Ductless Mini Split Cooling Design
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Beads
All thumbs
This is not an exact match to the OP's situation, but deserves to be scanned if someone is contemplating cooling areas with doors separating them from the cooling unit:
Long-Term Monitoring of Mini-Split Ductless Heat Pumps in the Northeast Building America Report - 1407 December 2014 Kohta Ueno and Honorata Loomis.
Long-Term Monitoring of Mini-Split Ductless Heat Pumps in the Northeast Building America Report - 1407 December 2014 Kohta Ueno and Honorata Loomis.
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Robert Simpson
New Member
Here is what I came up with after a full year of research on the sizing issue of a Mini Split for my two story 1800 sq ft summer/ winter cottage in Canada on the water front of Lake Huron.
Why you should buy a small unit!
First of all you must understand that you are going to turn the unit on and let it run for 10 years. Keeping this in mind and keeping the temp at 47f (inside and out) a 9k or 12k unit will use a minimum of 150 watts per hour or 3.6 Kilowatts per day or 1314 Kwh per year at .25¢ per Kwh then which will cost you $328.00 unit per year. Ten years $3280.00 !
An increase or decrease in either temp. (inside or out will change this base figure).
If you go to a larger unit 15,000-18,000 unit then the smallest amount of watts the unit will run on is 520 watts per hour , which is 12.5 kwh per day or 4562 kWh per year.
At .25¢ per kwh this equals $1,140 per year just for a base price. ($11,140 ten year base)
An increase or decrease in either temp. (inside or out will change this base figure).
Conclusion : Mini Splits are great, just stick to using the smaller units in well sealed rooms! If I need to use another form of heat to maintain comfort then I have $1140-$328= $812 dollar per year to buy warm slipper or a nice house coat or invest in a supplement heat source.
I walk into my cottage and I say to myself... I LOVE my Mini Split system! I never had that thought about any other systems I purchased on my 66 years of living!
The unit is currently running, I'm in Flordia and it is keeping the building at 50f using 300 watts of energy at 32f outside costing me $1.80 per day. About $55 a month.... why would you use anything else!
They are all good units, I went with the nearest dealer with a family to support, I know if I need service he will be there!
Robert
Why you should buy a small unit!
First of all you must understand that you are going to turn the unit on and let it run for 10 years. Keeping this in mind and keeping the temp at 47f (inside and out) a 9k or 12k unit will use a minimum of 150 watts per hour or 3.6 Kilowatts per day or 1314 Kwh per year at .25¢ per Kwh then which will cost you $328.00 unit per year. Ten years $3280.00 !
An increase or decrease in either temp. (inside or out will change this base figure).
If you go to a larger unit 15,000-18,000 unit then the smallest amount of watts the unit will run on is 520 watts per hour , which is 12.5 kwh per day or 4562 kWh per year.
At .25¢ per kwh this equals $1,140 per year just for a base price. ($11,140 ten year base)
An increase or decrease in either temp. (inside or out will change this base figure).
Conclusion : Mini Splits are great, just stick to using the smaller units in well sealed rooms! If I need to use another form of heat to maintain comfort then I have $1140-$328= $812 dollar per year to buy warm slipper or a nice house coat or invest in a supplement heat source.
I walk into my cottage and I say to myself... I LOVE my Mini Split system! I never had that thought about any other systems I purchased on my 66 years of living!
The unit is currently running, I'm in Flordia and it is keeping the building at 50f using 300 watts of energy at 32f outside costing me $1.80 per day. About $55 a month.... why would you use anything else!
They are all good units, I went with the nearest dealer with a family to support, I know if I need service he will be there!
Robert
Robert: I don't understand your math.
The standby consumption of mini-splits are nowhere near 150 watts- most will be less than 15 watts, many than 5 watts. The minimum modulated output when the compressor and blowers are running might be 150 watts, but when there's no load they aren't running.
Most mini-splits won't cool to 47F, or was that intended to be 74F? Or are you talking about minimum heating, keeping place at 47F when unoccupied?
With a pan heater and crankcase heater running it might have standby losses as high as 150W, but for most vendors those don't kick on until the outdoor temps are under +15F, often lower.
Nobody's power rates are 0.25 cents/kwh. Was that intended to be 25 cents? Most people are paying well under 25 cents.
Modulation ranges aren't infinite, and in heating mode when they're cycling on/off at a 50% duty cycle during milder seasons they won't average better than 2.5 or so for an average COP, even at outdoor temps where it would hit a COP of 4 or better if running continuously. Sizing them, relative to the actual loads are critically important for getting maximal efficiency out of them, whether in heating or cooling mode.
The standby consumption of mini-splits are nowhere near 150 watts- most will be less than 15 watts, many than 5 watts. The minimum modulated output when the compressor and blowers are running might be 150 watts, but when there's no load they aren't running.
Most mini-splits won't cool to 47F, or was that intended to be 74F? Or are you talking about minimum heating, keeping place at 47F when unoccupied?
With a pan heater and crankcase heater running it might have standby losses as high as 150W, but for most vendors those don't kick on until the outdoor temps are under +15F, often lower.
Nobody's power rates are 0.25 cents/kwh. Was that intended to be 25 cents? Most people are paying well under 25 cents.
Modulation ranges aren't infinite, and in heating mode when they're cycling on/off at a 50% duty cycle during milder seasons they won't average better than 2.5 or so for an average COP, even at outdoor temps where it would hit a COP of 4 or better if running continuously. Sizing them, relative to the actual loads are critically important for getting maximal efficiency out of them, whether in heating or cooling mode.
Beads
All thumbs
So what is the minimum power consumption for housekeeping and running the indoor blower motor? Dana, do you know that number?
What is the right size/capacity? Since VS heat pumps run more efficiently under partial load than at full speed, it seems like a complex decision whether to size them exactly or oversize them some. In some cases, it may boil down to how you are using them, setback or no setback.
Robert, do you have remote control over your systems so you can turn it off if you want to? Do you run it on auto changeover mode to keep humidity low in warmer times when you are not there?
I like the mini split operation. I'll tell you one reason, however, that I might not fill a multi-room house with mini splits again. There is a great increase in mechanical complexity. I've replaced one blower motor for about $150. Beyond the cost, it was hard for me to purchase since most HVAC supply places don't seem to want to sell to homeowners. I hope that I don't need to replace more of them.
Last summer, I pulled out the blower cages on my Mistu MSZ indoor units and spent 4-5 hours each cleaning of 6 of them. The blower cages and the inside of the case that they can "throw stuff at" were disgusting after 5 years; black gunk was everywhere. (See the comments on the video that I post below.) I did the blower cages in the driveway with neutral detergent followed by a brief hit with bleach. While I was out there I also cleaned the outer case, both sets of louvers/vanes. the drip tray (nozzle assembly), and front panel. A soft gong brush, tooth brush, a common hose-end sprayer and cotton swabs were useful. Note that vertical louvers have been a PITA for me to release and hinge out of the way. I bought a bib kit to clean the indoor coils and remaining parts on the wall and it was well worth it. I sprayed what little visible stuff was caught in the coils with foaming cleaner and then thoroughly sprayed with a tank sprayer with Nu-Calgon Evap Pow'r-C and rinsed.
Note that Mitsubishi finally posted some disassembly vids on YouTube. They were helpful. The service manual not so much for neither the cage removal, nor blower motor replacement. Honestly, the manual was a PITA for the latter. Jeff is my new best friend:
I just had a look and there are a lot more vids available now. I can't comment on the quality.
What is the right size/capacity? Since VS heat pumps run more efficiently under partial load than at full speed, it seems like a complex decision whether to size them exactly or oversize them some. In some cases, it may boil down to how you are using them, setback or no setback.
Robert, do you have remote control over your systems so you can turn it off if you want to? Do you run it on auto changeover mode to keep humidity low in warmer times when you are not there?
I like the mini split operation. I'll tell you one reason, however, that I might not fill a multi-room house with mini splits again. There is a great increase in mechanical complexity. I've replaced one blower motor for about $150. Beyond the cost, it was hard for me to purchase since most HVAC supply places don't seem to want to sell to homeowners. I hope that I don't need to replace more of them.
Last summer, I pulled out the blower cages on my Mistu MSZ indoor units and spent 4-5 hours each cleaning of 6 of them. The blower cages and the inside of the case that they can "throw stuff at" were disgusting after 5 years; black gunk was everywhere. (See the comments on the video that I post below.) I did the blower cages in the driveway with neutral detergent followed by a brief hit with bleach. While I was out there I also cleaned the outer case, both sets of louvers/vanes. the drip tray (nozzle assembly), and front panel. A soft gong brush, tooth brush, a common hose-end sprayer and cotton swabs were useful. Note that vertical louvers have been a PITA for me to release and hinge out of the way. I bought a bib kit to clean the indoor coils and remaining parts on the wall and it was well worth it. I sprayed what little visible stuff was caught in the coils with foaming cleaner and then thoroughly sprayed with a tank sprayer with Nu-Calgon Evap Pow'r-C and rinsed.
Note that Mitsubishi finally posted some disassembly vids on YouTube. They were helpful. The service manual not so much for neither the cage removal, nor blower motor replacement. Honestly, the manual was a PITA for the latter. Jeff is my new best friend:
I just had a look and there are a lot more vids available now. I can't comment on the quality.
Beads
All thumbs
P.S. I am using condenser tabs now to reduce growth in the drip tray and drain lines. I have one at each end of the top and one at each end of the bottom coils for a total of 4 in each unit.
The standby number varies by vendor & model, as does the efficiency & capacity.
The interior head's blower does not need to run when there is no load and doesn't, unless programmed to run that way with the remote (not all models have that as an option). Running the blower with no load just uses more power than is needed for heating/cooling.
To determine the sizing one needs to calculate the loads (ACCA Manual-J is the gold standard) at the 99% and 1% outside design temperatures at the geographical location where it will be installed. From there one may have to consult the extended capacity temperature charts in the engineering manuals for the mini-spits in question to ensure that the unit has sufficient capacity.
The high part-load efficiency is easily given up by excessive oversizing when the average loads are above the minimum output of the units. (Modulation turn-down ratios are not infinite.) Minimum outputs are specified under standard HSPF/SEER testing conditions the submittal sheets, from which one can estimate at what outdoor temperature the thing is guaranteed to be cycling on/off. For instance, if the heating load of the zone/room at +47F outdoors/70F indoors is say, 2300 BTU/hr, the Mitsubishi FH15 will be cycling on/off most of the time during the shoulder seasons due to it's 5120 BTU/hr minimum output, whereas the FH09 has plenty of modulating room to spare, since it can dial back to 1600 BTU/hr.
A heat load of 2500 BTU/hr @ 47F with a 70F indoor temp, a temperature difference of 23F, using a linear approximation of 2300/23F= 10 BTU/hr per degree-F. If your 99% outside design temp is +5F that's a 65F delta, and a load of about 6500 BTU/hr @ +5F, which the FH09 can clearly handle with ease. If your 99% outside design temp is -10F that's an 80F delta, and an ~8000 BTU/hr heat load, which the FH09 can still (barely) muster at that temperature (under most humidity conditions) but you'd need to consult the engineering manuals to know that.
Caving in to the temptation to oversize with the FH12 would be a mistake, since it's minimum modulation output is 3700 BTU/hr, which in this sample case would imply that it goes into cycling mode whenever it's above freezing. Even though running continuously at minimum modulation it's efficiency would be very high it's as-used efficiency is dramatically lower due to having to spin up the compressor & blowers.
Setback strategies are universally less efficient than "set & forget" where the conditioned space is used daily, since at full speed during the recovery ramp the efficiency is less than half what it is when modulating in the lower third of it's modulation range, over a wide range of outdoor temperatures. (In heating mode at tempertures below +15F that may no longer be true- it narrows.)
The interior head's blower does not need to run when there is no load and doesn't, unless programmed to run that way with the remote (not all models have that as an option). Running the blower with no load just uses more power than is needed for heating/cooling.
To determine the sizing one needs to calculate the loads (ACCA Manual-J is the gold standard) at the 99% and 1% outside design temperatures at the geographical location where it will be installed. From there one may have to consult the extended capacity temperature charts in the engineering manuals for the mini-spits in question to ensure that the unit has sufficient capacity.
The high part-load efficiency is easily given up by excessive oversizing when the average loads are above the minimum output of the units. (Modulation turn-down ratios are not infinite.) Minimum outputs are specified under standard HSPF/SEER testing conditions the submittal sheets, from which one can estimate at what outdoor temperature the thing is guaranteed to be cycling on/off. For instance, if the heating load of the zone/room at +47F outdoors/70F indoors is say, 2300 BTU/hr, the Mitsubishi FH15 will be cycling on/off most of the time during the shoulder seasons due to it's 5120 BTU/hr minimum output, whereas the FH09 has plenty of modulating room to spare, since it can dial back to 1600 BTU/hr.
A heat load of 2500 BTU/hr @ 47F with a 70F indoor temp, a temperature difference of 23F, using a linear approximation of 2300/23F= 10 BTU/hr per degree-F. If your 99% outside design temp is +5F that's a 65F delta, and a load of about 6500 BTU/hr @ +5F, which the FH09 can clearly handle with ease. If your 99% outside design temp is -10F that's an 80F delta, and an ~8000 BTU/hr heat load, which the FH09 can still (barely) muster at that temperature (under most humidity conditions) but you'd need to consult the engineering manuals to know that.
Caving in to the temptation to oversize with the FH12 would be a mistake, since it's minimum modulation output is 3700 BTU/hr, which in this sample case would imply that it goes into cycling mode whenever it's above freezing. Even though running continuously at minimum modulation it's efficiency would be very high it's as-used efficiency is dramatically lower due to having to spin up the compressor & blowers.
Setback strategies are universally less efficient than "set & forget" where the conditioned space is used daily, since at full speed during the recovery ramp the efficiency is less than half what it is when modulating in the lower third of it's modulation range, over a wide range of outdoor temperatures. (In heating mode at tempertures below +15F that may no longer be true- it narrows.)
Robert Simpson
New Member
Dana, & others,
Thanks for the review of my analysis.
Here is my math from actual figures and well documented on my end.
Lets start with the kWh per hour rate... I'm in Ontario, Canada and if you take the total bill and divide it by the kWh used it come out to 0.25¢ CANADIAN money per kWh which is 0.20¢ US funds per kWh. So...at this expense I'm VERY concerned over what it cost me to keep my property comforable.
The only thing that is hooked up to my meter is the mini split :
model Mitsubishi MSZ-FE12 NA unit so I do have some actual numbers. I run the unit on standby mode in the winter which keeps my place at 50f and keeps air movement going 24/7.
The numbers are also on
spec sheet for the Mitsubishi products: States that "power consumption minimum" is 150 watts for(both units in&out) for the 12k unit and and 520 watts (minimum) for the 15k unit. I have confirmed the 12k numbers with monitoring equipment I have on the unit. When the room is up to temp and the fan is on both units draw 150 minimum.
That number alone is the point I was trying to make that mini splits use a minimum amount of power 24/7 with or without a demand for heating or cooling and that must be taken into consideration. The 15k uses more energy on low (520 watts minimum) in an hours than the 12k unit. ( 150 watts minimum)
The 47f Number comes off the product spec sheets for model MSZ-FE12 NA as a base figure to start all my calculation.
Based on that numbers I have I'm able to project how many kWh I will use tomorrow based on weather conditions.
Since the mini split is the only breaker turned on, on my panel... I'm confident in my numbers. I take the daily total of kWh used and divide that by 24 to get watts per hour ... I'm concerned with total daily use which includes highs and lows of the unit running.
When everything is 47f (in side and out) my wattage use is 150 watts per hour. This number goes up or down at predictable rate if I raise the inside temp or the outside Temp goes up or down.
Example last week it was 10f and I used 550 watts per hour and the week before I used 200 watts at 38F. This week it will be 32F , I will use 250 watts per hour.
Bottom line is this:
With the Internet of THINGS coming on line the home owner will be able to gather the data and make choices based on actual data which relates to dollars and cents and make the right choices based on their situation.
Mini splits use energy 24/7 and that base cost must be figured into the annual cost of running the unit. The smaller units 6-12k will have 1/4 the base cost of the larger units, and provide enough comfort if sized right according to the Manual J numbers. ( less 20% for not having to heat up the metal duct work).
To the other posters.... thank you for sharing your knowledge about figures and CLEANING!
Please also note in CANADA we seal our buildings up as tight as possible and use Heat recovery ventilation systems when they are occupied. Mini Splits are GREAT for this application.... not so great for an unsealed building!
I hope this information helps soneone decide how to stay comfortable and safe that is affordable$.
Robert
Property owner
Thanks for the review of my analysis.
Here is my math from actual figures and well documented on my end.
Lets start with the kWh per hour rate... I'm in Ontario, Canada and if you take the total bill and divide it by the kWh used it come out to 0.25¢ CANADIAN money per kWh which is 0.20¢ US funds per kWh. So...at this expense I'm VERY concerned over what it cost me to keep my property comforable.
The only thing that is hooked up to my meter is the mini split :
model Mitsubishi MSZ-FE12 NA unit so I do have some actual numbers. I run the unit on standby mode in the winter which keeps my place at 50f and keeps air movement going 24/7.
The numbers are also on
spec sheet for the Mitsubishi products: States that "power consumption minimum" is 150 watts for(both units in&out) for the 12k unit and and 520 watts (minimum) for the 15k unit. I have confirmed the 12k numbers with monitoring equipment I have on the unit. When the room is up to temp and the fan is on both units draw 150 minimum.
That number alone is the point I was trying to make that mini splits use a minimum amount of power 24/7 with or without a demand for heating or cooling and that must be taken into consideration. The 15k uses more energy on low (520 watts minimum) in an hours than the 12k unit. ( 150 watts minimum)
The 47f Number comes off the product spec sheets for model MSZ-FE12 NA as a base figure to start all my calculation.
Based on that numbers I have I'm able to project how many kWh I will use tomorrow based on weather conditions.
Since the mini split is the only breaker turned on, on my panel... I'm confident in my numbers. I take the daily total of kWh used and divide that by 24 to get watts per hour ... I'm concerned with total daily use which includes highs and lows of the unit running.
When everything is 47f (in side and out) my wattage use is 150 watts per hour. This number goes up or down at predictable rate if I raise the inside temp or the outside Temp goes up or down.
Example last week it was 10f and I used 550 watts per hour and the week before I used 200 watts at 38F. This week it will be 32F , I will use 250 watts per hour.
Bottom line is this:
With the Internet of THINGS coming on line the home owner will be able to gather the data and make choices based on actual data which relates to dollars and cents and make the right choices based on their situation.
Mini splits use energy 24/7 and that base cost must be figured into the annual cost of running the unit. The smaller units 6-12k will have 1/4 the base cost of the larger units, and provide enough comfort if sized right according to the Manual J numbers. ( less 20% for not having to heat up the metal duct work).
To the other posters.... thank you for sharing your knowledge about figures and CLEANING!
Please also note in CANADA we seal our buildings up as tight as possible and use Heat recovery ventilation systems when they are occupied. Mini Splits are GREAT for this application.... not so great for an unsealed building!
I hope this information helps soneone decide how to stay comfortable and safe that is affordable$.
Robert
Property owner
Robert Simpson
New Member
Mini Split Cleaning:
I paid $4,200 CA / $3,200 US for my Mitsubishi MSZ-FE12 NA installed! With a 10 year warrenty plan.
I have my Licensed Contractor / installer come in each year and perform standard maintenance and cleaning of the unit. This I feel will keep me healthy and I will feel much better knowing that the unit was looked at just before winter sets in. Plus not void my warrenty package by trying to do the cleaning my self. He has all the right equipment and knows what he is doing.
It clearly states in the warrenty paperwork that "service" is only to be performed by a Licensed Contractor to keep the warrenty valid!
General Cleaning is taking a vacuum to the unit weekly, taking a screw driver to the unit would surely void the warrenty!
With the money this unit saved me over my old heating system I can justify paying them to maintain the unit... a small price to pay for keeping it clean and giving me piece of mind.
Plus.....he needs the cash flow to stay in business, so he is still in business when I need him!
Robert
I paid $4,200 CA / $3,200 US for my Mitsubishi MSZ-FE12 NA installed! With a 10 year warrenty plan.
I have my Licensed Contractor / installer come in each year and perform standard maintenance and cleaning of the unit. This I feel will keep me healthy and I will feel much better knowing that the unit was looked at just before winter sets in. Plus not void my warrenty package by trying to do the cleaning my self. He has all the right equipment and knows what he is doing.
It clearly states in the warrenty paperwork that "service" is only to be performed by a Licensed Contractor to keep the warrenty valid!
General Cleaning is taking a vacuum to the unit weekly, taking a screw driver to the unit would surely void the warrenty!
With the money this unit saved me over my old heating system I can justify paying them to maintain the unit... a small price to pay for keeping it clean and giving me piece of mind.
Plus.....he needs the cash flow to stay in business, so he is still in business when I need him!
Robert
"Thanks for the review of my analysis.
Here is my math from actual figures and well documented on my end.
Lets start with the kWh per hour rate... I'm in Ontario, Canada and if you take the total bill and divide it by the kWh used it come out to 0.25¢ CANADIAN money per kWh which is 0.20¢ US funds per kWh"
You are still two orders of magnitude off on the rate. It's CDN20 (US 20 ) cents)/kwh, not CDN0.25 (US0.20) cents/kwh.
"The numbers are also on
spec sheet for the Mitsubishi products: States that "power consumption minimum" is 150 watts for(both units in&out) for the 12k unit and and520 watts (minimum) for the 15k unit. "
The 150 watts for the FE12 is at the minimum rated heating output (3000 BTU/hr if it's 47F outside, 70F inside, a COP of over 6 at that temp) , not at zero output, no motor turning, no fans, no compressors. So yes, if the fan is blowing it's indeed 150 watts, if it's cycling on/off it's less that that on average, but the spin-up/spin-down eats into the COP efficiency by a large amount when cycling. When the heat load is lower than ~3000 BTU/hr it is not drawing 150 watts continuously- it cycles between some very low number, and 150 watts. When the heat load is substantially more than 3000 BTU/hr it draws substantially more than 150 watts. Most homes would have a heat load well over 3000 BTU/hr when it's 47F outside, so the fact that it's still modulating delivers the 150watt baseline. But at some outdoor temperature it will begin cycling, and run at somewhat lower efficiency relative to what it would be if running constantly.
"Since the mini split is the only breaker turned on, on my panel... I'm confident in my numbers. I take the daily total of kWh used and divide that by 24 to get watts per hour ... I'm concerned with total daily use which includes highs and lows of the unit running.
When everything is 47f (in side and out) my wattage use is 150 watts per hour. This number goes up or down at predictable rate if I raise the inside temp or the outside Temp goes up or down.
Example last week it was 10f and I used 550 watts per hour and the week before I used 200 watts at 38F. This week it will be 32F , I will use 250 watts per hour. "
You are conflating units in a confusing way- "watts per hour" is a rate of a rate (an acceleration), which isn't what you measured. The daily kilowatt-hours divided by hours yields the average load in watts, not "watts per hour." You used 200 watt-hours (not 200 watts), at 38F.
With a range of temps between 25-45F the efficiency will be pretty flat as long at it's running continuously, and power use will change pretty linearly with the average difference between indoor & outdoor temperatures. But when the thing is running at more than half it's max capacity and the temperatures are below 15F the raw efficiency is half what it is at 35F+/- 10F. Third party bench testing on a couple of 1-tons bears this out.
Sized correctly for the load the FE12 will deliver a seasonal average COP efficiency of about 3 in locations that average about 20-25F in January (binned hourly mean temperature), about half the COP of 6 it delivers at a continuous minimum modulation when it's in the mid 40s F out. The curve isn't super-linear with temperature, and at +5F and lower it's delivering a COP of 2 or less. If you screw up the sizing by either oversizing to where it's rarely modulating or undersizing so that it's almost always running at a high modulation rate it's seasonal COP will be less than 3.
Here is my math from actual figures and well documented on my end.
Lets start with the kWh per hour rate... I'm in Ontario, Canada and if you take the total bill and divide it by the kWh used it come out to 0.25¢ CANADIAN money per kWh which is 0.20¢ US funds per kWh"
You are still two orders of magnitude off on the rate. It's CDN20 (US 20 ) cents)/kwh, not CDN0.25 (US0.20) cents/kwh.
"The numbers are also on
spec sheet for the Mitsubishi products: States that "power consumption minimum" is 150 watts for(both units in&out) for the 12k unit and and520 watts (minimum) for the 15k unit. "
The 150 watts for the FE12 is at the minimum rated heating output (3000 BTU/hr if it's 47F outside, 70F inside, a COP of over 6 at that temp) , not at zero output, no motor turning, no fans, no compressors. So yes, if the fan is blowing it's indeed 150 watts, if it's cycling on/off it's less that that on average, but the spin-up/spin-down eats into the COP efficiency by a large amount when cycling. When the heat load is lower than ~3000 BTU/hr it is not drawing 150 watts continuously- it cycles between some very low number, and 150 watts. When the heat load is substantially more than 3000 BTU/hr it draws substantially more than 150 watts. Most homes would have a heat load well over 3000 BTU/hr when it's 47F outside, so the fact that it's still modulating delivers the 150watt baseline. But at some outdoor temperature it will begin cycling, and run at somewhat lower efficiency relative to what it would be if running constantly.
"Since the mini split is the only breaker turned on, on my panel... I'm confident in my numbers. I take the daily total of kWh used and divide that by 24 to get watts per hour ... I'm concerned with total daily use which includes highs and lows of the unit running.
When everything is 47f (in side and out) my wattage use is 150 watts per hour. This number goes up or down at predictable rate if I raise the inside temp or the outside Temp goes up or down.
Example last week it was 10f and I used 550 watts per hour and the week before I used 200 watts at 38F. This week it will be 32F , I will use 250 watts per hour. "
You are conflating units in a confusing way- "watts per hour" is a rate of a rate (an acceleration), which isn't what you measured. The daily kilowatt-hours divided by hours yields the average load in watts, not "watts per hour." You used 200 watt-hours (not 200 watts), at 38F.
With a range of temps between 25-45F the efficiency will be pretty flat as long at it's running continuously, and power use will change pretty linearly with the average difference between indoor & outdoor temperatures. But when the thing is running at more than half it's max capacity and the temperatures are below 15F the raw efficiency is half what it is at 35F+/- 10F. Third party bench testing on a couple of 1-tons bears this out.
Sized correctly for the load the FE12 will deliver a seasonal average COP efficiency of about 3 in locations that average about 20-25F in January (binned hourly mean temperature), about half the COP of 6 it delivers at a continuous minimum modulation when it's in the mid 40s F out. The curve isn't super-linear with temperature, and at +5F and lower it's delivering a COP of 2 or less. If you screw up the sizing by either oversizing to where it's rarely modulating or undersizing so that it's almost always running at a high modulation rate it's seasonal COP will be less than 3.
Robert Simpson
New Member
Dana,
Thank you so much for your review of my comments and my use of words! I learned something today!
And your knowledge of the US Energy report on mini splits is exactly what I needed to have a better understanding of how my unit works.
Everyone that is thinking of owning a mini split should read it over BEFORE they purchase a unit!
http://www.nrel.gov/docs/fy11osti/52175.pdf
Thank you for taking the time to review reports online and make other have a better understanding of the heating and cooling industry. Your service is what makes the internet a great place to share information.
Thank you!
Robert
Thank you so much for your review of my comments and my use of words! I learned something today!
And your knowledge of the US Energy report on mini splits is exactly what I needed to have a better understanding of how my unit works.
Everyone that is thinking of owning a mini split should read it over BEFORE they purchase a unit!
http://www.nrel.gov/docs/fy11osti/52175.pdf
Thank you for taking the time to review reports online and make other have a better understanding of the heating and cooling industry. Your service is what makes the internet a great place to share information.
Thank you!
Robert
