Cheaper to burn oil than run electric heat pump -)

[Xenoilphobe]

What are you doing for maintenance? What's the cleaning routine?

I'm near salt water, so I did a couple things, first I mounted these units about 5 feet off the ground so that the lawn debris / Lawn equipment / cars / etc do not hit my condenser coils. This also helps with cooling getting these away from the dense humid air that sits at ground level here on the coast. I mounted the condenser coils to the North face (again to help with cooling) of my house with brackets, into the studs (real 2x6), I was getting some resonate vibrations at certain loads, so I had to install anti-vibration isolation mounts, (Cylindrical Mounts V10Z64-MN10) which fixed the problem.

I also have the gold coils, I cleaned them with a low pressure washer (ryobi 18 volt to garden hose) and some coil cleaner (end of summer) - TURN OFF POWER before spraying water on the condenser.

Monthly I pull the interior filters and clean them with hot water and soap, the worst one is usually in the kitchen because of all the cooking off gassing. Also drop a little vinegar or diluted bleach down the drip trays at the beginning of cooling season and make sure your condensate lines are clear (summer issue only). In the winter make sure your outdoor condenser coils are allowing condensate to drip out of the coil tray away from the coils, if they are blocked, it will create an ice dam and effect the efficiency of the unit, resolve by clearing the holes in the bottom and giving the water a path away from the coil (again why I mounted them higher and not ground mounted). Mitsubishi provides an optional base pan heater that helps with this as well. https://gotductless.com/cdn/shop/files/SUBMITTAL-3C30NA3.pdf?v=12788115341421047312


Also had to remove a smart bird, who had built a nest inside one of the line set cover box on the outdoor condenser (relocated to a bird house I bought), fixed that with a little chicken wire, so I don't have to mess with that again.

I don't know you config, but a lot of installers overload the outdoor condenser coil with too many heads, this reduces efficiency and could be impacting your low temp performance. (one of the reasons I went with single units verses multi heads to one condenser). Another issue I had with one unit in the first week was a leak, we found it and recharged, no issues yet...

I would check your interior filter first, then look at the back of your coil and see if there is debris (leaves, lawn grass, bugs, nests, etc...) A dirty coil has a huge impact on both heating and cooling. Keep everything away from the coil, there are minimum standoffs also, and a lot of people ignore those, which impact efficiency (see below).

Make sure your coil isn't in a wind path, you can block that path with bushes or even a low wall, but again follow the standoffs provided by Mitsubishi...Below ere are the LG stand offs, I mounted five units on one wall using the Case 5 standoffs below, following the standard factors. Mounting the unit 4 inches from the exterior wall (measurement D) of my house would have reduced efficiency 10%, so I gave these units plenty of room for air flow, and chose the standard 12 inches of "D" from the house as recommended in Case 5, below.

 

[Xenoilphobe]

The new outdoor unit is a Mitsubishi HyperHeat (MXZ-3C30NA?) rated down to -15F, and it has kept running thus far. The old Mitsubishi was rated to around 5F and wouldn't do much at around 15-20F.

Here's the spec on the new unit:

View attachment 1010456

Waiting on tech to come and take a look to see if there's a leak somewhere.

I believe MXZ-3C30NAXXX is only rated to 5 degrees... https://gotductless.com/cdn/shop/files/SUBMITTAL-3C30NA3.pdf?v=12788115341421047312, do the last digits end in HZ? That is the Hyper Heating Designation.

 

[zƬesla]

I believe MXZ-3C30NAXXX is only rated to 5 degrees... https://gotductless.com/cdn/shop/files/SUBMITTAL-3C30NA3.pdf?v=12788115341421047312, do the last digits end in HZ? That is the Hyper Heating Designation.

It is the MXZ3C30NAHZ3

 

[Xenoilphobe]

It is the MXZ3C30NAHZ3

I assume you have 3 heads in a non-ducted install, notice the COP (coefficient of performance) #'s drops from 4.0 to 2.0 or a 50% drop @ 17F, then drops another 5% below that, which means at -14F it must be like COP of less than 1.0.... which is really inefficient ( 1 = resistance heaters)

Also note that you are only getting 28K BTU max @ 17F verses 36K BTU's @ 47F. Once this unit hits -13F max output is 25K BTUs pulling 4430 watts! verses 36K BTUs @ 4540 watts @ 47F.

If this were a Zero Turn Lawnmower - @ 47F assume you are getting 35 MPG, @ 5 F you are getting 17 MPG @ -14 you are getting 7 MPG, but you are also losing top end

Maxed out using 4540 watts @47F = 36,000 BTUs (14 HP ZTR Lawnmower analogy again)
Rated capacity using 2190 watts @ 47F = 28,600 (11.2 HP) COP 4.0 or 400% efficient.
Maxed out using 4192 watts @17F = 28,600 BTUs (11.2 HP)
Rated Capacity using 1990 watts @17F - 18,000 BTUs (7 HP)
Maxed out using 4290 watts @5F = 28,600 BTUs (11.2 HP) COP 1.95 or 195% efficient
Maxed out using 4430 watts @-14F= 25,200 BTUs (9.89 HP) COP of less than 1 or 100% efficient same as resistance electric heat.

System might be undersized for your peak demands.... this also explains your electrical usage... how large is your house? Insulation type? # of windows etc...
BTW the specs on the single system LG's have the similar degradation numbers for heating. 47F @ 12K BTU's become 9600 BTU's @ 5F, only difference is power consumption is lower due to higher HSPF. the MXZ is an excellent HP for the price.

 

[zƬesla]

@Xenoilphobe There are 3 heads (18, 12, 6). The old MXZ was a non-hyperheat 36K supporting up to 4 heads. When it was replaced last spring, I think the MXZ3C30NAHZ3 was the largest model before moving up $/size to the double units. The 6K head rarely if ever calls for heat; we had a resistor clipped so it would stop circulating heat as the small room would get too warm. The 18 unit is in a vaulted living room with open stairwell, hallway, and dining room. The 12 is in an office with half vaulted ceiling. Ceiling fans are running in both the living room and office (in reverse) to circulate heat.

The new MXZ is probably somewhat undersized, although I wonder if something else isn't going on too. We have also had an unusual number of days in the 0-20F range which doesn't help. So far we've managed to make do with warm clothing and blankets.

 

[BGbreeder]

Thanks for the helpful and illuminating commentary @Xenoilphobe and @zƬesla!

All the best,

BG

 

[wwu123]

I'm near salt water, so I did a couple things,

[...]

When I noticed your profile says Fairfax County, i lived and worked there for four years, so I thought, wait, isn't the Potomac freshwater???? But went back upthread and realized you're talking about your beach house....

But I did grow up in Hawaii, most houses have louvered windows to allow the salty trade winds for cooling - everything electrical or electronic is lucky to last five years - computers, monitors, modems, window air conditioners, they all rust or corrode like crazy. The beach being only a mile away in two directions, and a saltwater marina just two blocks away, didn't help things.

 

[charlesj]

.... It seems close to break even with gas at $1.50/therm, although last year at this time it was $3-4/therm, and off peak energy at $0.22/kWh. ...

You are lucky. I am looking at my PG&E bill, period ended Jan 17. $2.25438/Therm to end of December and $2.43888/therm to the 17th.
On top of that, the gas procurement cost per therm went down from $0.90733 to $0.75508 for those two halves of billing cycle.

 

[zƬesla]

After almost two months I was able to get the HyperHeat installer out and he found the refrigerant to be down to 5lbs from the 8lbs it's supposed to come from the factory with. Hoping this resolves the issue and that we don't have a leak somewhere in the piping.

 

[Xenoilphobe]

Damn that is a lot for a minisplit. That would explain the performance degradation