Trane Variable speed mode during heating?

[lp]

I have a Trane 3 ton AHU (TWE037E13FB) & 14i condensing/heat pump unit.

The unit appears to be working properly, but I would like to tailor some items to better suit my needs.
My question is that I would like to lower the fan speed during heating & would like some opinions on the best/proper methods.

At first I tried to set the cfm/ton settings, but seems that this is for cooling only.

The unit is flowing a considerable amount of air to the point of feeling drafts & consequently more noise than I would like. My old 2 ton GE unit was having a hard time keeping up on cold days & only flowed air similar to the 50% setting I have now. I understand that the aux electric heat (BAYHTR1415BRKB needs 1300 cfm, but during heatpump only mode can this be safely reduced & how? If aux heat is needed, I can live with the increased noise, but during moderate conditions I do not feel I need the full airflow heat mode.

For instance, if it is 40deg out, then I want lower flow & longer run time to get a more stable temp rise & when it is in the 20’s with the aux reheat running, I’ll accept the increased flow to match.

I am using the Enhanced mode programmed in the AHU & wonder if I should switch to using the variable speed settings in the stat (XR402). BK mode is currently disabled. This would also allow me to adjust the minimum fan speed which I would like to be slightly less than 50% as well.

My main questions are:

Can the AHU be wired to think it is in cooling mode to allow the reduced setting of the AHU or through the stat?

How should this be done?

Will the speed still switch to high when the aux heat kicks in if I lower the heating airflow?

Any help or additional advice is greatly appreciated.

Thanks,
Lonnie

[amickracing]

As long as your running in enhanced mode you are likely getting everything out of the unit it can and will give.

Since you may have made some changes to the CFM, you need to verify that you are getting the proper CFM for the size unit you have. If you're not you can kill the efficiency or kill the unit depending.

I'm not trying to be rude but I really think you need to contact a professional to fix this matter. To put it simply there's no need to "fool" the unit into thinking it's in cooling, it's smart enough to provide the air flow needed with out you outsmarting it.

And no.... don't mess with the BK jumper either.

[lp]

I think you may be looking further into this than I had intended. My intent is not to alter anything in the system, nor do I intend to do anything that will void my 10yr warranty. The reason I ask these questions is so I do not attempt to experiment with the unit. My installer, who has to stand behind this work, will be the one doing the actual work. I was attempting to gain some knowledge on the best methods to achieve my goals without bringing my installer out 6 times to try different methods & consequentially dropping $100 bills everytime I want to "try" a different control method.

I would just like to use the system to its fullest abilities. As I stated in my first post, I do not need all unit can give, I would like slightly less output for sound & draft considerations. Essentially the enhanced mode that peaks at 80% output is what I am looking for & possibly the unit operating at 40% when in continuous run mode. Is this possible?

I have worked in building controls & the design/build HVAC industry since the early 90's so I would like to understand this for my own knowledge & to get all that I paid for out of the system. I just do not want to go to Trane school just to understand how my AHU is tuned.

[beenthere]

Did they also replace you old duct work?

[Advanced Response]

lp,

I agree with beenthere...Did they replace all the ductwork to larger size to accomodate the addition cfm needed for the larger unit??

Was a load calculation performed that indicated a need for a 3ton system? This would be a manual J, that requires measurement of all the house structure and windows and doors and insulation value..

Your old system needed nominal 800cfm(2ton) and your new unit needs nominal 1200cfm(3ton) which is 400cfm more needed to be moved thru the old ducts... Even in the minimum of 350 per ton, your new system would need 1050cfm and that is still 250 cfm more than the old system moved..

You need your contractor to do a rooom by room load calculation on your home and see if the 3ton system is the correct size and if so have them redo the ductwork to manual D for the new furnace which needs to move more airflow than the previous size unit..

My crystal ball is telling me that your unit is oversized for your ductwork or your ductwork is undersized for your furnace!! lol

You can do your own load calc, for a small fee you can get use of the homeowner version of hvac calc, just click the Red tab at the top of the page..

Good luck
J

[airworx]

1 ton oversized maybe your key. did they increase your return air. will you ducts carry 400 cfm more air flow.
also i find most heat pumps are not wired correctly, usually find all strips wired up to come on anytime theres a call for aux,heat, emer. heat are defrost which raises your electric bill and kills the benefit of having a heat pump. now you should not have any drafts and if so then i would have them come out and check it. if unit just installed then they should not charge you anything.

[Special Ed]

lp, if you know so much about A/C, why didn't you install the system yourself? Furthermore, if you wanna try to figure out why your system is doing what it's doing & why, just read the instructions that come with it. But I would rather you talk to the installing co. before you mess with those dip switches. If they don't know how to set them then they shouldn't be installing Tranes.

[lp]

To answer the duct questions, the basement was originally unfinished. This with the addition of a sunroom upstairs has increased the energy requirements over the original 2 ton unit. The calcs showed 2.8tons, which for a heat pump would generally lean toward upsizing to the 3 ton instead of dropping to a 2.5. The original 2 ton was adequate for the upstairs only which was proven during the cold months... it would drop below setpoint (2 deg)enough to use the aux heaters if I tried to condition the basement. I used it this way for a few years, knowing the 20yr old heat pump would eventually need replacement... why spend 5-6K before you have to?

Additional supply & return ductwork modification were added to the downstairs & was already considered in the design.

Airworx, I appreciate your insight on the aux heaters. The smaller 5kw portion is coming on first during defrost. The temp is supposed to be in the teens tonight, so I'll see how well the rest of it works.

Craig.... I hope I am reading too far into your first 2 sentences. You seem to be directing a lot of animosity towards me? I came to this site to learn, not to be ridiculed. I read the directions numerous times & saw limited info other than switch settings & wiring diagrams. There was not 1 sequence of operation anywhere that detailed the speed control other than a little graph of the enhanced mode. If I am overreacting, I apologize as well, but you could choose your words better. One of your future customers could be reading.

To clarify, I am not an installer or a dealer of any HVAC products, so I buy them just like everybody else. I am not a licensed installer, nor do I have a sheetmetal shop, so I paid for the install as well. There is nothing wrong with the functionality of the system I paid for, I just wondered if it could work better by using the speed control function of the stat or some other method. That is why I came here.

My installer is coming back to make some changes per my request. I just wish I was armed with a better understanding of what works best before hand.

[Advanced Response]

lp,

This is what they need to do:
1.) Make sure the low voltage wires are hooked up correctly.
2.) Make sure the variable speed selections and jumpers are correctly configued..
3.) They need to take a return static after the filter before the coil..
4.) They need to take a supply static after the airhandler in the supply plenum..
5.) They need to add the return static to the supply static ignoring the negative or positive.. Example a return static of -.3 and a supply static of +.3 would equal a TESP(total external static pressure) of .6 TESP...
6.) They need to plot the TESP on the airflow chart from the manufacturer.. If this number is over .6 it could lead to airflow noise..
7.) If it is over .6 and the noise is objectionable then the ductwork is not the correct size..They need to do the following:
7a.) Room by Room load calculation
7b.) Determine the cfm needed for each room in house.
7c.) Use a balometer to see what the current cfm per room is..
7d.) Determine if all the ductwork needs to be redone or if just some needs to be modified to work correctly..
7e.) Consult Manual D, to see what a proper duct design would intail..
7f.) Replace either all the ductwork or some of it depending on if any can be salvaged..
7g.) Then recheck and balance with a balometer each room..
7h.) Then after balancing is done,, have the TESP rechecked.. and if they did their job right it will be under .6 and noise will not be objectionable..
8.) Tell you your system is operating propely and they will see you for your anual checks and have fun with your new system..

Sorry for the long post.. but this is what needs to be done..

Good luck
J

[lp]

Thank you for the great response.

The TESP will be checked today. Heading downstairs with my manometer to verify the pressures. I'll have to get the flow curve of the unit. They do not seem to put the details in the owner manuals. I'll have to look in my Trane CD on Monday.

I also just happened to bring home a balance hood today to see how the rooms are doing.

Thanks again.

[pstu]

LP, I am a homeowner with a gas furnace from the Trane/American Standard family. My model number is AUD080R9V4K, which is 80% efficiency, 80K BTU input (therefore 64K output), and 4 ton air handler capacity. Two stage heating.

The gas furnaces are clearly documented to allow for low, medium, or high airflow. In the case of the 80K furnace (true also with a 3 ton air handler) the 2nd stage can be set to 1090, or 1240, or 1400 CFM airflow. This is no doubt a naive question, but why would the company set 3 choices for a gas furnace and not for a heat pump?

This information is from a manual called "SERVICE FACTS". There is also one called "Users Information Guide" and one called "Installers Guide". Perhaps your tech has given you the user manual but not the others.

Hope this helps -- Pstu

[mark beiser]

Originally posted by pstu
The gas furnaces are clearly documented to allow for low, medium, or high airflow. In the case of the 80K furnace (true also with a 3 ton air handler) the 2nd stage can be set to 1090, or 1240, or 1400 CFM airflow. This is no doubt a naive question, but why would the company set 3 choices for a gas furnace and not for a heat pump?

The airflow on a gas furnace is adjusted based on the temperature rise through the system after installation.

The airflow in the VS air handlers is actually much more adjustable than in the gas furnaces, but there is a minimum "required" airflow, depending on the size of the heat pump.

The problem with reducing the airflow through a heat pump is that when the weather is mild, you can have high pressure problems. Having less airflow definatly makes for more comforterable heating when it is colder out though.

With a little creativity, a heat pump system with a VS blower can be set up to run a higher blower speed when it is warmer outside, then step the blower speed down some when it is colder outside.