Balancing Air Temperature
adjustable 2-story air balancing
hi, I’ve done a large addition on a 2-story duplex in Central VA and am replacing the whole HVAC & duct system (heat pump + gas furnace).
Previously the HVAC system was not well designed and the upstairs was always much hotter than the downstairs. Obviously hoping to remedy that but stuck working within confines of very limited space for mechanicals & ductwork, 8′ ceilings, and an unconditioned attic with blown insulation on the floor.
To avoid attic ductwork, I’m planning to run all ducts off a main trunk along ceiling of 1st floor with takeoffs running through the 2×8 floor joists to supply at the perimeter (ceilings of 1st floor and floors of 2nd floor).
I used this software Load-Calc (loadcalc.net) to estimate heating and cooling loads for each room and am working out duct sizing based on that. (side question: doesn’t seem like this takes stack effect into account. Anyone have any recommendations on how to account for that?)
The issue of course is that heating loads are higher downstairs and cooling loads higher upstairs. So if I size my ductwork for one, it will be off for the other. I’ve looked into zoning as one potential solution, but seems like there are some downsides to that. As a potentially simpler, more affordable, and better for my situation approach I have the following idea:
1. Balance the ductwork to meet cooling requirements based on the aforementioned load calculations. This should make it comfortable in the summer but too hot upstairs in the winter.
2. Get bedroom registers with dampers (all bedrooms are upstairs–plus a hall and 2 baths). Then occupants can throttle airflow down if it’s too warm.
3. Upsize all of the supply branches so that I don’t put too much static pressure on the system when the bedroom registers are throttled back
Some potential drawbacks I can think of would be:
– noise at registers from partially closing dampers
– occupants having to manually adjust things
– velocity getting too low in supply ducts (but is this a problem since they’re in a conditioned space?)
– getting too little throw & mixing at registers (but wouldn’t this be a problem for variable speed equipment anyway?)
Very curious to hear others’ thoughts or warnings about potential pitfalls since I haven’t heard of others doing this.
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