heating and cooling a two-story room 2

[southernair]

I am currently designing a hvac system (through the use of a condensing unit and air handler) in which i am heating/cooling a two-story room. The air flow has plenty of pitch to reach from the celing where the diffusers are down to the floor where the thermostat is. The problem is that on cold days/nights, the air handler works hard to heat the space and inevitably ends up heating only the higher parts of the space, which have a hall way out of the space. Therefore the air is heading out of the top of the space and down the hallway at temperatures over 90 degrees farenheit. I was wondering if anyone knows a quick and easy fix to prevent so much of the air from traveling up and away from the thermostat causing the unit to over produce heat.

 

[dcasto]

Could you use a remote temperature probe in the return air duct?

 

[MikeHalloran]

Ceiling fans, blowing down.



Mike Halloran
Pembroke Pines, FL, USA

 

[SnTMan]

Close the hall door

 

[RockEngineer]

Ceiling fans blowing up with the air then following the natural pitch of the roof down can often be more effective than ceiling fans blowing down (or so I have been told by several HVAC people).

 

[CorBlimeyLimey]

Only two story ... imagine trying to cool a library.

 

[MikeHalloran]

To assist in cooling the room, which is not the extant problem, I'd suggest ceiling fans hung down to the second floor level, blowing up.

I was thinking that fans mounted immediately under the registers, blowing down hard, might be able to splash some hot air off the floor, or at least provide a few pockets of barely warm air in which to curl up with a book. Wishful thinking, fighting Mother Nature and all.

To heat a cold room using hot air injected at the top, the fans will have to run fast and noisy, whichever way they blow. Wherever the fans end up, consider making them reversible, so the occupants can screw up the airflow to their satisfaction.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

southernair (Mechanical)
Where is your return air duct? Is it on the lower floor low down? or is it in one of the ceilings?
If you are injecting warm air at the top of a room, you can reduce the stratification if you can pull the return air off at ground level.
B.E.

 

[bklauba]

About 1 year ago I completed the restoration of a 3 story row house in Philadelphia, which also included replacement of the ancient oil-fired FA furnace with one of the new 90% efficiency gas units (Rheem, bought on-line). I also added AC, using a Rheem 3.5 ton unit (which features a screw compressor!!; pretty quiet and smooth running).

To make the AC work, I built a three story return, which included a 10" vent fan, 2 speed, 2 and 3.5 amps, located at the top of the return. This pulls air from the two top floor BR's (about 300 sq ft, 8' ceiling) thru a soffit on a common wall. The near-to-ceiling grids mounted on each side of the soffit are 8" X 30", and there is a 8" X 8" in the stairwell/hallway, at the end of the soffit.

During the winter, the return vent fan is not used, and the original in-floor returns (a 15" X 40" in the centrally located DR, where the thermostat is, and a 8" X 12" in the entrance hall way, both on the first floor) are used as the original heating system was planned.

During the summer, the 15" X 40" is sealed off, and the return fan is run with the AC. This arrangement works quite well; guests sometimes complain that the top floor is too cold in the summer, despite a flat roof, and full western exposure of the front of the building. (We did blow insulation above the ceiling.) The middle floor's two vents we open in the summer, keep half to 2/3rds closed in the winter. 1st floor is ~ 700 sq ft, 2nd ~ 600, each of these have 10' ceilings.

Ceiling fans on the 3rd floor are directed upwards, and help the AC (less so when directed downwards), and are not run in the winter.

All of the supply (i.e., not return) vents are either in-floor, or low in-wall. Our feeling is that the partial vacuum created by the return vent fan and furnace blower (the cover on the large return is nicely sucked down and seals when the AC is on) pulls cold air up to the 3rd floor pretty well, while the partial closing the 1st and 2nd floor's supply vents in the winter provides plenty of warm air to be sent throughout the house.

My point is: Seasonal adjustment of the supply and return flows are required to heat / cool a multi-story using a single HVAC system.

BK

 

[rb1957]

not being an HVAC type, could you reverse the flow in the ducts ... i think you want to supply AC air at the roof and return it from the floor (cold air sinks, of course), what if your furnace supplied hot air into the AC return ? ... you'd need two return fans ... dumb ?

 

[plasgears]

Make up air from the upper reaches.

 

[safetydan]

Try this site:

http://www.bigassfans.com

We have them in our facility and they work very well in the winter months.

 

[dik]

One of the large automanufacturers was using ducts at the high level to collect hot air and redirect it to the lower level.

Dik

 

[dimjim]

Safetydan,
What happens when one of the blades separate?

 

[safetydan]

We have not had a blade separate, but I suppose it would be similar to having anything overhead fall, it will hit the ground.

 

[MiketheEngineer]

Fans - blow down in summer - up in winter.

Have almost the same layout in my house and the upper bedroom with opening to 2-story great room would get to 90 degrees real quick.

This works great!!

 

[leDouche]

Some simple balancing of the system may help. There may be too much air being supplied to the upstairs spaces.
Depending on the capacity of the fan and or motor, you may be able to set it to high speed or adjust a sheave, depending on what type of syestem you have (direct drive or one with an adjustable sheave). The outlets upstairs may be a bit too large to get a decent velocity out of them...the air could be sort of "falling" out of them, rather than being "thrown" out of them. Also, returns are as essential as supplies...air in equals air out.

 

[lilliput1]

I have high & low returns. In the winter I put sheets of paper on the low return to block most of it. Thus the heating system draws most of return from the high heated air. I also set the fan to run continuosly thereby mixing the air better. Do not close doord so air can flow in and out back to the return grilles.