dslreports logo
 
    All Forums Hot Topics Gallery
spc
Search similar:


uniqs
1439
nma851
Premium Member
join:2013-10-13
USA

nma851

Premium Member

[HVAC] Premature Low-Ambient AUX concurrent kick-in/HP SP lockout

Hello fellow tradesmen/tradeswomen -

Trying my best to be thorough, my apologies for the length in advance. Trying to be thorough with all that I installed and all I have done thus far. I am officially at the scratching my head point.

Installed my HP/AHU w/Nat Gas auxiliary almost 4 years ago. I planned on replacing the furnace just to get the AHU into the center of the house due to the size, layout, & age of the house. Old furnace was 13 years, it was the only source of heat before I changed it out to a HP system, furnace intention was/is to be used as AUX only after deciding on the HP. Plus, figured might as well with the amount of work already being done and needing to reconfigure the location of the AHU since I could w/direct venting.

Went with all Goodman: GSH13036 HP, TXV cased, GMH950904CX 2-stage, multi-speed Nat Gas (Aux/Emerg), 4" filtration, humidifier, controlled via Honeywell VisionPro Stat applicable & setup for HP 2H/1C (2 stage Aux (gas) is controlled via the furnace board).

As a Mechanical Engineer, yeah I had to get all the bells & whistles since I have to live with it Nonetheless, fuel bills in both summer/winter have been what I anticipated over these years, periodic maintenance ALWAYS performed, full system tests performed, etc. etc. Then an anomaly occurred late last year's heating season and up until 5 days ago, when I got both elec/gas bills, it confirmed that I'm switching over to AUX prematurely - AUX is kicking in when outdoor ambient is WELL above the 30d threshold. Since I am disabled now as well, I couldn't exactly "trot on outside" to where the HP is for me to observe regularly; however, I was able to confirm it is operating as designed on heat, changeover valve & other electrical testing OK when OHM'd out, no obvious "symptoms" that would kick a light bulb on in (what is left of) my brain. Defrost has not kicked in yet due to minimal usage and temps have not been low enough but I did check power & resistance going to the defrost board, everything is falling within specs.

Previous setup was a 150BTU gas-guzzler, stat on the lower level (smart eh?), major temp swings for obvious reasons, and I wouldn't even say "nominal" cooling in the upstairs bedrooms. We used a window-shaker on 90+ days just to get the upstairs below 80d while you could hang meat in the living room area. Common issue in split-levels, I know, and it doesn't help the configuration had the old furnace at one end of the basement with the hottest bedroom being at the opposite end of the house. Age of the home does not really help either (1940's) & the multiple additions, before I acquired the home, should have triggered some bells in someone's head to zone the place given it was opened-up at one point or another to accommodate the additional loads on an upper floor.

Needless to say, once the existing A/C said its farewell, it was time for some re-configurations and the ultimate deciding factor on changing out the furnace too, despite deciding to put in an HP which would use less fossil-fuel heat. Re-configuration was made possible due to the direct-vent capability ( gotta love that fact in and of itself!) - why not get this thing as much in the center of the house as possible & help eliminate some of the "dead" zones? Last, trying to zone it out & use 2 systems was not possible either; it would cost more to dive into the (closed-off) attic space(s), find a home for the AHU, re-duct, plumb, elec., etc. etc. The costs involved were far from the ability to recoup & most of my crew agreed. Last but not least, I played the "dumb" role of "have no clue homeowner" to get some quotes/opinions on both single/dual zones which supported the "keep it as it is" theory.

Now that I'm done giving my dissertation on background, moving on to the issues at hand.

First, before I hear about the 30 degrees as the changeover to gas, the rationale is due to the age of my home, the fact it is a Tri-Level (actually a quad but that is semi-conditioned space & used as mechanical/laundry/storage), located in the midwest, and months of trial/error to get the best heating while maintaining efficiency. Granted, I'm used to commercial apps, however I ensured the system is sized & distributed properly. At 25d, the HP would not keep up & the lower levels would drop to the "uncomfortable" range (less than 65) and even the upper levels would fail to get above 70. Prior to changing the entire system, we ALWAYS had a temp drop of +/- 10d in the living area (downstairs level) and a rise of 10d +/- in the bedroom areas (upstairs) & were constantly opening/closing dampers. Main floor was fairly consistent with being "in the middle".

I'm actually contemplating a DDC damper system, controlled by remote sensors, in turn controlling damper actuators, in order to send more supply air where it is needed and less where it is not needed. This may be an aspect to revisit at a later time given the current situation

The new system has served well up until late last heating season as mentioned before, cooling operated just fine all summer, and now that we're in heating mode again, gas bill (and supply temps) confirm HP is still operating *most* of the time. The problem, a big one, is that it is A) NOT locking out the HP on a "premature" low ambient (but does when truly below the lockout SP); B) Aux is kicking in concurrently with the HP (BIG NO NO w/Gas AUX - wayyyy too much heat on that coil), and C) Occurring between 40-45 which is not the lockout SP.

The HP can handle the load just fine - especially at those temps (40-45) but what makes no sense is why the either the stat or furnace 'decides' it should kick in AUX to 'help it out' whenever it is set for fossil fuel, not electric, which will damage the HP. There is simply no justification either for the AUX to kick in even if this were an electric AUX setup (no long run times, air supply temp keeps up the demand, calls are not abnormally high or long calls, etc.). Since I do not have electric as the AUX, the furnace should NEVER be coming on with the HP ever. I'm just not sure if the furnace board has anything to do with supplemental or if the stat is the sole deciding factor here.

Going with the former, this makes me think the stat has an issue and I verified the program settings on the Stat as follows: 0170=7 (HP 2H/1C w/Aux), 0200=1 (fossil AUX), 0210=0 (no fossil fuel kit - I have an outdoor sensor installed), 0300=1 (auto xover), 0310=3 (deadband 3d), 0340=2 (outdoor sensor HP lockout), 0350=30 (HP lockout at 30d).

Further checked if the HP would go on lockout by manually turning on emerg heat, only gas runs, switched it back to auto/auto & the HP kicks back in, Aux shuts down, 5 mins later Aux is back on with the next call (or during a call). To rule out an outdoor sensor issue, once we were heading to have a less than 30 degree night, I stayed up until I saw the stat go into lockout & what outdoor temp reading I had on the stat. Stat kicked out the HP at 30d, as programmed, and solely used the gas Aux. At that time, just to see what would happen, I had my brother warm up the outdoor sensor to get it above lockout, he got it to 34 before lockout disengaged, the HP came on, however the gas Aux still continued to run for the remainder of the call & some of the subsequent calls. Naturally, the outdoor temp came back down again once an hour of keeping the outdoor temp sensor above 30 became cumbersome (LOLOL) & subsequently went back into HP lockout as programmed/designed at 30d.

At one point, I lowered the lockout to 25d to test it, the gas Aux shut down, and nothing BUT the HP ran and ran. The moment I raise the lockout to anything above 25, I had the quasi-combo HP/Aux. I am leaning towards a stat going/gone bad here, however I am still hesitant as the "magic number" of 25d should not result in any different behavior than other lockout SP's. If this aspect of the stat has or is 'going bad', then I *should* be having the issue irrespective of the lockout temp setting. This occurs whether it be 15 (lowest) all the way up to 30d. Interestingly, anything ABOVE a 30d lockout SP: Aux NEVER kicks in at all UNLESS the outdoor ambient drops below that. It just doesn't make sense yet the Stat is, from what I've gathered, the only control for this. The furnace's stages are, again from my understandings, 100% independent from the stat and/or HP; all the furnace does is get "told" by the stat to come on/off & the furnace itself stages independently. Now if the stat was also controlling the stages of the furnace, I could understand it but this is not the case - unless I am wrong & that's a possibility!!!

Before I go shelling out hundreds on a new stat just to be a "part swapper", what are your thoughts about the troubleshooting thus far based on the aforementioned? I'm open to any/all suggestions of course. Please feel free to speak your minds & do not hesitate to ask for more info if needed (hopefully I've supplied MORE than enough). This just doesn't make any sense that an "above 30d" lockout setpoint is triggering the Aux to kick in without just cause AND concurrently w/HP on top of it.

Again I apologize for the length here. As silly as it may sound, given I used to be commercial/industrial, I'm sure you're thinking I *should* know but I'm drawing a blank. It's not a BAS or 30 story high-rise w/chillers & boilers :):). Hence, I am relying on the expertise & suggestions of you all on here as I'm to that point of banging my head on the wall. It's been a long time since I've messed around with residential - the last time being when I installed this system in my house. I feel like I have done all I can but I am simply not 100% convinced. I am still leaning towards the stat being the culprit due to this occurring ONLY at or above the 30d lockout SP as well as the concurrent supp/HP on a fossil-fuel AUX. I would imagine it would be an "all or nothing" type ordeal but who knows how these algorithms & boards are made!!

My sincerest appreciation in advance for any & all replies. I truly do value the input and again thank you very much.

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

Tex

Premium Member

I find nothing wrong with the program settings. The issue is the thermostat is causing both the HP and the fossil fuel furnace to operate at the same time when the outdoor temperature is above 30 degrees, which is the lockout setting. That leads me to believe the thermostat is the culprit. But, as you said, before being a "part swapper", why not give Honeywell a call?

1-800-468-1502
nma851
Premium Member
join:2013-10-13
USA

nma851

Premium Member

Thank you for the response Tex.

Will give HW a holler in the morning & hopefully make some headway. Chances are it may be "unsupported" since it's 3 or 4 years old but I won't know until I try. With as many of these I've installed/programmed/etc. in the past, it would be my luck that MINE is the one that crapped out this soon! What happened to our simpler days of mechanical/electro-mechanical?

It's times like this that I get so frustrated at my inability to walk/move around, much less do what I do best, as I'd already have changed it out just to "rule it out" officially. However, with you confirming the same suspicions I had, I'm relatively confident now that the stat is failing. Could be worse though; control failure versus an equipment failure - not as costly (well, that all depends on *what* control nowadays with everything being digital/electronic actually!!!).

I suppose the bright side is it's going bad at the right time. I've wanted to get that RTH9590WF (WIFI & Voice capability and of course, the 'wow' factor) and this could be a sign to do it.

Thanks again for confirming my suspicions & your time as well. Take it easy

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to nma851

Premium Member

to nma851
said by nma851:

First, before I hear about the 30 degrees as the changeover to gas, the rationale is due to the age of my home, the fact it is a Tri-Level (actually a quad but that is semi-conditioned space & used as mechanical/laundry/storage), located in the midwest, and months of trial/error to get the best heating while maintaining efficiency.

The rationale should be based *ONLY* on cost of heat produced by HP vs cost of heat produced by gas. Based on the utility prices the threshold may be anywhere between the minimum temperature at which the HP will operate and "never" - your HP may be cheaper to use than gas at any temperature or gas may be cheaper at any temperature. For example I have oil and it is still cheaper to use the HP at 10F than to use the aux oil.
Now back to switching to AUX - some thermostats will kick the AUX heat whenever the difference between the set point and actual temperature is 2F or more; you can avoid this by setting the intelligent recovery mode when available; in addition AUX will start when the HP goes in defrost, which can happen differently based on outside temperature and humidity.

Jack_in_VA
Premium Member
join:2007-11-26
North, VA

Jack_in_VA

Premium Member

said by cowboyro:

Now back to switching to AUX - some thermostats will kick the AUX heat whenever the difference between the set point and actual temperature is 2F or more; you can avoid this by setting the intelligent recovery mode when available; in addition AUX will start when the HP goes in defrost, which can happen differently based on outside temperature and humidity.

Why would anyone want to prevent the equipment from maintaining the desired thermostat set point. If I set 72 degrees then I want 72 degrees but realize with the aux heat it will maintain at about 70 degrees.

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro

Premium Member

said by Jack_in_VA:

Why would anyone want to prevent the equipment from maintaining the desired thermostat set point. If I set 72 degrees then I want 72 degrees but realize with the aux heat it will maintain at about 70 degrees.

When the thermostat changes between setpoints the difference can be greater than 2F and call for aux. Same when someone manually changes the setpoint to a higher value. Same when the HP cannot maintain the setpoint.

Jack_in_VA
Premium Member
join:2007-11-26
North, VA

Jack_in_VA

Premium Member

said by cowboyro:

said by Jack_in_VA:

Why would anyone want to prevent the equipment from maintaining the desired thermostat set point. If I set 72 degrees then I want 72 degrees but realize with the aux heat it will maintain at about 70 degrees.

When the thermostat changes between setpoints the difference can be greater than 2F and call for aux. Same when someone manually changes the setpoint to a higher value. Same when the HP cannot maintain the setpoint.

That still doesn't answer the question as to why someone would want to defeat a feature of the equipment designed to maintain the desired set point of the thermostat as close as possible. When I set 72 deg I want the temp to be as close to 72 deg as possible even if it does require the use of aux heat.
nma851
Premium Member
join:2013-10-13
USA

nma851

Premium Member

said by cowboyro:

Now back to switching to AUX - some thermostats will kick the AUX heat whenever the difference between the set point and actual temperature is 2F or more; you can avoid this by setting the intelligent recovery mode when available; in addition AUX will start when the HP goes in defrost, which can happen differently based on outside temperature and humidity.

I understand where you're coming from relating to indoor ambient vs. indoor SP's, defrost timing, AUX "helping" as-needed, & how the stat is designed to maintain the indoor ambient as close to the indoor SP as possible while using the most cost-effective method (HP vs. AUX). FYI, intelligent recovery is active - I did not post that point simply because it does not appear to be applicable to the issue(s) at hand. I agree 100% that cost is the determining factor as it relates to the BP SP. However, given the comfort level (or lack thereof) & the temp sways since I cannot zone out the house, it only makes sense to have 10 mins of AUX @130d supplying heat to get the lower levels comfortable and closer to 70 degrees versus an hour of struggling HP operation while only achieving 65 degrees & still having uncomfortable conditions. Granted this may be a "personal" preference, however this is what is necessary to achieve the most comfortable conditions in the house.

I completely agree with this statement as well as it further supports my necessity to maintain the temp desired:
said by Jack_in_VA:

That still doesn't answer the question as to why someone would want to defeat a feature of the equipment designed to maintain the desired set point of the thermostat as close as possible. When I set 72 deg I want the temp to be as close to 72 deg as possible even if it does require the use of aux heat.

If it uses it, it uses it; I have to in my case due to the multi-levels & the inability to keep my lower levels anywhere close to 70 degrees without using the AUX at or below 30d. Believe me, I've tried. Even setting the BP SP to 25d causes the lower levels to drop to around 62-65 which is VERY uncomfortable. Given the upper level (bedrooms) are dampered slightly so it's not getting up to 80 up there, without the ability to zone out the upper/lower, this is the best I can do & the best the system can do. Sure, it's not the most "optimum" use of an HP system, however I don't have any other choice either.

Nevertheless, the main issue at hand here, as discussed in detail in my original post, is that my fossil fuel AUX is concurrently operating with the HP. That 130+d air from the natural gas furnace hitting the downstream coil is WAY too much heat subjecting the system to damage. Conversely, it would be no different than letting 40d outside ambient air flowing through condenser operating in cool mode without an LA kit. As you already know, all that will do is flood the evap, suck liquid back through the suction line, slug the compressor, eventually damaging it. May not be the "best" comparison but the point is this *concurrent* operation that should never happen.

Up until now, whenever my balance point was reached per the BP SP, the HP would cease to operate while the gas AUX came on. That is the design for any fossil fuel setup - one or the other, never both. Compounding this problem is the failure of the HP to cease as well should the indoor conditions warrant AUX to get it up to the indoor SP. Should the indoor ambient demand be "determined" by the Stat's logic to be insufficient, such as during morning recovery or when we're getting close to that BP SP, that HP must shut off when AUX kicks in. Once satisfied via AUX, it must shut down before the HP resumes/takes back over. If I had strips as my AUX, I would certainly not be concerned about the concurrent operation as there is no risk of equip damage, but I would still be concerned as to why the AUX is kicking in (concurrently) before the indoor ambient warrants such, such as your example of 2d or more difference.

Obviously, once it's below that 30d BP SP, the HP should never operate period if it was following the BP SP for lockout/AUX operation.

The Stat is set as "Fossil-Fuel Aux", along with all my other setup settings as verified by Tex:
said by Tex:

find nothing wrong with the program settings. The issue is the thermostat is causing both the HP and the fossil fuel furnace to operate at the same time when the outdoor temperature is above 30 degrees, which is the lockout setting.

. The stat's settings are *supposed* to make the operation as one or the other - not concurrent - it must always be HP or Furnace, never both concurrently.

Last, Honeywell offered no real "solution" other than the stat is likely bad & I need to replace it. It's out of warranty so either way I'm looking at a new Stat regardless as it appears we've all ruled-out any other malfunction with the equipment. I'm going to pick up the new Stat come next "payday" (fixed-income sucks more than being crippled) as I don't want to rack up a credit card, but until that time, in order to ensure I don't kill my HP with concurrent operations, I've switched over to emerg to prevent such. It's averaging 30-40 outside anyway & around 3 weeks or so of gas-only usage, before I can replace it, is FAR cheaper than having to replace a compressor or more by both AUX/HP operating concurrently.

Thank you all again for your help on this. I certainly do appreciate it even though you may not necessarily agree with me having that 30d BP when it comes to the BP SP aspect of this conversation. I wish it WAS feasible - but it just doesn't cut it on my lower levels where I am most of the day.

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro

Premium Member

said by nma851:

That 130+d air from the natural gas furnace hitting the downstream coil is WAY too much heat subjecting the system to damage

If the coils are after the furnace then it's installed wrong; additional heating should come *AFTER* the coils, so that the HP operates efficiently. The efficiency of a heat pump is inversely proportional to the difference in temperature between indoor and outside. Since you are basically creating a "130F indoor environment" for those coils, the performance is completely ruined. You may very well operate less efficient than by just having the AUX while both are running by returning refrigerant at a higher temperature than what it comes from the compressor.
The thermostat isn't supposed to fire one or another, it's supposed to fire the HP at all times and add AUX when extra heat is needed, not instead of the HP. A lockout thermostat may prevent the HP from running below a certain outside temperature, but such thermostat should enable the AUX to fire when there is a call for HP.
mj3431
join:2003-04-21
STL, MO

mj3431

Member

said by cowboyro:

The thermostat isn't supposed to fire one or another, it's supposed to fire the HP at all times and add AUX when extra heat is needed, not instead of the HP. A lockout thermostat may prevent the HP from running below a certain outside temperature, but such thermostat should enable the AUX to fire when there is a call for HP.

Depends on the stat. I use the Ecobee Smart stat that can be configured to fire HP or Aux, or both, with temp lockouts on each. I prefer not to fire both at the same time because supply temps jump up and it creates a temp swing in the house.

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

Tex to cowboyro

Premium Member

to cowboyro
said by cowboyro:

said by nma851:

That 130+d air from the natural gas furnace hitting the downstream coil is WAY too much heat subjecting the system to damage

If the coils are after the furnace then it's installed wrong; additional heating should come *AFTER* the coils, so that the HP operates efficiently.

It is not installed wrong. This is a dual-fuel or hybrid system, not your "typical" heat pump system with an electric heat air handler where the indoor coil is before the blower and the electric heating elements. Installing the indoor coil before the gas furnace would create too much air restriction thereby causing the furnace to overheat.

PSWired
join:2006-03-26
Annapolis, MD

1 recommendation

PSWired

Member

How does the refrigerant coil being before or after the burner change the amount of restriction it adds to the flow path?

Or is the blower not rated to operate with the low inlet pressure that'd be caused by having the coil upstream of it?
nma851
Premium Member
join:2013-10-13
USA

nma851 to cowboyro

Premium Member

to cowboyro
said by cowboyro:

If the coils are after the furnace then it's installed wrong; additional heating should come *AFTER* the coils, so that the HP operates efficiently.

I did not install strips (elect resistance) with my system for my AUX and/or E heat. This is a natural gas (fossil-fuel) AUX/E heat (Hybrid System). While this WOULD be an incorrect setup if I had strips as the AUX/E, the absence of strips & presence of natural gas as the AUX dictate the coils to be downstream of the fossil-fueled AUX (just the same as if this was a "standard" H/C system).

Installing that coil upstream would cause my HE's to rust out from condensation forming during the cooling season. I'd have cool, dry, 55d or cooler air hitting those HE's, which are already sitting in a humid & warmer ambient environment in the bsmt. When it cycles off, the HE's will warm back up; when it cycles back on, this "cool-down" of the HE's will repeat every time, they're going to condense, & they're going to rust-out from these repeated cycles. While this is a condensing furnace by design (92%), it's not designed for the primary/secondary HE's to be subjected to the above. Eventually that condensation will also likely make its way into the combustion chamber. Thus, the coil has to be downstream even if this was not a hybrid HP system.

As FYI, Blower ratings on this AHU at an ESP of 0.1"wc = 1718CFM, 47 rise. Whenever I did the duct pressure reads back when I installed it, I came in with a total ESP a little over 0.3"wc, which includes my 4" filtration, giving me +/- 1632CFM, 49 rise consistent w/specs. Worst case (dirty filter, e.g.) is I get up to an ESP of 0.4"wc, for example, giving me +/- 1586CFM and upwards of a 51d rise. Assuming the higher of the two and at 70d ambient, the gas-fired furnace alone gives me a temp of 121d, rounding up to 130d just to ensure I wouldn't result in an overheat situation. No equipment damage will occur within these specs.

Since I pulled the spec sheets to get the blower ratings for the info above, it is within range/specs for the design.
nma851

nma851 to Tex

Premium Member

to Tex
said by Tex:

Installing the indoor coil before the gas furnace would create too much air restriction thereby causing the furnace to overheat.

Thanks Tex. I didn't see this reply before posting my other one. It is more/less incorporated into my last reply to cowboyro See Profile about the "coil installed incorrectly".

I provided the blower rating specs for my AHU in that response as well which more/less coincides with your reply about the overheat aspect, just the condensing aspect, of having that coil upstream instead of downstream as it is. While I did not specifically touch on the air restriction side of things, there's enough info in my last reply about the ratings to where anyone reading it can draw the same conclusion(s) on the "Why" it's downstream.

My guess it is 'uncommon' for Hybrids such as this? I suppose it depends on a variety of factors when it comes to selection, particularly that of geographic location. It's just my opinion, but here in the Midwest, we have more below freezing days during the winter than we do above, making a Hybrid more viable. Granted, the "norm" appears to be the use of strips, however if I went THAT route, based on average outdoor temps being in the 20-30 range, e.g., those strips would cost a fortune compared to the Hybrid.

I'd EASILY be getting $300-350+ elec bills versus a $100 elec and $50-80 gas based on how often supplemental is being used. I won't bore you all with the math, however $1,200 (minimum) alone in savings based on the difference between hybrid & strictly HP/Strip speaks for itself.

My appreciation again for everyone's input here . Great conversations

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to Tex

Premium Member

to Tex
said by Tex:

It is not installed wrong. This is a dual-fuel or hybrid system, not your "typical" heat pump system with an electric heat air handler where the indoor coil is before the blower and the electric heating elements.

However for such a system the heating source must be one or the other, never both. So a condition of temperature below the setpoint or inability of holding the setpoint will cause the expensive aux heat ONLY to fire until the temperature gets close to the setpoint. Therefore incorrect setup.
cowboyro

cowboyro to nma851

Premium Member

to nma851
said by nma851:

nstalling that coil upstream would cause my HE's to rust out from condensation forming during the cooling season. I'd have cool, dry, 55d or cooler air hitting those HE's, which are already sitting in a humid & warmer ambient environment in the bsmt. When it cycles off, the HE's will warm back up; when it cycles back on, this "cool-down" of the HE's will repeat every time, they're going to condense, & they're going to rust-out from these repeated cycles.

The system is insulated (or should be). Therefore no condensation. If what you are saying was true then all metal ducts would rust - and they don't.
nma851
Premium Member
join:2013-10-13
USA

nma851 to cowboyro

Premium Member

to cowboyro
Click for full size
COIL_INSTALL···FLOW.pdf
181,221 bytes
Upflow Install
said by cowboyro:

However for such a system the heating source must be one or the other, never both. So a condition of temperature below the setpoint or inability of holding the setpoint will cause the expensive aux heat ONLY to fire until the temperature gets close to the setpoint. Therefore incorrect setup

OK I'm not looking for a debate over how the install was done. The original issue is not even being discussed anymore, rather the positioning of a matching, manf. spec'd case coil downstream just as the manufacturer intended.

First, given ALL components of this setup are the same manufacturer, all the pieces simply fit together where they are supposed to - which in an upflow install means the cased coil goes on top of the upflow furnace. It even has "tabs" or whatever you want to call them that make the install easier/fit together. Again, this is a Gas Furnace Aux Setup A/K/A Hybrid, A/K/A Duel-Fuel. If this had an electric strip AUX, I would have digressed a long time ago but we are NOT dealing with an electric resistance Auxiliary Heating Supplemental System. We're dealing with a natural gas system or, "Conventional Split System".

See the specs & read the FIRST sentence in this PDF (attached "Coil_Install_Upflow.pdf") from the Manf that states: "When the furnace is used in connection with a cooling unit, the furnace should be installed in parallel with or on the upstream side of the cooling unit to avoid condensation in the heating element."

An evaporator before the blower will be in negative pressure; evaporator coil after is under positive pressure. Blow-through systems (Positive-Pressure) are common when coils are attached to a gas or oil furnace, as most furnace makers call for coils to be placed downstream of the heat exchanger. There are a few exceptions regarding coil placement in the air stream generated by a furnace blower, but unless the furnace is listed and labeled to be downstream of a coil, passing cooled air over the heat exchanger will result in extensive corrosion of the furnace, premature failure of the heat exchanger and moisture damage to the surroundings.

Google it & you'll find the same results/answers. At the same time while googling, you will also find the SAME exact rationale listed above as to why the coil cannot - cannot be placed before the gas furnace (ie upstream or in the return) as per the Manufacturer's Specifications for my equipment. Furthermore, this is common, more/less, across the board. I have not found any Manufacturer Specs so far that WOULD allow the coil placement to be upstream on a gas-fired furnace.

Google it; I did and found these:
"It would rust out the heat exchanger if it was tried on a gas furnace."
hvac-talk.com/vbb/showth ··· r-return)
www.doityourself.com/for ··· n.html#b)
Manf for my equipment/setup: »www.goodmanmfg.com/Porta ··· MH95.pdf
"The evaporator coil must be installed in the discharge
(supply) air of a gas or oil furnace. Do not install an
evaporator coil in the return air, or excessive condensation
will occur within the furnace." Page 4 at: (»www.whirlpoolcomfort.com ··· 8101.pdf)

These all support the evaporator being installed where it has been installed, particularly with the PDF shown which is the Manufacturer of my equipment. Again, I would completely 100% agree if this had electric resistance strips as Supplemental/AUX/E heat but this is NOT the case.

Please put this particular issue to rest; it has been explained & justified by manufacturer specs as to why the coil is setup the way it is & is not even the issue at hand.

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro

Premium Member

said by nma851:

Please put this particular issue to rest; it has been explained & justified by manufacturer specs as to why the coil is setup the way it is & is not even the issue at hand.

Only this is not a furnace-AC system, it's a HP system. A whole different thing. You *WILL* have bad performance with the install when using the HP, don't even expect efficiency as you will likely remove more heat from the system than what it can bring. You cannot change the laws of physics.
nma851
Premium Member
join:2013-10-13
USA

nma851

Premium Member

Agreed it's not a standard SS; nor do I expect to have the same, maximum efficiency as compared to operation of the HP more so than the AUX. However, conditions dictate the use of such and I'm OK with that (unless the bills were in the opposite direction than they are). There is no "getting around" the use of strictly the HP, down to 10,15, or 20d, in the climate of the Midwest as well as the house being a multi-level. If I had the ability to zone it out & have 2 systems, this would change the story completely. Unfortunately, this is not possible.

Comparing my heating costs prior to this install to the present, the savings still speak for themselves. I'm actually taking the time to put all the figures into an Excel sheet & show the performance (graphed out as well) of this system over the last year to get an idea. Granted again & as I stated before, I'm intentionally using a balance point that provides "as close to optimum" comfort on ALL levels of the house & that, in turn, is likely losing *some* efficiency, but let us remember that, for example, an hour of the HP running to achieve less than "close to optimum comfort" is still eating up more on the electric side than a 10 min cycle on the gas side. Taking the respective fuel cost rates for gas and electric, I STILL come out on top & this Excel sheet of the costs of the Hybrid will show such.

I'm even throwing in a hypothetical of a "Traditional" HP system only (non-Hybrid) on the Excel sheet; just seeing THESE numbers, thus far, without considering the close-to-optimum-comfort, already exceed that of the Hybrid in just one month, far less the entire heating season. Had I gone with a traditional HP instead of a Hybrid, I'd have electric bills close to my Mortgage payment as the electric strip AUX would be kicking in often & making my meter spin like a fan motor. Essentially, it would operate more on the strips than the HP or HP/AUX combo and again, the numbers show/support this.

Don't get me wrong, I "get" what you're saying as dual-fuel is not necessarily the "norm" on HP's. At the same time, however, the proof is in the numbers - those bills do not reflect poor performance in the least. Quite the opposite & once I get this Excel sheet done, HOPEFULLY TODAY, everyone will see what this Hybrid has done for me as far as the drastic drop in energy costs.

What do you mean by "removing more heat thank what it can bring"? Where/Why would it be "lost"? I'm not clear on where I am losing you here nor how I can explain Dual-Fuel/Hybrids much more without it turning into a Hybrid/Dual-Fuel systems training course so to speak. I do not state this sarcastically either and you certainly have my interest & attention. As an educator and Mechanical Engineer, it's my objective to get the knowledge out particularly in "Special Circumstances" which I (coincidentally) happen to be a real-life part of.

I simply want these to be beneficial two-way conversations, not one-way counterproductive, and as educational for the benefit of EVERYONE as possible. This is a unique setup, no questions asked on that. If you're unclear I'll do what I can as you continue to ask. I'll do all I can to find the answers or find someone that does. At the same time, if I am unclear or not understanding, as is the case with the questions I've posed in the preceding paragraph, please do the same for me so I may understand as best as possible. I look at this as a learning experience/educational experience for all of us as it relates to a Dual-Fuel/Hybrid. Please just tell me where I'm losing you, or where/what you need me to focus on some more, & I'll do all I can to get that info for you.
nma851

nma851

Premium Member

Found this, in the meantime, and is a PERFECT summary of the Hybrids. I've bolded key points for reference:

Hybrid heating systems use electric heat pump technology when the weather is chilly and gas furnace technology when it gets really cold. This makes the home far more comfortable than any single system alone. When it is chilly, people prefer heat pumps over furnaces. The heat pump delivers a consistent “mellow” heat, while a gas furnace delivers intermittent blasts of hot air during mild weather.

Of course, when it gets really cold, people prefer furnaces. They enjoy the “toasty” feeling of the higher temperature air a furnace provides. Because heat pumps deliver lower temperature air than furnaces, heat pumps can feel drafty during colder weather. If it gets too cold, heat pumps cannot keep up with the loss of heat through windows, poorly insulated walls and doors. Usually a supplemental heat strip is required to maintain a comfortable temperature and that can be very expensive to operate for extended periods.

Hybrid systems take advantage of both heating technologies and automatically switch to the one most efficient for the temperature. When it is chilly, the system operates off electricity, providing the heat pump’s steady, mellow heat. But when it turns cold, the hybrid system automatically switches to the gas furnace and its warmer, toasty air. The result is the ultimate in comfort. Even better, hybrid systems cost less to operate.

But, as the temperature drops, a point is reached where the heat pump can no longer keep up with the heating demand. At this “balance point,” it becomes more economical to use a gas furnace for heating. This eliminates the need for the expensive supplemental heat strip. A hybrid system usually switches from heat pump to furnace at a comfort balance point, which is a few degrees above the economic balance point.

Actual savings can vary based on the efficiencies of hybrid units, the utility rate at any given month, how you use your system, and, of course, the weather. With today’s skyrocketing energy prices, a hybrid system, could save you as much as 40% over last year’s bill and that is nothing to sneeze at.

The advantages are clear. Not only do you get the energy savings and environmental benefits, but those are really only bonuses compared to the comfort. Hybrid systems are way-way more comfortable. Simply spend a cold January with a hybrid system, and you will never return to a conventional heating system.

In short, a hybrid heating system offers homeowners a new, more efficient way of heating and cooling their homes. When taking into consideration rising energy costs, the increases in efficiency, the comfort factor, the environmental benefits, and the tax incentive savings, it is a wonder that everyone isn't wanting a hybrid heating system for their family.
Full Text available at: »www.energymiserfurnace.c ··· ings.htm

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to nma851

Premium Member

to nma851
said by nma851:

What do you mean by "removing more heat thank what it can bring"? Where/Why would it be "lost"?

Think of how the system works normally. The refrigerant enters the heat exchanger at about 120-130F in normal operation and leaves at the temperature of the air in your return ducts - 65-75F. If you are placing the heat exchanger in hot air, the return line will be 130F; if you are increasing the temperature of the refrigerant you are removing heat from the house and dumping it outside.
nma851
Premium Member
join:2013-10-13
USA

nma851

Premium Member

said by cowboyro:

If you are placing the heat exchanger in hot air, the return line will be 130F; if you are increasing the temperature of the refrigerant you are removing heat from the house and dumping it outside.

Hybrids NEVER run the Fossil-Fuel AND heat pump at the same time! NEVER

Now if they did, sure this would be accurate, but NOT WITH A HEAT PUMP THAT IS PART OF A HYBRID/DUAL-FUEL SYSTEM.

I've posted about all I can for anyone to read & understand HOW a Dual-Fuel/Hybrid works and is DESIGNED to work. I'm doing nothing more than going in circles here when everything posted, and what ANY person would find by Googling a "Hybrid or Dual-Fuel System." You'll find the exact same stuff I've already posted & discussed.

It's either Heat Pump operating or Furnace running - nothing more, nothing less, & NEVER BOTH CONCURRENTLY.....

Dennis
Mod
join:2001-01-26
Algonquin, IL

Dennis to nma851

Mod

to nma851
Can we please keep this thread OT?