HVAC Fan cycling, how frequent?

[paulbates]

I have programs that cycle the furnaces' fans after an hour of inactivity and sensored doors windows / are closed.

 

Currently, I have the program run the fans 15 minutes straight each hour that its in that inactive state, and idle for 45 minutes, and repeat. The purpose is to level the temp across the covered areas, and filter the air regularly. Historically this cadence has worked ok, but I'm wondering about the advantages of doing it differently?

 

My question is not about programming, but operational...what runtime  cadence works best for others that do this, eg 5 minutes every 15 minutes as opposed to 15 straight? Or something else, and why it works better.

 

Thanks

 

Paul

[Teken]

Paul,

 

Back in the day when I had no reference about temperature / humidity in my home. I did something similar thinking it would help but after deploying my 1 wire sensor array this idea proved to be wrong and a waste of energy resources.

 

My environment is obviously much different then yours given age, build, design which impacts my personal findings.

 

Essentially my home is very tight meaning very little air leakage. It's very well insulated and thus requires less heating / cooling to maintain long term ambient temperatures through out the home.

 

Since the sensor grid has been deployed the fan is activated only 3 times a day set at 8 hour intervals and operates for 15 minutes or extends based on variables met / not met.

 

The final outcome is stable temps as before but less energy consumption during the 8 long winter months.

 

 

Ideals are peaceful - History is violent

[paulbates]

Thanks Teken, interesting.  I don't have sensors everywhere which would help this. I have accurite temp/humidity sensors that I move around which help even the temp by helping set the vent openings in each room for distribution. I also turn the fans full on when its >82F outside.

 

From an operational point of view, what sorts of things do the variables in your programs track to extend the cycle time? That's the kind of info I'm thinking about

 

Thanks

Paul

[larryllix]

Even every few hours would be good from my experience depending on the cold spots in your house.

 

I find one of the most important times is about 3 AM whem you temperature setback has caused the fan to not run for hours and the bedroom air is getting stale.

 

Of course, length of cycle can be varied for economics of energy by sensing away etc.

Edited November 1, 2015 by larryllix

[paulbates]

Larry, good point on extending at night. that would probably help and be easily accommodated in programs.

 

The furnaces are new with DC motors, there is actually no reason, beyond power use, to not keep them running 24x7. There is a balance between the cost of running the fan vs delaying / avoiding an HVAC cycle. Sensors are not out of the question, but that has the potential to be an expensive and time consuming project. 

 

At this point I'm continuing down the empirical path. The 3 am extension' is an idea to try. Thanks

Paul 

[larryllix]

The same problem occurs during A/C season when the house hits it's temp mark and it is cool outside in the middle of the night. No circulation occurs.

 

During A/C season I set my stat Wake period to 3 AM with a temp drop of 0.5 degrees just to prompt an air circulation and avoid that stuffiness that happens when your bedroom fills up with carbon dioxide from exhaling.

[bipto]

Interesting question / topic, Paul - so here's my 2 cents...

 

Ever since we had our new furnace / heat pump system installed last summer, I run the blower fan FULL-TIME during waking hours when the house is occupied.  I was first presented with this suggestion by the system installer, and have done significant research through the manufacturer and other sources to validate the idea.  I was skeptical at first with concerns of noise, drafts / constant air movement, and power consumption, but none of those turned out to be an issue.  At the low speed that the new ECM motors offer in Fan On mode, the noise and air movement are barely perceptible, and power consumption is rated at a very reasonable 75W continuous.  I'm assuming your modern equipment has the same variable-speed capabilities.

 

I do not run the fan 24/7 as I do make adjustments based on time of day and occupancy.  During sleeping hours the fan is programmed to run 12 minutes per hour (apart from heating, cooling and humidity demands of course), and when the house is unoccupied the fan is simply set to auto, effectively off as heating and cooling set points are significantly set back in this situation as well.

 

After running with this policy for nearly the entire year+ that we've had the new equipment, I could not be more pleased.  

 

The obvious upsides were 1) that with the constant circulation we have a more consistent temp across the entire house with little to no perception of the temperature change across the two degree deadband, and 2) with basement ductwork not allowed to cool below room temp between heat cycles, we no longer get that annoying "cold blow" for thirty seconds when the furnace first starts as it is bringing the ductwork to temp.  Another potential benefit worth noting is that the allergy sufferers in our household seem to have had a much better year.  Obviously one year is not enough time to attribute this improvement solely to increased air circulation / filtration, but I'm betting it played a part.  

 

The only downside that I have noted is that I now have to change my filter more aggressively than I was used to with our old system, which, with the increased air circulation was certainly to be expected.

 

These are my observations based on our particular circumstances; your mileage may vary.  Questions, comments and criticisms are welcome and encouraged...

 

--Bill  

[paulbates]

Thanks Bill, very indepth.

 

That's an interesting approach. My programs have been focused on these transition times of the year of moderate temps yielding fewer, shorter cycles and the fan not running..... when allergy conditions are the worst. During the rest of the winter, heat or humidification cycles run it frequently, but I should try running it full on during the day. 

 

My new gas heaters do have variable speed fans. The choices on controlling them were limited... 1) use carrier's stat where it controls speeds automatically, or 2) statically configure separate ones for heat. cool and fan on.  There's a procedure in the manual for speed: fan on, wait 2 seconds fan off, and fan on... that is supposed to step through them, but haven't had luck getting that to work.. and stepping through the highest speed will get noticed, it will be heard. 

 

I just used my DTE power app and turned one fan on and off, leaving everything else alone. 3 trials over 5 minutes = .206kw difference from the meter... looks like my fans are using 200watts each at their set speed for 'fan on'.   . I might have to ask my hvac company if there is a lower speed that fan on can be set to for 'fan on'. If I can, the fan on should have a less noticeable cold blow and it should help power consumption.

 

Avoiding the "cold blow" phenomenon by leaving it on is a good point and has the potential to delay the next cycle. I like it. My house is problematic because its a colonial, 2 stats, each stat covering part of both floors, front and back. So if we're cooking / entertaining in the kitchen/family room... where one stat is, that area is warmer and the upstairs bedroom doesn't get what it needs. Shuffling the air a little helps, but full time obviously more. Pulling new wire upstairs for a stat or sensor is extremely difficult. 

 

I can confirm the improvements for allergy sufferers by running the fan at some regular interval. I've had fan cycling programs for ~10 years, starting on RCS TX15B stats, it was one of the reasons I got controllable stats. We all suffer from allergies in different ways at my house, and Michigan can be brutal in that department in the spring and fall. Using fan cycling on the highest allowable HEPA filter has made an incredible difference during that time. Less symptoms and complaints, less trips to the allergist, etc.

 

The new filters I use are HEPA13 and the spec says change them yearly. I'm in my second year with these furnaces and I've been changing filters every 6 months and that's been consistent. The filters are $35 a piece if you buy them at the right time, that much money vs better health is an easy tradeoff for me too. (Got them for $28 at Menards a few weeks back)

 

I'm going to have another look at the manual on changing the speed for 'fan on' lower if possible and measure that power usage,  and look a longer fan run times during occupied times.

 

Thanks Bill!

 

Paul

[Scott847]

At home I have a Carrier Infinity 100,000 BTU furnace with a variable speed ECM fan. The Infinity thermostat allows the fan to run continuously at low, medium or high speeds.

 

I leave it running 24x7 at low speed, which circulates at about 525 CFM (high is about 1250 CFM) and only uses about 40 watts at this speed.

 

Aside from continous filtering it also distributes our fresh air intake of about 100 CFM, and helps keep temperatures stable. The fresh air intake is a separate, not as efficient fan that uses about 33 watts and goes through a separate filter into the furnace air return.

 

The fresh air intake keeps the house slightly positively pressurized, which reduces air infiltration of dust and allergens.

 

If your furnace has an ECM fan and the thermostat can be set to continuous low fan this can help a lot with indoor air quality.

[Teken]

Thanks Teken, interesting.  I don't have sensors everywhere which would help this. I have accurite temp/humidity sensors that I move around which help even the temp by helping set the vent openings in each room for distribution. I also turn the fans full on when its >82F outside.

 

From an operational point of view, what sorts of things do the variables in your programs track to extend the cycle time? That's the kind of info I'm thinking about

 

Thanks

Paul

 

Paul,

 

Not sure why my subscription didn't tell me there were replies here?!?!?

 

Anyways, the variables monitor some key attributes which in my opinion matter most to the over all (perceived) comfort of the home and to the occupants. Most people know or soon realize that it requires more energy to heat up a humid environment. The second part is determining at what level is acceptable to the end users and what goal is sought.

 

IMHO 40 - 55% relative humidity is perfect in the cold north where I live . . .

 

Once the home is at this level the next important aspect for me is what area is colder / hotter? To some their expectation is to have all (living spaces) to be the same etc. That's fine if that is your goal but for me I've found that to be a waste of resources and is really unnecessary.

 

Meaning if I see a 1 degree change in temperature from another area, floor, zone, that doesn't concern me and I certainly will not chase the rabbit in enabling my systems to compensate for. Note, I am not talking about sensor error or variance but actual temperature differences in the home.

 

All of my sensors have been tested, spec'd, and validated to have a variance of less than 0.5 degree's so in my case I am comparing a Apple to Apple and not to a Water Mellon!

 

Ha . . .

 

Next unlike many the HVAC is not my first line of defense or system to balance the homes environmental temperatures. For me the first things that get enabled and deployed are zoned ceiling fans which during summer / winter offer the bulk of circulation in the home. Obviously the rotation of the fan is adjusted to season its going to operate in so this is my first line of defense.

 

Next are two variable fans which are located high up ( 12 feet on ledge ) which push or suck all the hot air from the vaulted ceiling. Depending upon what is required the fans are either configured to push air or to suck air. This is where the massive 1 wire system grid comes into play because the system is programmed to compare anywhere from 2 to 32 sensors and five humidity sensors.

 

Based on thresholds met / not met the system will continue to (stage) and add more time or bring in other sub systems to meet the final goal. Next, the system will bring on line the over head range and its only goal is to evacuate the home and suck down the hot air being pushed by the two ledge fans. This causes massive movement of air in my home and normally with in 15 minutes all of that wasted and trapped hot air is forced down to the living space where it should be used and enjoyed.

 

At that point if the system has determined the home has met its target the system will shut down all systems until called upon again. If at this point the home still has not met the target the central exhaust is brought on line suck out more air but the key thing at this juncture is that the intake air is not brought on line.

 

The house for all intense of purpose is operating in a negative pressure environment . . .

 

I've found in my home because its so freaking tight that this method allows me to suck out lots of heat during the summer with out the negative impact of in taking hot / humid air. During the winter the furnace is allowed to operate and when the central exhaust is activated fresh cool air is brought in. Same as Scott847 this causes a positive pressure envelope in the home.

 

My red neck method to see air movement and to validate my ideas have all come from using incense sticks. The fragile smoke it billows out allows absolute visuals as to air movement and the impact it has on different circulation methods.

 

With the Autelis Bridge, Dash Box, and Green Eye Monitor, SEG, I can see live all areas, floors, zones, for immediate temperature / humidity and whether or not my systems are working or not. As stated above this empirical data has been outstanding to confirm ideas, systems, and goals.

 

The main reason I pushed to go this route is because it doesn't take much for a person to *feel* like things are fine / not fine. Feeling something is often not very accurate especially as people get older etc. This is why I stressed at the very top control and management of humidity in the home plays more on (Human) then actual temperature.

 

Essentially, I am cheating using humidity to give a perceived warmth, when in fact its actually colder than the family thinks it is. In the summer its the same I let the humidity go straight down in the 30's and this allows the house to be physically hotter and the (perceived) heat is manageable and bearable for all.

 

Hope the above proves helpful to some of you . . .

 

As my main driver has been energy consumption while balancing a healthy home for all.

[larryllix]

Who wouldn't want the maximum air from thr top of a mountain though ?

 

I was trying to keep my humidity over 50% but I was going through 4-5 gallons of water from a portable humidifier per day. I carted water way too often. After a few years of I decided just under 40% was fine but slightly dry on the throat times. The water consumption to maintain that was brutal and now much more reasonable.

 

My HRV needs to be backed down somewhat in the winter as it is a big burden for the humidity changing with dry winter air.

 

This my next project to automate the air exchange on a smarter basis.

[bipto]

...

 

My new gas heaters do have variable speed fans. The choices on controlling them were limited... 1) use carrier's stat where it controls speeds automatically, or 2) statically configure separate ones for heat. cool and fan on.

...

 

I'm going to have another look at the manual on changing the speed for 'fan on' lower if possible and measure that power usage,  and look a longer fan run times during occupied times.

 

...

 

Like your Carrier units, Rheem also has their own line of "smart" thermostats that allow control of total control of fan speeds, burner levels, etc., but they run a proprietary network and would have been damn near impossible to automate, so I chose to go with what Rheem calls their "legacy thermostat support."  For people who run in their legacy mode there is a series of dip switches on the control board that allow for some fine tuning of the fan speeds for the various modes and stages in this setup.  If I remember correctly, the default "Fan On" speed is about half of the stage one speed, but this was adjustable +/- 300 cfm or so via dip switch settings.  In my case, all this information was listed in the Rheem homeowner's guide. Hopefully you'll find the same...

[Teken]

Who wouldn't want the maximum air from the top of a mountain though ?

 

I was trying to keep my humidity over 50% but I was going through 4-5 gallons of water from a portable humidifier per day. I carted water way too often. After a few years of I decided just under 40% was fine but slightly dry on the throat times. The water consumption to maintain that was brutal and now much more reasonable.

 

My HRV needs to be backed down somewhat in the winter as it is a big burden for the humidity changing with dry winter air.

 

This my next project to automate the air exchange on a smarter basis.

 

Oh Larry,

 

You always make me laugh and bring a smile to my face, thanks!

[paulbates]

 

At home I have a Carrier Infinity 100,000 BTU furnace with a variable speed ECM fan. The Infinity thermostat allows the fan to run continuously at low, medium or high speeds.

 

I leave it running 24x7 at low speed, which circulates at about 525 CFM (high is about 1250 CFM) and only uses about 40 watts at this speed.

 

Aside from continous filtering it also distributes our fresh air intake of about 100 CFM, and helps keep temperatures stable. The fresh air intake is a separate, not as efficient fan that uses about 33 watts and goes through a separate filter into the furnace air return.

 

The fresh air intake keeps the house slightly positively pressurized, which reduces air infiltration of dust and allergens.

 

If your furnace has an ECM fan and the thermostat can be set to continuous low fan this can help a lot with indoor air quality.

 

 

 

Like your Carrier units, Rheem also has their own line of "smart" thermostats that allow control of total control of fan speeds, burner levels, etc., but they run a proprietary network and would have been damn near impossible to automate, so I chose to go with what Rheem calls their "legacy thermostat support."  For people who run in their legacy mode there is a series of dip switches on the control board that allow for some fine tuning of the fan speeds for the various modes and stages in this setup.  If I remember correctly, the default "Fan On" speed is about half of the stage one speed, but this was adjustable +/- 300 cfm or so via dip switch settings.  In my case, all this information was listed in the Rheem homeowner's guide. Hopefully you'll find the same...

 

Thanks Scott and Bill. I went back to the furnace manual. I got Carrier Series 100s, where 100 < Infinity .  It looks like there are only 2 speeds, High and low and I am configured for low. I remember when I first got both furnaces set up, that one of them constantly blew at a very low rate when not heating. I had to use a tissue on a vent to prove it was actually going and go listen for faint motor noise. The root cause was the green fan wire was miss connected. I re-terminated it to the thermostat fan call, and it now uses the 200w "low" speed.

 

I'm going to review the manual, there are a number of dip switch settings and headers. I might call carrier as well. If that is the lowest speed, that's 400w when both are running will be impactful electric bill wise and I have to consider how much to run it.

 

Scott I would love that free cooling / exchange feature, but it would have been surgery to get it physically installed my house.

[paulbates]

Paul,

 

Not sure why my subscription didn't tell me there were replies here?!?!?

 

Anyways, the variables monitor some key attributes which in my opinion matter most to the over all (perceived) comfort of the home and to the occupants. Most people know or soon realize that it requires more energy to heat up a humid environment. The second part is determining at what level is acceptable to the end users and what goal is sought.

 

IMHO 40 - 55% relative humidity is perfect in the cold north where I live . . .

 

Once the home is at this level the next important aspect for me is what area is colder / hotter? To some their expectation is to have all (living spaces) to be the same etc. That's fine if that is your goal but for me I've found that to be a waste of resources and is really unnecessary.

 

Meaning if I see a 1 degree change in temperature from another area, floor, zone, that doesn't concern me and I certainly will not chase the rabbit in enabling my systems to compensate for. Note, I am not talking about sensor error or variance but actual temperature differences in the home.

 

All of my sensors have been tested, spec'd, and validated to have a variance of less than 0.5 degree's so in my case I am comparing a Apple to Apple and not to a Water Mellon!

 

Ha . . .

 

Next unlike many the HVAC is not my first line of defense or system to balance the homes environmental temperatures. For me the first things that get enabled and deployed are zoned ceiling fans which during summer / winter offer the bulk of circulation in the home. Obviously the rotation of the fan is adjusted to season its going to operate in so this is my first line of defense.

 

Next are two variable fans which are located high up ( 12 feet on ledge ) which push or suck all the hot air from the vaulted ceiling. Depending upon what is required the fans are either configured to push air or to suck air. This is where the massive 1 wire system grid comes into play because the system is programmed to compare anywhere from 2 to 32 sensors and five humidity sensors.

 

Based on thresholds met / not met the system will continue to (stage) and add more time or bring in other sub systems to meet the final goal. Next, the system will bring on line the over head range and its only goal is to evacuate the home and suck down the hot air being pushed by the two ledge fans. This causes massive movement of air in my home and normally with in 15 minutes all of that wasted and trapped hot air is forced down to the living space where it should be used and enjoyed.

 

At that point if the system has determined the home has met its target the system will shut down all systems until called upon again. If at this point the home still has not met the target the central exhaust is brought on line suck out more air but the key thing at this juncture is that the intake air is not brought on line.

 

The house for all intense of purpose is operating in a negative pressure environment . . .

 

I've found in my home because its so freaking tight that this method allows me to suck out lots of heat during the summer with out the negative impact of in taking hot / humid air. During the winter the furnace is allowed to operate and when the central exhaust is activated fresh cool air is brought in. Same as Scott847 this causes a positive pressure envelope in the home.

 

My red neck method to see air movement and to validate my ideas have all come from using incense sticks. The fragile smoke it billows out allows absolute visuals as to air movement and the impact it has on different circulation methods.

 

With the Autelis Bridge, Dash Box, and Green Eye Monitor, SEG, I can see live all areas, floors, zones, for immediate temperature / humidity and whether or not my systems are working or not. As stated above this empirical data has been outstanding to confirm ideas, systems, and goals.

 

The main reason I pushed to go this route is because it doesn't take much for a person to *feel* like things are fine / not fine. Feeling something is often not very accurate especially as people get older etc. This is why I stressed at the very top control and management of humidity in the home plays more on (Human) then actual temperature.

 

Essentially, I am cheating using humidity to give a perceived warmth, when in fact its actually colder than the family thinks it is. In the summer its the same I let the humidity go straight down in the 30's and this allows the house to be physically hotter and the (perceived) heat is manageable and bearable for all.

 

Hope the above proves helpful to some of you . . .

 

As my main driver has been energy consumption while balancing a healthy home for all.

 

 

Who wouldn't want the maximum air from thr top of a mountain though ?

 

I was trying to keep my humidity over 50% but I was going through 4-5 gallons of water from a portable humidifier per day. I carted water way too often. After a few years of I decided just under 40% was fine but slightly dry on the throat times. The water consumption to maintain that was brutal and now much more reasonable.

 

My HRV needs to be backed down somewhat in the winter as it is a big burden for the humidity changing with dry winter air.

 

This my next project to automate the air exchange on a smarter basis.

 

Thanks Tekan and Larry. I agree that lots of sensed datapoints would allow the most opportunity for control. I would love to put dampers in ducts in the newer part of my house, but they are all routed and split in a tiny crawlspace. I have thoughts about the controllable floor vents. I can detect when the familyroom/kitchen is likely warmer and could restrict venting to the family room. I have an additional T5900 thermostat that I can install upstairs and want to wire it in parallel to the current one... but again getting the wire there for it (or remote sensor) would be extremely difficult... I'm not a fan of controller setpoint manipulations, I want the HVAC layer to fully manage that.

 

I use the venstar's humidification cycle keep the humidity at 34%... I burn through the pads above that. I've also empirically played with it. 30% is where people start complaining. There is also a range on what is the acceptable low. Also, given our cold snaps, I have io_guy's programs to step humidity down with temperature so the windows don't frost up. 34% allows that to step down.

 

Paul

[larryllix]

....

 

I'm going to review the manual, there are a number of dip switch settings and headers. I might call carrier as well. If that is the lowest speed, that's 400w when both are running will be impactful electric bill wise and I have to consider how much to run it.

 

....

Ouch. 400 Watts. Yeah you don't want to be running those babies continuously. I was involved in electrical utility high bill complaints and 15-20 years back running a furnace fan continuously added about 40-50 dollars to your monthly bill. I would hate to think what is would cost these days with the energy ransom going on.

 

Simple calcs would show.

400 Watts  x 24 x 30 x $0.25/kWh (guess) = $72 per month. YMMV. We found the old fan motors didn't really cut back much energy consumption on lower speeds either.

 

One of the problems I have suspected with low speeds also is, in some systems a few registers will not even get any air to come out. The piping system is a very tricky thing. Once air gets moving through one vent it can hog  most all the air because the others have turbulence etc. Worse, once some get warmed up the chimney effect can draw most of the air hogging the major share of it again, even after the furnace fan shuts down. The old gravity fed furnace effect and problem.

 

In short I believe you want at least a medium to high speed on a cyclic basis. Continuous low speeds on an AC induction fan motor are probably not the best solution. The occasional 'shots" of higher speeds are probably best.

 

Your insulation project will help all this big time with less draughts and less energy consumption. Fan circulation will be needed less and easy to adjust with ISY. Nice week coming for last minute outside work!

[MWareman]

 

 

Ever since we had our new furnace / heat pump system installed last summer, I run the blower fan FULL-TIME during waking hours when the house is occupied. I was first presented with this suggestion by the system installer, and have done significant research through the manufacturer and other sources to validate the idea. I was skeptical at first with concerns of noise, drafts / constant air movement, and power consumption, but none of those turned out to be an issue. At the low speed that the new ECM motors offer in Fan On mode, the noise and air movement are barely perceptible, and power consumption is rated at a very reasonable 75W continuous. I'm assuming your modern equipment has the same variable-speed capabilities.

 

We have a Honeywell ventilation controller hooked to our system able to override the fan to distribute air separately from the heat or cool cycles, and it self adjusts to the cadence of the heating or cooling needs. Seems to have about a 1 on 2 off cadence to it, unless the stat is calling for heat (or cool).

 

Problem I have is that while only the fan is running, the furnace circuit draws over 600 watts! (According to my Brultech meter).

 

It's a new house (just passed 1 year), and a very modern high efficiency furnace.

[larryllix]

We have a Honeywell ventilation controller hooked to our system able to override the fan to distribute air separately from the heat or cool cycles, and it self adjusts to the cadence of the heating or cooling needs. Seems to have about a 1 on 2 off cadence to it, unless the stat is calling for heat (or cool).

 

Problem I have is that while only the fan is running, the furnace circuit draws over 600 watts! (According to my Brultech meter).

 

It's a new house (just passed 1 year), and a very modern high efficiency furnace.

Yeah. I thought I was smart and went after an ECM motor for just that reason but I got screwed on some of the less obvious features, like an odd filter that costs a fortune and only from the furnace company or custom made. I found  more common size that fits with an inch hanging out and ignore the leakage. The other item is howl at high speed but that was an installation flaw from the local "professionals" in a small town. The A/C suffers with the lower fan speeds.

[MWareman]

I will say, the HVAC system is very tight. Extremely low leakage - all joints taped, all returns ducted. I personally checked every joint before the drywall went up! The builder installed the ventilation controller and there is a solenoid damper that opens to allow ventilation. As far as I can tell, the main fan is a single speed only, but I am *very* surprised it draws so much power. My moving average is about 350 watts, and it consumes more power than my pretty extensive MythTV system when it's recording on 4 tuners, transcoding and playing back all at the same time.

 

Honestly, at this point I'm not sure if this is 'normal' or not. It's a carrier, and supposed to be pretty efficient....

[larryllix]

I wonder if some of that is from the burner electronics or mostly all fan motor? Trouble is furnaces don't usually plug in and a clampon wattmeter is required to measure properly. Fan motors vary their power factor a lot depending on air movement.

 

When lots of air is being moved the power consumption (Watts) is high, and when the filter is clogged or vents are closed the power consumption (Watts) is low but the current (amperes) do not change much. The power factor just drops as the motor is mostly an inductive load not doing much work. ECM motors are a whole different beast though.

 

I would be surprised that any furnace would only offer 1 speed on the motor. If nothing else, usually the second speed offers isolation for the A/C fan control so  an extra isolation relay isn't needed.

Edited November 3, 2015 by larryllix

[MWareman]

Sounds like its time to put a clamp meter directly onto the fan - to see if it's that or something else.

[jerlands]

I will say, the HVAC system is very tight. Extremely low leakage - all joints taped, all returns ducted. I personally checked every joint before the drywall went up! The builder installed the ventilation controller and there is a solenoid damper that opens to allow ventilation. As far as I can tell, the main fan is a single speed only, but I am *very* surprised it draws so much power. My moving average is about 350 watts, and it consumes more power than my pretty extensive MythTV system when it's recording on 4 tuners, transcoding and playing back all at the same time.

 

Honestly, at this point I'm not sure if this is 'normal' or not. It's a carrier, and supposed to be pretty efficient.... 

 

I've heard of air handlers that offer different speeds for "single speed" operation; being designed for use in a range of tonnage size.  If your registers seem to blow a lot of air you might look at the prints to see if it's possible and also what speed the installer set it up in.  Before changing anything you'd want to calculate needed CFM though (350 to 400 CFM per ton.)

 

 

Jon...

[stusviews]

Virtually all consumer motors have been brushless (ECM) for decades. Clogged filters combined with closed vents can overheat both the motor and control board due to higher power consumption and lead to premature failure. Newer electronics can sometimes circumvent failure by decreasing the fan motor's effort.

[Scott847]

Virtually all consumer motors have been brushless (ECM) for decades. Clogged filters combined with closed vents can overheat both the motor and control board due to higher power consumption and lead to premature failure. Newer electronics can sometimes circumvent failure by decreasing the fan motor's effort.

 

Unfortunately a number of furnaces are still PSC motors. I looked up the specs for the furnace Michael had shown in his energy efficiency label and it's a PSC motor (if I read the model number correctly).

 

Carrier 59SC2A Series 100 Furnace: http://dms.hvacpartners.com/docs/1009/public/02/59sc2a-02pd.pdf

[larryllix]

Here is a description of the three types used and some history.

 

http://www.achrnews.com/articles/112674-comparing-motor-technologies