Lost Electricity -2

Page 2 of 4  
YES, do tell how this works.
s

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't think that's what she said. If you want the temp to be 70, then set the t-stat to 80. It will cycle once or twice, then set it to 70. This is from a "cold" start where the temp is way below the setting. It takes time to bring the furnishings, &c up to temp, so having the t-stat set at 80 helps with this. Yes?
[snip]
--
charles

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article
snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

No. A thermostat is an on-off switch. As long as the room temperature is lower than the thermostat's setpoint, it's on. When the room temperature reaches the setpoint, it turns off. That's all.
--
Regards,
Doug Miller (alphageek at milmac dot com)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Jan 2008 11:27:05 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

I've found that it does help, even if it shouldn't. At least I've seen this with a particular gas furnace. When expected to raise the temperature 20 degrees of so, the furnace would cut off well before reaching the set temperature.
--
Mark Lloyd
http://notstupid.laughingsquid.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mark Lloyd wrote:

snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

Again, unless there are different heating rates available dependent on the difference between measured and setpoint, it's thermodynamically impossible. If it turned off, it simply either reached the demand point _at the location of the thermostat_ or there was/is another interlock on the system coming into play.
The thermostat turns the unit on; it runs until demand is satisfied. Heat input is fixed while the unit is on; off when it isn't. Loss to fixtures, etc., is dependent on the surface temperature differential and the local heat transfer characteristics and has nothing whatsoever to do w/ the setpoint.
It is true that if one overshoots an end temperature significantly (say 80F instead of 70F) and lets that reach an equilibrium there will be more retained heat in fixtures, etc., than there is at 70F which, some of which will gradually be re-radiated and convected back into the room, but the overall heat input required will be greater than if simply set to the desired end setpoint.
The only way the setpoint matters on rate is if there is a variable input source that is dependent on the temperature differential between setpoint and actual.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Jan 2008 08:28:13 -0600, dpb wrote:

snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

No post (at least that I saw) claimed that setting the thermostat up increased the rating of a standard residential hot air furnace.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Claiming that setting the thermostat higher than the desired temperature will cause the room to reach that temperature faster is _exactly_equivalent_ to claiming that setting the thermostat higher than the desired temperature will increase the output of the furnace. :-)
--
Regards,
Doug Miller (alphageek at milmac dot com)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Jan 2008 17:00:34 +0000, Doug Miller wrote:

So, who wrote that" (Hint: It wasn't me.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Jan 2008 17:00:34 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

No it isn't. Don't forget about run time.
In this case, we turned on the heat in a 50-degree house, with the thermostat set for 70. The furnace cut off when the temperature was about 60. Each additional heat cycle would raise this some until it got to 70.
--
Mark Lloyd
http://notstupid.laughingsquid.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That indicates a defective thermostat, which renders the example meaningless.
--
Regards,
Doug Miller (alphageek at milmac dot com)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Doug Miller wrote:

Or one not leveled properly, if it is an old Honeywell mercury-switch deal.
nate
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I don't remember the brand, but it defiantly did use a mercury switch. This happened around 1974.

Still it made no sense to call it meaningless.
--
Mark Lloyd
http://notstupid.laughingsquid.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 23 Jan 2008 01:43:09 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

That is what HAPPENED (defective or not). How is reality meaningless? Are you saying it is now impossible for thermostats to be defective?
--
Mark Lloyd
http://notstupid.laughingsquid.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
(Doug Miller) wrote:

No one claimed that doing so would cause the room to reach temp sooner. I was claiming (and maybe Ann was as well) that doing so would allow the room to reach the desired temp with fewer "cycles" of off/on.
I'll try again to explain. If I want my house at 70, I might sent the t-stat to 80. The furnace comes on, then cycles off as the air near the t-stat is 80. As the heat in the air warms the rest of the stuff, its temp drops, and the furnace cyles on. Once the system has done this a few time, I reset the t-stat to 70.
If I had set it at 70 and left it there it would have reached equilibrium at roughly the same time, but while it was doing so, the temp in the house would have been <70 during the periods when the furnace was off, before it kicks on again. I find this uncomfortble and would rather the chill was gone while eq. temp is reached.
--
charles

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Jan 2008 14:06:34 -0800, snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

How quaint. You're obviously American.
The rest of the planet understands thermostats.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike wrote:

Methinks you exaggerate. I've seen places in other countries where the people live in unheated buildings. I'm reasonably certain some of them don't understand thermostats.
--
He\'s so slick that he can\'t keep his socks up.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Doug Miller wrote:

^^^^^^^^^^^^^^^^^^^^^^^
Focus on this bit for a minute instead of the bit you've been focused on. What is "the room?" It's not the thermostat and it's immediate surroundings. What is "reach?" It's not the first time you're asymptotically within a delta -- it's when you've established it with some stability.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mark Lloyd wrote:

snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

Most thermostats also have an "anticipator" setting. They will stop calling for heat when the room temperature gets close to the set point. The objective is to prevent the room temperature from oscillating above the set point due to residual heat being released into the room by radiators. It's not usually an issue with hot air systems because they warm the air directly. But hot water, steam, and radiant electric systems usually need it. If you have a hot air system and the anticipator is engaging as if it were a hot water system, that could account for having it cut off too soon.
--
This is an election year. By common law,
the truth is legally suspended.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

snipped-for-privacy@earthlink.net (Charles Bishop) wrote:

for heat when the room temperature gets close to the set point. The objective is to prevent the room temperature from oscillating above the set point due to residual heat being released into the room by radiators. It's not usually an issue with hot air systems because they warm the air directly. But hot water, steam, and radiant electric systems usually need it. If you have a hot air system and the anticipator is engaging as if it were a hot water system, that could account for having it cut off too soon.
It was probably the heat anticipator that caused the situation I described (furnace shutting off too soon).
Now, If I had access to that house in the last 20 years, I might know what needs fixing. I haven't seen it where I'm now (same type of furnace).
--
Mark Lloyd
http://notstupid.laughingsquid.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The point is that different parts of the house heat up at different rates, because they have different heat capacities. Air has a low heat capacity, so it heats up quickest. Denser parts of the house, e.g. drywall, concrete or plaster, heat up more slowly.
In the usual case, a furnace is just trying to maintain a set temperature. The heat loss to the outside will be fairly constant, the temperature differences between different parts of the house fairly small, and the different rates (heat capacities) of the building materials not so important.
But if the house starts off "cold", say everything at 50 degrees, and you want to raise the temperature significantly, say to 70 degrees, then the different heat capacities have an effect. If you set your furnace thermostat to 70 degrees, it will shut off when the air around the thermostat reaches 70 degrees. Other parts of the house that have higher heat capacities will not have reached 70 degrees yet, so they will continue to absorb heat and cool the air down.
That is, even though the thermostat shut off, the average temperature of all the materials in the house is not yet 70 degrees--only the air temperature is at 70 degrees. As the cooler parts of the house continue to absorb heat from the air, the air temperature will drop and cause the furnace to run again to bring the air temperature up to 70 degrees. This process will repeat until all the materials in the house reach 70 degrees.
Now if you initially set the thermostat to 80 degrees, and then reset it to 70 degrees, you will initially overshoot your target temperature by 10 degrees as far as air temperature. But at this point the average temperature of the materials in the house will be closer to 70 degrees. You will reach equilibrium with everything at 70 degrees sooner.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.