Optimizing operation of heat pump for efficiency

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mooch91

Member
Jan 3, 2021
30
NJ
Hi all,

The perfect storm of a new whole-house heat pump system, installation of an energy monitor and rising electric prices has me really trying to dial in the operation of my new heat pump for maximum efficiency.

Long story short, I moved from a 5-ton 16-SEER two-stage heat pump (Nordyne, 14 years old) to a 5-ton 17-SEER non-communicating variable-speed inverter heat pump (GE Connect = Gree Flexx = Mr. Cool). For a variety of reasons, including supply chain availability and contractor workmanship, it was not a great experience.

The new system has not been as efficient as I would have expected.

I've had to resolve a number of issues on my own, particularly with the controls of the system. Part of the limitation I had with the new system was an existing zoning configuration (two zones managed with a pneumatic control panel). I think I've got it operating well, but I'm looking to see if there are other considerations for optimizing energy efficiency.

Some specific questions I had:
  • I know that setbacks on a heat pump system are not recommended, particularly when resistance (backup) heat is involved. Let's assume I have no need for resistance heat, and it stays locked out, is it still more favorable to keep the temperature set at a constant value day and night, or will a couple of degree setback at night be more efficient? I've been trying to test this with the energy meter, but there are too many variables (heating degree days, efficiency changes with temperature, etc.) to confirm if one is a better option than the other.
  • My ducts are reasonably well insulated and most are within the conditioned space. Due to some static pressure issues I was having, I have a small bypass in the unconditioned (58-62 degree) basement in the form of two vents on the supply line and one vent cut in to the return. I don't like this, but it was the only way my contractor could offer to resolve the static pressure issues. I'm wondering how much efficiency I'm losing by pulling in cold basement air in to the system, and if I should be looking to an alternate contractor to look at ductwork modifications to allow me to close up the basement bypass.
  • My thermostats allow for a "circulate" function on the air handler fan. I can set a % of an hour that the fan will be expected to remain on. Should I use it? I would normally say "yes", except for the situation I mention above where I'm drawing in cooler air from the basement via the bypass when the system is on.
  • I keep my temperature a little lower than I like - 67 vs. say a more ideal 68-70. I've also seen estimates of 1% improvement in energy efficiency for every degree lower on the thermostat. This seems awfully low to me. Any real-world experience of how much difference the temperature setpoint can actually make?
  • Any other thoughts or ideas I should consider for some efficiency improvements?
Thanks in advance for any discussion.
 

gthomas785

Minister of Fire
Feb 8, 2020
865
Central MA
The difference between 16 seer and 17 seer is pretty small. The vents in your basement are definitely your biggest issue of the ones you described. You can try just adding a duct connecting the two in a pinch.

The savings you get by adjusting the thermostat directly depends on what the outside temperature is. If it's 50 out and your thermostat is 60, a 1 degree adjustment would be a 10% change in heating demand. But if it's 0 out and your thermostat is at 70, 1 degree would only be a 1.4% difference
 

Highbeam

Minister of Fire
Dec 28, 2006
20,382
Mt. Rainier Foothills, WA
The difference between 16 seer and 17 seer is pretty small. The vents in your basement are definitely your biggest issue of the ones you described. You can try just adding a duct connecting the two in a pinch.

The savings you get by adjusting the thermostat directly depends on what the outside temperature is. If it's 50 out and your thermostat is 60, a 1 degree adjustment would be a 10% change in heating demand. But if it's 0 out and your thermostat is at 70, 1 degree would only be a 1.4% difference
So you think heat demand is linear? Based on a Fahrenheit scale?
 

gthomas785

Minister of Fire
Feb 8, 2020
865
Central MA
So you think heat demand is linear? Based on a Fahrenheit scale?
Yes, based on delta T.
On any temperature scale
(Edit: yes there may be some nonlinear effects due to different humidity, air convection etc but the overall R factor of a house is usually pretty constant).
 
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mooch91

Member
Jan 3, 2021
30
NJ
Thanks so far.

Yea, I'd rather not be sucking in any basement air, but for some reason this system has had a static pressure issue that the old one did not (though honestly the old system may have had issues I just never recognized). This unit is a single-stage air handler, while the old one was two-stage (worked better with the zoning system, would run at slower speed when only one zone was open). If I don't leave the vent on the return in the basement open, on occasion the fan will stop with a fault.

I've been trying to understand the staging on the heat pump itself. Though this is a variable speed inverter compressor, it does not operate like what I'm used to with a mini-split (speed matched to load). I've read a lot about the Bosch IDS heat pumps which are similar non-communicating ducted systems and they appear to modulate to control a coil temperature. I don't believe the brand I have does that; instead, it seems to just stage up progressively over time. It ramps up over about 20-25 minutes until it's operating at full speed and drawing 7 kW. I've never seen it modulate down. It gets great temperature differentials - I've seen 42 degrees differential on 20 degree days - but it seems to be just gobbling up the electricity to do so.

A couple of other efficiency questions I had:
  • I'm using the default "medium" cycles per hour on the thermostat. I've contemplated changing it to "slow" - fewer cycles per hour - but knowing that might just keep the compressor at its max speed (and power consumption) longer, I wasn't sure if that would be a benefit.
  • I have three devices in my system which all have "compressor protection" - my thermostat, my zone panel, and the compressor itself. That is, they will not allow the compressor to short cycle if it's been running within the last few minutes. What this results in are more periods of time where the indoor fan is running and the outdoor unit is not. Indoor fan draws about 500-600 watts, which isn't a huge consumption, but I wonder if all of the safeties are necessary and if I'd see any efficiency by letting the compressor manage its own protection.
 

spuldup

Member
Nov 1, 2022
174
16137
Can you elaborate on the static pressure issues? Is sounds like the system static is higher than the rated static of the furnace, so they just opened some holes closer to the furnace.

The best fix is upsizing the ductwork, but since that's very costly and destructive, another solution is a duct booster fan.
 

EbS-P

Minister of Fire
Jan 19, 2019
4,488
SE North Carolina
The difference between 16 seer and 17 seer is pretty small. The vents in your basement are definitely your biggest issue of the ones you described. You can try just adding a duct connecting the two in a pinch.

The savings you get by adjusting the thermostat directly depends on what the outside temperature is. If it's 50 out and your thermostat is 60, a 1 degree adjustment would be a 10% change in heating demand. But if it's 0 out and your thermostat is at 70, 1 degree would only be a 1.4% difference
Are we taking SEER or SEER2. The difference is probably negligible on your electric bill 16 to 17 and probably any improvements are in the realm of being on the order of losses for high static pressure.

Your heat load depends on heat loss which does depends on the temp difference and it’s probably not linear. Set back is fine as long as heat-strips don’t turn on.

But remember your efficiency depends greatly on outside temperatures. I know I loose 20% efficiency at 32 vs 45 outside. Likewise I gain a lot of efficiency above 52 degrees outside.

So my setback routine depends on the outside temperature. It must manually adjusted so I don’t kick on my heat strips. I will overheat the house when it’s warmer outside , think thermal battery, and let it cool down to 66 at night not turning the thermostat back up until it’s warmed up enough outside.

What kind of filter are you using? How many heated/cooled sq ft?
 

mooch91

Member
Jan 3, 2021
30
NJ
Can you elaborate on the static pressure issues? Is sounds like the system static is higher than the rated static of the furnace, so they just opened some holes closer to the furnace.

The best fix is upsizing the ductwork, but since that's very costly and destructive, another solution is a duct booster fan.

Yes - thanks for asking. This is a place where I could use any advice. I am not in the industry, but I am an engineer who has needed to learn quite a bit about static pressure as multiple companies, install techs, service techs, and sales folks have hardly recognized the potential that I had an issue. In their defense, they were replacing a 5-ton system that would have appeared to operate correctly with a same capacity unit, so there probably wasn't much to tip them off.

Details of the system: 5-ton (target 2000 cfm air flow), high ESP (up to 1.0"WC) air handler.

First issue I had was soon after startup. I had installed a standard pleated filter in the 1" slot beneath the air handler. Same filter (think it was MERV 8, nothing crazy) I had been using on the old system. At that point, I noticed really low airflow from the vents in the house. The filter was getting drawn very tightly against the drain pain of the coil as well.

Contractor recommended using a lower restriction spun fiberglass filter instead. I installed and situation improved, and I also became aware of the speed settings on the motor which could be adjusted to match ESP. Contractor had not made any setting changes to the system. Bought myself an inexpensive manometer and began measuring total external static pressure (made all the proper considerations for where to measure and filter in/out of system). My measurements showed moderate static (0.4-0.5"WC) but very low flow. I was seeing 1400 cfm with both zones open, and flow would drop to 1200-1300 cfm with only a single zone calling. Again, this is a 5-ton system where I was expecting closer to 2000 cfm of flow. So I bumped it up near the upper end of the static range (0-7-0.8"WC) and flow was better, nearing 1900 cfm with both zones calling, 1700-1800 with only a single zone calling.

Things ran well for a month, then one morning I heard compressor running but no fan. Pulled the cover on the air handler to find the indoor fan flashing a generic fault code. Contractor came back out, said yep must be high static, and cut the single 8x10 (or so) register in to the return line in the basement.

I've since tried sealing the vent and have had the blower motor trip off again. Funny thing is, it runs well for a month or so, then just suddenly has an issue. Breaker reset always brings it back to life. I'm sure the fact that I'm seeing 40 degree temperature differential at times (leaving air temp of 108 degrees) doesn't help with keeping the fan cool at higher static operation.

I've remeasured and readjusted pressures and airflow. Right now I'm operating in the 0.6-0.7"WC range, and I'm getting 1800 cfm with both zones calling and 1500-1600 cfm with only a single zone. My feeling has been this is "close enough" and a decent compromise, but again, it's relying on having the supply and return to the basement both open, creating the bypass.

dimensions.jpg IMG_0210.jpg
 

mooch91

Member
Jan 3, 2021
30
NJ
Are we taking SEER or SEER2. The difference is probably negligible on your electric bill 16 to 17 and probably any improvements are in the realm of being on the order of losses for high static pressure.

Your heat load depends on heat loss which does depends on the temp difference and it’s probably not linear. Set back is fine as long as heat-strips don’t turn on.

But remember your efficiency depends greatly on outside temperatures. I know I loose 20% efficiency at 32 vs 45 outside. Likewise I gain a lot of efficiency above 52 degrees outside.

So my setback routine depends on the outside temperature. It must manually adjusted so I don’t kick on my heat strips. I will overheat the house when it’s warmer outside , think thermal battery, and let it cool down to 66 at night not turning the thermostat back up until it’s warmed up enough outside.

What kind of filter are you using? How many heated/cooled sq ft?
Thanks. Some details in the reply I just posted.

House is about 3300 sq ft in central PA (zone 5). I have heat strips completely locked out in the controls; never use them, don't have a need even when we are at 1 deg F.

Being a variable speed inverter heat pump, it is supposed to have good performance down to lower temperatures, at least better than the two-stage system it replaced.

Included performance charts if that helps.

1675257963523.png
 

gthomas785

Minister of Fire
Feb 8, 2020
865
Central MA
What size and MERV filter are you using?
Edit: nevermind, already answered and I missed it
 
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EbS-P

Minister of Fire
Jan 19, 2019
4,488
SE North Carolina
How is the zone controller connected? is it calling second stage whenever the second zone calls for heat?

Is the system configureable between 4 and 5 tons?

I’m guessing you are over sized for cooling. What is the first stage heating and cooling output? Was a manual J done when it was installed?

I have spent a lot of time learning about heatpumps this year. What I’ve leaned. Many or most contractors won’t do a load calc on a system change out. They ask “were there any problems”. You say no it seemed fine. Most ductwork is undersized and equipment oversized. This all is not as evident during heating season because we love the really hot air coming out of the vents. Come cooling season however the the over sized unit does a poor job at dehumidifying and short cycles can be more apparent.

Can you confirm that this has a two stage compressor with a variable speed blower?
 
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spuldup

Member
Nov 1, 2022
174
16137
You are getting a lot of details from others so I'll just add that you are correct in your suspicion of the vents in the basement. The supply is marginally acceptable, but return air should never be taken from a basement.
 

woodgeek

Minister of Fire
Jan 27, 2008
5,082
SE PA
Did you tell us how big the return (and thus 1" filter) is?

When I had a 4 ton ASHP system put in the yokel installer put in a too small return with a see through floss filter, and told met to avoid pleated filters bc they 'had too much resistance'.

That return was loud as heck, would whistle even at full flow. The return was louder in the house than the handler in the attic.

I looked up the specs and there is a minimum return area per ton (or cfm), that his return was about 30% under.

I called on him to upsize the return (requiring him to build a new custom plenum), and withheld my final payment. He asserted that this was the return size that he always installed on 4 ton systems. I showed him the engineering spec docs, and he relented. He build a sturdy but leaky plenum from sheet metal, and I paid him. And then I airsealed his plenum. This is what you get with the low bid, I suppose.

My new return corresponds to the largest retail 1" filter size, 24x30" IIRC. It is still quite loud. And it is just at the engineering minimum, and I think my system runs at 1500 or 1600 cfm.

Given the above, I don't think it is possible to have a single return serve a 5 ton unit and be in spec for cfm/sqft. It would need to be 30" by 30" or larger.

So my guess is that your previous system had a too small return and plenum. And so your new system does too.

So even though new units are designed to work with 1" filters (they really are, and the high MERV filters from 3M are now lower friction than old MERV 8 filters)... if your return area is too small due to install/design defect... then THAT is your problem.

Give us some details on your return.
 

mooch91

Member
Jan 3, 2021
30
NJ
How is the zone controller connected? is it calling second stage whenever the second zone calls for heat?

Is the system configureable between 4 and 5 tons?

I’m guessing you are over sized for cooling. What is the first stage heating and cooling output? Was a manual J done when it was installed?

I have spent a lot of time learning about heatpumps this year. What I’ve leaned. Many or most contractors won’t do a load calc on a system change out. They ask “were there any problems”. You say no it seemed fine. Most ductwork is undersized and equipment oversized. This all is not as evident during heating season because we love the really hot air coming out of the vents. Come cooling season however the the over sized unit does a poor job at dehumidifying and short cycles can be more apparent.

Can you confirm that this has a two stage compressor with a variable speed blower?

Answers to some of the questions above:

Unit is variable speed compressor with single stage blower. It's non-communicating, so it uses traditional thermostat connections and has a logic built in to the condensing unit to vary the speed based upon temperatures and pressures.

Unit replaced a two-stage compressor and two-stage blower. Same capacity, 5 ton.

Yes, the system is configurable between 4 and 5 ton with a dip switch setting in the condensing unit

Manual J was not done. As you mentioned - the only thing asked was "did the old unit work well?". I've since run some alternative calculations (using Cool Calc software) and have come up with a range of 52,000 - 58,000 heating load, depending on some of the assumptions I use (there are some details of construction for which I can't be entirely sure).

Thanks.

Edit, added: Zone controller just manages the calls from the two zone thermostats. It can stage up both the compressor and air handler, but is not currently configured to do so since the compressor varies on its own and there is no staging to the air handler. It's kind of dumbed down to just manage and prioritize the zone calls at this point.
 
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mooch91

Member
Jan 3, 2021
30
NJ
Did you tell us how big the return (and thus 1" filter) is?

When I had a 4 ton ASHP system put in the yokel installer put in a too small return with a see through floss filter, and told met to avoid pleated filters bc they 'had too much resistance'.

That return was loud as heck, would whistle even at full flow. The return was louder in the house than the handler in the attic.

I looked up the specs and there is a minimum return area per ton (or cfm), that his return was about 30% under.

I called on him to upsize the return (requiring him to build a new custom plenum), and withheld my final payment. He asserted that this was the return size that he always installed on 4 ton systems. I showed him the engineering spec docs, and he relented. He build a sturdy but leaky plenum from sheet metal, and I paid him. And then I airsealed his plenum. This is what you get with the low bid, I suppose.

My new return corresponds to the largest retail 1" filter size, 24x30" IIRC. It is still quite loud. And it is just at the engineering minimum, and I think my system runs at 1500 or 1600 cfm.

Given the above, I don't think it is possible to have a single return serve a 5 ton unit and be in spec for cfm/sqft. It would need to be 30" by 30" or larger.

So my guess is that your previous system had a too small return and plenum. And so your new system does too.

So even though new units are designed to work with 1" filters (they really are, and the high MERV filters from 3M are now lower friction than old MERV 8 filters)... if your return area is too small due to install/design defect... then THAT is your problem.

Give us some details on your return.
Some answers to these questions:

Dimensions of everything are on one of the images above. The angles represent length, width, and depth. I am guessing the return drop is undersized for 5-ton (2000 cfm) flow. It's about 27x12, and that's duct-board, so I think inner dimensions take at least an inch off the exterior dimensions. With the trunk lines being of similar size, I'm not certain if upsizing the drops and plenum around the air handler will help, but I'm no expert for sure.

The filter is about a 23x20, but since it sits right at the opening to the drain pain of the coil, it's effectively filtering through a 20x20 area. I've since learned that the 1" filter openings are also not necessarily appropriate for good filtration; external filters should always be considered.

Thanks.
 

woodgeek

Minister of Fire
Jan 27, 2008
5,082
SE PA
Some answers to these questions:

Dimensions of everything are on one of the images above. The angles represent length, width, and depth. I am guessing the return drop is undersized for 5-ton (2000 cfm) flow. It's about 27x12, and that's duct-board, so I think inner dimensions take at least an inch off the exterior dimensions. With the trunk lines being of similar size, I'm not certain if upsizing the drops and plenum around the air handler will help, but I'm no expert for sure.

The filter is about a 23x20, but since it sits right at the opening to the drain pain of the coil, it's effectively filtering through a 20x20 area. I've since learned that the 1" filter openings are also not necessarily appropriate for good filtration; external filters should always be considered.

Thanks.

OK. I think your duct system is designed for higher pressure (thus your high SP blower) than conventional, so your duct trunks are a bit smaller than mine (a 4 ton system).

I won't say that's a problem, just different.

But you can google up the specs on pleated filters (like the 3M filtrete) regarding max cfm, and expected static pressure at max cfm. Then you can either use them with that arrangement (use the working area of the filter if it is smaller due to install), or not. And you can decide if the static pressure is too high for the blower, or not.

My low SP blower has no problems with MERV 11 filtretes, so it would be ironic if your high SP blower can't handle them. These were engineered to be lower SP than older pleated filters with poorer filtration.

I have the filter holder on the entrance to a single central return (a common retrofit configuration).... I don't have returns in many rooms. I like this bc it means I am not collecting dust anywhere in my ductwork. It all looks shiny and clean inside when I look, after 15 years in service.

If you have only 1 or 2 returns, you might consider installing filter holders there? If you wanted MERV11 or near HEPA whole house filtration.
 

gthomas785

Minister of Fire
Feb 8, 2020
865
Central MA
Definitely agree with what woodgeek is saying, but if your system as-installed is having airflow issues then I do think it's worth trying a less restrictive filter. Anyway the filter isn't meant to fully clean the air, just protect the blower/coil from dust which you can do with a MERV 2. If you want higher level of filtration for health reasons, then you can get get a standalone air purifier or do the necessary duct work to make your system happy with the higher filtration level.
 
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EbS-P

Minister of Fire
Jan 19, 2019
4,488
SE North Carolina
Answers to some of the questions above:

Unit is variable speed compressor with single stage blower. It's non-communicating, so it uses traditional thermostat connections and has a logic built in to the condensing unit to vary the speed based upon temperatures and pressures.

Unit replaced a two-stage compressor and two-stage blower. Same capacity, 5 ton.

Yes, the system is configurable between 4 and 5 ton with a dip switch setting in the condensing unit

Manual J was not done. As you mentioned - the only thing asked was "did the old unit work well?". I've since run some alternative calculations (using Cool Calc software) and have come up with a range of 52,000 - 58,000 heating load, depending on some of the assumptions I use (there are some details of construction for which I can't be entirely sure).

Thanks.
Is the zone controller tied to the system in any way? Running with out a call from the second zone(damper closed) will definitely increase static pressure.

Other than adding more supply vents and returns in the upstairs you seem to have done as much as you can.

Back to the question of efficiency. Im wondering if it would be more efficient to run it at the 4 ton setting (most of the time) because according to these charts for a Mr cool 5 tons system the cop decreases with increasing output. But it’s probably splitting hairs. Keep the filters clean, clean the coils twice a year. That probably has more impacts.

267ED891-8C7B-4D4A-B2CE-2FA12E5DC866.png 6B65A635-F852-4537-9174-E7E505A0E98F.png 7A73BEFD-D3A1-42C3-97FB-1F2125251D0C.png
 

EbS-P

Minister of Fire
Jan 19, 2019
4,488
SE North Carolina
Some answers to these questions:

Dimensions of everything are on one of the images above. The angles represent length, width, and depth. I am guessing the return drop is undersized for 5-ton (2000 cfm) flow. It's about 27x12, and that's duct-board, so I think inner dimensions take at least an inch off the exterior dimensions. With the trunk lines being of similar size, I'm not certain if upsizing the drops and plenum around the air handler will help, but I'm no expert for sure.

The filter is about a 23x20, but since it sits right at the opening to the drain pain of the coil, it's effectively filtering through a 20x20 area. I've since learned that the 1" filter openings are also not necessarily appropriate for good filtration; external filters should always be considered.

Thanks.
I use a 20x30 filter for my 3 ton system. FWIW
 

mooch91

Member
Jan 3, 2021
30
NJ
Is the zone controller tied to the system in any way? Running with out a call from the second zone(damper closed) will definitely increase static pressure.

Other than adding more supply vents and returns in the upstairs you seem to have done as much as you can.

Back to the question of efficiency. Im wondering if it would be more efficient to run it at the 4 ton setting (most of the time) because according to these charts for a Mr cool 5 tons system the cop decreases with increasing output. But it’s probably splitting hairs. Keep the filters clean, clean the coils twice a year. That probably has more impacts.

View attachment 308994 View attachment 308995 View attachment 308996

The zone controller only controls pneumatic supply dampers. It opens and closes depending on which zone is calling. There is no bypass damper on the system. I've measured that static pressure is higher when only one zone is calling.

I had tried, for a very short period, running the condensing unit in 4-ton mode. But I'm not clear on exactly what it does. I was observing that the power consumption profile looked almost identical to when operating in 5-ton mode. The unit was ramping up to about 7kW of power consumed after about 20-25 minutes. And I was still measuring 40+ degree temperature differential. I would have thought the 4-ton mode would have limited compressor output, and hence required less power input, but if it did, it was marginal (couple hundred watts) at best.
 
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mooch91

Member
Jan 3, 2021
30
NJ
Definitely agree with what woodgeek is saying, but if your system as-installed is having airflow issues then I do think it's worth trying a less restrictive filter. Anyway the filter isn't meant to fully clean the air, just protect the blower/coil from dust which you can do with a MERV 2. If you want higher level of filtration for health reasons, then you can get get a standalone air purifier or do the necessary duct work to make your system happy with the higher filtration level.

I think that's where I'm at currently. The spun fiberglass are as low restriction as available, unless I use what was supplied with the unit, but I had not been very comfortable with that (see below).
Photo Sep 06, 2 32 35 PM.jpg
 

mooch91

Member
Jan 3, 2021
30
NJ
Is the zone controller tied to the system in any way? Running with out a call from the second zone(damper closed) will definitely increase static pressure.

Other than adding more supply vents and returns in the upstairs you seem to have done as much as you can.

Back to the question of efficiency. Im wondering if it would be more efficient to run it at the 4 ton setting (most of the time) because according to these charts for a Mr cool 5 tons system the cop decreases with increasing output. But it’s probably splitting hairs. Keep the filters clean, clean the coils twice a year. That probably has more impacts.

View attachment 308994 View attachment 308995 View attachment 308996

@EbS-P Can you help me understand what you were seeing in the data? Nor sure if this is the equivalent of my system, but I'd like to understand what you saw that led you to the recommendation to run in 4-ton mode. Thanks.

Edit:
I do believe this is the link to my exact system:
 
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EbS-P

Minister of Fire
Jan 19, 2019
4,488
SE North Carolina
@EbS-P Can you help me understand what you were seeing in the data? Nor sure if this is the equivalent of my system, but I'd like to understand what you saw that led you to the recommendation to run in 4-ton mode. Thanks.

Edit:
I do believe this is the link to my exact system:
I was looking at the COP. And how it changed with the the output, max, rated, min.

I’m not sure how the on board logic works but it’s probably targeting a coil temp (hopefully), while measuring return supply and whether thermostat is still calling. It may have a set ramp rate. I don’t know really. My guess that it is the simplest cheapest logic they can make function. So it’s likely that you have never needed the last ton of capacity (again just a guess). The higher static pressure may result is lower air flow which the system might not be aware of. It thinks it’s seeing 40 degree delta at 1750 cfm when it’s really getting less so if it’s running if it’s coil temp sensor it says is putting out enough heat.

All of this is just guessing if it’s not measuring coil or supply or return temps it has no way of knowing the actual heating demand and will follow its program untill the thermostat satisfies. Dampered zoning is just problematic. I am avoiding it completely with a new ductwork install.

Which circles back the to most efficient way. My guess it is to run at the lowest compressor output and fan spend at 100% duty cycle. Then if that doesn’t satisfy after X amount of time it increase the output a bit and run it for X again. But the X should be a long amount of time. Like 30 minutes or an hour. But this might not be comfortable. Especially if you use a set back routine. It would take too long to come back up to higher set temp. But if you are like me trying to eat every ounce of efficiency out I increase the thermostat 1 degree at a time to keep running on only my first stage and some my strips never kick on. (I can’t lock them out). I Think that the reduction in static pressure saves energy but it might not.

At the end of the day spending the money saved on a system like this (vs an higher end heatpump) on air sealing and insulation will give much bigger payback than trying to squeeze more efficiency out of the unit.
 

mooch91

Member
Jan 3, 2021
30
NJ
I was looking at the COP. And how it changed with the the output, max, rated, min.

I’m not sure how the on board logic works but it’s probably targeting a coil temp (hopefully), while measuring return supply and whether thermostat is still calling. It may have a set ramp rate. I don’t know really. My guess that it is the simplest cheapest logic they can make function. So it’s likely that you have never needed the last ton of capacity (again just a guess). The higher static pressure may result is lower air flow which the system might not be aware of. It thinks it’s seeing 40 degree delta at 1750 cfm when it’s really getting less so if it’s running if it’s coil temp sensor it says is putting out enough heat.

All of this is just guessing if it’s not measuring coil or supply or return temps it has no way of knowing the actual heating demand and will follow its program untill the thermostat satisfies. Dampered zoning is just problematic. I am avoiding it completely with a new ductwork install.

Which circles back the to most efficient way. My guess it is to run at the lowest compressor output and fan spend at 100% duty cycle. Then if that doesn’t satisfy after X amount of time it increase the output a bit and run it for X again. But the X should be a long amount of time. Like 30 minutes or an hour. But this might not be comfortable. Especially if you use a set back routine. It would take too long to come back up to higher set temp. But if you are like me trying to eat every ounce of efficiency out I increase the thermostat 1 degree at a time to keep running on only my first stage and some my strips never kick on. (I can’t lock them out). I Think that the reduction in static pressure saves energy but it might not.

At the end of the day spending the money saved on a system like this (vs an higher end heatpump) on air sealing and insulation will give much bigger payback than trying to squeeze more efficiency out of the unit.
Thanks @EbS-P .

What you described is what I had expected, after reading up on the strategy the Bosch IDS / BOVA units use. I would have thought control for this system were similar. But I honestly think the Gree/Mr. Cool/Gree setups don't control to a target coil temp. Or at least not one that isn't 130 degrees+ in heating. I think they strictly ramp up over time, and that ramp rate may be affected by parameters like line temps and ambient temp. I have never seen this unit modulate down; it always ramps up to what looks like max (7000W) and hold, no matter how long it then runs.

Ideally, in my opinion, it would modulate to keep a set coil temp. If it finds it has ramped too fast and overshot the coil temp, it would back off on compressor output. Similarly if air flow were low, coil temp would rise, and it would reduce compressor output. Based on my observations, this is not the way this system is designed to work.

Attached is a pretty typical power consumption curve for a setback recovery (from 65 to 67) on a 27 deg F morning. Each bar is the average kW used over 1 minute of time. Have never seen a situation where the power consumption modulated down before the setpoint was reached, regardless of how long it has run. It always plateaus at max.
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begreen

Mooderator
Staff member
Nov 18, 2005
99,726
South Puget Sound, WA
I use a 20x30 filter for my 3 ton system. FWIW
Our 3 ton HP system has 20 x 25" air filters. There is a 1" prefilter and then a 4" Merv 13 box filter. It's an Am Std. Heritage 16 system with a variable-speed DC air handler. Static pressure has never been an issue.

Mooch91, what is the air handler brand and model number? Does it have a multispeed (mulit-tap) motor and if so, what setting is it at?