Trane 4TFE VS AHU "Fan On" Speed When AC Is Off


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Old 05-26-08, 08:27 PM
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Trane 4TFE VS AHU "Fan On" Speed When AC Is Off

I just got a new Trane XR13 and 4TFE compact variable speed air handler installed. The Comfort-R "Enhanced Mode" works great. I really like how the AHU fan fades in and out rather than being a step function, as was the case with the old system.

My question has to do with the fan speed when the AC and heat are off. I like to open the windows once in a while and circulate fresh air. The default "constant run" fan speed is really low (~10% of max speed?) even when the fan switch on the thremostat is set to ON (AUTO / ON) and the AC is OFF (COOL / OFF / HEAT).

Model Numbers and Settigs:

AC: 4TTR3024A1000A
AHU: 4TFE3F25B1D08A
Thermostat: Hunter 44360

AHU DIP switch settings:

1, 2: OFF, ON (2.0 TON)
3, 4: OFF, OFF (NORM-400 CFM / TON)
5, 6: ON, ON (ENHANCED MODE)
7, 8: OFF, ON (AUX HEAT AIRFLOW MEDIUM / LOW 800 CFM)

At face value it seems like the only thing I can do is to change DIP switches 3, 4 to change the nominal airflow setting to 450 CFM / TON but that will have a very minor effect at the slow "constant run" speed. The 100% air flow is already high enough for my 1000 sq. ft. apartment with the current settings. Is there anything else that can be done that cranks up the AHU fan speed when the AC is off independently of the DIP switch settings?

EDIT: Other than this issue everything works as it should, including the electric heater.

P.S. Related topic:

http://forum.doityourself.com/showthread.php?t=267340

Maybe somebody has figured this out since this topic was last discussed in the "Heat Pumps and Electric Heating" discussion.
 

Last edited by YachtClubWay; 05-26-08 at 08:29 PM. Reason: Additional Information Added
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Old 05-27-08, 05:51 AM
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Originally Posted by YachtClubWay View Post
My question has to do with the fan speed when the AC and heat are off. I like to open the windows once in a while and circulate fresh air. The default "constant run" fan speed is really low (~10% of max speed?) even when the fan switch on the thremostat is set to ON (AUTO / ON) and the AC is OFF (COOL / OFF / HEAT).
With the fan switch to ON, it will only run 50% speed, so in your case of set up, it's moving 400 CFM of air.

There is a couple of ways you can bump up the speed.

-Rewire the controls, but you'll lose the Comfort-R profile.
-Turn off the breaker for the outdoor unit, and switch stat to COOL.

I would suggest turning off the breaker. That is what I do on mine if I need more air movement in the home if the windows are closed. Otherwise, I shut the fan off when I open the windows, I see no point of loading up my media filter.

Thermostat: Hunter 44360
Is this a new stat, or already had it when system was put in? If it's an older stat, I would suggest upgrading into the Honeywell IAQ stat, and you can get the full effect of the dehumidity control on a humid days. Also, What is your heat source?
 
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Old 05-27-08, 06:58 AM
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Jay11J, thanks for your prompt reply!!!

-Turn off the breaker for the outdoor unit, and switch stat to COOL.
Simple is best - that's what I'll do. Still, I find it hard to believe that the "constant run" speed is 50% of the maximum, the reason being that 100% is really loud and "constant run" is virtually inaudible.

Is this a new stat, or already had it when system was put in?
The Hunter 44360 was the existing thermostat, it is nicer than the one the installer was going to put in.

Which Honeywell IAQ thermostat model number is appropriate for my equipment and location (South Florida, where just about every day is a hot, humid day...)?

Also, What is your heat source?
The heat source is an 8 kW electric coil in the AHU. It is totally overkill for 1 or 2 days a year. The new unit was specified to be 5 kW, the same as the old unit (4TFE3F25B1D08A vs. 4TFE3F25B1D05A), but the contractor showed up with an 8 kW unit saying that he didn't have 5 kW in stock and that swapping out the coil would be a long lead time special order... He said that my #8 wiring can handle it and changed out the breaker from 40 A to 45 A per the spec. on the AHU.
 
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Old 05-27-08, 08:46 AM
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Originally Posted by YachtClubWay View Post
Jay11J, thanks for your prompt reply!!!
Glad to help. Killing time in between laundry! :-)


Still, I find it hard to believe that the "constant run" speed is 50% of the maximum, the reason being that 100% is really loud and "constant run" is virtually inaudible.
That's the ideal behind the slower speed, quiet, and no draft feeling.
I have 2 ton A/C in my home, and I bearly hear mine when it ramps up to full speed. Sounds like you may have undersized ductwork, and/or returns.

You could try bump the CFM/Ton down to 350 since you are down in the deep tropics!


Which Honeywell IAQ thermostat model number is appropriate for my equipment and location (South Florida, where just about every day is a hot, humid day...)?
There is only one model of the IAQ, YTH9421

Also the stat is able to stage the electric heat in 3 stages, vs all 8k at once. (Hook up W1, W1, and W3 on air handler)
 
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Old 05-27-08, 10:15 AM
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Jay, thanks again for all replies!!!

Sounds like you may have undersized ductwork, and/or returns. You could try bump the CFM/Ton down to 350 since you are down in the deep tropics!
Well, it's "really loud" as in it's "as loud as the old system". My ductwork is pretty minimal, as in there should be more ducts going to more places. I don't know if they're sized right - I think it's safe to say that they were built to cost and not to size. There are no return ducts, I have the AHU in a closet configured as front return.

Why is a lower flowrate better for my tropical locale? Better de-humidification? Doesn't the Comfort-R profile take care of that?

There is only one model of the IAQ, YTH9421
Will I need to pull a new control wire with more conductors between the thermostat wall location and the AHU? I have 4 wires in my current installation.

EDIT: I just looked at the installation instructions, it looks like the thermostat itself needs only 3 wires.

Also the stat is able to stage the electric heat in 3 stages, vs all 8k at once. (Hook up W1, W1, and W3 on air handler)
Is there a way for me to configure the heater coil for lower power with my existing thermostat? I would be perfectly happy with 4 kW for the 1 or 2 days a year it gets below 50 degrees!
 
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Old 05-27-08, 11:08 AM
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Originally Posted by YachtClubWay View Post
There are no return ducts, I have the AHU in a closet configured as front return.
Is the noise coming from that location? What size is the grill opening(s) do you have there?

Why is a lower flowrate better for my tropical locale? Better de-humidification? Doesn't the Comfort-R profile take care of that?
Slower speed is able to pull out more humidity out of the air by having the air have more "contact" time with the coil, and also makes the coil colder, and colder coil will pull more humidity.

Comfort-R kinda helps with this, but only runs 50% speed for a min to get the coil cold, then ramps up 80% speed for 8 min, then up to 100%.

And, if you use the IAQ stat, with dehumidity control, the blower will stay at 80% speed untill it reaches set point.

EDIT: I just looked at the installation instructions, it looks like the thermostat itself needs only 3 wires.
That's right, and the control will be mounted near the air handler.



Is there a way for me to configure the heater coil for lower power with my existing thermostat? I would be perfectly happy with 4 kW for the 1 or 2 days a year it gets below 50 degrees!
Come up to Minnesota, you'll need more than 4kW of heat when it gets down to -25˚. :-)

Take a look at the air handler and see if there is a jumper wire between the W's.
 
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Old 05-27-08, 11:11 AM
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I also just add that since I had my variable speed Trane with the IAQ, I run my set point at 76˚ to 78˚ with humidity control set to 45%.

Where in the past, I used to run it 72˚ to get the cooler feeling, but with a better humidity control, able to bump it up, and save on energy.
 
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Old 05-27-08, 11:50 AM
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Is the noise coming from that location? What size is the grill opening(s) do you have there?
The supply registers are the kind you get at Lowes, like this one:

http://www.lowes.com/lowes/lkn?actio...126&lpage=none

I believe that the air movement noise is coming from them. The AHU is in a closet so its grille openings are a louvered bifold door. Opening and closing the bifold door has no effect on the general ambient noise level. (Other than when standing right next to it, etc.)

And, if you use the IAQ stat, with dehumidity control, the blower will stay at 80% speed untill it reaches set point.

I also just add that since I had my variable speed Trane with the IAQ, I run my set point at 76˚ to 78˚ with humidity control set to 45%.

Where in the past, I used to run it 72˚ to get the cooler feeling, but with a better humidity control, able to bump it up, and save on energy.
The Honeywell IAQ is kind of pricey, it might be worth the trouble and expense of installing it just for this reason.

Question: how does the Honeywell IAQ adjust and control fan speed on the Trane AHU? Wouldn't the Trane just crank up the speed on its own anyway according to its preset Comfort-R profile?

Right now I have the thermostat set to 76 with a "SPAN" of 1, which on this thermostat equals +/- 0.5 degree. The actual temperature in different rooms is always less than 77 degrees and it feels cool and dry to me. I don't know what the actual relative humidity is, I'm thinking of buying an inexpensive terrarium hygrometer from a pet store to measure it.

Thanks again for all replies!!!
 
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Old 05-27-08, 02:14 PM
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Originally Posted by YachtClubWay View Post
The supply registers are the kind you get at Lowes, like this one:
Do you know what size the ducts are going to these vents? And how many you have total in the whole place?

The Honeywell IAQ is kind of pricey, it might be worth the trouble and expense of installing it just for this reason.
You can find some deals on e-bay or other web sites.

Question: how does the Honeywell IAQ adjust and control fan speed on the Trane AHU? Wouldn't the Trane just crank up the speed on its own anyway according to its preset Comfort-R profile?
The IAQ is tied to the boards' BK wire, and when humidity is higher than set point, then it will keep the blower at 80% speed. The Comfort-R is still there, but just stays in 80%.
 
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Old 05-27-08, 04:53 PM
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Do you know what size the ducts are going to these vents? And how many you have total in the whole place?
I have no idea what the duct size is. The original configuration was 4 outlets, 2 in the main living area and 1 in each bedroom. Last year I added a 6" duct from the plenum to the master bathroom. (Backs up against the AHU closet - it was an easy modification.)

The IAQ is tied to the boards' BK wire, and when humidity is higher than set point, then it will keep the blower at 80% speed. The Comfort-R is still there, but just stays in 80%.
The default factory configuration has R tied to BK with a brass shorting jumper. After removing the jumper, would I use a NO or NC relay contact on the IAQ?

Thanks again for replies - you da man!!!
 
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Old 05-27-08, 07:02 PM
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Originally Posted by YachtClubWay View Post
I have no idea what the duct size is. The original configuration was 4 outlets, 2 in the main living area and 1 in each bedroom. Last year I added a 6" duct from the plenum to the master bathroom. (Backs up against the AHU closet - it was an easy modification.)
Yikes, I can see why you can hear it. You are pushing 160 some CFM per vent. I would add a vent in the kitchen, bathroom, and dinning area.

Maybe bumping down to 350 will help out some.

The default factory configuration has R tied to BK with a brass shorting jumper. After removing the jumper, would I use a NO or NC relay contact on the IAQ?
NC is used. (Advance set up #379 to 1)
 
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Old 05-28-08, 03:58 AM
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Re:

Also the stat is able to stage the electric heat in 3 stages, vs all 8k at once. (Hook up W1, W1, and W3 on air handler)
Is there a way for me to configure the heater coil for lower power with my existing thermostat? I would be perfectly happy with 4 kW for the 1 or 2 days a year it gets below 50 degrees!

Come up to Minnesota, you'll need more than 4kW of heat when it gets down to -25˚. :-)
Take a look at the air handler and see if there is a jumper wire between the W's.
Question: Getting back to the heater... Is it a standard installation procedure to section a small heating strip like the 8 kW one installed in my AHU? The Hunter thermostat is hooked up to W1, there are no connections to W2 and W3. (Not shorted to W1 or anything else.)
 
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Old 05-28-08, 06:09 AM
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Originally Posted by YachtClubWay View Post
Question: Getting back to the heater... Is it a standard installation procedure to section a small heating strip like the 8 kW one installed in my AHU? The Hunter thermostat is hooked up to W1, there are no connections to W2 and W3. (Not shorted to W1 or anything else.)
To behonest, I have not been around electric heat strip aronnd here, it's other gas or oil up here...

Follow the W's low voltage wire at the air handler and see if any of the wire going to a relay that may be tied to the electric heat strips.
 
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Old 05-28-08, 07:23 AM
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Follow the W's low voltage wire at the air handler and see if any of the wire going to a relay that may be tied to the electric heat strips.
I'll try to trace it out the next time I have a reason to open the AHU. Like I said earlier, the heater is a low priority given the amount of use it will get. It would be nice if it turns out that it is staged but I kind of doubt it...

Yet Another Question: Can I use a simple humidistat, like the Honeywell H8908B1002, to augment my existing thermostat? The Honeywell IAQ system is very nice but I figure I can mount the humidistat inside the closet next to the AHU, hook up a couple of wires (+24VAC and BK), and be done with it at much less cost and disruption.

https://customer.honeywell.com/honey...spx/H8908B1002
 
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Old 05-28-08, 09:09 AM
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Originally Posted by YachtClubWay View Post
Yet Another Question: Can I use a simple humidistat, like the Honeywell H8908B1002, to augment my existing thermostat? The Honeywell IAQ system is very nice but I figure I can mount the humidistat inside the closet next to the AHU, hook up a couple of wires (+24VAC and BK), and be done with it at much less cost and disruption.
Oh yeah, I was going to suggest that if it turns out your 8K is only single stage, and no point of spending lot of money on the IAQ.

And also i was going to suggest if it turns out your 8k is single stage, and yet you want a new stat, look into the VisionPro TH8110.
 
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Old 05-28-08, 10:47 AM
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Jay, thanks for the thermostat suggestion.

Do you think that my humidistat idea will work? It's a simple nylon strip-type that should be good enough to extend the dehumidify interval on my variable-speed AHU. See link in my previous post.

Thanks again for all replies!!!
 
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Old 05-28-08, 11:56 AM
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Yes, the basic humidistat will work out.. Only downfall on those has a large swing from set point.
 
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Old 05-28-08, 12:59 PM
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Originally Posted by Jay11J View Post
Yes, the basic humidistat will work out.. Only downfall on those has a large swing from set point.
Good point. How about a digital one like the Generalaire E2/7035? I figure it could work for me in its manual mode.
 
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Old 05-28-08, 01:05 PM
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The digital are better and has a tighter range.
 
 

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