multi-split heat pump standby losses

bpm636 · 07-19-11, 08:52 PM

I have a Mitsubishi heat pump MXZ-2B20NA-1 just installed in my house together with two 12000 BTU interior units. After monitoring outdoor unit with energy monitor in standby mode I was shocked with bizarre number 180 watts! Compressor heater adds on top of that 40 more watts every other 30 minutes. My installer has checked the current and that is in 0.75-0.95 amps range. He called manufacturer and they said that this is expected. Heating "current test" also shows 0.75a above the calibrated curve. Overall losses per year would be in 1500 kWh range (3 times more than my new refrigerator). Any experience with stand by mode measurements on Mr Slim heat pump? This model is used in many zero-energy-home projects in California. I have pellet stove insert in my home but based on heat pump COP it should be quite competitive and outperform efficiency ( but not overall output) of pellet stove down to single digit temperatures. To save energy I have to turn/off disconnect before/after use of HP instead of set back night time thermostat.

Piwoslaw · 07-20-11, 09:16 AM

180 watts?!? And that's supposed to be normal? Geez, and I thought that the 32W that my automatic gate's motor is sucking 24/7 is a lot. I wonder where that 180W is coming from, and whether other models do better/worse? And what is the compressor heater for every 30 min?

bpm636 · 07-20-11, 09:36 AM

Service manual says that compressor uses 50W every other 30 minutes in stand by mode for pre-heating. I see this increase every other 30 minutes as 180->220W increase.
Service technician from very reputable company (installer) told me that they never check stand by current during installations. This issue puzzles him too. I think that 180W is a permanent loss even during regular work of compressor. When I turn the unit on with remote, the power returns back to 180W and starts to grow from there for standard operation. Single unit heating test for current under 48Hz steady compressor frequency shows 4.75A instead of 3.9-4.0A based on curves from service manual. My technician promised to check other similar units he is servicing and let me know. In any other aspect the unit works flawlessly.,
Based on efergy monitor these 180W losses is a big chunk in daily work of A/C

AC_Hacker · 07-20-11, 12:34 PM

I put a kill-a-watt on my 3/4 Ton Sanyo, and I was seeing a 30 watt standby loss, I didn't notice any periodic compressor heater surges... I probably didn't look long enough.

But the 30 watt standby was what I saw. And I was rather shocked at 30 watts... 24/7. There are some energy star refrigerators with power consumption less than that. My little Arduino data logger only draws 3 watts, and something on that scale could be used as a power-on sentinel.

In the summer I usually shut off power to the unit unless there is a need for air conditioning.

-AC_Hacker

Xringer · 08-07-11, 10:12 AM

The measurements on my Sanyo 24,000 BTU aren't super accurate,
but it seems to be using 10 to 30w during the summer and 50-60 during cold weather.

There is a relay on my main board that's connected to the heating coil,
(wrapped around the base of the compressor) and that seems to be
where most of the standby power is going.

During warm weather, the power use sometimes drops a lot (Zero on the TED),
but in cold weather it's a steady drain.

After reading a lot of comments about Standby mode on mini-splits, I've come to
believe that it's okay to use the breaker to save power during the warmer months.
(Since the outdoor temperature will keep the compressor warm)
But, it's not a good practice to save power during the cold months, unless you
turn Standby back On to pre-heat your oil a few hours before using the heat mode.

Two more points:

The smaller 18,000 BTU version of my Sanyo does not even have a compressor heater!

In case of a winter time grid failure, my system could restart itself
(when the grid came back up) while the compressor was still very cold..
(And not self-destruct).

~~~~
I've been thinking about using my DIY electronic circuit breaker
http://ecorenovator.org/forum/applia...r-limiter.html
to control my summer time standby power drain.

It uses a +5V power supply. That's always plugged in..
If I moved that little drainer to an X10 type device,
I could kill it's drain and the Sanyo standby drain with one shot..

Edit 8/20/11:
I've added a new X10 switch and it works fine. We just had a few days w/o the need for
AC, and we've saved a little money on power.
The X10 takes the Sanyo completely off-line, so it might even be useful for vacation mode
and during thunderstorms. (If the SSR devices provide any HV isolation).
I've installed

Piwoslaw · 08-07-11, 10:25 AM

Instead of constantly keeping the compressor warm, couldn't there be an option to preheat it only when needed? Compressor heating would start only when the thermostat sends an 'ON' request to the mini-split, delaying heating/cooling by 10-30 minutes, but saving lots of energy. The delay could be easily countered by slightly adjusting the thermostat's temperature settings.

Xringer · 08-07-11, 10:42 AM

The variable here is the outdoor temperature. So if you used a fixed-time pre-heat,
it should be set for the worse-case outdoor temperature. Around here, that's about 10F.

IIRC, it's not just the oil that has to be warmed up, I think there was also postings
about liquid-state refrigerant accumulating inside the compressor, when it should it should be in a gaseous state.?.
I think someone said that's not too good in these types (scroll?) compressors..

bpm636 · 08-07-11, 04:06 PM

The issue with high standby losses 180 watts has been resolved.
All systems with inverters produce quite high reactive load when in standby.
After turning off all breakers in the house (except Mitsubishi HP) I was able to see 0-15 Watts on our house exterior power meter. When pre-heating kicks in, the consumption goes to 65 watts. Efergy meter shows 180->220 increase.
The discrepancy between exterior meter and efergy still noticeable with low frequencies of compressor but when power goes beyond 650 watts the real load is very close to total load. It's interesting that according to spec of outdoor unit the power factor for single unit operation is 0.95 and for 2-unit operation it's 0.97.
Simple estimate gives ~100 watts background reactive load. The exact number can be a function of precision of tuning of the power board. Xringer is a lucky man if his efergy (before dying) and then TED gives standby power very close to 0.
All Mithubishi outdoor units have a switch on PC control board to disable pre-heating of compressor. It's written in the service manual for my unit.
Service manual for european variants have much more information about on board switches.

Xringer · 08-07-11, 05:52 PM

Nice work. Sometimes investigating losses like that can be problematic.
But, logically looking at it, why would it need so much power on standby.?. Just doesn't make sense.

I think the reason mine reads pretty close, is the heater is non-inductive like a toaster.

And, it's being driven by AC.

I wonder if your heating element is power by DC.?.

~~~

Speaking of power use, last night it was pretty cool outdoors, but we left
the Sanyo running all night. Because it was so cool out, it hardly used any power at all.
That left us with a very humid house this AM, when the rain started!
It was 100% humidity outdoors and about 70 to 75% in here..

Last 24 Hours Weather: ,

So, since it was cool both inside and out, I tried out the Dehumidifier mode.
It's taken us down to 45% this afternoon and not really used a lot of power.
(TED says 3.8kw since midnight. The last 9 of 19 hours was in Dehumi mode.
The setpoint is 24C and it's been coasting down to 23C.
Very little air from the indoor unit, but the indoor coil is at 37F..
This Sanyo is a very nice whole-house dehumidifier.

07-19-11, 08:52 PM	#1
bpm636 Lurking Renovator Join Date: Jul 2011 Location: New Hampshire Posts: 4 Thanks: 0 Thanked 0 Times in 0 Posts	multi-split heat pump standby losses I have a Mitsubishi heat pump MXZ-2B20NA-1 just installed in my house together with two 12000 BTU interior units. After monitoring outdoor unit with energy monitor in standby mode I was shocked with bizarre number 180 watts! Compressor heater adds on top of that 40 more watts every other 30 minutes. My installer has checked the current and that is in 0.75-0.95 amps range. He called manufacturer and they said that this is expected. Heating "current test" also shows 0.75a above the calibrated curve. Overall losses per year would be in 1500 kWh range (3 times more than my new refrigerator). Any experience with stand by mode measurements on Mr Slim heat pump? This model is used in many zero-energy-home projects in California. I have pellet stove insert in my home but based on heat pump COP it should be quite competitive and outperform efficiency ( but not overall output) of pellet stove down to single digit temperatures. To save energy I have to turn/off disconnect before/after use of HP instead of set back night time thermostat.

07-20-11, 09:16 AM	#2
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	180 watts?!? And that's supposed to be normal? Geez, and I thought that the 32W that my automatic gate's motor is sucking 24/7 is a lot. I wonder where that 180W is coming from, and whether other models do better/worse? And what is the compressor heater for every 30 min? __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

07-20-11, 12:34 PM	#4
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	I put a kill-a-watt on my 3/4 Ton Sanyo, and I was seeing a 30 watt standby loss, I didn't notice any periodic compressor heater surges... I probably didn't look long enough. But the 30 watt standby was what I saw. And I was rather shocked at 30 watts... 24/7. There are some energy star refrigerators with power consumption less than that. My little Arduino data logger only draws 3 watts, and something on that scale could be used as a power-on sentinel. In the summer I usually shut off power to the unit unless there is a need for air conditioning. -AC_Hacker __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...

08-07-11, 10:12 AM	#5
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The measurements on my Sanyo 24,000 BTU aren't super accurate, but it seems to be using 10 to 30w during the summer and 50-60 during cold weather. There is a relay on my main board that's connected to the heating coil, (wrapped around the base of the compressor) and that seems to be where most of the standby power is going. During warm weather, the power use sometimes drops a lot (Zero on the TED), but in cold weather it's a steady drain. After reading a lot of comments about Standby mode on mini-splits, I've come to believe that it's okay to use the breaker to save power during the warmer months. (Since the outdoor temperature will keep the compressor warm) But, it's not a good practice to save power during the cold months, unless you turn Standby back On to pre-heat your oil a few hours before using the heat mode. Two more points: The smaller 18,000 BTU version of my Sanyo does not even have a compressor heater! In case of a winter time grid failure, my system could restart itself (when the grid came back up) while the compressor was still very cold.. (And not self-destruct). ~~~~ I've been thinking about using my DIY electronic circuit breaker http://ecorenovator.org/forum/applia...r-limiter.html to control my summer time standby power drain. It uses a +5V power supply. That's always plugged in.. If I moved that little drainer to an X10 type device, I could kill it's drain and the Sanyo standby drain with one shot.. Edit 8/20/11: I've added a new X10 switch and it works fine. We just had a few days w/o the need for AC, and we've saved a little money on power. The X10 takes the Sanyo completely off-line, so it might even be useful for vacation mode and during thunderstorms. (If the SSR devices provide any HV isolation). I've installed Last edited by Xringer; 08-20-11 at 07:13 AM..

08-07-11, 10:25 AM	#6
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	Instead of constantly keeping the compressor warm, couldn't there be an option to preheat it only when needed? Compressor heating would start only when the thermostat sends an 'ON' request to the mini-split, delaying heating/cooling by 10-30 minutes, but saving lots of energy. The delay could be easily countered by slightly adjusting the thermostat's temperature settings. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

07-20-11, 09:36 AM	#3
bpm636 Lurking Renovator Join Date: Jul 2011 Location: New Hampshire Posts: 4 Thanks: 0 Thanked 0 Times in 0 Posts	Service manual says that compressor uses 50W every other 30 minutes in stand by mode for pre-heating. I see this increase every other 30 minutes as 180->220W increase. Service technician from very reputable company (installer) told me that they never check stand by current during installations. This issue puzzles him too. I think that 180W is a permanent loss even during regular work of compressor. When I turn the unit on with remote, the power returns back to 180W and starts to grow from there for standard operation. Single unit heating test for current under 48Hz steady compressor frequency shows 4.75A instead of 3.9-4.0A based on curves from service manual. My technician promised to check other similar units he is servicing and let me know. In any other aspect the unit works flawlessly., Based on efergy monitor these 180W losses is a big chunk in daily work of A/C

08-07-11, 10:42 AM	#7
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The variable here is the outdoor temperature. So if you used a fixed-time pre-heat, it should be set for the worse-case outdoor temperature. Around here, that's about 10F. IIRC, it's not just the oil that has to be warmed up, I think there was also postings about liquid-state refrigerant accumulating inside the compressor, when it should it should be in a gaseous state.?. I think someone said that's not too good in these types (scroll?) compressors..

08-07-11, 04:06 PM	#8
bpm636 Lurking Renovator Join Date: Jul 2011 Location: New Hampshire Posts: 4 Thanks: 0 Thanked 0 Times in 0 Posts	The issue with high standby losses 180 watts has been resolved. All systems with inverters produce quite high reactive load when in standby. After turning off all breakers in the house (except Mitsubishi HP) I was able to see 0-15 Watts on our house exterior power meter. When pre-heating kicks in, the consumption goes to 65 watts. Efergy meter shows 180->220 increase. The discrepancy between exterior meter and efergy still noticeable with low frequencies of compressor but when power goes beyond 650 watts the real load is very close to total load. It's interesting that according to spec of outdoor unit the power factor for single unit operation is 0.95 and for 2-unit operation it's 0.97. Simple estimate gives ~100 watts background reactive load. The exact number can be a function of precision of tuning of the power board. Xringer is a lucky man if his efergy (before dying) and then TED gives standby power very close to 0. All Mithubishi outdoor units have a switch on PC control board to disable pre-heating of compressor. It's written in the service manual for my unit. Service manual for european variants have much more information about on board switches.

08-07-11, 05:52 PM	#9
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Nice work. Sometimes investigating losses like that can be problematic. But, logically looking at it, why would it need so much power on standby.?. Just doesn't make sense. I think the reason mine reads pretty close, is the heater is non-inductive like a toaster. And, it's being driven by AC. I wonder if your heating element is power by DC.?. ~~~ Speaking of power use, last night it was pretty cool outdoors, but we left the Sanyo running all night. Because it was so cool out, it hardly used any power at all. That left us with a very humid house this AM, when the rain started! It was 100% humidity outdoors and about 70 to 75% in here.. Last 24 Hours Weather: , So, since it was cool both inside and out, I tried out the Dehumidifier mode. It's taken us down to 45% this afternoon and not really used a lot of power. (TED says 3.8kw since midnight. The last 9 of 19 hours was in Dehumi mode. The setpoint is 24C and it's been coasting down to 23C. Very little air from the indoor unit, but the indoor coil is at 37F.. This Sanyo is a very nice whole-house dehumidifier.