AC on solar and battery. Is SEER 33 that much of a power savings?

[Porch]

I just did a bunch of measurements on my two split units as I was thinking of replacing the SEER 14 unit with a better unit. This is not an apples to apples comparison as the the Fujitsu is an older, and very basic model next to the Mitsubishi.
Watts is measures after my OutBack inverters. I am 100% off grid, so the DC draw is the really critical number and keeps me from messing with power factor math.

Fujitsu AOU9CQ SEER 14 9,700BTU
Watts are DC draw on 48 volt battery bank after Inverters.
75F air input temp.

Unit Off	11 Watts
Fan High	23 Watts
Full Cool	903 Watts
Full Heat	N/A

Mitsubishi MSZ-FH06NA SEER 33 6,000BTU
Watts are DC draw on 48 volt battery bank after Inverters.
75F air input temp.

Unit Off	14 Watts
Fan High	28 Watts
Full Cool	636 Watt
Full Heat	977 Watts*

*Unit seems to very pump output greatly when in heat mode. 1500+ Watts was noticed at times.

The Fujitsu is an older, basic model. The pump cycles between 900 watts and 700 watts, and off. It seems to only have 2 power levels.
The Mitsubishi is new top of the line model. It varies the pump speed on demand.

I am also expecting the Mitsubishi can provide more BTUs as both units air output temp is 50F (with an input of 75F). I suspect Mitsubishi slowed down it's compressor to limit the output air temp to 50F.

If you add it up, the Fujitsu is slightly more efficient at 10.7 BTUs a watt over the Mitsubishi 9.4 BTU a watt. Seems strange that the higher SEER unit is less efficient at full output, but I suspect I am missing something. Possibility the efficiency gains of the SEER 33 rating only really happen at lower speeds.

My goal of the measurements was to see if I should replace the older Fujitsu in my living room with the higher SEER Mitsubishi, but I don't see the power advantage when running at full speed, and I only run it in the day when I am home, and it's on full speed anyway.

I have the Mitsubishi in my bedroom and I run it all night. I love the heck out of this unit for the bedroom. I have measured it running as low as 60 watts just maintaining the room temp all night. That is the same amount of power the fans I was running in the room consumed before I went with an AC.

A note on the Mitsubishi FHXXNA series. The FH06NA (SEER 33) is the 6,000 BTU model. Next to a circuit board change, there is no difference between it and the FH09NA 9,000 BTU (SEER 30) model based on the spare parts catalog. The FH12NA 12,000 BTU (SEER 26) model does have a different pump in the outdoor unit, but that, and the circuit board is it.

I suspect Mitsubishi gets that high SEER 33 number out of the 6,000 BTU unit by basically running the 12,000 BTU unit at half speed, but using the same evaporator and condenser (and maybe a smaller pump). So if the if the BTUs might be needed for a larger room, the 12,000 BTU unit might be the way to go as you will likely get the max BTUs when you need it, but the SEER 33 efficiency if you set to half power.

I guess I should answer the SEER question. Does a higher SEER unit generate more BTUs per watt? At max cool, for an average home application, not that I can tell.

 

[Bob B]

I think to do an accurate comparison the 2 units would need to be the same BTU .... but it does seem a unit with over twice the seer rating should be doing a lot better than that.

 

[time2roll]

I would not change it out for efficiency alone. Especially as you have described it.
Money might be better spent on more panels or battery.

 

[Lt.Dan]

I would almost want to see the amount of energy used over a period of time, in the same environment. Do you have the possibility to run them both for 24 hours and monitor kWh used?

I'm curious if they have a vastly different SEER rating, but a relatively similar EER rating, which is causing the not so great efficiency at high output.

 

[rcrracer]

https://ashp.neep.org/#!/ has data. In effort to find 120v single phase, search: slider 0-13000BTU, 0-13000BTU, single zone non-ducted wall placement, All Brands. This should produce a quantity of 537 Heat Pumps(these may or may not be 120v). Some standouts when working at low speeds: Fujitsu 204740067, Panasonic 8860533, Haier 8862047, and Bosch 9966839 with a low seer of 20.9. That Bosch would easily outperform the 42 seer Midea 201753970. Ex. cooling COP @ 95F: Bosch 7.59 COP 3885 BTU, Midea 4.54 COP 3252 BTU. Seer number calculation methodology allows the manufacturers to game the results. It appears a person should buy two mini-splits. One designed to be used during moderate temperatures and the other for more extreme temperatures.

 

[curiouscarbon]

EER is efficiency at a constant outdoor temperature of like 100f. It’s an indicator of how many BTU per watt delivered during the most stressful season.

SEER is an average ranging from the harshest to mildest days. It’s an indicator of how many BTU per watt delivered, averaged over the season.

EER is almost always less than SEER rating.

Both EER and SEER are in units of BTU per Watt hour, if I understand correctly.

That means EER 30 is an incredible device that will deliver 30 BTU/Wh in the hot of summer.

EER 15 is a decent device that will deliver 15BTU/Wh in the hot of summer.

edit: the models used..
EER = 95f outside 80f indoor return temp 50% relative humidity
SEER = 65-104f outside (with some dips below) 80f indoor return temp 50% relative humidity

so same indoor condition but different outdoor range. hope this is helpful in some way!

ok one more thing. you can calculate the Coefficient of Performance by dividing the EER by 3.412 BTU/W. This is the measure of raw efficiency of how many units of heat per energy. So EER 15/3.412 = 4.39 COP so 4x more heat pumped than created so to speak.

 

[eXodus]

If you add it up, the Fujitsu is slightly more efficient at 10.7 BTUs a watt over the Mitsubishi 9.4 BTU a watt. Seems strange that the higher SEER unit is less efficient at full output, but I suspect I am missing something. Possibility the efficiency gains of the SEER 33 rating only really happen at lower speeds.

Correct observation.

How often do you need full power? When you are not in a super hot climate - you only need full power a handful (20-60 / 365) of days in the year - every day other of the year the higher SEER unit is more efficient.

You can optimize a single speed units efficiency at peak performance - balance all components - while a variable speed inverter - has a sweet-spot somewhere below max capacity where it's usually hanging out 80% + of it's life


A inverter unit is most efficient when it runs all day long - when I'm gauging the HVAC trade talks correctly - for inverter you probably have to size systems differently.

All those sizing charts had been designed for single speed units - which is not moving a lot of heat for the first 1-2 minutes runtime until the pressure reached operating conditions and the coils got to temperature. So - meaning for the same amount of power you are getting a lot more "REAL BTU" in a inverter compared with a single speed.

I've replace a old 30.000 BTU ton single speed unit with 20.000 BTU Inverter unit in a house in Florida - and it's actually cooling better. It gets the humidity lower and the temperature. (Sure the old system was on it's last leg)

 

[Porch]

I would almost want to see the amount of energy used over a period of time, in the same environment. Do you have the possibility to run them both for 24 hours and monitor kWh used?

I'm curious if they have a vastly different SEER rating, but a relatively similar EER rating, which is causing the not so great efficiency at high output.

The two units are in different rooms, so the kWh would be different.
The Fujitsu has an SEER of 14.3, and an EER of 11.8.
The Mitsubishi has an SEER of 33.1, and an EER of 19.1

 

[Porch]

Manufactures SEER rating are good in all, but I was hoping to see real world, measurable numbers. Something that is lacking everyplace I look. All I can find is more SEER, more efficient. Nothing that I can find that says you will save X Kwh more with a SEER 33 over a SEER 18.

 

[Porch]

https://ashp.neep.org/#!/ has data. In effort to find 120v single phase, search: slider 0-13000BTU, 0-13000BTU, single zone non-ducted wall placement, All Brands. This should produce a quantity of 537 Heat Pumps(these may or may not be 120v). Some standouts when working at low speeds: Fujitsu 204740067, Panasonic 8860533, Haier 8862047, and Bosch 9966839 with a low seer of 20.9. That Bosch would easily outperform the 42 seer Midea 201753970. Ex. cooling COP @ 95F: Bosch 7.59 COP 3885 BTU, Midea 4.54 COP 3252 BTU. Seer number calculation methodology allows the manufacturers to game the results. It appears a person should buy two mini-splits. One designed to be used during moderate temperatures and the other for more extreme temperatures.

So you may have just solved the riddle.

ASHP

ashp.neep.org

The Mitsubishi list a range of BTUs. 6,000 BTU is the average, but the MAX is 9,000+ BTUs (at about 600 watts).
The Fujitsu just list 9,700 BTUs. I can't find anything showing it can put out more, but being an older model, maybe it's just not documented?

So making more assumptions,
Fujitsu still makes 10.7 BTU a watt.
Mitsubishi now makes 14.15 BTU a watt.

Not being an AC guy, I am not sure why the manufactures will rate a unit at 6,000 BTU, but it can produce 9,000 BTUs. Maybe the 9,000 BTU numbers is before the condenser becomes too hot and the cooling performance drops?

 

[curiouscarbon]

if you can estimate how many BTU/year you need pumped them comparing EER/SEER to calculate kWh savings is a single multiplication right?

 

[Porch]

if you can estimate how many BTU/year you need pumped them comparing EER/SEER to calculate kWh savings is a single multiplication right?

If you know that BTU/year number. I sure don't.

 

[curiouscarbon]

me too i would have to calculate how many hours of runtime over the year and multiply by the rating if my unit, and keep track of it it’s in first or second stage….

 

[rcrracer]

So you may have just solved the riddle.

ASHP

ashp.neep.org

The Mitsubishi list a range of BTUs. 6,000 BTU is the average, but the MAX is 9,000+ BTUs (at about 600 watts).
The Fujitsu just list 9,700 BTUs. I can't find anything showing it can put out more, but being an older model, maybe it's just not documented?

So making more assumptions,
Fujitsu still makes 10.7 BTU a watt.
Mitsubishi now makes 14.15 BTU a watt.

Not being an AC guy, I am not sure why the manufactures will rate a unit at 6,000 BTU, but it can produce 9,000 BTUs. Maybe the 9,000 BTU numbers is before the condenser becomes too hot and the cooling performance drops?

You seem to have https://ashp.neep.org/#!/product/34476. It appears to be identical to https://ashp.neep.org/#!/product/34468. Same SEER and EER. Look at the COP at 17 F and 5 F. Your model is far superior. It appears SEER, EER, HSPF are irrelevant at temperature extremes. It's questionable if they are relevant at any temperature. HSPF difference between those two models is 0.7%(?). COP difference at 17 F of 71%(?). Down to 47 F there is no difference in the COP. Let's say every model from every manufacturer functions just like these two(not even close to true statement). It might be a good idea to determine how much time is spent more than 28 F (47 F) below a set temperature of 75 F. https://www.degreedays.net/ set the base temp at 47 F and let it calculate the heating degree days. Download the spreadsheet. Or for averages https://www.greencastonline.com/tools/soil-temperature. Or Wundermap https://www.wunderground.com/dashboard/pws/KFLJACKS3451/graph/2021-07-9/2021-07-9/monthly The Calculation methodology: https://www.aceee.org/files/proceedings/2004/data/papers/SS04_Panel1_Paper08.pdf More calculation stuff: http://www.fsec.ucf.edu/en/publications/html/fsec-pf-413-04/ I'm not an AC guy either. Nothing to sell. No agenda other than saving electricity.

 

[Bob B]

You seem to have https://ashp.neep.org/#!/product/34476. It appears to be identical to https://ashp.neep.org/#!/product/34468. Same SEER and EER. Look at the COP at 17 F and 5 F. Your model is far superior. It appears SEER, EER, HSPF are irrelevant at temperature extremes. It's questionable if they are relevant at any temperature. HSPF difference between those two models is 0.7%(?). COP difference at 17 F of 71%(?). Down to 47 F there is no difference in the COP. Let's say every model from every manufacturer functions just like these two(not even close to true statement). It might be a good idea to determine how much time is spent more than 28 F (47 F) below a set temperature of 75 F. https://www.degreedays.net/ set the base temp at 47 F and let it calculate the heating degree days. Download the spreadsheet. Or for averages https://www.greencastonline.com/tools/soil-temperature. Or Wundermap https://www.wunderground.com/dashboard/pws/KFLJACKS3451/graph/2021-07-9/2021-07-9/monthly The Calculation methodology: https://www.aceee.org/files/proceedings/2004/data/papers/SS04_Panel1_Paper08.pdf More calculation stuff: http://www.fsec.ucf.edu/en/publications/html/fsec-pf-413-04/ I'm not an AC guy either. Nothing to sell. No agenda other than saving electricity.

Good information there .... but I would like it a LOT better if it wasn't just a wall of text.

A lot more people will get your points if you learn to separate the text in a way that brings out your ideas.

Sorry .... I've just been seeing this too much and most times don't even read a post that isn't formatted ... Of course, it could be that I just have a reading comprehension issue.

 

[curiouscarbon]

totally agree; really good content! some newlines might help with readability ?

i too had difficulty reading it due to formatting, and also found the post to have really really good contents!

learned from the links provided, thank you

 

[bgflyguy]

Are the numbers from ASHP for heating? I think I'm missing something for AC.

 

[RCinFLA]

edit: the models used..
EER = 95f outside 80f indoor return temp 50% relative humidity
SEER = 65-104f outside (with some dips below) 80f indoor return temp 50% relative humidity

50% relative humidity is a lot easier spec for reduced A/C btu consumption. It takes a lot more btu's to remove humidity then just keep air cool. It can be argued that reason for this spec is it represents run rate after area has been cooled down and humidity removed.

For house construction efficiency, you hear a lot about insulation, not so much on air leakage/exchange due to gaps in window/door framing, and a bunch of kids continously opening doors to go in and outside often. Letting outside humid air in really hurts. Boiling water on stove hurts. Taking a lot of showers hurts.

One thing you should try to get info on any inverter A/C or inverter refrig is its AC power factor or how the AC to high voltage DC for inverter supply is accomplished. Almost never shown on unit specs. When powering from batteries with DC-AC inverter, a poor power factor increases inverter losses and cabling losses due to higher peak current. Some inverter A/C units and refrig's just use simple rectifier-filter cap giving a very poor power factor in the 0.6 range.

My Samsung inverter refrig has PF of 0.6 normally and never gets better then 0.65. It uses just rectifier-filter cap for 120vac to HV DC for its three phase inverter.