Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 exptools 1/6/84; site ihuxl.UUCP Path: utzoo!watmath!clyde!burl!hou3c!hocda!houxm!mhuxl!ihnp4!ihuxl!seifert From: seifert@ihuxl.UUCP (D.A. Seifert) Newsgroups: net.misc,net.physics Subject: Why don't thermostats work? Message-ID: <877@ihuxl.UUCP> Date: Thu, 2-Feb-84 08:05:49 EST Article-I.D.: ihuxl.877 Posted: Thu Feb 2 08:05:49 1984 Date-Received: Tue, 7-Feb-84 15:12:51 EST Organization: AT&T Bell Labs, Naperville, IL Lines: 67 { This should really be in net.mechanical_engineering, or net.control_theory, but there isn't any, so... } Question: why don't thermostats work? I'm talking about the standard bi-metallic strip which opens and closes electrical contacts to control a furnace (or ac) and supposedly maintain a steady inside temperature dispite a varying outside temperature. (fig 1) What usually happens is that as the outside temp falls, the inside temp also falls, (see fig 2) and you have to adjust the thermostat to maintain a reasonable inside temp. With the current weather conditions (30F below one day, 40F above the next), this is quite a pain. inside | ideal thermostat set at 70F / temp | (furnace only, furnace runs / 80 | out of BTUs at -10F) / | / 70 | ________________________________/ | / 60 | / | / 50 | / | / | / |__________________________________________________ | | | | | | -20F 0 20 40 60 80 outside temp fig 1 inside | real thermostat set at 70F / temp | (furnace only, furnace runs / 80 | out of BTUs at -10F) / | / 70 | _________/ | _________/ 60 | ______/ | _____/ 50 | / | / | / |__________________________________________________ | | | | | | -20F 0 20 40 60 80 outside temp fig 2 (the graph in fig 2 should be a smooth line, not a stair step, but until we all get graphics terminals...) Anyone know why this happens? The thermostat doesn't know what temperature it is outside, it should only know "it's below 70 in here => turn furnace on". But somehow it's getting fooled into thinking that the inside temp is 70 when it's really 60. Sometimes it seems that a knob controlling the duty cycle (with no feedback) would do just as well. -sigh- -- _____ /_____\ from the flying doghouse of /_______\ Snoopy |___| ____|___|_____ ihnp4!ihuxl!seifert