I've been collecting a lot of data, studying the way my thermostat makes decisions about when to fire the furnace and when to not. By and large it does a pretty good job of maintaining the desired temperature
at the thermostat - in fact, it's got the temperature in that part of the house down to a science. However, therein lies the problem with almost every residential HVAC in North America - a single control makes decisions that affect all parts of the house
without any feedback from any of them! This scenario would be similar to having a single light switch that controlled every light in your house, or a single water valve that controlled the flow of every tap, sink and shower in your house. Put in that context, it sounds quite silly, and yet we have a single thermostat, typically centrally mounted, that determines how much heat every room, hallway and space in the house gets.
This is normally where I'd jump into the zoning bandwagon, and I zoned my last house quite successfully with Honeywell ARD-5 Automatic Round Dampers. Venturii monitored temperature sensors around the house, upstairs and down, and even some door contacts & motion sensors, and shut off certain ducts when rooms were either too warm, unoccupied, or both. The result was a much more comfortable living space throughout the house, and we saved on gas and electricity too. The Honeywell dampers were an "all or nothing" valve-like damper though, and short of doing some well-timed pulse magic on the relay controlling each damper, it was virtually impossible to get them to open "half-way" and stay in that position because of their spring-return mechanism. I'm in the process of designing my own dampers which I'll prototype in my own house since I have access to every one of the ducts supplying conditioned air to 18 vents throughout.
Anyway, I'm getting way off (what I had intended this topic to be) which was a change I made to the furnace control system last night. As it is, my thermostat provides an input to Venturii, which for the most part, simply passes that control data to a relay which is connected to the heat call circuit of our forced air furnace. It's a Carrier 80% efficient Induced Draft furnace. One piece of important information my thermostat does not have at it's disposal is the outside air temperature. Therefore, to help it along, I've now implemented some primitive
runoff logic that basically evaluates the temperature of the outside air, and adds a number of seconds proportional to that temperature to the end of each heating cycle, causing the furnace to run longer the colder it is outside. So far today, the house feels a lot warmer, though that could just be me who is now hypersensitive to the air temperature given my recent logic change
behind the scenes. My wife will be the real barometer of whether or not this change has helped or not.
