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nma851
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join:2013-10-13
USA

nma851 to pende_tim

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to pende_tim

Re: [HVAC] Goodman 2 Stage HP Defrost

Hey pende_tim See Profile

I do not have the "rights" yet to reply/add to your post but the Mods got this re-opened for me to pose the following. I still cannot reply and/or quote as I need to, so alot of this is being done manually. I do apologize in advance but I can ONLY post to the "Original" or the Mods who re-opened it through their post (guess it gives another "14 days" with their posts only).

Since I have the same equipment, more/less the same circumstances, with the exception of having Natural Gas as the AUX/E heat versus strips (or propane as I didn't see which you have), I'm asking for some of your time for comparison/contrast discussion. It is unclear though if you have a Hybrid (Dual-Fuel) like myself since there is mention of Propane being considered, but no mention of Propane being used as the Supplemental specifically. I'll assume you have the "traditional" setup of HP/elec strips as your Supplemental (AUX/E-heat). Whenever you mentioned the propane costs & the 50-60% savings you're experiencing via the HP in our climates, I am VERY glad to have a "real-life" savings comparison now. I'm curious on some other items that may be helpful to you as well. Granted, this isn't the same as natural gas rates/propane rates, but our similarity is our climates, HP's, comfort/temp-swings, and most importantly, savings.

First & foremost, would you mind posting your Model # of that HP and the AHU (or furnace if you DO have an LP as your Supplemental)? I do not want to error by using the wrong model's specs. Next, were you able to get the charge verified and/or resolved as previously indicated?

I'm in the Midwest & installed a Hybrid system (Dual-Fuel) myself a couple years back after doing the same as you did - comparing bills, doing the math, and for that I want to say KUDOS right off the bat too! Since I am disabled now, all I can be is an "Educating Mechanical Engineer" versus a "Real-World-Working" one. Life can be cruel at times I suppose.

Further, I as well concur with Jack_in_VA See Profile to where the defrost should *only* be controlled by the coil temp; having some timer kick-in a defrost, every hour, is unnecessary.
said by Jack_in_VA:

Why? The defrost cycle only needs to operate if it is needed by frost/low temp on the coils. A temperature sensor on the coil controls it. The timer will put the unit in defrost only if the temperature sensor is calling for a defrost.

Now I understand you changed that back and I guess I'm still wondering "why" this is a changeable option to begin with whenever a defrost is based on need, not by time. It can poll it every minute (in theory) for all I care; however, the only rationale for a defrost is to ensure optimum heat xfer, and I suppose I fail to see the point of why the Manf. would even offer a "user-configurable timer" to initiate the defrost based on "time" versus "temperature". Guess this is a topic for another day about this particular aspect. Learn something new each day!!

Nonetheless, my decision was based on all the same/similar costs of electric/gas/previous gas-only & over-sized furnace. More info on the entire system and a Hybrid is at my thread here if you're interested: »[HVAC] Premature Low-Ambient AUX concurrent kick-in/HP SP lockout .

My bills have been cut in half as well, despite having the size & type of home I have. My only drawback, regardless of the system being used, is that I have a split-level home (quad to be exact), my lower floors tend to stay cooler anyways, and once the outdoor ambient gets to 30d or less, the ONLY way to overcome the 60-65 temps downstairs was by placing my lockout SP (lockout setpoint - making the HP stop & switch over to Natural Gas) at 30d. While this is not essentially "ideal" on traditional HP systems, in the case of a Hybrid (using the natural gas once below 30d, using the HP above 30d), my actual bill comparisons DO prove there are still significant savings while also achieving the comfort desired on the lower levels. If I'm losing you, just let me know. I'll take all the time needed to clarify.

Since it is unknown as to what your Supplemental heat is (assuming strips unless you advise you're using a Hybrid as I am - yours being propane, mine being natural gas, if that IS the case), do you know what that lockout SP is? Reason I'm asking is to basically confirm you're as "optimized" as possible given we are in MUCH colder climates than the "traditional" HP users are & as equally curious about your comfort levels on each floor/room/etc.

Back to comparisons, my Goodman HP system (GSH13048, TXV Cased Indoor Coil, & Supplemental is GMH950904C 2-stage natural gas) is not the one controlling the SP's/Lockouts - my Stat is. This is due to having an outdoor ambient sensor which allows me to control all aspects of the system from the Stat. Otherwise, I would have to have a fossil-fuel kit if the Stat wasn't controlling). Auto changeover from HP to AUX occurs at 30d, if the HP is struggling (such as during AM recovery), it will kick-out the HP and kick-on the Gas to get the temps up, and the Stat does all of this for me. Defrost is controlled by the HP coil temp, not by time as previously discussed, and for the first time this year I actually hit a defrost cycle before going into full Natural Gas at 10PM or so last night - the time of this post. We're not getting above 25 or so today, likely will be no HP today/tonight either.

Since the nat gas is my supplemental, it not only runs ALOT less than the HP, but it also maintains a far better comfort level in the lower living room. The upstairs bedrooms are slightly dampered to avoid huge temp swings upstairs, however I'll take THAT drawback over the 60-63 degrees downstairs any day.

I certainly apologize for the lengthy post . All being said, since you're located in an area that has lower outdoor ambients during the winter months, how is your system fairing as to the aforementioned "System Summary/History" I've posted? It would be nice to finally be able to compare/contrast to someone who is utilizing an HP in primarily colder climates and the impacts on our fuel costs.

If you're still having issues as well, please let us know. The rest, if you're up to it, would be nice to just have some discussion about.

Thank you for your time & hope you have a good one as well as ALL issues resolved!!

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

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pende_tim

1 edit

pende_tim to nma851

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to nma851
Sorry for not following up on the original post.

The tech came out and checked the charge and the superheat and subcooling were all in spec, however the subcooling was at 7* which is the low end or the 7-9* range, I asked about adding a bit a 410a to bring it up a degree and he said he did not recommend this as overcharging can be a real problem. Since it was technically in range, no problem. He ran a manual defrost cycle and it seemed to work as designed.

He then said that 120 minutes was way to long of a defrost timer and suggested a 90 minute setting.

We have not been there recently to monitor the performance but should be back later this week. It will be cold so I will be able to give it a good test.

The system I have is a ASZC180361 2 stags heat pump and a AVPTC313714 Air handler with 10Kw resistance supplemental strips. It is installed in Southern Delaware near Ocean City, MD.

With my system I have the strips locked out above 25* and the Communicating thermostat takes care of managing the 2 stages and the strips. For the most part, the strips are seldom used even when the OAT gets down to 20*. The key is to avoid radical manual changes in room temperature. If I have a scheduled temperature change, the 'stat anticipates the upcoming change and starts the heatpump early so it has time to make the adjustment. I have this system on the main floor and the floor plan is fairly open, so temperature variations are not a real issue for me.

My defrost is a time/temperature sequence. If the sensor is below 28* and a heating call is active, the timer will start a count down. If the temperature goes above 28*, it is my understanding the timer will reset.

I made my cost savings calculation by looking at the ft^3 of propane used per heating degree day from the past 2 years. I read my meters every day when I am there so I have a pretty good handle on use.

Last year I did a pro-forma calculation of the propane use each day and compared it to the use I estimated my heat pump added to the base load of the house. Even if this estimate was way off, at the end of the heating season, my total electric bill ( which included a second 18,000 btu heat pump in the " upstairs bonus room/ 4th bedroom" was much less than just the propane bill would have been.

Hope this helps.

Tex
Dave's not here
Premium Member
join:2012-10-20

Tex

Premium Member

According to the product specifications, superheat at the suction service valve is 7-9°F. Subcooling is 8-10°F. I would have liked to see 10°F subcooling, but that's just me.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

Premium Member

Thanks, Tex.
Sure is hard to find a good tech, that is why I usually end up doing a lot of stuff myself. However when it comes to HVAC, I do not have the experience or tools. Maybe since I am retired, this could be an excuse to go back to school? ( Just kidding ).

Since the measurement was done when the unit was on high speed, it looks like we were 3* too low on the subcooling to reach your 10* target.

Now to get into a little theory: how much of an impact does this 3* make on Heating performance as far as efficiency and Delta T? How much of an impact will this make on Cooling performance?

....And to get a feel for how "short" the charge may be, the unit shipped with 188oz of R410a for 15' of line set? Any ideal how many oz are required per foot of additionaal line set? If I recall correctly the installer did not add any R410a to the system when it was installed. I have not measured the line set length, but it is pretty close to 15'.

Thanks Tim

F100
join:2013-01-15
Durham, NC
Alcatel-Lucent G-010G-A
(Software) pfSense
Pace 5268AC

F100 to nma851

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to nma851
nma851, thanks for your post about the duel fuel units. Is yours a package unit or split system?

We have a Natural Gas package unit with AC and just had to replace the combustion blower and collector box. Box had rust and fan wouldn't spin. Our unit was made in 1995 and so is on the verge of getting ready to be replaced. Glad I didn't have to do it yesterday. I'm looking at replacing it with a system like yours that uses heat pump most of the time but can use NG for the Aux heat since I have NG. Since a package unit has all the parts for AC, really all they have to do is add the reversing components to make the heat pump. Then just add the extra controls like yours. I believe the stat you have requires a 7 wire setup. It sounds like the best way to go. The stat does all the controlling.

I was reading about the Goodmans yesterday so just wondering how you like yours. I'm trying to find a system that I like. We have about 1800sf but 2 story. The one unit serves both floors but we have to close downstairs vents to get enough flow upstairs. The 2.5 ton unit we have now works pretty well for us.
F100

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to pende_tim
pende_tim, I didn't see this mentioned in this post but from what I understand R410a isn't as easy to recharge. It is a blend of refrigerants not a compound like R22. So if it is low, or leaking, the mix in the blend of the R410a that is left is not the same since the refrigerants that make up the mix bleed off at different rates which changes the composition of what is left in the system. That makes it hard to just top off like the old R22 that I have. You have to pull all the puron (brand name) and replace with new to do it correctly. You can't fix the blend by adding more puron.

When R22 leaks, it is still R22 in the system. You can add more R22 and the mix is the same. The R22 freon acts more like water. You can change it's state but it is always water, event when it evaporates or escapes the system. R410a is like a mixed drink, some parts settle out at different places. Some float on top, some sink to the bottom, some in between. If it's sealed inside the system , the mix is fine. Let some out and one part of the mix escapes while the rest stays.

Tex and others seem to know better than I but R410a seems to be more sensitive to the amount of charge in the system to operate best. I don't know if it's the higher pressures or what.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

Premium Member

I suspect the system was never fully charged from the get go, no leaks AFAIK.

Yes I do appreciate that R410a needs to be charged as a liquid, not vapor to make sure the blend is proper.
nma851
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join:2013-10-13
USA

nma851 to pende_tim

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to pende_tim
No apology needed at all. This scenario got my attention when I saw a few things, especially the climate and the SP's for the OAT's. This gives ME a good "comparison point" and you certainly exhibit quite a bit of vigilance, not to mention knowledge, by doing the right things according to Manf. Specs. Further glad to know you're within a good range at this stage of the game. It is difficult to get a good charge/read during colder temps. Ideally, I'm sure you're going to recheck again once warmer since you know what you're doing/up against/using your brain. I'd love to be retired vs disabled, but we're NEVER too "old" to learn!

I don't want to be too repetitive/redundant here either so I apologize in advance if I do.

Also, happened to notice the HP model # appears to be an Amana; could be some Goodman/Amana" joint effort of some sort but all I'm pulling are Amana specs. The "Communicating Stat" and "Comfort Net" portion kinda made me think a bit more on that, & whenever I use that model# you've provided, it's bringing up Amana instead of Goodman. Don't worry about it - just FYI for ya. Amana-Goodman, Goodman-Amana - they all seem to be commingled when searching; story of our lives LOL. That manual Tex See Profile provided is the same one I found for the model#.

I'll try to not irritate much this time & keep it to the "bare bones" :)

Tex See Profile is one heck of a good knowledge base as well. I've read MANY of his posts since joining and I look up to him whether he realizes it or not . His "outside the box" thinking makes ME think/explore when I otherwise would not have.

OK -
said by pende_tim:

My defrost is a time/temperature sequence. If the sensor is below 28* and a heating call is active, the timer will start a count down. If the temperature goes above 28*, it is my understanding the timer will reset.

Since we're similar in all aspects except our Supplemental heat (you having 10k strips, me having natural gas), I looked up that timer just to get a better idea of what I'm dealing with before speaking about it. This OT18-60A (Outdoor Temp), which I found in the Amana accessories from your model's spec manual, I see where I misinterpreted. That timer only "tolls" during a call, and from what I was seeing in the post(s), I believe I merely misunderstood that it was "tolling" irrespective of what temperature the coil was at. Specs clearly define the operation as: "...clamped to a feeder tube entering the outdoor coil. Defrost timing periods of 30, 60, or 90 minutes may be selected by connecting the circuit board jumper to 30, 60, or 90 respectively. Accumulation of time for the timing period selected starts when the sensor closes (approximately 34° F), and when the room thermostat calls for heat. At the end of the timing period, the unit’s defrost cycle will be initiated provided the sensor remains closed. When the sensor opens (approximately 60° F), the defrost cycle is terminated and the timing period is reset. If the defrost cycle is not terminated due to the sensor temperature, a ten minute override interrupts the unit’s defrost period." It has a fail-safe as well, so once the 10min mark is reached, the defrost cycle terminates & HP operation resumes & the entire process repeats itself.

Strip SP of 25, IMO, is a good SP for our climates & given the Stat/System is calculating the best use for you, even at the 20d you mentioned, not bad in the least!!!

This is a prime example of GOOD use of staging on an all-electric ("Traditional") HP system in a primarily COLDER climate.

Again, my apologies for the mis-read and believing that REGARDLESS of run-time, you're getting a defrost whether you want one or not! Lesson learned on MY part!
said by pende_tim:

The key is to avoid radical manual changes in room temperature. If I have a scheduled temperature change, the 'stat anticipates the upcoming change and starts the heatpump early so it has time to make the adjustment.

Right on the money again; good use of the Stat's function to gradually bring up the temp upon a change in occupancy. Amazing what the recovery function will do - such as today, when we were in the teens, this gave me the first "true" ability to assess the Stat & System's ability to recover without under/overshooting while also ensuring the HP wasn't kicking in. Since you do not have the "Multi-Level Syndrome" as I call it, not feeling the variations is certainly a plus.
said by pende_tim:

Now to get into a little theory: how much of an impact does this 3* make on Heating performance as far as efficiency and Delta T? How much of an impact will this make on Cooling performance?

Ughhh... Well - while we want to be as optimum as possible, getting that 10d sub in these OAT's is gonna be a challenge. You're on 410A as well, that "kinda" changes things a bit but the concept remains the same. Of course, having the specs Tex found helps and using that, while using these "general rules of thumb" so to speak, about all we'd be doing is "Guesstimating" of which I DETEST . I'll probably be crucified by my colleagues over this but I'll post it anyway for REFERENCE (there - hopefully this disclaimer saves me LOL).

Subcooling at 7d and ?? on superheat (from your post) would generally indicate your under a bit, but I agree with the Tech who did not want to do that as over would cause problems as well. Once you're in good OAT's, then you'll be *truly* optimized, no guessing, no speculating.

Low subcooling & high superheat= Under;
Low superheat & high subcooling= Over;
Low subcooling & low superheat= (Not your problem here - you would be getting what you are if the case) is a backwards orifice, and yeah I've seen it before unfortunately, no orifice at all, or refrigerant is free-flowing due to an open (or missing) orifice.
Very high superheat & slightly high sub: Usually indicative of a blockage anywhere from the coil/dryers/orifice/TXV/list goes on. Also not the case in your situation
Could have blockage in coil, TXV strainer screen - settings, etc., orifice, filter dryers etc.

Hopefully, the tech took his readings properly to get your current charge proper. 410A's, depending on how much you've read/learned/etc., require multiple measurements of temperatures using a dry & wet bulb readings as well as 410A temp/pressure conversion chart for saturation temps (unless you're gauge set does this for you). The "simplified" version of getting the accurate reads is by following a precise method - there is no way around it. FYI, this aspect can go on forever in a day, as sat temps change with the refrigerant being used, and I don't want to inundate .

As reference for ya as it relates to 410A charging for your subcooling:
Measure OAT;
Measure the dry bulb temperature @ the return duct;
Measure wet bulb temperature the same way as the dry bulb @ return; the difference between the wet/dry bulb gives the "load" on the evap;
Measure the liquid-line temperature (has to be attached WELL & a few inches from the service valve) to determine sub-cooling;
Attach gauges & measure liquid and suction pressures. Now we use the conversion chart to change the high side pressure to the saturation temp;
Now we subtract the liquid-line temp from the sat temp giving us the subcooling.
Then we look at the Manf Spec sheet, find the applicable pressures for the OAT as well as the subcooling level needed based on those specs;
If the subcooling is too low, additional refrigerant is needed; if too high, too much refrigerant is in the system & will need to be recovered PROPERLY, not just vented.
Subcooling can have a "double-check" by also measuring the temp @ the TXV to see if there's any differences in the read as you shouldn't have a difference.

On the gauge set I have, it's an expensive one I got before my "demise" & inability to walk again, all this gets all the reads & sats through the age of digital technology. Some of the older gauges/temp sets would as well & if all else fails, we look at the old-faithful paper charts.

Superheat is performed in the same fashion, but obviously through different reads from the opposite side of the system (Suction side). Superhead temp checked at the end of the evap, at or as close to the TXV expansion bulb, that is in turn converted into saturation temp per the 410A chart, & comparing that read to the read of the ambient at the bulb & the load (WB/DB difference). We get our suction read, convert to saturation the same way, and compare to the ambient temp close to that suction line read.

Obviously, I didn't go totally in-depth as I'm just trying to give the overview.

Delta T: (TD), temp difference across the coil, if you do not know how to take these measurements::
Measure temp @ supply near the coil;
measure temp @ return near the AHU;
Difference between the two is your TD;
Should be around 15-20 degrees. This can also help confirm your subcooling/superheat are up to par. YOUR specs call for 7-9SH & 8-10SC, but - again - risking the overcharge did not outweigh the benefit of throwing in a bit more refrigerant to hit that 10d mark on your subcooling. I would say it's fairly negligible, for now, as long as you are still getting that TD range. If you are NOT, then I would worry about it. Come summertime, you'll be able to get the best charge under the most ideal conditions.

Again, not to get anyone irritated or the equivalent, this was all for FYI or Reference-type purposes only, not for "Have at it" purposes.
nma851

nma851 to F100

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to F100
said by F100:

thanks for your post about the duel fuel units. Is yours a package unit or split system?

Hey there - glad to hear from another Hybrid owner for once!!

Mine is a split system. As far as I am concerned, the system I chose and put in with my wonderful two hands has served me VERY well. Switching over from an 80% AFUE gas-only that was located at one end of the house to a Hybrid (and moving it to the center of the house) really made the world of difference on the bills. I actually anticipated LESS but got a heck of alot more. I am actually saving about 50-60% as compared to the old system. Moving my Stat to the "main" level as well made the world of difference. Why they put the thing on the LOWER level to begin with was beyond me. Maybe that was their "cure" to get it warmer - while being able to sunbathe upstairs. In the summer, it would be the same - hang meat downstairs & sunbathe upstairs. Initially after getting this place, I moved the stat to the main level which made a huge impact on both heating & cooling, but I still had to damper off rooms (in the basement, not at the supply vents to not lose static pressure), respective to whether cooling was operating or heating was operating. It was a never-ending hassle! :)

My only drawback is I STILL cannot overcome the "Multi-Level Syndrome" as I call it - due to the age of the house, insulation, etc. etc. The lower level (large family room, bathroom) is still cooler than the rest of the place in the winter. Despite moving the location of the furnace to the center of the house, since I was able to do that now (direct vent - no chimney needed on a 93% efficient furnace), "sort of" made a little dent in the problem. We still have to damper the upper/lower floors in winter/summer, but without utilizing TWO independent Split-Systems, it's unlikely to ever overcome the major temp differences between the 3 levels (4 if I include the basement/laundry/mechanical 'level').
said by F100:

Then just add the extra controls like yours. I believe the stat you have requires a 7 wire setup. It sounds like the best way to go. The stat does all the controlling.

You are correct that I opted to utilize the Stat to do all my controlling. Instead of getting a fossil fuel kit, which would be required to ensure that the Gas Furnace does NOT EVER operate with the HP, I went with the Outdoor Temp Sensor that I could get with the Stat. Mine is the Honeywell VisionPro (well, now its the Honeywell RTH9590WF wifi-voice Stat) and that handles the functions of HP lockout SP's, fossil-fuel kit, you name it. I'm STILL learning new features I knew nothing about. Word of caution - DO NOT EVER SAY 'THERMOSTAT' FOLLOWED BY SOMETHING TEMPERATURE RELATED! It WILL respond & end up reacting to that voice command LOLOLOLOL! I think I said something about "see if the thermostat says 62 or 70", so I could see if the iPhone app was showing the same as the Stat, and I ended up lowering my temp to the nighttime setting of 62 degrees at 7:00 at night. Was totally comical after-the-fact but prior to, I thought the dang system went out on me! Technology has come a long way, but there are a few 'quirks' :).
said by F100:

We have about 1800sf but 2 story. The one unit serves both floors but we have to close downstairs vents to get enough flow upstairs. The 2.5 ton unit we have now works pretty well for us.

Any multi-level, IMO, is going to have it's bit of differences up/down stairs. Depending if the ductwork is sized properly now, enough returns/supplys, and locations, it will impact your airflow by restricting it. I had to replace several going to the upper level as they were too small (4") but I wasn't about to tear into walls to make the ENTIRE run to those 3 rooms 100% "right". This would have cost WAY too much money for me & getting 75% of it "up to standards" was acceptable to me. I do NOT recommend that, as that was my own personal decision based on funds/conditions however if they are accessible and/or not costing an arm, leg, and some remaining fingers/toes from the other arm/leg, it would be in your best interests to get the ductwork 100% correct for your home throughout. Ideally, it would need to be throughout but since the additions were done prior to me buying it, I wasn't going to pay all that additional money to tear into walls, ceilings, and attics just to have 2 systems to "zone" the upper from the lower floors.

I'm surprised, however, that 2.5 tons of cooling is sufficient and is likely the 'main' problem with having to close the downstairs supply vents. At 1800SQFT, you should really have a 3 ton, especially with a 2-story home. That is just a "guesstimate" of course, but I would definitely get a 3-ton for your cooling (if you don't go with a heat pump). Again, there is NO way anyone could accurately give that 'magic number' as to the tonnage/BTU's for you online without doing a proper load calculation, but IMO, I would seriously consider going up a notch. Further, oversizing will cause just as many issues as undersizing. In the summer, if oversized, you'll cool too quickly without removing enough humidity. Undersized, that A/C will never stop running. Since you're in NC, that's even a warmer zone (trying to do a load calc example here), and at 3 tons you're still at the "pushing it" end to where you might need a 3.5 ton. Before you DO decide on any of this, ensure the house has a full & proper load calculation done otherwise you will never get the benefits of that new system, even if you decide to go with an HP or not.

Where I am in the Midwest, it's primarily cooler, which is one of the main reasons why I went with the natural gas as the Supplemental (or "Auxiliary" "AUX") heat. If my HP cannot keep up on a given day, which given my house conditions and everything else, is give/take 25-30 degrees. Chances are, it will automatically switch over to the Aux and the HP stops. Same with the morning recovery from the night time temp to the day time temp. The system stages which is the most efficient and the most comfortable means to heat/cool. These systems & controls have come a LONG way but will be virtually useless and of no benefit unless properly sized for the home & without proper airflow through the home.

I'm not really a residential person either - before becoming disabled I was a commercial/industrial mechanical engineer but the concepts for residential were not difficult for me to figure out. There are MANY others on here that are far more familiar and experienced than I am as it relates to residential applications. Before moving forward, I suggest to open a new thread with this question, link these posts to the NEW thread, so that way others will see the subject & be able to add to the conversation. This way, you'll be getting far more responses than you would through this post being "hidden" within a different/unrelated post. Hopefully that will help you all out further before moving forward. If your main question was more/less about the Hybrid HP setup & was answered, no biggie either & hopefully my own personal experience with my setup helps with your decisions.

Either way you go, before getting that replaced, please ensure you have the contractor perform a PROPER load calculation for your home. I wouldn't keep repeating it if it wasn't of the utmost importance! :)

Feel free to ask anything else if you have any more questions, if I missed something, etc. & I'll do my best to answer (or let someone else that has better knowledge answer). Take it easy & take care

Tex
Dave's not here
Premium Member
join:2012-10-20

Tex to pende_tim

Premium Member

to pende_tim
Too low or too high subcooling affects both cooling and heating efficiency. Keep in mind, many manufacturers will allow ± 2-3°F when taking readings. Most importantly, when taking temperature and pressure readings, having accurate instruments is critical. Otherwise, the readings are useless. Using today's advanced digital manifold gauges (Testo, MasterCool, Fieldpiece, Yellow Jacket, etc.) are the most reliable and accurate method for measuring superheat and subcooling.

I would not get too caught up with the line set length, unless the line set is unusually long (80' or longer). In your case, charging the system using subcooling is perfectly acceptable.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

Premium Member

Thanks, Tex.

So from your experience, how much of an impact would having 7* subcooling on High speed, where the manufacturer's spec calls for 8-10*?

This is assuming the readings were 100% accurate: he read the gauges correctly, they were calibrated and the digital clamp on thermometer was recording the true gas temperature, etc? As you point out there will be some inaccuracies in the measurements, but lets call it an ideal world for discussion.

I am just trying to get a feel for how sensitive performance is VS subcooling and I appreciate there is probably not a big performance hit. Just curious .