[jotato]

This is borderline a tangent, but I think manufactures should be required to provide data regarding efficiency at specific temperatures. We moved into a house with a heat pump almost 2 years ago. For the most part it is great, but I noticed that in cold(ish) temps it can't keep up. I'm not talking single digits temperatures.

I called the manufacturer and asked for data about my model. They refused to give it to me because I wasn't an authorized installer.

It took me a long time and many sensors and calculations later but I have learned that below 36F it can't pull heat fast enough to raise the temperature of my house. The house doesn't get colder - that is the "break even" point. To be fair, it was installed in 2010 and I'm sure it was good for its time.

Why can't they just provide a spec that says how much heat/kw can be created at given temps? Even in steps like 10, 20, 30, 40 etc... I think that would go a long way to debunk the myth

[throw0101a]

> This is borderline a tangent, but I think manufactures should be required to provide data regarding efficiency at specific temperatures.

These are available, and there are standards for EnergyStar approval and for being able to call yourself a "cold climate" air source heat pump (ccASHP):

* https://ashp.neep.org/#!/

* https://neep.org/heating-electrification/ccashp-specificatio...

Mitsubishi data sheet with COPs at various temperature:

* https://mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.c...

[jotato]

Mine isn't listed. My takeaway is that it isn't rated for cold climates. For what it is worth, I know the HSPF rating is 8.8 but I don't know at what temperature that is calculated at.

[Volundr]

Sounds like it was undersized for your house (unless your doing something crazy like trying to hold 80+). FWIW I was able to get efficiency charts and such at various temperatures from my salesperson, but I gather most don't bother. He was pretty surprised when I asked about them and more surprised when I took the time to (kind of) understand them, which was a huge pain in the ass. I certainly understand why most people would pay attention to the SEER values and just let the salesperson size the thing.

[jotato]

> Sounds like it was undersized for your house (unless your doing something crazy like trying to hold 80+).

It was set to 69 and held steady at 67 running for 8.5 hours. It wasn't until the temperature outside broke 36 that the inside temp slowly started to climb. It is a 3ton system for a 2500sqft home. From what I have read it should be enough. I think the problem is that it is an older heat pump and just doesn't perform well below 35.

> FWIW I was able to get efficiency charts and such at various temperatures from my salesperson, but I gather most don't bother.

I think this is my point? This was here when I moved it. I shouldn't have to go to a salesperson. I should be able to look it up in the specs or even the manual. At a minimum the manufacturer should provide it when asked.

[throw0101a]

> It was set to 69 and held steady at 67 running for 8.5 hours. It wasn't until the temperature outside broke 36 that the inside temp slowly started to climb.

This may be normal. Standard practice, per ASHRAE, is to design for 99% of days, and for the remaining 1% (~4 days per year) the system may have to run 24/7 (either for heating or cooling):

* https://www.energyvanguard.com/blog/we-are-the-99-design-tem...

* https://www.ba-inc.com/hvac-systems-what-is-a-design-day/

This allows for equipment that is "right-sized", as issues can arise (including premature death of equipment from short-cycling) if they are oversized:

* https://www.energyvanguard.com/blog/why-an-oversized-air-con...

* https://www.cooltoday.com/blog/3-problems-caused-by-an-overs...

* https://bryantlincoln.com/understanding-the-risks-of-oversiz...

By designing for 99% of the time, your gear should be just enough to handle things.

[jotato]

I live in the pacific northwest. Winter are low 30s at night for 3 months out of the year :( Granted, highs are mid-high 40s so it works fine during the day 90% of the time

[thsksbd]

If the unit is sized correctly for the appropriate climate, then its broken. There's no reason the system cant deal with 0C, the COP should still be well above 1.

Get the refrigerant level checked by someone that didn't install the system.

For what its worth this is why I don't like to rely on heat pumps. Furnaces are really primitive, simple devices: little more than a heat exchanger and a blower. A heat pump has a hermetically sealed volatile liquid undergoing phase changes by a compressor with seals.

They're cool. They're efficient. They're great.., but they're also far more complicated and we're living in an era of cheaply built consumer goods

[throw0101a]

30F is hardly anything.

Mitsubishis can work down to -13F/-25C and still have a COP of 2.08:

* https://www.mitsubishicomfort.com/articles/keep-warm-this-wi...

* https://mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.c...

Heat pumps that look like standard ACs often can run at 100% capacity down to 5F and still have a COP>2 (1=resistive heating).

Also worth perhaps looking into how leaky your house is:

* https://www.energy.gov/energysaver/blower-door-tests

and then after that maybe insulation.

[PaulDavisThe1st]

The COP numbers for Mitsubishi and Fujitsu are all online and readily accessible. If you're not using one of those brands, I suggest doing so.

[jotato]

It is a Trane. Sadly switching isn't like distro hopping :/

[bjornasm]

Think you should consider changing out your heatpump. My heatpump is said to deliver 3800 W at 5 fahrehheit.

[jotato]

I'm considering it. I have an energy audit scheduled next week. Depending on what they find I may consider buying something new. This one is 13 years old and I'm sure they've improved a lot since it was installed.

[thsksbd]

Heat pumps are over a century old; 13 years ago had great heat pumps. They didn't have fancy motor drives ("inverter technology"), but they probably had better refrigerants (we keep banning them).

You system is old, though, and the coolant might have leaked. Or it was never properly installed to begin with.