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Air to Air Heat Pump in cold temperatures
I live in South Dakota and currently, it is 11 degrees. I recently had to completely rebuild my home. I used Spray Foam insulation and have an Air to Air Heat Pump with electric backup.
Prior to the rebuild, the heat pump could not keep up with the cold temps so Auxiliary Heat always kicked in when it was this cold. Now, the auxiliary heat only kicks in during the defrost cycle. The heat pump is providing enough heat to keep the house at temperature.
My question is efficiency. If I switch to emergency heat, the air handler runs for a short time to heat the house perhaps 5 minutes). When on normal heating, the heat pump runs and heats the house but it runs for about 3 times the time to heat the house and the compressor goes on and off several times during the heat cycle. During normal use, the compressor draws about 4 KVA. Emergency heat draws about 15 KVA.
Would it be more economical to continue to run the Heat Pump for 15 minutes verses running the Emergency heat for 5 minutes? Another factor that can't be measured is wear and tear an the heat pump.
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UA Local 32 retired as of Jan 2020
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Up here, in Northern MINNESOTA it is common to have a heat pump and a gas furnace. The tipping point with gas is about 20 degrees. At that temp, the gas furnace takes over for less cost than the heat pump.
If my math is right, you pay for 15KVA for 5 minutes on electric heat, and 12KVA (4 X 3j for the heat pump. Sounds like running the heat pump is the way to go. If it gets much colder, you might need to reassess.
If God didn't want us to eat animals... He wouldn't have made them out of MEAT.
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What do you have for a heat pump. Wondering the efficiency rating.
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You need to look at the C.O.P data in the install manual and that will give you actual performance numbers.
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Why go COP? If you know the runtimes, compare the AMPS being used. Then you can convert to wattage and cost for each scenario.
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The scenario isn't a constant.
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I'm in manitoba just north of you.
The heat pump will be more efficient at 10 degrees than strip heat. Probably cop of around 1.5 depending on make_model.
So keep running it
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Originally Posted by
MADHVACTECH
You need to look at the C.O.P data in the install manual and that will give you actual performance numbers.
Might also take into consideration equipment runtimes with relation to equipment service life.
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I once talked to an engineer about this question. His belief was a HP compressor was likely to last
longer if kept running because the compressor oil would be in circulation and not as likely to migrate.
They will always be more efficient than strip heat even when they can't satisfy the load.
I had a HP in N Ill. I kept it running but often worried I was wearing it out. Most of the analysis of HP's don't
consider mechanical costs and how many techs fall short on proficiency when understanding them.
The HP I had was in a house I built and got a special deal on electric rates. At the time the electric co, was pushing all
electric houses. A few years later a consumer group sued and I lost my rates.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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Don’t use emergency heat mode unless your heat pump stops heating your home.
Switching your thermostat to emergency means: just using your backup heat (if I am correct). The heat pump works as an electric heater, or it is using the backup heat.
The backup works more efficiently, but less efficient than the heat pump pulling in heat.
Emergency cases used for normal operation are strongly not recommended for any systems. Heating ones, which are most reactive, is the best case where not to use an emergency for normal operation. Soon you might need a repair team to go and check your system, I believe.
Use emergency heat only if your heat pump isn’t heating your home at all.
Edited: if you already invested in the backup, it should switch on without your action, I guess, and keep the system going. With no need for emergency.
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Originally Posted by
hvacker
I once talked to an engineer about this question. His belief was a HP compressor was likely to last
longer if kept running because the compressor oil would be in circulation and not as likely to migrate.
They will always be more efficient than strip heat even when they can't satisfy the load.
I had a HP in N Ill. I kept it running but often worried I was wearing it out. Most of the analysis of HP's don't
consider mechanical costs and how many techs fall short on proficiency when understanding them.
The HP I had was in a house I built and got a special deal on electric rates. At the time the electric co, was pushing all
electric houses. A few years later a consumer group sued and I lost my rates.
This doesn't match what I see in the real world. Real world I see gas furnace and AC combo outlasting heat pumps.
I haven't come across any data that shows the compressor in a heat pump models is built for 2x runtime vs ac only application compressors.
I would welcome to be proven wrong though for my own knowledge and better understanding.
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They definitely won't "always be more efficient " there is a balance point.
Also they operate year around vs seasonally.
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Originally Posted by
hvacker
I once talked to an engineer about this question. His belief was a HP compressor was likely to last
longer if kept running because the compressor oil would be in circulation and not as likely to migrate.
Here is some ammo to help make your point. AE17-1743
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
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So I quoted the wrong post. But that was an interesting read.
My stance is that heat pumps should* be designed for 2x runtime vs ac only units, but I haven't seen anything that supports this is being done?
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Originally Posted by
Kroaler
So I quoted the wrong post. But that was an interesting read.
My stance is that heat pumps should* be designed for 2x runtime vs ac only units, but I haven't seen anything that supports this is being done?
I have not seen anything in the field to make me think that a heat pump properly installed and maintained lasts any differently than an ac. If a unit cycles a lot it will die early but if it runs long cycles and gets at least some maintenance they last much longer.
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
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No mention of a crankcase heater 🤔
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Originally Posted by
VTP99
No mention of a crankcase heater
Also I typed the number wrong above its AE17-1243
"Is this before or after you fired the parts cannon at it?" - senior tech
I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
Unless we change direction we are likely to end up where we are going.
"It's not new, it's better than new!" Maru.
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Originally Posted by
Kroaler
This doesn't match what I see in the real world. Real world I see gas furnace and AC combo outlasting heat pumps.
I haven't come across any data that shows the compressor in a heat pump models is built for 2x runtime vs ac only application compressors.
I would welcome to be proven wrong though for my own knowledge and better understanding.
I believe you might have misunderstood. By caparison a gas furnace & AC would outlast a HP that was built 30 years ago. That was what the engineer I mentioned was referring to. 1980's.
I have no data on how that compares today. Today could be different but modern furnaces are more likely to fail more often but for a different reason, the added technology meaning more parts.
HP's have an expected working life and HP's work longer and harder so I have no disagreement with what you wrote. What the engineer said back then I believe is still valid in keeping a HP compressor running might be a better survivor.
When I had a HP I couldn't get comfortable seeing it covered in snow and running all night long. Seemed like a self destruct event.
That a HP can be more efficient than straight strip is true to a point. And a HP's output falls fast so what is looked at isn't the BTU output as
compared to strip heat, it's BTU's out compared to input. The strip is going to put out more heat at 100% efficiency. The HP will put out less but at a slightly higher efficiency. Nothing like what a HP can put out at 50 degF.
We are here on Earth to fart around ......Kurt Vonnegut
You can be anything you want......As long as you don't suck at it.
USAF 98 Bomb Wing 1960-66 SMW Lu49
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Inverter heat pumps retain high efficiency and high output to very low temperatures.
Though the government is not my favorite source of information, here's an article about "cold climate heat pumps."
https://www.energy.gov/eere/building...ay-warm-winter
I have my dual fuel system (or "duel" fuel if you're an internet speller) set to lock out the furnace above 15°F. House temperature maintains 72°F. I have read of some with dual fuel who haven't used the furnace in two years.
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