Heat Pump Efficiency Setting

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Old 02-10-20, 12:46 PM
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Heat Pump Efficiency Setting

My heat pump controller board has a setting for Comfort or Efficiency mode to control the speed of the motor. The manual describes the settings as follows:

HP-COMFORT Provides approximately 315 CFM per ton for higher normal heating air delivery temperature. Provides approximately 350 CFM per ton cooling airflow for good humidity removal

HP-EFF Provides same airflow for heating and cooling modes; approximately 350 CFM per ton

My understanding is that running at a higher CFM in heating mode will move more heat away from the coils which should allow for better heat exchange. Better heat exchange would mean a slightly lower balance point (or shorter runs when not as cold). The comfort mode reduces the speed so the moving air doesn't create as much of a "breeze," but means the compressor isn't being as efficient at heat transfer. Is that a correct understanding? The wording in the manual makes it seem like the opposite.

I'm asking because when the technician was last here he moved the setting to the comfort setting to slow down the blower (to reduce noise/vibration). My subjective impression is the Aux heat has been kicking in a bit more than previously, and I wanted to know if this could explain that.
 
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Old 02-10-20, 07:02 PM
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If you weren't getting enough airflow in heating....... the room temperature could dip below the set point further.
Typically the AUX coils are activated when the room temperature is more than three degrees below the setpoint or the outside condenser is shut down on low outside temperature.

What are you using for a thermostat ?
A proper thermostat could be fully programmed to control the AUX exactly as preferred.
 
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Old 02-14-20, 02:32 AM
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Correct

Less airflow = less heat transfer = less efficiency

Comfort is just higher temp discharge air in heat mode
 
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Old 02-15-20, 09:35 AM
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Correct, the thermostat automatically engages AUX heat when the temp drops 3 degrees below the set point. I was thinking the lower airspeed might be causing it to drop lower more often on cold days, but it looks like I might have a compressor issue.

It was very cold overnight (in the teens) and I noticed that the fan on the outside compressor was starting up and running for about 45 seconds. It would then stop and the unit was making a hissing sound (almost like it was in defrost mode). The fan would stay stopped for a few minutes and the process starts over. There is no ice on the outside unit or coil.

I can't imagine this is good for the compressor, so I've put it in emergency heat (to stop the compressor from trying to start) and have a service tech coming by later today. I'm hoping it's just the reverse valve stuck or whatever temperature sensor is kicking it into defrost mode since the compressor was working fine when it was in the 30s. The unit is 15 years old and freon based, so if it's the compressor then I'm probably looking at a system replacement.
 
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Old 02-15-20, 09:57 AM
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Depending on the heat pump.... in really cold weather the condenser fan will cycle but the compressor will remain running. This method keeps the head pressure up on the compressor.

If you compressor is actually shutting down then it may be a defrost issue.
It could possibly be a misplaced coil freeze sensor.
 
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Old 02-15-20, 10:30 AM
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I don't think the compressor was running since it wasn't making any noise. It's also warmed up to 32 and still doing the same thing.

Technician says it was low on pressure and it's cycling off since the pressure is too low. Seems like it's been leaking for a while which is probably why I was starting to see more aux heat usage. He wasn't sure how much freon it would need, but worst case would be in the $500- $600 range. It seems like a terrible idea to do that both environmentally and financially (even with high electricity rates), instead of using that towards a new system. The air handler wasn't in great shape anyway.




 
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Old 02-15-20, 11:17 AM
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So this is an older R-22 system ?
A R-410a system should not cost that much to recharge.
 
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Old 02-15-20, 12:04 PM
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Yes it's R-22.

With it no longer being made, they charge $145 a pound. He said he wasn't getting any real pressure reading, so he couldn't know for sure how much it needed until he started filling it up. I asked about worst case and he said if it had been leaking since the last service in the fall it was possible the entire system was empty and it would be 4-5 pounds (the sticker on the unit says factory charge is 5.2 lbs, so I think he was being honest).

Based on what we were told when we bought the house, it's somewhere between 16 and 17 years old. The compressor is a Carrier 38YRA018 which is 12 seer. I think it's 1.5 tons / 18,000 BTU and he said it was a pretty decent system for the time. The air handler is a FK4DNF002 with a 5kw backup electric coil which has been enough even with the weather in the teens overnight. He said a comparable replacement would probably be in the $5-6,000 range installed and be a 15-16 seer unit. He also said they have advanced units that use an android powered thermostat with a bunch of sensors that balance the compressor, fan over 30 speeds, but those are well north of $10k, but probably won't be worth the difference for the size system we have. I'll have to wait until Monday or Tuesday to get some quotes. I'm tempted to look at a gas furnace since electricity is pretty expensive here, but I'm not sure the payback will make sense since we'd need to deal with running a gas line and adding venting upstairs. Fortunately we have a separate downstairs gas furnace that we can turn up a little to help keep the electric costs down while we wait for estimates.
 

Last edited by JAHMD; 02-15-20 at 12:58 PM.
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Old 02-15-20, 01:25 PM
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Those high eff inverter type systems are very problematic.30 fan speeds probably and the compresser is variable too.. I would stay away..

If your duct work is sized correct go with a 2 stage system.. youll be happy you did.. better humidity control..

Where are you located?

Leave it on eff.. I tried the comfort setting on mine and it didnt work well..
 
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Old 02-15-20, 02:36 PM
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Im in Maryland outside of DC.

I think we would benefit from a two stage system to help control humidity in the summer. We added some insulation and afterwards we were getting shorter run times when it wasnt too hot.

The efficiency setting right now doesnt matter since were running on backup only (fan speed is fixed when using the coils). I think the technician adjusted it to lower fan noise (the blower was in bad shape), but if we get a new system then we will keep it in efficiency mode.
 

Last edited by JAHMD; 02-15-20 at 03:00 PM.
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Old 02-19-20, 01:07 PM
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Not sure if I should start a new thread or not, but I've got a few quotes on replacement and was hoping for some advice on the different options or if the quotes were way out of line / had red-flags.

Everyone has suggested I stay with Carrier/Bryant given they make an air handler that works for my space constraints and will fit the existing ducting. They've also all said my existing duct work is more than enough for a 2-ton unit. All the quotes include reusing coolant lines (after flushing/testing). They all include a new line filter drier, condenser pad, exterior fuse/disconnect. They all include separate trips for removal and installation so I can have the knee-wall properly air-sealed between removal and installation. First company claims a two-stage and fully variable unit will meet requirements for a $300 federal tax credit, but it's not included in these quotes. Second company didn't mention it, but I assume it would apply to their two-stage system as well.

Company A - 10 Year warranty on equipment / 5 Year labor:
  • Single Stage 1.5 Ton Carrier Comfort 25HCE418A003 and FB4CNF024L00 airhandler : $6,230
  • Two Stage 2 ton Carrier Performance 25HCB624A003 and FV4CNF002L00 airhandler : $7,255
  • Five Stage 2 ton Carrier Infinity 25VNA825A003 and FE4ANF002L00 airhandler: $8,228
  • Variable Stage 2 ton Carrier Infinity 25VNA024 and FE4ANF002L00 airhandler: $8,879

Company B - 10 Year warranty on equipment / 2 Year labor. Additionally these these include a UV light in the air handler (maybe not necessary if I am able to properly air seal) plus adding one supply vent in the room with the knee-wall.
  • Single Stage 1.5 Ton Bryant 225BNA018 and FV4CNF002L airhandler: $7,183 (doesn't make sense)
  • Two Stage 2 ton Bryant 226ANA024 and FV4CNF002L airhandler: $7,274

If the tax credit information is correct, it's about a $700 difference to move up to a 2-stage system. Now that I think about it, a 2-ton unit operating in low stage is going to be similar to the 1.5 ton system I had. That means the main benefit will be the extra capacity in the winter - I'd use less auxiliary on the colder nights and it would be able to recover if I wanted to set it back while sleeping for comfort.

It looks like these air-handlers have a lower speed to help control humidity, but if I want to benefit from better humidity control, presumably I'd need to move to the 5-stage or fully variable so it could run at a lower capacity than my current unit. Does anyone have experience with their reliability? The estimator says he gets fewer maintenance calls on the inverter based compressors and the technology has been well proven in mini-split systems. He didn't seem to think moving to fully variable from the 5-stage unit would make a huge difference. We plan to be in the house for the life of the unit.

Appreciate any advice.
 

Last edited by JAHMD; 02-19-20 at 02:37 PM. Reason: update for humidity
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Old 02-19-20, 04:03 PM
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The estimator says he gets fewer maintenance calls on the inverter based compressors and the technology has been well proven in mini-split systems.
hes telling lies to you.

Inverters are communicating, t stat and all. if You have issue and get tired of the breakdowns. Tech cant fix. He changes t stat and turns your inverter system to a regular staging unit. so all the extra money spent is wasted.

That bryant has a $700 t stat. Ask if they are putting that in.. And if that t stat breaks where are you going to get one? I prefer honeywell as if mine breaks I can just go out and get a 2 stage stat and fix myself..

I have a honeywell t6 pro..

anyway the bryant is a good unit. Ill look at carrier later. not a fan.

https://refripartes.com.do/uploads/F...n%20Manual.pdf

page 7 and like my tempstar a 2 stage system will dehumidify well. I have 2 ton here in myrtle beach and I run low and slow all summer. never go to 2nd stage. My humidity hovers around 43%.

Now if you have humid issues you get a t stat with a humidistat and wire it to the dehumid terminal in the air handler. on a call for dehumid it will slow the fan speed to get more moisture out.I have this feature but dont use it.

Your best installing a seperate whole house 90 pint a day dehumidifier for the rainy days and shoulder seasons when no call for cooling if you have issues..
 
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Old 02-19-20, 04:14 PM
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My subjective impression is the Aux heat has been kicking in a bit more than previously
I have my t stat set so my aux heat never comes on. dont need it. I have the drrop set 10 degrees. Now if it did get cold I would change that setting to 3 degrees say. so if the heat pump cannot keep up then the strips will kick on when the t stat drops 3 degrees below set point. but thats just me.
 
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Old 02-19-20, 04:27 PM
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problem with the bryant is the t stat as I stated. Ask what they are putting in. needs an additional modual and I belive it communicates with the outdoor unit. again IMO problematic. A simple ecobee with humidistat will do all you want.. Maybe save you some $$$... $700 bucks for a tstat... ha ha ha.. crazy man..
 
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Old 02-19-20, 06:15 PM
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Thanks for the input.

I believe the Bryant is their lower end two-stage unit in the "preferred" series. I think the "evolution" comes with the fancy thermostat you mentioned and looks to be slightly quieter. The manual for this unit says it has humidity control when used with the "housewise" thermostat which is the same as the Carrier Cor (~$200).

The two stage Carrier quoted from company A was the equivalent of the "evolution" series.

If I get a two stage system, I was planning on using an existing Ecobee. I'm clarifying with the installer if that can take advantage of the variable speed blower to control de-humification. I use portable dehumidifiers in the basement in the summer, but we still have some issues upstairs. Moving to a whole home system might be tricky because our house has two systems (AC with gas furnace for the basement and first floor and a heat pump for upstairs). I mention humidity since the low stage on the two-stage unit should be similar to our current 1.5 ton unit and we had some humidity issues last summer when it was only moderately hot.

Your overall responses make it seem like Company B might be better. They didn't quote an inverter model and they don't seem to be pushing me for more than I need.
 
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Old 02-19-20, 06:50 PM
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To clarify, the Bryant quotes do not include a thermostat (I have an existing ecobee). The two non-inverter carrier units come with a carrier tc-php01 which is a standard programmable thermostat with a touch screen. Ill ask to use my own thermostat which will probably knock a small amount off the price.
 
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Old 02-19-20, 07:48 PM
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They are all evolutions I believe. The packaged units are the preferred from what I see.

https://www.bryant.com/en/us/products/spp/

Ahhh I see now.., ok..

https://www.bryant.com/en/us/products/spp/
 
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Old 02-19-20, 08:02 PM
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#2 here on the ecobee. To the dehumidify terminal on the air handler.

https://www.ecobee.com/2010/07/ecobe...umidification/
 
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Old 02-19-20, 08:31 PM
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and when it gets hot out call them back to check charge and subcooling gets set to 11f on this unit. They will know when you ask them.

https://dms.hvacpartners.com/docs/10...PDS226A-01.pdf

Also what size return and supplied do you have now? This is a 700 cfm system. make sure they check static pressures and chose your filter wisly. Those pleated ones are very restrictive. They should be changed monthly.

I use poly purolators.. no fiberglass for these lungs..

https://www.purolatorairfilters.com/p312

 
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Old 02-19-20, 08:36 PM
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Old 02-20-20, 09:33 AM
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Thanks.

The standard split heat pumps are here: https://www.bryant.com/en/us/products/heat-pumps/
The two-stage units are the the 226A (Preferred) vs the 226B (Evolution). I believe the difference is the sound proofing and possibly an extra controller to support any special control offered by the $700 thermostat.

I looked at the air handler manual as you suggested and it looks like it only support 4 fan-speeds for A/C operation (low stage normal, low stage dehumid, high stage normal, high stage dehumid) and the Ecobee can work with that as in the link you provided. While the Bryant thermostat might control when dehumid mode is on differently than the Ecobee, I don't see how it would do anything functionally different. Perhaps the "Evolution" model can be paired with a different Air Handler.

I see the part in the manual where it says the subcooling needs to be set to 11f. I assume from your comment that this cannot be tested in the winter / heating mode, so I should make sure it's tested in the spring.

This unit should use the same odd size filter (16.5 x 21.5 x 1) that our current unit uses. We have a metal washable electrostatic filter (looks something like this: https://neverbuyanotherfilter.com/pr...furnace-filter), and a blue hog-hair one we put in temporarily when washing the metal one. The guy who came out for the quote mentioned they could build an insert so that we could use standard size disposable filters if we prefer.

Airflow hasn't been a problem with our current system and all the estimators said the ducts should be fine with a two ton unit. It looks like my current air handler is running at 625cfm when it's only using the electric coils. We have two returns hooked up to flexible round ducts, so I'll measure the radius of each tonight to confirm (using this https://hvacdirect.com/hvac/pdf/Fiel...zing-chart.pdf). Would they do the static pressure test prior to install?
 

Last edited by JAHMD; 02-20-20 at 10:52 AM.
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Old 02-20-20, 10:42 AM
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You can get a static test now to see how your duct work stacks up. Mind you your coil may be dirty from the years.

basicall after unit is installed you want a static pressure to be below .5 ... say .4

then when the filter clogs it will rise to the . 5 at the end of the month. If its a high static to begin with life of the unit will be reduced and maybe airflow issues when running 2nd stage.

min should be 14 return. Maybe get at least a 20 x 20 filter collar. Trunk line should be 12 at least.

ideally 16 return 14 supply.

the 2 stage are 2 speed fans. But will maintain cfm as long as static is not over .7. Dehumidify will slow down the fan.

if you think you need a 5 speed go for it.
 
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Old 02-20-20, 07:52 PM
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I can't easily remove the return registers, so best guess measurements by eye-balling it against the grill is that the main return is about a 12" diameter duct with a 18" x 16" register on it and the other looks like it's probably a 7" diameter duct with a 12" by 10" register. The larger return is probably only a 6 foot run (basically the length of the air handler plus 1 or 2 feet).

I can't easily tell what size the supply ducts are, but there are 4 12" x 6" registers and 2 8" x 6" registers. We also plan to add one more small supply on the wall of the knee-wall.

This is for the upstairs only (3 bedrooms / 2 bathrooms), so I think the runs are relatively short. The manual of my current unit says the fan runs at 625 cfm with the resistive heating. You can definitely hear air moving through the main return, but rest of the system is pretty quiet and not very noticeable unless you are listening for it or it's night time and quiet in the house.
 
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Old 02-24-20, 10:51 AM
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Can someone verify if my math makes sense?

My current air handler with a 1.5 ton unit is running 525CFM in cooling or non-aux heating modes and 625CFM when the aux coils are on (what it's been running at the last week). The main return is the loudest part of our system and while I can tell the difference between the two, the higher fan speed is neither dramatically louder or loud enough to bother anyone. This makes me assume (maybe incorrectly) current static pressure levels aren't too bad.

These new air-handler when setup for 2 tons will run at 700CFM for stage 2 cooling/ heating and 725 when Aux coils are on. For the stage 2, that's 12% higher CFM than I'm running right now which should translate to 25-26% higher static pressure (~35% for Aux heat). That doesn't seem trivial.

The new air-handler when set to the low fan speed jumper will run at 630CFM for stage 2 cooling/heating and 650CFM when the Aux coils are on. For stage 2 that's only 0.8% higher CFM which should translate to 1.6% higher static pressure (8% when Aux coils are on) which doesn't seem likely to have a huge impact.

Both contractors have suggested that if there are any static pressure issues, running the new air handler in low is going to be better than trying to redo duct work and should be fine (both with the existing duct work and the operation of the unit). This seems to check out based on the math above.

I think the main return could be enlarged without being terribly destructive (I think it would mostly require removing insulation which I'm getting re-done anyone). I know you can't have too much return, but no one seems particularly interested in doing it and it's not clear I have a problem. The main reason I'm asking is because doing this now while the air handler is out and I'm getting the insulation redone anyway would be easier than doing it later (which will require removal of the air handler and re-insulating).
 
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