Heat Pump ?'s
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In theory it is easier to bring in heat than to take out heat. The electricity used to compress the refrigerant will go into your home when heating, instead of being wasted and has to be dissipated when it is cooling a home.
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I would guess that the heat mode would use more power. I wouldn't have one myself as they or trouble prone. Even with the improvement made in the switching valves over the years. Saw too many instances of HVAC techs visiting neighbors having problems in the heating months.Power companies like the one I worked for love em. Bring on the statistics heat pump lovers.
The compressor and fan require the same energy in either mode. The efficiency depends on the ambient air temperature. I'm assuming cooling mode is more efficient due to a greater different in temperature between the outside air and the hot condenser. However, in heating mode, some of the heat created by compressing the fluid is used to heat the house whereas it's wasted in cooling mode.
The amount of BTU's transferred to the inside (heat pump) or to the outside (A/C) is a function of inside and outside temps. The closer the outside is to the inside the more heat will be moved.
In colder climates if the heat pump can't satisfy demand it will use an auxiliary heat strip to
raise the discharge air temp. That electric heat strip will use a lot more electric.
raise the discharge air temp. That electric heat strip will use a lot more electric.
For a given temperature differential, you'll get more heating than cooling, because in heating mode, you have the "benefit" of the inefficiencies that in cooling mode have to be transferred out to the environment.
Depending on locale, they Temperature differentials aren't equal 'though. Here an average summer day to 21C indoors is about 12C, in winter about 16C...peak summer 16C, cold winter 26C, so there's really no "all things being equal".
In warming mode, there's also icing of the evaporators that put a hold on things.
Most new Oz installations are inverter controlled, and efficiencies are greater than ever before...It generates less CO2 to burn the coal at work and run reverse cycle than to burn the coal in my loungeroom at even 100% efficiency (neighbour does at around 15%).
That said, nope, I don't have it.
But if I was doing a renovation, it would be first on my list...heating with gas is the same per BTU as running the house on regular unleaded.
Depending on locale, they Temperature differentials aren't equal 'though. Here an average summer day to 21C indoors is about 12C, in winter about 16C...peak summer 16C, cold winter 26C, so there's really no "all things being equal".
In warming mode, there's also icing of the evaporators that put a hold on things.
Most new Oz installations are inverter controlled, and efficiencies are greater than ever before...It generates less CO2 to burn the coal at work and run reverse cycle than to burn the coal in my loungeroom at even 100% efficiency (neighbour does at around 15%).
That said, nope, I don't have it.
But if I was doing a renovation, it would be first on my list...heating with gas is the same per BTU as running the house on regular unleaded.
Originally Posted By: metalone
I just had a new heat pump system installed.
I starting thinking about energy usage.
But the question is.
If a heat pump runs 10 minutes supplying heat or cold air is one or the other modes more
energy intensive than the other?
It all depends on the relative temperatures of indoor and outdoor air. The bigger the temperature differential, the more energy the unit has to expend to work against it.
Absolute temperature has an effect also. When its really hot on the outside and you're running in cooling mode, the condensor pressure stays high and keeps a load on the compressor. When you're running in heat mode and it gets near freezing, efficiency drops because ice builds up on the outside unit. This requires periodically running the system in cooling mode to "defrost" the outside unit. When that's going on, the electric resistance heat kicks in and that costs a lot of energy. Even in low humidity where outside unit icing is less of a problem, efficiency starts dropping when it gets into the 20s (farenheit) just because the refrigerant condenses too easily and doesn't pick up much heat from the environment outside.
I just had a new heat pump system installed.
I starting thinking about energy usage.
But the question is.
If a heat pump runs 10 minutes supplying heat or cold air is one or the other modes more
energy intensive than the other?
It all depends on the relative temperatures of indoor and outdoor air. The bigger the temperature differential, the more energy the unit has to expend to work against it.
Absolute temperature has an effect also. When its really hot on the outside and you're running in cooling mode, the condensor pressure stays high and keeps a load on the compressor. When you're running in heat mode and it gets near freezing, efficiency drops because ice builds up on the outside unit. This requires periodically running the system in cooling mode to "defrost" the outside unit. When that's going on, the electric resistance heat kicks in and that costs a lot of energy. Even in low humidity where outside unit icing is less of a problem, efficiency starts dropping when it gets into the 20s (farenheit) just because the refrigerant condenses too easily and doesn't pick up much heat from the environment outside.
It would be a good idea in FL, shouldn't be too many cold days, efficiency starts to drop below 40F-has to be cheaper to install than a gas furnace & central air system too.
Originally Posted By: Fsharp
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job. You're lucky if you can cool the house to 75 degrees if it's 95 outside. Still HP's are a decent compromise for moderate climates.
Personally if I had to have a heat pump, I'd prefer nat gas as the backup over electric any day.
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job. You're lucky if you can cool the house to 75 degrees if it's 95 outside. Still HP's are a decent compromise for moderate climates.
Personally if I had to have a heat pump, I'd prefer nat gas as the backup over electric any day.
A small heat pump (air to water) would be sufficient for my heating needs likely 320 days a year, well about 100 of those don't require any heating anyway. But in the coldest of winter I'd likely need to start the oil furnace for half an hour after we get home from working to get the temperature just where we want, including hot water for washing. Beats running the heater all evening, I suppose.
The coldest average temperatures here are about 40°F during december/january. But that doesn't mean I haven't seen it get as low as -20F or as hot as 60F in that same period.
The coldest average temperatures here are about 40°F during december/january. But that doesn't mean I haven't seen it get as low as -20F or as hot as 60F in that same period.
Originally Posted By: NormanBuntz
Originally Posted By: Fsharp
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job. You're lucky if you can cool the house to 75 degrees if it's 95 outside. Still HP's are a decent compromise for moderate climates.
Personally if I had to have a heat pump, I'd prefer nat gas as the backup over electric any day.
Is your system old? I have a hybrid HP with oil heat. But its been horribly hot and humid this year and my Bryant HP
on a 100 degree day will freeze you and so far its doing it rather cheaply too. So far I'm really impressed with it.
Originally Posted By: Fsharp
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job. You're lucky if you can cool the house to 75 degrees if it's 95 outside. Still HP's are a decent compromise for moderate climates.
Personally if I had to have a heat pump, I'd prefer nat gas as the backup over electric any day.
Is your system old? I have a hybrid HP with oil heat. But its been horribly hot and humid this year and my Bryant HP
on a 100 degree day will freeze you and so far its doing it rather cheaply too. So far I'm really impressed with it.
Originally Posted By: Shannow
For a given temperature differential, you'll get more heating than cooling, because in heating mode, you have the "benefit" of the inefficiencies that in cooling mode have to be transferred out to the environment.
Depending on locale, they Temperature differentials aren't equal 'though. Here an average summer day to 21C indoors is about 12C, in winter about 16C...peak summer 16C, cold winter 26C, so there's really no "all things being equal".
In warming mode, there's also icing of the evaporators that put a hold on things.
Most new Oz installations are inverter controlled, and efficiencies are greater than ever before...It generates less CO2 to burn the coal at work and run reverse cycle than to burn the coal in my loungeroom at even 100% efficiency (neighbour does at around 15%).
That said, nope, I don't have it.
But if I was doing a renovation, it would be first on my list...heating with gas is the same per BTU as running the house on regular unleaded.
Yea, heating should be a bit more efficient for any given 10 minutes given equal delta T. The reality is that over the heating and cooling season that will vary widely. You have to look at the SEER(cooling) and HSPF(heating) numbers to see the real story. Those test the units in a manner that will make things as equal as possible over a typical cooling or heating season. A 16 SEER unit will have an HSPF of 9-9.5. As Shannow pointed out heating is usually dealing with greater delta T and the defrost cycle takes a big hit in overall efficiency. During defrost the unit is running in cooling mode to heat the coils and thus pumping cold air into the house. The heating coils are switched on to mitigate the effect on house temperature so you're taking a double hit to the efficiency.
New units do pretty well in the cold these days. They can provide nearly 100% of their rated BTUs at 47F and about 2/3 their rated BTUs at 17F.
I just replaced my 20 year old Trane with an 18 SEER, 11 HSPF unit from Carrier. The actual numbers for my size system are 17.5 SEER and 10.5 HSPF. You have watch the advertised efficiencies as they are "up to". The actual efficiency will vary by tonnage and the exact coils and air handler installed. For example, one Trane that I got a quote on was up to 9.5. HSPF. The actual HSPF for my size and the air handler quoted was only 8.7. Here in the PNW the heating efficiency is far more important than the cooling. You may need at least a little heat 9 months of the year. The cooling might be "necessary" maybe 9 days a year.
We had three record breaking days a week ago. I can program the thermostat with the electricity cost and get a read out of the cost to run the unit daily. The first day was 88F and the cost to keep the house at 74F as $0.15(Yea thermal mass of a log home). The second day was 90F and the cost was $0.57(boo thermal mass). It cooled down more that night and was only about 86F the third day. Cost was $0.11(yea thermal mass). I am pleased. I'm also looking forward to the 25%-30% lower heat bills this winter.
Ed
For a given temperature differential, you'll get more heating than cooling, because in heating mode, you have the "benefit" of the inefficiencies that in cooling mode have to be transferred out to the environment.
Depending on locale, they Temperature differentials aren't equal 'though. Here an average summer day to 21C indoors is about 12C, in winter about 16C...peak summer 16C, cold winter 26C, so there's really no "all things being equal".
In warming mode, there's also icing of the evaporators that put a hold on things.
Most new Oz installations are inverter controlled, and efficiencies are greater than ever before...It generates less CO2 to burn the coal at work and run reverse cycle than to burn the coal in my loungeroom at even 100% efficiency (neighbour does at around 15%).
That said, nope, I don't have it.
But if I was doing a renovation, it would be first on my list...heating with gas is the same per BTU as running the house on regular unleaded.
Yea, heating should be a bit more efficient for any given 10 minutes given equal delta T. The reality is that over the heating and cooling season that will vary widely. You have to look at the SEER(cooling) and HSPF(heating) numbers to see the real story. Those test the units in a manner that will make things as equal as possible over a typical cooling or heating season. A 16 SEER unit will have an HSPF of 9-9.5. As Shannow pointed out heating is usually dealing with greater delta T and the defrost cycle takes a big hit in overall efficiency. During defrost the unit is running in cooling mode to heat the coils and thus pumping cold air into the house. The heating coils are switched on to mitigate the effect on house temperature so you're taking a double hit to the efficiency.
New units do pretty well in the cold these days. They can provide nearly 100% of their rated BTUs at 47F and about 2/3 their rated BTUs at 17F.
I just replaced my 20 year old Trane with an 18 SEER, 11 HSPF unit from Carrier. The actual numbers for my size system are 17.5 SEER and 10.5 HSPF. You have watch the advertised efficiencies as they are "up to". The actual efficiency will vary by tonnage and the exact coils and air handler installed. For example, one Trane that I got a quote on was up to 9.5. HSPF. The actual HSPF for my size and the air handler quoted was only 8.7. Here in the PNW the heating efficiency is far more important than the cooling. You may need at least a little heat 9 months of the year. The cooling might be "necessary" maybe 9 days a year.
We had three record breaking days a week ago. I can program the thermostat with the electricity cost and get a read out of the cost to run the unit daily. The first day was 88F and the cost to keep the house at 74F as $0.15(Yea thermal mass of a log home). The second day was 90F and the cost was $0.57(boo thermal mass). It cooled down more that night and was only about 86F the third day. Cost was $0.11(yea thermal mass). I am pleased. I'm also looking forward to the 25%-30% lower heat bills this winter.
Ed
Originally Posted By: bullwinkle
It would be a good idea in FL, shouldn't be too many cold days, efficiency starts to drop below 40F-has to be cheaper to install than a gas furnace & central air system too.
My home in SW Florida has an electric air handler AC unit that has a heating coil inside for the 10 days a year it drops below 50F. Nobody has a furnace.
It would be a good idea in FL, shouldn't be too many cold days, efficiency starts to drop below 40F-has to be cheaper to install than a gas furnace & central air system too.
My home in SW Florida has an electric air handler AC unit that has a heating coil inside for the 10 days a year it drops below 50F. Nobody has a furnace.
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When I installed a new A/C, the company talked me into the heat pump. During the consultation, he warned against using it in below freezing temperatures, as it can freeze up.
What I didn't realize then is that, because I like it cold in the house, I never call upon a heater until the outside temp drops near or below freezing, so in a majority of the cases where I actually got cold and wanted some heat, I had to turn on the heat strips because it was too cold to use the heat pump.
It's money wasted in this climate (North Texas).
What I didn't realize then is that, because I like it cold in the house, I never call upon a heater until the outside temp drops near or below freezing, so in a majority of the cases where I actually got cold and wanted some heat, I had to turn on the heat strips because it was too cold to use the heat pump.
It's money wasted in this climate (North Texas).
Originally Posted By: NormanBuntz
Originally Posted By: Fsharp
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job.
Totally disagree here. In "cool" mode, a heat pump is exactly as efficient as any other central air unit, there's no reason it shouldn't be. The only difference is a valve that reverses refrigerant flow for heating mode. I've had heat pumps in Central Texas since 1985 through several summers with weeks where every day was over 100F, and *none* of them, not even that first 1985 Lennox, failed to cool perfectly. And heat doesn't really deteriorate until the mid 30s, either in my experience... even colder if its very dry outside. The limiting factor is when the outdoor humidity freezes on the outdoor coils and forces a lot of defrost cycles. When its really cold and DRY, the aux heat didn't have to kick in much until the high 20s.
Their shortcoming is that they don't blow HOT air like a gas furnace or electric strip heat, so they can't heat a stone-cold house as fast and they run more hours blowing warm air. If you like letting the house get cold then warming it quickly, you'll hate a heat pump. But if you set the T-stat and leave it alone, they cost less than electric heat, often less than LP gas(*), but definitely more than natural gas.
* I refuse to live in a house plumbed for LP gas anyway. Way too dangerous since its heavier than air and accumulates in low-lying pockets of walls and basements, and I personally know a victim of an LP-gas home explosion (sole survivor of 4 people in the house at the time, and now confined to a care facility as a result).
Originally Posted By: Fsharp
The efficiency depends on the ambient air temperature.
+1 here
I've had various brands of heat pumps for 37 years. Basically they are a compromise. They don't heat as efficiently as a furnace, and they don't cool as efficiently as a central air conditioner. Heat pumps only heat OK down to about 40 degrees. Above 95 degrees, forget about a heat pump really doing the job.
Totally disagree here. In "cool" mode, a heat pump is exactly as efficient as any other central air unit, there's no reason it shouldn't be. The only difference is a valve that reverses refrigerant flow for heating mode. I've had heat pumps in Central Texas since 1985 through several summers with weeks where every day was over 100F, and *none* of them, not even that first 1985 Lennox, failed to cool perfectly. And heat doesn't really deteriorate until the mid 30s, either in my experience... even colder if its very dry outside. The limiting factor is when the outdoor humidity freezes on the outdoor coils and forces a lot of defrost cycles. When its really cold and DRY, the aux heat didn't have to kick in much until the high 20s.
Their shortcoming is that they don't blow HOT air like a gas furnace or electric strip heat, so they can't heat a stone-cold house as fast and they run more hours blowing warm air. If you like letting the house get cold then warming it quickly, you'll hate a heat pump. But if you set the T-stat and leave it alone, they cost less than electric heat, often less than LP gas(*), but definitely more than natural gas.
* I refuse to live in a house plumbed for LP gas anyway. Way too dangerous since its heavier than air and accumulates in low-lying pockets of walls and basements, and I personally know a victim of an LP-gas home explosion (sole survivor of 4 people in the house at the time, and now confined to a care facility as a result).
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Regarding 440Magnum's opinion, my house is on the NC waterfront, where it is often humid in the summer and damp in the winter. I have a 13 year old 5 ton York heat pump (likely a 10 SEER) to heat one story of 2,000 square feet. Besides the York unit being less reliable than most heat pumps I've had, in the winter below 30 degrees it frequently freezes and goes into defrost mode. My backup heat is electric, certainly less preferred than in past houses where I had heat pumps with either oil or natural gas backup heat.
It's a matter of personal preference and the climate you live in. I get your points, 440Magnum. But my preferred setup would be straight AC and a natural gas furnace. BTW my go to brand now is Trane. I've replaced two systems with Trane equipment in the past three years.
It's a matter of personal preference and the climate you live in. I get your points, 440Magnum. But my preferred setup would be straight AC and a natural gas furnace. BTW my go to brand now is Trane. I've replaced two systems with Trane equipment in the past three years.
Just a little warning about Trane....Had a new Trane EVERYTHING installed in February. Expansion valve malfunctioned in late July and the unit ran about 20 hours a day (no exaggeration) and never got the house below 78 degrees. Technician said this is becoming the 'norm' with them. The whole ordeal went on for about 3 weeks before they did an accurate diagnosis, got the part in, and got over to fix it. They thought the unit was overcharged on the first visit, but letting some freon out had no effect.
Keep your eyes on how well your Tranes are cooling. You could end up with a sky-high electric bill and swelter in your house in spite of it.
Keep your eyes on how well your Tranes are cooling. You could end up with a sky-high electric bill and swelter in your house in spite of it.
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