Hey, I'm getting an education too. In some respects it's fun. I like "thinking out loud" because it hopefully opens up possibilities and closes others. Finding something simple is sometimes hard. This seemed to be a mini fun research project as well. I'm used to getting things initially ridiculed, but as I'm telling it helps to home in on a solution.
There is cheap. There is easily serviceable. There is comfort. There is manual. There is automatic. There are combinations. You don't want things to be too complex that after you sell the condo, you have to provide a 100 page manual just to operate the HVAC system <G>.
A few things are now apparent:
1. There are no standards
3. There are low voltage and high voltage solutions.
4. Contact ratings were not addressed yet.
5. Most solutions are designed for hospitality industry.
6. The fan running all the time for some solutions makes no sense to me at all.
The most sensible system would vary the fan speed depending on how far the setpoint is from measured value. This results in the quietest system and the most energy efficient.
This is why I was trying to make a conventional thermostat stage select a particular fan speed. This gets off on the wrong track because stage 3 (fossel fuel) is way different than a heat pump. If the manufacturers of the tstat made the characteristics of the stages independently selectable rather than a system type, life would be easier.
The most sensible system would not allow one to get a blast of the wrong temperature air and would make it more marketable to a new buyer of the condo.
Having the fan run all the time defeats your purpose and won't work. Most stats being hospitality oriented with occupancy sensors and door open sensors doesn't help the selection. Your fan coil is super simple, thus you may have found out about the way your HVAC system operated AFTER you bought the condo. The guys building the condo put in the cheapest toaster (HVAC system) that they could find and your paying for it in terms of reduced comfort (high noise levels, no reduced temp for sleeping) and higher electric bills.
My proposed design is elegant providing assuming a stat with the following characteristics are found:
1. Programmable FAN coil stat
2. Multiple fan speeds that change automatically
3. A fan that won't run unless there is a call for heat or cooling.
4. The contact ratings for the fan is adequate in the stat.
5. A change-over sensor isn't required for the proposed stat.
#3 is a MUST.
There is still versions of HVAC1000's suggestions:
Place fan speed control at fan coil where it should not be moved when fan is running. Switch must be properly rated.
Place a seasonal switch in the fan coil area. e.g. Only allows heat or cool.
Variations of adding a contactor and low voltage AC supply to turn the fan on. The thermostat just uses simple on/off control.
And now we are almost right back where we started from adding complexity to make something else work or an elegant solution providing a better tstat choice can be found.
I may try to sketch a simple control ckt. The current tstat choice doesn't change the speeds automatically and it seems that the fan doesn't run all the time.
What are the markings on the blower motor label?
