here is explanation from an HVAC pro in another forum. Pretty much what I posted in another thread here today.

"Carrier has a system where the intervals between defrosts are based on how long previous defrosts took. They assume that if defrosts took longer, the coil was frostier and it should defrosts more often. Not EDD by any means but a hair better than a fixed timer I'd think.

Then again, longer defrosts could just mean colder out. Colder out, less frost yet this system would defrost more often."

TD

Hey Tiger,

Wish I had gotten to this sooner, sorry about that. But the above description pretty much agrees with my understanding of the Carrier "AUTO" defrost setting, in which previous defrost cycle times are monitored and the subsequent defrost intervals (60, 90 min, etc.) are adjusted based on past history. Not too sure on the specifics of how this algorithm works beyond that, but it certainly isn't true "demand" defrost that you find in Trane heat pumps and a few other brands.

Take care.

Thx for reply Ryan...

TD

I spoke with a very well informed Carrier authorized dealer today who indicated that all Carrier HPs are a âÂÂcombinationâ of timed & demand defrost. That at regular âÂÂintervalsâÂÂ, coil measurements are taken to determine if a defrost cycle is necessary, if not it defaults to the next âÂÂtimed intervalâ for another âÂÂevaluationâÂÂ. The explanation of the defrost sequence itself âÂÂsoundedâ much like that of the Trane demand method.

Frankly, even though I trust this person, IâÂÂm not completely satisfied with the explanation, particularly where it comes to the lower end Carrier HPs.

IâÂÂve also read the data on the Trane Demand Defrost method and IâÂÂm likewise not convinced thereâÂÂs a substantial difference as compared to Carrier.

My background before coming to geothermal & HVAC was in electronics, so I do get it, not just block or wiring diagrams but detailed electronic schematics as well.

My opinion is that the ultimate authority on efficiency, demand, timed or âÂÂwhateverâÂÂ, rests with the âÂÂAHRI Certificate of Product Ratingsâ with an âÂÂAHRI Certified Reference Numberâ for any given system or combination - for YOUR geographical region - period. This represents the highest âÂÂtheoretical performance factorâ as espoused by the manufacturer as when they state the âÂÂUp toâÂÂ, whatever SEER or HSPF.

Beyond that, what other reliable references do we âÂÂPlebeiansâ have to compare apples with apples, oranges with oranges?

We otherwise may as well be debating how many angels can dance on the head of a pin!

IMO

SR

For FSQ

I won't beat a dead horse. You have your opinion. I have mine. I personally think the Carrier resource you quote is blowing smoke.

This is a big deal about nuisance and unnecessary defrost calls. This is an issue with Carrier/Bryant including the fact about wear and tear on the condenser.

IMO

For those interested in this HVAC issue, here is a link to Infinity Defrost control. As said, I think this is nothing more than jazzed up time/temp method.

IMO

Here is a link that might be useful: Carrier Infinity Defrost Control

To compare Carrier's time/temp method( even the jazzed up time/temp method as Tiger so correctly described it) to Trane's true demand defrost is not even a close call. Thats like comparing any BMW to a Ford Focus.

But that being said.You won't find to much Carrier bashing here. I find that they make a lot of fine products. It is just fine time that they step up and include demand defrost in their heat pumps. All other upper quality ac manufacturers already have. Just my opinion.

Thanks Tiger. If you would please provide a âÂÂlikeâ pdf document explaining the Trane defrost method IâÂÂd appreciate it (your time permitting of course).

This is not to challenge you but rather for my own education and understanding.

TNX,

SR

Agree with Harlem.

Not a Carrier basher either. They make great products and in many cases are technologically ahead of Trane in research,performance and efficiency.

I just have a pet peeve about their HPs and failure to make EDD a feature.

And for FSQ, I will try to find some product info on Trane's HP EDD feature. Perhaps others who see this post can provide this.

TD

explanation on page 4

Here is a link that might be useful: Trane Service facts

Good info....

Thx for assist Harlem...

TD

I have read the Trane and Carrier defrost cycle descriptions. They are not well written so they are open to some interpretation.

Maybe I am missing something, but it is not obvious to me which method would cause more defrost cycles. It would seem the Trane method only will cause a defrost when needed. But description says the defrost condition is determined by the change in the difference in temperature between the coil and ambient. How does this work to minimize the defrost cycles?

The Carrier method will only do a defrost at the end of an accumulated run time interval if the conditions are met. However if the coil does not reach 32 degrees (which direction is not clear) the time interval is reset. This would seem to reduce the number of defrost cycles.

The other question I have is if the Carrier method wastes more energy than the Trane method, then where is that reflected in the SEER rating? The energy ratings of the two products are about the same. My assumption is the energy used in a defrost cycle is very small or it is not used in the SEER calculation. Which is it?

For Mike

I suppose you mean HSPF rating not SEER.

Anytime you reduce defrost cycles, you are saving money, not to mention unnecessary wear and tear on the condenser.

I can't answer the question about whether defrost cycles are taken into consideration in the HSPF efficiency. I really don't see how they could be. Perhaps I will send this question to AHRI for an explanation since they are the proverbial authority.

For myself, I am convinced under same conditions, you will have more defrost cycles with Carrier than Trane.

And just for disclosure purposes, I have an 8 yr old Trane DF system and HP has EDD feature.

IMO

This post was edited by tigerdunes on Tue, Nov 19, 13 at 13:36

Very thought provoving questions Mike . I went to a very detailed class on Trane defrost several years ago that tackled some of the questions you ask but can not find my paperwork from it right now. I will try to explain as best as I can remember.

Trane itself never comes out and says it reduces the amount of defrost cycles(at least not that I have seen) as it could be more defrost cycles on say a 20 degree for a high temp day. It does however say its heat pumps defrost only when a defrost if needed.It could be said that it is just as bad on a compressor and efficiency to run with a coil completely covered in ice waiting on the next time check. It takes the ambient into account vs coil temp to know whether ice is really present or it is just that the ambient is below freezing. Time /temp is going to go into a defrost when temp outside is below freezing with no regard to the presence of actual ice or amount of ice.

As to the HSPF rating being different. I don't know whether or not the defrost method is considered in the calculation. I would guess not but don't know. That figures to be hard for them to calculate in a lab and also kinda puts AHRI into picking sides. Dont see them doing that. Great discussion none the less.

This post was edited by harlemhvacguy on Tue, Nov 19, 13 at 14:30

"As to the HSPF rating being different. I don't know whether or not the defrost method is considered in the calculation. I would guess not but don't know."

Actually, energy used to defrost is included in the HSPF calculation.

This came off the energy.gov web site(if you put stock in .gov info)

" " These are some other factors to consider when choosing and installing air-source heat pumps:

â¢Select a heat pump with a demand-defrost control. This will minimize the defrost cycles, thereby reducing supplementary and heat pump energy use. " "

salti,
Can you elaborate on the enery used to defrost is included in the HSPF calculation. I see where one thing i read said strip heat was factored. But I also know that HSPF is calculated using set assumed parameters such as using climate region 4 and heating load hours and so on. If defrost is used in the calculation I would assume the calculation has a set amount of the times it defrosts. If so defrost method is not taken into account only amount of enery used to do so.

I stand corrected on the SEER vs. HSPF rating. I am not very knowledgeable when it comes to heat pumps. They are very rare where I live.

I find it interesting that Carrier is not competitive with Trane on the demand defrost feature. Perhaps there is a patent blocking a practical implementation.

harlem,

Ex Staten Islander here.

As I read it, defrost method IS used. However, the energy used by the Strip Heaters are NOT included because they contribute to heating the house.

Gotta think about that one. lol

EDIT Thought about it. Makes sense.

Here is a link that might be useful: HSPF and Defrost

This post was edited by saltidawg on Tue, Nov 19, 13 at 16:59

IâÂÂve read the HSPF and Defrost document that was linked to by Salti. According the document, ARI does not take into account the energy used by heat strips into the HSPF calculation. Therefore, as testing methodology is the same, only the relative HSPF & SEER ratings matter. Defrost method is irrelevant as it relates to this efficiency rating. Only the assigned numerical value is relevant to the efficiency rating. Defrost method may be a factor with regard to lifecycle cost, as fewer defrost cycles may result in a longer lifecycle due to possibly fewer reversing modes.

Real world calculations would have to account for backup usage, staged or otherwise, as well as energy consumption of the crankcase heater element.

I would base my own purchase decision on AHRI HSPF & SEER rating for MY region or escape the whole debate by installing geothermal which has no defrost cycles, unless improper design and installation results in you freezing the ground. A discussion for a different thread!

Please see the link below where you can download an Excel file containing over 600,000 make/model combos including AHRI Verification numbers and classification, SEER, EER and HSPF for regions IV & V as well as other useful data. The data suggests that to date the Carrier Infinity Greenspeed is far and away the most efficient air-source heat pump for all zones.

âÂÂClickâ on the link: âÂÂDownload all models (ZIP Format)âÂÂ

SR

Here is a link that might be useful: AHRI Heat Pump Energy Efficiency Ratings

" Defrost method is irrelevant as it relates to this efficiency rating."

The linked document does not say that... indeed, the defrost method is one of the parameters entered into the model. The model does calculate the heat pump energy while in heat pump mode as the unit attempts to cool the house.

Re: Salti

âÂÂThe linked document does not say that... indeed, the defrost method is one of the parameters entered into the model. The model does calculate the heat pump energy while in heat pump mode as the unit attempts to cool the house.âÂÂ

You are in fact correct, however, no heat strips are included in the calculation.

âÂÂDefrost method is irrelevant as it relates to this efficiency rating.âÂÂ

This is not a direct quote from anywhere, just my opinion.

Below is a direct quote from the âÂÂFlorida Solar Energy Centerâ document that you linked to.

âÂÂAlthough the vast majority of air-source heat pumps operate auxiliary strip heat during the defrost cycle to prevent "cold blow," the ARI procedure specifically requires that strip resistance heaters be prevented from operating during the frost accumulation test. (Section 4.2.1.3).âÂÂ

As I previously stated, since the testing methodology is the same for all air-source heat pumps perhaps the relative number of HSPF & SEER would be a good enough guide as defrost mode, irrespective of type, is already accounted for.

Perhaps weâÂÂre giving this matter far too much attention.

IMO

SR