5774500 Active Systems PLATINUM XM AMERICAN STANDARD, INC. 4A6H7036A1 4TXCB004CC3 910 750 *UH2B060A9V3 34600 12.50 16.00 32800 9.00 21600 1 HRCU-A-CB 268 772 Yes

What size home?

Very nice system.

Who is your electric provider? Your nat gas provider?

All rates should be all inclusive of charges if you expect to know the leverage between the fuels.

Here are the results, about a 30% differential between the fuels for heating.
I personally think you have been oversold based on your location.

Cost per 100,000 btu of useable heat
Electric baseboard: $1.99
Heat pump: $0.81
Natural gas: $1.10

I would set the changeover from electric to gas around 30-32 degrees. Then make adjustments up or down based on system's operation and your indoor comfort. I live just down 85 from you. I have an older Trane DF system and have my changeover at 30 degrees. I do not like large setbacks. HPs are good for maintaining temperature, poor on recovery depending on load and condenser's capacity. If you have confidence in your dealer, he should have a software program that could calculate your temperature balance point. I won't say this calculation is worthless but it should be used as a guide only. I believe in the KISS principle. Don't over complicate a nice system.

Two added thoughts. You want to make certain furnace staging is controlled by thermostat and dealer sets up dehumidify on demand for AC cooling.

IMO

This post was edited by tigerdunes on Wed, Jun 11, 14 at 7:43

@tigerdunes YAY! I was hoping you'd respond as you were the most active in the previous dual fuel threads.

Size of home: 3,000 sq ft
Nat Gas: Piedmont Natural Gas
Electric: Energy United

Technically I'm up at the lake in Cornelius, but for the benefit of people outside of the Charlotte metro area I just say Charlotte as most people know where that is at.

All inclusive cost:
Nat Gas: $1.17/Therm - (Feb 2014 bill)
Electric: $0.11/kWhr - (Feb 2014 bill)

I would agree on the oversold part in 99% of situations but for me it was literally $200 cheaper to put in a Dual Fuel HP as opposed to traditional A/C + Furnace. I work for the mega parent company and so when you factor in that our employee discount is larger for heat pumps then tack on the $300 Energy United rebate for a high efficiency heat pumps my out-of-pocket cost was lower for the dual fuel. It would have been different if Energy United gave a similar discount for HE A/C but that is not the case.

Do you know much about the Prestige IAQ stat configurations? I think most HVAC contractors here probably do 95% traditional systems so I'm not sure how proficient they are at maximizing the stat configuration for a dual fuel system. For example: It appears they did configure it for dual fuel but it appears they left most of it at the default settings out of the box. I.e. compressor cut of at 40 degrees (I cut it back to 30), no furnace cut-off set (I set it at 40), everything set to "comfort" setting allowing the furnace to kick on at anytime to keep it within 1 degree of set temp, etc....

All that would be fine and normal for a traditional set-up, as there is only one heat fuel source, but with dual fuel it seems like it would be killing the benefits.

Also it doesn't appear that they really configured the Delta T alerts, or dry contact alerts. I know my stat came with the EIM & ODT and they did appropriately install the discharge and return sensors as I ran the Delta T program and could see the differentials. I'm not sure if they wired it for any dry contact alerts - but considering I'm using a condenser pump due to elevation of the unit in the crawl space I would LOVE to know if that pump fails and the drain pain fills up. That is what happened in my old system and the furnace was soaking wet sitting in a big pool of water.

That being said I think the company I used did a good job,they were extremely professional, and the owner personally walked me through what they would do, the finishing polish touches on the hardware install were excellent, etc - the only lacking point was explaination after they had finished installing the stat and I went back in a looked at what they had configured and I had a lot of questions.

I think a lot of that has to do with contractors in the area being proficient and knowledgeable of how to install a Dual Fuel system, but then not necessarily being aware of how to configure the stat to take maximum advantage of it, and from my understanding if you get that last part wrong you can defeat the whole benefit.

I understand how that happens because I would be in the same boat if I did 100 installs and only 5 were dual fuel I would have a hard time remembering specialty configurations, but when you are forking out this much $$ you expect it to be right out of the gate.

Anyway that was a little long winded but I look forward to your reply.

To be clear, you have one system or two?

If one system, I would say you are undersized but I assume you have done your homework. Your home may be very tight.

I am not an expert on the 9421 but I do know it's major capabilities/features. I think you are over thinking the stat settings. Do you know if dehumidify on demand was set up? This is important feature especially for climates with high summertime humidity like yours. How about the staging of the furnace? How long since your install?

These new rates change the leverage decidedly.

Cost per 100,000 btu of useable heat
Electric baseboard: $2.90
Heat pump: $1.17
Natural gas: $1.20

I agree with your reasoning on the HP. You have a unique situation.

"but considering I'm using a condenser pump due to elevation of the unit in the crawl space I would LOVE to know if that pump fails and the drain pain fills up. That is what happened in my old system and the furnace was soaking wet sitting in a big pool of water."

Not sure I understand above statement. Furnace is elevated and sits in drain pan in crawl space? If so, there should be safety cutoff. Condensate pump line drains to outside? It should.

You are correct about the Prestige IAQ. But some reading goes a long way. Many dealers just want the fast and easy. I have thought many times about installing the IAQ with WiFi but my system works great and I thought leave well enough alone. It is nearing 10 yrs old, XV90 with XL14i HP and I just had to replace a capacitor two weeks ago. First repair. Not bad at all.

IMO

tigerdunes,

"Electric baseboard: $2.90
Heat pump: $1.17
Natural gas: $1.20"

This suggests a COP of like 2.47 for the HP Calculation, I believe.

How do we go from that calculation to determine the crossover calculation?

TIA

Thanks for the reply!

It is a two system house. I just replaced the downstairs unit - they did the install yesterday 6/10/14. The upstairs unit is an 18 year old 2.5 ton Carrier AS/Furnace. I had planned on replacing it next season.

It looks like with those rates there is not a definitive difference so if furnace heat "feels" better to the wifey there would be no downside from setting the cutoff to 35 or 40. I only use 2 degree setbacks at night. Wifey is a stay at home mom we keep the temp pretty constant throughout the day downstairs.

On the condensate pump - the old unit sat in a pan but was not elevated...additionally the condensate pipe that ran outside was level to slightly inclined, additionally it appears the builders never actually tied the drain pipe into the french drain and it clogged regularly as well. Long story short the unit didn't drain.

The new unit has a pump to push the water out the pipe away from the house. All I'm saying is I would like the alerts configured to notify me if things start to act up.

Thanks for all your help.

So again, furnace is elevated off ground in crawl space and sits in old pan? There should be a cut off switch for drain pan. If you don't see one, ask installer.

Condensate line drains to outside through an external wall? This is generally the correct method for crawl spaces. I have a little through the brick wall plug with condensate line connected that has never stopped up. Pumps to outside. Condensate spills over into old gutter concrete splash that slopes away from foundation.

It seems to me that you should list all lingering questions on stat in writing and ask installer from dealer to come back out and review.

IMO

For Salti,

There is a down and dirty calculation that I always use when HSPF is known but COP is not. In this particular case, I used 2.75. If you want to quibble over that figure, that's fine. Use what you want.

TD

TD,

I wasn't quibbling nor seeking to use something different. Simple question asking for some help, or so I thought.

I would assume that the crossover point for HP vs NG is where the COST of heating with HP equals COST of heating with gas.

This equality yields a COST of electricity that dictates a specific COP. In an ideal world, I'd go into a performance curve for my HP and find THE COP for my utility rate that creates that equality in NG and electric costs.

The crossover temp would be that temp that yields the COP found above.

At least, that is what I thought you had taught me.

The COP that you used in your fuel cost comparison - 2.47 - would suggest an outside temp in the 40s or 50s I would have thought. A COP around 30 degrees anbient temp would seemingly be down in the 1-1.25 range for many regular HPs.

This is not a loaded question nor any attempt to be disrespectful

I'm simply asking how to reach the answer of about 30 degrees as the crossover.

@TigerDunes

1st Thanks so much for all the valuable info - I'm greatly appreciative!

Yes the new installation I think includes a new pan. Not sure if elevated or on bare earth which. All I know is they added a condensate pump.

Regardless I'm not so much concerned with that as configuring the dry sensors to throw the "Full Drain Pan Alert" - I trust their installation, but would still want to be alerted if something breaks or isn't functioning correctly prior to it creating a larger problem.

Yep Dealer called me and is coming end of this week to hold my hand and walk me through some of the configurations. I told him I know I'm annoying but I work in IT so I naturally dig into IT details....he shouldn't have given me the Prestige IAQ it's like crack to an IT guy.

For my own knowledge where can I get COP info or calculate it on my own?

I have the AHRI certificate of product ratings which gives the following:

Cooling Capacity (Btuh): 33800
EER Rating (Cooling): 12.00
SEER Rating (Cooling): 16.00
Heating Capacity (Btuh) @ 47F: 31600
Region IV HSPF Rating (Heating): 9.00
Heating Capacity (Btuh) @17 F: 21000

Thanks again!

When doing the doing the calculation of using gas vs. electricity, you should subtract out the upfront utility charges. The idea is you are going to pay that charge regardless whether you use the gas furnace or heat pump. Therefore you don't want to add it to the cost of operating either equipment. This is the fairest way to calculate the cost of supplying the BTUs.

You have a low electric rate which makes the operating costs close to equal for both system. I would think you are going to set your balance point based on comfort and not economics.

There are two balance points, temperature and economic.

A lot of these calculations depend first on an accurate Man J calculation which is rare and the software necessary to produce each of these reports. Of course you must have accurate rates and efficiency. Most dealers don't know how to do this or have the software and time to produce these calculations. But it is available. Frankly I think good dealers should be able to provide this at a reasonable cost with the amount deducted from the cost of an installed system. All these manufacterer residential experts on staff at the respective distributors can do these reports. This is both a knowledge and time issue.

Of course you and I know that the COP is reduced as the temp drops and these intersecting lines will vary from home to home.

But you have to go on what you do know. I would never be concerned about the economic balance point when oil and propane are the backups. You just run the heat pump as low as it can go and/or comfort issues come into play.

Nat gas though is where knowing the economic balance point could prove to be handy if you want to be operationally efficient as possible with fuel choice. Not my strong suit and I don't have the time to waste on this without being reimbursed. And that's always an issue in the HVAC business.

Keep in mind most of the people who contribute to this forum do have an outside life. Sometimes these posters forget that. Everyone wanting your knowledge for nothing.

It is generally accepted that COP begins to really take a hit around freezing. Of course lower for the GreenSpeeds and higher for low end junk that unfortunately there is plenty of supply.

"The COP that you used in your fuel cost comparison - 2.47 - would suggest an outside temp in the 40s or 50s I would have thought. A COP around 30 degrees anbient temp would seemingly be down in the 1-1.25 range for many regular HPs."

As I said I used 2.75 COP in this thread which may be conservative but I believe is fair. And you are correct that this COP is based on mid 40s outside temp. But as I have said previously, you must go on what you know. And I always preface these results to be used as a guide only. I would not agree with you that at freezing COP would be in the range of 1-1.25 for a high quality HP system.

TD

@Mike

Yep I did that initially the straight rate without fixed costs are below.

Utility Rates:
Electric (May-Oct): $0.0909
Electric (Nov-Apr): $0.0756 *Applicable rate in Winter when dual fuel is used.
Nat Gas: $1.08/Therm

I appreciate all the input I can get!

@TigerDunes

Totally understand you have an outside life. Didn't mean to offend you nor abuse your time. I'm an IT auditor by trade so I tend to be overly fascinated with details and extremely thorough. I like to fully understand things. If I have put you out with my questions I apologize. I was after exactly the information you provided which was general settings to configure the system to maximize efficiency 80% of the time. I don't want to go rejigging the settings every time my gas/electric rates change, while I am thorough I'm not that anal :)

You gave me what I was after which was to set the compressor lockout between 30-35. For that I'm very appreciative, so thank you!

I saw the Manual J calculation, my dealer does have the software. I validated the size of the units were appropriate per the Manual J calculation, but at the time I didn't think to look at anything else.

The other questions on calculating COP, stat set-up and options, etc...just for my general curiousity - I just like to know how to do things myself if I can.....you know the whole teach a man to fish thing.

Anyway again thank you for giving some of your time to explain things to a tech dork!

No offense taken at all...maybe a little cranky this morning....my bad...

Always glad to help a homeowner when possible...and I think I understand DF as well as possible plus knowledge of area climate helps...

You have a great system. I do want you to follow up with installer about the dehumidify on demand feature. A wonderful option available to you.

TD

That furnace should be elevated whether in a pan or not. Please check this ASAP. You do not place a furnace on the ground or flat in a drain pan. It should be elevated and level on usually cinder blocks. Post back. I find it troubling that any reputable dealer would do this.

Dealer should be able to give you a rated COP. Don't take a verbal number. Tell him you want to see it in writing. AHRI #5774500.

IMO

It does appear that is on horizontal cinder blocks. I didn't realize how big that thing is...wow!

I'll follow-up with dealer on the dehumidify on demand! Thanks again for all your help.

I registered for this forum just to say "Thank You!" to all for these informative posts.

I recently purchased a 30-yr-old 2250 sq ft home in Richmond, VA which came equipped with a natural gas furnace for heat and a Carrier/AS 4A6H3 (14.5 SEER/9.0 HSPF) heat pump for cooling.

Since I needed to update the old mechanical t-stat anyway, I thought: Wouldn't it be awesome to have a dual-fuel system, and purchased a new Honeywell VisionPRO stat complete with wireless remote outside temp/humidity sensor.

Now that it's all wired up and working, I'm not so sure it was worth the trouble or the expense. Based on my latest utility bills, I end up with the following (excluding monthly fixed service charges for gas):

Dominion Power: $ 0.11 / kWh
Columbia Gas of VA: $ 1.14 / Ccf

I used the WarmAir.net calculator at:
http://www.warmair.net/html/fuel_cost_comparisons.htm

If I select COP of 2.4,for the HP that makes it almost a wash, and the advantage swings very quickly to natural gas as ambient temperature falls.

I guess that should teach me to do my due diligence first, huh?

(Nah!)

:-)

This post was edited by JayWinter on Sun, Oct 5, 14 at 12:22