Circulate basement air upstairs

[oil pan 4]

It all depends on what kind of motor the fan uses.

[redpoint5]

PWM is more efficient than a rheostat, no?

... and that reminds me of this video:

https://www.youtube.com/watch?v=ZZC0SP02PqY

[freebeard]

Similar to this:


https://thumbs1.ebaystatic.com/d/l22...hlr95oICJw.jpg

PWM is more efficient than a rheostat, no?

What reading I did suggested varying the frequency instead of chopping into pulses. It made me wonder if you could use a diode to make a half-sine wave and then switch it in and out for a two-speed control.

[oil pan 4]

You can try half wave.
The only way to reduce speed on an induction motor with out burning it up is change the number of windings or changing the frequency.
Or design the motor to run horribly inefficient and not burn up with partial voltage.

[aerohead]

Originally Posted by redpoint5

I've got a 2-level house that has a single air handler in the basement level, as well as an air return on each level. The temperature in the basement level is 70 degrees while upstairs it's 80. Would it be a bad idea to block the upstairs return, forcing hot air down the stairwell into the basement return to get the air to mix? I'd also want to close the downstairs registers.

The protocol is to leave the returns alone,and add adjustable and lockable dampers behind the diffusers on the supply side.Intake ducts can collapse with a restriction,not so for the pressure side.
Systems which are engineered will spec out the design flow volume which can be directly measured with traversing of the actual duct with a pitot-tube and manometer/magnehelic,or at the face of the diffusers with an average of velometer readings,based upon the manufacturers criteria.
You're just trying to choke down an overflow condition until the entire space is at a uniform temp.By having the dampers behind the diffusers,you won't be accelerating the flow beyond 1,200 feet/minute,where things begin to get noisy.
Once its adjusted you shouldn't ever have to touch it again.

[redpoint5]

I've been running the fan in the evenings, but I'm still not sure that's efficient with just a 3 degree difference. I've read that an air handler can pull 500w, which is not insignificant. At that point it might be more efficient periodically running the AC, which also mixes upstairs and downstairs air, than continuously running the fan.

I've got the upstairs vents open and the downstairs vents closed at the moment. The idea is that when AC is called, it starts upstairs where it's warm and absorbs heat before going downstairs. When only the blower is on, the air will exhaust upstairs, and force heated air downstairs as it moves towards the return. There's also an upstairs return, but the extra positive pressure upstairs should force more of it through the downstairs return (I think).

In the winter my plan is to open bottom registers and close the top ones. It will be a struggle to even the heating out I'm guessing.

[aerohead]

Originally Posted by redpoint5

I've been running the fan in the evenings, but I'm still not sure that's efficient with just a 3 degree difference. I've read that an air handler can pull 500w, which is not insignificant. At that point it might be more efficient periodically running the AC, which also mixes upstairs and downstairs air, than continuously running the fan.

I've got the upstairs vents open and the downstairs vents closed at the moment. The idea is that when AC is called, it starts upstairs where it's warm and absorbs heat before going downstairs. When only the blower is on, the air will exhaust upstairs, and force heated air downstairs as it moves towards the return. There's also an upstairs return, but the extra positive pressure upstairs should force more of it through the downstairs return (I think).

In the winter my plan is to open bottom registers and close the top ones. It will be a struggle to even the heating out I'm guessing.

Seems that since the unit is in the basement,that there would be less restriction in the return air there,just like you're thinking.
Question? When the thermostat is satisfied and the unit shuts off,does the air stratify upstairs?

[redpoint5]

Yes, I think the hot air rises upstairs, unimpeded by the open stairwell. That, and I'm not sure how well the insulation between the levels is, but a layer of drywall and layer of MDF probably isn't much. Finally, it's a daylight basement, so the portion in contact with the earth is having heat drawn away.

I bought a FLIR phone attachment on sale ($150) to play with finding areas lacking proper insulation. I'll have to spend some time with it to see what I find. I'll probably never recoup the cost, but I like playing with new gadgets, and I can use it at multiple houses to help others.

[slowmover]

Originally Posted by aerohead

The protocol is to leave the returns alone,and add adjustable and lockable dampers behind the diffusers on the supply side.Intake ducts can collapse with a restriction,not so for the pressure side.
Systems which are engineered will spec out the design flow volume which can be directly measured with traversing of the actual duct with a pitot-tube and manometer/magnehelic,or at the face of the diffusers with an average of velometer readings,based upon the manufacturers criteria.
You're just trying to choke down an overflow condition until the entire space is at a uniform temp.By having the dampers behind the diffusers,you won't be accelerating the flow beyond 1,200 feet/minute,where things begin to get noisy.
Once its adjusted you shouldn't ever have to touch it again.

Winner chicken dinner.

Most $$ disappear with duct leaks (30% is norm). After that is ducting improperly-sized. Then, “tight turns”.

In short - with an AC system — the money is in the ducting both as to integrity, but mainly as to design where flow is emphasized. Any radius reduction or turns are a problem (which will have been “solved” as cheaply as construction permits allow).

It’s perilous to mess with it as Aerohead notes. Flow to each room needs balance with each other. Have a look in the GRAINGER catalog as to the types of tools sold to pros (will aid in understanding).

Flow measurement is the thing.

On the oldest houses with designed-in HVAC the far more efficient ceiling-central location was used for a circular diffuser. I far prefer these and would retrofit for them. The supply air flow is EVERYTHING (versus SEER ratings, etc).

Ducting for returns isn’t as critical. The basic measurements suffice so long as supply and return have a basic match in each room.

Were it possible (floorplan) a single chimney from the basement upwards with its own time-controlled fan would be worth looking into versus screwing with the HVAC system.

The guys using in-ground cooling loops might have insights.

.

[aerohead]

Originally Posted by slowmover

Winner chicken dinner.

Most $$ disappear with duct leaks (30% is norm). After that is ducting improperly-sized. Then, “tight turns”.

In short - with an AC system — the money is in the ducting both as to integrity, but mainly as to design where flow is emphasized. Any radius reduction or turns are a problem (which will have been “solved” as cheaply as construction permits allow).

It’s perilous to mess with it as Aerohead notes. Flow to each room needs balance with each other. Have a look in the GRAINGER catalog as to the types of tools sold to pros (will aid in understanding).

Flow measurement is the thing.

On the oldest houses with designed-in HVAC the far more efficient ceiling-central location was used for a circular diffuser. I far prefer these and would retrofit for them. The supply air flow is EVERYTHING (versus SEER ratings, etc).

Ducting for returns isn’t as critical. The basic measurements suffice so long as supply and return have a basic match in each room.

Were it possible (floorplan) a single chimney from the basement upwards with its own time-controlled fan would be worth looking into versus screwing with the HVAC system.

The guys using in-ground cooling loops might have insights.

.

As of the mid-1980s,the TITUS TMS was considered one of the most efficient diffusers on the market.They were primarily for commercial applications though.