Alternative heat source, minisplits for real?

[twd000]

yeah, days like this (mid-50's) are where it seems silly to burn wood, even with the BK Princess chugging away at a low tstat setting. I would love to let a heat pump carry the load until it gets real cold again.

I'm not familiar with that HSPF metric, but the $13.33/MBTU you quoted equals COP=3.5 which I'm more familiar with. That is pretty admirable, if it can average that high COP across the heating season.

 

[CaptSpiff]

I find propane prices to be very regional. We get choked here on Long Island:

https://www.nyserda.ny.gov/Researchers-and-Policymakers/Energy-Prices/Propane/Average-Propane-Prices

 

[begreen]

Likewise in our area. Propane prices are high here.

 

[CaptSpiff]

Another added benefit of these mini splits is they don't dry out the air according to my sensor monitoring on the return and supply.
View attachment 240185

I always thought the "dry indoor air in winter" was more the result of exchanging indoor air with outdoor air, as in "leaky house allows warm humid air to escape and be replaced with dry outside air which is heated and becomes even dryer".

 

[woodgeek]

I'm not familiar with that HSPF metric, but the $13.33/MBTU you quoted equals COP=3.5 which I'm more familiar with. That is pretty admirable, if it can average that high COP across the heating season.

HSPF is just COP*3.412, its the BTU/Wh expected, while COP is Wh(heat)/Wh(electrical). SEER is on the same basis.

 

[twd000]

HSPF is just COP*3.412, its the BTU/Wh expected, while COP is Wh(heat)/Wh(electrical). SEER is on the same basis.

thanks I didn't realize it was a simple linear relationship. Will the same minisplit have different COP/HSPF based on climate heating degree days?

 

[woodgeek]

Yeah...its a seasonal average COP (or SCOP) for some reference climate...that I do not know.

 

[peakbagger]

There is report out of the web done by DOE or some other organization that looks at real time efficiency of minisplits over a range of outdoor temperatures, my googling didn't find it but it definitely showed more than a linear degradation of performance as the temps dropped.

 

[maple1]

The main issue with apparent performance loss - is that not only is there less heat to move in the outside air when it is colder out, but your house also needs more heat to maintain because heat loss is going up at the same time.

 

[Brian26]

The main issue with apparent performance loss - is that not only is there less heat to move in the outside air when it is colder out, but your house also needs more heat to maintain because heat loss is going up at the same time.

That has been my observations a few weeks in on running mine. I have mine dialed in pretty good on when to run it and when to fall back on my oil furnace. Im down on the CT shoreline were winter temps are pretty mild most of the time in winter. This week its been mild and it has been running all week pumping out great heat. Its definitely cut back huge on running the oil furnace when I am at work during the day.

I did run it the other week when it was around zero here at night and it still puts out heat. I still had to run the oil furnace but my downstairs was way warmer than before the minisplit went in. It also appears to really cut down on the oil furnace runtime when ran together when its cold.

 

[DBoon]

Before I purchased an installed a Fujitsu 12kBTU RLS2 mini split (rated down to -17 deg F), I researched the COP at different temperatures. I recall that this model was still a COP 2 or so at -5 degree F and was rated to deliver 12kBTU at or close to that temperature. And in below zero weather, it still heated the house and there was warm air coming out of the unit. But at -5 degree F, the house lost a lot more heat, so overall effectiveness went down.

 

[Ashful]

Based on the reports here, of these things actually working in sub-zero, I’ve been playing with mine. Unfortunately, or fortunately, our sub-zero temps ended the day I started experimenting, and it’s been too warm ever since for any real data.

I see three general possibilities as the source of the trouble with mine:

1. First floor indoor unit may be undersized for the load. I have two machined PVC overhead doors (10 footers) in that space, and I believe the person who calc’d the HVAC load assumed a much higher R-value on those doors. Of course, the doors are too beautiful and expensive to even consider swapping out, it’d cost much less to just replace that indoor unit with something larger.

2. Temp sensing was set to be in the indoor unit, rather than in the wall-mounted thermostat, and this may be tricking the system to think the space is much warmer than it really is. It was set up this way because I have the thermostats for both floors located next to the entry door, meaning one is on a different floor than the zone it is controlling. I will see the dreaded “wait” symbol frequently appearing on the LCD thermostats, which is an indicator that one of the head units may be calling for cooling while the other is calling for heating.

3. The system is set up or charged wrong, although I’ve already had this checked. The real indicator here will be measuring inlet/outlet air temp during our next sub-zero event.

For now, I’ve switched the temp sensing to be in the wall-mounted thermostats, and temporarily (and inconveniently) relocated the second floor thermostat to the second floor. This seems to have ended some of the crazy behavior, like finding it’s 45F in the shop when I go out there for the evening, even though both thermostats were set to hold 55F.

 

[maple1]

Based on the reports here, of these things actually working in sub-zero, I’ve been playing with mine. Unfortunately, or fortunately, our sub-zero temps ended the day I started experimenting, and it’s been too warm ever since for any real data.

I see three general possibilities as the source of the trouble with mine:

1. First floor indoor unit may be undersized for the load. I have two machined PVC overhead doors (10 footers) in that space, and I believe the person who calc’d the HVAC load assumed a much higher R-value on those doors. Of course, the doors are too beautiful and expensive to even consider swapping out, it’d cost much less to just replace that indoor unit with something larger.

2. Temp sensing was set to be in the indoor unit, rather than in the wall-mounted thermostat, and this may be tricking the system to think the space is much warmer than it really is. It was set up this way because I have the thermostats for both floors located next to the entry door, meaning one is on a different floor than the zone it is controlling. I will see the dreaded “wait” symbol frequently appearing on the LCD thermostats, which is an indicator that one of the head units may be calling for cooling while the other is calling for heating.

3. The system is set up or charged wrong, although I’ve already had this checked. The real indicator here will be measuring inlet/outlet air temp during our next sub-zero event.

For now, I’ve switched the temp sensing to be in the wall-mounted thermostats, and temporarily (and inconveniently) relocated the second floor thermostat to the second floor. This seems to have ended some of the crazy behavior, like finding it’s 45F in the shop when I go out there for the evening, even though both thermostats were set to hold 55F.

You can't manually set them to heating mode?

 

[Ashful]

You can't manually set them to heating mode?

Yes, I can. I probably should for the dead of winter, but I usually tend to leave all of my minisplit systems on auto-changeover, as they’re all in spaces that we might not see for a week or more at a time. I also tend to treat every household system as if I could disappear tomorrow, leaving my wife and kids to figure it out. In that case, my shop or music studio (our two minisplit systems) might sit un-visited several months or even a year at a time, and I’d rather not have everything in those spaces ruined for them when temps hit 0F or 100F.

 

[Brian26]

Based on the reports here, of these things actually working in sub-zero, I’ve been playing with mine. Unfortunately, or fortunately, our sub-zero temps ended the day I started experimenting, and it’s been too warm ever since for any real data.

I see three general possibilities as the source of the trouble with mine:

1. First floor indoor unit may be undersized for the load. I have two machined PVC overhead doors (10 footers) in that space, and I believe the person who calc’d the HVAC load assumed a much higher R-value on those doors. Of course, the doors are too beautiful and expensive to even consider swapping out, it’d cost much less to just replace that indoor unit with something larger.

2. Temp sensing was set to be in the indoor unit, rather than in the wall-mounted thermostat, and this may be tricking the system to think the space is much warmer than it really is. It was set up this way because I have the thermostats for both floors located next to the entry door, meaning one is on a different floor than the zone it is controlling. I will see the dreaded “wait” symbol frequently appearing on the LCD thermostats, which is an indicator that one of the head units may be calling for cooling while the other is calling for heating.

3. The system is set up or charged wrong, although I’ve already had this checked. The real indicator here will be measuring inlet/outlet air temp during our next sub-zero event.

For now, I’ve switched the temp sensing to be in the wall-mounted thermostats, and temporarily (and inconveniently) relocated the second floor thermostat to the second floor. This seems to have ended some of the crazy behavior, like finding it’s 45F in the shop when I go out there for the evening, even though both thermostats were set to hold 55F.

I setup a return and supply temp sensor on mine that logs the data. Acurite that sells weather stations has cheap sensors.

The units have a temp sensor on the top intake that they use to regulate the temp. In cooling mode they work great but in heating mode the intake is significantly air temp higher. I found about a 5-8 degree temp difference from 4 ft from the floor than on the intake. All that hot air rises. I can use thr follow me feature where my remote is the sensor. Works way better but has to constantly be in communication with the wall unit.

Another test is go measure the temps on the lines coming out of the condenser outside. There is a big one and a small one. My bigger line is usually around 125-150 degrees depending on outdoor temps and load. That seems to be a rough number on most splits from research.

You can probably find the service manual online. It has a wealth of information on how they run.

 

[twd000]

another anecdote for what it's worth. Just talked to a guy at church who had a Mitsu Hyperheat installed in his office a couple years ago. I asked him how it did with our -5 cold snap last week, and he had only good things to say. Toasty warm from his report.

 

[Brian26]

another anecdote for what it's worth. Just talked to a guy at church who had a Mitsu Hyperheat installed in his office a couple years ago. I asked him how it did with our -5 cold snap last week, and he had only good things to say. Toasty warm from his report.

The Mitsbushi's can crank out some serious heat even in cold temps. Conventional heat pumps are getting crushed on efficiency.

This is no doubt going to be the future of heating and cooling...

100 percent heating capacity at 5 degrees is straight out nuts

Mine is running right now at 25 degrees and putting out 100 percent heat...

 

[Highbeam]

The Mitsbushi's can crank out some serious heat even in cold temps. Conventional heat pumps are getting crushed on efficiency.

This is no doubt going to be the future of heating and cooling...

100 percent heating capacity at 5 degrees is straight out nuts

Mine is running right now at 25 degrees and putting out 100 percent heat...

View attachment 240517

Just a matter of time before the conventional split system folks pull their heads out of their butts and improve their equipment to match.

Also heads in butts for those manufacturers who still haven’t decided to heat water with this technology.

 

[begreen]

Their head must be up there pretty far. I've been waiting 12 yrs now and what mostly has changed is that the companies that I saw overseas are now owning the market.

 

[woodgeek]

Just a matter of time before the conventional split system folks pull their heads out of their butts and improve their equipment to match.

Also heads in butts for those manufacturers who still haven’t decided to heat water with this technology.

Actually, they HAVE. All the major brands now have their top of the line compressors using inverter driven variable speed motors, with suitable controllers. And they are getting higher SEER and HPSF bc of that. Its just that they are still selling the one and crappy two speed compressors a bit cheaper, and most people will go for the slightly lower install cost. And IIRC Goodman was largely purchased by one of the East Asian HVAC companies several years ago, around the same time this tech rolled out.

Getting broad adoption (and resulting efficiency) would prob require DOE regulation. In the meantime the makers will just see an opportunity to charge early adopters a premium.

As for water....most people delivering heat by hot water want temps high enough for passive radiators...and that is like 20-40°F hotter than air delivery temps, killing the COP. And no cooling in practice. So it might be popular in some nice, drier climates...but in the US with a lot of heat and humidity where most of the people live, its gonna be air delivery for a long time.

Unless you meant heating DHW....in which case the tech also already exists and is available at HomeDespot with COPs of 3+. My 6 yo HPWH unit is going strong, but only has a COP of 2 or so.

And those are being forced in (slowly) with Obama-era DOE regs.

 

[Brian26]

Another observation and based on my monitoring and some research these inverter units definitely have some kind of algorithm to help compressor life. My unit will always start out at the min speed and slowly ramp up capacity in small increments. Starting a conventional AC/Heat pump unit its either on or off at full capacity. That has to be a ton of strain on the equipment and effect equipment life. These units don't do that even when you try and force them to full capacity by activating the turbo mode.

My unit also has a compressor heating element wrap that will preheat the compressor on cold starts.

 

[Brian26]

Their head must be up there pretty far. I've been waiting 12 yrs now and what mostly has changed is that the companies that I saw overseas are now owning the market.

Pioneer has a whole house ducted inverter unit with some impressive numbers running a Mitsbushi compressor.

https://www.pioneerminisplit.com/co...ditioner-heat-pump-system?variant=33504387920

 

[Ashful]

Unless you meant heating DHW....in which case the tech also already exists and is available at HomeDespot with COPs of 3+. My 6 yo HPWH unit is going strong, but only has a COP of 2 or so.

I check on this every year, and I’m due to check again, but I have never been able to find any HPWH solution that can handle reasonable demand with an indirect system. Do any exist today?

I’m running an Amtrol Boilermate on my oil-fired boiler, and I’ve asked a few HVAC contractors about adding indirect HPWH to the system, but they all say my system is about the best thing they see, and they woudn’t change a thing. What they are not acknowledging is the secondary factors, beyond direct operating cost:

1. The cooling and dehumidification benefits. My basement is not air-conditioned, but it is finished space that we use. It's fine thru the first half of the summer, but it can start to get a little warm down there by August.

2. I’m also burning almost $200/mo in running dehumidifiers down there thru summer, something that would be mostly or entirely offset by the HPWH’s dehumidification. Those dehumidifiers also pump a lot of unwanted heat into the basement.

3. My boiler is under our kitchen, and the floor between is not insulated. The kitchen is already the hottest room in the house in July, between having lots of glass, poorer insulation that adjacent areas, and cooking. Shutting the boiler down would help keep the kitchen from being warmer than the rest of the house.

Our constraints are primarily very-occasional high usage and long delivery distances. We have more than ten sinks, four toilets, three showers, two tubs, two dishwashers, and two clothes washers. I’d bet there are times (holidays/guests) when both dishwashers, a clothes washer, and three showers or a tub are all running simultaneously. We also have to deliver that water more than 100 feet, in some cases, thru mostly un-insulated copper tubing.

Because of the distance, we have the thermostat set higher than any HPWH can deliver, but that’s mostly a winter thing. I’d be happy with cooler water in summer, which is when those secondary advantages mentioned above can also benefit me most. This is why I only consider indirect an option, as I’d be decommissioning it every winter. Alternatively, if there were one that could be set up in tandem with the boiler to run all winter, that could work... but again, we’re then talking two tanks?

The only indirect systems I found go into the DHW loop on a boilermate, via coaxial dip tube. This won’t work, as the restriction of going coaxial on the dip tube would kill our delivery volume. We need at least 3/4” thru the whole system, given the number of simultaneous appliances. I’d be happy going with a commercial unit, as long as we could find one that’s single-phase on the mains supply.

 

[SpaceBus]

I check on this every year, and I’m due to check again, but I have never been able to find any HPWH solution that can handle reasonable demand with an indirect system. Do any exist today?

I’m running an Amtrol Boilermate on my oil-fired boiler, and I’ve asked a few HVAC contractors about adding indirect HPWH to the system, but they all say my system is about the best thing they see, and they woudn’t change a thing. What they are not acknowledging is the secondary factors, beyond direct operating cost:

1. The cooling and dehumidification benefits. My basement is not air-conditioned, but we have an exercise studio, movie theater, and kids rec-room down there. They’re fine thru the first half of the summer, but it can start to get a little warm by August.

2. I’m also burning almost $200/mo in running dehumidifiers down there thru summer, something that would be mostly or entirely offset by the HPWH’s dehumidification. Those dehumidifiers also pump a lot of unwanted heat into the basement.

3. My boiler is under our kitchen, and the floor between is not insulated. The kitchen is already the hottest room in the house in July, between having lots of glass, poorer insulation that adjacent areas, and cooking. Shutting the boiler down would help keep the kitchen from being warmer than the rest of the house.

Our constraints are primarily very-occasional high usage and long delivery distances. We have fourteen sinks, four toilets, three showers, two tubs, two dishwashers, and two clothes washers. Setting aside the fourteen sinks, I’d bet there are times (holidays/guests) when both dishwashers, a clothes washer, and three showers or a tub are all running simultaneously. We also have to deliver that water more than 100 feet, in some cases, thru mostly un-insulated copper tubing.

Because of the distance, we have the thermostat set higher than any HPWH can deliver, but that’s mostly a winter thing. I’d be happy with cooler water in summer, which is when those secondary advantages mentioned above can also benefit me most. This is why I only consider indirect an option, as I’d be decommissioning it every winter. Alternatively, if there were one that could be set up in tandem with the boiler to run all winter, that could work... but again, we’re then talking two tanks?

The only indirect systems I found go into the DHW loop on a boilermate, via coaxial dip tube. This won’t work, as the restriction of going coaxial on the dip tube would kill our delivery volume. We need at least 3/4” thru the whole system, given the number of simultaneous appliances. I’d be happy going with a commercial unit, as long as we could find one that’s single-phase on the mains supply.

What do you do for a living?

 

[Ashful]

Research and development. Am I showing my cards?