Software
Houzz Logo Print
jocoman

Optimizing Efficiency of New System

16 years ago

Hi all. I'm an avid reader of the forums but this is my first post.

I had a 5 ton American Standard dual fuel heat pump/NG split system of the communicating variety installed a few months ago and have been pretty happy with the results from a comfort perspective thus far. I have spent a lot of time doing research on this site (and others) post install that I wish I had done pre install for ways to optimize the efficiency of my system. Unfortunately shortly after moving into this house my A/C died and I needed to get something quickly and before I had an opportunity to tackle my weatherization projects.

My house is a 2 story colonial in Overland Park, KS (built 1997) with 2500 sq. ft. of living space and another 1200 sq. ft. of unfinished basement that does get supply heat since we spend some time down there (workout equipment, etc.). I have high ceilings and many windows (32 to be exact). The house faces south and is insulated according to 1997 area standards with more attic insulation on the to do list.

The system I purchased is a Heritage 16 2-stage heat pump (Model #4A6H6060C1000AA), Freedom 95 3-stage furnace (Model #AUH3D120ACV5VAB), Coil (Model #4TXCD064BC3HCAA) and the American Standard required thermostat ((Model #ACONT900AC43UAA). All components are 5 ton capacity and communicating models. This system replaced a builder grade Lennox 5 ton furnace and A/C (no idea of the model) and was attached to existing ductwork that seems to be able to handle the load pretty well based on information gathered from this site. I probably need more return and a better filter which I'm having done hopefully this Spring.

So with all of that out of the way, my load calc done by my installer at the time came out to me needing 4.5 tons. I'm pretty sure that's based on heating needs and not cooling as our heating season is longer than the cooling season.

Is it OK to do things such as reduce the CFM settings on the air handler to more exactly match the air flow requirements and load calculations? Given my setup, are there any settings in the thermostat that I should be looking at changing to better optimize my system? I'm not looking to do this on whim as I'm not trying to destroy a very expensive system by playing around with it. I will definitely discuss these options with my contractor, and don't mind paying for such service as liability insurance so to speak. He admittedly isn't very experienced with the newer communicating equipment and pretty much let it be plug and play. So I'm reaching out to the fine folks on this forum to maybe give me some guidance. The only thing I've done myself is to lower the heat pump cut off point to 20 deg. since I'm getting a special heat pump electric rate from my utility company. My primary objective is to optimize my system for when I'm finished with my weatherization projects. I'm sure I'll be over sized when all said and done, but what's done is done and I'm just looking to make the best of it.

Comments (20)

  • 16 years ago

    a couple of suggestions.

    dip switch settings should be dbl checked. setting guide should be on inside furnace cabinet door.

    I will assume you did not install zoning controls-that would have been better. you have manual dampers on ductwork system? if so, check to see how they are set and particularly the supply airflow for upstairs.

    what is your average winter temp? I personally think 20 deg switchover for HP is ridiculous. Why even bother with a nice furnace for backup? I would move the switchover to 28 degrees and adjust from that point as necessary. On dual fuel, you need to balance comfort and operating cost.

    IMO

  • 16 years ago

    Thanks for the response. I'm not aware of any dip switches in the furnace. There are dip switches at the heat pump to set line set length. Are you referring to those dip switches? This is a communicating system with very minimal mechanical controls or wiring. The CFM settings for both heating and cooling are just set at a small LCD terminal inside the air handler with the touch of a button. I can choose CFM/ton settings of 450, 430, 400, 370, 350, 310 or 290. The heating settings are 2340, 2040, 1850, and 1660. So the system is very flexible and easy to adjust to airflow requirements but I'm not wanting adjust any of these if it can potentially cause damage. Lower settings would be better for my duct work especially return but I don't want to damage any heat exchangers or compressors in the process. I know I'm over sized and will be even more so as I add insulation etc. so essentially I'm wondering if it's permissible to lower these settings to more closely match what my actual load is or will be.

    I do have manual dampers at the major trunks. My system sits almost directly center of my basement with two main trunks feeding each side of the lower level. There is a third larger trunk that goes up to a plenum in the attic that feeds the branch runs. There are manual dampers on each of the three trunks and on the attic plenum. I have adjusted all of these several times trying to achieve balance, which I think is much better now.

    I agree that's it's disheartening to have such a nice furnace and barely use it, but after doing all the calculations my heat pump is actually cheaper to run down to 15 deg. The heat pump seems to do quite well in the lower temps (probably because it's oversized) and I have the thermostat set to upstage to the furnace quickly if the HP can't keep up. I've tested the capabilities and it seems to want to upstage below 20 but not at or above. So since I'm comfortable (I keep my temp at 69) I chose to save money. My electric rate during the heating months is only .06 including surcharges, etc. while my NG rate is .92 per therm including the business charges. I did not include that actually customer charges in either calculation as they are static charges and apply no matter how much I use.

    Sorry for the long response but I felt I needed to give you more information about my system.

    Thanks again.

  • 16 years ago

    jocoman

    what are your current dip switch settings? I would think 400/2000 would be a good choice.

    I do believe you are oversized both HP and furnace by one size.

    Of course that's a good electric rate especially for HP heating. You have a very expensive air handler though that will rarely be used as a furnace. Of course that's your decision.

    I take from your last post that you have good temperature constantcy between main and second floors. If true, that indicates a very good and correctly sized/designed ductwork system, a rare occurrence without zoning controls.

    your performance/efficiency numbers for that HP selection are mediocre to poor. Sorry, but you should know.

    IMO

  • 16 years ago

    tigerdunes,

    I currently have the CFM/ton setting at 370 and the heating setting at 1850. This seems to work a little better with my ductwork from a noise and static pressure perspective. I need to upgrade my return and get a better filter which will also help. I have them set this way to better match my initial 4.5 ton load calc. My research has pretty much indicated exactly what you say that I'm about 1 size too big. I wish I had been able to all of this research and learning pre sale instead of post sale but it is what it is. Since it's a 2-stage heat pump it does spend a good deal of time at the lower stage and runs quieter. My only concern is that lowering the setting even further to get closer to that 4 ton load may cause damage. I would be looking at keeping the furnace at 1850 since it never went to high fire even at single digit temps. I would however consider moving the CFM setting down to 350 especially for better cooling. That would put the 1st stage CFM at 280. Do you see issues with that? Should I even be concerned with this stuff since it's all multi-stage equipment?

    The only room in the house that is noticeably colder is our master bedroom, which sits over an insulated yet unheated garage. I'm pretty certain that the garage along with it being the longest runs from the heat source are the primary reasons. I figure I can maybe fix that by installing branch dampers off of the attic plenum to lock down airflow where it isn't needed and supply more flow to my bedroom. I spent a good two weeks making adjustments before I finally got it about as good as I can.

    I read some not so nice things about the heating efficiency of the heritage line of HP. Again, if only I had been able to research before making a decision. I would have also been more educated to know what to look for in a contractor that may have discussed more of these options with me. This is why I've chosen to reach out to people in the know. Do you care to share the numbers that you have on my unit? I haven't been able to find much info regarding COP values and such.

    Thanks for your help

  • 16 years ago

    jocoman

    If that setting is working well for you, then I would leave it there. No lower though. was that what your dealer recommended?

    Finished rooms over garage commonly called FROGs are notorius for cooling and heating. You need to get more CFMs into that room. You do have one or two returns upstairs?

    Am Standard Heritage Line of heat pumps are excellent equipment. However, I have never cared for the two stg Heritage 16 and am surprised that AS and Trane have not given that unit a complete makeover or dropped it altogether from the line. AS and Trane HPs above 3 1/2 ton models drop off in performance/efficiency. Of course Trane and AS furnaces are excellent and it appears you have a three stg top of line communicating mdl that has firing rates of 40,65,100% output. That's why it is a shame it will rarely be used.

    This appears to be your AHRI matching number.

    3187783 Discontinued Systems HERITAGE 16 AMERICAN STANDARD, INC. 4A6H6060C1 4TXCD064BC3 *UH3D120ACV5 55500 10.70 14.00 50500 8.80 31000

    Not certain why it lists your system as discontinued. You can see that it is short on cooling and heating BTUs for a five ton mdl. Poor EER, mediocre SEER. HSPF pretty good. You can get a close COP number by dividing HSPF by 3.3 which yields about 2.66-not bad.

    IMO

  • 16 years ago

    tigerdunes,

    Thanks for the info. You can imagine how disappointed I am at those efficiency numbers. Maybe I should use my furnace more just out of spite...LOL. I guess it's a good thing I got the $1500 tax credit on the furnace. The reality though is that it seems to do just great at keeping the house warm even in cold temperatures and my overall utility bills are very reasonable given how much it runs. At what temp does the 2.66 COP value come from? How would I calculate COP given a range of temps?

    I have at least one return in almost every room in the house. My bedroom and family room have a 32x8 return grill and all other returns (5 of them) are 16x8. 4 returns are downstairs and 3 are upstairs. They are all just wall cavities that run down to a 24x8 return plenum that feeds a 25x12 main trunk into the air handler. One difference in my master bed return is that it actually goes up to the attic where it's attached to a flex duct that feeds to a cavity down to the return plenum. I believe this is called a jumper duct. There doesn't seem to be much airflow into return so this is on the list of things to improve. Do you have any other advice for resolving the known issues with FROG rooms?

    Thanks for your help once again.

  • 16 years ago

    "At what temp does the 2.66 COP value come from?"

    Jocoman

    That value is at 47 deg and obviously slides as outside temp decreases. Keep in mind there are two balance points to be taken into consideration-thermal and economic.

    I will assume that your home and FROG has excellent insulation properties. So by process of deduction the FROG's problem lies with insufficient airflow/CFMs. My best advice is to get your installing dealer involved to make recommendations for improvement.Obviosly ductwork to upstairs living area should be thoroughly inspected.

    IMO
    Good Luck!

  • 16 years ago

    Thanks. I would say that my house is "adequately" tight and insulated due to an observed (at my thermostat) heat loss rate of about 2-3 deg/hour at 20 deg outdoor temp. I'm sure it could be better and will be. I've sealed all my duct work (that I could get to), attic, basement and other problem areas myself to which very noticeable differences have been achieved. I plan on adding additional attic insulation to bring it up to modern standards.

    I plan on having my contractor come out soon to give me quotes on increasing my return and adding a nice 4-5" media filter or air cleaner so I'll ask him what can be done about my bedroom air flow. In the meantime would you advise closing down registers in unused spaces (closets, small bathrooms, little used guest bedroom) in order divert air to my master bed? I've heard and read that doing so on variable speed blowers could hurt more than help due to increase static pressures and such. I also run my blower constantly to try help even out the temperatures, which is also debatable. What is your opinion on those two tactics?

    Thanks so much for answering my questions.

  • 16 years ago

    jocoman

    at the moment,how are you protecting your blower motor and evap coil as well as filtering return air for good IAQ? Dealer should have given you a nice 4-5" pleated filter media cabinet like AprilAire or Honeywell 200 when he installed your nice system.

    I am not a proponent of closing supply registers. and I do believe in running fan on VS blower 24/7 except in summer cooling season.

    There are ductwork booster fans that some people use to increase airflow to problem areas. Ask dealer about these.

    IMO
    Good Luck!

  • 16 years ago

    tigerdunes,

    I guess the only accurate answer to you question is...not very well. I only have a standard 1" 25x25 Merv 6 filter. I'm making sure to change them every month but I know that I need a major upgrade in that department. This is why I'm having a contractor come out soon to look at increasing my return capacity and adding the correct filtering system.

    Before I started researching all of this HVAC stuff post install I simply did not have the necessary knowledge to require such work to be done or to even know to hire a better contractor that would simply do the right thing as part of the job. Now that I am better armed with knowledge thanks to people like yourself and the information contained in this and other message boards, I will be hiring a better contractor to do this round of work.

    It sounds like I'm doing the right things all in all to make what I have as good as it can be. At least the things under my control and within the realm of my capabilities. I just need some duct work upgrades here and there.

    I hope that I can become more of a contributor rather than a leach on this board. I've learned a lot in a short amount of time and maybe I can give back a bit.

    Thanks for all of your time and information.

  • 16 years ago

    where is this filter located? in a furnace filter rack? it should at least be of the pleated variety. you could move up to a MERV 8-10 for better protection.

    IMO

  • 16 years ago

    The filter is located between the main return trunk and the air handler about 3" away from the chassis. I'm not sure you can call it a filter rack in that it's pretty much just a cutout in the return with internal rails to form a filter slot. The filter itself is pleated. I bought the Flanders EngergyAire brand. I've stayed away from 3M after reading about how restrictive they can be.

    Hopefully I won't have to deal with it much longer. I'm waiting for the temps to raise enough to where I don't need to heat my house while the upgrade work is being done.

    Thanks

  • 16 years ago

    jocoman

    to me this sounds like a jury rigged system that should be replaced ASAP.

    please tell me that your dealer proposed a true filter cabinet and you turned him down.

    installing a filter cabinet will not take long.

    IMO

  • 16 years ago

    Yes. I agree and it will be. The subject never came up at all in our discussions. All he said was that my existing ductwork was fine for the new system and I didn't know enough at the time to question him. I guess the sad part is that of the three contractors that came to my house for evaluation and estimates he seemed to be the most thorough one while in the middle price wise.

    I started doing my own research after the install because I started to suspect some things weren't right. I'm glad I did because now I know enough to make sure the right job is being done.

    Thanks

  • 16 years ago

    jocoman

    if this was my system, I would not run continuous fan "on" until a correct whole house filter cabinet was installed.

    my first choice would be AS Perfect Fit because it fits the furnace like a hand should fit a glove. after that, look at Honeywell 200 and Aprilaire 2210 media cabinets. I would not have an "EAC" cleaner.

    IMO

  • 16 years ago

    Thanks for the advise. I will set my fan to auto and start making some calls. I've heard and read about both the Honeywell and Aprilaire models, but not the AS. I'll be sure and check it out and ask contractors if they install these models.

    Thank you for your time. You've been more than helpful.

  • 16 years ago

    jocoman

    I have the Trane Perfect Fit Media Cabinet. Same as AS. Like I said, it looks and fits the return end of the furnace like it should. I change my filter once a year. Takes about a minute. Replacement OEM filters are not cheap because Trane/AS filters are not a standard size. Cheaper generics though are readily available from online stores on the Internet and they work just fine.

    IMO

    Here is a link that might be useful: American Standard(AS) Filter Cabinets

  • 16 years ago

    Ah...you meant American Standard. Not enough coffee yet I guess...LOL. Yes, I've already checked those out and it's good to know that the one made for the system is also good quality. There are plenty of Trane/AS dealers in my area so I'll get some quotes for installing it.

    Thanks!

  • 16 years ago

    jocoman

    yep. you got it. and yes you better get another cup of joe.

    IMO

  • 16 years ago

    5 ton sounds kinda big for that house. Well, atleast you have more than one stage for everthing so you can run in low stage most of the time.