line of water or air. I dont do any hvac myself so I have little knowledge of their use in air handlers. The name implies liquid, and my uses have been limited to the above and boilers. Hopefully I didnt confuse anyone or step on any feet. If you use it another way and it works, do post up so we can all learn.

 

[trythis]

My Aquastat may be different than what you are used to and I may have described it wrong in the earlier post. It has 7 zones to attach thermostats to, demand from any turns on a main loop pump. It also tells my heat pump when to kick in because of the water temp in the loop tank. The thermostats in the zones open solenoids depending on the zone.

My air conditioning uses the same water loop in a chiller coil which can be air heat as well. This solenoids is controlled by a thermostat which also sends a demand signal to the aquastat.

 

[littletoes]

Tool *****, maybe on a light commercial application, but on hydronic boilers, there are usually TWO aquastat's. One used as an operator, the second as a High Limit.
The first's job is to enable the boilers burner when the temp of the medium hits the lower end of the set point (the job to watch the operation/safety of the boiler as it fires is the Microcomputer Processor Controler). The next, the High Limit is set higher, and when this temp is reached, it trips, and MUST be a manual resetable type.

Think of this as a "Loop-Loop" type of system, where the boiler is maintained at a constant working temp, and the system Loop is allowed to vary to the demand. Lets say for example, in September, you won't have the same heating demand as you would in January.

Make sense?

 

[littletoes]

I forgot to mention, there is usually a flow switch or some type of pressure switch that must "prove" in order for a boiler to fire. That means the T-stat operates the pumps.