Air Handler Electric Consumption
Paul_Z
| Posted in Energy, Heating & Insulation on
I have a split level house with 3 floors in Maryland. During the heating season the basement floor is freezing. The middle floor is comfortable and the top floor is too hot.
I have a forced air heating and cooling system. In the future I am going to zone off each floor seperatly when I have the time and money. In the mean time I have the fan motor set to on instead of auto, to help increase the air circulation throughout the house.
How much extra electricity am I using letting the fan run continously rather than just when the furnace is running
Replies
How many watts is your fan motor?
Billy
Where in MD PaulZ? I have same style house and don't have that problem. Maybe we could compare notes / houses and you could solve the problem without resorting to zoning?
You need to balance the system, or hire someone to do it for you.
Typically you have a roughly 1/2 HP motor drawing on the order of 300-500 watts, IIRC. That's on the order of 7-12KWH per day of operation.
I WANT one of them there 300W, 1/2 HP motors, 500 W is a pretty good single phase motor itself.
I could drive a generator with a 300W 1/2 HP motor and make some money <G>
The motor is rarely running at full load -- really producing maybe 0.2HP. At 745W per HP and 60% efficiency the motor producing 0.2HP will draw about 250W.Of course, non-full-load efficiency for a frac HP induction motor is a crapshoot, which is why the variable speed DC motors are such a good idea, efficiency-wise.
God is REAL, unless explicitly declared INTEGER
Paul,
You are right to worry that the electrical consumption of your blower motor is expensive. Some blower motors draw 700 or 800 watts. If you know the kwh price of electricity in your area, you can do the math.
But no one has yet described the best solution to your problem: You need to perform air-sealing work. You have infiltration in the basement and exfiltration through your second-floor ceiling. That's why your basement is cold and your top floor is too hot. Perform air sealing work in the basement, especially at the rim joist area, and in the attic (around chases, penetrations, the attic access hatch, and the long gaps between partition top plates and the drywall). Spend $500 on spray foam. If you don't know how to do it, hire someone who does.
You are giving him the correct advice....good job!!!
Dan H did the math for you. About 745 watts per (used) HP ... but you may only load a fan say to 50-70% of rated HP on a continuous basis. Then add the motor inefficiency in (Dan said around 65%, I think). You could measure the amps and convert the actual fan draw into KWH if you wanted.
I tend to agree w/ MartinHolladay, though. You've got an air leakage problem and the thermal stack affect of 3 levels is illustrating this very well. Cold air in at the lower level and warm air out at the top. Is your basement finished? Ideally before you go to the trouble of zoning, you should think about the air sealing issue a little.
You certainly don't need to have air leakage to have it cold below and warm above. The simplest way to deal with that is to mostly shut the registers on the upper floors, while maybe even adding registers on the bottom floor. Reverse the setup in the summer.
God is REAL, unless explicitly declared INTEGER
Dan,
I disagree. We are so accustomed to leaky homes that we take it for granted that the bottom floor of a 3-story building should be cold and the top floor hot.
A very well sealed building will have relatively uniform temperatures from room to room and floor to floor.
If you say so.
God is REAL, unless explicitly declared INTEGER
But what if there are open stairwells that heat can travel up?
Or did he say there wasn't open stairwells? Did I miss that?
PopaWheelie,
Air will not move up a stairway unless there are enough air leaks in the lower room to provide makeup air to replace the air rising up the stairway. Consider a large, sealed glass jug. The air in the bottom of the jug has no reason to rise to the top of the jug because there is no replacement air available.If the bottom floor of your home feels drafty, you can try to locate the air leaks on the bottom floor and seal them. That will help. Alternatively, you can try to locate the air leaks into your attic. That will also help, because if no air is leaking into your attic, then no exterior air will be drawn into leaks on the bottom floor.The best approach, of course, is to seal both the attic leaks and the first-floor leaks.
What about the HVAC ductwork?
God is REAL, unless explicitly declared INTEGER
DanH,
Okay, I'll bite: what about it?
Air will flow through the ductwork when the fan isn't operating, providing a potential return path you claim is missing.But probably more to the point, in an open stairway there are two air streams operating. Cold air flows down the steps like water, while warm air flows upward along the ceiling. A "circulation" that heats the upper floor and cools the lower floor is easily established.
God is REAL, unless explicitly declared INTEGER
But why is there a hypothetical pool of cold air on the upper floors, eager to flow down the stairway? And why is there a hypothetical pool of hot air in the basement, eager to flow up the stairway? I thought the top floor was the hottest, and the basement was the coolest.Really, the only explanation that accounts for the facts is that there is a serious air leak in the top floor ceiling, balanced by a serious air leak in the basement.
Windows. Mostly it's cold air from above flowing down, pushing the warm air up.
God is REAL, unless explicitly declared INTEGER
From what I understand a stairwell is plenty big enough to have a convection loop. The return and supply are in the same space.
People here talk about a convection loop in fiberglass insulation in a wall cavity.
If it's happening there it certainly would happen in a stairwell.
I'm not saying air infiltration isn't a factor. By all means seal it up.
Maybe it was common sense in the past to dampen your registers in the house according to the seasons.
People learned it and passed it down. That has stopped because people are to busy.
now people just want everything automatic until you give them the price. But they still don't take personal responsibility.
I have gone around the house and adjusted registers according to the seasons.
But all it takes is one hot or cold day and people in the house adjust them for their immediate needs. So it is hard to keep them set.
Edited 1/13/2009 11:08 am ET by popawheelie
Generally, I disagree, too. Given a furnace in the basement and mediocre duct design, I would guess the top floor to be heated less than a basement ... which in winter should be easy to heat. Instead, it seems to be just the opposite. Only time it would be different is if the ductwork were designed w/ to much heat going to the 3rd level (which I would surmise that it isn't and would be surprised if it was ... which is what you are implying).
Maybe what you are implying is that if it was sized for that big summer cooling load on the upper level, that in the heating mode, it would naturally be skewed toward more heat on the upper level? Not sure if that is right, either ... the basement should be relatively a piece of cake to heat.
Heat rises. In the winter you want to pour the heat into the bottom floor and let it rise to the top. In the summer you route the cold air into the top floor and let it tumble down.
God is REAL, unless explicitly declared INTEGER
You got that right ... heat rises ... and as it does it loses heat to the surroundings. When it gets to the upper level, it isn't hotter, it's cooler. I've measured stratification under various conditions and if you put heat into a space near the floor, there is relatively little temperature stratification between floor/ceiling. I had a house that actually had reverse stratification despite an open stairway ... warm on the main level and cool upstairs (usually put no heat upstairs).
Ditto with A/C ... put the cooling upstairs and as it 'falls' it 'loses' its cool on the way down resulting in again relatively good balance of air temps.
During the heating season the basement floor is freezing. The middle floor is comfortable and the top floor is too hot.
Oh my, it's Goldilocks time!
Ok, "we" will ned a bit more information to really work this problem.
The simple answer might be just getting the warm air up top pulled down to the lower level with return ducting (unless the a/h is in the attic, then you might need more supply).
Another majot issue is whether or not the system was designed, as opposed to merely installed.
If the ductwork was never designed to move the correct amounts of air to the different levels, then the hvac system could be perfectly adequate, and not work well. This is also true is the supply ducts were correctly sized, but no returns were installed (or were/are imballanced).
Not to change the subject here, but is it normal for "some" air handlers to run even with the thermostat off? I have a Trane electric split system that does this. It's only two years old and has always had this condition. The guy that sold it to me said that the blower is designed to run at a creep speed all the time. You can feel a very slight breeze even with the thermostat turned completely off. The only way to stop the blower entirely is to flip the breaker for the air handler to the off position. Could that really be normal?
New knowledge is priceless.
Used knowledge is even more valuable.