dual zone hvac conversion



Ok here is my solution to a cost effective solution for single to dual
zone conversion. Some assumptions are that the AC/Furnance is big enough
to heat the whole structure.
Must say I have not done this but my engineering logic and Handyman
experience says this would be cheap and effective... You HVAC guys please
feel free to challenge this design.

Steps would be:
1) Find out where your upper and lower (output) vents are connected and
install a motorized damper.
- Damper just toggles between upstairs and downstairs ductwork and does
not allow blockage of both.
2) Locate where the input (Cold air return) upper and lower ducts are
connected. Install motorized damper that toggles between uppper and lower
but never blocks both.

This is the missing critical piece:
3) Install appropriate sized duct just before your motoried damper on both
input side and output side. (Size would be determined by the amount of
backup pressure you may to handle.) I would start with 6in and monitor
system for backup.
4) Install adjustable spring loaded pressure release damper. Not sure the
term is correct but it is a simple damper that opens when it sees too much
pressure or too much vacuum (Same damper only reversed to be pressure or
vacuum sensitive.
5) Hook onto this damper and go into home. Not important where since this
is just to prevent CFM backup in your air handler.

Note: The above setup handles variables such as someone shutting all the
vent on a zone or one zone with less flow than the other.
My experience tells me any project that requires high tolerances is doomed
to fail and expensive to maintain.

6) Buy or build your 24VAC controller to run thermostats and dampers.
7) Locate your thermostats at the proper locations, normally near center
of zone and near cold air return so the sample it is taking represents the
rest of the zone.

8) Run system and adjust backflow dampers to eliminate backup pressure or
vacuum that would be under manufactures specs of minimum air flow

Notes: The cold air return control would be just as important as the
heat/cold output. I would think the best performance would be to close
lower input and output while the uppper is open or visa versa.

I cannot imagine, if this was DIY application, that you would be spending
more than $500.00 but that is just a guess.

Steps 3-5 are probably the most important to keep the cfm regulated

I think the issues with blocked CFM are that your A-Frame (AC) can ice up
if flow is restricted or the Heat transfer unit (heating) can get too hot
if the flow is not there.

All modern furnances have a heat sensor near the heat transfer area and
will shut down the flame if it reaches unsafe temperatures. Usually flame
cycling is a good indicator of air flow problem.

Disclaimer: This is the opinion of an analytical Handyman. This process or
system has not been verified so use at your own risk. My two story home
will be dual zone with the above process in the next year, and I will give
feedback on sucess or failure.



No Body

This is a pretty well established technology.. The use of variable speed
fans and staged cooling systems deals nicely with the variable demand.

There are individual defuser dampers, which allow you to meter air
flow according to demand in the room served.. so a south facing room with
windows can be cooled on a hot day.

There is even a company with a retrofit system that goes in very easily.


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