Can't beat Mini-splits for heating/cooling

[volsboy1]

My heat pump went out in my house about 4 years ago and I paid over 7000 bucks for a new system its a Ruud. I don't know what is wrong with it but heating it just can't do it seems. The air that comes out of the vents even at 40f outside is maybe 78 degrees it feels cold. I had the installer come out over and over and finally he told me that these new heat pumps blow tons of air but cooler than normal.
That is a lie cause the Gibson heat pump that was in my place heated much better and it did not have a TXV on the outside or the inside unit. My Ruud constantly turns on the Aux heat and thats when your bill really goes nuts. When it got down below zero I turned it off and just used ceramic heaters to heat. I installed a 18k Btu mini-split by chance two years ago. Turbo(Greenland) is what it says on the outside of it. This thing rocks and I mean rocks. I only paid 800 bucks for it and installed it myself when I got a quote from a contractor (6400). I don't even use my main system anymore and it was like 7 the other night and the air coming out is HOT and I have it turned up and I just uses fans to circulate the heat and no Aux heat cost. When it defrosts it so fast you don't notice it. The best part is you don't hear it outside at all unless you put your hand on it. I will never go back to these huge systems and the prices they are charging now is unreal.

 

[wayupnorth]

Many people have installed those mini-split systems around here. The only major drawback I can see is with our extremely cold winters (last 4 mornings were well below 0) the electric resistant heat comes on and defeats any savings with our very high electricity costs. HVAC techs suggest that in extreme cold weather to turn them off and use your central oil or gas heating.

 

[petek]

My new Navien condensing boiler was working flat out the past couple of days trying to maintain the house at 70 so I dropped it to 68 and all was good until the other half starts complaining how cold it is in the house (which I don't find). I didn't bother turning on the mini split because I figured at these low temps it's not going to do much and why risk starting it up and having something go wrong. I would had the boiler failed completely.

 

[volsboy1]

My Mini split heats until it is -22F degrees below zero and has full capacity until it is -13F so don't have Aux heat at all in mine. That was my main issue with my normal one the heating was soo bad the Aux heat 5k watt strip heat was coming on and killing me on my power bill. That is on top of the power to run the unit also thats what I can't get past.Your trying to save money with a heat pump and that Aux comes on every time it defrosts or it can't make the temp. I have a friend that lives in Minnesota and it gets down to -25 and his system is keeping his place at 69 F without any type of Aux heat running. He does have gas furnace tied into his system but its old and not very efficient and he uses it for emergency heat which he never uses he like me does not have Aux heat hook up.

 

[henene4]

Forced air heat just like forced air conditioning is INCREDIBLY reliant on proper airflow.

If the new system has a TXV and the old one didn't, that screams airflow issue.

If there is just a static flow restrictor (capillary/orfice) and a single speed compressor, with low airflow, the heat exchanger temp just goes up/down.
That however means the efficiency goes down (heat pump efficiency basically boils down to the temperature differential between both heat exchangers when everything else is equal - the lower the better).

A TXV - in theory, simplified - keeps heat exchanger temps as constant as possible, keeping efficiency as constant as possible.
If the airflow is sufficient, that would mean you could always move heat away from the heat exchanger sufficiently.
Then, the TXV only has to respond to other factors that might impact that. For example, if the coolant could pick up a lot of heat outside, you'd need less of it to keep the heat exchanger inside at a sufficient temperature, and it would reduce the flow.

Now, however, the same could happen if the airflow is to low.
Heat exchanger temp goes up, the "dumb" TXV dosen't know if it's because less air moves through the heat exchanger or if the refrigerant is hotter, throttles the flow of refrigerant down, resulting in less heat being moved - but at about the same efficiency.

That btw could also lead to more frequent defrosts - low refrigerant flow means pressures drop/rise. A lower temperature on the cold side means more condensation and thus more frost buildup.

That's why central heat pumps want more airflow at lower temps - it's just more efficient.

Btw the same goes true when the AUX heat comes on: The heat pump STILL is more efficient than resistive heat no matter what, as long as it runs.
All electricity it uses is the compressor's power and over 90% of that go into compressing the gas, which results in heat.
Any heat the gas picks up outside is "free" and there's always some.

The reason those mini splits give hotter air is that their heat exchangers and fans are significantly smaller. Less surface area and airflow per unit power means higher temperature differential to move the same amount of heat.
They however often use inverter compressors and electronic expansion valves (EEVs) that can modulate all factors much more precisely than a single speed compressor and TXV to offset the otherwise lower efficiency due to higher Td's.

That's btw how ultra low temp heatpumps work.
They often use EEVs and inverter compressors, and to get sufficient heat from outside, they ramp the compressor up and lower refrigerant flow.
That results in a colder cold side so they are always sufficiently below ambient temp to retrieve enough heat energy.

 

[tomturbomatic]

Some years ago, I remember a member in the north discovering that the reason his mini split system was performing poorly was because the air filter was allowing too much dust to get past it and clog up the fins. I noticed this with new window units so I always augment the thin flat "filter" with an old fashion foam filter which actually traps crap and keeps the fins clean.

 

[volsboy1]

My Heat pump has vapor injection that boost's its ability to heat when it is cold outside. Vapor injection makes a huge difference in heating ability,when you add that plus a inverters ability it go much much faster than normal single phase heat pumps.My heat pump will heat to -22 but at that temp it only has 70% capacity which is not bad considering how cold that is. My Ruud system is just terrible I don't know why I need to have it look at by somebody that is older and more experience than the others. My Dads house has two American Standard 5 ton from 2008 its a twin reciprocating compressor heat pump and it works fantastic even when it gets cold.

 

[kalanikaau1]

very high electricity costs

I'm curious, how much are you charged for a k/W per hour in your location?

Here in Honolulu, I was charged almost 37 cents on my December bill, I do believe Hawaii has the highest rate in the country.

Although we do not need heating for our homes, we do need A/C during the summer months.

Mini-splits are a no-brainer here, I cringe when I see homes with multiple window units, there is a large home in my neighborhood which has 7 energy hogging window units...

 

[ea56]

We pay 40 cents a KWH for tier 1 and 50 cents per KWH for tier 2 and I’m pretty certain that we have just about the highest electric rate in the USA.  Last month our PGE bill was $505. 24 for 1120 KWH of electricity for our all electric 1260 sq ft townhouse, and our January bill will be about the same.  And this is with the thermostats set at 68 F.

 

We get a break in the Summer when we don’t need heat and we don’t have AC and really have no need for it either, plenty of shade trees and fans in every room keep us cool enough.   But in the Winter we need the heat.

 

Eddie

 

[volsboy1]

I am charged 13 cents a hour for power. That is one advantage of living in Tenn with Tva everywhere. Duct work is a huge loss of capacity thats another reason I think that my 18,000 BTU system can heat and cool my place with no issues at all. The main Ruud is a 2.5 ton but the duct work goes through the attic and they all leak and in the summer it gets over 130 up there. Mini splits don't have Aux heaters in them if there on your wall. My Defrost is on demand it's not timed or anything, I have noticed it running days non stop no defrost and then other days where it defrosts every other hour. That's what saves soo much money not having that 5000 watt strip come on on top of the running compressor.

 

[henene4]

Huh

My current rate is about 30 cents per kWh.
I use just about 1000kWh a year, and about the same for heat and hot water (which is central gas in the apartment block I live in, which comes to about 10 cent per kWh gas).

Though I have to say: My flat is only about 270 sqft and I've trained myself to live at 16C / 61F most of the time, with only a small boost up to 65F in the morning.

My partner lives considerably warmer (mainly due to the birds), his flat is twice the size pretty much spot on and the house it's in is from the 50s, never renovated.

He uses about 12k kWh of gas a year; this year, since we got the wood oven, we're projected to get that down to half.

My mum uses about 2000 liters of oil, so about 20k kWh, for the 2600 sqft house per year. That used to be 30k when all 7 of us were still living there.
House has been insulated in the late 80s when it was extended, and has all underfloor heating except for 3 radiators.

Cutting the temp, even by a few degrees, REALLY adds up.
The wisdom is that a 1C/2F drop down saves between 5 and 10 percent of heating costs.
Same goes with dropping temps when going out to work etc.

Don't have to go as low as 60F, but every bit helps.

 

[petek]

John ; I think that was me regarding my previous mini split (Mitsubishi) allowing dust to bypass the filter. I didn't get the life out of it I was hoping for partially because of that problem and it eventually leaked. Stung a little more being as it cost a good penny more than other brands. Replaced it two years ago with a Carrier(Midea) heat pump model at about slightly over half the price of a similar Mitsubishi and so far so good.

 

[tomturbomatic]

What kind of birds?

 

[kalanikaau1]

What kind of birds?

Here in the tropics we don't have an issue with birds, rather geckos, and other creatures which have an affinity for the sealing compound used on most split unit AC units circuit boards.

Evidently these lizards liken the compound to filet mignon, I do believe that Mitsubishi has addressed this concern, perhaps it's taste is akin to my mother in laws cooking?

Ditto with Ford Motor Company products engine management devices, a particular ant here in Hawaii finds the same compound especially tasty.

 

[DADoES]

 
Jeff, I believe Tom is referencing Henrik's statement "My partner lives considerably warmer (mainly due to the birds) ..."

I take it to mean that the partner keeps birds as pets and they need a warmer environment than 61°F that Henrik maintains ... not a reference to birds causing damage to HVAC equipment.

 

[kalanikaau1]

Reply# 11

You are correct!
I made an incorrect inference...Mahalo!

 

[combo52]

Mini splits can be very efficient

Indefinite fill a niche market, however, there are many disadvantages.

They're expensive,

They're ugly and devalue properties

They don't filter the air adequately, they don't humidify the air in the winter

They don't mix the air throughout the home so different areas of the home can take on different odors.

Most don't provide back up heat, and if you have a system in your home with several terminal units in different rooms a breakdown of the system can wipe the whole thing out till it's repaired, refrigerant leaks are particularly difficult to find and repair because of the large amount of tubing, running all over the house up and down the sides of the building, often in the entire system has to be replaced.

One of the biggest problems with Central air conditioning is the drain system for the evaporator coil. It can clog and cause problems, when you put a mini split system in a large home with 4 to 6 terminal units, you have 4 to 6 times the problems of having one central system because you have drains everywhere that have to be maintained and cleaned.

Hi Wes, there is something terribly wrong with your new ream system ducted heat pump systems should provide nice warm air, I have two heat pump systems one in my primary home and one is the heating and cooling in the mountain house in both homes they make nice warm air when heating and do a good job.

John

 

[volsboy1]

Thanks Henrik you just gave me a great Idea. I am going to have the TXV valves replaced for EEV Valves on both the outside and inside air handlers on my Ruud .
My Mini-split was cheap very cheap and I am not being bitched out by my neighbors because that ruud has a two blade fan that is very steep pitch and the RPMs of it is 1200 and it rattles like crazy it says 81 on the Decibel meter. My Dads American Standard Heat pump has a two blade fan and you can barley hear it but it spins at 675 on low. My Mini was only 800 bucks its a Turbo Greenland brand but Midea is who makes it and you can't hear it at all outside unless its below 10F but even then you don't hear much. I had my Ruud installer out here about 10times in the first 6 months and he told me that there is nothing wrong with it.
Yea John you are right they are tacky looking but I am paying 75 bucks a month on electric compared to 160 during Xmas in 22 when it goes down to -3 and that whole month was cold. When this one breaks I am going with the Cassette ones that fit in the ceiling.

 

[william8]

Natural Gas

Here in Northern Michigan, NG is so cheap a heat pump is more expensive to run. Of course this will vary by area. And then there are all the flaws Combo52 mentions above with mini splits.

If you really want to save money, with AC and Heat, insulate and seal your house. I added R60 insulation to the ceiling of the entire house when I put on an addition. My bills dropped over 35% immediately. Few years later switched to a 95% furnace, and it dropped even further.