Upgrade Path Advice Needed

[cherokee180c]

I currently have a N.G./A/C setup for a 2200ft2 house in MD. 80K BTU Trane 90% single stage furnace that is 12 years old using combustion air from the basement, not outside. The A/C is an XE 1200 12 SEER unit that is starting to have failures. Blower motor last year and Starting capacitor this year. The house is 12 years old as the system is original.

My goal is to eventually replace everything with a dual fuel HP/N.G. setup, but I can not afford to do it all at once. My A/C bills are high at almost $0.16 / kWh. I estimate 600-700 kWh for A/C peak during the hottest months in the summer. FLA on my A/C is 17 amps, which I verified during normal running. I just installed the Honeywell IAQ stat to solve some of the humidity and airflow issues in the house and it has worked fantastic so far so I have decided to go full out with 2 stage heating and 2 stage heat pump with variable speed.

I am thinking that since I want to end up with a 16-18 SEER HP using a dual stage copland compressor that I need to install a variable speed ECM furnace first. I have read that the amp draw on these high efficiency HP's can be as low as 6-7amps on the first stage only, which should be a big improvement over 17 amps. I have looked into retrofitting the current Trane furnace with ECM, but it makes no sense financially or practically. My main goals here are to make a serious dent in the kWh spent on A/C and also lower my heating costs. N.G was $1.67/ therm last month and other than a short break for a month or two I think it is headed even higher in the next few years. I am 99% sure my furnace was oversized at 80K because the stupid installer ran 3/8" warflex to it and I didn't catch the problem until 10 years later when I finished the basement and changed it to 1/2" warflex to supply the full BTU's. Manuals show that the 3/8" line should have only been providing 40K BTU's. I am right to think about changing out the furnace with a VS unit first and then go for the high efficiency HP next year if I need to break up the expenditures over 2 years? I will look at Trane again, but the Goodman GMV95 series 70K unit seems like a very good unit at a great price. Please comment on my plan or any other advice.

My assumptions are that I will get some savings this winter (approximately 10%) from:
1. 95% unit vs. 90%.
2. 2 stage burner running at lower stage vs. single stage burner.
3. Properly sizing unit to 70K from 80K.
4. ECM blower running at more efficient speed vs. PSC motor.

In summer I should get better humidity control from VS blower and lower blower motor amp draw until I install 2 stage higher efficiency HP.

[beenthere]

Nothing wrong with doing furnace first, then upgrading to a heat pump next year.

If your compressor has an FLA rating of 17, and your drawing 17 amps.
It needs serviced, something is most likely wrong. That rating isn't what it should draw.

[cherokee180c]

Thanks Beenthere as you are the one who answered most of my T-stat question on the IAQ.

I will check again as I just measured the amp draw for the entire A/C system by accurately timing my electric meter when everything else was off in the house so I did a baseline and then turned on the A.C. It was pulling 16.8 amps total, so that would inclued the fan motor outside as well as the blower motor inside.

As far as the order to upgrade, I don't think I can get any of the benefits from buying a two stage HP without the VS blower inside, is that correct? Also do you think I will see a 10% savings overall from the points above before I add the 2 stage HP?

Thanks again

[beenthere]

You'll get a 10% plus reduction in gas consumption.

if you were reading the total amp draw of the A/C system, ok.
I thought you meat the compressor alone was drawing 17 amps.

[cherokee180c]

What would a typical total amp draw be for the entire system on a 3.5 Ton 16 or 18 SEER HP in cooling mode while in singe stage mode with a vs airhandler with ECM motor. I know there are a ton of other variables but I am only looking for a range to compare.

Also do you think I will get any efficiency improvement that will show up on my utility bill from reduced air infiltration in the winter by installing the new system using outside combustion air instead of inside air?

[amd]

Since you have relatively modern and efficient equipment, consider upgrading the building envelope.

Adding insulation, draft proofing, and providing summer shading will give you a much better return than getting sophisticated equipment.

My assumptions are that I will get some savings this winter (approximately 10&#37 from:
1. 95% unit vs. 90%.
2. 2 stage burner running at lower stage vs. single stage burner.
3. Properly sizing unit to 70K from 80K.
4. ECM blower running at more efficient speed vs. PSC motor.

1. Marginal and insignificant - your existing unit could already be 92%.
2. The AFUE rating is what it is - having two stages will not reduce fuel consumption. Some furnaces are actually slightly less efficient on low than high. (take a look at some spec sheets) Lower output = increased runtime. Two stage is for comfort.
3. High efficiency furnaces do not have very high startup and shutdown losses; savings will be negligible.
4. ECMs are inherently more efficient than PSC motors, especially on low speeds. However, the savings are a result of how the motors are designed, not the speed at which they run; PSCs can run at low speeds too.

16 SEER may not save you much over 12 SEER unless you run your A/C during milder weather; take a look at the performance numbers at high temperature conditions. From what I have seen on spec sheets, two-stage high efficiency HPs/ACs don't perform significantly better than their 13 and 14 SEER counterparts, especially in heating mode. The more sophisticated the equipment is, the greater your repair costs will be. I don't see the logic in spending thousands of dollars on a new furnace to get an ECM motor and two-stage outdoor unit provided that the existing furnace is in good condition. (Average lifespan is 20-25 years)

Also run time is just as important as amp draw; do not shop based on instantaneous energy usage. (Look at EER, COP, HSPF, and cold weather heating performance)

Energy = Power x Time. Reducing the power won't save anything if time goes up proportionally.

[amd]

What would a typical total amp draw be for the entire system on a 3.5 Ton 16 or 18 SEER HP in cooling mode while in singe stage mode with a vs airhandler with ECM motor. I know there are a ton of other variables but I am only looking for a range to compare.

Check out the extended data in Goodman's spec sheets.

Also do you think I will get any efficiency improvement that will show up on my utility bill from reduced air infiltration in the winter by installing the new system using outside combustion air instead of inside air?

Theoretically yes. Your existing furnace can probably use outdoor air for combustion. (If you change your mind and decide to keep it, have a contractor connect the combustion air intake)

[cherokee180c]

amd, thanks for the great response. I am actually a mechanical engineer, so I was worried about your points, but posted the question to see how much savings I could expect from the equipment alone.

I really should have posted my total plan. I plan to hire an energy auditing company primarily for the negative blower door test and to the the IR imaging results for each room. This month I have to replace my front door due to dry rotting, so I am selecting an energy star unit and having that put in first. I have already gone into my attic and found several areas where the blown insulation was totally blown away from the ceiling over my walk in closet because the cheap foam inserts at the soffit that were supposed to direct air up over the insulation broke and are no longer there. I also had two joist bays on my cathedral ceiling knee wall in the attic where the rolled insulation fell down, so these areas had an R value of 1. After the energy auditing company comes in and we go through the house, I was going to evaluate the value to paying a sealing company to come in and seal the envelop or if I should just do this work myself. I was then going to increase the blown insulation depth in the attic to get to R-49. I definitely plan to fix the envolope issues first as that is an immediate and direct pay back that will show up in my energy bill.

My desire to replace the existing equipment is more a fundemental shift to want to go to a dual fuel setup using a heat pump as the primary heating source. The only reason I was even looking at all to replace the furnace was to get the VS capability. I figure the with the current string of failures on the A/C side, I have 4 years at most for that system to last (16 years total service) and maybe less. If I can generate enough savings through higher SEER units and N.G. gas savings, I thought I might be able to offset some of the time value of money lost by replacing the units a few years before failure.

Oh yea one last thing I was trying to evaluate was if Aeroseal would be a good way to improve HVAC performance by reducing duct leakage into the floors and walls significantly. My house only has 3 main air returns on interior walls one on each floor and all the ducts are in the floors and walls between floors. Not sure if it is worth the investment though.

[aircooled53]

What would a typical total amp draw be for the entire system on a 3.5 Ton 16 or 18 SEER HP in cooling mode while in singe stage mode with a vs airhandler with ECM motor. I know there are a ton of other variables but I am only looking for a range to compare.

Also do you think I will get any efficiency improvement that will show up on my utility bill from reduced air infiltration in the winter by installing the new system using outside combustion air instead of inside air?

Low speed about @6.0amps
High speed about 12.0 amps.

But, if you get away from the CHOO-CHoo and go to an Infinity Hybrid Heat Pump system

Low speed @ 4.0 amps
High speed @ 10.1 amps

[beenthere]

As earlier envolope improvements can do more to save then just an equipment upgrade. And you seem to have a good plan for that already.

Although I haven't pulled 13 SSER and replace it with 2 stage yet. I have pulled 12 SEER and they do save a considerable amount over the 12 SEER.

A sealed combustion 90% furnace saves a lot over a non sealed 80%. You won't be pulling in cold dry outdoor air that you would have to reheat. And it may help keep your humidity up a little better in the winter.

[amd]

Sounds like a good plan; if anything on the equipment side going dual fuel should save a substantial amount of energy depending on your climate.

Seems like the fundamental question is whether a 16 or 18 SEER unit will save a substantial amount of energy over a standard 13/14 SEER unit, and if the savings justify installing a new 2-stage furnace with an ECM.

I forgot to mention that pairing a ECM with a standard outdoor unit increases the SEER rating. (16 SEER+ rating is obtained with an ECM, I would think) So if you get a 14 SEER heatpump now and replace the furnace in a few years, it could be around 15 SEER. (Check the ratings to verify this)

Good luck.

Edit:

Any ball park % savings your customers have seen pulling a 12 for a two stage 16 with vs? Are we talking as much as 20% savings? My current unit is a 12.

Though I'm knowledgable from reading service manuals, this board, other sources and a little bit of formal education, I am not a technician or installer.

[cherokee180c]

Any ball park % savings your customers have seen pulling a 12 for a two stage 16 with vs? Are we talking as much as 20% savings? My current unit is a 12.

If I install a 2 stage heat pump and new matching coil now, but uilize my current furnace with psc motor will I actually be able to gain the saving from running in stage 1 for cooling and heat with my new IAQ stat, or are the higher SEER ratings simply from the reduced amp draw of the ECM motors vs. the PSC motors? I am just struggling with which to do first if I don't really have enough money right now to do both.

[beenthere]

You should see 15 to 20% (closer to 20)going with a 2 stage with VS blower. Depend on how well the 12 SEER is removing moisture. And on your duct system.

Putting in a 16 SEER 2 stage using your current furnace. You won't get the savings.
You won't get teh same humidity removal in first stage with a standard blower motor. It won't slow enough without spending money on a speed controller.

[amd]

or are the higher SEER ratings simply from the reduced amp draw of the ECM motors vs. the PSC motors?

It's a combination of things.

It is my understanding that operating a compressor at lower capacity within a given system increases efficiency. Here's why: The compression ratio determines amp draw relative to capacity. Having oversized coils improves heat transfer, thus allowing a system to run lower head temperature and higher suction temperature; this results in a lower head pressure and higher suction pressure.

Your existing furnace control board most likely does not have separate relays and lead connections for two-speed cooling. (Blower speed must be reduced for second stage operation - if not, humidity removal will really suffer and it will be impossible to get the charge right for 1st stage operation) The installer would have to rig it with a relay to switch between 1st and 2nd stage cooling speeds. (Not recommended, blower speed still might be too high on 1st stage)