YATT - yet another thermostat thread

[spidey07]

Boy that was a family argument that never ended.

"why are you setting the thermostat to 60 degrees! It isn't going to cool the home/car down any quicker!"

Of course mom insisted that boiling water faster made the water hotter as dad just buried his hands in disbelief. Go figure.

But I will say that in my car, if I set the thermostat to like 65 degrees it WILL turn the fan up. So what's the deal? Modern thermostats no longer an on/off proposition in autos/homes?

 

[91TTZ]

I don't know about that. In my car, it will turn it on full blast until it gets near that temperature, then it will throttle it down.

 

[spidey07]

I think it probably has something to do with efficiency (HVAC guys chime in?)

It realizes 'crap, I gotta do a lot of cooling work...better to go full bore for a while than the slow and steady route'

 

[Rubycon]

If it's a standard single stage with one mercury bulb that shorts the yellow and red wires together doesn't care if the dial is on 80 or 55. It just tilts back further meaning it stays on longer. That's a good way to ice up your coil too.

Now if you have a multistage system it's going to be different. The same essentially applies to VAV/DD, etc. with PID, active feedback, etc. But then it gets difficult and you have to really be an engineer to understand what's going on.

How many times do you see someone hitting the up/down button at the elevator landing - AGAIN! Hey if the light is on, the controller already is latched to go to that floor and hitting that button does absolutely NOTHING. But people do it anyway. :laugh:

 

[spidey07]

Wanna heat my coil baby? Grrrr.

Anyway, so you're telling me that modern thermostats are not ON/OFF. Or are you saying that modern thermostats are indeed accurate and it is the control systems that say "turn fan up higher" based on input/output/ambient temp?

 

[Rubycon]

Old style - aka T87F - uses a mercury bulb mounted on top of a bi-metal coil. Modern thermostat - the cheap knock off ones you find in DIY stores use a simple electronic controller and small relay in place of the hg switch/aneroid coil.

Pretty simple, eh?

 

[spidey07]

Originally posted by: MS Dawn
Old style - aka T87F - uses a mercury bulb mounted on top of a bi-metal coil. Modern thermostat - the cheap knock off ones you find in DIY stores use a simple electronic controller and small relay in place of the hg switch/aneroid coil.

Pretty simple, eh?

yeah, I remember those lovey. It was fun to bust them open and play with the mercury, that stuff is super fun to play with. It's metal AND it's liquid. good times.

But I'm talking modern control systems where the "turning the thermostat to 60 degress woin't cool the environment any faster" may not necessarily hold true.

 

[Rubycon]

Originally posted by: spidey07

yeah, I remember those lovey. It was fun to bust them open and play with the mercury, that stuff is super fun to play with. It's metal AND it's liquid. good times.

But I'm talking modern control systems where the "turning the thermostat to 60 degress woin't cool the environment any faster" may not necessarily hold true.

Depleted mercury cells were the best. They were full of the stuff and it was easy to extricate from them too.

Systems found in most homes will not cool any faster whether the setting is just a degree below calling for cooling or 20.

PID systems will provide more cooling when the difference between setpoint and ambient is greater. Often these have tampers built in and can detect such settings which can do a number of things to prevent user induced oscillation that otherwise would trick even the tightest anti hysteresis servo controllers. The cold deck dampers will open further, lowering the pressure in that line. The controller will then do certain things depending on the mechanical design of the system - variable vanes or variable speed motor controllers. Larger AHU's with relief houses often have motors > 500kW and are controlled by cycloconverters. These are efficient and complex and make scary noises when unqualified persons put their dick skinners in places they should not! :laugh:

 

[T9D]

I always get women that do that same thing but with the heater. They turn the thermostat in the house to 85 thinking it will heat it faster.

NO. Why cant they comprehend this? A thermostat makes it turn off or on at a certain temperature. 99 percent of houses are like this. Always have been. Maybe a few fancy mroe expensive ones are different.

In a car it's different. It mixes the amount of hot air and cold air to give the desired temperature. But there are different ways different cars work their heating systems.

 

[spidey07]

MS Dawn,

Can you please expound in more laymans terms. Pretty please.

My 500kW coi,l having can't get through the tampers put into place, are preventing my oscillation. I'm thinking I need a cold deck damper to relieve pressure, lest scary noises ensue.

*chuckle*

 

[Rubycon]

Originally posted by: spidey07
MS Dawn,

Can you please expound in more laymans terms. Pretty please.

My 500kW coi,l having can't get through the tampers put into place, are preventing my oscillation. I'm thinking I need a cold deck damper to relieve pressure, lest scary noises ensue.

*chuckle*

Mercury traveling twice the speed of sound will burn you. :laugh:

 

[woowoo]

(Impressed by Ms Dawn's knowledge of HVAC)